CA2098011C - Communication signal having a time domain pilot component - Google Patents
Communication signal having a time domain pilot componentInfo
- Publication number
- CA2098011C CA2098011C CA002098011A CA2098011A CA2098011C CA 2098011 C CA2098011 C CA 2098011C CA 002098011 A CA002098011 A CA 002098011A CA 2098011 A CA2098011 A CA 2098011A CA 2098011 C CA2098011 C CA 2098011C
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- Prior art keywords
- signal
- samples
- predetermined
- pilot
- original information
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/345—Modifications of the signal space to allow the transmission of additional information
- H04L27/3455—Modifications of the signal space to allow the transmission of additional information in order to facilitate carrier recovery at the receiver end, e.g. by transmitting a pilot or by using additional signal points to allow the detection of rotations
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/02—Channels characterised by the type of signal
- H04L5/12—Channels characterised by the type of signal the signals being represented by different phase modulations of a single carrier
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0224—Channel estimation using sounding signals
- H04L25/0226—Channel estimation using sounding signals sounding signals per se
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
- H04L27/261—Details of reference signals
- H04L27/2613—Structure of the reference signals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2668—Details of algorithms
- H04L27/2673—Details of algorithms characterised by synchronisation parameters
- H04L27/2675—Pilot or known symbols
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
- H04L27/3411—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
- H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
- H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
- H04B2201/70701—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation featuring pilot assisted reception
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/2627—Modulators
- H04L27/2637—Modulators with direct modulation of individual subcarriers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
Abstract
A quad 16 QAM transmission (132-136) and reception (600) methodology wherein a time domain pilot reference is advantageously associated therewith. There may be one or more such pilot references for each packet of multiple 16 QAM pulses (200). Depending upon the embodiment, each 16 QAM pulse can include a time domain pilot reference, or an estimated pilot reference (402 and 301) for that pulse can he determined either by reference to pilot references in other pulses sharing the same packet, or by reference to pilot references for other previously received 16 QAM pulses corresponding to that same pulse.
Description
2 ~ ~ 8 ~
COMMUNICATION SIGNAL HAVING A TIME DOMAIN
PILOT COMPONENr Technical Field This invention relates generally to communication 10 methodology, and more particularly to communication signals having information components that require the presence of a pilot component in order to facilitate recovery of the information components.
15 Background of the Invention .
Various communication systems are known in the art. Pursuant to many such systems, an information signal is modulated on to a carrier signal and transmitted 20 from a first location to a second location. At the second location, the information signal is demodulated and recovered.
Typically, the communication path used by such a system has various limitations, such as bandwidth. As a 25 result, there are upper practical limitations that restrict the quantity of information that can be supported by the communication path over a given period of time. Various . modulation schemes have been proposed that effectively increase the information handling capacity of the ~ ' WO 93/09622 PCI /US92/06768 209~oil communication path as measured against other modulation techniques. For example, a 16 point quadrature amplitude modulation (QAM) approach provides a constellation of modulation values (distinguished from one another by 5 phase and amplitude) wherein each constellation point represents a plurality of information bits.
Such QAM signals are typically transmitted in conjunction with a pilot component. For example, the information components of the QAM signal can be 10 broadcast in conjunction with one or more pilot tones that are offset in frequency from the information content itself. These pilot components can be utilized to support synchronization, and to otherwise support recovery of the information component in a variety of ways.
Unfortunately, such frequency offset pilot components themselves consume bandwidth, thereby reducing the amount of bandwidth available in a communication path to support the information components. If the information components are themselves parsed into frequency offset data packages, the problem increases as further spectrum must be utilized to support the multiplicity of pilot references that are typically required to allow recovery of the various information packets.
In partial response to this situation, the prior art has proposed the use of time domain pilot components.
For example, the information components of a particular QAM transmission are combined with an inband predetermined pilot reference component that appears in a periodic manner. (Since the pilot component appears only from time to time, the component is referred to as WO 93/09622 PCr/US92/06768 existing in the time domain, as distinguished from the frequency domain pilot components di.scussed above.) Though suitable for many applications, QAM
transmissions that include time domain pilot components ~ 5 are not satisfactory in all applications. For example, in an RF communication environment, where communication units may be in motion with respect to one another, such prior art time domain pilot reference QAM methodologies may provide unacceptable performance. In particular, the land-mobile radio channel is characterized by multipath fading that causes the channel phase and amplitude to vary over time as the receiving or transmitting unit moves about. Such variations must be compensated or otherwise allowed for in order to provide proper reception. Typically, phase and frequency modulation schemes avoid the need for compensation since channel amplitude variations can be ignored and differential or discriminator reception techniques can automatically account for the channel phase variations. However, phase and frequency modulation are not very bandwidth efficient. While QAM techniques can introduce bandwidth efficiency by comparison, QAM requires more complicated channel compensation methods, such as those prior art techniques that use one or more pilot tones in ~ssoci~tion with the information content.
Another problem associated with the multipath nature of the radio channel is that of frequency-ssloctive fading. This occurs whenever the delay difference between the various multipath components that arrive at the reciever become large enough relative to the signalling rate in the channel. When this happpens, the channel's frequency response will no longer appear to be WO 93/09622 PCr/US92/06768 ~09~o~l flat in the band of interest, but will exhibit phase and amplituds variations with frequency, which in turn will vary with time as the transmitter or receiver moves about. This frequency-selective effect causes si~nal 5 distortion that is present independent of the strength of the received signal. In data communication systems, this distortion manifests itself as an irreducible bit error rate, or error floor, that persists regardless of how strong the received signal becomes. In addition, the 10 distortion effect worsens as the information capacity of the signal increases.
Accordingly, a need exists for a communication methodology that will provide efficient use of QAM (and the like) modulation techniques while simultaneously 15 substantially avoiding spectral inefficiencies that may occur through use of certain prior art pilot component techniques and other multipath compensation techniques.
This technique will preferably remain substantially robust in a varying multipath operating environment.
Summary of the Invention These needs and others are substantially met through provision of the communication techniques 25 disclosed herein. Pursuant to this invention, an original information signal is converted into a parallel plurality of processe~ information signal sample sequences. At least one of these sequences is then combined with a reference sequence containing at least one predetermined sample, 30 which sample serves as a time domain pilot reference that a receiver utilizes to effectively recover a signal corresponding to the original information signal.
In one embodiment of the invention, the original information signal can be in the form of a serial data stream, and the conversion step operates upon preselected serial portions thereof.
~ 5 In one embodiment of the invention, the conversion step further includes converting groups of bits that comprise the original information signal into corresponding multibit symbols. In a further embodiment, a predetermined plurality of these symbols constitutes a processed information signal sample sequence.
In one embodiment of the invention, the combining step includes combining the predetermined sample (which represents the time domain pilot reference) with at least two of the sample sequences. In another embodiment, all of the sequences are combined with a pilot tone reference in this manner.
In yet another embodiment, the time domain pilots can be provided in some, but not all, of a group of subchannels. To provide for channel compensation in the subchannels that do not have a pilot, the time domain pilots that are provided can be utilized to provide an estimation of a pilot for that subchannel. In effect, then, the occassionaly sent pilots can be utilized to interpolate both over time and over frequency to allow for channel compensation of the information signals.
Rrjef Description of the Drawin~s Fig. 1 comprises a block diagram depiction of a signal processor suitable for use in a transmitter in accordance with the invention;
WO 93/09622 PCl'/US92/06768 2,098011 6 Fig. 2 comprises a depiction of a 16 QAM symbol constellation;
Fig. 3 comprises a depiction of a symbol constellation wherein one of the symbols constitutes a 5 predetermined pilot reference symbol;
Figs. 4a-g comprise timing diagrams representative of a series of symbol sequences as provided in various embodiments in accordance with the invention;
FIG. 4H comprises a graphical representation of how 10 pilot symbols might be used in interpolating data symbols, in accordance with one embodiment of the invention;
Fig. 5 comprises a spectral diagramatic representation of a plurality of sample sequences, each having been combined with a predetermined symbol, in 15 accordance with the invention;
Figs. 6a-b comprise block diagrams depicting a receiver suitable for use in receiving a signal in accordance with the invention;
Fig. 7 comprises a graph illustrating interpolated 20 channel gains as determined in accordance with the invention; and Fig. 8 comprises a graph illustrating phase vs.
frequency response characteristics of a preselector filter, as determined in accordance with the invention.
Rest Mode For Carryin~ Out The Invention A signal processor for preparing a signal for 30 transmission in accordance with the invention is generally depicted in Fig. 1 by the reference numeral 100.
Though depicted in block diagram format for the convenience of explanation and understanding, it should be understood that the invention can be practiced in a variety of embodiments; in particular, a digital signal processor, such as from the Motorola DSP 56000 or DSP 96000 - 5 families, is readily programmable to accomplish the functions set forth below. Also, although describsd below in the context of a 16 QAM application, it should also be understood that the teachings herein are also applicable for use with other modulation schemes as well.
A processing unit (102) receives an original information signal (101). In this particular embodiment, this information signal constitutes a serial bit stream having an effective baud rate of 53.2 kilobits per second.
This bit stream can represent, for example, true data, digitized voice, or other appropriate signals. Alternate embodiments of the invention contemplate an analog original information signal (101). An analog original information signal (e.g., voice information) would, prior to conversion into QAM-symbols, be converted to a digital form.
The processing unit (102) functions to convert groups of 16 serial bits of the original information signal into four 16 QAM complex signal points (symbols). For example, Fig. 2 depicts a 16 QAM complex signal symbol constellation (200). Each symbol in the constellation represents a different combination of four serial bits.
For example, a first one of these symbols (201) represents the bits "0001.H A second symbol (202), on the other hand, represents the bits ~0100,~ all in accordance with well understood prior art methodology.
For each serially received 16 original information bits, the processing unit (102) outputs, in parallel, on each of 4 signal paths (103-106), an appropriate 209~011 representative multibit symbol as described above. A
pilot insertion unit (107-110), located in each signal path (103-106), inserts a predetermined symbol following receipt of 7 serially received information symbols from 5 the processing unit (102) pursuant to one embodiment of a communication methodology in accordance with the invention. For example, with reference to the constellation (300) depicted in Fig. 3, the symbol depicted by reference numeral 301 can, by way of example, serve 10 as the predetermined symbol inserted by the pilot insertion unit (107-110). (Other symbols within the constellation could of course be used. Arbitrary si~nal points not within the constellation could also be used in an appropriate application. Furthermore, althou~h a 15 particular symbol is used to represent the pilot reference in this manner, this does not mean that this same symbol cannot serve as a multibit symbol for other symbol locations in the symbol stream. The preferred embodiment would in fact allow the predetermined 20 symbol to perform this dual function. Lastly, it is not necess~ry that all of the pilot symbols be identical or sp~ced in time by a regular, uniform interval; it is only necessary that they be selected in a predetermined way.) The resulting output from the pilot insertion units 25 (107-110) comprises a symbol stream (in this embodiment having a symbol rate of 3.8 kilosymbols per second) that is as generally depicted in Fig. 4a by reference numeral 400. As depicted, a predetermined symbol (402) constituting a pilot reference serially 30 appears following each seven informational data symbols (401). This symbol stream forms a composite signal that includes one non-informational pilot reference symbol for W O 93/09622 PC~r/US92/06768 every seven informational data symbols. These composite signals are provided to pulse shaping filters (116-119) that appropriately shape the symbols for transmission.
Thereafter, each composite signal is mixed using - S mixers (121 -124) with an appropriate offset, or injection signal (126-129) of the form e Om~ to produce offset symbol- streams wherein j is the square root of negative one, t is time, and fOffk comprises an offset frequency corresponding to the kth composite signal. All of the 10 above parameters will be identical for each of the injection signals (126-129) with the exception of the frequency offset value. In this embodiment, the first injection signal (126) has an offset frequency value of minus 6.27 kHz. The second injection signal (127) has an 15 offset frequency of minus 2.09 kHz. 2.09 kHz comprises the offset frequency for the third inje--tion signal (128), and 6.27 kHz comprises the offset frequency for the fourth injection signal (129).
The filtered and offset composite signals are 20 thereafter combined (131) to form a modulation signal.
The real and imaginary parts of this complex modulation signal are separated (132, 133) and provided to a quadrature upconverter (134), following which the signal is amplified (135) and applied to an antenna (136) for 25 transmission, the latter occurring in accordance with well-understood prior art methodology.
The resultant shaped, frequency offset, and combined 16 QAM symbol sequences are generally represented in Fig. 5 by reference numeral 500. As 30 generally depicted in this spectral diagram, there are four effective sub-channels of symbol information (501), each being offset from the others in correlation to the offset WO 93/09622 PCr/US92/06768 2098~~1 10 frequencies referred to above. In this embodiment, each subchannel symbol also includes a time domain pilot reference sequence (figuratively represented by reference numeral 502) embedded therein. (It is not necess~ry that 5 each 16 QAM subchannel symbol of this quad 16 QAM
packet include an embedded time domain pilot reference.
For example, only one of the QAM signals might include the pilot reference, as illustrated in Fig. 4b, with interpolation techniques being used durin~ reception to 10 provide an estimated pilot reference for use in recovering the remaining 16 QAM subchannels. In addition, or in the alternative, pilot sequences for the various subchannels mi~ht be staggered in time relative to each other, as depicted in Fig. 4c, to allow interpolation over time and 15 frequency of estimated pilot references for use in recovering symbols for all subchannels.
The filter interpolation technique, later described, may be applied to other pilot sequences as well. For example, FIG. 4D shows a pilot sequence which has both time 20 staggered, and time coincident characteristics. In particular, at times 402, 404, 406, the pilot symbols on subchannel 1 and subchannel 2 are time coincident with each other, while subchannel 3 and subchannel 4 have no pilot symbols. By contrast, at times 405, 407, 409 subchannels 3 25 and 4 have time coincident pilot symbols, while subchannels 1 and 2 have no pilot symbols. In FIG. 4D, the occurrences of pilot symbol sequences in channels 1 and 2 and the occurrences of pilot sequences in channels 3 and 4 are considered to be mutually exclusive. In a preferred 30 embodiment pilot symbols are inserted, on mutually exclusive subchannel subsets, such as ~1&2~, ~3&4}, {1&3}, etc. wherein the elements of each subset are mutually exclusive .
FIG. 4E shows another grouping or arrangement of subchannel pilot occurrences. A first subset of channels, i.e.
5 1 and 3, has pilots on channels 1 and 3 at time 411. A
second subset of subchannels, i.e. subchannels 1 and 2, have pilots on subchannels 1 and 2 at time 413. A third subset of channels, i.e. channel 3, shows only a single subchannel (4) being piloted at time 415, while time 417 has pilots on the 10 first subset of channels, 1 and 3. (It should be noted that the occurrences of pilots shown in FIG. 4E are aperiodic. Other embodiments would of course include periodic pilots in these subchannels as well.) Another embodiment of the invention might have time 15 coincident pilot symbols on all 4 subchannels at times 421 and 423, as shown in FIG. 4F. Having several time coincident pilots serves as an excellent point to make phase/amplitude correction calculations, which process is later described.
FIG. 4G shows yet another stream of information-20 bearing QAM symbols and combined pilot sequences, whichmight be employed, for example, in a time division multiplex (TDM) system having multi-slot data frames. Such systems generally make pilot symbols available only for the slot to which the user is assigned, such as when the receiver 25 is cycled on only for the assigned slot (e.g., to save battery power). This limitation on pilot availability has significant implications on pilot interpolation filter design. In particular, use of an interpolation technique having a fixed number of sample points (e.g., fixed number of pilots per 30 time slot) must properly weight these sample points according to where they are with respect to the data symbol being interpolated. It should be noted that periodically ~O9SO~
occurring pilot symbois (e.g. as shown on subchannels 2 & 4) are not readily suitable for maintaining a uniform interpolation error across the timeslot. By contrast, aperiodically spaced pilot symbols (e.g., as shown on 5 subchannels 1 & 3), in concert with appropriate weighting factors, or coefficients, allows the interpolation error to be made substantially uniform across the time slot. (i.e., interpolated values at the beginning, i.e. times 431, 433, and 437, and ends, i.e. times 441, 445, and 447, are 10 substantially as accurate as those in the center (439) of the time slot). Further, these coefficients may be stored in memory and indexed according to subchannel and data symbol position, as later described.
Accordingly, the present invention contemplates 15 pilot symbol sequences which are periodic in nature, as well as aperiodic. Further, subsets of subchannels may be employed, as later described, to provide enhanced pilot channel gain sample corrections, which subsets may or may not be mutually exclusive with alternate subsets. Of 20 particular importance is that the position (the time of occurrence) of the pre-determined pilot symbols is known at each subchannel receiver. With this information, channel gain (which is a complex entity that scales and rotates a transmitted signal and includes the phase 25 and/or amplitude modulation of a signal by the transmission channel) is interpolated over time and/or frequency, and is compensated for by the receiver(s), as necessary for that particular subchannel, to recover the information of interest. Doing so results in an effective 30 pilot rate increase without a corresponding increase in the total number of required pilots (i.e. pilot overhead).
What is important is that a plurality of QAM signals be substantially simultaneously provided, in a manner frequency offset from one another, wherein at least one of the QAM signals includes a time domain pilot reference.) A receiver suitable for use in recovering the above described signal has been set forth in Fig. 6a (600).
Following appropriate reception of the transmitted signal as provided by, for example, an antenna (601), preselector (602), and quadrature downconverter (603), a composite signal centered substantially at zero frequency is provided to a bank of subchannel receivers (604a-d), for the purpose of recovering the original 16 QAM signals.
Operation of the subchannel recievers is further illustrated in Fig. 6b. The composite signal still comprising 4 parallel subchannels is mixed (606) with the appropriate injection signal of the form e d~, in orderto center the desired subchannel at approximately zero trequency (i.e., to remove the frequency offset introduce~ at the l-ans-"itler).
A receiver pulse shaping filter (607) receives this mixed signal and appropriately shapes the received signal and filters out the other subchannel signals and noise to produce a single subchannel signal. A symbol sampler (608) then allows individual symbols to be sampled and provided to both of two processing paths (609 and 610).
The first signal processing path (609) includes a pilot sampler (611) that selects the pilot symbols from the composite symbol sequence comprising data and pilot symbols. The pilot samples are then multiplied (612) by the reciprocal (613) of the original transmitted pilot symbol (which is known at the receiver by virtue of having been predetermined), to provide an estimate of the channel gain corresponding to the pilot sampling instant.
WO g3/09622 PCI /US92/06768 209~ol~
A pilot interpolation filter (614) then processes this recovered pilot sequence to obtain an estimate of the channel gain at the intervening data symbol instants.
The pilot interpolation filter (614) may be one-dimensional, 5 i.e. for time domain only pilots as shown in FlGs. 4A and 4B, or two-dimensional, i.e. for pilots varying with both time and frequency as shown in FlGs. 4C-G. The operation of the interpolation filter (614), either one- or two-dimensional, may be better understood in consideration of FIG. 4H and the 10 following equation, which shows the interpolation channel gain estimate, Yj,m, for the jth data symbol on subchannel m:
y~ m] = ~ ~, (W[i,k],[j,m]) (P[i~]) k~ K[j,m] i~
(1) where:
W[j m] [i kl = interpolation weighting coefficient for the data symbol at time j of subchannel m using the pilot symbol at time i of subchannel k.
P[ik]z corrected pilot channel gain sample for the pilot symbol at time i of subchannel k.
~[i m] = predetermined subset of subchannels to be used for interpolation for the ~ata symbol at time j on subchannel m.
Ik= predetermined subset of the available corrected pilot channel gain samples for the subchannel denoted by k.
~0 93/09622 PCI /US92/06768 Equation (1) may be implemented in each of the subchannel receivers (604A-604D), one of which receiver is 5 shown in the simplified block diagram of FIG. 6B. As an example, interpolation for the data symbol at time 461 on subchannel 2 is graphically shown in FIG. 4H. It is assumed that this symbol is interpolated over time (i.e. using 3rd and 4th pilots on subchannel 2) and frequency (i.e. usin~ 2nd and 10 3rd pilots from the adjacent subchannel 1). In accordance with the above equation, each of the corrected pilot channel gain sample values (Pi,k) are weighted (453~56), using the appropriate weighting coefficient (W[i~k]~ m])~ and summed (457, 458) for each subchannel. Each of these signals are 15 then summed (459), if appropriate, across subchannels to yield the interpolated channel gain estimate for use in detecting data symbol (461).
The aforementioned embodiment does not take into account the phase and amplitude differences between the 20 raw pilot symbols taken from different subchannels. Such differences arise due, at least in part, to the phase-versus-frequency response of the preselector filter (602, shown in FIG.6A). That is, since the pilots used-for (two-dimensional) interpolation are necessarily taken from subchannels having 25 different frequencies, the effect of this difference in frequency must be removed before the raw pilot data can be used. Namely, the phase and/or amplitude values of the raw pilot symbols taken from other subchannels (i.e. Uoff-channeln) must be corrected to correspond to the subchannel 30 in which the data symbol is being interpolated (i.e. "on-channel"). To illustrate the phase rotation caused by the receiver filtering, FIG. 8 shows a phase vs. frequency WO93/09622 Pcl/US92/067 ~9~ 1 6 response curve 801, for a particular preselector filter. At a frequency f1 (803) the filter causes a phase rotation of ~1 (809). Similarly, at a frequency f2 (805) the filter causes a phase rotation of ~2 (807). While the phase vs. frequency 5 response of the filter is shown as being substantially linear, it is anticipated that it could be described by a polynomial of an order higher than 1.
In the preferred embodiment, phase and/or amplitude correction factors for the off-channel pilot channel ~ain 10 samples are calculated and applied to the raw pilot channel gain samples (P'i,k in FIG. 6B) to yield the corrected pilot channel gain samples (Pi,k). (The corrected pilot channel ~ain samples are then multiplied by the wei~htin~
coefficient (w[j k],[j,m]) as shown in FIG. 4H.) These 15 complex correction factors are calculated for time coincident pairs of pilot samples which will be used in the interpolation for an on-channel data symbol.
Mathematically, the raw pilot channel ~ain samples on subchannels m and subchannel k can be represented in 20 vector form by:
P;,m~
(2) 25 and, P;.k = ai,keJ~i~= ai,~(0+~m)
COMMUNICATION SIGNAL HAVING A TIME DOMAIN
PILOT COMPONENr Technical Field This invention relates generally to communication 10 methodology, and more particularly to communication signals having information components that require the presence of a pilot component in order to facilitate recovery of the information components.
15 Background of the Invention .
Various communication systems are known in the art. Pursuant to many such systems, an information signal is modulated on to a carrier signal and transmitted 20 from a first location to a second location. At the second location, the information signal is demodulated and recovered.
Typically, the communication path used by such a system has various limitations, such as bandwidth. As a 25 result, there are upper practical limitations that restrict the quantity of information that can be supported by the communication path over a given period of time. Various . modulation schemes have been proposed that effectively increase the information handling capacity of the ~ ' WO 93/09622 PCI /US92/06768 209~oil communication path as measured against other modulation techniques. For example, a 16 point quadrature amplitude modulation (QAM) approach provides a constellation of modulation values (distinguished from one another by 5 phase and amplitude) wherein each constellation point represents a plurality of information bits.
Such QAM signals are typically transmitted in conjunction with a pilot component. For example, the information components of the QAM signal can be 10 broadcast in conjunction with one or more pilot tones that are offset in frequency from the information content itself. These pilot components can be utilized to support synchronization, and to otherwise support recovery of the information component in a variety of ways.
Unfortunately, such frequency offset pilot components themselves consume bandwidth, thereby reducing the amount of bandwidth available in a communication path to support the information components. If the information components are themselves parsed into frequency offset data packages, the problem increases as further spectrum must be utilized to support the multiplicity of pilot references that are typically required to allow recovery of the various information packets.
In partial response to this situation, the prior art has proposed the use of time domain pilot components.
For example, the information components of a particular QAM transmission are combined with an inband predetermined pilot reference component that appears in a periodic manner. (Since the pilot component appears only from time to time, the component is referred to as WO 93/09622 PCr/US92/06768 existing in the time domain, as distinguished from the frequency domain pilot components di.scussed above.) Though suitable for many applications, QAM
transmissions that include time domain pilot components ~ 5 are not satisfactory in all applications. For example, in an RF communication environment, where communication units may be in motion with respect to one another, such prior art time domain pilot reference QAM methodologies may provide unacceptable performance. In particular, the land-mobile radio channel is characterized by multipath fading that causes the channel phase and amplitude to vary over time as the receiving or transmitting unit moves about. Such variations must be compensated or otherwise allowed for in order to provide proper reception. Typically, phase and frequency modulation schemes avoid the need for compensation since channel amplitude variations can be ignored and differential or discriminator reception techniques can automatically account for the channel phase variations. However, phase and frequency modulation are not very bandwidth efficient. While QAM techniques can introduce bandwidth efficiency by comparison, QAM requires more complicated channel compensation methods, such as those prior art techniques that use one or more pilot tones in ~ssoci~tion with the information content.
Another problem associated with the multipath nature of the radio channel is that of frequency-ssloctive fading. This occurs whenever the delay difference between the various multipath components that arrive at the reciever become large enough relative to the signalling rate in the channel. When this happpens, the channel's frequency response will no longer appear to be WO 93/09622 PCr/US92/06768 ~09~o~l flat in the band of interest, but will exhibit phase and amplituds variations with frequency, which in turn will vary with time as the transmitter or receiver moves about. This frequency-selective effect causes si~nal 5 distortion that is present independent of the strength of the received signal. In data communication systems, this distortion manifests itself as an irreducible bit error rate, or error floor, that persists regardless of how strong the received signal becomes. In addition, the 10 distortion effect worsens as the information capacity of the signal increases.
Accordingly, a need exists for a communication methodology that will provide efficient use of QAM (and the like) modulation techniques while simultaneously 15 substantially avoiding spectral inefficiencies that may occur through use of certain prior art pilot component techniques and other multipath compensation techniques.
This technique will preferably remain substantially robust in a varying multipath operating environment.
Summary of the Invention These needs and others are substantially met through provision of the communication techniques 25 disclosed herein. Pursuant to this invention, an original information signal is converted into a parallel plurality of processe~ information signal sample sequences. At least one of these sequences is then combined with a reference sequence containing at least one predetermined sample, 30 which sample serves as a time domain pilot reference that a receiver utilizes to effectively recover a signal corresponding to the original information signal.
In one embodiment of the invention, the original information signal can be in the form of a serial data stream, and the conversion step operates upon preselected serial portions thereof.
~ 5 In one embodiment of the invention, the conversion step further includes converting groups of bits that comprise the original information signal into corresponding multibit symbols. In a further embodiment, a predetermined plurality of these symbols constitutes a processed information signal sample sequence.
In one embodiment of the invention, the combining step includes combining the predetermined sample (which represents the time domain pilot reference) with at least two of the sample sequences. In another embodiment, all of the sequences are combined with a pilot tone reference in this manner.
In yet another embodiment, the time domain pilots can be provided in some, but not all, of a group of subchannels. To provide for channel compensation in the subchannels that do not have a pilot, the time domain pilots that are provided can be utilized to provide an estimation of a pilot for that subchannel. In effect, then, the occassionaly sent pilots can be utilized to interpolate both over time and over frequency to allow for channel compensation of the information signals.
Rrjef Description of the Drawin~s Fig. 1 comprises a block diagram depiction of a signal processor suitable for use in a transmitter in accordance with the invention;
WO 93/09622 PCl'/US92/06768 2,098011 6 Fig. 2 comprises a depiction of a 16 QAM symbol constellation;
Fig. 3 comprises a depiction of a symbol constellation wherein one of the symbols constitutes a 5 predetermined pilot reference symbol;
Figs. 4a-g comprise timing diagrams representative of a series of symbol sequences as provided in various embodiments in accordance with the invention;
FIG. 4H comprises a graphical representation of how 10 pilot symbols might be used in interpolating data symbols, in accordance with one embodiment of the invention;
Fig. 5 comprises a spectral diagramatic representation of a plurality of sample sequences, each having been combined with a predetermined symbol, in 15 accordance with the invention;
Figs. 6a-b comprise block diagrams depicting a receiver suitable for use in receiving a signal in accordance with the invention;
Fig. 7 comprises a graph illustrating interpolated 20 channel gains as determined in accordance with the invention; and Fig. 8 comprises a graph illustrating phase vs.
frequency response characteristics of a preselector filter, as determined in accordance with the invention.
Rest Mode For Carryin~ Out The Invention A signal processor for preparing a signal for 30 transmission in accordance with the invention is generally depicted in Fig. 1 by the reference numeral 100.
Though depicted in block diagram format for the convenience of explanation and understanding, it should be understood that the invention can be practiced in a variety of embodiments; in particular, a digital signal processor, such as from the Motorola DSP 56000 or DSP 96000 - 5 families, is readily programmable to accomplish the functions set forth below. Also, although describsd below in the context of a 16 QAM application, it should also be understood that the teachings herein are also applicable for use with other modulation schemes as well.
A processing unit (102) receives an original information signal (101). In this particular embodiment, this information signal constitutes a serial bit stream having an effective baud rate of 53.2 kilobits per second.
This bit stream can represent, for example, true data, digitized voice, or other appropriate signals. Alternate embodiments of the invention contemplate an analog original information signal (101). An analog original information signal (e.g., voice information) would, prior to conversion into QAM-symbols, be converted to a digital form.
The processing unit (102) functions to convert groups of 16 serial bits of the original information signal into four 16 QAM complex signal points (symbols). For example, Fig. 2 depicts a 16 QAM complex signal symbol constellation (200). Each symbol in the constellation represents a different combination of four serial bits.
For example, a first one of these symbols (201) represents the bits "0001.H A second symbol (202), on the other hand, represents the bits ~0100,~ all in accordance with well understood prior art methodology.
For each serially received 16 original information bits, the processing unit (102) outputs, in parallel, on each of 4 signal paths (103-106), an appropriate 209~011 representative multibit symbol as described above. A
pilot insertion unit (107-110), located in each signal path (103-106), inserts a predetermined symbol following receipt of 7 serially received information symbols from 5 the processing unit (102) pursuant to one embodiment of a communication methodology in accordance with the invention. For example, with reference to the constellation (300) depicted in Fig. 3, the symbol depicted by reference numeral 301 can, by way of example, serve 10 as the predetermined symbol inserted by the pilot insertion unit (107-110). (Other symbols within the constellation could of course be used. Arbitrary si~nal points not within the constellation could also be used in an appropriate application. Furthermore, althou~h a 15 particular symbol is used to represent the pilot reference in this manner, this does not mean that this same symbol cannot serve as a multibit symbol for other symbol locations in the symbol stream. The preferred embodiment would in fact allow the predetermined 20 symbol to perform this dual function. Lastly, it is not necess~ry that all of the pilot symbols be identical or sp~ced in time by a regular, uniform interval; it is only necessary that they be selected in a predetermined way.) The resulting output from the pilot insertion units 25 (107-110) comprises a symbol stream (in this embodiment having a symbol rate of 3.8 kilosymbols per second) that is as generally depicted in Fig. 4a by reference numeral 400. As depicted, a predetermined symbol (402) constituting a pilot reference serially 30 appears following each seven informational data symbols (401). This symbol stream forms a composite signal that includes one non-informational pilot reference symbol for W O 93/09622 PC~r/US92/06768 every seven informational data symbols. These composite signals are provided to pulse shaping filters (116-119) that appropriately shape the symbols for transmission.
Thereafter, each composite signal is mixed using - S mixers (121 -124) with an appropriate offset, or injection signal (126-129) of the form e Om~ to produce offset symbol- streams wherein j is the square root of negative one, t is time, and fOffk comprises an offset frequency corresponding to the kth composite signal. All of the 10 above parameters will be identical for each of the injection signals (126-129) with the exception of the frequency offset value. In this embodiment, the first injection signal (126) has an offset frequency value of minus 6.27 kHz. The second injection signal (127) has an 15 offset frequency of minus 2.09 kHz. 2.09 kHz comprises the offset frequency for the third inje--tion signal (128), and 6.27 kHz comprises the offset frequency for the fourth injection signal (129).
The filtered and offset composite signals are 20 thereafter combined (131) to form a modulation signal.
The real and imaginary parts of this complex modulation signal are separated (132, 133) and provided to a quadrature upconverter (134), following which the signal is amplified (135) and applied to an antenna (136) for 25 transmission, the latter occurring in accordance with well-understood prior art methodology.
The resultant shaped, frequency offset, and combined 16 QAM symbol sequences are generally represented in Fig. 5 by reference numeral 500. As 30 generally depicted in this spectral diagram, there are four effective sub-channels of symbol information (501), each being offset from the others in correlation to the offset WO 93/09622 PCr/US92/06768 2098~~1 10 frequencies referred to above. In this embodiment, each subchannel symbol also includes a time domain pilot reference sequence (figuratively represented by reference numeral 502) embedded therein. (It is not necess~ry that 5 each 16 QAM subchannel symbol of this quad 16 QAM
packet include an embedded time domain pilot reference.
For example, only one of the QAM signals might include the pilot reference, as illustrated in Fig. 4b, with interpolation techniques being used durin~ reception to 10 provide an estimated pilot reference for use in recovering the remaining 16 QAM subchannels. In addition, or in the alternative, pilot sequences for the various subchannels mi~ht be staggered in time relative to each other, as depicted in Fig. 4c, to allow interpolation over time and 15 frequency of estimated pilot references for use in recovering symbols for all subchannels.
The filter interpolation technique, later described, may be applied to other pilot sequences as well. For example, FIG. 4D shows a pilot sequence which has both time 20 staggered, and time coincident characteristics. In particular, at times 402, 404, 406, the pilot symbols on subchannel 1 and subchannel 2 are time coincident with each other, while subchannel 3 and subchannel 4 have no pilot symbols. By contrast, at times 405, 407, 409 subchannels 3 25 and 4 have time coincident pilot symbols, while subchannels 1 and 2 have no pilot symbols. In FIG. 4D, the occurrences of pilot symbol sequences in channels 1 and 2 and the occurrences of pilot sequences in channels 3 and 4 are considered to be mutually exclusive. In a preferred 30 embodiment pilot symbols are inserted, on mutually exclusive subchannel subsets, such as ~1&2~, ~3&4}, {1&3}, etc. wherein the elements of each subset are mutually exclusive .
FIG. 4E shows another grouping or arrangement of subchannel pilot occurrences. A first subset of channels, i.e.
5 1 and 3, has pilots on channels 1 and 3 at time 411. A
second subset of subchannels, i.e. subchannels 1 and 2, have pilots on subchannels 1 and 2 at time 413. A third subset of channels, i.e. channel 3, shows only a single subchannel (4) being piloted at time 415, while time 417 has pilots on the 10 first subset of channels, 1 and 3. (It should be noted that the occurrences of pilots shown in FIG. 4E are aperiodic. Other embodiments would of course include periodic pilots in these subchannels as well.) Another embodiment of the invention might have time 15 coincident pilot symbols on all 4 subchannels at times 421 and 423, as shown in FIG. 4F. Having several time coincident pilots serves as an excellent point to make phase/amplitude correction calculations, which process is later described.
FIG. 4G shows yet another stream of information-20 bearing QAM symbols and combined pilot sequences, whichmight be employed, for example, in a time division multiplex (TDM) system having multi-slot data frames. Such systems generally make pilot symbols available only for the slot to which the user is assigned, such as when the receiver 25 is cycled on only for the assigned slot (e.g., to save battery power). This limitation on pilot availability has significant implications on pilot interpolation filter design. In particular, use of an interpolation technique having a fixed number of sample points (e.g., fixed number of pilots per 30 time slot) must properly weight these sample points according to where they are with respect to the data symbol being interpolated. It should be noted that periodically ~O9SO~
occurring pilot symbois (e.g. as shown on subchannels 2 & 4) are not readily suitable for maintaining a uniform interpolation error across the timeslot. By contrast, aperiodically spaced pilot symbols (e.g., as shown on 5 subchannels 1 & 3), in concert with appropriate weighting factors, or coefficients, allows the interpolation error to be made substantially uniform across the time slot. (i.e., interpolated values at the beginning, i.e. times 431, 433, and 437, and ends, i.e. times 441, 445, and 447, are 10 substantially as accurate as those in the center (439) of the time slot). Further, these coefficients may be stored in memory and indexed according to subchannel and data symbol position, as later described.
Accordingly, the present invention contemplates 15 pilot symbol sequences which are periodic in nature, as well as aperiodic. Further, subsets of subchannels may be employed, as later described, to provide enhanced pilot channel gain sample corrections, which subsets may or may not be mutually exclusive with alternate subsets. Of 20 particular importance is that the position (the time of occurrence) of the pre-determined pilot symbols is known at each subchannel receiver. With this information, channel gain (which is a complex entity that scales and rotates a transmitted signal and includes the phase 25 and/or amplitude modulation of a signal by the transmission channel) is interpolated over time and/or frequency, and is compensated for by the receiver(s), as necessary for that particular subchannel, to recover the information of interest. Doing so results in an effective 30 pilot rate increase without a corresponding increase in the total number of required pilots (i.e. pilot overhead).
What is important is that a plurality of QAM signals be substantially simultaneously provided, in a manner frequency offset from one another, wherein at least one of the QAM signals includes a time domain pilot reference.) A receiver suitable for use in recovering the above described signal has been set forth in Fig. 6a (600).
Following appropriate reception of the transmitted signal as provided by, for example, an antenna (601), preselector (602), and quadrature downconverter (603), a composite signal centered substantially at zero frequency is provided to a bank of subchannel receivers (604a-d), for the purpose of recovering the original 16 QAM signals.
Operation of the subchannel recievers is further illustrated in Fig. 6b. The composite signal still comprising 4 parallel subchannels is mixed (606) with the appropriate injection signal of the form e d~, in orderto center the desired subchannel at approximately zero trequency (i.e., to remove the frequency offset introduce~ at the l-ans-"itler).
A receiver pulse shaping filter (607) receives this mixed signal and appropriately shapes the received signal and filters out the other subchannel signals and noise to produce a single subchannel signal. A symbol sampler (608) then allows individual symbols to be sampled and provided to both of two processing paths (609 and 610).
The first signal processing path (609) includes a pilot sampler (611) that selects the pilot symbols from the composite symbol sequence comprising data and pilot symbols. The pilot samples are then multiplied (612) by the reciprocal (613) of the original transmitted pilot symbol (which is known at the receiver by virtue of having been predetermined), to provide an estimate of the channel gain corresponding to the pilot sampling instant.
WO g3/09622 PCI /US92/06768 209~ol~
A pilot interpolation filter (614) then processes this recovered pilot sequence to obtain an estimate of the channel gain at the intervening data symbol instants.
The pilot interpolation filter (614) may be one-dimensional, 5 i.e. for time domain only pilots as shown in FlGs. 4A and 4B, or two-dimensional, i.e. for pilots varying with both time and frequency as shown in FlGs. 4C-G. The operation of the interpolation filter (614), either one- or two-dimensional, may be better understood in consideration of FIG. 4H and the 10 following equation, which shows the interpolation channel gain estimate, Yj,m, for the jth data symbol on subchannel m:
y~ m] = ~ ~, (W[i,k],[j,m]) (P[i~]) k~ K[j,m] i~
(1) where:
W[j m] [i kl = interpolation weighting coefficient for the data symbol at time j of subchannel m using the pilot symbol at time i of subchannel k.
P[ik]z corrected pilot channel gain sample for the pilot symbol at time i of subchannel k.
~[i m] = predetermined subset of subchannels to be used for interpolation for the ~ata symbol at time j on subchannel m.
Ik= predetermined subset of the available corrected pilot channel gain samples for the subchannel denoted by k.
~0 93/09622 PCI /US92/06768 Equation (1) may be implemented in each of the subchannel receivers (604A-604D), one of which receiver is 5 shown in the simplified block diagram of FIG. 6B. As an example, interpolation for the data symbol at time 461 on subchannel 2 is graphically shown in FIG. 4H. It is assumed that this symbol is interpolated over time (i.e. using 3rd and 4th pilots on subchannel 2) and frequency (i.e. usin~ 2nd and 10 3rd pilots from the adjacent subchannel 1). In accordance with the above equation, each of the corrected pilot channel gain sample values (Pi,k) are weighted (453~56), using the appropriate weighting coefficient (W[i~k]~ m])~ and summed (457, 458) for each subchannel. Each of these signals are 15 then summed (459), if appropriate, across subchannels to yield the interpolated channel gain estimate for use in detecting data symbol (461).
The aforementioned embodiment does not take into account the phase and amplitude differences between the 20 raw pilot symbols taken from different subchannels. Such differences arise due, at least in part, to the phase-versus-frequency response of the preselector filter (602, shown in FIG.6A). That is, since the pilots used-for (two-dimensional) interpolation are necessarily taken from subchannels having 25 different frequencies, the effect of this difference in frequency must be removed before the raw pilot data can be used. Namely, the phase and/or amplitude values of the raw pilot symbols taken from other subchannels (i.e. Uoff-channeln) must be corrected to correspond to the subchannel 30 in which the data symbol is being interpolated (i.e. "on-channel"). To illustrate the phase rotation caused by the receiver filtering, FIG. 8 shows a phase vs. frequency WO93/09622 Pcl/US92/067 ~9~ 1 6 response curve 801, for a particular preselector filter. At a frequency f1 (803) the filter causes a phase rotation of ~1 (809). Similarly, at a frequency f2 (805) the filter causes a phase rotation of ~2 (807). While the phase vs. frequency 5 response of the filter is shown as being substantially linear, it is anticipated that it could be described by a polynomial of an order higher than 1.
In the preferred embodiment, phase and/or amplitude correction factors for the off-channel pilot channel ~ain 10 samples are calculated and applied to the raw pilot channel gain samples (P'i,k in FIG. 6B) to yield the corrected pilot channel gain samples (Pi,k). (The corrected pilot channel ~ain samples are then multiplied by the wei~htin~
coefficient (w[j k],[j,m]) as shown in FIG. 4H.) These 15 complex correction factors are calculated for time coincident pairs of pilot samples which will be used in the interpolation for an on-channel data symbol.
Mathematically, the raw pilot channel ~ain samples on subchannels m and subchannel k can be represented in 20 vector form by:
P;,m~
(2) 25 and, P;.k = ai,keJ~i~= ai,~(0+~m)
(3) Equations (2) and (3) show the respective phase and 30 amplitude values for raw pilot channel gain samples transmitted on subchannels m and k, respectively. These raw pilot vectors may be used to interpolate a particular ~0 93/09622 PCI/US92/06768 20980~1 data symbol on subchannel m, while subchannel k is considered to be an "off-channel". In order to determine the phase difference between the on-channel pilots and the off-channel pilots, the product of the on-channel pilot vector 5 and the complex conjugate of the off-channel pilot vector is calculated as follows:
a = Pim Pi.lc = ai,me)~im ailcei( +~L)
a = Pim Pi.lc = ai,me)~im ailcei( +~L)
(4) = ai,mai,kej0 The phase difference between the two vectors, then is given by arg~a~, i.e. -0. In a preferred embodiment, the phase correction factor for each pair of subchannels is derived by calculating the intermediate result, a, for one or more pairs of time coincident raw pilot channel gain samples and then summing these intermediate results to ~enerate an "average" value. The resulting accuracy of the phase correction factor increases as more time coincident pairs are included in this summation.
Similarly, the amplitude ratio (a unitless real quantity, b) can be calculated as:
b = P;.m = ai,m P;.m OCi,k Thus, the complex correction factor, ck, m, which allows using pilots from subchannel k in the interpolation calculations for subchannel m, is given by:
WO 93/09622 .~L PCI/US92/06768 cLm = b e~ arg(a) = i~m ej0 ai~
In the preferred embodiment, a unique correction factor is calculated for each subchannel pair. This calculation may be
Similarly, the amplitude ratio (a unitless real quantity, b) can be calculated as:
b = P;.m = ai,m P;.m OCi,k Thus, the complex correction factor, ck, m, which allows using pilots from subchannel k in the interpolation calculations for subchannel m, is given by:
WO 93/09622 .~L PCI/US92/06768 cLm = b e~ arg(a) = i~m ej0 ai~
In the preferred embodiment, a unique correction factor is calculated for each subchannel pair. This calculation may be
5 made, for example, at a time when all subchannel pilots are time coincident with respect to each other, such as times 421, and 423 in FIG. 4F. The corrected pilot channel gain sample, Pi,k, is given by the equation:
Pi.k = Ck,m P;,k Compensation of channel phase and amplitude distortion and recovery of the original data symbols are carried out as follows. Delay (616) provided in the second processing path (610) serves to time-align the estimated 15 channel gains with the corresponding data symbols. The delayed data symbols are multiplied (617) by the complex conjugates (618) of the estimated channel gains. This operation corrects for channel phase but results in the symbol being scaled by the square of the channel 20 amplitude. This is taken into account in the decision block (619) with appropriate input from a threshold adjustment multiplier (621 ) that itself utilizes nominal threshold information and a squared representation of the complex channel gain estimate (622).
2~ The symbols received may have suffered de~radation due to, for example, phase rotation and/or amplitude variations due to transmission and reception difficulties.
By use of information regarding phase and/or amplitude discrepancies and/or effects that can be gleaned from the 30 pilot interpolation filter, however, the symbols as output W O 93/09622 P(~r/US92/06768 1 9 from the mixer are properly phase compensated. Having been thusly phase compensated, and given the appropriately adjusted decision thresholds as are also provided by the pilot filter, a decision can then be made 5 as to which symbol has been received, and the detected symbol passed on for further processing as appropriate.
Such processing would typically include, for example, combining detected symbols from different subchannel receivers, and conversion to a serial format.
Referring to Fig. 7, the function of the pilot interpolation filter (608) can be described in more detail.
Complex channel gain relative to the overall transmission path can be seen as generally depicted by reference numeral 701. Pilot samples provide information regarding 15 channel gain at the various time instants depicted by reference numeral 702. Based upon this sample information, interpolated channel gain estimates (703) can be made, which channel gain estimates are suitable for use in recovering data samples as described above.
This same methodology could of course be utilized to support transmission and reception of independent information signals that are to be sent in parallel with one another on a carrier. In effect, pursuant to this 25 embodiment, the various subchannels described above would each carry information symbols that are independent of the other subchannels, but wherein the time domain pilot symbol(s) are interpolated over time (and frequency, if desired, as described above) to 30 estimate channel conditions to thereby assist in the proper recovery of the information symbols from the various subchannels.
WO 93/09622 PCr/US92/06768 2~980~Li 20 What is claimed is:
Pi.k = Ck,m P;,k Compensation of channel phase and amplitude distortion and recovery of the original data symbols are carried out as follows. Delay (616) provided in the second processing path (610) serves to time-align the estimated 15 channel gains with the corresponding data symbols. The delayed data symbols are multiplied (617) by the complex conjugates (618) of the estimated channel gains. This operation corrects for channel phase but results in the symbol being scaled by the square of the channel 20 amplitude. This is taken into account in the decision block (619) with appropriate input from a threshold adjustment multiplier (621 ) that itself utilizes nominal threshold information and a squared representation of the complex channel gain estimate (622).
2~ The symbols received may have suffered de~radation due to, for example, phase rotation and/or amplitude variations due to transmission and reception difficulties.
By use of information regarding phase and/or amplitude discrepancies and/or effects that can be gleaned from the 30 pilot interpolation filter, however, the symbols as output W O 93/09622 P(~r/US92/06768 1 9 from the mixer are properly phase compensated. Having been thusly phase compensated, and given the appropriately adjusted decision thresholds as are also provided by the pilot filter, a decision can then be made 5 as to which symbol has been received, and the detected symbol passed on for further processing as appropriate.
Such processing would typically include, for example, combining detected symbols from different subchannel receivers, and conversion to a serial format.
Referring to Fig. 7, the function of the pilot interpolation filter (608) can be described in more detail.
Complex channel gain relative to the overall transmission path can be seen as generally depicted by reference numeral 701. Pilot samples provide information regarding 15 channel gain at the various time instants depicted by reference numeral 702. Based upon this sample information, interpolated channel gain estimates (703) can be made, which channel gain estimates are suitable for use in recovering data samples as described above.
This same methodology could of course be utilized to support transmission and reception of independent information signals that are to be sent in parallel with one another on a carrier. In effect, pursuant to this 25 embodiment, the various subchannels described above would each carry information symbols that are independent of the other subchannels, but wherein the time domain pilot symbol(s) are interpolated over time (and frequency, if desired, as described above) to 30 estimate channel conditions to thereby assist in the proper recovery of the information symbols from the various subchannels.
WO 93/09622 PCr/US92/06768 2~980~Li 20 What is claimed is:
Claims (22)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of transmitting an original information signal, comprising the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining at least one of the parallel plurality of digital information symbols with at least a first predetermined time domain pilot reference symbol to produce at least one composite signal whose constituent symbols occupy temporally separatedsymbol locations;
wherein said at least a first predetermined time domain pilot reference symbol is independent of the original information signal and is positioned such that at least a first information symbol of the symbol stream is temporally separatedfrom the first predetermined time domain reference symbol by greater than one symbol location, and C) mixing each of:
the at least one composite signal; and those of the parallel plurality of digital information symbols that were not combined with said at least a first predetermined time domain pilot reference symbol; with an offset signal to produce a plurality of offset symbol streams.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining at least one of the parallel plurality of digital information symbols with at least a first predetermined time domain pilot reference symbol to produce at least one composite signal whose constituent symbols occupy temporally separatedsymbol locations;
wherein said at least a first predetermined time domain pilot reference symbol is independent of the original information signal and is positioned such that at least a first information symbol of the symbol stream is temporally separatedfrom the first predetermined time domain reference symbol by greater than one symbol location, and C) mixing each of:
the at least one composite signal; and those of the parallel plurality of digital information symbols that were not combined with said at least a first predetermined time domain pilot reference symbol; with an offset signal to produce a plurality of offset symbol streams.
2. The method of claim 1, wherein each of:
the at least one composite signal; and those of the parallel plurality of digital information symbols that were not combined with said at least a first predetermined time domain pilot reference symbol; is mixed with said a different offset signal.
the at least one composite signal; and those of the parallel plurality of digital information symbols that were not combined with said at least a first predetermined time domain pilot reference symbol; is mixed with said a different offset signal.
3. The method of claim 1 and further including the step of:
D) combining the plurality of offset symbol streams to provide a modulation signal.
D) combining the plurality of offset symbol streams to provide a modulation signal.
4. A method of transmitting an original information signal, comprising the steps of;
A) converting a serial portion of the original information signal, a parallel plurality of digital information symbols;
B) combining at least two, but not all, of the parallel plurality of digital information symbols with at least a first predetermined time domain pilot reference symbol to produce a at least two composite signals whose constituent symbols occupy temporally separated symbol locations;
wherein said at least a first predetermined time domain pilot reference symbol is independent of the original information signal and is positioned such that at least a first information symbol of the symbol stream is temporally separatedfrom the first predetermined time domain reference symbol by greater than one symbol location; and C) mixing each of:
the at least two composite signals; and those of the parallel plurality of digital information symbols that were not combined with said at least a first predetermined time domain pilot reference symbol;
with an offset signal to produce a plurality of offset symbol streams.
A) converting a serial portion of the original information signal, a parallel plurality of digital information symbols;
B) combining at least two, but not all, of the parallel plurality of digital information symbols with at least a first predetermined time domain pilot reference symbol to produce a at least two composite signals whose constituent symbols occupy temporally separated symbol locations;
wherein said at least a first predetermined time domain pilot reference symbol is independent of the original information signal and is positioned such that at least a first information symbol of the symbol stream is temporally separatedfrom the first predetermined time domain reference symbol by greater than one symbol location; and C) mixing each of:
the at least two composite signals; and those of the parallel plurality of digital information symbols that were not combined with said at least a first predetermined time domain pilot reference symbol;
with an offset signal to produce a plurality of offset symbol streams.
5. The method of claim 4, wherein each of:
the at least two composite signals; and those of the parallel plurality of digital information symbols that were not combine with said at least a first predetermined time domain pilot reference symbol;
is mixed with a different offset signal.
the at least two composite signals; and those of the parallel plurality of digital information symbols that were not combine with said at least a first predetermined time domain pilot reference symbol;
is mixed with a different offset signal.
6. The method of claim 4 and further including the step of:
D) combining the plurality of offset symbol streams to provide a modulation signal.
D) combining the plurality of offset symbol streams to provide a modulation signal.
7. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) combining each of the parallel plurality of processed information signal sample sequences a periodically with at least one predetermined sample, wherein said at least one predetermined sample is independent of, the original information signal, to form a plurality of composite signals and wherein each of said at least one predetermined sample serves as a time domain pilot reference;
C) processing the plurality of composite signals; and D) transmitting the processed composite signals;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, the at least one pilot reference associated therewith;
D) using the at least one recovered pilot reference to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) combining each of the parallel plurality of processed information signal sample sequences a periodically with at least one predetermined sample, wherein said at least one predetermined sample is independent of, the original information signal, to form a plurality of composite signals and wherein each of said at least one predetermined sample serves as a time domain pilot reference;
C) processing the plurality of composite signals; and D) transmitting the processed composite signals;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, the at least one pilot reference associated therewith;
D) using the at least one recovered pilot reference to recover the original information signal.
8. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) combining at least one of the parallel plurality of processed information signal sample sequences a periodically with at least one predetermined sample, wherein said at least one predetermined sample is independent of the original information signal, to form at least one composite signal, and wherein each of said at least one predetermined sample serves as a time domain pilot reference;
C) processing the at least one composite signal to produce the transmitted signal;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the at least one composite signal from the received signal;
C) recovering, from the at least one composite signal the pilot reference associated therewith;
D) using the recovered pilot reference to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) combining at least one of the parallel plurality of processed information signal sample sequences a periodically with at least one predetermined sample, wherein said at least one predetermined sample is independent of the original information signal, to form at least one composite signal, and wherein each of said at least one predetermined sample serves as a time domain pilot reference;
C) processing the at least one composite signal to produce the transmitted signal;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the at least one composite signal from the received signal;
C) recovering, from the at least one composite signal the pilot reference associated therewith;
D) using the recovered pilot reference to recover the original information signal.
9. The method of claim 8, wherein the step of using the recovered pilot reference to recover the original information signal includes the steps of:
D1) using the recovered pilot reference to recover the original information signal contained in a corresponding one of the parallel plurality of processed information signal sample sequences, which sequence constitutes the sequence that the recovered pilot reference was previously combined with.
D1) using the recovered pilot reference to recover the original information signal contained in a corresponding one of the parallel plurality of processed information signal sample sequences, which sequence constitutes the sequence that the recovered pilot reference was previously combined with.
10. The method of claim 9, wherein the step of using the recovered pilot reference to recover the original information signal further includes the steps of:
D2) using the recovered pilot reference to-recover the original-information signal contained in one of the parallel plurality of processed information signal sample sequences, which sequence constitutes a sequence that the recovered pilot reference was not previously combined with.
D2) using the recovered pilot reference to-recover the original-information signal contained in one of the parallel plurality of processed information signal sample sequences, which sequence constitutes a sequence that the recovered pilot reference was not previously combined with.
11. The method of claim 10, wherein the step of using the recovered pilot reference to recover the original information signal contained in one of the parallel plurality of processed information signal sample sequences, which sequence constitutes a sequence that the recovered pilot reference was not previously combined with, includes the step of using the recovered pilot reference to form an estimated pilot reference for use in recovering the original information signal contained in the sequence that was not previously combined with the pilot reference.
12. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) combining at least two, but not all, of the parallel plurality of processed information signal sample sequences a periodically with at least one predetermined sample to form composite signals;
wherein, each of the at least one predetermined sample serves as a time domain pilot reference;
C) processing the composite signals to produce the transmitted signal;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from the composite signals, the pilot reference associated therewith;
D) using the recovered pilot reference to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) combining at least two, but not all, of the parallel plurality of processed information signal sample sequences a periodically with at least one predetermined sample to form composite signals;
wherein, each of the at least one predetermined sample serves as a time domain pilot reference;
C) processing the composite signals to produce the transmitted signal;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from the composite signals, the pilot reference associated therewith;
D) using the recovered pilot reference to recover the original information signal.
13. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a first serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) selecting at least one, but not all, of the parallel plurality of processed information signal sample sequences to form a selected sequence;
C) combining each selected sequence with at least one predetermined sample to form composite signals, wherein the predetermined sample comprises a time domainpilot reference;
D) processing the composite signals and unselected sequences to form frequency offset signals;
E) combining the frequency offset signals to form a modulation signal;
F) using the modulation signal to modulate a carrier and thereby form the transmitted signal;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering the pilot references from the composite signals to form currently recovered pilot references, and storing information regarding at least some of the currently recovered pilot references;
D) using the currently recovered pilot references to recover the selected sequences that were each previously combined with an associated predetermined sample;
E) using both the currently recovered pilot references and at least some previously stored pilot reference information to form estimated pilot references for use in recovering the unselected sequences that are not combined with an associated predetermined sample;
F) using the recovered selected sequences and unselected sequences to recover an information signal corresponding to the original information signal.
A) converting a first serial portion of the original information signal into a parallel plurality of processed information signal sample sequences;
B) selecting at least one, but not all, of the parallel plurality of processed information signal sample sequences to form a selected sequence;
C) combining each selected sequence with at least one predetermined sample to form composite signals, wherein the predetermined sample comprises a time domainpilot reference;
D) processing the composite signals and unselected sequences to form frequency offset signals;
E) combining the frequency offset signals to form a modulation signal;
F) using the modulation signal to modulate a carrier and thereby form the transmitted signal;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering the pilot references from the composite signals to form currently recovered pilot references, and storing information regarding at least some of the currently recovered pilot references;
D) using the currently recovered pilot references to recover the selected sequences that were each previously combined with an associated predetermined sample;
E) using both the currently recovered pilot references and at least some previously stored pilot reference information to form estimated pilot references for use in recovering the unselected sequences that are not combined with an associated predetermined sample;
F) using the recovered selected sequences and unselected sequences to recover an information signal corresponding to the original information signal.
14. A method of transmitting a plurality of original information signals, comprising the steps of:
A) combining at least one of the plurality of original information signals a periodically with at least one predetermined sample, wherein the at least one predetermined sample serves as a time domain pilot reference that is independent of the at least one of the plurality of original information signal;
B) combining the plurality of original information signals with a carrier.
A) combining at least one of the plurality of original information signals a periodically with at least one predetermined sample, wherein the at least one predetermined sample serves as a time domain pilot reference that is independent of the at least one of the plurality of original information signal;
B) combining the plurality of original information signals with a carrier.
15. The method of claim 14, and further including the step of:
C) transmitting the combined plurality of original information signals and carrier.
C) transmitting the combined plurality of original information signals and carrier.
16. A method of transmitting an original information signal, comprising the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information signals;
B) during a first period of time, combining each of the parallel plurality of digital information signals with at least one first predetermined sample, which first predetermined samples are all substantially time coincident with one another andwhich first predetermined samples serve as time domain pilot references;
C) during a second recurring interval, combining at least one of the parallel plurality of digital information signals a periodically with at least one secondpredetermined sample, at least some of which second predetermined samples are not substantially time coincident with one another and which second predetermined sample serves as a time and frequency domain pilot reference wherein each of said first and said second predetermined samples are independent of the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information signals;
B) during a first period of time, combining each of the parallel plurality of digital information signals with at least one first predetermined sample, which first predetermined samples are all substantially time coincident with one another andwhich first predetermined samples serve as time domain pilot references;
C) during a second recurring interval, combining at least one of the parallel plurality of digital information signals a periodically with at least one secondpredetermined sample, at least some of which second predetermined samples are not substantially time coincident with one another and which second predetermined sample serves as a time and frequency domain pilot reference wherein each of said first and said second predetermined samples are independent of the original information signal.
17. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are not time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, amplitude correction factors;
E) producing, from said amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are not time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, amplitude correction factors;
E) producing, from said amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
18. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are not time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase correction factors;
E) producing, from said phase correction factors and from the raw pilot channelgain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are not time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase correction factors;
E) producing, from said phase correction factors and from the raw pilot channelgain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
19. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are not time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase and amplitude correction factors;
E) producing, from said phase and amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are not time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase and amplitude correction factors;
E) producing, from said phase and amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
20. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, amplitude correction factors;
E) producing, from said amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, amplitude correction factors;
E) producing, from said amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
21. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase correction factors;
E) producing, from said phase correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering, responsive to the step of receiving, the composite signals from the received signal;
C) recovering, from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase correction factors;
E) producing, from said phase correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
22. A method of receiving a transmitted signal, wherein the transmitted signal comprises a signal formed from an original information signal by the steps of:
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering responsive to the step of receiving, the composite signals from the received signal;
C) recovering from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase and amplitude correction factors;
E) producing, from said phase and amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
A) converting a serial portion of the original information signal into a parallel plurality of digital information symbols;
B) combining a first subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
C) combining a second subset of said parallel plurality of digital information symbols with predetermined samples, which predetermined samples are substantially time coincident with one another;
wherein, each of the predetermined samples serve as pilot references;
the method comprising the steps of:
A) receiving the transmitted signal to produce a received signal;
B) recovering responsive to the step of receiving, the composite signals from the received signal;
C) recovering from each of the composite signals, raw pilot channel gain samples associated therewith;
D) deriving from the raw pilot channel gain samples, phase and amplitude correction factors;
E) producing, from said phase and amplitude correction factors and from the raw pilot channel gain samples, recovered corrected pilot channel gain samples;
F) using the recovered corrected pilot channel gain samples to recover the original information signal.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/783,289 US5519730A (en) | 1990-06-12 | 1991-10-28 | Communication signal having a time domain pilot component |
| US783,289 | 1991-10-28 | ||
| PCT/US1992/006768 WO1993009622A1 (en) | 1991-10-28 | 1992-08-14 | Communication signal having a time domain pilot component |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2098011A1 CA2098011A1 (en) | 1993-04-29 |
| CA2098011C true CA2098011C (en) | 1999-06-22 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002098011A Expired - Lifetime CA2098011C (en) | 1991-10-28 | 1992-08-14 | Communication signal having a time domain pilot component |
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| Country | Link |
|---|---|
| US (1) | US5519730A (en) |
| JP (1) | JP3455537B2 (en) |
| KR (1) | KR960012169B1 (en) |
| CN (1) | CN1042886C (en) |
| AU (1) | AU663109B2 (en) |
| BR (1) | BR9205509A (en) |
| CA (1) | CA2098011C (en) |
| GB (1) | GB2266645B (en) |
| HK (1) | HK1000870A1 (en) |
| MX (1) | MX9206164A (en) |
| WO (1) | WO1993009622A1 (en) |
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-
1991
- 1991-10-28 US US07/783,289 patent/US5519730A/en not_active Expired - Lifetime
-
1992
- 1992-08-14 CA CA002098011A patent/CA2098011C/en not_active Expired - Lifetime
- 1992-08-14 AU AU24677/92A patent/AU663109B2/en not_active Expired
- 1992-08-14 WO PCT/US1992/006768 patent/WO1993009622A1/en active Application Filing
- 1992-08-14 BR BR9205509A patent/BR9205509A/en not_active IP Right Cessation
- 1992-08-14 GB GB9312028A patent/GB2266645B/en not_active Expired - Lifetime
- 1992-08-14 KR KR1019930701966A patent/KR960012169B1/en not_active IP Right Cessation
- 1992-08-14 JP JP50837793A patent/JP3455537B2/en not_active Expired - Fee Related
- 1992-09-24 CN CN92110850A patent/CN1042886C/en not_active Expired - Lifetime
- 1992-10-26 MX MX9206164A patent/MX9206164A/en unknown
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1997
- 1997-12-16 HK HK97102445A patent/HK1000870A1/en not_active IP Right Cessation
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| MX9206164A (en) | 1993-04-01 |
| JPH06504176A (en) | 1994-05-12 |
| BR9205509A (en) | 1994-04-05 |
| AU663109B2 (en) | 1995-09-28 |
| WO1993009622A1 (en) | 1993-05-13 |
| AU2467792A (en) | 1993-06-07 |
| GB2266645B (en) | 1996-05-08 |
| KR960012169B1 (en) | 1996-09-16 |
| GB9312028D0 (en) | 1993-08-18 |
| CN1072048A (en) | 1993-05-12 |
| JP3455537B2 (en) | 2003-10-14 |
| KR930703767A (en) | 1993-11-30 |
| CN1042886C (en) | 1999-04-07 |
| US5519730A (en) | 1996-05-21 |
| CA2098011A1 (en) | 1993-04-29 |
| HK1000870A1 (en) | 1998-05-01 |
| GB2266645A (en) | 1993-11-03 |
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