CA2411286C - Low complexity maximum likelihood detection of concatenated space codes for wireless applications - Google Patents
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Abstract
Good transmission characteristics are achieved in the presence of fading with a transmitter that employs a trellis coder followed by a block coder. Correspondingly, the receiver comprises a Viterbi decoder followed by a block decoder. Advantageously, the block coder and decoder employ time-space diversity coding which, illustratively, employs two transmitter antennas and one receiver antenna.
Description
Low Complexity Maximum Likelihood Detection Of Concatenated Space Codes For Wireless Applications Background of the Invention This invention relates to wireless communication and, more particularly, to techniques for effective wireless communication in the presence of fading and other degradadons.
The most effective technique for mitigating multipath fading in a wireless radio channel is to cancel the effect of fading at the transmitter by controlling the transmitter's power. That is, if the channel conditions are known at the transmitter (on one side of the link), then the transmitter can pre-distort the signal to overcome the effect of the channel at the receiver (on the other side). However, there are two fundamental problems with this approach.
The first problem is the transmitter's dynamic range. For the transmitter to overcome an x dB fade, it must increase its power by x dB which, in most cases, is not practical because of radiation power limitations, and the size and cost of amplifiers. The second problem is that the transmitter does not have any knowledge of the channel as seen by the receiver (except for time division duplex systems, where the transmitter receives power from a known other transmitter over the same channel). Therefore, if one wants td control a transmitter based on channel characteristics, channel information has to be sent from the receiver to the transmitter, which results in throughput degradation and added complexity to both the transmitter and the receiver.
Other effective techniques are time and frequency diversity. Using time interleaving together with coding can provide diversity improvement. The same holds for frequency hopping and spread spectrum. However, time interleaving results in unnecessarily large delays when the channel is slowly varying.
Equivalently, frequency diversity techniques are ineffective when the cohetentx lo bandwidth of the channel is large (small delay spread).
It is well known that in most scattering environments antenna diversity is the most practical and effective technique for reducing the effect of multipath fading.
The classical approach to antenna diversity is to use multiple antennas at the receiver and perform combining (or selection) to improve the quality of the received signal.
is The major problem with using the receiver diversity approach in current wireless communication systems, such as IS-136 and GSM, is the cost. size and power consumption constraints of the receivers. For obvious reasons, small size, weight and cost are paramount. The addition of multiple antennas and RF chains (or selection and switching circuits) in receivers is presently not be feasible.
As a result, 2o diversity techniques have often been applied only to improve the up-link (receiver to base) transn~issiori quality with multiple antennas (and receivers) at the base station.
Since a base station often serves thousands of receivers, it is more economical to add equipment to base stations rather than the receivers Recently, some interesting approaches for transmitter diversity have been z5 suggested. A delay diversity scheme was proposed by A. Wittneben in ''Base Station Modulation Diversity for Digital SIMULCAST," Proceeding of the 1941 IEEE Vehicular Technology Conference (VTC 41st), PP. 848-853, May 1991, and in "A New Bandwidth Efficient Transmit Antenna Modulation Diversity Scheme Far Linear Digital Modulation," in Proceeding of the 1993 IEEE International 3o Conference on Comraunications (IICC'93), pF.1630-ib34, May 1993. The proposal is for a base station to transmit a sequence of symbols through one antenna, and the same sequence of symbols -but delayed - through another antenna.
U.S. patent 5,479,448, issued to Nambirajan Seshadri on December 26, 1995, discloses a similar arrangement where a sequence of codes is transmitted 33 through two antennas. The sequence of codes is routed through a cycling switch that directs each code to the various antennas, in succession. Since copies of the same
The most effective technique for mitigating multipath fading in a wireless radio channel is to cancel the effect of fading at the transmitter by controlling the transmitter's power. That is, if the channel conditions are known at the transmitter (on one side of the link), then the transmitter can pre-distort the signal to overcome the effect of the channel at the receiver (on the other side). However, there are two fundamental problems with this approach.
The first problem is the transmitter's dynamic range. For the transmitter to overcome an x dB fade, it must increase its power by x dB which, in most cases, is not practical because of radiation power limitations, and the size and cost of amplifiers. The second problem is that the transmitter does not have any knowledge of the channel as seen by the receiver (except for time division duplex systems, where the transmitter receives power from a known other transmitter over the same channel). Therefore, if one wants td control a transmitter based on channel characteristics, channel information has to be sent from the receiver to the transmitter, which results in throughput degradation and added complexity to both the transmitter and the receiver.
Other effective techniques are time and frequency diversity. Using time interleaving together with coding can provide diversity improvement. The same holds for frequency hopping and spread spectrum. However, time interleaving results in unnecessarily large delays when the channel is slowly varying.
Equivalently, frequency diversity techniques are ineffective when the cohetentx lo bandwidth of the channel is large (small delay spread).
It is well known that in most scattering environments antenna diversity is the most practical and effective technique for reducing the effect of multipath fading.
The classical approach to antenna diversity is to use multiple antennas at the receiver and perform combining (or selection) to improve the quality of the received signal.
is The major problem with using the receiver diversity approach in current wireless communication systems, such as IS-136 and GSM, is the cost. size and power consumption constraints of the receivers. For obvious reasons, small size, weight and cost are paramount. The addition of multiple antennas and RF chains (or selection and switching circuits) in receivers is presently not be feasible.
As a result, 2o diversity techniques have often been applied only to improve the up-link (receiver to base) transn~issiori quality with multiple antennas (and receivers) at the base station.
Since a base station often serves thousands of receivers, it is more economical to add equipment to base stations rather than the receivers Recently, some interesting approaches for transmitter diversity have been z5 suggested. A delay diversity scheme was proposed by A. Wittneben in ''Base Station Modulation Diversity for Digital SIMULCAST," Proceeding of the 1941 IEEE Vehicular Technology Conference (VTC 41st), PP. 848-853, May 1991, and in "A New Bandwidth Efficient Transmit Antenna Modulation Diversity Scheme Far Linear Digital Modulation," in Proceeding of the 1993 IEEE International 3o Conference on Comraunications (IICC'93), pF.1630-ib34, May 1993. The proposal is for a base station to transmit a sequence of symbols through one antenna, and the same sequence of symbols -but delayed - through another antenna.
U.S. patent 5,479,448, issued to Nambirajan Seshadri on December 26, 1995, discloses a similar arrangement where a sequence of codes is transmitted 33 through two antennas. The sequence of codes is routed through a cycling switch that directs each code to the various antennas, in succession. Since copies of the same
2 symbol are transmitted through multiple antennas at different times, both space and time diversity are achieved. A maximum likelihood sequence estimator (MLSE) or a minimum mean squared error (MMSE) equalizer is then used to resolve multipath distortion and provide diversity gain. See also N. Seshadri, J.H. Winters, "Two Signaling Schemes for Improving the Error Performance of FDD Transmission Systems Using Transmitter Antenna Diversity,"
Proceeding of the 1993 IEEE Vehicular Technology Conference (VTC 43rd), pp. 508-511, May 1993; and J.H. Winters, "The Diversity Gain of Transmit Diversity in Wireless Systems with Rayleigh Fading," Proceeding of the 1994 ICClSUPERCOMM, New Orleans, Vol. 2, pp. 1121-1125, May 1994.
Still another interesting approach is disclosed by Tarokh, Seshadri, Calderbank and Naguib in U.S. Patent No. 6,115,427, issued September 5, 2000, where symbols are encoded according to the antennas through which they are simultaneously transmitted, and are decoded using a maximum likelihood decoder. More specifically, the process at the transmitter handles the information in blocks of M1 bits, where M1 is a multiple of M2., i.e., Ml=k*M2. It converts each successive group of M2 bits into information symbols (generating thereby k information symbols), encodes each sequence of k information symbols into n channel codes (developing thereby a group of n channel codes for each sequence of k information symbols), and applies each code of a group of codes to a different antenna.
Yet another approach is disclosed by Alamouti and Tarokh in U.S.
Patent No. b,185,258, issued February 6, 2001, and titled "Transmitter Diversity Technique for Wireless Communications" where symbols are encoded using only negations and conjugations, and transmitted in a manner that employs channel diversity.
Still another approach involves dividing symbols into groups, where each group is transmitted over a separate group of antennas and is encoded with a group code C that is a member of a product code.
Summary An advance in the art is realized with a transmitter that employs a trellis coder followed by a block coder. Correspondingly, the receiver comprises a Viterbi decoder followed by a block decoder. Advantageously, the block coder and decoder employ time-space diversity coding which, illustratively, employs two transmitter antennas and one receiver antenna.
In accordance with one aspect of the present invention there is provided a transmitter comprising: a trellis encoder that encodes incoming digital data to generate complex numbers representing constellation symbols defined as so and s~, wherein the trellis encoder transmits by a first antenna and a second antenna, respectively, during a first time or frequency interval; a space-block encoder responsive to the constellation symbols to encode two adjacent constellation symbols as a block comprising two trellis-coded symbols and two parity symbols chosen from a group consisting of negated trellis-coded symbols, complex conjugates of the trellis-coded symbols, and negative complex conjugates of the trellis-coded symbols, wherein the space-block encoder is adapted to feed two antennas such that a different symbol is transmitted by each antenna; and wherein the symbols sl* and so* are generated by the space-block encoder and transmitted by the first antenna and the second antenna, respectively, during a second time or frequency interval, wherein s;* is defined as a complex conjugate of a symbol s~.
Brief Description of the DraWlriE
FIG. 1 presents a block diagram of an embodiment in conformance with the principles of this invention.
Detail Descriution FIG. 1 presents a block diagram of an arrangement comporting with the principles of this invention. It comprises a trellis code modulation (TCM) encoder 10 followed by a two-branch space block encoder 20. The output is applied to antenna circuitry 30, which feeds antenna 31, and antenna 32 FIG.1 shows only two antennas, but this is merely illustrative. Arrangements can be had with a larger number of antennas, and it should be understood that the principles disclosed herein apply with equal advantage to such arrangements.
TCM encoder 10 generates complex numbers that represent constellation symbols, and block encoder 20 encodes (adjacent) pairs of symbols in the manner described in the aforementioned U.S. Patent No. 6,115,427. That is, symbols so and s,, forming a pair, are sent to antenna 31 and antenna 32, respectively, and in the following time period symbols -s~
and so* are sent to antennas 31 and 32, respectively. Thereafter, symbols s2 and s3 are sent to antenna 31 and 32, respectively, etc. Thus, encoder 20 creates channel diversity that results from 4a s signals traversing from the transmitter to the receiver at different times aad over different channels.
The signals transmitted by antennas 31 and 32 are received by a receiver after traversing the airlink and suffering a multiplicative distortion and additive noise. Hence, the received signals at the two consecutive time intervals duriag t o which the signals s~, s!, -s,*, and so* are sent correspond to:
ro(t) = hflsfl +h,s, +no, (1) and r, (t)=h,so-hos; +n,, l s (2) where l~ represents the channel from antenna 31, h, . represents the channel from antenna 32, no is the received noise at the first time interval, and n, is the received noise at the second time interval.
The receiver compzises a receive antenna 40, a two-branch space block 2o combiner 50, and a Viterbi decoder 60. The receiver also includes a channel estimator, but since that is perfectly conventional and does not form a part of the invention, FIG. 1 does not explicitly show it. The following assumes that the receiver possesses ha and h, , which are estimates of ho and h, , respectively. Thus, the received signals at the first and second time intervals arc combined in element 50 25 to form signals so = ho ro -!' ~r1
Proceeding of the 1993 IEEE Vehicular Technology Conference (VTC 43rd), pp. 508-511, May 1993; and J.H. Winters, "The Diversity Gain of Transmit Diversity in Wireless Systems with Rayleigh Fading," Proceeding of the 1994 ICClSUPERCOMM, New Orleans, Vol. 2, pp. 1121-1125, May 1994.
Still another interesting approach is disclosed by Tarokh, Seshadri, Calderbank and Naguib in U.S. Patent No. 6,115,427, issued September 5, 2000, where symbols are encoded according to the antennas through which they are simultaneously transmitted, and are decoded using a maximum likelihood decoder. More specifically, the process at the transmitter handles the information in blocks of M1 bits, where M1 is a multiple of M2., i.e., Ml=k*M2. It converts each successive group of M2 bits into information symbols (generating thereby k information symbols), encodes each sequence of k information symbols into n channel codes (developing thereby a group of n channel codes for each sequence of k information symbols), and applies each code of a group of codes to a different antenna.
Yet another approach is disclosed by Alamouti and Tarokh in U.S.
Patent No. b,185,258, issued February 6, 2001, and titled "Transmitter Diversity Technique for Wireless Communications" where symbols are encoded using only negations and conjugations, and transmitted in a manner that employs channel diversity.
Still another approach involves dividing symbols into groups, where each group is transmitted over a separate group of antennas and is encoded with a group code C that is a member of a product code.
Summary An advance in the art is realized with a transmitter that employs a trellis coder followed by a block coder. Correspondingly, the receiver comprises a Viterbi decoder followed by a block decoder. Advantageously, the block coder and decoder employ time-space diversity coding which, illustratively, employs two transmitter antennas and one receiver antenna.
In accordance with one aspect of the present invention there is provided a transmitter comprising: a trellis encoder that encodes incoming digital data to generate complex numbers representing constellation symbols defined as so and s~, wherein the trellis encoder transmits by a first antenna and a second antenna, respectively, during a first time or frequency interval; a space-block encoder responsive to the constellation symbols to encode two adjacent constellation symbols as a block comprising two trellis-coded symbols and two parity symbols chosen from a group consisting of negated trellis-coded symbols, complex conjugates of the trellis-coded symbols, and negative complex conjugates of the trellis-coded symbols, wherein the space-block encoder is adapted to feed two antennas such that a different symbol is transmitted by each antenna; and wherein the symbols sl* and so* are generated by the space-block encoder and transmitted by the first antenna and the second antenna, respectively, during a second time or frequency interval, wherein s;* is defined as a complex conjugate of a symbol s~.
Brief Description of the DraWlriE
FIG. 1 presents a block diagram of an embodiment in conformance with the principles of this invention.
Detail Descriution FIG. 1 presents a block diagram of an arrangement comporting with the principles of this invention. It comprises a trellis code modulation (TCM) encoder 10 followed by a two-branch space block encoder 20. The output is applied to antenna circuitry 30, which feeds antenna 31, and antenna 32 FIG.1 shows only two antennas, but this is merely illustrative. Arrangements can be had with a larger number of antennas, and it should be understood that the principles disclosed herein apply with equal advantage to such arrangements.
TCM encoder 10 generates complex numbers that represent constellation symbols, and block encoder 20 encodes (adjacent) pairs of symbols in the manner described in the aforementioned U.S. Patent No. 6,115,427. That is, symbols so and s,, forming a pair, are sent to antenna 31 and antenna 32, respectively, and in the following time period symbols -s~
and so* are sent to antennas 31 and 32, respectively. Thereafter, symbols s2 and s3 are sent to antenna 31 and 32, respectively, etc. Thus, encoder 20 creates channel diversity that results from 4a s signals traversing from the transmitter to the receiver at different times aad over different channels.
The signals transmitted by antennas 31 and 32 are received by a receiver after traversing the airlink and suffering a multiplicative distortion and additive noise. Hence, the received signals at the two consecutive time intervals duriag t o which the signals s~, s!, -s,*, and so* are sent correspond to:
ro(t) = hflsfl +h,s, +no, (1) and r, (t)=h,so-hos; +n,, l s (2) where l~ represents the channel from antenna 31, h, . represents the channel from antenna 32, no is the received noise at the first time interval, and n, is the received noise at the second time interval.
The receiver compzises a receive antenna 40, a two-branch space block 2o combiner 50, and a Viterbi decoder 60. The receiver also includes a channel estimator, but since that is perfectly conventional and does not form a part of the invention, FIG. 1 does not explicitly show it. The following assumes that the receiver possesses ha and h, , which are estimates of ho and h, , respectively. Thus, the received signals at the first and second time intervals arc combined in element 50 25 to form signals so = ho ro -!' ~r1
(3) and s, = h,~ro -h~r't ,
(4}
3o and those signals are applied to Viterbi decoder 60.
- The Viterbi decoder builds the following metric for the hypothesized branch symbol s, corresponding to the first transmitted symbol so:
s M(so~sr)~d'Iso~(~o~'~'~I:)srJ~
(s) Similarly, the Viterbi decoder builds the following metric for the hypothesized branch symbol s, corresponding to the first transmitted symbol s~:
.M(s~.sr) =d2I~~~~x +~~ )sr, io (6) (Additional metrics are similarly constructed in arrangements that employ a larger number of antennas and a correspondingly larger constellation of signals transmitted at any one time.) If Trellis encoder 10 is a multiple TCM encoder, then the Viterbi decoder builds the following metric:
is ~(so~s,),(sr~s;)l= M{so.s,)+ M{s"s~) .
('~
or equivalently, _ ~(SO~se)~(stns;)~=d~(TO,I~s;+h,sl)+il=(r,,h,s; -hosJ).
(x) 2o The Viterbi decoder outputs estiraates of the transmitted sequence of signals.
The above presented an illustrative embodiment. However, it should be understood that various modifications and alternations might be made by a skilled artisan without departing from the spirit and scope of this invention.
3o and those signals are applied to Viterbi decoder 60.
- The Viterbi decoder builds the following metric for the hypothesized branch symbol s, corresponding to the first transmitted symbol so:
s M(so~sr)~d'Iso~(~o~'~'~I:)srJ~
(s) Similarly, the Viterbi decoder builds the following metric for the hypothesized branch symbol s, corresponding to the first transmitted symbol s~:
.M(s~.sr) =d2I~~~~x +~~ )sr, io (6) (Additional metrics are similarly constructed in arrangements that employ a larger number of antennas and a correspondingly larger constellation of signals transmitted at any one time.) If Trellis encoder 10 is a multiple TCM encoder, then the Viterbi decoder builds the following metric:
is ~(so~s,),(sr~s;)l= M{so.s,)+ M{s"s~) .
('~
or equivalently, _ ~(SO~se)~(stns;)~=d~(TO,I~s;+h,sl)+il=(r,,h,s; -hosJ).
(x) 2o The Viterbi decoder outputs estiraates of the transmitted sequence of signals.
The above presented an illustrative embodiment. However, it should be understood that various modifications and alternations might be made by a skilled artisan without departing from the spirit and scope of this invention.
Claims (61)
1. A transmitter comprising:
a trellis encoder, wherein the trellis encoder generates a first symbol so and a second symbol S1, and a block encoder responsive to the trellis encoder and adapted to feed two antennas, wherein the block encoder generates a block including the first symbol, the second symbol, a third symbol generated using a complex conjugation of the first symbol, and a fourth symbol generated using a negative complex conjugation of the second symbol, and wherein in a first time period the first and second symbol s0, s1 are forwarded to said two antennas respectively, and wherein in a second time period said fourth and third symbols are forwarded to said two antennas, respectively.
a trellis encoder, wherein the trellis encoder generates a first symbol so and a second symbol S1, and a block encoder responsive to the trellis encoder and adapted to feed two antennas, wherein the block encoder generates a block including the first symbol, the second symbol, a third symbol generated using a complex conjugation of the first symbol, and a fourth symbol generated using a negative complex conjugation of the second symbol, and wherein in a first time period the first and second symbol s0, s1 are forwarded to said two antennas respectively, and wherein in a second time period said fourth and third symbols are forwarded to said two antennas, respectively.
2. The transmitter of claim 1 wherein the block encoder is a multi-branch block encoder.
3. The transmitter of claim 1 wherein the block encoder is a space-time block encoder.
4. A receiver for receiving blocks of symbols sent by the transmitter of claims 1-3, two said receiver comprising:
a space block combiner configured for receiving data transmitted from the two transmitting antennas, and a Viterbi decoder responsive to output signals of the space block combiner.
a space block combiner configured for receiving data transmitted from the two transmitting antennas, and a Viterbi decoder responsive to output signals of the space block combiner.
5. The receiver of claim 4 wherein the combiner combines a frame of received symbols, wherein the frame consists of n time slots and in each time slot concurrently provides m symbols to the combiner.
6. The receiver of claim 5 wherein n=m.
7. The receiver of claim 6 wherein n=m=2.
8. The receiver of claim 4 wherein the Viterbi decoder develops the metric , wherein S i is a hypothesized signal at a first time interval, s i is a hypothesized signal at a second time interval, s 0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of the receiver, and ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
9. The receiver of claim 4 wherein the Viterbi decoder develops the metric to recover the symbol s0, and the metric to recover the symbol s1, where s j is a hypothesized signal at a first time interval, s i is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of the receiver, and ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
10. The receiver of claim 4, wherein the Viterbi decoder develops the metric M[(s0,s1 ),(s i,s j)]=M(s0,s i)+M(s1,s j) where where s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver, ~0 is one signal developed by the combiner, and ~1 is another signal developed by the combiner.
11. The receiver of claim 4 wherein the combiner creates signals * * *
~0= ~0r0 +~1r1* and ~1 = ~l*r0 - ~0r1* , where r0 is a received signal at one time interval, r1 is a received signal at another time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, and it, ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
~0= ~0r0 +~1r1* and ~1 = ~l*r0 - ~0r1* , where r0 is a received signal at one time interval, r1 is a received signal at another time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, and it, ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
12. In a receiver, a method for linking trellis codes with block codes, the method comprising:
receiving on a single receiver antenna, a first baseband signal and a second baseband signal, wherein the first and second baseband signals were transmitted using space-time coding;
determining channel estimates for the received first and second baseband signals;
using the determined channel estimates, generating a first contained signal based on the first received baseband signal and a second combined signal based on the second received signal, the first and second combined signals including a complex multiplicative distortion factor;
based on the first generated combined signal, building a first metric corresponding to a first hypothesized symbol, the first hypothesized symbol replicating the received first baseband signal prior to transmission; and based on the second generated combined signal, building a second metric corresponding to a second hypothesized symbol, the second hypothesized symbol replicating the received second baseband signal prior to transmission.
receiving on a single receiver antenna, a first baseband signal and a second baseband signal, wherein the first and second baseband signals were transmitted using space-time coding;
determining channel estimates for the received first and second baseband signals;
using the determined channel estimates, generating a first contained signal based on the first received baseband signal and a second combined signal based on the second received signal, the first and second combined signals including a complex multiplicative distortion factor;
based on the first generated combined signal, building a first metric corresponding to a first hypothesized symbol, the first hypothesized symbol replicating the received first baseband signal prior to transmission; and based on the second generated combined signal, building a second metric corresponding to a second hypothesized symbol, the second hypothesized symbol replicating the received second baseband signal prior to transmission.
13. The method of claim 12 wherein the first baseband signal and the second baseband signal include noise and interference, including multipath fading.
14. The method of claim 12 wherein the first baseband signal is received at a first time and wherein the second baseband signal is received at a second time.
15. The method of claim 12 wherein the first and second combined signals are generated using a multiple branch space block combiner.
16. In a receiver, an apparatus for linking trellis codes with block codes, the apparatus comprising:
means for receiving on a single receiver antenna, a first baseband signal and a second baseband signal, wherein the received first and second baseband signals were encoded at a transmitter having at least two transmit antennas coupled to an at least two branch trellis encoder;
means, coupled to the means for receiving, for determining channel estimates for the received first and second baseband signals;
means, coupled to the means for determining, for using the determined channel estimates and generating a first combined block signal based on the first received baseband signal and a second combined block signal based on the second received signal, wherein the first and second combined signals include a complex multiplicative distortion factor; and means for building a combined metric for a hypothesized branch symbol, the hypothesized symbol replicating both the received first and second symbols.
means for receiving on a single receiver antenna, a first baseband signal and a second baseband signal, wherein the received first and second baseband signals were encoded at a transmitter having at least two transmit antennas coupled to an at least two branch trellis encoder;
means, coupled to the means for receiving, for determining channel estimates for the received first and second baseband signals;
means, coupled to the means for determining, for using the determined channel estimates and generating a first combined block signal based on the first received baseband signal and a second combined block signal based on the second received signal, wherein the first and second combined signals include a complex multiplicative distortion factor; and means for building a combined metric for a hypothesized branch symbol, the hypothesized symbol replicating both the received first and second symbols.
17. A transmitter comprising:
a trellis encoder, wherein the trellis encoder generates a first symbol and a second symbol, and a block encoder responsive to the trellis encoder and adapted to feed a plurality of antennas, wherein the block encoder generates a block including the first symbol, the second symbol, a third symbol generated using a complex conjugation, negation, or negative complex conjugation of the first symbol, and a fourth symbol generated using a complex conjugation, negation, or negative complex conjugation of the second symbol.
a trellis encoder, wherein the trellis encoder generates a first symbol and a second symbol, and a block encoder responsive to the trellis encoder and adapted to feed a plurality of antennas, wherein the block encoder generates a block including the first symbol, the second symbol, a third symbol generated using a complex conjugation, negation, or negative complex conjugation of the first symbol, and a fourth symbol generated using a complex conjugation, negation, or negative complex conjugation of the second symbol.
18. The transmitter of claim 17 further comprising the plurality of antennas.
19. The transmitter of claim 17 wherein the trellis encoder is a multiple trellis code modulation encoder.
20. The transmitter of claim 17 wherein the block encoder is a multi-branch block encoder.
21. The transmitter of claim 17 wherein the block encoder is a space-time block encoder.
22. In a transmitter, a method for linking trellis codes with block codes, the method comprising:
receiving input data;
trellis encoding the received data, including generating complex numbers, each complex number representing a constellation symbol;
receiving the generated complex numbers;
block encoding the received complex numbers, including generating a block of symbols, wherein the block of symbols includes the generated complex numbers and at least one of a complex conjugation, negation, or negative complex conjugation of at least some of the generated complex numbers; and outputting the blocks of symbols for transmission by two or more transmitting antennas.
receiving input data;
trellis encoding the received data, including generating complex numbers, each complex number representing a constellation symbol;
receiving the generated complex numbers;
block encoding the received complex numbers, including generating a block of symbols, wherein the block of symbols includes the generated complex numbers and at least one of a complex conjugation, negation, or negative complex conjugation of at least some of the generated complex numbers; and outputting the blocks of symbols for transmission by two or more transmitting antennas.
23. The method of claim 22 wherein the received data is binary data.
24. The method of claim 22 wherein the block encoding includes taking a first complex number and a second complex number as input and generating a complex conjugate of the first complex number and a negative complex conjugate of the second complex number.
25. The method of claim 22 wherein the block encoding includes ordering the block to provide a first complex number, a second complex number, a negative complex conjuration of the second complex number and a complex conjugation of the first complex number.
26. The method of claim 22, further comprising, transmitting the blocks of symbols over the two or more antennas.
27. In a transmitter, an apparatus for generating encoded symbols for transmission over a wireless link, the apparatus comprising:
means for receiving input data;
means, coupled to the means for receiving input data, for generating a first symbol and a second symbol; and means, coupled to the means for generating first and second symbols, for generating a block, the block including the first symbol, the second symbol, a third symbol generated using a complex conjugation, negation, or negative complex conjugation of the first symbol, and a fourth symbol generated using a complex conjugation, negation, or negative complex conjugation of the second symbol.
means for receiving input data;
means, coupled to the means for receiving input data, for generating a first symbol and a second symbol; and means, coupled to the means for generating first and second symbols, for generating a block, the block including the first symbol, the second symbol, a third symbol generated using a complex conjugation, negation, or negative complex conjugation of the first symbol, and a fourth symbol generated using a complex conjugation, negation, or negative complex conjugation of the second symbol.
28. The apparatus of claim 27 further comprising:
means for sending, at a first time, the first symbol from a first antenna and the second symbol from a second antenna; and means for sending, at a second time, the forth symbol from the first antenna and the third symbol from the second antenna.
means for sending, at a first time, the first symbol from a first antenna and the second symbol from a second antenna; and means for sending, at a second time, the forth symbol from the first antenna and the third symbol from the second antenna.
29. The apparatus of claim 27 further comprising:
means for sending, on a first carrier the first symbol from a first antenna and the second symbol from a second antenna; and means for sending, on a second carrier, the third symbol from a second antenna and the fourth symbol from a first antenna.
means for sending, on a first carrier the first symbol from a first antenna and the second symbol from a second antenna; and means for sending, on a second carrier, the third symbol from a second antenna and the fourth symbol from a first antenna.
30. The apparatus of claim 27 wherein the block is generated using a two-branch space block encoder.
31. The apparatus of claim 27 wherein the block is generated using a multiple-branch space block encoder.
32. The receiver of claim 5 wherein the combiner develops n signals that represent estimates of signals transmitted by a transmitter.
33. The receiver of claim 4 wherein the Viterbi decoder generates a separate metric for soft decision of a transmitted symbol.
34. The receiver of claim 4 wherein the Viterbi decoder is a multiple trellis code modulation decoder.
35. A method for use in a transmitter for linking trellis codes with block codes, the method comprising:
receiving input data;
trellis encoding the received data, including generating a first symbol so and a second symbol s1;
block encoding the received symbols including generating a block of symbols, wherein the block of symbols includes the first symbol, the second symbol a third symbol generated using a complex conjugation of the first symbol, and a fourth symbol using negative complex conjugation of the second symbol.
receiving input data;
trellis encoding the received data, including generating a first symbol so and a second symbol s1;
block encoding the received symbols including generating a block of symbols, wherein the block of symbols includes the first symbol, the second symbol a third symbol generated using a complex conjugation of the first symbol, and a fourth symbol using negative complex conjugation of the second symbol.
36. A method for use in a receiver for receiving blocks of symbols transmitted in accordance with the method of claim 35, the method comprising:
receiving on a single receiver antenna, a first signal and a second signal, wherein the first and second signals were transmitted using space-time coding;
determining channel estimates for the received first and second signals;
using the determined channel estimates, generating a first combined signal based on the sum of the first and second received signals and a second combined signal based on the difference of the first and second received signals, the first and second combined signals including a distortion component; and based on the first generated combined signal, building a first metric corresponding to a first hypothesized symbol, the first hypothesized symbol replicating the received first signal prior to transmission; and based on the second generated combined signal, building a second metric corresponding to a second hypothesized symbol, the second hypothesized symbol replicating the received second signal prior to transmission.
receiving on a single receiver antenna, a first signal and a second signal, wherein the first and second signals were transmitted using space-time coding;
determining channel estimates for the received first and second signals;
using the determined channel estimates, generating a first combined signal based on the sum of the first and second received signals and a second combined signal based on the difference of the first and second received signals, the first and second combined signals including a distortion component; and based on the first generated combined signal, building a first metric corresponding to a first hypothesized symbol, the first hypothesized symbol replicating the received first signal prior to transmission; and based on the second generated combined signal, building a second metric corresponding to a second hypothesized symbol, the second hypothesized symbol replicating the received second signal prior to transmission.
37. The method of claim 36 wherein the first signal and the second signal include noise and interference, including multipath fading.
38. In a data communication system employing space diversity via two or more transmitting antennas, a receiver comprising:
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the Viterbi decoder develops the metric wherein s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of the receiver, and ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the Viterbi decoder develops the metric wherein s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of the receiver, and ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
39. The receiver of claim 38 wherein the combiner combines a frame of received symbols, wherein the frame consists of n time slots and in each time slot concurrently provides m symbols to the combiner.
40. The receiver of claim 39 wherein n=m.
41. The receiver of claim 40 wherein n=m=2.
42. The receiver of claim 39 wherein the combiner develops n signals that represent estimates of signals transmitted by a transmitter.
43. The receiver of claim 38 wherein the Viterbi decoder generates a separate metric for soft decision of a transmitted symbol.
44. In a data communication system employing space diversity via two or more transmitting antennas, a receiver comprising:
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the Viterbi decoder develops the metric to recover the symbol s0, and the metric to recover the symbol s1, where s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, and ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the Viterbi decoder develops the metric to recover the symbol s0, and the metric to recover the symbol s1, where s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, and ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
45. In a data communication system employing space diversity via two or more transmitting antennas, a receiver comprising:
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the Viterbi decoder develops the metric M[(s0,s1),(s i,s j)]=M(s0,s i)+M(s1,s j) where where s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, ~
is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver, ~0 is one signal developed by the combiner, and ~1, is another signal developed by the combiner.
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the Viterbi decoder develops the metric M[(s0,s1),(s i,s j)]=M(s0,s i)+M(s1,s j) where where s i is a hypothesized signal at a first time interval, s j is a hypothesized signal at a second time interval, s0 is a transmitted signal at the first time interval, s1 is a transmitted signal at the second time interval, ~ is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, ~
is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver, ~0 is one signal developed by the combiner, and ~1, is another signal developed by the combiner.
46. In a data communication system employing space diversity via two or more transmitting antennas, a receiver comprising:
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the combiner creates signals , where r0 is a received signal at one time interval, r1 is a received signal at another time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, and it, ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
a space block combiner configured for receiving data transmitted from the two or more transmitting antennas, a Viterbi decoder responsive to output signals of the space block combiner;
wherein the Viterbi decoder is a multiple trellis code modulation detector;
and wherein the combiner creates signals , where r0 is a received signal at one time interval, r1 is a received signal at another time interval, ~0 is an estimate of channel characteristics between a transmitting antenna that transmits signal s0 and a receiving antenna of said receiver, and it, ~1 is an estimate of channel characteristics between a transmitting antenna that transmits signal s1 and the receiving antenna of the receiver.
47. The apparatus of claim 16 wherein the first baseband signal and the second baseband signal include noise and interference, including multipath fading.
48. The apparatus of claim 16 wherein the first baseband signal is received at a first time and wherein the second baseband signal is received at a second time.
49. The apparatus of claim 16 wherein the first baseband signal is received via a first frequency and wherein the second baseband signal is received via second frequency.
50. A mobile device comprising:
a space block combiner and a decoder to decode incoming codes generated based on concatenated trellis and space block coding; and wherein the incoming codes include a first code and a second code, wherein the first code includes a first symbol and a second symbol and wherein the second code includes a third symbol generated using a complex conjugation, negation, or negative complex conjugation of the first symbol and a fourth symbol generated using a complex conjugation, negation, or negative complex conjugation of the second symbol.
a space block combiner and a decoder to decode incoming codes generated based on concatenated trellis and space block coding; and wherein the incoming codes include a first code and a second code, wherein the first code includes a first symbol and a second symbol and wherein the second code includes a third symbol generated using a complex conjugation, negation, or negative complex conjugation of the first symbol and a fourth symbol generated using a complex conjugation, negation, or negative complex conjugation of the second symbol.
51. The mobile device of claim 50 wherein the block coding includes space-time block coding.
52. The mobile device of claim 50 wherein the block coding includes space-frequency coding.
53. The mobile device of claim 50, wherein the processor decodes the incoming codes using at least a space block combiner and a Viterbi decoder.
54. In a wireless communication system, a method of communicating information over a wireless link, the method comprising:
generating complex numbers that represent constellation symbols; and encoding adjacent pairs of symbols, including the generated complex numbers, to produce a set of concatenated codes, wherein the set of concatenated codes include a first code including a first symbol and a second symbol and a second code including a third symbol generated using a complex conjugation, or negative complex conjugation of the first symbol and a fourth symbol generated using a complex conjugation, or negative complex conjugation of the second symbol.
generating complex numbers that represent constellation symbols; and encoding adjacent pairs of symbols, including the generated complex numbers, to produce a set of concatenated codes, wherein the set of concatenated codes include a first code including a first symbol and a second symbol and a second code including a third symbol generated using a complex conjugation, or negative complex conjugation of the first symbol and a fourth symbol generated using a complex conjugation, or negative complex conjugation of the second symbol.
55. The method of claim 54 wherein the complex numbers that represent constellation symbols are generated, at least in part, using a trellis code modulation (TCM) encoder.
56. The method of claim 54 wherein the adjacent pairs of symbols are encoded using a block encoder.
57. The method of claim 54 wherein the first code is sent at a first time and the second code is sent at a second time that is distinct from the first time.
58. In a wireless communication system, a method of communicating information over a wireless link, the method comprising:
receiving incoming codes generated based on concatenated trellis and space block coding, wherein the incoming codes include a first code and a second code, wherein the first code includes a first symbol and a second symbol and wherein the second code includes a third symbol generated using a complex conjugation, or negative complex conjugation of the first symbol and a fourth symbol generated using a complex conjugation, or negative complex conjugation of the second symbol;
performing a first decoding of the incoming codes, wherein the first decoding includes combining at least the first incoming code and the second incoming code together to form one or more signals; and performing a second decoding, wherein the second decoding includes applying Viterbi decoding to the one or more signals.
receiving incoming codes generated based on concatenated trellis and space block coding, wherein the incoming codes include a first code and a second code, wherein the first code includes a first symbol and a second symbol and wherein the second code includes a third symbol generated using a complex conjugation, or negative complex conjugation of the first symbol and a fourth symbol generated using a complex conjugation, or negative complex conjugation of the second symbol;
performing a first decoding of the incoming codes, wherein the first decoding includes combining at least the first incoming code and the second incoming code together to form one or more signals; and performing a second decoding, wherein the second decoding includes applying Viterbi decoding to the one or more signals.
59. The method of claim 58 wherein the first incoming code is received at a first time, and wherein the second incoming code is received at a second time distinct from the first time.
60. The method of claim 58 wherein the first incoming code is received after the first symbol is transmitted over a first channel and the second symbol is transmitted over a second channel that is distinct from the first channel.
61. The method of claim 58 where the Viterbi decoding includes generating a separate metric for soft decision of an incoming code.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US6379497P | 1997-10-31 | 1997-10-31 | |
| US60/063794 | 1997-10-31 | ||
| CA002276207A CA2276207C (en) | 1997-10-31 | 1998-10-16 | Low complexity maximum likelihood detection of concatenated space codes for wireless applications |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002276207A Division CA2276207C (en) | 1997-10-31 | 1998-10-16 | Low complexity maximum likelihood detection of concatenated space codes for wireless applications |
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| Publication Number | Publication Date |
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| CA2411286A1 CA2411286A1 (en) | 1999-05-14 |
| CA2411286C true CA2411286C (en) | 2010-02-23 |
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| Application Number | Title | Priority Date | Filing Date |
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| CA2411286A Expired - Fee Related CA2411286C (en) | 1997-10-31 | 1998-10-16 | Low complexity maximum likelihood detection of concatenated space codes for wireless applications |
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| Country | Link |
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| CA (1) | CA2411286C (en) |
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| CA2411286A1 (en) | 1999-05-14 |
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