The burden of designing multiple training sequences for systems having multiple transmit antennas, is drastically reduced by employing a single sequence from which the necessary multiple sequences are developed. The single sequence is selected to create sequences that have an impulse-like autocorrelation function and zero cross correlations. A sequence of any desired length nt can be realized for an arbitrary number of channel taps, L. The created sequences can be restricted to a standard constellation (that is used in transmitting information symbols) so that a common constellation mapper is used for both the information signals and the training sequence. In some applications a a training sequence may be selected so that it is encoded with the same encoder that is used for encoding information symbols. Both block and trellis coding is possible in embodiments that employ this approach.

Patent
   RE44827
Priority
Apr 09 2001
Filed
Mar 18 2013
Issued
Apr 08 2014
Expiry
Sep 20 2021

TERM.DISCL.
Assg.orig
Entity
Large
0
21
EXPIRED
1. A space-time diversity transmitter that includes (a) n transmitting antennas, where n is greater than one, (b) first encoder responsive to an applied information bit stream, said encoder developing n symbol streams, and (c) a constellation mapper responsive to said n symbol streams, for mapping symbols of each of said n symbol streams into a standard signal constellation to create a corresponding mapped stream, said constellation mapper applying each of the created n mapped streams to a different one of said n antennas in blocks of nt mapped symbols that are synchronized in time to each other, the improvement comprising:
a training generator for generating either n sequences of signals or a sequence of signals that contains n subsequences of signal;
a second encoder for creating n training symbol sequences from said signals created by said training generator, each containing nt symbols, where nt represents a training sequence length; and
said constellation mapper is configured to map said n training symbol sequences onto a standard constellation to develop n mapped training sequences, and to apply the n mapped training sequences to said n antennas at times when said constellation mapper stops applying said n mapped stream to said n antennas;
where said n training symbol sequences have an impulse-like autocorrelation function and zero cross correlation.
17. A space-time diversity transmitter that includes (a) n transmitting antennas, where n is greater than one, (b) first encoder responsive to an applied information bit stream, said encoder developing n symbol streams, and (c) a constellation mapper responsive to said n symbol streams, for mapping symbols of each of said n symbol streams into a standard signal constellation to create a corresponding mapped stream, said constellation mapper applying each of the created n mapped streams to a different one of said n antennas in blocks of nt mapped symbols that are synchronized in time to each other, the improvement comprising:
a training generator for generating either n sequences of signals or a sequence of signals that contains n subsequences of signal;
a second encoder for creating n training symbol sequences from said signals created by said training generator, each containing nt symbols, where nt represents a training sequence length; and
said constellation mapper is configured to map said n training sequences onto a standard constellation to develop n mapped training sequences, and to apply the n mapped training sequences to said n antennas at times when said constellation mapper stops applying said n mapped stream to said n antennas;
where said n training sequences have an impulse-like autocorrelation function and zero cross correlation, and where n2 n=2, said generator creates a sequence s, and said second encoder creates a first training sequence that is equal to −s concatenated with s, and a second training sequence that is equal to s concatenated with s.
2. The transmitter of claim 1 where said n training symbol sequences are selected to enable a receiver that receives said n training symbol sequences to determine characteristics of a medium through which said n antennas communicate to said receiver.
0. 3. The transmitter of claim 2 where said n training sequences have a common length nt that is related to transmitted symbols memory, L−1, of said medium, nt being at least equal to 2L−1.
4. The transmitter of claim 1 where said constellation mapper employs a constellation taken from a set that includes binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), and 8-point phase shift keying (8-PSK).
5. The transmitter of claim 1 where n=2, said generator creates a sequence s composed of sequence d1 followed by sequence d2, and said second encoder creates a first training sequence that is −d1 concatenated with {tilde over (d)}2*, and a second sequence that is d2 concatenated with d1* where {tilde over (d)}2* corresponds to the sequence d2 with its elements in reverse order and converted to their respective complex conjugates, and the sequence d1* corresponds to the sequence d1 with its elements converted to their complex conjugate values.
6. The transmitter of claim 5 where said sequence d1 and said sequence d2 contain nt/2 nt symbols each, where nt is related to number of channel parameters, L, that a receiver which seeks to receive signals from an antenna of said transmitter estimates.
7. The transmitter of claim 1 where n=2, said generator creates a sequence d, and said second encoder creates a first training sequence that is −d concatenated with {tilde over (d)}*, and a second sequence that is d concatenated with d*, where the sequence d* corresponds to the sequence d with its elements converted to their complex conjugate values and the sequence {tilde over (d)}* corresponds to the sequence d with its elements in reverse order and converted to their respective complex conjugate values.
8. The transmitter of claim 1 where n2 n=2, said generator creates a sequence d, and said second encoder creates a first training sequence that is −d concatenated with {tilde over (d)}*, and a second sequence that is {tilde over (d)} concatenated with d*, where the sequence d* corresponds to the sequence d with its elements converted to their complex conjugate values and the sequence {tilde over (d)}* corresponds to the sequence d with its elements in reverse order and converted to their respective complex conjugate values.
9. The transmitter of claim 1 where n=2, said generator creates a sequence d, and said second encoder creates a first training sequence that is −d concatenated with d, and a second sequence that is {tilde over (d)}* concatenated with d*, where the sequence d* corresponds to the sequence d with its elements converted to their complex conjugate values and the sequence {tilde over (d)}* corresponds to the sequence d with its elements in reverse order and converted to their respective complex conjugate values.
10. The transmitter of claim 1 where said first encoder and said second encoder embodied in a single module that creates either said n symbol streams or said n training symbol sequences.
11. The transmitter of claim 1 where said second encoder is a trellis encoder.
0. 12. The transmitter of claim 11 where
(a) said n training sequences are selected to enable a receiver that receives said n training sequences to determine characteristics of a transmission medium between said transmitter and said receiver, and
(b) said generator develops said symbols sequence to comprise nt+(n−2)L+m symbols long, where L is the number of channel parameters that describe a channel within said transmission medium from one of said n transmitter antennas to a receiving antenna of said receiver, m is number of symbols stored in a memory of said trellis encoder, and nt is not less than 2L−1.
13. The transmitter of claim 11 where said training sequence mapper employs symbols from a set composed of elements ei2πpk/8, pk=0,1,2, . . . , 7.
14. The transmitter of claim 13 where said generator develops a symbols sequence s(k), and said second encoder develops a first sequence s1 (k)=s(k), and a second sequence s2(k)=(−1)pk−1s(k−1).
15. The transmitter of claim 14 where said sequence s(k) is composed of a first segment, seven, that comprises symbols from a set composed of ei2πpk/8, pk=0, 2, 4, 6, and a second segment, sodd, where sodd=αseven, and α=eiπk/4 for any k=1, 3, 5, 7.
16. The transmitter of claim 15 where said seven, and a corresponding α are any one of the following:
Seven α
−1 1 1 1 1 −1 −I −1 1 1 −1 1 1 exp(i5π/4)
1 1 −1 1 I I 1 −I I −1 −1 −1 1 exp(i3π/4)
1 −1 −1 −I I −I 1 1 1 −I −1 1 1 exp(iπ/4)
1 −1 −1 −I 1 −1 1 −I −I − I −1 1 1 exp(iπ/4)
1 I 1 1 I −1 −1 I 1 −1 1 I 1 exp(iπ/4)
1 I 1 I −1 −1 1 −1 −1 I 1 I 1 exp(i3π/4)
1 −I 1 1 −I −1 −1 −I 1 −1 1 −I 1 exp(i7π/4)
1 −I 1 −1 I 1 −1 −I 1 1 1 −I 1 exp(i5π/4)
−1 1 1 1 −1 −1 −I −1 −1 1 −1 1 1 exp(i3π/4)
−1 I −1 −I 1 −I I I 1 I 1 −I 1 exp(i7π/4)
−1 −I −1 I 1 I −I −I 1 −I 1 I 1 exp(iπ/4)
−1 −I −1 I −1 I −I −I −1 −I 1 I 1 exp(i3π/4).
18. The transmitter of claim 17 where said sequence s contains nt/2 symbols, where nt is related to number of channel parameters, L, that a receiver which seeks to receive signals from an antenna of said transmitter estimates.

This application
where S is a convolution matrix of dimension (Nt′−L′+1)×L′. Again, for optimality, the imposed requirement is that

S H ( L , N t ) S ( L , N t ) = ( N t - L + 1 ) I 2 L , ( 10 )
and once the sequence s is found, the task is to create the subsequences s1 and s2 from the found sequence s. Preferably, the subsequences s1 and s2 can be algorithmically generated from sequence s. Conversely, one may find subsequences s1 and s2 that satisfy the requirements of equation (8) and be such that sequence s can be algorithmically generated. This permits the use of a single training signal generator that, through a predetermined algorithm (i.e., coding) develops the subsequences s1 and s2. Both approaches lead to embodiment depicted in FIG. 3, where information signals are applied to encoder 13 that generates two streams of symbols that are applied to constellation mapper 14 via switches 15 and 16. Generator 5 creates a training sequence that is applied to encoder 9, and encoder 9 generates the subsequences s1 and s2 that are applied to constellation mapper 14 via switches 15 and 16.

Actually, once we realized that the complexity of the training sequence determination problem can be reduced by focusing on the creation of a single sequence from which a plurality of sequences that meet the requirements of equation (8) can be generated, it became apparent that there is no requirement for s to be longer than s1 and s2.

FIG. 4 presents one approach for generating optimal subsequences s1 and s2 that meet the requirements of equation (8) and that can be generated from a single sequence. In accordance with FIG. 4, generator 5 develops a sequence s of length Nt/2, and encoder 9 develops therefrom the sequences s1=−s|s and s2=s|s, where the “|” symbol stands for concatenation; e.g., sequence s1 comprises sequence −s concatenated with, or followed by, sequence s. Thus, during the training sequence, antenna 11 transmits the sequence −s during the first Nt/2 time periods, and the sequence s during the last Nt/2 time periods. Antenna 12 transmits the sequence s during both the first and last Nt/2 time periods.

In response to the training sequences transmitted by antennas 11 and 12, receiving antenna 21 develops the signal vector y (where the elements of the vector y are the signals received from antennas 11 and 12). Considering the received signal during the first Nt/2 time periods as y1 and during the last Nt/2 time periods as y2, and employing only the useful portion of the signal (that is, the portions not corrupted by signals that are not part of the training sequence) one gets

[ y 1 y 2 ] = [ - S S S S ] [ h 1 h 2 ] + [ z 1 z 2 ] ( 11 )
where S is a convolution matrix of dimension (Nt−L+1)×L. In accordance with the principles disclosed herein, the FIG. 3 receiver multiplies the received signal in processor 25 with the transpose conjugate matrix SH, yielding

[ r 1 r 2 ] = [ - S H S H S H S H ] [ y 1 y 2 ] = [ 2 S H S 0 0 2 S H S ] [ h 1 h 2 ] + [ z _ 1 z _ 2 ] ( 12 ) where [ z _ 1 z _ 2 ] = [ - S H S H S H S H ] [ z 1 z 2 ] . ( 13 )
If the sequence s is such that SHS=(Nt−L+1)IL, then

[ r 1 r 2 ] = 2 ( N t - L + 1 ) [ h 1 h 2 ] + [ [ z _ 1 z _ 2 ] ] . ( 14 )
If the noise is white, then the linear processing at the receiver does not color it, and the channel transfer functions correspond to

h 1 = 1 / 2 ( N t - L + 1 ) r 1 h 2 = 1 / 2 ( N t - L + 1 ) r 2 . ( 15 )
with a minimum squared error, MSE, that achieves the lower bound expressed in equation (7); to wit,

MSE = 2 σ 2 L ( N t - L + 1 ) ( 16 )

The above result can be generalized to allow any matrix U to be used to encode the training sequence, s, so that

[ y 1 y 2 ] = U [ h 1 h 2 ] + [ z 1 z 2 ] ( 17 )
as long as UHU=2I for a two antennas case, and UHU=KI for an K antenna case.

Whereas FIG. 4 presents a method for developing sequences s1 and s2 of length Nt from a sequence s that is Nt/2 symbols long, FIG. 5 presents a method for developing sequences s1 and s2 of length Nt from a sequence s that is 2Nt symbols long, which consists of a sequence d1=[s(0) s(1) . . . s(Nt−1)] followed by a sequence d2=[s(0) s(1) . . . s(Nt−1)]. In accordance with this approach, s1=d1|−{tilde over (d)}2* and s2=d2|{tilde over (d)}1*. The sequence {tilde over (d)}1 corresponds to the sequence d1 with its elements in reverse order. The symbol {tilde over (d)}1* operation corresponds to the sequence d1 with its elements in reverse order and converted to their respective complex conjugates.

The FIG. 5 encoding is very similar to the encoding scheme disclosed by Alamouti in U.S. Pat. No. 6,185,258, issued Feb. 6, 2001, except that (a) the Alamouti scheme is symbols-centric whereas the FIG. 5 encoding is sequence-centric, and (b) the Alamouti scheme does not have the concept of a reverse order of a sequence (e.g., {tilde over (d)}1*). See also E. Lindskog and A. Paulraj titled “A Transmit Diversity Scheme for Channels With Intersymbol Interference,” ICC, 1:307-311, 2000. An encoder 9 that is created for developing training sequences s1 and s2 in accordance with FIG. 5, can be constructed with a control terminal that is set to 1 during transmission of information and set to another value (e.g., 0, or to Nt to indicate the length of the generated block) during transmission of the training sequence, leading to the simplified transmitter realization shown in FIG. 6. More importantly, such an arrangement leads to a simplified receiver because essentially the same decoder is used for both the information signals and the training signals.

With a signal arrangement as shown in FIG. 5, the signal captured at antenna 21 of receiver 20 is

[ y 1 y 2 ] = [ - D ~ 1 * D ~ 1 * D 1 D 2 ] [ h 1 h 2 ] + [ [ z _ 1 z _ 2 ] ] ( 18 )
where the matrices Di and {tilde over (D)}i (for i=1, 2) are convolution matrices for d1 and {tilde over (d)}1, respectively, of dimension (Nt−L+1)×L. Recalling from equation (8) that MMSE is achieved if and only if DHD has zeros off the diagonal; i.e.,

- D ~ 1 T D ~ 2 * + ( D 2 * ) T D 1 = 0 ( 19 ) and - D ~ 2 T D ~ 1 * + ( D 1 * ) T D 2 = 0 , ( 20 )
and identity matrices on the diagonal; i.e.,

D ~ 2 T D ~ 2 * + ( D 1 * ) T D 1 = 2 ( N t - L + 1 ) I L ( 21 ) and D ~ 1 T D ~ 1 * + ( D 2 * ) T D 2 = 2 ( N t - L + 1 ) I L . ( 22 )

Various arrangements that interrelate sequences d1 and d2 can be found that meet the above requirement. By way of example (and not by way of limitation), a number of simple choices satisfy these conditions follow.

(1) (D1*)TD1=(Nt−L+1)IL, {tilde over (D)}1=D1, and D2=D1. To show that equation (21) holds, one may note that {tilde over (D)}2T{tilde over (D)}2* (the first term in the equation) becomes D1TD1*, but if (D1*)TD1 is a diagonal matrix then so is {tilde over (D)}2T{tilde over (D)}2*. Thus, according to this training sequence embodiment, one needs to only identify a sequence d1 that is symmetric about its center, with an impulse-like autocorrelation function, and set d2 equal to d1. This is shown in FIG. 7.
(2) (D1*)TD1=(Nt−L+1)IL, and {tilde over (D)}2=D1. To show that equation (21) holds, one may note that the {tilde over (D)}2T{tilde over (D)}2* first term in the equation also becomes D1TD1*. Thus, according to this training sequence embodiment, one needs to only identify a sequence d1 with an impulse-like autocorrelation function, and set d2 equal to {tilde over (d)}1. This is shown in FIG. 8.
(3) (D1*)TD1=(Nt−L+1)IL, and {tilde over (D)}2*=D1. To show that equation (21) holds, one may note that the {tilde over (D)}2T{tilde over (D)}2* first term in the equation becomes (D1*)TD1. Thus, according to this training sequence embodiment, one needs to only identify a sequence d1 with an impulse-like autocorrelation function, and set d2 equal to {tilde over (d)}1*. This is shown in FIG. 9.
Training Sequences Employing Trellis Coding

Consider a trellis code with m memory elements and outputs from a constellation of size C, over a single channel with memory 2mC(L−1)−1. To perform joint equalization and decoding one needs a product trellis with 2mC(L−1) states. For a space-time trellis code with m memory elements, n transmit antennas and one receive antenna, over a channel with memory (L−1), one needs a product trellis with 2mCn(L−1).

The receiver can incorporate the space-time trellis code structure in the channel model to create an equivalent single-input, single output channel, heq, of length m+L. The trellis, in such a case, involves C(m+L−1) states. The approach disclosed herein uses a single training sequence at the input of the space-time trellis encoder to directly estimate heq used by the joint space-time equalizer/decoder. The channel heq that incorporates the space-time code structure typically has a longer memory than the channel h1 and h2 (in a system where there are two transmitting antennas and one receiving antenna).

To illustrate, assume an encoder 30 as depicted in FIG. 10 that employs an 8-PSK constellation of symbols to encode data from a training sequence generator into a sequence s of symbols taken from the set ei2πpk/8, pk=0,1, 2, . . . , 7, where the training sequences s1 and s2 are algorithmically derived within encoder 30 from sequence s. Specifically, assume that s1(k)=s(k), and that s2(k)=(−1)pk−1s(k−1), which means that s2(k)=s(k−1) when s(k−1) is an even member of the constellation (ei0, eiπ/2, e, and ei3π/2), and s2(k)=−s(k−1) when s(k−1) is an odd member of the constellation.

With such an arrangement, the received signal at time k can be expressed as

y ( k ) = i = 0 L - 1 h 1 ( i ) s ( k - i ) + i = 0 L - 1 h 2 ( i , k ) ( - 1 ) p k - i - 1 s ( k - i - 1 ) + z ( k ) = i = 0 L - 1 h eq ( i ) s ( k - i ) + z ( k ) , ( 23 ) where h eq ( i , k ) = { h 1 ( 0 ) for i = 0 h 1 ( i ) + ( - 1 ) p k - i h 2 ( i - 1 ) for 0 < i < L ( - 1 ) p k - L h 2 ( L - 1 ) for i = L . ( 24 )
A block of received signals (corresponding to the useful portion of the training sequence block) can be expressed in matrix form by
y=Sheq+z   (25)
where

S = [ s ( L ) s ( L - 1 ) s ( 0 ) s ( L + 1 ) s ( L ) s ( 1 ) s ( N t - 1 ) s ( N t - 2 ) s ( N t - L - 1 ) ] [ h eq ( 0 , L ) h eq ( 1 , L + 1 ) h eq ( L , N t - 1 ) ] ( 26 )
and following the principles disclosed above, it can be realized that when the training sequence is properly selected so that SHS is a diagonal matrix, i.e., SHS=(Nt−L)IL+1, an estimate of heq that is, ĥeq, is obtained from

h ^ eq = S H y ( N t - L ) . ( 27 )
If the training sequence were to comprise only the even constellation symbols, ei2πk/8, k=0, 2, 4, 6, per equation (24), the elements of {tilde over (h)}eq would correspond to

h eq even = [ h 1 ( 0 ) , h 1 ( 1 ) + h 2 ( 0 ) , h 1 ( 2 ) + h 2 ( 1 ) , h 1 ( L - 1 ) + h 2 ( L - 2 ) , h 2 ( L - 1 ) ] . ( 28 )
If the training sequence were to comprise only the odd constellation symbols, ei2πk/8, k=1, 3, 5, 7, the elements of {tilde over (h)}eq would correspond to

h eq odd = [ h 1 ( 0 ) , h 1 ( 1 ) - h 2 ( 0 ) , h 1 ( 2 ) - h 2 ( 1 ) , h 1 ( L - 1 ) - h 2 ( L - 2 ) , h 2 ( L - 1 ) ] . ( 29 )
If the training sequence were to comprise a segment of only even constellation symbols followed by only odd constellation symbols (or vice versa), then channel estimator 22 within receiver 20 can determine the heqeven coefficients from the segment that transmitted only the even constellation symbols, and can determine the heqodd coefficients from the segment that transmitted only the even constellation symbols. Once both heqeven and heqeven and heqodd are known, estimator 22 can obtain the coefficients of h1 from

[ h 1 ( 0 ) , h 1 ( 1 ) , h 1 ( 2 ) , h 1 ( L - 1 ) ] = h eq even + h eq odd 2 ( 30 )
and the coefficients of h2 from

[ h 2 ( 0 ) , h 2 ( 1 ) , h 2 ( 2 ) , h 2 ( L - 1 ) ] = h eq even - h eq odd 2 . ( 31 )
What remains, then, is to create a single training sequence s of length Nt where one half of it (the seven portion) consists of only even constellation symbols (even sub-constellation), and another half of it (the sodd portion) consists of only odd constellation symbols (odd sub-constellation). The sequences s1 and s2 of length Nt are derived from the sequence s by means of the 8-PSK space-time trellis encoder. The sequences s1 and s2 must also meet the requirements of equation (8). Once seven is found, sodd can simply be
sodd=αseven, where α=eiπk/4 for any k=1,3,5, 7.   (32)
Therefore, the search for sequence s is reduced from a search in the of 8Nt to a search for seven in the space 4(Nt/2) such that, when concatenated with sodd that is computed from seven as specified in equation (32), yields a sequence s that has an autocorrelation function that is, or is close to being, impulse-like.

For a training sequence of length Nt=26, with an 8-PSK space-time trellis encoder, we have identified the 12 training sequences specified in Table 1 below.

TABLE 1
sequence # α Se
1 exp(i5π/4) −1 1 1 1 1 −1 −i −1 1 1 −1 1 1
2 exp(i3π/4) 1 1 −1 1 i i 1 −i i −1 −1 −1 1
3 exp(iπ/4) 1 −1 −1 −i i −i 1 1 1 −i −1 1 1
4 exp(iπ/4) 1 −1 −1 −i 1 −1 1 −i −i −i −1 1 1
5 exp(iπ/4) 1 i 1 1 i −1 −1 i 1 −1 1 i 1
6 exp(i3π/4) 1 i 1 i −1 −1 1 −1 −1 i 1 i 1
7 exp(i7π/4) 1 −i 1 1 −i −1 −1 −i 1 −1 1 −i 1
8 exp(i5π/4) 1 −i 1 −1 i 1 −1 −i 1 1 1 −i 1
9 exp(i3π/4) −1 1 1 1 −1 −1 −i −1 −1 1 −1 1 1
10 exp(i7π/4) −1 i −1 −i 1 −i i i 1 i 1−i 1
11 exp(iπ/4) −1 −i −1 i 1 i −i −i 1−i 1 i 1
12 exp(i3π/4) −1 −i −1 i −1 i −i −i −1 −i 1 i 1

Construction of Training Sequence

While the above-disclosed materials provide a very significant improvement over the prior art, there is still the requirement of selecting a sequence s1 with an impulse-like autocorrelation function. The following discloses one approach for identifying such a sequence without having to perform an exhaustive search.

A root-of-unity sequence with alphabet size N has complex roots of unity elements of the form

ⅈ2π k N , k = 1 , 2 , ( N - 1 ) .
As indicated above, the prior art has shown that perfect roots-of-unity sequences (PRUS) can be found for any training sequence of length Nt, as long as no constraint is imposed on the value of N. As also indicated above, however, it is considered disadvantageous to not limit N to a power of 2. Table 2 presents the number of PRUSs that were found to exist (through exhaustive search) for different sequence lengths when the N is restricted to 2 (BPSK), 4 (QPSK), or 8 (8-PSK). Cell entries in Table 2 with “-” indicate that sequence does not exist, and blank cells indicate that an exhaustive search for a sequence was not performed.

TABLE 2
Nt =
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
BPSK  8
QPSK  8  32 128 6144
8-PSK 16 128 512

A sequence s of length Nt is called L-perfect if the corresponding training matrix S of dimension (Nt−L+1)×L satisfies equation (8). Thus, an L-perfect sequence of length Nt is optimal for a channel with L taps. It can be shown that the length Nt of an L-perfect sequence from a 2p-alphabet can only be equal to

N t = { 2 ( L + i ) for L = odd 2 ( L + i ) - 1 for L = even } for i = 0 , 1 , , ( 33 )
which is a necessary, but not sufficient, condition for L-perfect sequences of length Nt. Table 3 shows the minimum necessary Nt for L=2, 3, . . . 10, the size of the corresponding matrix S, and the results of an exhaustive search for L-perfect sequences (indicating the number of such sequences that were found). Cell entries marked “x” indicate that sequences exist, but number of such sequences it is not known.

TABLE 3
L
2 3 4 5 6 7 8 9 10
Nt  3  6  7 10 11  14 15 18 19
S 2 × 2 4 × 3 4 × 4 6 × 5 6 × 6 8 × 7 8 × 8 10 × 9 10 × 10
BPSK  4  8  8
QPSK 16  64  64 128 x
8-PSK 64 512 512 x x

It is known that with a PRUS of a given length, NPRUS, one can estimate up to L=NPRUS unknowns. It can be shown that a training sequence of length Nt is also an L-perfect training sequence if
Nt=kNPRUS+L−1 and k≧1.   (34)
Accordingly, an L-perfect sequence of length kNPRUS+L−1 can be constructed by selecting an NPRUSsequence, repeating it k times, and circularly extending it by L−1 symbols. Restated and amplified somewhat, for a selected PRUS of a given NPRUS, i.e.,

s p ( N PRUS ) = [ s p ( 0 ) s p ( 1 ) s p ( N PRUS - 1 ) ] , ( 35 )
the L-perfect sequence of length kNPRUS+L−1 is created from a concatenation of k sp(NPRUS) sequences followed by the first L−1 symbols of sp(NPRUS), or from a concatenation of the last L−1 symbols of sp(NPRUS) followed by k sp(NPRUS) sequences.

To illustrate, assume that the number of channel “taps” that need to be estimated, L, is 5, and that a QPSK alphabet is desired to be used. From the above it is known that NPRUS must be equal to or greater than 5, and from Table 2 it is known that the smallest NPRUS that can be found for QSPK that is larger than 5 is NPRUS=8. Employing equation (34) yields

N t = kN PRUS + L - 1 = k · 8 + 5 - 1 = 12 , 20 , 28 , ( 36 ) for k = 1 , 2 , 3 ,

While an L-perfect training sequence cannot be constructed from PRUS sequences for values of Nt other than values derived by operation of equation (34), it is known that, nevertheless, L-perfect sequences may exist. The only problem is that it may be prohibitively difficult to find them. However, in accordance with the approach disclosed below, sub-optimal solutions are possible to create quite easily.

If it is given that the training sequence is Nt long, one can express this length by
Nt=kNPRUS+L−1+M, where M>0   (37)
In accord with our approach, select a value of NPRUS≧L that minimizes M, create a sequence of length kNPRUS+L−1 as disclosed above, and then extend that sequence by adding M symbols. The M added symbols can be found by selecting, through an exhaustive search, the symbols that lead to the lowest estimation MSE. Alternatively, select a value of NPRUS≧L that minimizes M′ in the equation,
Nt=kNPRUS+L−1−M′, where M′>0   (38)
create a sequence of length kNPRUS+L−1 as disclosed above, and then drop the last (or first) M′ symbols.

The receiver shown in FIG. 2 includes the channel estimator 22, which takes the received signal and multiplies it SH as appropriate; see equation (12), above.

Al-Dhahir, Naofal, Fragouli, Christine, Turin, William

Patent Priority Assignee Title
Patent Priority Assignee Title
5914982, Jun 13 1997 PCTEL, Inc Method and apparatus for training linear equalizers in a PCM modem
5949819, Jun 13 1997 Synaptics Incorporated Method and apparatus for training linear equalizers in a PCM modem
6424679, Oct 07 1998 Intel Corporation Space time block coded transmit antenna diversity for WCDMA
6449314, Oct 07 1998 Intel Corporation Space time block coded transmit antenna diversity for WCDMA
6643338, Oct 07 1998 Intel Corporation Space time block coded transmit antenna diversity for WCDMA
6788661, Nov 12 1999 Nikia Networks Oy Adaptive beam-time coding method and apparatus
6865237, Feb 22 2000 UNWIRED BROADBAND, INC Method and system for digital signal transmission
6891897, Jul 23 1999 Apple Inc Space-time coding and channel estimation scheme, arrangement and method
7006579, Sep 04 2000 UNWIRED BROADBAND, INC ISI-robust slot formats for non-orthogonal-based space-time block codes
7139324, Jun 02 2000 Intellectual Ventures I LLC Closed loop feedback system for improved down link performance
7200182, Oct 07 1998 Intel Corporation Space time block coded transmit antenna diversity for WCDMA
7272192, Apr 14 2000 BROAD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIVERSITY Time-reversal block transmit diversity system for channels with intersymbol interference and method
7366266, Oct 07 1998 Intel Corporation Space time block coded transmit antenna diversity for WCDMA
7613259, Oct 07 1998 Intel Corporation Mobile receiver phase correction circuit
7701916, Feb 25 1999 Texas Instruments Incorporated Space time transmit diversity for TDD with cyclic prefix midamble
20020067309,
20040013211,
20050157683,
20050157684,
20050185734,
RE39165, Jun 13 1997 PCTEL, Inc Method and apparatus for training linear equalizers in a PCM modem
/
Executed onAssignorAssigneeConveyanceFrameReelDoc
Mar 18 2013AT&T Intellectual Property II, L.P.(assignment on the face of the patent)
Date Maintenance Fee Events
Feb 19 2014ASPN: Payor Number Assigned.
Nov 20 2017M1552: Payment of Maintenance Fee, 8th Year, Large Entity.
Feb 14 2022REM: Maintenance Fee Reminder Mailed.
Aug 01 2022EXP: Patent Expired for Failure to Pay Maintenance Fees.


Date Maintenance Schedule
Apr 08 20174 years fee payment window open
Oct 08 20176 months grace period start (w surcharge)
Apr 08 2018patent expiry (for year 4)
Apr 08 20202 years to revive unintentionally abandoned end. (for year 4)
Apr 08 20218 years fee payment window open
Oct 08 20216 months grace period start (w surcharge)
Apr 08 2022patent expiry (for year 8)
Apr 08 20242 years to revive unintentionally abandoned end. (for year 8)
Apr 08 202512 years fee payment window open
Oct 08 20256 months grace period start (w surcharge)
Apr 08 2026patent expiry (for year 12)
Apr 08 20282 years to revive unintentionally abandoned end. (for year 12)