CA2002883A1 - Differential correlator for spread spectrum communication system - Google Patents
Differential correlator for spread spectrum communication systemInfo
- Publication number
- CA2002883A1 CA2002883A1 CA002002883A CA2002883A CA2002883A1 CA 2002883 A1 CA2002883 A1 CA 2002883A1 CA 002002883 A CA002002883 A CA 002002883A CA 2002883 A CA2002883 A CA 2002883A CA 2002883 A1 CA2002883 A1 CA 2002883A1
- Authority
- CA
- Canada
- Prior art keywords
- spread spectrum
- spreading code
- code sequence
- chip
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/709—Correlator structure
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/70718—Spread spectrum techniques using direct sequence modulation with asynchronous demodulation, i.e. not requiring code synchronisation
Abstract
Abstract A spread spectrum communications system includes an encoder for differentially encoding a spread spectrum spreading code sequence in accordance with an input data signal.
Each chip of the spreading code sequence is inverted, or not inverted, relative to the polarity of a corresponding chip of the spreading code sequence a fixed time delay previously, depending on whether the input data is a logic one or zero, respectively. At the receiver, the data is recovered in a differential data decoder wherein the presently received chip of the spread spectrum signal and a previously received chip of spread spectrum signal, a fixed time delay previously, are compared one chip at a time.
Since it is the spreading code sequence that is differentially encoded and differentially decoded, there is no need for a synchronized code sequence generator at the receiver, and data synchronization is achieved after one cycle time of the received spread spectrum spreading code sequence has elapsed.
Each chip of the spreading code sequence is inverted, or not inverted, relative to the polarity of a corresponding chip of the spreading code sequence a fixed time delay previously, depending on whether the input data is a logic one or zero, respectively. At the receiver, the data is recovered in a differential data decoder wherein the presently received chip of the spread spectrum signal and a previously received chip of spread spectrum signal, a fixed time delay previously, are compared one chip at a time.
Since it is the spreading code sequence that is differentially encoded and differentially decoded, there is no need for a synchronized code sequence generator at the receiver, and data synchronization is achieved after one cycle time of the received spread spectrum spreading code sequence has elapsed.
Description
~`: Z00213~33 . ..
DIFFERENTIAL CORRELATOR FOR
SPREAD SPECTRUM COMMUNICATION SYSTEM
Field Of The Invention This invention relates to spread spectrum communication systems. In particular, this invention relates to a data correlator for use in spread spectrum communication systems.
Backaround Of The Invention , Spread spectrum systems are well known. In a spread spectrum data communication system, the individual data bits are modulated with a code sequence, called a spreading code sequence. The individual bits the spreading code sequence are called chips. In order to transmit each data bit in a spread spectrum communication system, each individual data bit is first multiplied by the spreading code sequence in an exclusive OR gate.
:, ' Thus for example, for a data bit of zero, the spreading -1- DOCKET NO. 1015 :
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code itself is transmitted; while for a data bit of one, the inverse of the spreading code is transmitted. Since the spreading code has a higher clock rate than the data, the resulting signal has a higher frequency content i.e., a higher bandwidth than the original data signal.
Specifically, the clock rate of the spread spectrum signal will be hi~her than that of the input data by the chosen spectrum spreading ratio. Thus, the spread spectrum signal energy content is more dispersed throughout the frequency spectrum. Spread spectrum communication systems are therefore less susceptible to noise and interference as well as have greater resistance to multipath distortion delays.
At the receiver, the spreading code sequence is detected in ~-order to recover the original transmitted data. The :;
general problem in spre~d spectrum systems is to correlate the received signal with the ~nowledge of the original spreading code sequence. Detection of the spreading code typically corresponds to the reception of a first logic level, while detection of the inverse of the spreading code correspond~ to detection of the opposite logic level.
In the prior art, there are many types of code correlators for detecting a received spreading code.
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DIFFERENTIAL CORRELATOR FOR
SPREAD SPECTRUM COMMUNICATION SYSTEM
Field Of The Invention This invention relates to spread spectrum communication systems. In particular, this invention relates to a data correlator for use in spread spectrum communication systems.
Backaround Of The Invention , Spread spectrum systems are well known. In a spread spectrum data communication system, the individual data bits are modulated with a code sequence, called a spreading code sequence. The individual bits the spreading code sequence are called chips. In order to transmit each data bit in a spread spectrum communication system, each individual data bit is first multiplied by the spreading code sequence in an exclusive OR gate.
:, ' Thus for example, for a data bit of zero, the spreading -1- DOCKET NO. 1015 :
" X0()2E~8~
code itself is transmitted; while for a data bit of one, the inverse of the spreading code is transmitted. Since the spreading code has a higher clock rate than the data, the resulting signal has a higher frequency content i.e., a higher bandwidth than the original data signal.
Specifically, the clock rate of the spread spectrum signal will be hi~her than that of the input data by the chosen spectrum spreading ratio. Thus, the spread spectrum signal energy content is more dispersed throughout the frequency spectrum. Spread spectrum communication systems are therefore less susceptible to noise and interference as well as have greater resistance to multipath distortion delays.
At the receiver, the spreading code sequence is detected in ~-order to recover the original transmitted data. The :;
general problem in spre~d spectrum systems is to correlate the received signal with the ~nowledge of the original spreading code sequence. Detection of the spreading code typically corresponds to the reception of a first logic level, while detection of the inverse of the spreading code correspond~ to detection of the opposite logic level.
In the prior art, there are many types of code correlators for detecting a received spreading code.
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-2- DOCKET NO. 1015 ., ..
'' ` ' Z002~3~33 In one prior art approach, the signal is applied to an analoq delay line and compared in parallel fashion using programmable analog inverters and adders programmed with a stored version of the spreading code. In operation, the analog delay line tap outputs are inverted or not, according to the spreading sequence in use. When the incoming signal lines up in time with the inverter programming, all outputs will add to produce a one chip long correlation spike. This process is known mathematically as autocorrelation.
The analog delay line, inverters and adders can be combined on a single surface acoustic wave (SAW) device. The latter approach can be costly, especially for small production quantities, and it is difficult to reprogram the SAW for different spreading code sequences. Fully digital correlators are available from such companies as TRW Inc., but they are expensive and use a considerable amount of power.
Another method of correlating the received signal with the original spreading code sequence is to synchronize a local code sequence generator with the incoming signals. In the ~
.:
'' ` ' Z002~3~33 In one prior art approach, the signal is applied to an analoq delay line and compared in parallel fashion using programmable analog inverters and adders programmed with a stored version of the spreading code. In operation, the analog delay line tap outputs are inverted or not, according to the spreading sequence in use. When the incoming signal lines up in time with the inverter programming, all outputs will add to produce a one chip long correlation spike. This process is known mathematically as autocorrelation.
The analog delay line, inverters and adders can be combined on a single surface acoustic wave (SAW) device. The latter approach can be costly, especially for small production quantities, and it is difficult to reprogram the SAW for different spreading code sequences. Fully digital correlators are available from such companies as TRW Inc., but they are expensive and use a considerable amount of power.
Another method of correlating the received signal with the original spreading code sequence is to synchronize a local code sequence generator with the incoming signals. In the ~
.:
-3- DOCKET NO. 1015 latter case, considerably less hardware is required. If the received signal is digitized before being applied to the correlator, then a single exclusive OR gate can be used to compare the incoming signal to the output of the local j synchronized code generator. The problem then becomes one ~;
of synchronizing the local code generator to the code generator in the transmitter. However, sequence -synchronization can taXe many bits to achieve, adding to the overhead needed for the operation of a packet protocol, and in some cases, making existing protocols very difficult~ ~-to implement. -In these circumstances, it would be desirable to find a spread spectrum technique which offers the low cost of a synchronized receiver, while providing very short synchronization time.
~ : -Summary O~ The Invention In the prssent invention, a spreading code sequence is differentially encoded in accordance with an input data signal.
.
of synchronizing the local code generator to the code generator in the transmitter. However, sequence -synchronization can taXe many bits to achieve, adding to the overhead needed for the operation of a packet protocol, and in some cases, making existing protocols very difficult~ ~-to implement. -In these circumstances, it would be desirable to find a spread spectrum technique which offers the low cost of a synchronized receiver, while providing very short synchronization time.
~ : -Summary O~ The Invention In the prssent invention, a spreading code sequence is differentially encoded in accordance with an input data signal.
.
-4- DOCKET NO. 1015 . :;
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Specifically, if the input data signal is a one, the present chip of the spreading code sequence is inverted relative to a corresponding chip of the spreading code sequence a fixed time delay previously. If the input data signal is a zero, the present chip of the spreading code sequence is no~ inverted relative to a corresponding chip of the spreading code sequence a fixed time delay previously. In other words, the polarity of the spreading code sequence is either inverted or not inverted relative to the polarity of the spreading code sequence a fixed time period previously, depending on whether the input data signal is a one or zero, respectively.
At the receiver, in accordance with the present invention, each received chip of the spreading code sequence is compared with the previously received chip of the spreading code sequence. Since the spreading code sequence was originally differentially encoded at the transmitter, if the received chip of the spreading code sequence and the previously received chip of the spreading code seguence are ~;
the same, then received data is a zero logic level.
Conversely~ if the received chip of the spreading code sequence is the inverse of the previously received chip of the spreading code seguence, then the received data is a one logic level.
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Specifically, if the input data signal is a one, the present chip of the spreading code sequence is inverted relative to a corresponding chip of the spreading code sequence a fixed time delay previously. If the input data signal is a zero, the present chip of the spreading code sequence is no~ inverted relative to a corresponding chip of the spreading code sequence a fixed time delay previously. In other words, the polarity of the spreading code sequence is either inverted or not inverted relative to the polarity of the spreading code sequence a fixed time period previously, depending on whether the input data signal is a one or zero, respectively.
At the receiver, in accordance with the present invention, each received chip of the spreading code sequence is compared with the previously received chip of the spreading code sequence. Since the spreading code sequence was originally differentially encoded at the transmitter, if the received chip of the spreading code sequence and the previously received chip of the spreading code seguence are ~;
the same, then received data is a zero logic level.
Conversely~ if the received chip of the spreading code sequence is the inverse of the previously received chip of the spreading code seguence, then the received data is a one logic level.
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It is not necessary that the time duration of one input ~ ;
data bit be equal to the time duration of one cycle of the spread spectrum spreading code sequence. In general, the number of chips per data bit may be less than, equal to, or greater than the number of chips in the spread spectrum spreading code sequence. In all cases, however, both in the transmitter encoding process, and in the receiver correlation process, each chip is compared to the corresponding chip of the previous spreading code sequence.
It is noted that by use of the present invention, there is no need for a sequence generator at the receiver, and the entire data correlator is simple in operation and low in cost. Furthermore, synchronization of the receiver is achieved after one cycle of the spreading code sequence.
.
Description Of the Drawinas :, Figure 1 shows a block diagram of a general purpose spread spectrum communication system embodying the present ~-invention~
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It is not necessary that the time duration of one input ~ ;
data bit be equal to the time duration of one cycle of the spread spectrum spreading code sequence. In general, the number of chips per data bit may be less than, equal to, or greater than the number of chips in the spread spectrum spreading code sequence. In all cases, however, both in the transmitter encoding process, and in the receiver correlation process, each chip is compared to the corresponding chip of the previous spreading code sequence.
It is noted that by use of the present invention, there is no need for a sequence generator at the receiver, and the entire data correlator is simple in operation and low in cost. Furthermore, synchronization of the receiver is achieved after one cycle of the spreading code sequence.
.
Description Of the Drawinas :, Figure 1 shows a block diagram of a general purpose spread spectrum communication system embodying the present ~-invention~
,~
-6- DOCKET NO. 1015 20028~33 Figures 2a, 2b, and 2c is a time diagram illustrating a spreading code sequence which may be used in conjunction with the present invention.
' Figure 3 is a block diagram of a spread spectrum modem including a spread spectrum transmitter and a spread spectrum receiver in accordance with the present invention.
Figure 4 is a prior art spread spectrum data encoder.
Figure 5 is a prior art spread spectrum data correlator.
''' `' Figure 6 is a spread spectrum data encoder in accordance with the present invention.
Figure 7 is one embodiment of a spread spectrum data correlator in accordance with the present invention. ¦~
~ Figure 8 is a second embodiment of a spread spectrum data ¦~ correlator embodying the present invention. -.. ...
Det~ilç~_~5~crip~ion :'..",.'~':
¦ -7- DOCKET N0. 1015 ' : ."'.''''' , . ' ' ' .
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A generalized illustration of a data communication system is shown in ~igure 1. It is intended that data input at terminal 10 will be transmitted through the system and be available as data output on terminal 24.
Data input at terminal 10 is applied to spread spectrum modulator 12 which is in turn input to RF transmitter 14.
The output of RF transmitter 14 is applied to a transmitting antenna 16. After the transmission through a suitable medium and reception by receiving antenna 18, the signal is applied to RF receiver 20. The output of RF
receiver 20 is applied to a spread spectrum demodulator 22 in order to recover the original data.
The spread spectrum modulator 12 contains a sequence generator in order to provide a spreading code sequence. As illustrated in figure 2a, the sequence generator produces a repeating sequence M chips in length starting at time Tl and ending at time T2. Methods for generating repeating code sequences, such as maximal length pseudo random code qenerators, are well known in the art and form no part of the presQn~ invention. Also, as noted in figure 2a, ~ince the sequence is repeating every M chips, it makes no difference where the sequence begins and ends so long as ;;
-8- DOCKET N0. 1015 ~, , . , , . , .. . . , . , . , ,, , ~ ... .
Z002~383 there are M chips per cycle of the sequence. Thus, time T3 may be the starting time of the sequence, and time T4 the ending time.
The number of chips per data bit, however, need n~t be equal to the number of chips per spreading code sequence.
As illustrated in Figure 2b, the number of chips per data bit may be less than the number of chips per cycle of the spreading code sequence, or, as illustrated in Figure 2c, the number of chips per data bit may be greater than the number of chips per cycle of the spreading code sequence.
..... :. :' Regardless of the number of chips per data bit, the transitions of the data bits should be coincident with the transitions of the individual chips. Thus, in Figure 2b, the data transition at Tl is coincident with the system chip clock, and in Figure 2c, the data transition at T4 is -also coincident with the system chip clock A block diagram o~ a spread spectrum radio modem for transmitting and receiving digital data is shown in figure 3. m e transmitter portion comprises spread spectrum ~
encoder 28 transmitter chip clock 30, PSK modulator 34 and `
RF transmitter 14. The receiving portion comprises RF
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-9- DOC Æ T N0. 1015 ; -... .
.. .
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: 2002883 receiver 20, PSK demodulator 40, receiver chip clock 42, spread spectrum correlator 46 and filter and threshold ..
circuits 50. The transmit/receive switch 36 permits an antenna 38 to be shared between the transmitter and receiver.
Data output from a data device 26 which may be a computer or ~ computer terminal is applied to spread spectrum -encoder 28. Output of the spread spectrum encoder 28 which has been increased in bandwidth due to the higher frequency transmitter chip clock, is applied to PSK modulator 34 and RF transmitter 14 for transmission through transmit/receive switch 36 and to antenna 38.
In the receive mode, transmit/receive switch 36 connects antenna 38 to RF receiver 20. The output of RF receiver 20 is applied to PSK demodulator 40. The receiver chip clock ..
42 is derived from the received spread spectrum signal in .
PSK demodulator 40.
The reconstruction or derivation of the receiver chip clock :~.
42 from the.signal received at PSK demodulator 40 is well known to those skilled in the art and forms no part of the present invention. The recovered receiver chip clock is - -10- DOCKET N0. 1015 applied to spread spectrum correlator 46 as is the output of PSK demodulator 40. Within the spread spectrum correlator 46, the received signal is correlated with the spreading code sequence which was used in the transmitter, in order to derive the received data. The output of correlator 46 is in connected to filter and threshold circuits 50 which provide a data input to the data device 26.
A typical prior art spread spectrum encoder 28 is shown in figure 4. The encoder 28 consists of an exclusive OR gate 52 having one input connected to the data input terminal 10. The othar input of exclusive OR 52 gate is connected to the output of a sequence generator 54 which is driven by -~
the transmitter chip clock 30. The output of exclusive OR
gate 52 on conductor 51 is the output fed to the PSX ,-modulator. Depending upon whether the data input at terminal 10 is a one or a zero, either an inverted or not :;~
inverted version of the spreading code sequence from .
sequence generator 54 will be fed to the modulator on conductor 51.
~, ~ W CKET NO. 1015 .......
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20028~33 . .
A prior art data correlator is shown in figure 5. The data correlator consists of a four quadrant analog multiplier 60 having one input 63 from the demodulator and another input 61 connected to synchronized generator 52 which is driven by receiver chip clock 42. Methods of synchronizing the sequence generator 62 in the correlator with the sequence generator 54 in the encoder (figure 4) are well known in the prior art.
Data correlator 46 of fiqure 5 may also be implemented in digital form. If so, the signal input on conductor 63 is first digitized. The output of the synchronized sequence generator 62 would then be digital in nature. In the case of one bit quantization, the four quadrant multiplier 60 would be replaced with a two input exclusive OR gate.
Alternatively, if the signal input on conductor 63 is digitized in a digital to analog converter having a plural bit parallel output, then multiplier 60 would then be replaced with a digital multiplier.
If the received code sequence on conductor 63 is the same as the s~nchronized code se~uence on conductor 61 , then the output on conductor 59 would indicate a zero data bit.
Conversely, if the received code seguence on conductor 63 ,~:
-12- DOCKET NO. 1015 i i~ the inverse of the synchronized code sequence on conductor 61, then the output on conductor 59 would indicate a one data bit. ;
It is noted that the sequence generator 62 at the receiver correlator 46 i~ figure 5 must be synchronized with the sequence generator 30 at the encoder 28 in figure 4. Such synchronization may take a long time to achieve and also may add a considerable amount of hardware.
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A data encoder in accordance with the present invention is -~
shown in figure 6. The data encoder 28 includes a data ;~
input terminal 10 connected to one input terminal of an exclusive QR qate 70. The output of exclusive OR gate 70 ~ .
at conductor 73 is connected to an input of a delay means 72. Delay means 72 may be implemen~ed by using a shift register or other type of delay memory. The delay means 72 provides a signal delay substantially equal to the length ~
of the spreading code sequence provided by sèquence ~ `
generator 54 on conductor 75. The output of delay means 72 - `
on conductor 71 is input to the second input of exclusive OR gate 70.
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-13- DOCKET NO. 1015 ; ~
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2002~383 :.`-` i The output of exclusive OR gate 70 on conductor 73 is one input to exclusive OR gate 74. The other input to exclusive OR gate 74 on conductor 75 is the output of the sequence generator 54. The resulting output of exclusive OR gate is the spread spectrum signal on conductor 51 which is applied to tbe modulator.
Figure 7 shows an analog correlator 46 for receiving the spread spectrum signal from encoder 28 of figure 6.
Correlator 46 consists of four quadrant multiplier 80 and delay means 82. Again, delays means 82, which may for example, be a charge coupled device (CCD), or other delay memory, provides a signal delay substantially equal to the length of one cycle of the spreading code sequence. The signal from the demodulator is applied to one input of the four quadrant multiplier 80 on conductor 83 and also to the input to the delay means 82. The other input of the four quadrant multiplier 80 is connected to the output of delay ~;
means 82 on conductor 81. The output of the four quadrant multiplier 80 on conductor 84 is the data output which is connected to the filter and threshold circuits 50 (from figure 3~_ : ', .
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-14- DOCKET NO. 1015 1 2002~383 A digital version of the data correlator of figure 7 is shown in figure 8. A threshold circuit 44 is used to digitize, i.e. one bit quantize, the signal coming from the demodulator on conductor 9S. In lieu of analog multiplier, the digital data correlator of figure 8 includes an exclusive OR gate 90. The output of threshold circuit 44 ~ -on conductor 93 is connected to one input of exclusive OR
gate 90 and also to the input of delay means 92. Again the - `
delay means 92 which in the digital case may be a shift register, provides a delay substantially equal to one cycle of the spreading code sequence. The output of delay means 92 on conductor 91 is connected to the other input of -exclusive OR gate 90. The output of exclusive OR gate 90 ~- ~
on conductor 94 is the data output to the remainder of the ~ -receiving system.
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The four quadrant analog multiplier 80 as shown in figure 7 is analogous to the two input exclusive OR gate 90 shown in `~
figure 8. This is true because the rules for multiplying ~`
signed numbers is analogous to the logic table for an -exclusive OR gate function. That is, if the signal inputs to the multiplier 80 have the same polarity, i.e. are both -~
positive or both negative, the output is positive. On the other hand, i~ the signal inputs are of opposite polarity, ,, "
-15- DOCKET NO. 1015 . . .
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2002~383 -.`.
the output of multiplier 80 is negative. Thus, while an exclusive OR gate provides an indication of equality of logic level, a four quadrant multiplier provides an indication of equality of signal polarity.
In reference to the following discussion regarding the operation of the encoder and correlator, it is assumed that there is a transparent data path from conductor 51 of figure 6 to conductor 95 of figure 8. That is, it is assumed that the remainder of the transmission system including the PSK modulator and PSX demodulator the RF
transmitter and RF receiver will deliver the spread ~pectrum signal from conductor 51 of figure 6 to conductor 95 of figure 8. ~
In operation, the intended purpose of the encoder of figure ~:
6 is to invert, or not invert, the polarity o~ each chip of `.
the spreading code sequence, relative to the polarity of ~-the corresponding chip of the spreading code seguence a .:
fixed time delay previously, in accordance with the value of the input data. Specifically, if the present input data signal is ~.logic one, the polarity of the spreading code sequence, relative to the polarity of the spreading code sequence a fixed time delay previously will be inverted; if -16- DOCKET NO. 1015 .
2002~383 the present input data signal is a zero, the encoder of figure 6 will not invert the polarity of the present chip of the spreading code sequence, relative to the polarity of the spreading code sequence a fixed time delay previously.
Exclusive OR gate 74 acts on the output of the spreading :
code sequence generator 54 to invert or not invert each chip of the spreading code sequence depending upon the value of an inversion control logic signal on conductor 73. Thus, if the signal on conductor 73 is a logic one, the present chip from the spreading code sequence from . :
sequence generator 54 on conductor 75 is inverted at the output of exclusive OR 74 on conductor 51. Conversely, if the signal on conductor 73 is a logic zero, the present -~
chip from the spreading code sequence from sequence generator 54 at the output on conductor 75 is not inverted.
.: , The inversion control signal on conductor 73 is recorded in `~
delay means 72 so that the previous inversion control signal, a fixed time delay previously, is presented as one ;~
input to exclusive OR gate 70 on conductor 71. It can be seen tha~ the data at input terminal 10 is a logic one, then exclusive OR gate 70 inverts the previous inversion control signal to form the present inversion control ;:
-17- DOCKET NO. 1015 i:,,, 200~83 - :
signal, while if the data input is a logic zero, exclusive OR gate 70 does not invert the previous inversion control signal to form the present inversion control signal.
More specifically, if the previous chip (the corresponding chip of the previous cycle of the spreading code sequence) was inverted and the data input is a logic one, then the present chip is not inverted. If the previous chip was not inverted, and the data input is a logic one, then the present chip is inverted. If the previous chip was inverted, and the data input is a logic zero, then the present chip is also inverted. If the previous chip was not inverted, and the data input is a logic zero, then the present chip is also not inverted.
At the receiver, the signal input on conductor 95 of figure 8 is effectively digitized i.e., one bit quantized or bit sliced by threshold circuit 44 so that such signal appears in digital form on conductor 93.
Delay means 92 stores the individual received chips of the spread spe~trum signal. The output of the delay means 92 is the corresponding chip of the previous spreading code !
sequence.
-18- DOCKET NO. 1015 ' , -.
, -~002883 Now, exclusive OR gate 90 compares each received chip of the presently received spreading code sequence with a corresponding chip of the previously received spreading code sequence. Either the presently received chip of the spreading code sequence is the sam~ as the previously received chip of the previously received sequence, in which case the received data is a logic zero, or it is the opposite of the previously received sequence, in which case the received data is a logic one.
,:' In either event, the output of exclusive O~ gate 90 on conductor 94 will be a series of comparisons one data bit in total length, one comparison for each chip of the ;~
spreading code sequence, the total number of comparisons being equal to the total number of chips per data bit. The ~
analog correlator of figure 7 operates in a similar manner, ~-by comparing the polarity of each chip of the received ~;
spreading code sequence to the polarity of a corresponding chip of the previously received spreading code sequence, ;~
and providing a first analog output indication (a positive -signal~ if ~he polarities are the same, and a second analog output indication (a negative signal) if the polarities are opposite.
-19- DOCKET NO. 1015 2002t383 Following the output of the data correlator 46 is a majority vote logic in order to determine whether the received data bit is a one or a zero. Under ideal conditions, all of the output chips over one data bit interval from exclusive OR 90 will be of the sam~
polarity. In the presence of noise, some of them will be in error. However, by a ma;ority vote of the output chips on conductor 94, improved communications reliability is achieved.
It is noted that data correlator 46 has no sequence generator at all. Therefore, there is no sequence generator to synchronize. Instead, synchronization is automatically achieved after one complete cycle of the spreading code sequence, i.e. once delay reqister 92 is filled.
As noted above, the number of chips per data bit need not equal the number of chip per spreading code sequence.
However, as long as the delay memory 72 in the encoder (Figure ~-and the delay memory 82, 92 in the correlator (Figures 7,8), provide respective delays substantially equal to the number of chips in the spreading code ;
-20- DOCKET NO. 1015 200288~ `
`' sequence, differential encoding and differential correlation will provide a data path through the spread spectrum system. ;~
Thus, a simple economical data correlator and data encoder has been described for use in conjunction with a spread spectrum communication system. The described system is low -.
in cost and will rapidly synchronize with the received .
spread spectrum signal. ~
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' Figure 3 is a block diagram of a spread spectrum modem including a spread spectrum transmitter and a spread spectrum receiver in accordance with the present invention.
Figure 4 is a prior art spread spectrum data encoder.
Figure 5 is a prior art spread spectrum data correlator.
''' `' Figure 6 is a spread spectrum data encoder in accordance with the present invention.
Figure 7 is one embodiment of a spread spectrum data correlator in accordance with the present invention. ¦~
~ Figure 8 is a second embodiment of a spread spectrum data ¦~ correlator embodying the present invention. -.. ...
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¦ -7- DOCKET N0. 1015 ' : ."'.''''' , . ' ' ' .
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A generalized illustration of a data communication system is shown in ~igure 1. It is intended that data input at terminal 10 will be transmitted through the system and be available as data output on terminal 24.
Data input at terminal 10 is applied to spread spectrum modulator 12 which is in turn input to RF transmitter 14.
The output of RF transmitter 14 is applied to a transmitting antenna 16. After the transmission through a suitable medium and reception by receiving antenna 18, the signal is applied to RF receiver 20. The output of RF
receiver 20 is applied to a spread spectrum demodulator 22 in order to recover the original data.
The spread spectrum modulator 12 contains a sequence generator in order to provide a spreading code sequence. As illustrated in figure 2a, the sequence generator produces a repeating sequence M chips in length starting at time Tl and ending at time T2. Methods for generating repeating code sequences, such as maximal length pseudo random code qenerators, are well known in the art and form no part of the presQn~ invention. Also, as noted in figure 2a, ~ince the sequence is repeating every M chips, it makes no difference where the sequence begins and ends so long as ;;
-8- DOCKET N0. 1015 ~, , . , , . , .. . . , . , . , ,, , ~ ... .
Z002~383 there are M chips per cycle of the sequence. Thus, time T3 may be the starting time of the sequence, and time T4 the ending time.
The number of chips per data bit, however, need n~t be equal to the number of chips per spreading code sequence.
As illustrated in Figure 2b, the number of chips per data bit may be less than the number of chips per cycle of the spreading code sequence, or, as illustrated in Figure 2c, the number of chips per data bit may be greater than the number of chips per cycle of the spreading code sequence.
..... :. :' Regardless of the number of chips per data bit, the transitions of the data bits should be coincident with the transitions of the individual chips. Thus, in Figure 2b, the data transition at Tl is coincident with the system chip clock, and in Figure 2c, the data transition at T4 is -also coincident with the system chip clock A block diagram o~ a spread spectrum radio modem for transmitting and receiving digital data is shown in figure 3. m e transmitter portion comprises spread spectrum ~
encoder 28 transmitter chip clock 30, PSK modulator 34 and `
RF transmitter 14. The receiving portion comprises RF
.:
-9- DOC Æ T N0. 1015 ; -... .
.. .
. .
. :
: 2002883 receiver 20, PSK demodulator 40, receiver chip clock 42, spread spectrum correlator 46 and filter and threshold ..
circuits 50. The transmit/receive switch 36 permits an antenna 38 to be shared between the transmitter and receiver.
Data output from a data device 26 which may be a computer or ~ computer terminal is applied to spread spectrum -encoder 28. Output of the spread spectrum encoder 28 which has been increased in bandwidth due to the higher frequency transmitter chip clock, is applied to PSK modulator 34 and RF transmitter 14 for transmission through transmit/receive switch 36 and to antenna 38.
In the receive mode, transmit/receive switch 36 connects antenna 38 to RF receiver 20. The output of RF receiver 20 is applied to PSK demodulator 40. The receiver chip clock ..
42 is derived from the received spread spectrum signal in .
PSK demodulator 40.
The reconstruction or derivation of the receiver chip clock :~.
42 from the.signal received at PSK demodulator 40 is well known to those skilled in the art and forms no part of the present invention. The recovered receiver chip clock is - -10- DOCKET N0. 1015 applied to spread spectrum correlator 46 as is the output of PSK demodulator 40. Within the spread spectrum correlator 46, the received signal is correlated with the spreading code sequence which was used in the transmitter, in order to derive the received data. The output of correlator 46 is in connected to filter and threshold circuits 50 which provide a data input to the data device 26.
A typical prior art spread spectrum encoder 28 is shown in figure 4. The encoder 28 consists of an exclusive OR gate 52 having one input connected to the data input terminal 10. The othar input of exclusive OR 52 gate is connected to the output of a sequence generator 54 which is driven by -~
the transmitter chip clock 30. The output of exclusive OR
gate 52 on conductor 51 is the output fed to the PSX ,-modulator. Depending upon whether the data input at terminal 10 is a one or a zero, either an inverted or not :;~
inverted version of the spreading code sequence from .
sequence generator 54 will be fed to the modulator on conductor 51.
~, ~ W CKET NO. 1015 .......
`,;
20028~33 . .
A prior art data correlator is shown in figure 5. The data correlator consists of a four quadrant analog multiplier 60 having one input 63 from the demodulator and another input 61 connected to synchronized generator 52 which is driven by receiver chip clock 42. Methods of synchronizing the sequence generator 62 in the correlator with the sequence generator 54 in the encoder (figure 4) are well known in the prior art.
Data correlator 46 of fiqure 5 may also be implemented in digital form. If so, the signal input on conductor 63 is first digitized. The output of the synchronized sequence generator 62 would then be digital in nature. In the case of one bit quantization, the four quadrant multiplier 60 would be replaced with a two input exclusive OR gate.
Alternatively, if the signal input on conductor 63 is digitized in a digital to analog converter having a plural bit parallel output, then multiplier 60 would then be replaced with a digital multiplier.
If the received code sequence on conductor 63 is the same as the s~nchronized code se~uence on conductor 61 , then the output on conductor 59 would indicate a zero data bit.
Conversely, if the received code seguence on conductor 63 ,~:
-12- DOCKET NO. 1015 i i~ the inverse of the synchronized code sequence on conductor 61, then the output on conductor 59 would indicate a one data bit. ;
It is noted that the sequence generator 62 at the receiver correlator 46 i~ figure 5 must be synchronized with the sequence generator 30 at the encoder 28 in figure 4. Such synchronization may take a long time to achieve and also may add a considerable amount of hardware.
. .
::,:'~;' '~
A data encoder in accordance with the present invention is -~
shown in figure 6. The data encoder 28 includes a data ;~
input terminal 10 connected to one input terminal of an exclusive QR qate 70. The output of exclusive OR gate 70 ~ .
at conductor 73 is connected to an input of a delay means 72. Delay means 72 may be implemen~ed by using a shift register or other type of delay memory. The delay means 72 provides a signal delay substantially equal to the length ~
of the spreading code sequence provided by sèquence ~ `
generator 54 on conductor 75. The output of delay means 72 - `
on conductor 71 is input to the second input of exclusive OR gate 70.
".
~'~.'`, `
-13- DOCKET NO. 1015 ; ~
'`'''";",~
2002~383 :.`-` i The output of exclusive OR gate 70 on conductor 73 is one input to exclusive OR gate 74. The other input to exclusive OR gate 74 on conductor 75 is the output of the sequence generator 54. The resulting output of exclusive OR gate is the spread spectrum signal on conductor 51 which is applied to tbe modulator.
Figure 7 shows an analog correlator 46 for receiving the spread spectrum signal from encoder 28 of figure 6.
Correlator 46 consists of four quadrant multiplier 80 and delay means 82. Again, delays means 82, which may for example, be a charge coupled device (CCD), or other delay memory, provides a signal delay substantially equal to the length of one cycle of the spreading code sequence. The signal from the demodulator is applied to one input of the four quadrant multiplier 80 on conductor 83 and also to the input to the delay means 82. The other input of the four quadrant multiplier 80 is connected to the output of delay ~;
means 82 on conductor 81. The output of the four quadrant multiplier 80 on conductor 84 is the data output which is connected to the filter and threshold circuits 50 (from figure 3~_ : ', .
~,''.
-14- DOCKET NO. 1015 1 2002~383 A digital version of the data correlator of figure 7 is shown in figure 8. A threshold circuit 44 is used to digitize, i.e. one bit quantize, the signal coming from the demodulator on conductor 9S. In lieu of analog multiplier, the digital data correlator of figure 8 includes an exclusive OR gate 90. The output of threshold circuit 44 ~ -on conductor 93 is connected to one input of exclusive OR
gate 90 and also to the input of delay means 92. Again the - `
delay means 92 which in the digital case may be a shift register, provides a delay substantially equal to one cycle of the spreading code sequence. The output of delay means 92 on conductor 91 is connected to the other input of -exclusive OR gate 90. The output of exclusive OR gate 90 ~- ~
on conductor 94 is the data output to the remainder of the ~ -receiving system.
" `; " ;~
The four quadrant analog multiplier 80 as shown in figure 7 is analogous to the two input exclusive OR gate 90 shown in `~
figure 8. This is true because the rules for multiplying ~`
signed numbers is analogous to the logic table for an -exclusive OR gate function. That is, if the signal inputs to the multiplier 80 have the same polarity, i.e. are both -~
positive or both negative, the output is positive. On the other hand, i~ the signal inputs are of opposite polarity, ,, "
-15- DOCKET NO. 1015 . . .
:. :,, - - '1~-.~.'"', . .
, . ,,:
~, ...
2002~383 -.`.
the output of multiplier 80 is negative. Thus, while an exclusive OR gate provides an indication of equality of logic level, a four quadrant multiplier provides an indication of equality of signal polarity.
In reference to the following discussion regarding the operation of the encoder and correlator, it is assumed that there is a transparent data path from conductor 51 of figure 6 to conductor 95 of figure 8. That is, it is assumed that the remainder of the transmission system including the PSK modulator and PSX demodulator the RF
transmitter and RF receiver will deliver the spread ~pectrum signal from conductor 51 of figure 6 to conductor 95 of figure 8. ~
In operation, the intended purpose of the encoder of figure ~:
6 is to invert, or not invert, the polarity o~ each chip of `.
the spreading code sequence, relative to the polarity of ~-the corresponding chip of the spreading code seguence a .:
fixed time delay previously, in accordance with the value of the input data. Specifically, if the present input data signal is ~.logic one, the polarity of the spreading code sequence, relative to the polarity of the spreading code sequence a fixed time delay previously will be inverted; if -16- DOCKET NO. 1015 .
2002~383 the present input data signal is a zero, the encoder of figure 6 will not invert the polarity of the present chip of the spreading code sequence, relative to the polarity of the spreading code sequence a fixed time delay previously.
Exclusive OR gate 74 acts on the output of the spreading :
code sequence generator 54 to invert or not invert each chip of the spreading code sequence depending upon the value of an inversion control logic signal on conductor 73. Thus, if the signal on conductor 73 is a logic one, the present chip from the spreading code sequence from . :
sequence generator 54 on conductor 75 is inverted at the output of exclusive OR 74 on conductor 51. Conversely, if the signal on conductor 73 is a logic zero, the present -~
chip from the spreading code sequence from sequence generator 54 at the output on conductor 75 is not inverted.
.: , The inversion control signal on conductor 73 is recorded in `~
delay means 72 so that the previous inversion control signal, a fixed time delay previously, is presented as one ;~
input to exclusive OR gate 70 on conductor 71. It can be seen tha~ the data at input terminal 10 is a logic one, then exclusive OR gate 70 inverts the previous inversion control signal to form the present inversion control ;:
-17- DOCKET NO. 1015 i:,,, 200~83 - :
signal, while if the data input is a logic zero, exclusive OR gate 70 does not invert the previous inversion control signal to form the present inversion control signal.
More specifically, if the previous chip (the corresponding chip of the previous cycle of the spreading code sequence) was inverted and the data input is a logic one, then the present chip is not inverted. If the previous chip was not inverted, and the data input is a logic one, then the present chip is inverted. If the previous chip was inverted, and the data input is a logic zero, then the present chip is also inverted. If the previous chip was not inverted, and the data input is a logic zero, then the present chip is also not inverted.
At the receiver, the signal input on conductor 95 of figure 8 is effectively digitized i.e., one bit quantized or bit sliced by threshold circuit 44 so that such signal appears in digital form on conductor 93.
Delay means 92 stores the individual received chips of the spread spe~trum signal. The output of the delay means 92 is the corresponding chip of the previous spreading code !
sequence.
-18- DOCKET NO. 1015 ' , -.
, -~002883 Now, exclusive OR gate 90 compares each received chip of the presently received spreading code sequence with a corresponding chip of the previously received spreading code sequence. Either the presently received chip of the spreading code sequence is the sam~ as the previously received chip of the previously received sequence, in which case the received data is a logic zero, or it is the opposite of the previously received sequence, in which case the received data is a logic one.
,:' In either event, the output of exclusive O~ gate 90 on conductor 94 will be a series of comparisons one data bit in total length, one comparison for each chip of the ;~
spreading code sequence, the total number of comparisons being equal to the total number of chips per data bit. The ~
analog correlator of figure 7 operates in a similar manner, ~-by comparing the polarity of each chip of the received ~;
spreading code sequence to the polarity of a corresponding chip of the previously received spreading code sequence, ;~
and providing a first analog output indication (a positive -signal~ if ~he polarities are the same, and a second analog output indication (a negative signal) if the polarities are opposite.
-19- DOCKET NO. 1015 2002t383 Following the output of the data correlator 46 is a majority vote logic in order to determine whether the received data bit is a one or a zero. Under ideal conditions, all of the output chips over one data bit interval from exclusive OR 90 will be of the sam~
polarity. In the presence of noise, some of them will be in error. However, by a ma;ority vote of the output chips on conductor 94, improved communications reliability is achieved.
It is noted that data correlator 46 has no sequence generator at all. Therefore, there is no sequence generator to synchronize. Instead, synchronization is automatically achieved after one complete cycle of the spreading code sequence, i.e. once delay reqister 92 is filled.
As noted above, the number of chips per data bit need not equal the number of chip per spreading code sequence.
However, as long as the delay memory 72 in the encoder (Figure ~-and the delay memory 82, 92 in the correlator (Figures 7,8), provide respective delays substantially equal to the number of chips in the spreading code ;
-20- DOCKET NO. 1015 200288~ `
`' sequence, differential encoding and differential correlation will provide a data path through the spread spectrum system. ;~
Thus, a simple economical data correlator and data encoder has been described for use in conjunction with a spread spectrum communication system. The described system is low -.
in cost and will rapidly synchronize with the received .
spread spectrum signal. ~
'.
" ' ~, '
Claims (15)
1. A differential spread spectrum data encoder comprising:
an input terminal for receiving an input data signal;
an output terminal;
means for generating a spread spectrum spreading code sequence;
differential encoding means responsive to said spread spectrum spreading code generator means and said input data signal at said input terminal, for providing a spread spectrum signal at said output terminal;
said differential encoding means including means for inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence a fixed time delay previously at said output terminal, if said present input data signal is a first logic level; and said differential encoding means including means for means for not inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence said fixed time delay previously at said output terminal, if said present input data signal is a second logic level.
an input terminal for receiving an input data signal;
an output terminal;
means for generating a spread spectrum spreading code sequence;
differential encoding means responsive to said spread spectrum spreading code generator means and said input data signal at said input terminal, for providing a spread spectrum signal at said output terminal;
said differential encoding means including means for inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence a fixed time delay previously at said output terminal, if said present input data signal is a first logic level; and said differential encoding means including means for means for not inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence said fixed time delay previously at said output terminal, if said present input data signal is a second logic level.
2. A differential spread spectrum data encoder in accordance with claim 1, wherein said differential encoding means comprises:
an exclusive OR gate having first and second input terminals and an output terminal, said first input terminal of said exclusive OR gate being connected to said input terminal;
delay means having an input and an output terminal, said output terminal of said delay means being connected to said second input terminal of said exclusive OR gate, said input terminal of said delay means being connected to said output terminal of said exclusive OR gate; and means for combining the signal at said output of said exclusive OR gate and the output of said spread spectrum spreading code sequence generator means.
an exclusive OR gate having first and second input terminals and an output terminal, said first input terminal of said exclusive OR gate being connected to said input terminal;
delay means having an input and an output terminal, said output terminal of said delay means being connected to said second input terminal of said exclusive OR gate, said input terminal of said delay means being connected to said output terminal of said exclusive OR gate; and means for combining the signal at said output of said exclusive OR gate and the output of said spread spectrum spreading code sequence generator means.
3. A differential spread spectrum data encoder in accordance with claim 2, wherein said combining means comprises:
a second exclusive OR gate having respective first and second input terminals and a respective output terminal;
means coupling said first input terminal of said second exclusive OR gate to the output terminal of said first exclusive OR gate;
means coupling said second input terminal of said second exclusive OR gate to the output of said spread spectrum spreading code sequence generator means: and means coupling said output terminal of said second exclusive OR gate to said output terminal.
a second exclusive OR gate having respective first and second input terminals and a respective output terminal;
means coupling said first input terminal of said second exclusive OR gate to the output terminal of said first exclusive OR gate;
means coupling said second input terminal of said second exclusive OR gate to the output of said spread spectrum spreading code sequence generator means: and means coupling said output terminal of said second exclusive OR gate to said output terminal.
4. A differential spread spectrum data encoder comprising:
an input terminal for receiving a data input signal;
first and second exclusive OR gates having respective first and second input terminals and respective output terminals, said first input terminal of said first exclusive OR gate being connected to said input terminal;
delay means having an input terminal coupled to the output terminal of said first exclusive OR gate, and said delay means also having an output terminal coupled to the second input terminal of said first exclusive OR gate;
means for generating a spread spectrum spreading sequence;
means coupling the output of said spread spectrum spreading code sequence generator to the second input terminal of said second exclusive OR gate;
means coupling the output terminal of said first exclusive OR gate to the first input terminal of said second exclusive OR gate; and an output terminal coupled to the output terminal of said second exclusive OR gate.
an input terminal for receiving a data input signal;
first and second exclusive OR gates having respective first and second input terminals and respective output terminals, said first input terminal of said first exclusive OR gate being connected to said input terminal;
delay means having an input terminal coupled to the output terminal of said first exclusive OR gate, and said delay means also having an output terminal coupled to the second input terminal of said first exclusive OR gate;
means for generating a spread spectrum spreading sequence;
means coupling the output of said spread spectrum spreading code sequence generator to the second input terminal of said second exclusive OR gate;
means coupling the output terminal of said first exclusive OR gate to the first input terminal of said second exclusive OR gate; and an output terminal coupled to the output terminal of said second exclusive OR gate.
5. In a spread spectrum communication system including a spread spectrum signal having a spreading code sequence differentially encoded in accordance with an input data signal, a data correlator comprising:
an input terminal for receiving said spread spectrum signal;
an output terminal;
differential decoding means, coupled to said input terminal for determining whether at least one chip of the presently received spread spectrum spreading code sequence at said input terminal and at least one chip of a previously received spread spectrum spreading code sequence are substantially equal;
said differential decoding means further providing a first logic level output at said output terminal when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are substantially equal; and said differential decoding means further providing a second logic level output at said output terminal when said chip of said presently received spread spectrum spreading code sequence and of said chip of said previously received spread spectrum spreading code sequence are substantially not equal.
an input terminal for receiving said spread spectrum signal;
an output terminal;
differential decoding means, coupled to said input terminal for determining whether at least one chip of the presently received spread spectrum spreading code sequence at said input terminal and at least one chip of a previously received spread spectrum spreading code sequence are substantially equal;
said differential decoding means further providing a first logic level output at said output terminal when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are substantially equal; and said differential decoding means further providing a second logic level output at said output terminal when said chip of said presently received spread spectrum spreading code sequence and of said chip of said previously received spread spectrum spreading code sequence are substantially not equal.
6. In a spread spectrum communication system including a spread spectrum signal having a spreading code sequence differentially encoded in accordance with an input data signal, a data correlator comprising:
an input terminal for receiving said spread spectrum signal;
an exclusive OR gate having first and second input terminals and an output terminal, said input terminal for receiving said spread spectrum signal being coupled to said first input terminal of said exclusive OR gate;
delay means having input and output terminals, said input terminal of said delay means being coupled to said input terminal for receiving said spread spectrum signal, said output terminal of said delay means being coupled to said second input terminal of said exclusive OR gate; and an output terminal coupled to said output terminal of said exclusive OR gate.
an input terminal for receiving said spread spectrum signal;
an exclusive OR gate having first and second input terminals and an output terminal, said input terminal for receiving said spread spectrum signal being coupled to said first input terminal of said exclusive OR gate;
delay means having input and output terminals, said input terminal of said delay means being coupled to said input terminal for receiving said spread spectrum signal, said output terminal of said delay means being coupled to said second input terminal of said exclusive OR gate; and an output terminal coupled to said output terminal of said exclusive OR gate.
7. A data correlator in accordance with claim 6, wherein the time delay provided by said delay means is essentially equal to the time duration of one cycle of said spread spectrum spreading code sequence.
8. In a spread spectrum communication system including a spread spectrum signal having a spreading code sequence differentially encoded in accordance with an input data signal, a data correlator comprising:
an input terminal for receiving said spread spectrum signal;
an output terminal;
differential decoding means, coupled to said input terminal for determining whether at least one chip of the presently received spread spectrum spreading code sequence at said input terminal and at least one chip of the previously received spread spectrum spreading code sequence are of the same polarity;
said differential decoding means further providing a first analog signal output indication at said output terminal when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are of the same polarity; and said differential decoding means further providing a second analog signal output indication at said output terminal when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are of opposite polarity.
an input terminal for receiving said spread spectrum signal;
an output terminal;
differential decoding means, coupled to said input terminal for determining whether at least one chip of the presently received spread spectrum spreading code sequence at said input terminal and at least one chip of the previously received spread spectrum spreading code sequence are of the same polarity;
said differential decoding means further providing a first analog signal output indication at said output terminal when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are of the same polarity; and said differential decoding means further providing a second analog signal output indication at said output terminal when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are of opposite polarity.
9. In a spread spectrum communication system including a spread spectrum signal having a spreading code sequence differentially encoded in accordance with an input data signal, a data correlator comprising:
an input terminal for receiving said spread spectrum signal;
an analog multiplier having first and second input terminals and an output terminal, said input terminal for receiving said spectrum signal being coupled to said first input terminal of said analog multiplier;
analog delay means having an input and an output terminal, the input terminal of said analog delay means being coupled to said input terminal for receiving said spread spectrum signal, and the output terminal of said analog delay means being coupled to the second input terminal of said analog multiplier means; and an output terminal coupled to said output terminal of said analog multiplier.
an input terminal for receiving said spread spectrum signal;
an analog multiplier having first and second input terminals and an output terminal, said input terminal for receiving said spectrum signal being coupled to said first input terminal of said analog multiplier;
analog delay means having an input and an output terminal, the input terminal of said analog delay means being coupled to said input terminal for receiving said spread spectrum signal, and the output terminal of said analog delay means being coupled to the second input terminal of said analog multiplier means; and an output terminal coupled to said output terminal of said analog multiplier.
10. A data correlator in accordance with claim 9, wherein said time delay provided by said analog delay means is essentially to the time duration of one cycle of said spread spectrum spreading code sequence.
11. A method for encoding a spread spectrum signal with a data input signal said method comprising:
generating a spread spectrum spreading code sequence;
inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence a fixed time delay previously, if said present input data signal is a first logic level; and not inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence said fixed time delay previously, if said present input data signal is a second logic level.
generating a spread spectrum spreading code sequence;
inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence a fixed time delay previously, if said present input data signal is a first logic level; and not inverting the polarity of said spread spectrum spreading code sequence, relative to the polarity of said spread spectrum spreading code sequence said fixed time delay previously, if said present input data signal is a second logic level.
12. A method for encoding a spread spectrum signal in accordance with claim 11, further comprising a method for generating a present inversion control signal for controlling the inversion of said chip of said spreading code sequence, said method comprising the steps of:
storing at least some portion of the previous inversion control signal in a delay memory; and calculating the exclusive OR of the present input data signal and said previous inversion control signal stored in said delay memory to form the present inversion control signal.
storing at least some portion of the previous inversion control signal in a delay memory; and calculating the exclusive OR of the present input data signal and said previous inversion control signal stored in said delay memory to form the present inversion control signal.
13. In a spread spectrum communication system including a spread spectrum signal having a spreading code sequence differentially encoded in accordance with an input data signal, a method for correlating said data signal on said spectrum signal comprising:
determining whether at least one chip of the presently received spread spectrum spreading code sequence and at least one chip of the previously received spread spectrum spreading code sequence are substantially equal;
providing a first output signal indication when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are substantially equal; and providing a second output signal indication when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are substantially not equal.
determining whether at least one chip of the presently received spread spectrum spreading code sequence and at least one chip of the previously received spread spectrum spreading code sequence are substantially equal;
providing a first output signal indication when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are substantially equal; and providing a second output signal indication when said chip of said presently received spread spectrum spreading code sequence and said chip of said previously received spread spectrum spreading code sequence are substantially not equal.
14. A method for correlating a spread spectrum signal in accordance with claim 13, wherein the said step of determining whether at least one chip of said presently received spread spectrum spreading code sequence and at least one chip of said previously received spread spectrum spreading code sequence are substantially equal, further comprises:
storing the previously received spread spectrum spreading code sequence in a delay memory; and calculating the exclusive OR of at least one chip of said presently received spread spectrum spreading code sequence, and at least one chip of said stored spread spectrum spreading code sequence.
storing the previously received spread spectrum spreading code sequence in a delay memory; and calculating the exclusive OR of at least one chip of said presently received spread spectrum spreading code sequence, and at least one chip of said stored spread spectrum spreading code sequence.
15. A method for correlating a spread spectrum signal in accordance with claim 13, wherein the said step of determining whether at least one chip of said presently received spread spectrum spreading code sequence and at least one chip of said previously received spread spectrum spreading code sequence are substantially equal, further comprises:
storing the previously received spread spectrum spreading code sequence in a delay memory; and calculating the product of at least one chip of said presently received spread spectrum spreading code sequence, and at least one chip of said stored spread spectrum spreading code sequence.
storing the previously received spread spectrum spreading code sequence in a delay memory; and calculating the product of at least one chip of said presently received spread spectrum spreading code sequence, and at least one chip of said stored spread spectrum spreading code sequence.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/271,614 US4964138A (en) | 1988-11-15 | 1988-11-15 | Differential correlator for spread spectrum communication system |
| US07/271,614 | 1988-11-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2002883A1 true CA2002883A1 (en) | 1990-05-15 |
Family
ID=23036318
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002002883A Abandoned CA2002883A1 (en) | 1988-11-15 | 1989-11-14 | Differential correlator for spread spectrum communication system |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4964138A (en) |
| EP (1) | EP0369703A3 (en) |
| JP (1) | JPH02223243A (en) |
| CA (1) | CA2002883A1 (en) |
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| US3337803A (en) * | 1962-01-09 | 1967-08-22 | Gen Electric | Data transmission system |
| US4545061A (en) * | 1962-09-28 | 1985-10-01 | Sylvania Electric Products Inc. | Synchronizing system |
| US3864635A (en) * | 1972-08-04 | 1975-02-04 | Westinghouse Electric Corp | Correlation receiver with rapid frequency, time and phase acquisition |
| US3917999A (en) * | 1974-06-18 | 1975-11-04 | Frank S Gutleber | Multiplexed pseudo noise pulse burst codes with space taper |
| US4653069A (en) * | 1975-11-06 | 1987-03-24 | General Electric Company | Spread spectrum correlation receiver |
| US4112372A (en) * | 1977-01-11 | 1978-09-05 | Texas Instruments Incorporated | Spread spectrum communication system |
| DE2742696C2 (en) * | 1977-09-22 | 1979-11-15 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Circuit for the synchronization of a pseudo-random generator arranged on the receiver for message transmission systems with pseudo-random phase shift modulation |
| US4291409A (en) * | 1978-06-20 | 1981-09-22 | The Mitre Corporation | Spread spectrum communications method and apparatus |
| US4291410A (en) * | 1979-10-24 | 1981-09-22 | Rockwell International Corporation | Multipath diversity spread spectrum receiver |
| JPS56103557A (en) * | 1980-01-21 | 1981-08-18 | Matsushita Electric Ind Co Ltd | Receiving device |
| US4387465A (en) * | 1981-04-13 | 1983-06-07 | Trw Inc. | Sequential threshold detector |
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| US4561089A (en) * | 1984-03-23 | 1985-12-24 | Sangamo Weston, Inc. | Correlation detectors for use in direct sequence spread spectrum signal receiver |
| JPH0693670B2 (en) * | 1984-12-29 | 1994-11-16 | 京セラ株式会社 | Spread spectrum communication system |
| US4672658A (en) * | 1985-10-16 | 1987-06-09 | At&T Company And At&T Bell Laboratories | Spread spectrum wireless PBX |
| JPS62257224A (en) * | 1986-04-30 | 1987-11-09 | Nec Home Electronics Ltd | Method and apparatus for spread spectrum power line carrier communication |
-
1988
- 1988-11-15 US US07/271,614 patent/US4964138A/en not_active Expired - Fee Related
-
1989
- 1989-11-13 JP JP1294764A patent/JPH02223243A/en active Pending
- 1989-11-13 EP EP19890311707 patent/EP0369703A3/en not_active Withdrawn
- 1989-11-14 CA CA002002883A patent/CA2002883A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| US4964138A (en) | 1990-10-16 |
| EP0369703A2 (en) | 1990-05-23 |
| EP0369703A3 (en) | 1992-03-18 |
| JPH02223243A (en) | 1990-09-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19920516 |