Summary of the invention
Technical problem: the objective of the invention is in the MIMO cdma system, to provide the circulating space-time block code transmitting and diversity project in a kind of code division multiple access system, be used for solving traditional space-time block code transmitting and diversity when emission fate not high shortcoming of code efficiency greater than 2 time, and can resist the rapid fading multipath channel effectively.
Technical scheme: technical characterictic of the present invention is exactly the coding and decoding and the launching technique of circulating space-time block code.
One of design criterion of Space-Time Block Coding is an orthogonal design, and promptly the Space-Time Block Coding matrix satisfies orthogonality, still,, does not also have such sign indicating number battle array to satisfy orthogonality condition at present and makes that code efficiency is 1 greater than 2 o'clock for complex signal and number of transmit antennas; In addition, the decoding of Space-Time Block Coding has individual restrictive condition, and that is exactly under quasi-static channel opens, and promptly channel is constant in a code character, and this is difficult to satisfy in actual applications.
Circulating space-time block code in this programme is that input information symbol (supposing that every group has M the code word) loop coding that divides into groups is become a symmetric code battle array (M * M ties up matrix), the code word of different rows adopts different orthogonal intersections to carry out launching (corresponding M the spreading code of M root antenna) by corresponding antenna behind the spread spectrum respectively in the symmetric code battle array, that is: the corresponding transmitting antenna of row in the sign indicating number battle array, the corresponding orthogonal intersection of every transmit antennas.Since the circulating space-time group coding, and at the different different spreading codes of transmitting antenna employing, this equals to have given orthogonal property to institute's channel transmitted, and promptly Deng Xiao generalized channel matrix is an orthogonal matrix.During decoding, at first collect all information in the code character time cycle, the spread spectrum code character that is adopted when the information that is received in each symbol period in the code character is all used emission (M spreading code altogether) is carried out despreading, like this, the information of interior all symbol periods of code character is formed a sign indicating number battle array (the despreading information in respective symbol cycle is listed as accordingly corresponding to matrix) after despreading, just in time opposite during with coding, circulate the information matrix after the despreading is counter respectively, utilize channel parameter just can translate code word again.This programme is fit to input signal arbitrarily, and also is not limited to quasi-static channel opens during decoding.
Circulating space-time block code transmitting and diversity project in the code division multiple access system of the present invention is to adopt circulating space-time group coding and decoding method, and adopt different orthogonal intersections at different transmitting antennas, make the generalized channel matrix of equivalence have orthogonality, thereby make decoding the same simple with traditional Space-Time Block Coding, only need do some simple linear operations after the receiving terminal despreading to received signal and can translate code word, concrete step is; At transmitting terminal the M transmit antennas is arranged:
1), at first input information is divided into groups, every group contains M information symbol is b
1, b
2... b
M, use b
mRepresent m information symbol, m is integer and 1≤m≤M,
2), this M information symbol formed a M * M dimension sign indicating number battle array,
3), successively capable all information symbols of m in the sign indicating number battle array are circulated left and move the m-1 position to finish loop coding m be integer and 1≤m≤M,
4), all capable information symbols of m in the sign indicating number battle array behind the loop coding be multiply by a spread spectrum codes C
mLaunch from m root antenna the back, wherein, and C
mRepresent m spreading code,
At receiving terminal N root reception antenna number is arranged:
21), at first collect first the reception information to M symbol period,
22), M spreading code being adopted when all multiply by emission respectively of information that each symbol period is received carry out despreading, that is: to the received signal r of each symbol period
N, mUse C respectively
1, C
2C
MCarry out despreading, wherein, n represents n root reception antenna,
23), the despreading information of M symbol period is formed a sign indicating number battle array,
H wherein
M, nRepresent that the m transmit antennas is to the channel parameter between n root reception antenna, ψ
nRepresent the white Gaussian noise matrix on the n root reception antenna, n=1~N; D represents despreading,
24), just in time opposite with when coding, respectively with the information matrix R after the despreading
N, dCapable the circulation to the right of m move the m-1 position, the matrix D of getting back like this
N, d,
25), utilize channel information to carry out linearity to merge,
26), sue for peace after the information on all reception antennas done same processing,
27), at last the information of summation is adjudicated recovery emission information.
Beneficial effect: use this programme that following advantage is arranged:
Circulating space-time block code transmitting and diversity based on the MIMO cdma system in this programme has overcome the transmit diversity code efficiency not high shortcoming of emission fate greater than 2 o'clock employing Space-Time Block Codings, and can resist the rapid fading multipath channel effectively.This programme adopts the circulating space-time group coding, and adopt different orthogonal intersections at different transmitting antennas, make the generalized channel matrix of equivalence have orthogonality, therefore its decoding is the same simple with traditional Space-Time Block Coding, only need do some simple linear operations after the receiving terminal despreading to received signal, can translate code word.
1, overcome in the space-time block code transmitting and diversity project for complex signal when number of transmit antennas not high shortcoming of code efficiency greater than 2 time, and this programme is applicable to any signal and number of transmit antennas arbitrarily.
2, this programme can resist the rapid fading multipath channel effectively, and space-time block code transmitting and diversity project only is applicable to the quasistatic fading channel.
Embodiment
Circulating space-time block code (C-STBC) coding and decoding method
For the MIMO cdma system with M transmit antennas, N root reception antenna, the input information symbol at first is grouped, and every group contains M symbol (b
M=[b
1, b
2..b
m..b
M]), b wherein
MExpression information symbol vector, b
mThe expression information symbol.With this M symbol loop coding is M * M dimension sign indicating number battle array B
M, the specific coding method is: B
MM capable be with b
MCirculation left moves the symbol that the m-1 position obtains.For convenience of explanation, with M=4 be the coding and decoding method of example explanation circulating space-time block code.b
4=[b
1, b
2, b
3, b
4], the loop coding matrix B
4For
As can be seen, the loop coding matrix is symmetrical matrix, i.e. a B
4=B
4 TBehind the loop coding, B
44 row symbols in 4 symbol periods, launch after adopting 4 different spreading code spread spectrums respectively corresponding to 4 transmit antennas.Loop coding matrix behind the spread spectrum is
Wherein
Represent the spreading code on the m root antenna, c
M, q=± 1, Q is a spreading gain.Suppose each transmitting antenna at a distance of enough far away, promptly each transmitting antenna is independent to the channel between reception antenna, and the hypothesis channel is a flat fading channel.If h
4, n=[h
1, n, h
2, n, h
3, n, h
4, n]
TBe the channel parameter vector of this 4 transmit antennas to n root reception antenna, wherein h
M, nRepresent the m transmit antennas to the channel parameter between n root reception antenna, then the received signal in 4 symbol periods on the n root reception antenna can be expressed as (assumes synchronization mechanism improve and do not have ISI and ICI)
ξ wherein
nBe that variance is σ
2The white Gaussian noise vector of I, r
N, mRepresent r
N, 1, r
N, 2, r
N, 3, r
N, 4One of in, representing the received signal of m symbol period of n root reception antenna, T represents transposition.Received signal r to each symbol period
N, mUse C respectively
1, C
2... C
4Carry out despreading.Like this, the despread signal of 4 symbol periods can be formed a matrix R
N, d
R wherein
N, dIn the element of each row be respectively to use r
N, mWith C
1, C
2... C
4Carry out the result of despreading, ψ
nBe 4 * 4 dimension white Gaussian noise matrixes.Just in time opposite during with coding, respectively with the information matrix R after the despreading
N, dCapable the circulation to the right of m move the m-1 position, the matrix D of getting back like this
N, d
ψ ' wherein
nBe ψ
nCyclic shift matrices.Suppose channel parameter vector h
4, n=[h
1, n, h
2, n, h
3, n, h
4, n]
TEstimate, then former emission information can draw from following formula
Wherein Dec (.) expression judgement computing,
Expression b
4Estimation, H represents conjugate transpose.For N root reception antenna, then
More than provided the concrete grammar of code coding/decoding when circulation is empty.The another kind that can draw the empty time-code of circulation from formula (3) is represented mode.
Wherein
Because the circulating space-time group coding, and at the different different spreading codes of transmitting antenna employing, this equals to have given orthogonal property to institute's channel transmitted, i.e. Deng Xiao generalized channel matrix F
4, nBe orthogonal matrix, promptly
So
Circulating space-time block code and Space-Time Block Coding send the comparison of code word in the MIMO cdma system
Table 1 has provided circulating space-time block code transmitting and diversity project (C-STBC) and space-time block code transmitting and diversity project (STBC) send signal in two symbol periods comparison (number of transmit antennas M=2).
Table 1
Emulation relatively
Space-time block code transmitting and diversity project and circulating space-time block code transmitting and diversity project are carried out emulation relatively in the same environment under the MIMO cdma system.Suppose number of users K=4, information source is the 2PSK signal, spreading code adopts 32 Walsh sign indicating numbers, multiple access disturbs MAI=10dB, channel adopts single footpath rayleigh fading channel and four footpath rayleigh fading channels respectively, four footpaths are during rayleigh fading channel, and each footpath postpones to differ a chip period and each footpath amplitude of fading differs 4dB.
Simulation result is (error rate obtains after 5000 symbols of reception are averaged among the figure) as depicted in figs. 1 and 2.
Fig. 1 be under the fading channel environment of single footpath error performance relatively, as can be seen from the figure, no matter be two one receive or two two receipts situations under, the error performance of two kinds of schemes is more approaching.Fig. 2 is that the error performance under four footpath fading channel environment compares, as can be seen from the figure, no matter be two one receive or two two receipts situations under, circulating, all the error performance than space-time block code transmitting and diversity project is good for empty time-code emission diversity scheme, and the empty time-code emission diversity scheme anti-multipath decline of this explanation circulation ability is strong.
Concrete implementation step:
One, transmitting terminal (supposing to have the M transmit antennas)
1, at first input information is divided into groups, every group contains M symbol (b
M=[b
1, b
2..b
m..b
m]).
2, this M information symbol formed a M * M dimension sign indicating number battle array (is example with 4 antennas),
3, successively the capable information symbol of m in the sign indicating number battle array is circulated left and move the m-1 position and finish loop coding
4, will encode and launch from corresponding antenna after the information symbol of corresponding line multiply by a spreading code in the cyclic code battle array of back, the loop coding matrix behind the spread spectrum is
Wherein
Represent the spreading code on the m root antenna, c
M, q=± 1, Q is a spreading gain.
Two, receiving terminal (N is the reception antenna number, is example with 4 transmit antennas still)
1, at first collects the reception information of M symbol period.Suppose h
4, n=[h
1, n, h
2, n, h
3, n, h
4, n]
TBe the channel parameter vector of this 4 transmit antennas to n root reception antenna, wherein h
M, nRepresent the m transmit antennas to the channel parameter between n root reception antenna, then the received signal in 4 symbol periods on the n root reception antenna can be expressed as (assumes synchronization mechanism improve and do not have ISI and ICI)
ξ wherein
nBe that variance is σ
2The white Gaussian noise vector of I, r
N, mRepresent r
N, 1, r
N, 2, r
N, 3, r
N, 4One of in, represent the received signal of m symbol period of n root reception antenna.
M the spreading code that is adopted when 2, the information that each symbol period is received all multiply by emission respectively carries out despreading, that is: to the received signal r of each symbol period
N, mUse C respectively
1, C
2, C
3, C
4Carry out despreading.
3, the despreading information of M symbol period is formed a sign indicating number battle array.That is: the despread signal of 4 symbol periods can be formed a matrix R
N, d
R wherein
N, dIn the element of each row be respectively to use r
N, mWith c
1, c
2, c
3, c
4Carry out the result of despreading, ψ
nBe 4 * 4 dimension white Gaussian noise matrixes.
Just in time opposite during 4, with coding, respectively with the information matrix R after the despreading
N, dCapable the circulation to the right of m move the m-1 position, the matrix D of getting back like this
N, d
ψ ' wherein
nBe ψ
nCyclic shift matrices.
5, utilize channel information to carry out linearity and merge,
6, after being done same processing, the information on all reception antennas sues for peace
7, at last the information of summation is adjudicated, recover emission information
Wherein Dec (.) expression judgement computing.