CA2103497C - Method and apparatus for synchronizing a received signal in a digital radio communication system - Google Patents
Method and apparatus for synchronizing a received signal in a digital radio communication systemInfo
- Publication number
- CA2103497C CA2103497C CA002103497A CA2103497A CA2103497C CA 2103497 C CA2103497 C CA 2103497C CA 002103497 A CA002103497 A CA 002103497A CA 2103497 A CA2103497 A CA 2103497A CA 2103497 C CA2103497 C CA 2103497C
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- Canada
- Prior art keywords
- synchronization
- signal
- correlation signal
- synchronization information
- magnitude
- 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.)
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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
- H04B1/713—Spread spectrum techniques using frequency hopping
- H04B1/7156—Arrangements for sequence synchronisation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/04—Speed or phase control by synchronisation signals
- H04L7/041—Speed or phase control by synchronisation signals using special codes as synchronising signal
- H04L7/042—Detectors therefor, e.g. correlators, state machines
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/04—Speed or phase control by synchronisation signals
- H04L7/041—Speed or phase control by synchronisation signals using special codes as synchronising signal
Abstract
A method and apparatus is provided for synchronizing a received communication signal. A synchronization signal is derived from a received signal having a plurality of synchronization words. Each synchronization word has a predetermined number of synchronization symbols. The synchronization signal is filtered. The filtering is characterized by spacing each filter tap to correspond to synchronization word length increments. Synchronization information is generated which is based on a comparison of the filtered synchronization signal to a threshold. Finally, the synchronization information is output based on a confidence decision derived from the synchronization information.
Description
2~t)~
METIIOD ~ND APPARATUS FOR SYNCHRONIZING A i~
RECEIVED SIGNAL IN A DIGITAL RADIO COMilAlJN3CATlQN : - S Y S T E M
~ ~ ', . .
Fieldofthe Invention The present invention relates to radio communication systems and, mora particularly, to a method and apparatus for synchronizing a ~ :
received si~nal in a digital radio communication system.
.
Background of the Invention ~ ~
- ::
Cellular radio communication systems typically include a number of central communication base sites. Each central communication site ;~ has a servic~ area coverage for servicing mobile communication units 5 within the service area. The service areas typically are arranged such that adjacent remote base site service coverage areas overlap in a - manner that provides a subs~antially continuous service region. The substantially con~inuous service region provides uninterrupted service by handing off mobile communication units from one base site serving a service area to an adjacsnt base site serving another service arèa.
.' Pedestrian as well as mobile users will typicaily access the same cellular radio communication systems. For purposes of this discussion, - 25 a pedestrian user is one who walks or roams slowly (traveling at 10 kilometers per hour (kph) or less) as opposed to a mobile user who rides in a vehicle (traveling up to 100 kph or more). However, these cellular communication systems are typically designed to provide adequate p~rformance for the worst case environment (i.e., the mobile 5 user). As such, the cellular radio communication systems typically provide continual overhead measurements used by the system to maintain chann~l quality or perform hand-off functions. Since ~hese m~asurements require the same amount of processing whether a user is a mobile user or a pedestrian user, the pedestrian user is charged at 10 the same air-time rate for using their cellular phone as the user who is a mobile user.
Therafore, there exists a need in the industry for a personal communication system (PCS) which would provide a low ~ier system for pedestrian users at a reduced cost. The low tier system would provide 15 access via radio frequency (RF) link to a basic cellular network which may or may not provide hand-off car~hility between low tier service areas. In addition, a high tiar system should be provided for the mobile user. This high tier system, unlike the low tier system, would have many of the features found in current cellular systems including hand-off 20 between high tier service areas and high quality error protection.
Both the high tier and the low tier systems share some basic design constraints. One such constraint is that both systems require initial synchronization of signals between a central communication base site and a mobile communication unit which are communicating, via a 25 radio communication link, with each other. This initial synchronization is particularly important in the high tisr system, because this system must be designed to handle synchronization even though the mobile comrnunication unit may be traveling at 100 kph. Synchronization of the two communication devices is necessary to allow the originally 30 transmitted signal to be quickly and easily recovered from a received signal.
In communication systems, with respect to synchronization, two general areas of uncertainty of the signal exist which must be resolved before a received signal can be recovered. These areas of uncertainty 35 are phase and frequency of the carrier. In addition, the clock rate can be a source of synchronization uncertainty. Most of this uncertain~y may be ~liminated by utilizing accurate frequency sources in both ' :
METIIOD ~ND APPARATUS FOR SYNCHRONIZING A i~
RECEIVED SIGNAL IN A DIGITAL RADIO COMilAlJN3CATlQN : - S Y S T E M
~ ~ ', . .
Fieldofthe Invention The present invention relates to radio communication systems and, mora particularly, to a method and apparatus for synchronizing a ~ :
received si~nal in a digital radio communication system.
.
Background of the Invention ~ ~
- ::
Cellular radio communication systems typically include a number of central communication base sites. Each central communication site ;~ has a servic~ area coverage for servicing mobile communication units 5 within the service area. The service areas typically are arranged such that adjacent remote base site service coverage areas overlap in a - manner that provides a subs~antially continuous service region. The substantially con~inuous service region provides uninterrupted service by handing off mobile communication units from one base site serving a service area to an adjacsnt base site serving another service arèa.
.' Pedestrian as well as mobile users will typicaily access the same cellular radio communication systems. For purposes of this discussion, - 25 a pedestrian user is one who walks or roams slowly (traveling at 10 kilometers per hour (kph) or less) as opposed to a mobile user who rides in a vehicle (traveling up to 100 kph or more). However, these cellular communication systems are typically designed to provide adequate p~rformance for the worst case environment (i.e., the mobile 5 user). As such, the cellular radio communication systems typically provide continual overhead measurements used by the system to maintain chann~l quality or perform hand-off functions. Since ~hese m~asurements require the same amount of processing whether a user is a mobile user or a pedestrian user, the pedestrian user is charged at 10 the same air-time rate for using their cellular phone as the user who is a mobile user.
Therafore, there exists a need in the industry for a personal communication system (PCS) which would provide a low ~ier system for pedestrian users at a reduced cost. The low tier system would provide 15 access via radio frequency (RF) link to a basic cellular network which may or may not provide hand-off car~hility between low tier service areas. In addition, a high tiar system should be provided for the mobile user. This high tier system, unlike the low tier system, would have many of the features found in current cellular systems including hand-off 20 between high tier service areas and high quality error protection.
Both the high tier and the low tier systems share some basic design constraints. One such constraint is that both systems require initial synchronization of signals between a central communication base site and a mobile communication unit which are communicating, via a 25 radio communication link, with each other. This initial synchronization is particularly important in the high tisr system, because this system must be designed to handle synchronization even though the mobile comrnunication unit may be traveling at 100 kph. Synchronization of the two communication devices is necessary to allow the originally 30 transmitted signal to be quickly and easily recovered from a received signal.
In communication systems, with respect to synchronization, two general areas of uncertainty of the signal exist which must be resolved before a received signal can be recovered. These areas of uncertainty 35 are phase and frequency of the carrier. In addition, the clock rate can be a source of synchronization uncertainty. Most of this uncertain~y may be ~liminated by utilizing accurate frequency sources in both ' :
3 2 ~ 7 communication devices which are communicating with each other.
However, some uncertainty can not be eliminated by the use of accurate frequency sour~es. Doppler-related frequency errors typically can not be predicted and will affect the carrier frequency. The amount of Doppler-related frequency uncertainty present in a received signal is a function of the relativa velocity of the receiver which received the signal with respect to the transmi~ter which l,~ns",illed the signal as well as the frequency (or frequency range3 at which the signal was transmitted.
Further, if a mobile communication unit i5 in motion, then a relative phase change will occur with each change in relative position of the mobile communication unit with respect to the central communication base site inthe communication link. Furthermore, affxed-position or slow moving mobile communication unit can experience variations in phase and carrier frequency due to signal propagation-path-length changes in the communication channel.
Therefore, a need exists for a synchronization technique which is simple enough to be inexpensively built for use by low tier communication unit while at the same time providing rapid synchronization for use by a communication unit operating in the high tier communication system. The high tier communication system needs rapid synchronization, because ~he high tier communication system may utilize a spread spectrum communication process such as frequency hopping code division multiple access (FH-CDMA) to communicate between a mobile communication unit and a central communication base site. In FH-CDMA systems, a receiving mobile communication unit, for example, may not know the hopping pattern used by the transmitting central communication base site prior to the start of transmission. Thus, the mobile communication unit must be able to synchronize within the time period of one frequency hop so that the mobile communication unit can deterrnine the frequency of the next hop. I ~.
In addition, it is desirable to design the synchronizing technique to minimize it's vulnerability to false correlation due to the presence of noise and/or interference in the communication channel.
3~ Summary ofthe Inven$ion 4 ~ a~
A method and apparatus are provided for synchronizing a received communication signal. A synohronization signal is derived from a receiv0d signal having a plurality of synchronization words. Each synchronization word has a pred~termined number of synchronization symbols. The synchronization signal is filtered. The filtering is ~:
chara.;lesli,ed by spacing each filter tap to correspond to synchronization word length increments. Synchronization information is ~enerated which is based on a comparison of the filtered synchronization signal to a lhleshold. Finally, the synchronization information is output based on a confidence decision derived from the synchronization information.
Brief Description of the Drawings FIG. 1 is a diagram showing the preferred embodiment synchronization information generator in accordance with the present invention.
FIG. 2 is a diagram showing a first alternative preferred embodiment synchronization information generator in accordance with tha present invention.
FIG. 3 is a diagram showing a second alternative preferred embodiment synchronization information generator in accordance with the present invention.
FIG. 4 is a diagram shoJ~;ng a third alternative preferred embodirnent synchronization information generator in accordance with the present invention.
FIG. 5 shows flowchart of how a combined magnitude correlation . signal is compared to a predetermined magnitude threshold in accordance with a preferred embodiment of the present invention.
FIG. 6showsflowchartof howsynchronization information is generated in accordance with a preferred embodiment of the present invention.
FIG. 7 shows a diagram of a preferred embodiment synchronization sequence fsr use in accordance with the present invention.
D~tailed Description ' ,. ' ' ~ , ~ Q~ ~
Referring now to FIG. 1, a preferred embodiment synchronization information generator in accordance with the present inven~ion is shown. The synchronization information generator initially synchronizes 5 a recaiver t~ an input data sequence by determinin~ several types of synchronization information. When the receiver is unsynchronized (e.g., on power up of the receiver), the preferred embodiment synchronization information generator is used to synchronize the receiver. The preferred embodiment synchronization information generator is optimized for use 10 in a time division multiple access (TDMA) communication system which may or may not frequency hop. If the TDMA communication system frequency hops, then it is typioally referred to as a FH-CDMA
communication system. The synchronization information required for ~-such a hopping or non-hopping TDMA communication system includes:
15 the phase and frequency of the input data sequence as well as the relative locations of symbols, slots, frames, and superframes within the input data sequence.
Phase synchronization information may be generated by ~ -frequancy translating the input data sequence constellation so that the effect of any Doppler fr~quency shift is cli",i"~led. For the preferred embodiment g0nerator, the Doppler frequency shift is assumed to be constant throughout ia single time slot (or a single hop when the system froquisncy hops). Frequency synchronization information may be obtained by estimating the frequency offset between the input data sequence carrier and a local oscillator used by the prefcrred embodiment generator. The frequency offset estimate may then be used to Irequerlcy translate the input data sequence consteilation to G~ e the eflect of the frequency offset. Symbol synchronization information can be determined by locating the input data sequenoe symbol boundaries. After locating the symbol boundaries, the preferred !
embodiment synchronization information generator or an ~.~soci~ted receiver apparatus preferably decimates an oversampled input data sequence down to a rate of one sample per symbol. Slot and frame synchronization information, like symbol synchronization information, may be generated by determining the respective slot and frame boundaries within the input data sequence. Superframe synchronization information may be genera~ed by determining the . -~ .
However, some uncertainty can not be eliminated by the use of accurate frequency sour~es. Doppler-related frequency errors typically can not be predicted and will affect the carrier frequency. The amount of Doppler-related frequency uncertainty present in a received signal is a function of the relativa velocity of the receiver which received the signal with respect to the transmi~ter which l,~ns",illed the signal as well as the frequency (or frequency range3 at which the signal was transmitted.
Further, if a mobile communication unit i5 in motion, then a relative phase change will occur with each change in relative position of the mobile communication unit with respect to the central communication base site inthe communication link. Furthermore, affxed-position or slow moving mobile communication unit can experience variations in phase and carrier frequency due to signal propagation-path-length changes in the communication channel.
Therefore, a need exists for a synchronization technique which is simple enough to be inexpensively built for use by low tier communication unit while at the same time providing rapid synchronization for use by a communication unit operating in the high tier communication system. The high tier communication system needs rapid synchronization, because ~he high tier communication system may utilize a spread spectrum communication process such as frequency hopping code division multiple access (FH-CDMA) to communicate between a mobile communication unit and a central communication base site. In FH-CDMA systems, a receiving mobile communication unit, for example, may not know the hopping pattern used by the transmitting central communication base site prior to the start of transmission. Thus, the mobile communication unit must be able to synchronize within the time period of one frequency hop so that the mobile communication unit can deterrnine the frequency of the next hop. I ~.
In addition, it is desirable to design the synchronizing technique to minimize it's vulnerability to false correlation due to the presence of noise and/or interference in the communication channel.
3~ Summary ofthe Inven$ion 4 ~ a~
A method and apparatus are provided for synchronizing a received communication signal. A synohronization signal is derived from a receiv0d signal having a plurality of synchronization words. Each synchronization word has a pred~termined number of synchronization symbols. The synchronization signal is filtered. The filtering is ~:
chara.;lesli,ed by spacing each filter tap to correspond to synchronization word length increments. Synchronization information is ~enerated which is based on a comparison of the filtered synchronization signal to a lhleshold. Finally, the synchronization information is output based on a confidence decision derived from the synchronization information.
Brief Description of the Drawings FIG. 1 is a diagram showing the preferred embodiment synchronization information generator in accordance with the present invention.
FIG. 2 is a diagram showing a first alternative preferred embodiment synchronization information generator in accordance with tha present invention.
FIG. 3 is a diagram showing a second alternative preferred embodiment synchronization information generator in accordance with the present invention.
FIG. 4 is a diagram shoJ~;ng a third alternative preferred embodirnent synchronization information generator in accordance with the present invention.
FIG. 5 shows flowchart of how a combined magnitude correlation . signal is compared to a predetermined magnitude threshold in accordance with a preferred embodiment of the present invention.
FIG. 6showsflowchartof howsynchronization information is generated in accordance with a preferred embodiment of the present invention.
FIG. 7 shows a diagram of a preferred embodiment synchronization sequence fsr use in accordance with the present invention.
D~tailed Description ' ,. ' ' ~ , ~ Q~ ~
Referring now to FIG. 1, a preferred embodiment synchronization information generator in accordance with the present inven~ion is shown. The synchronization information generator initially synchronizes 5 a recaiver t~ an input data sequence by determinin~ several types of synchronization information. When the receiver is unsynchronized (e.g., on power up of the receiver), the preferred embodiment synchronization information generator is used to synchronize the receiver. The preferred embodiment synchronization information generator is optimized for use 10 in a time division multiple access (TDMA) communication system which may or may not frequency hop. If the TDMA communication system frequency hops, then it is typioally referred to as a FH-CDMA
communication system. The synchronization information required for ~-such a hopping or non-hopping TDMA communication system includes:
15 the phase and frequency of the input data sequence as well as the relative locations of symbols, slots, frames, and superframes within the input data sequence.
Phase synchronization information may be generated by ~ -frequancy translating the input data sequence constellation so that the effect of any Doppler fr~quency shift is cli",i"~led. For the preferred embodiment g0nerator, the Doppler frequency shift is assumed to be constant throughout ia single time slot (or a single hop when the system froquisncy hops). Frequency synchronization information may be obtained by estimating the frequency offset between the input data sequence carrier and a local oscillator used by the prefcrred embodiment generator. The frequency offset estimate may then be used to Irequerlcy translate the input data sequence consteilation to G~ e the eflect of the frequency offset. Symbol synchronization information can be determined by locating the input data sequenoe symbol boundaries. After locating the symbol boundaries, the preferred !
embodiment synchronization information generator or an ~.~soci~ted receiver apparatus preferably decimates an oversampled input data sequence down to a rate of one sample per symbol. Slot and frame synchronization information, like symbol synchronization information, may be generated by determining the respective slot and frame boundaries within the input data sequence. Superframe synchronization information may be genera~ed by determining the . -~ .
-6~ q~
preferred ernbodiment's communication system channelization scheme ~including the hopping pattern when the system frequency hops).
It will be appreciated by those skilled in the art that the principles discuss herein with resp0ct to a TDMA cornmunication system may be 5 readily appliecl to other types of communication systems such as direct sequence code division communication systems and the like.
Complex oversampled data sequence 100 (i.e., oversampled data which may have real and imaginary componenls~ is input to a first-in-lirst-out (FIFO) buffer 128 for storage during the synchronization 10 process. In addition the complex oversamplad data sequence 100 is input to a complex matched ~ilter 102. Tha matched filter 102 preferably is a finite impulse respanse filter ~FIR? which is matched to a known predetermined synchronization word. The known predetermined synchronization word preferably is a part of a known predetermined 15 synchronization sequence 700 which consists of a plurality of ; synchronization words 702, 704, 7û6, 708, and 710, as shown shown in FIG. 7. Each synchronization word preferably includes one or more symbols. The synchronization words 702, 704, 706, 708, and 710 preferably include the same number of symbols and are ordered in the 20 same symbol pattern. However, some of the synchronization words 702, 704, 706, 708, and 710 rnay be inverted so that the predetermined synchronization sequence may be differentially encoded - (e.g., an encoding pattern uO, U1, u~, .. , uk may be multiplied with the synchronication words as in 7Q2, 704, 706, 708, and 710, 25 resp~ctively to generat~ an encoded pattern synchronization sequence 700). I~ will be appreciated by those skiiled in the art that other encodingtechniques, besidesdi~ferential encoding, may be employed without departing from the scope and spirit of the presen~ invantion. In addition, it will be appreciated by those skilled in the art that the 30 synchronization words may also differ in the number of symbols, so long as the synohronization words are known, without departing from the ~i scope and spirit of the present invention. This synchronization sequence preferably is transmitted over a communication channel ; -periodically on a predetermined frequency such that the receiver 35 ~ssoci~ted with the synchronization information generator may locate the transmitted synchronization sequence during a synchronization -.; process. The synchronization sequence may be transmitted along with . ~ ~
;"' ~, :.
preferred ernbodiment's communication system channelization scheme ~including the hopping pattern when the system frequency hops).
It will be appreciated by those skilled in the art that the principles discuss herein with resp0ct to a TDMA cornmunication system may be 5 readily appliecl to other types of communication systems such as direct sequence code division communication systems and the like.
Complex oversampled data sequence 100 (i.e., oversampled data which may have real and imaginary componenls~ is input to a first-in-lirst-out (FIFO) buffer 128 for storage during the synchronization 10 process. In addition the complex oversamplad data sequence 100 is input to a complex matched ~ilter 102. Tha matched filter 102 preferably is a finite impulse respanse filter ~FIR? which is matched to a known predetermined synchronization word. The known predetermined synchronization word preferably is a part of a known predetermined 15 synchronization sequence 700 which consists of a plurality of ; synchronization words 702, 704, 7û6, 708, and 710, as shown shown in FIG. 7. Each synchronization word preferably includes one or more symbols. The synchronization words 702, 704, 706, 708, and 710 preferably include the same number of symbols and are ordered in the 20 same symbol pattern. However, some of the synchronization words 702, 704, 706, 708, and 710 rnay be inverted so that the predetermined synchronization sequence may be differentially encoded - (e.g., an encoding pattern uO, U1, u~, .. , uk may be multiplied with the synchronication words as in 7Q2, 704, 706, 708, and 710, 25 resp~ctively to generat~ an encoded pattern synchronization sequence 700). I~ will be appreciated by those skiiled in the art that other encodingtechniques, besidesdi~ferential encoding, may be employed without departing from the scope and spirit of the presen~ invantion. In addition, it will be appreciated by those skilled in the art that the 30 synchronization words may also differ in the number of symbols, so long as the synohronization words are known, without departing from the ~i scope and spirit of the present invention. This synchronization sequence preferably is transmitted over a communication channel ; -periodically on a predetermined frequency such that the receiver 35 ~ssoci~ted with the synchronization information generator may locate the transmitted synchronization sequence during a synchronization -.; process. The synchronization sequence may be transmitted along with . ~ ~
;"' ~, :.
7 2~
an associ~ted control channel sequence. The control channel sequence may be transmitted in the same slot as the synchronization sequence. Alternatively, the control channel sequence may be transmitted in a subsequent sequence. The control channel sequence 5 preferably includes the superframe synchronization information. Once tha other s~nollruni,~lion information is retrieved from the synchronization sequence, the control channel sequence may be reliably de~ected and the superframe synchronization information retrieved.
Tha matched filter's 102 output 104 is input ~o a magnitude squared function device 196 which converts the input complex oversampled data sequence 104 to a magnitude sequence 108 (also known as a magnitude correlation signal) which is a function of ~he magnitude of the input complex oversampled data sequence 104. The ~ ;
magnitude sequence 108 is input to an M-tap FIR filter 110 which is matched to the known predetermined synchronization sequence. The M-tap FIR filter 110 output 112 is input to a peak detection mechanism 114. Peak detection mechanism 114 determines if the known predetermined synchronization sequence is present in the output 112 20 of the M-tap FIR filter 110. If the synchronization sequence is detscted, then decision logic 152 is notified of the detection through an output signal 116 by peak detection mechanism 114.
In addition, the peak detection mechanism 114 sends a peak filter output 132 of the M-tap FIR filter output 112 to the FIFO buffer 128 25 so that the peak filter output 132 can be saved along with the input data sequence 100 at the location of whera the peak filter output 132 occurred in the input data sequence 100. This location provides the exact position of the synchronization sequence within the input data sequence 100. By knowing this position, the input data sequence 100 30 frame, slot, and bit synchronization information can be generated. In addition, a decimator (not shown) may be adjusted as a function of the peak filter output 132 to properly decimate the input data sequence 100 which is stored in FIFO buffer 128 into one sample per symbol in the input data sequence 100.
3~ The peak filter output 132 is also input to an initial phase astimator 118. The initial phase estimator 118 computes a complex phase correction value 120 from input matched filter output 104 and ~' . .
an associ~ted control channel sequence. The control channel sequence may be transmitted in the same slot as the synchronization sequence. Alternatively, the control channel sequence may be transmitted in a subsequent sequence. The control channel sequence 5 preferably includes the superframe synchronization information. Once tha other s~nollruni,~lion information is retrieved from the synchronization sequence, the control channel sequence may be reliably de~ected and the superframe synchronization information retrieved.
Tha matched filter's 102 output 104 is input ~o a magnitude squared function device 196 which converts the input complex oversampled data sequence 104 to a magnitude sequence 108 (also known as a magnitude correlation signal) which is a function of ~he magnitude of the input complex oversampled data sequence 104. The ~ ;
magnitude sequence 108 is input to an M-tap FIR filter 110 which is matched to the known predetermined synchronization sequence. The M-tap FIR filter 110 output 112 is input to a peak detection mechanism 114. Peak detection mechanism 114 determines if the known predetermined synchronization sequence is present in the output 112 20 of the M-tap FIR filter 110. If the synchronization sequence is detscted, then decision logic 152 is notified of the detection through an output signal 116 by peak detection mechanism 114.
In addition, the peak detection mechanism 114 sends a peak filter output 132 of the M-tap FIR filter output 112 to the FIFO buffer 128 25 so that the peak filter output 132 can be saved along with the input data sequence 100 at the location of whera the peak filter output 132 occurred in the input data sequence 100. This location provides the exact position of the synchronization sequence within the input data sequence 100. By knowing this position, the input data sequence 100 30 frame, slot, and bit synchronization information can be generated. In addition, a decimator (not shown) may be adjusted as a function of the peak filter output 132 to properly decimate the input data sequence 100 which is stored in FIFO buffer 128 into one sample per symbol in the input data sequence 100.
3~ The peak filter output 132 is also input to an initial phase astimator 118. The initial phase estimator 118 computes a complex phase correction value 120 from input matched filter output 104 and ~' . .
-8- 2 ~
the peak fiUer output 132. The complex phase correction value 120 corresponds to the amount of phase offset in the input data sequence 100 reiative to the local oscil'~tor used by the preferred embodiment.
The complex phase correotion vaiue 120 is coupled to one input of combiner 122. The input data sequence 130 which was stored in FIFO
buffer 128 (in either decimated or non decimated form) is provided to the other input of combiner 122. Combiner 122 preferably generates a phase-corrected input data sequence 134 by multiplying the input data sequence 130 with the complex phase correction value 120. The phase-corrected input data sequence 134 is then preferably stored in a FIFO buffer 140.
The phase-corrected input data sequence 134 is also input to a frequency offset estimator 136. The frequency offset estimator 136 computes a complex frequency correction value 138. The complex frequency correction value ~38 corresponds to the amount of frequency offsst in ~he input data sequence 100 relative to the local oscillator used by the preferred embodiment synchronization information generator.
The complex frequency correction valuts 138 may be determined in one of several known methods. For exampllq, in the preferred embodiment, part of the phase-corrected input data sequence 134 is known (i.e., the predetermined synchronization sequence is known). Thus, using the known predetermined synchronization sequence, the slope of the phase trajectory can be determined. This phase trajectory slope can subsequently be mapped to the frequerlcy domain as the frequency offset to generate the complex frequency correction value 138.
Alternatively, the complex frequency correction value 138 may bedetermined inthefollowing manner. Inthe preferred embodiment, the phase-corrected input data sequence 134 includes a synchronization sequence preferably consisting of a plurality o~
synchronization words. The use of a plurality of synchronization words l can be exploited in determining a frequency offset by forming a set of complex values that contain peak values caused by the synchronization ~;
words in the matched filter 102 (e.~., if five synchronization words are uszd, then the set has five complex values). For this frequency offset c~lcul~tion method to work, tha matched filter 102 output 104 must be input to the frequency offset estimator 136. Subsequently, any differential encodin~ pattern is preferably removed from the set. In ; ~ ;~
:
2~ ~3l9~7 ~ 9 addition, the slope of the phase trajectory is determined. This slope is then mapp~d to the frequency domain as the frequency offset to generate the complax frequency correction value 138. This frequency offset c~'c~ tlon method has an advantage over the previous method that the samples used in the c~lcul~tion have a higher signal to noise ratio, since the samples come from the matched filter 102 output 104.
However, because the samples are spaced farther apart in time, this fr~quency offset estimation method can not handle as large of a frequency offset as the previously described one.
The complex frequency correction value 138 is coupled to one input of combiner 142. Th~ phase-correcteci input data sequence 141 which was stored in FIFO buffer 140 is provided to the other input of combiner 142. Combiner 142 preferably generates a frequency-corrected input data sequence 144 by multiplying the input data sequence 141 with the complex phase correction value 138.
Optionally, if the known predetermined synchronization sequence preferably consists of differentially encoded synchronization words, a differentially encoded pattern detector 146 may be coupled to the output 144 of combiner 142 (i.e., the frlequency-corrected input data sequence 144). The differentially encoded pattern detector 146 sends . a message, via a signal 148, to the decision logic 162 when the differentially encoded synchronization pattern is detected. Otherwise, if the known predetermined synchronization sequence does not consist of differentially encoded synchronization words, the frequency-corrected input data sequence 144 may be directly coupled via signal 148 to the decision logic ti52.
In addition, a received signal sl,~r,~ll, indicator (RSSI) signal optionally may be input to decision logic 152. The RSSI signal is used by the decision logic 152 to minimize faising problems when no input da~a sequence 100 is present. Decision logic 152 analyzes ail of the input decision factors 116,148, and 150 to derive a con~idence decision 154 of whether or not the known predetermined synchronization sequence was detected in the input data sequence 100. This confidence decision 154 as well as any other information (e.g., phase and frequency offset information) may then be output from the synchronization information generator by the decision logic 152.
, -;
, .i , o 2 ~
Referring now to FiG. 2, an alternative preferred embodiment synchronization information gsnerator is shown. The alternative preferred embodiment synchronization information generator is configured and oparated su~lanlially as described in reference to the 5 preferred embodiment synchronization information generator shown in FIG. 1. In this alternative embodiment, the M-tap FIR fil~er 110 has been replaced by elements 156,160,164 and 168 which input and output substantially the same information as previously described in reference to the M-tap FIR filter 110. For this alterna~ive preferred embodiment, 10 the known predetermined synchronization sequence prsferably consists of four synchronization words. The synchronization words prefsrably are of equal length and are ordered in the same symbol pattern. The magnitude correlation signal 108 is input to a summing device 168. -The magnitude correlation signal 108 is also input to delay mechanism 156 which delays the magnitude sequence by the length of one synchronization word. The one synchronization word d~layed magnitude correlation signal 158 is input to surnming device 168. The one synchronization word delayed magnitude correlation signal 158 is also input to delay mechanism 160 which delays the magnitude correlation signal 158 by the length of another synchronization word.
The two synchronization word delayed magnitude correlation signal 162 is input to summing device 168. The two synchronization word delayed magnitude correlation signal 162 is also input to delay mechanism ~64 which delays the magnilude correlation signal 162 by the length of another synchronization word. The three synchronization ' word delayed magnitude correlation signal 166 is input to summing device 16~. The se~ of four magnitude correlation signals 108,158, 162, and 166 are summed by summin~ circuit 168 to forrn a combined magnitude correlation signal 112 (CMCS) (i.e., output 112). The output 1112 will have a non-zero value which is input to peak datection mechanism 114. It wili be appreciated by those skilled in the art that the principles described in reference to four synchroniza~ion words in a synchronization sequenoe can readily extended t~ more or less synchronization words without departing from the scope and spirit of the present invention.
In addition, in this preferred alternative embodiment, the peak detection mechanism 114 determines if the known predetermined -1 1- 2 3 ~ 7 synchronization sequence is present in the combined magnitude correlation signal 112 according to an algorithm detailed by the flowchart shown in FIG. S. A predetermined magnitude thresholcl is set 500 to an initial threshold. The peak detection mechanism 114 then waits 502 for a combined magnitude correlation signal 112 to be input.
When a combined ma~nitude correlation signal 112 is input, it is compared 504 to the predetermined magnitud~ threshold. If the combined magnitude correlation signal 112 is not greater than the pr~d~ler~ined magnitude threshold, then th~ peak detection mechanism 114 will return to flo~,cha,l element 502 and oontinue steps according to the flowchar~ in FIG. 5. Otherwise, when the combined magnitude correlation signal 112 is greater than the predetermined magnitude threshold, the predetermined threshold is set 506 to equal ~he combined magnitude correlation signal 112.
In addition, a count value is set 5û6 equal to a prede~ermined time delay. The count value is used to delay nolitic~iion of the detection of the synchronization sequence for a short time period. This short time period delay ailows the peak detection mechanism to verify that the synchronization sequence was actually detected, ra~her than a false signal being detected. This delay function is preferably implemented as follows after flowchart element 506. The peak detection mechanism -114 waits 508 for another combined magnitude correlation signal 112 to be input. When another combined magnitude correlation signal 112 is input, it is compared 510 ~o the predatermined magnitude threshold.
if the combined magnitude correlation signal 112 is greater than the predetsrmined magnitude threshold, then the peak detection meohanism 11~4 returns to flowchar~ element 506 and continues steps accordin~ to the flowchart in FIG. 5. Otherwise, when the oombined magnitude correlation signal 112 is not greater than the predetermined magnitude threshold, the count value is decremented 512. if the count - value is not zero or null, then ths peak detection mechanism 114returns to flowchart element 508 and continues steps according to the flowchart in FIG. 5. Otherwise, if the count value is zero or null, then the peak detection mechanism 114 notifies 516 the decision logic 152 of .
35 the synchronization sequence detection through an output signal 116 such that synchronization information may be subsequently output by the alternative preferred embodiment synchronization information .
., 12 ~ 7 generator. In addition, the peak detection mechanism 114 sends a peak combined magnitude correlation signal 13? to the FIFO buffer 128 so that the peak combined magnitude correlation signal output 132 can be saved along with the input data sequence 100 at the 5 location of where the peak combined magnitude correlation signal 132 occurred in the input data sequence 100.
Referring now to FIG. 3, an alternative preferred embodiment synchronization information generator is shown. The alternativa preferred embodiment synchronization inforrnation generator is 10 configured and operated s~bstantially as described in reference to the prsferred embodiment synchronization information generator shown in FIG. 1. In this alternative embodiment, the M-tap FIR filter 110 has been replaced by elements 156,160,164 and 168 which are configured and operated substantially as described in reference to the alternative ~:
preferrecl embodiment synchronization information generator shown in FIG. 2.
In addition, in this preferred alternative embodiment, the peak detection mechanism 114 has been replaced by elements 170,174 and 180 which input and output substantially the sama information as previouslydescribed in referencetothe peakdetection mechanism 114. The combined magnitude correlation signal 112 is input to a comparison device 1~0. The combinad magnitude correlation signal 112 is also input to dalay mecllani~-" 170 which delays the combined magnitude sequence for the length of one synchronization word. The ~5 one synchronization word delayed combined magnitude correlation signal 172 is inpu~ to comparison device 18û. The one synchronization word delayed combined magnitude correlation signal 172 is also input to delay mechanism 174 which delays the combined magnitude correlation signal 172 by the length of another synchronization word. I -The two synchroni~ation word delayed combined magnitude correlation signal 176 is input to comparison device 180. It will be appreciated by those skilled in the ar~ that the delay mechanism 170 and 174 may - delay the combined magnitude sequence by substantially more or lass than one synchronization word without departing ~rom the scope and spirit of the present invention. : ~.
Subsequently, the two synchronization word delayed combined - .
magnitude correlation signal 176 is compared by comparison device .
..
.
180 to a predetermined magnitude ~hreshold. This comparison is continued by comparison device 180 until the compared two synchronization word delayed combined magnitude correlation signal is greater than the predetermined threshold. if the two synchronization word delay~d combined magnitude correlation signal 176 is greater than the pr~determined magni~ude threshold, then the synchronization information based on a maximum combinad magnitude correlation signal is prepared, by comparison device 180, for output after a synchronization pattern is detected. This maximum combined magnitude correlation si~nal is selected from among the combined magnitude correlation signal 112 and two formed delayed combined magnitude correlation signals 172 and 176. In addition, the comparison device 180 notifies the decision logic 152 of the synchronization sequence detection through an output signal 116 such that prepared synchronization information may be subsequently output by the alternative preferred embodiment synchronization information generator. Finally, ~he comparison device 180 sends the maximum combined magnitude correlation signal 132 to the FIFO buffer 128 so ~ i that the maximum combined magnitude correlation signal output 132 can be saved along with the input data sequence 10û at the location of -where the maximum combined magnitulde correlation signal 132 occurred in the input data sequence 1011.
Referring now to FIG. 4, an alternative preferred embodiment synchronization information generator is shown. The alterrlative pre~erred embodirnent synchronization information generator is confi~ured and operated substantially as described in reference to the preferred embodiment synehronization information generator shown in FIG. 1. In this alternative embodiment, the complex frequency correction value 138 generated by ~requency offset estimator 136 may be directly -coupled via signal 148 to the decision logic 152. This complex frequency correction value 138 may be used by decision logic 152 in deriving a confidence decision 1154. In addition, for this alternative preferred embodirnent, the known predetermined synchronization sequence preferably consists of differentially encoded synchronization words. As such a differentially encoded pattern detector 182 may be coupled to the output 104 of matched filter 102. The differentially encoded pattern detector 182 sends a rnessage, via a signal 184, to . ., ' 7~ ~ ~d ~
the decision logic 152 when the differentially encoded synchronization pattern is detected. This message signal 184 may be used by decision logic 152 in deriving a eonfidence decision 154.
Alternatively, the preferred embodiment received communication 5 signal synchronizing techn ~ le shown in FIG. 1 through FIC;. 5 can be described as follows with reference to FIG. 6. A method for synchronizing a received communication signai is provided. Initially, a received signal having a plurality of synchronization words is correlated 600 to generate a complex correlation si~nal. Each synchronization 10 word has a predetermined number of synchronization symbols. A
magnitude correlation signal is gensrated 602 from the complex correlation signal. The magnitude correlation signal is delayed 604 to form at least one delayed magnitude correlation signal for each received synchrcnization word. This magnitude correlation signal is 15 delayed 604 in increments of a synchronization word length.
Subsequently, the magnitude correlation signal and the delayed magnitude correlation signals are summed together 606 to generate a combined magnitude correlation signal. This combined magnitude ~-correlation signal is preferably compared to a predetermined magnitude 20 threshold according to one of two different algorithms. It will be appreciated by those skilled in the art that other similar algorithms may :;
'~ be readily substituted in place of th~se comparison algorithms without '~ departing irom the scope and spirit of the present invention.
. The first comparison algorithm 610 consi~l~ of delaying the 2~ combined magnitude correlation signal to form at least one delayed combined magnitude correlation signal. The combined ma~nitude correlation signal is then delayed in increments of a synchronization word length. SuhsQquQntly, the delayed combined magnitude correlation signal having the longest delay from among the formed 30 deJayed combined magnitude correlation signals is cornpared to a predetermined magnitude threshold. This comparison is continued until the compared delayed combined magnitude correlation signal is greater ' than the predeterminedthreshold. At which pointthe synchronization information based on a maximurn combined magnitude correlation 35 signal is prepared for output after a synchronization pattern is detected.
This rnaximum combined magnitude correl~tion signal is selected from ~, .
..
.~
. ~ :
the peak fiUer output 132. The complex phase correction value 120 corresponds to the amount of phase offset in the input data sequence 100 reiative to the local oscil'~tor used by the preferred embodiment.
The complex phase correotion vaiue 120 is coupled to one input of combiner 122. The input data sequence 130 which was stored in FIFO
buffer 128 (in either decimated or non decimated form) is provided to the other input of combiner 122. Combiner 122 preferably generates a phase-corrected input data sequence 134 by multiplying the input data sequence 130 with the complex phase correction value 120. The phase-corrected input data sequence 134 is then preferably stored in a FIFO buffer 140.
The phase-corrected input data sequence 134 is also input to a frequency offset estimator 136. The frequency offset estimator 136 computes a complex frequency correction value 138. The complex frequency correction value ~38 corresponds to the amount of frequency offsst in ~he input data sequence 100 relative to the local oscillator used by the preferred embodiment synchronization information generator.
The complex frequency correction valuts 138 may be determined in one of several known methods. For exampllq, in the preferred embodiment, part of the phase-corrected input data sequence 134 is known (i.e., the predetermined synchronization sequence is known). Thus, using the known predetermined synchronization sequence, the slope of the phase trajectory can be determined. This phase trajectory slope can subsequently be mapped to the frequerlcy domain as the frequency offset to generate the complex frequency correction value 138.
Alternatively, the complex frequency correction value 138 may bedetermined inthefollowing manner. Inthe preferred embodiment, the phase-corrected input data sequence 134 includes a synchronization sequence preferably consisting of a plurality o~
synchronization words. The use of a plurality of synchronization words l can be exploited in determining a frequency offset by forming a set of complex values that contain peak values caused by the synchronization ~;
words in the matched filter 102 (e.~., if five synchronization words are uszd, then the set has five complex values). For this frequency offset c~lcul~tion method to work, tha matched filter 102 output 104 must be input to the frequency offset estimator 136. Subsequently, any differential encodin~ pattern is preferably removed from the set. In ; ~ ;~
:
2~ ~3l9~7 ~ 9 addition, the slope of the phase trajectory is determined. This slope is then mapp~d to the frequency domain as the frequency offset to generate the complax frequency correction value 138. This frequency offset c~'c~ tlon method has an advantage over the previous method that the samples used in the c~lcul~tion have a higher signal to noise ratio, since the samples come from the matched filter 102 output 104.
However, because the samples are spaced farther apart in time, this fr~quency offset estimation method can not handle as large of a frequency offset as the previously described one.
The complex frequency correction value 138 is coupled to one input of combiner 142. Th~ phase-correcteci input data sequence 141 which was stored in FIFO buffer 140 is provided to the other input of combiner 142. Combiner 142 preferably generates a frequency-corrected input data sequence 144 by multiplying the input data sequence 141 with the complex phase correction value 138.
Optionally, if the known predetermined synchronization sequence preferably consists of differentially encoded synchronization words, a differentially encoded pattern detector 146 may be coupled to the output 144 of combiner 142 (i.e., the frlequency-corrected input data sequence 144). The differentially encoded pattern detector 146 sends . a message, via a signal 148, to the decision logic 162 when the differentially encoded synchronization pattern is detected. Otherwise, if the known predetermined synchronization sequence does not consist of differentially encoded synchronization words, the frequency-corrected input data sequence 144 may be directly coupled via signal 148 to the decision logic ti52.
In addition, a received signal sl,~r,~ll, indicator (RSSI) signal optionally may be input to decision logic 152. The RSSI signal is used by the decision logic 152 to minimize faising problems when no input da~a sequence 100 is present. Decision logic 152 analyzes ail of the input decision factors 116,148, and 150 to derive a con~idence decision 154 of whether or not the known predetermined synchronization sequence was detected in the input data sequence 100. This confidence decision 154 as well as any other information (e.g., phase and frequency offset information) may then be output from the synchronization information generator by the decision logic 152.
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Referring now to FiG. 2, an alternative preferred embodiment synchronization information gsnerator is shown. The alternative preferred embodiment synchronization information generator is configured and oparated su~lanlially as described in reference to the 5 preferred embodiment synchronization information generator shown in FIG. 1. In this alternative embodiment, the M-tap FIR fil~er 110 has been replaced by elements 156,160,164 and 168 which input and output substantially the same information as previously described in reference to the M-tap FIR filter 110. For this alterna~ive preferred embodiment, 10 the known predetermined synchronization sequence prsferably consists of four synchronization words. The synchronization words prefsrably are of equal length and are ordered in the same symbol pattern. The magnitude correlation signal 108 is input to a summing device 168. -The magnitude correlation signal 108 is also input to delay mechanism 156 which delays the magnitude sequence by the length of one synchronization word. The one synchronization word d~layed magnitude correlation signal 158 is input to surnming device 168. The one synchronization word delayed magnitude correlation signal 158 is also input to delay mechanism 160 which delays the magnitude correlation signal 158 by the length of another synchronization word.
The two synchronization word delayed magnitude correlation signal 162 is input to summing device 168. The two synchronization word delayed magnitude correlation signal 162 is also input to delay mechanism ~64 which delays the magnilude correlation signal 162 by the length of another synchronization word. The three synchronization ' word delayed magnitude correlation signal 166 is input to summing device 16~. The se~ of four magnitude correlation signals 108,158, 162, and 166 are summed by summin~ circuit 168 to forrn a combined magnitude correlation signal 112 (CMCS) (i.e., output 112). The output 1112 will have a non-zero value which is input to peak datection mechanism 114. It wili be appreciated by those skilled in the art that the principles described in reference to four synchroniza~ion words in a synchronization sequenoe can readily extended t~ more or less synchronization words without departing from the scope and spirit of the present invention.
In addition, in this preferred alternative embodiment, the peak detection mechanism 114 determines if the known predetermined -1 1- 2 3 ~ 7 synchronization sequence is present in the combined magnitude correlation signal 112 according to an algorithm detailed by the flowchart shown in FIG. S. A predetermined magnitude thresholcl is set 500 to an initial threshold. The peak detection mechanism 114 then waits 502 for a combined magnitude correlation signal 112 to be input.
When a combined ma~nitude correlation signal 112 is input, it is compared 504 to the predetermined magnitud~ threshold. If the combined magnitude correlation signal 112 is not greater than the pr~d~ler~ined magnitude threshold, then th~ peak detection mechanism 114 will return to flo~,cha,l element 502 and oontinue steps according to the flowchar~ in FIG. 5. Otherwise, when the combined magnitude correlation signal 112 is greater than the predetermined magnitude threshold, the predetermined threshold is set 506 to equal ~he combined magnitude correlation signal 112.
In addition, a count value is set 5û6 equal to a prede~ermined time delay. The count value is used to delay nolitic~iion of the detection of the synchronization sequence for a short time period. This short time period delay ailows the peak detection mechanism to verify that the synchronization sequence was actually detected, ra~her than a false signal being detected. This delay function is preferably implemented as follows after flowchart element 506. The peak detection mechanism -114 waits 508 for another combined magnitude correlation signal 112 to be input. When another combined magnitude correlation signal 112 is input, it is compared 510 ~o the predatermined magnitude threshold.
if the combined magnitude correlation signal 112 is greater than the predetsrmined magnitude threshold, then the peak detection meohanism 11~4 returns to flowchar~ element 506 and continues steps accordin~ to the flowchart in FIG. 5. Otherwise, when the oombined magnitude correlation signal 112 is not greater than the predetermined magnitude threshold, the count value is decremented 512. if the count - value is not zero or null, then ths peak detection mechanism 114returns to flowchart element 508 and continues steps according to the flowchart in FIG. 5. Otherwise, if the count value is zero or null, then the peak detection mechanism 114 notifies 516 the decision logic 152 of .
35 the synchronization sequence detection through an output signal 116 such that synchronization information may be subsequently output by the alternative preferred embodiment synchronization information .
., 12 ~ 7 generator. In addition, the peak detection mechanism 114 sends a peak combined magnitude correlation signal 13? to the FIFO buffer 128 so that the peak combined magnitude correlation signal output 132 can be saved along with the input data sequence 100 at the 5 location of where the peak combined magnitude correlation signal 132 occurred in the input data sequence 100.
Referring now to FIG. 3, an alternative preferred embodiment synchronization information generator is shown. The alternativa preferred embodiment synchronization inforrnation generator is 10 configured and operated s~bstantially as described in reference to the prsferred embodiment synchronization information generator shown in FIG. 1. In this alternative embodiment, the M-tap FIR filter 110 has been replaced by elements 156,160,164 and 168 which are configured and operated substantially as described in reference to the alternative ~:
preferrecl embodiment synchronization information generator shown in FIG. 2.
In addition, in this preferred alternative embodiment, the peak detection mechanism 114 has been replaced by elements 170,174 and 180 which input and output substantially the sama information as previouslydescribed in referencetothe peakdetection mechanism 114. The combined magnitude correlation signal 112 is input to a comparison device 1~0. The combinad magnitude correlation signal 112 is also input to dalay mecllani~-" 170 which delays the combined magnitude sequence for the length of one synchronization word. The ~5 one synchronization word delayed combined magnitude correlation signal 172 is inpu~ to comparison device 18û. The one synchronization word delayed combined magnitude correlation signal 172 is also input to delay mechanism 174 which delays the combined magnitude correlation signal 172 by the length of another synchronization word. I -The two synchroni~ation word delayed combined magnitude correlation signal 176 is input to comparison device 180. It will be appreciated by those skilled in the ar~ that the delay mechanism 170 and 174 may - delay the combined magnitude sequence by substantially more or lass than one synchronization word without departing ~rom the scope and spirit of the present invention. : ~.
Subsequently, the two synchronization word delayed combined - .
magnitude correlation signal 176 is compared by comparison device .
..
.
180 to a predetermined magnitude ~hreshold. This comparison is continued by comparison device 180 until the compared two synchronization word delayed combined magnitude correlation signal is greater than the predetermined threshold. if the two synchronization word delay~d combined magnitude correlation signal 176 is greater than the pr~determined magni~ude threshold, then the synchronization information based on a maximum combinad magnitude correlation signal is prepared, by comparison device 180, for output after a synchronization pattern is detected. This maximum combined magnitude correlation si~nal is selected from among the combined magnitude correlation signal 112 and two formed delayed combined magnitude correlation signals 172 and 176. In addition, the comparison device 180 notifies the decision logic 152 of the synchronization sequence detection through an output signal 116 such that prepared synchronization information may be subsequently output by the alternative preferred embodiment synchronization information generator. Finally, ~he comparison device 180 sends the maximum combined magnitude correlation signal 132 to the FIFO buffer 128 so ~ i that the maximum combined magnitude correlation signal output 132 can be saved along with the input data sequence 10û at the location of -where the maximum combined magnitulde correlation signal 132 occurred in the input data sequence 1011.
Referring now to FIG. 4, an alternative preferred embodiment synchronization information generator is shown. The alterrlative pre~erred embodirnent synchronization information generator is confi~ured and operated substantially as described in reference to the preferred embodiment synehronization information generator shown in FIG. 1. In this alternative embodiment, the complex frequency correction value 138 generated by ~requency offset estimator 136 may be directly -coupled via signal 148 to the decision logic 152. This complex frequency correction value 138 may be used by decision logic 152 in deriving a confidence decision 1154. In addition, for this alternative preferred embodirnent, the known predetermined synchronization sequence preferably consists of differentially encoded synchronization words. As such a differentially encoded pattern detector 182 may be coupled to the output 104 of matched filter 102. The differentially encoded pattern detector 182 sends a rnessage, via a signal 184, to . ., ' 7~ ~ ~d ~
the decision logic 152 when the differentially encoded synchronization pattern is detected. This message signal 184 may be used by decision logic 152 in deriving a eonfidence decision 154.
Alternatively, the preferred embodiment received communication 5 signal synchronizing techn ~ le shown in FIG. 1 through FIC;. 5 can be described as follows with reference to FIG. 6. A method for synchronizing a received communication signai is provided. Initially, a received signal having a plurality of synchronization words is correlated 600 to generate a complex correlation si~nal. Each synchronization 10 word has a predetermined number of synchronization symbols. A
magnitude correlation signal is gensrated 602 from the complex correlation signal. The magnitude correlation signal is delayed 604 to form at least one delayed magnitude correlation signal for each received synchrcnization word. This magnitude correlation signal is 15 delayed 604 in increments of a synchronization word length.
Subsequently, the magnitude correlation signal and the delayed magnitude correlation signals are summed together 606 to generate a combined magnitude correlation signal. This combined magnitude ~-correlation signal is preferably compared to a predetermined magnitude 20 threshold according to one of two different algorithms. It will be appreciated by those skilled in the art that other similar algorithms may :;
'~ be readily substituted in place of th~se comparison algorithms without '~ departing irom the scope and spirit of the present invention.
. The first comparison algorithm 610 consi~l~ of delaying the 2~ combined magnitude correlation signal to form at least one delayed combined magnitude correlation signal. The combined ma~nitude correlation signal is then delayed in increments of a synchronization word length. SuhsQquQntly, the delayed combined magnitude correlation signal having the longest delay from among the formed 30 deJayed combined magnitude correlation signals is cornpared to a predetermined magnitude threshold. This comparison is continued until the compared delayed combined magnitude correlation signal is greater ' than the predeterminedthreshold. At which pointthe synchronization information based on a maximurn combined magnitude correlation 35 signal is prepared for output after a synchronization pattern is detected.
This rnaximum combined magnitude correl~tion signal is selected from ~, .
..
.~
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9~
among the combined magnitude correlation siynal and the formed delayed combined magnitude correlation signals.
The second comparison algorithm 612 consists of comparing the combined magnitude correlation signal to ~ predetermined initial magnitude threshold until the combined magnitude correlation signal is ~ -greater than the pradetermined initial magnitude threshold. At which point the predetermined initial magnitude threshold is changed to equal the combined magnitude correlation signal. This comparison and magnitude threshold change is continued subse~uently until the magnitude threshold has not been changed for a predetermined period of time. Subsequently, synchronization information based on the combined magnitude correlation signal corresponding to the current -ma~nitude threshold is prepared for output after a synchronization pattern is detected. -After either c~mparison algorithm is completed, a phase offset for the received signal is determined and corrected based on the output synchronization information. In addition, a frequency offset of the phase corrected received signal is determined 616. Subsequently, if a synchronization pattern is employed, then it is preferrably detected 618 according to one of two different detecting al~orithms. It will be appreci~ted by those skilled in the art that other similar algorithms may be readily substituted in place of these Idetecting algorithms without departing from the scope and spirit of the present invention. The first detecting algorithm 620 consis~s of correcting the frequency offset of the phase correctsd received signal and generating first pattern confidence information by comparing the frequency corrected received signal to a predetermined pattern. The second detecting algorithm 622 consists of generating second pattern confidence information by comparing the complex correlation signal to a predeten"ined pattern.
After either detecting algorithm is completed, the prepared synchronization information is output 624 based on a confidence decision derived from at least one decision factor. The decision factors may include a received signal strength indicator, the synchronization information, the first pattern confidence information, the second pattern confidence information, and the frequency offset of the received signal.
Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure of embodiments has been rnade by way of example only and that numerous changes in the arrangement and combination of parts as well as steps may be resorted to by those skilled in the art without departing from the spifit and scope of the invention as claimed.
','~',',' ,"'~,'' ::
among the combined magnitude correlation siynal and the formed delayed combined magnitude correlation signals.
The second comparison algorithm 612 consists of comparing the combined magnitude correlation signal to ~ predetermined initial magnitude threshold until the combined magnitude correlation signal is ~ -greater than the pradetermined initial magnitude threshold. At which point the predetermined initial magnitude threshold is changed to equal the combined magnitude correlation signal. This comparison and magnitude threshold change is continued subse~uently until the magnitude threshold has not been changed for a predetermined period of time. Subsequently, synchronization information based on the combined magnitude correlation signal corresponding to the current -ma~nitude threshold is prepared for output after a synchronization pattern is detected. -After either c~mparison algorithm is completed, a phase offset for the received signal is determined and corrected based on the output synchronization information. In addition, a frequency offset of the phase corrected received signal is determined 616. Subsequently, if a synchronization pattern is employed, then it is preferrably detected 618 according to one of two different detecting al~orithms. It will be appreci~ted by those skilled in the art that other similar algorithms may be readily substituted in place of these Idetecting algorithms without departing from the scope and spirit of the present invention. The first detecting algorithm 620 consis~s of correcting the frequency offset of the phase correctsd received signal and generating first pattern confidence information by comparing the frequency corrected received signal to a predetermined pattern. The second detecting algorithm 622 consists of generating second pattern confidence information by comparing the complex correlation signal to a predeten"ined pattern.
After either detecting algorithm is completed, the prepared synchronization information is output 624 based on a confidence decision derived from at least one decision factor. The decision factors may include a received signal strength indicator, the synchronization information, the first pattern confidence information, the second pattern confidence information, and the frequency offset of the received signal.
Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure of embodiments has been rnade by way of example only and that numerous changes in the arrangement and combination of parts as well as steps may be resorted to by those skilled in the art without departing from the spifit and scope of the invention as claimed.
','~',',' ,"'~,'' ::
Claims (10)
1. A method for synchronizing a received communication signal, comprising:
(a) generating a synchronization signal derived from a received signal having a plurality of synchronization words, each synchronization word having a predetermined number of synchronization symbols;
(b) filtering the synchronization signal, the filtering being characterized by spacing each filter tap to correspond to synchronization word length increments, (c) generating synchronization information based on a comparison of the filtered synchronization signal to a threshold; and (d) outputting the synchronization information based on a confidence decision derived from the synchronization information.
(a) generating a synchronization signal derived from a received signal having a plurality of synchronization words, each synchronization word having a predetermined number of synchronization symbols;
(b) filtering the synchronization signal, the filtering being characterized by spacing each filter tap to correspond to synchronization word length increments, (c) generating synchronization information based on a comparison of the filtered synchronization signal to a threshold; and (d) outputting the synchronization information based on a confidence decision derived from the synchronization information.
2. The method of claim 1 wherein the step of:
(a) generating the synchronization signal comprises correlating the received signal to generate a complex correlation signal and generating a magnitude correlation signal from the complex correlation signal; and (b) filtering the synchronization signal comprises delaying the magnitude correlation signal to form at least one delayed magnitude correlation signal for each received synchronization word, the magnitude correlation signal being delayed in increments of a synchronization word length and subsequently summing the magnitude correlation signal and the delayed magnitude correlation signals to generate a combined magnitude correlation signal.
(a) generating the synchronization signal comprises correlating the received signal to generate a complex correlation signal and generating a magnitude correlation signal from the complex correlation signal; and (b) filtering the synchronization signal comprises delaying the magnitude correlation signal to form at least one delayed magnitude correlation signal for each received synchronization word, the magnitude correlation signal being delayed in increments of a synchronization word length and subsequently summing the magnitude correlation signal and the delayed magnitude correlation signals to generate a combined magnitude correlation signal.
3. The method of claim 2 wherein the step of generating synchronization information comprises:
(a) delaying the combined magnitude correlation signal to form at least one delayed combined magnitude correlation signal, the combined magnitude correlation signal being delayed in increments of a synchronization word length;
(b) comparing a delayed combined magnitude correlation signal having the longest delay from among the formed delayed combined magnitude correlation signals to a predetermined magnitude threshold; and (c) preparing synchronization information for output based o a maximum combined magnitude correlation signal from among the combined magnitude correlation signal and the formed delayed combined magnitude correlation signals, when the compared delayed combined magnitude correlation signal is greater than the predetermined magnitude threshold.
(a) delaying the combined magnitude correlation signal to form at least one delayed combined magnitude correlation signal, the combined magnitude correlation signal being delayed in increments of a synchronization word length;
(b) comparing a delayed combined magnitude correlation signal having the longest delay from among the formed delayed combined magnitude correlation signals to a predetermined magnitude threshold; and (c) preparing synchronization information for output based o a maximum combined magnitude correlation signal from among the combined magnitude correlation signal and the formed delayed combined magnitude correlation signals, when the compared delayed combined magnitude correlation signal is greater than the predetermined magnitude threshold.
4. The method of claim 2 wherein the step of generating synchronization information comprises:
(a) comparing the combined magnitude correlation signal to a predetermined initial magnitude threshold until the combined magnitude correlation signal is greater than the predetermined initial magnitude threshold and then changing the predetermined initial magnitude threshold to equal the combined magnitude correlation signal;
(b) continuing subsequently to change the magnitude threshold to equal the combined magnitude correlation signal when the combined magnitude correlation signal is greater than the magnitude threshold until the magnitude threshold is unchanged for a predetermined period of time;
and (c) preparing subsequently synchronization information for output based on the combined magnitude correlation signal corresponding to the current magnitude threshold.
(a) comparing the combined magnitude correlation signal to a predetermined initial magnitude threshold until the combined magnitude correlation signal is greater than the predetermined initial magnitude threshold and then changing the predetermined initial magnitude threshold to equal the combined magnitude correlation signal;
(b) continuing subsequently to change the magnitude threshold to equal the combined magnitude correlation signal when the combined magnitude correlation signal is greater than the magnitude threshold until the magnitude threshold is unchanged for a predetermined period of time;
and (c) preparing subsequently synchronization information for output based on the combined magnitude correlation signal corresponding to the current magnitude threshold.
5. The method of claim 1 wherein the step of outputting synchronization information comprises:
(a) determining and correcting a phase offset for the received signal based on the synchronization information;
(b) determining frequency offset of the phase corrected received signal; and (c) outputting synchronization information based on a confidence decision derived from the frequency offset of the received signal.
(a) determining and correcting a phase offset for the received signal based on the synchronization information;
(b) determining frequency offset of the phase corrected received signal; and (c) outputting synchronization information based on a confidence decision derived from the frequency offset of the received signal.
6. The method of claim 1 wherein the step of outputting synchronization information comprises:
(a) determining and correcting a phase offset for the received signal based on the synchronization information;
(b) determining and correcting a frequency offset of the phase corrected received signal;
(c) generating pattern confidence information by comparing the frequency corrected received signal to a predetermined synchronization pattern; and (d) outputting synchronization information based on a confidence decision derived from the pattern confidence information.
(a) determining and correcting a phase offset for the received signal based on the synchronization information;
(b) determining and correcting a frequency offset of the phase corrected received signal;
(c) generating pattern confidence information by comparing the frequency corrected received signal to a predetermined synchronization pattern; and (d) outputting synchronization information based on a confidence decision derived from the pattern confidence information.
7. The method of claim 2 wherein the step of outputting synchronization information comprises:
(a) generating pattern confidence information by comparing the complex correlation signal to a predetermined synchronization pattern; and (b) outputting synchronization information based on a confidence decision derived from the pattern confidence information.
(a) generating pattern confidence information by comparing the complex correlation signal to a predetermined synchronization pattern; and (b) outputting synchronization information based on a confidence decision derived from the pattern confidence information.
8. The method of claim 1 wherein the step of outputting synchronization information comprises outputting synchronization information based on a confidence decision derived from a received signal strength indicator.
9. A digital radio communication unit having signal synchronizing capability, comprising:
(a) synchronization signal generator means for generating a synchronization signal derived from a received signal having a plurality of synchronization words, each synchronization word having a predetermined number of synchronization symbols;
(b) filter means, operatively coupled to the synchronization signal means, for filtering the synchronization signal, the filtering being characterized by spacing each filter tap to correspond to synchronization word length increments;
(c) synchronization information generator means, operatively coupled to the filter means, for generating synchronization information based on a comparison of the filtered synchronization signal to a threshold; and (d) synchronization information output means, operatively coupled to the synchronization information generator means, for outputting synchronization information based on a confidence decision derived from the synchronization information.
(a) synchronization signal generator means for generating a synchronization signal derived from a received signal having a plurality of synchronization words, each synchronization word having a predetermined number of synchronization symbols;
(b) filter means, operatively coupled to the synchronization signal means, for filtering the synchronization signal, the filtering being characterized by spacing each filter tap to correspond to synchronization word length increments;
(c) synchronization information generator means, operatively coupled to the filter means, for generating synchronization information based on a comparison of the filtered synchronization signal to a threshold; and (d) synchronization information output means, operatively coupled to the synchronization information generator means, for outputting synchronization information based on a confidence decision derived from the synchronization information.
10. The digital radio communication unit of claim 9 wherein the synchronization signal generator means comprises correlation means for correlating the received signal to generate a complex correlation signal and for generating a magnitude correlation signal from the complex correlation signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/988,572 US5428647A (en) | 1992-12-07 | 1992-12-07 | Method and apparatus for synchronizing a received signal in a digital radio communication system |
| US988,572 | 1992-12-07 |
Publications (2)
| Publication Number | Publication Date |
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| CA2103497A1 CA2103497A1 (en) | 1994-06-08 |
| CA2103497C true CA2103497C (en) | 1999-03-09 |
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| CA002103497A Expired - Fee Related CA2103497C (en) | 1992-12-07 | 1993-11-19 | Method and apparatus for synchronizing a received signal in a digital radio communication system |
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| US (1) | US5428647A (en) |
| CA (1) | CA2103497C (en) |
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-
1992
- 1992-12-07 US US07/988,572 patent/US5428647A/en not_active Expired - Lifetime
-
1993
- 1993-11-19 CA CA002103497A patent/CA2103497C/en not_active Expired - Fee Related
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| Publication number | Publication date |
|---|---|
| US5428647A (en) | 1995-06-27 |
| CA2103497A1 (en) | 1994-06-08 |
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