WO1995008889B1 - High speed simulcast system using adaptive compensation - Google Patents
High speed simulcast system using adaptive compensationInfo
- Publication number
- WO1995008889B1 WO1995008889B1 PCT/US1994/010662 US9410662W WO9508889B1 WO 1995008889 B1 WO1995008889 B1 WO 1995008889B1 US 9410662 W US9410662 W US 9410662W WO 9508889 B1 WO9508889 B1 WO 9508889B1
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- WIPO (PCT)
- Prior art keywords
- signal
- data
- signals
- transmitters
- sequence
- Prior art date
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- 230000003044 adaptive Effects 0.000 title claims 10
- 230000004044 response Effects 0.000 claims abstract 39
- 230000001702 transmitter Effects 0.000 claims abstract 33
- 230000000051 modifying Effects 0.000 claims abstract 8
- 238000005562 fading Methods 0.000 claims abstract 7
- 238000000034 method Methods 0.000 claims abstract 2
- 238000005070 sampling Methods 0.000 claims 16
- 238000003672 processing method Methods 0.000 claims 5
- 230000000875 corresponding Effects 0.000 claims 3
- 230000003111 delayed Effects 0.000 claims 3
- 230000015556 catabolic process Effects 0.000 claims 2
- 230000004059 degradation Effects 0.000 claims 2
- 238000006731 degradation reaction Methods 0.000 claims 2
- 230000000737 periodic Effects 0.000 claims 2
- 238000006243 chemical reaction Methods 0.000 claims 1
- 238000011084 recovery Methods 0.000 claims 1
- 230000000644 propagated Effects 0.000 abstract 1
Abstract
In a simulcast communication system (26), a method and apparatus for compensating differences in propagation time, lack of synchronization in transmitters, and multipath fading to recover data transmitted to a receiving device. In a simulcast communication system (26) that comprises a plurality of transmitters (32a, 32b, 32c), a receiver (36) includes a digital signal processor (DSP) (86) that processes a demodulated received signal to adaptively compensate for changes in the channel through which a multipath signal is propagated from the transmitters to the receiver. In one embodiment, the DSP comprises a decision feedback equalizer (300). An error signal is produced by the equalizer through a comparison of the estimated symbols with symbols most likely transmitted, for use in updating filter coefficients used by the equalizer in processing the received signal. Another embodiment implements a Viterbi algorithm to make decisions of the most likely data symbols in response to estimates of the channel impulse response. Using any one of these embodiments, a linear modulated signal can be decoded to recover the data transmitted, even though the received signal has been degraded by propagation in a multipath fading channel.
Claims
1. Receiving apparatus for receiving simulcast signals transmitted by a plurality of transmitters that are remotely located from one another, each of the transmitters transmitting substantially identical data and being in substantial synchronization with one another, the substantially identical data transmitted by each transmitter including a plurality of sequentially transmitted blocks of predetermined reference symbols that are interspersed with sequences of data symbols that collectively are representative of the substantially identical data, each block of the plurality of blocks cf predetermined reference symbols including at least one reference symbol, said receiving apparatus comprising:
(a) demodulation means for demodulating a received signal to produce a demodulated signal, said received signal, at times, corresponding to a summation of the signals transmitted by at least two transmitters of said plurality of transmitters, said summation of said signals being subject to differences in propagation time between said at least two transmitters and said receiving apparatus; and,
(b) an adaptive equalizer connected for receiving said demodulated signal, said adaptive equalizer including processor means for adaptively processing the demodulated signal in accordance with a plurality of equalization coefficients to produce a processed signal that includes data that were transmitted by the plurality of transmitters, said processor means including means for periodically updating said plurality of equalization coefficients to compensate for at least one of a plurality of sources of received signal degradation, the sources of received signal degradation including:
(i) multi-path fading;
(ii) differences in propagation times for the transmitted signals from at least two of the transmitters to reach said receiving apparatus;
(iii) motion of the receiving apparatus;
(iv) differences in frequency of the transmitted signals; and
(v) a lack of synchronization between the plurality of transmitters; said means for periodically updating said plurality of equalization coefficients being responsive to said reference symbols of said blocks of at least one reference symbol and providing each updated set of said plurality of equalization coefficients solely on the basis of one or more of said reference symbols.
2. The receiving apparatus of Claim 1 wherein said processor means includes means for supplying an estimated channel impulse response for at least one reference symbol of each said block of predetermined reference symbols and wherein said means for updating said plurality of equalization coefficients supplies at least one updated set of said plurality of equalization coefficients in response to each said block of at least one reference symbol; said means for updating said plurality of equalization coefficients supplying at least one additional set of updated equalization coefficients during each period of time between two sequential blocks of at least one reference symbol, each set of said updated equalization coefficients supplied between two sequential blocks of said at least one reference symbol being determined by interpolation between at least one estimated channel response for each of the two sequential blocks of at least one reference symbol that define said period of time between said two sequential blocks of at least one reference symbol.
3. The receiving apparatus of Claim 2, wherein the interpolation for establishing estimation coefficients during said period of time between two sequential blocks of at least one reference symbol is based upon at least one of the following channel characteristics: Doppler fading frequency, relative signal strengths of the signals received from said at least two transmitters, propagation delay differences between signals received from said at least two transmitters, frequency offsets between signals received from at least said two transmitters and the signal-to-noise ratio of the signals received from said at least two transmitters.
4. The receiving apparatus of Claim 3, wherein the interpolation used for establishing estimation coefficients between sequential blocks of said at least one reference symbol is performed relative to each data symbol in said period of time between said two sequential blocks of at least one reference symbol.
5. The receiving apparatus of Claim 1 wherein said simulcast signal transmitted by each of said plurality of transmitters is linearly modulated with said substantially identical data and said demodulation means of said receiving apparatus includes means for demodulating a linearly modulated signal.
6. The receiving apparatus of Claim 5 wherein said processor means includes means for supplying an estimated channel impulse response for at least one reference symbol of each said block of predetermined reference symbols and wherein said means for updating said plurality of equalization coefficients supplies at least one updated set αf said plurality of equalization coefficients in response to each said block of at least one reference symbol; said means for updating said plurality of equalization coefficients supplying at least one additional set of updated equalization coefficients during each period of time between two sequential blocks of at least one reference symbol, each set of said updated equalization coefficients supplied between two sequential blocks of said at least one reference symbol being determined by interpolation between at least one estimated channel response for each of the two sequential blocks of at least one reference symbol that define said period of time between said two sequential blocks of at least one reference symbol.
7. The receiving apparatus of Claim 6, wherein the interpolation for establishing estimation coefficients during said period of time between two sequential blocks of at least one reference symbol is based upon at least one of the following channel characteristics: Doppler fading frequency, relative signal strengths of the signals received from said at least two transmitters, propagation delay differences between signals received from said at least two transmitters, frequency offsets between signals received from at least said two transmitters and the signal-to-noise ratio of the signals received from said at least two transmitters.
8. The receiving apparatus of Claim 7, wherein the interpolation used for establishing estimation coefficients between sequential blocks of said at least one reference symbol is performed relative to each data symbol in said period of time between said two sequential blocks of at least one reference symbol.
9. The receiving apparatus of Claim 1 further comprising analog-to-digital conversion means for converting said demodulated signal to a periodically sampled signal sequence r(-j)...., r(-l), r(0), r(l), ...,r(k), where the kth sample can be mathematically expressed as: 
where [H(k)] =..., h(k,-l),h(k,0), h(k,l), h(k,n), ... represents the discrete time channel impulse response for the received signal at the time of the λth signal of said sampled signal sequence, s(k - n) represents the transmitted signal at a time that corresponds to the Λth signal of said sampled signal sequence and n(k) represents the noise component of said received signal; and wherein said processor means for adaptively processing said demodulated signal supplies a signal 
as an estimate of said processed signal that includes data that were transmitted by the plurality of transmitters, where the summation limits (-J,K) define the number of signals in said sampled signal sequence that are used for a determination of each estimate 
and a (k,n) represents said plurality of equalization coefficients.
10. The receiving apparatus of Claim 9 wherein said processor means of said adaptive equalizer includes means for separating signals of said sampled signal sequence that represent said plurality of blocks of predetermined reference symbols from signals of said sampled signal sequence that represent said sequences of data symbols; and, wherein said signals representative of said plurality of blocks of predetermined reference symbols are used by said processor means for said periodically updating of said equalization coefficients.
11. The receiving apparatus of Claim 10 wherein said processor of said adaptive equalizer determines an estimated channel impulse response for each said sampled signal sequence that is representative of one of said blocks of reference signals, one or more of said estimated channel impulse responses being used by said processor means for periodically updating said equalization coefficients for determination of said signal 
when the kth signal of said sampled signal sequence corresponds to a data symbol of one of said sequences of data symbols.
12. The receiving apparatus of Claim 11 wherein a plurality of said estimated channel impulse responses are used for periodically updating said equalization coefficients for determination of said signal 
when the kth signal of said sampled signal sequence corresponds to a data symbol of one of said sequences of data symbols, a portion of said plurality of estimated channel impulse responses being for channel impulse responses for blocks of said referenced symbols received prior to said Ath signal and a portion of said estimated channel impulse responses being for blocks of said reference symbols received after said kth signal.
13. The receiving apparatus of Claim 12 wherein said processor means of said adaptive equalizer determines updated estimation coefficients for determination of said signal by interpolation of said plurality of said estimated channel impulse responses.
14. The receiving apparatus of Claim 13, wherein the interpolation for determining updated estimation coefficients when the kth signal of said sampled signal sequence corresponds to a data symbol is based upon at least one of the following channel characteristics: Doppler fading frequency, relative signal strengths of the signals received from said at least two transmitters, propagation delay differences between signals received from said at least two transmitters, frequency offsets between signals received from at least said two transmitters and the signal-to-noise ratio of the signals received from said at least two transmitters.
15. The receiving apparatus of Claim 14, wherein the interpolation used for determining updated estimation coefficients is performed relative to each kth signal of said signal sequence that corresponds to a data symbol.
16. The receiving apparatus of Claim 11 wherein said simulcast signal transmitted by each of said plurality of transmitters is linearly modulated with said substantially identical data and said demodulation means of said receiving apparatus includes means for demodulating a linearly modulated signal.
17. The receiving apparatus of Claim 16 wherein a plurality of said estimated channel impulse responses are used for periodically updating said equalization coefficients for determination of said signal 
when the kth signal of said sampled signal sequence corresponds to a data symbol of one of said sequences of data symbols, a portion of said plurality of estimated channel impulse responses being for channel impulse responses for blocks of said referenced symbols received prior to said kth signal and a portion of said estimated channel impulse responses being for blocks of said reference symbols received after said kth signal.
18. The receiving apparatus of Claim 17 wherein said processor means of said adaptive equalizer determines updated estimation coefficients for determination of said signal by interpolation of said plurality of said estimated channel impulse responses.
19. The receiving apparatus of Claim 18, wherein the interpolation for determining updated estimation coefficients when the kth signal of said sampled signal sequence corresponds to a data symbol is based upon at least one of the following channel characteristics: Doppler fading frequency, relative signal strengths of the signals received from said at least two transmitters, propagation delay differences between signals received from said at least two transmitters, frequency offsets between signals received from at least said two transmitters and the signallto-noise ratio of the signals received from said at least two transmitters.
20. The receiving apparatus of Claim 19, wherein the interpolation used for determining updated estimation coefficients is performed relative to each kth signal of said signal sequence that corresponds to a data symbol.
21. Apparatus for use in a radio receiver to process a demodulated signal for recovery of transmitted data, said apparatus comprising:
first and second decision feedback equalizers, each of said first and second decision feedback equalizers being connected for receiving the demodulated signal, said first decision feedback equalizer being responsive to a first set of estimation coefficients, said first decision feedback equalizer sequentially processing said demodulated signal in a forward direction relative to the time of signal reception to provide a first equalized output signal; said second decision feedback equalizer being responsive to a second set of estimation coefficients, said second decision feedback equalizer sequentially processing said demodulated signal in a reverse direction relative to the time of reception to supply a second equalized output signal; and
means for selecting as the output of said apparatus that one of said first and second equalized output signals that is most likely to correspond to the transmitted data, said means for selecting one of said first and second equalized output signals including means for selecting that one of said of first and second output signals that is most likely to correspond to the data transmitted to said radio receiver by a plurality of simulcast transmitters.
22. The apparatus of Claim 21, wherein said means for selecting one of said first and second equalized output signals as the output of said apparatus is a Viterbi decoder.
23. The apparatus of Claim 21, wherein said means for selecting for one of said first and second equalized output signals is responsive to a third set of estimation coefficients, and wherein said apparatus further comprises a channel estimator having an input coupled for receiving said demodulated signal, said channel estimator processing said demodulated signal to provide a channel impulse response estimate; said channel estimator periodically providing updated sets of said third estimation coefficients that are determined from said channel impulse response to said means for selecting one or said first and second equalized output signals as said output of said apparatus.
24. The apparatus of Claim 23 wherein said channel estimator further provides updated sets of said first and second estimation coefficients to said first and second decision feedback equalizers.
25. The apparatus of Claim 23, wherein said means for selecting one of said first and second equalized output signals as said output of said apparatus is a Viterbi decoder.
26. The apparatus of Claim 25 wherein said channel estimator provides updated sets of said first and second estimation coefficients to said first and second decision feedback equalizers.
27. The apparatus of Claim 23 wherein the demodulated signal is representative of transmitted data that includes a plurality of data frames, each data frame including N data symbols, and wherein:
(a) said first decision feedback equalizer supplies said first equalized output signal in the form of a signal sequence that corresponds to [U] = (u(l), u(2), ..., u(N));
(b) said second decision feedback equalizer supplies said second equalized output signal in the form of a signal sequence that corresponds to [V] =(v(l), v(2),..., v(N)); and
(c) said means for selecting that one of said first and second equalized output signals that is most likely to correspond to the data transmitted to said receiver includes means for selecting one of said signal sequences [U] and [V] to minimize the mean square error between the demodulated received signal r =...,r(-l), r(0),r(l).... and first and second equalized output signals, said first equalized output signal being defined by 
and said second equalized output signal being defined by 
where m is a predetermined integer and f(k,n) is the estimated channel impulse response for the kth signal element of said demodulated received signal, that one of said signal sequences [U] and [V] that minimizes said mean square error being selected as being most likely to correspond to said data transmitted to said receiver.
28. The apparatus of Claim 27 wherein said channel estimator further provides updated sets of said first and second estimation coefficients to said first and second decision feedback equalizers.
29. The apparatus of Claim 23 wherein the demodulated signal is representative of transmitted data that includes a plurality of data frames, each data frame including N data symbols, and wherein:
(a) said first decision feedback equalizer supplies said first equalized output signal in the form of a signal sequence that corresponds to [U] = (u(l), u(2), ..., u(N));
(b) said second decision feedback equalizer supplies said second equalized output signal in the form of a signal sequence that corresponds to ( v} = (v(i), v(2), ..., v(N)); and
(c) said means for selecting that one of said first and second equalized output signal that is most likely to correspond to the data transmitted to said receiver includes means for determining all possible N-length sequences for said signal sequences [U] and [V] and for supplying as said signal that is most likely to correspond to the data transmitted to said receiver. The N-length sequence that exhibits the lowest value, M(W), where
where a, b and m are predetermined integers, r(k) represents the kth signal element of a periodic sequence of signals representing said demodulated received signal, and f(k,n) is the estimated channel impulse response for said kth signal element of said periodic sequence of signals.
30. The apparatus of Claim 27 wherein said channel estimator further provides updated sets of said first and second estimation coefficients to said first and second decision feedback equalizers.
31. A signal processing method for recovering simulcast signal data that is transmitted to a receiver by a plurality of transmitters each of which synchronously transmit a modulated signal in which information is encoded as a plurality of signal frames with each signal frame including a preamble block, a data block that includes N data bits and a postamble block, said method being executable in a receiver that includes a data signal processor and associated memory, said method comprising:
demodulating the simulcast signal received by said receiver;
periodically sampling said demodulated signal to supply a signal sequence representative of said demodulated received signal;
processing said signal sequence representative of said demodulated received signal to supply a first signal sequence that is likely to correspond to a sequence of N data bits of the simulcast signal transmitted to said receiver, said processing of said signal sequence representative of said demodulated received signal comprising decision feedback equalization processing in a forward direction relative to the time of signal reception;
processing said signal sequence representative of said demodulated received signal to supply a second signal sequence that is likely to correspond to said sequence of N data bits of the simulcast signal transmitted to said receiver, said processing of said signal sequence representative of said demodulated received signal comprising decision feedback equalization processing in a reverse direction relative to the time of signal reception;
selecting one said first or second sequence of signals likely to correspond to said N data bits of said transmitted signal by determining which of said first and second sequences of signals is most likely to correspond to said N data bits.
32. The signal processing of Claim 31, wherein said step of selecting one of said sequences of signals comprises first and second processing the first and second sequences in accordance with a Viterbi algorithm.
33. A signal processing method for use in receiving simulcast signals transmitted by a plurality of disparately located base stations, the simulcast signals transmitted by each base station being modulated by a plurality of data symbol sequences that are representative of information being transferred from said base stations to one or more receivers which, at times, receive more than one simulcast signal, the data symbol sequences being interspersed with blocks of pilot symbols, said signal processing method being performed by the one or more receivers for recovering said information being transferred from said base stations to said receivers and comprising the steps of:
(a) demodulating a signal received from said one or more base stations;
(b) processing the signal supplied by said step of demodulating to separate each block of said pilot symbols from said interspersed sequences of data symbols;
(c) processing said blocks of said pilot symbols to provide estimated channel impulse responses, each of said estimated channel impulse responses being individually based upon a different one of said blocks of pilot symbols; and
(d) processing said interspersed sequences of said data symbols with an adaptive equalizer having signal transfer characteristics determined solely on the basis of said channel impulse responses.
34. The signal processing method of Claim 33 wherein said step of providing estimated channel impulse responses for said received signal includes the step of storing in a memory a plurality of channel impulse responses that correspond to a plurality of sequentially received blocks of pilot symbols; and wherein said step of processmg said sequence of data symbols includes the step of establishing said signal transfer characteristics of said adaptive equalizer by interpolation of said plurality of said channel impulse responses stored in memory.
35. The signal processing method of Claim 34 wherein said plurality of channel impulse responses is equal to an integer K that is equal to at least 2 with K/2 of said stored channel impulse responses corresponding to blocks of said pilot symbols received prior to receiving the block data symbols to be processed in said step of processing data symbols and K/2 of said channel impulse responses correspond to pilot symbols received subsequent to the block data symbols to be processed in said step of processing data symbols; and wherein the step of establishing the signal transfer characteristics of said adaptive equalizer comprises interpolation of said K channel impulse responses.
36. In a simulcast communication system, a method for transferring data to a receiving device from a plurality of base stations, said method comprising the steps of:
(a) transmitting from each said base station a signal modulated with a plurality of data symbol sequences that are interspersed with a plurality of pilot symbol blocks, each sequence of said data symbols being representative of a portion of said data being transferred to said receiving device, each said pilot symbol block including at least one predetermined pilot symbol;
(b) demodulating a received signal at the receiving device to produce a demodulated signal said received signal at times corresponding to the sum of the signals transmitted by at least two of said base stations;
(c) processing said demodulated signal to separate each sequence of data symbols from the biock of pilot symbols that is antecedent to said sequence of data symbols and from the block of pilot symbols that is subsequent to said sequence of data symbols;
(d) delaying a sequence of said data symbols being processed by an interval of time at least equal to K, where K is a positive integer multiple of the period of time between sequential blocks of pilot symbols and is at least 2;
(e) processing each said block of pilot symbols to provide an estimated channel impulse response for K/2 sequential blocks of pilot symbol blocks received prior to receiving said sequence of delayed dau symbols and K/2 sequential blocks of pilot symbols received after receiving said ddayed sequence of data symbols.
(f) processing the K estimated channel impulse responses to provide an interpolated channel impulse response; and,
(g) processing the delayed sequence of data symbols with said interpolated channel impulse response.
37. The method of Claim 36 further comprising the step of periodically sampling said demodulated signal to provide a sampled signal sequence r(-j),... , r(-l),r(0),r(l),...,r(k) and wherein said step of processing each data symbol of said delayed sequence of data symbols includes:
(a) determining an estimate 
of a portion of the data being transferred, said estimate s(k) being represented by the expression
where a(k,n) are a set of (J+K+l) equalization coefficients for the kth one of said sampled signal sequence;
(b) processing said estimate 
to provide a signal s(k) that is likely to correspond to the data transmitted by the plurality of base stations;
(c) determining the difference between said signals 
and s(k); and
(d) updating said set of equalization coefficients to minimize said difference between said signals 
and s(k) .
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU77997/94A AU7799794A (en) | 1993-09-20 | 1994-09-19 | High speed simulcast system using adaptive compensation |
| KR1019960701445A KR100299625B1 (en) | 1993-09-20 | 1994-09-19 | High speed simultaneous broadcasting system using adaptive compensation means |
| EP94928635A EP0720798A4 (en) | 1993-09-20 | 1994-09-19 | High speed simulcast system using adaptive compensation |
| SE9600966A SE9600966L (en) | 1993-09-20 | 1996-03-13 | High-speed transmitting system using adaptive compensation |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/124,155 | 1993-09-20 | ||
| US08/124,155 US5513215A (en) | 1993-09-20 | 1993-09-20 | High speed simulcast data system using adaptive compensation |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| WO1995008889A1 WO1995008889A1 (en) | 1995-03-30 |
| WO1995008889B1 true WO1995008889B1 (en) | 1995-04-13 |
Family
ID=22413111
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/US1994/010662 WO1995008889A1 (en) | 1993-09-20 | 1994-09-19 | High speed simulcast system using adaptive compensation |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5513215A (en) |
| EP (1) | EP0720798A4 (en) |
| KR (1) | KR100299625B1 (en) |
| CN (1) | CN1131490A (en) |
| AU (1) | AU7799794A (en) |
| CA (1) | CA2171634A1 (en) |
| SE (1) | SE9600966L (en) |
| WO (1) | WO1995008889A1 (en) |
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1994
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- 1994-09-19 WO PCT/US1994/010662 patent/WO1995008889A1/en not_active Application Discontinuation
- 1994-09-19 AU AU77997/94A patent/AU7799794A/en not_active Abandoned
- 1994-09-19 CN CN94193450A patent/CN1131490A/en active Pending
- 1994-09-19 CA CA002171634A patent/CA2171634A1/en not_active Abandoned
- 1994-09-19 EP EP94928635A patent/EP0720798A4/en not_active Withdrawn
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- 1996-03-13 SE SE9600966A patent/SE9600966L/en not_active Application Discontinuation
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