Method for co-channel interference suppression in orthogonal frequency division multiplexing (OFDM) systems with multiple receiving antennas

Abstract

A method for co-channel interference suppression in Orthogonal Frequency Division Multiplexing (OFDM) systems with multiple receiving antennas is provided, wherein the co-channel interference (CCI) in different directions is suppressed by the spatial technique provided by the antenna arrays, and the interference to a desired carrier caused by other sub-carriers is also taken into consideration, that is, the interference of other sub-carriers is cancelled by means of a multistage interference cancellation, thereby the performance for interference suppression is improved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below for illustration only, and which thus is not limitative of the present invention, and wherein:

FIG. 1A is a flow chart of detecting signals by a linear minimum mean square error (MMSE) of the present invention;

FIG, 1B is a block diagram 10 of detecting signals by the LMMSE of the present invention;

FIG. 2A is a flow chart of detecting signals by a multistage interference cancellation (MIC) of the present invention;

FIG. 2B is a block diagram of detecting signals by the MIC of the present invention;

FIG. 3A is a flow chart of detecting signals by an enhancement multistage interference cancellation (EMIC) of the present invention;

FIG. 3B is the other flow chart of detecting signals by an EMIC of the present invention; and

FIG. 3C is a flow chart of detecting signals by the EMIC of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The detailed features and advantages of the present invention are described in detail in the following detailed description, the text thereof enables any skilled in the art to understand the technical content of the present invention and implement accordingly, and any skilled in the art may understand the related objects and advantages of the present invention according to the disclosures, claims, and drawings of the specification.

Three embodiments of the present invention are illustrated, wherein each embodiment is implemented by an OFDM system with adaptive antenna arrays. A receiver with antenna arrays receives signals by using M antennas, the received signal of each antenna is expressed by Equation (1), and each embodiment deduces with a mathematical algorithm a desired information bit of the desired sub-carrier.

Three signal detection algorithms are used in each embodiment respectively: linear minimum mean square error (LMMSE) signal detection, multistage interference cancellation (MIC) signal detection, and enhancement multistage interference cancellation (EMIC) signal detection. By increasing the signal process resolution by the antenna arrays, accurately estimating the signals of other sub-carriers via multistage recursion detection, and then subtracting the interference item caused by other sub-carriers from the signal of the desired carrier, the whole interference cancellation process is completed, and thereby the desired information bit of the desired sub-carrier is resolved.

r _m(t)=s_m(t)+i_m(t)+n_m(t), m=1, 2, . . . , M   (1)

In Equation (1), r_m(t) represents the received signal of the mth antenna; n_m(t) represents the white Gaussian noise with a power spectral density of N₀/2 received by the mth antenna; i_m(t) represents a CCI interference received by the mth antenna; s_m(t) represents the OFDM signal received by the mth antenna after a channel effect, and is expressed by Equation (2) as follows.

$\begin{array}{cc}{s}_m\left(t\right)=\sum _{p=0}^{P-1}\sum _{q=0}^{N_c-1}\sqrt{2E_b}b\left(p,q\right)\sum _{k=0}^{K-1}c_{m,k}h_q\left(t-{\mathrm{pT}}_5-k\beta T_5/L\right)& \left(2\right)\end{array}$

Equation (2) describes that the OFDM signal s_m(t) is formed by passing multiple information bits or symbols carried through a channel having a channel effect and a multipath effect. That is, in Equation (2), P represents the number of symbols contained in an OFDM signal; N_c represents the number of sub-carriers contained in an OFDM signal; b(p,q) represents the uncorrelated coded information bit of the qth sub-carrier in the pth symbol; the b(p,q)ε{±1}, E_b represent the bit energy; K represents the number of paths the OFDM signal s_m(t) can be decomposed into; c_m,0,c_m,1, . . . , c_m,K-1 represent the fading channel coefficients of different paths under the mth antenna, and the coefficient is a complex-valued Gaussian random variable; h_q(t) represents a transfer function of channel effect of the qth sub-carrier; T_s indicates the symbol duration; L indicates the channel length; and β indicates the sampling factor. Therefore, the received signal of the 0th symbol received by the mth antenna is expressed by Equation (3) as follows.

$\begin{array}{cc}{\underset{\_}{r}}_m=\sum _{q=0}^{N_c-1}b\left(0,q\right){\underset{\_}{s}}_{m,q}+{\underset{\_}{i}}_m+{\underset{\_}{n}}_m& \left(3\right)\end{array}$

After the received signal of the 0th symbol received by all M antennas is expressed by Equation (3), a received signal vector r is generated, expressed by Equation (4).

r=[r₁^Tr₂^TK r_M^T]^T   (4)

Herein, the object of all embodiments is to calculate a desired information bit of the 0th symbol of the qth sub-carrier.

The first embodiment refers to FIG. 1A and FIG. 1B. FIG. 1A is a flow chart of detecting signals by the LMMSE and FIG. 1B is a block diagram 10 of detecting signals by the LMMSE, the embodiment comprises the following steps.

Generate an autocorrelation matrix R 113, according to the received signal vector r111 (Step 101), expressed by Equation (5) as follows.

R=E[rr^H]  (5)

Execute cross-correction to generate an OFDM signal s_q 114 of the qth sub-carrier, according to the received signal vector r111 and a series of known training bits b(n,q) 112 (Step 102), expressed by Equation (6) as follows.

s _q =E[r×b(n,q)]  (6)

Generate a detection vector v_q,LMMSE^T 115 of the qth sub-carrier, according to the autocorrelation matrix R 113 and the transpose matrix s_q^H of the OFDM signal s_q 114 of the qth sub-carrier (Step 103), expressed by Equation (7) as follows.

v _q,LMMSE ^T=s_q^HR⁻¹   (7)

Generate an information bit b(0,q) of the qth sub-carrier, according to the detection vector v_q,LMMSE^T 115 and the received signal vector r111, and referring to the MMSE detection algorithm (Step 104), the MMSE detection algorithm is expressed by the Equation (8) as follows.

E[|b(0, q)−v_q,LMMSE ^Tr|²]  (8)

Obtain a desired information bit b_LMMSE^%(0,q) 116 of the qth sub-carrier satisfying the MMSE (Step 105), expressed by Equation (9) as follows.

b_LMMSE^%(0, q)=v_q,LMMSE^Tr  (9)

The second embodiment refers to FIG. 2A and FIG. 2B. FIG. 2A is a flow chart of detecting signals by the MIC of the present invention and FIG. 2B is a block diagram 20 of detecting signals by the MIC of the present invention, the embodiment comprises the following steps.

Generate an autocorrelation matrix R 213, according to the received signal vector r211 (Step 201), expressed by Equation (10) as follows.

R=E[rr^H]  (10)

Execute cross-correction to generate an OFDM signal s_q 214 of the qth sub-carrier, according to the received signal vector r211 and a series of known training bits b(n,q) 212 (Step 202), expressed by Equation (11) as follows.

s _q =E[r×b(n,q)]  (11)

Generate a detection vector v_q,LMMSE^T 215 of the qth sub-carrier, according to the autocorrelation matrix R 213 and the transpose matrix s_q^H of the OFDM signal s_q 214 of the qth sub-carrier (Step 203), expressed by Equation (12) as follows.

v _q,LMMSE ^T =s _q ^H R ⁻¹   (12)

Generate a temporary estimated information bit {circumflex over (b)}(0,q) 216 of the qth sub-carrier, according to the detection vector v_q,LMMSE^T 215 and the received signal vector r211, and referring to the MMSE detection algorithm (Step 204), expressed by the Equation (13) as follows.

{circumflex over (b)}(0,q)=v_q,LMMSE^Tr  (13)

Subtract the interference item

$\sum _{u=0,u\ne q}^{N_c-1}\hat{b}\left(0,u\right){\underset{\_}{s}}_u$

217 caused by the temporary estimated information bit {circumflex over (b)}(0, q) 216 of other sub-carriers from the received signal vector r211 to complete the whole interference suppression process (Step 205), therefore, Obtain a desired information bit b_MIC^%(0,q) 218 of the qth sub-carrier (Step 206), expressed by Equation (14) as follows.

$\begin{array}{cc}{b}_{\mathrm{MIC}}^{\%}\left(0,q\right)={\underset{\_}{v}}_{q,\mathrm{LMMSE}}^T\left[\underset{\_}{r}-\sum _{u=0,u\ne q}^{N_c-1}\hat{b}\left(0,u\right){\underset{\_}{s}}_u\right]& \left(14\right)\end{array}$

The third embodiment refers to FIGS. 3A, 3B, and 3C. FIGS. 3A and 3B are flow charts of detecting signals by the EMIC of the present invention and FIG. 3C is a block diagram 30 of detecting signals by the EMIC of the present invention, the embodiment modifying the second embodiment and comprises the following steps.

Generate an autocorrelation matrix R 313 (Step 301), according to the received signal vector r311, expressed by Equation (15) as follows.

R=E[rr^H]  (15)

Execute cross-correction to generate an OFDM signal s_q 314 of the qth sub-carrier, according to the received signal vector r311 and a series of known training bits b(n, q) 312 (Step 302), expressed by Equation (16) as follows.

s _q =E[r×b(n, q)]  (16)

Generate a detection vector v_q,LMMSE^T 315 of the qth sub-carrier, according to the autocorrelation matrix R 313 and the transpose matrix s_q^H of the OFDM signal s_q 314 of the qth sub-carrier (Step 303), expressed by Equation (17) as follows.

v _q,LMMSE ^T =s _q ^H R ⁻¹   (17)

Generate a temporary estimated information bit 316 of the qth sub-carrier, according to the detection vector v_q,LMMSE^T 315 and the received signal vector r311, and referring to the MMSE detection algorithm (Step 304), expressed by the Equation (18) as follows.

{circumflex over (b)}(0,q)=v_q,LMMSE^Tr  (18)

Subtract the interference item

$\sum _{u=0,u\ne q}^{N_c-1}\hat{b}\left(0,u\right){\underset{\_}{s}}_u$

317 caused by the temporary estimated information bit {circumflex over (b)}(0,q) 316 other sub-carriers from the received signal vector r311, to obtain a modified received signal vector r_q (step 305), expressed by Equation (19) as follows. Referring to FIG. 3B, the subsequent steps continued by a procedure A as shown in the drawing.

$\begin{array}{cc}{\underset{\_}{r}}_q=\underset{\_}{r}-\sum _{u=0,u\ne q}^{N_c-1}\hat{b}\left(0,u\right){\underset{\_}{s}}_u& \left(19\right)\end{array}$

Generate a modified autocorrelation matrix R_q 319, according to the modified received signal vector r_q 318 (Step 306), expressed by Equation (20) as follows.

R_q=E[r_qr_q^H]  (20)

Execute cross-correction to generate an OFDM signal s_q′ 320 of the qth sub-carrier, according to the modified received signal vector r_q 318 and a series of known training bits b(n,q) 312 (Step 307), expressed by Equation (21) as follows.

s _q ′=E[r _q ×b(n,q)]  (21)

Generate a modified detection vector v_q,EMIC^T′ 321 of the qth sub-carriers, according to the modified autocorrelation matrix R_q 319 and the transpose matrix (s_q′)^H of the OFDM signal of the qth sub-carrier (step 308), expressed by Equation (22) as follows.

v _q,EMIC ^T=(s_q′)^HR_q⁻¹   (22)

Obtain an information bit b_EMIC^%(0,q) 322 of the qth sub-carrier, according to the modified detection vector v_q,EMIC^T 321 of the qth sub-carrier and the modified received signal vector r_q 318 and referring to the MMSE detection algorithm (Step 309), expressed by Equation (23) as follows.

b_EMIC^%(0,q)=v_q^Tr_q   (23)

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A method for co-channel interference suppression in Orthogonal Frequency Division Multiplexing (OFDM) systems with multiple receiving antennas, used in a receiver with a plurality of antennas, the methods comprises: capturing a plurality of received signals rm(t) through each antenna;capturing a plurality of training bits b(n, q) of the qth sub-carrier through each antenna;generating a received signal vector r according to each received signal rm(t);generating an autocorrelation matrix R according to the received signal vector r;generating a signal sq of the qth sub-carrier according to the received signal vector r and a plurality of training bits b(n,q) of the qth sub-carrier;generating a detection vector vq,LMMSET of the qth sub-carrier according to the autocorrelation matrix R and the transpose matrix sqH of the signal sq of the qth sub-carrier; andgenerating a desired information bit bLMMSE%(0,q) of the qth sub-carrier according to the detection vector vq,LMMSET of the qth sub-carrier and the received signal vector r.

2. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 1, wherein the received signal vector r is generated according to a first equation: r=[r1Tr2 TK rMT]T wherein, r1T represents a first received signal of each received signal; r2T represents a second received signal of each received signal; rMT represents an Mth received signal of each received signal, and M represents the number the antennas.

3. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 1, wherein the autocorrelation matrix R is generated according to a second equation: R=E[rrH]

4. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 1, wherein the signal sq of the qth sub-carrier is generated according to a third a third equation: sq=E[r×b(n,q)]wherein the received signal vector r and the plurality of the plurality of training bits b(n, q) of the qth sub-carrier is used for cross-correction.

5. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 1, wherein the detection vector vq,LMMSET of the qth sub-carrier is generated according to a fourth equation: vq,LMMSET=sqHR−1

6. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 1, wherein the desired information bit bLMMSE%(0,q) of the qth sub-carrier is generated according to a fifth equation: bLMMSE%(0,q)=vq,LMMSETr

7. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 6, wherein the fifth equation is in accordance with a minimum mean square error (MMSE) equation: E [|b(0,q)−vq,LMMSETr|2]wherein, b(0,q) represents an information bit of a qth sub-carrier.

8. A method for co-channel interference suppression in OFDM systems with multiple receiving antennas, used in a receiver with a plurality of antennas, the method comprises: capturing a plurality of received signals rm(t) through each antenna;capturing a plurality of training bits b(n,q) of the qth sub-carrier through each antenna;generating a received signal vector r according to each received signal rm(t);generating an autocorrelation matrix R according to the received signal vector r;generating a signal sq of the qth sub-carrier according to the received signal vector r and a plurality of training bits b(n,q) of the qth sub-carrier;generating a detection vector vq,LMMSET of the qth sub-carrier according to the autocorrelation matrix R and the transpose matrix sqH of the signal sq of the qth sub-carrier;generating a desired information bit bLMMSE%(0,q) of the qth sub-carrier according to the detection vector vq,LMMSET of the qth sub-carrier and the received signal vector r;performing an interference suppression process, according to the received signal vector r and the temporary information bit {circumflex over (b)}(0,q); andgenerating a desired information bit bMIC%(0,q) of the qth sub-carrier according to the detection vector vq,LMMSET of the qth sub-carrier, the received signal vector r, and the temporary information bit {circumflex over (b)}(0,q);wherein the interference suppression process is performed by subtract the interference item

9. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the received signal vector r is generated according to a first equation: r=[r1Tr2TK rMT]T wherein, riT represents a first received signal of each received signal; r2T represents a second received signal of each received signal; rMT represents an Mth received signal of each received signal, and M represents the number of the antennas.

10. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the autocorrelation matrix R is generated according to a second equation: R=E[rrH]

11. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the signal sq of the qth sub-carrier is generated according to a third a third equation: sq=E[r×b(n,q)]wherein the received signal vector r and the plurality of the plurality of training bits b(n,q) of the qth sub-carrier is used for cross-correction.

12. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the detection vector vq,LMMSET of the qth sub-carrier is generated according to a fourth equation: vq,LMMSET=sqHR−1

13. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the temporary information bit {circumflex over (b)}(0,q) is generated according to a fifth equation: {circumflex over (b)}(0,q)=vq,LMMSETr

14. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the interference suppression process is performed in accordance with a sixth equation:

15. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 8, wherein the desired information bit bMIC%(0,q) of the qth sub-carrier is generated according to a seventh equation:

16. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 13, wherein the fifth equation is in accordance with a minimum mean square error (MMSE) equation: E[|b(0,q)−vq,LMMSETr|2]wherein, b(0,q) indicates an information bit of a qth sub-carrier.

17. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 14, wherein the interference suppression process is a multistage interference cancellation.

18. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 15, wherein the generation of the desired information bit bMIC%(0,q) of the qth sub-carrier is a signal detection of a multistage interference cancellation.

19. A method for co-channel interference suppression in OFDM systems with multiple receiving antennas, used in a receiver with a plurality of antennas, the method comprises: capturing a plurality of received signals through each antenna rm(t);capturing a plurality of training bits b(n,q) of the qth sub-carrier through each antenna;generating a received signal vector r according to each received signal rm(t);generating an autocorrelation matrix R according to the received signal vector r;generating a signal sq of the qth sub-carrier according to the received signal vector r and a plurality of training bits b(n,q) of the qth sub-carrier;generating a detection vector vq,LMMSET of the qth sub-carrier according to the autocorrelation matrix R and the transpose matrix sq of the signal sq of the qth sub-carrier;generate a temporary information bit {circumflex over (b)}(0,q) according to the detection vector vq,LMMSET and the received signal vector r;generating a modified received signal vector rq according to the received signal vector r and the temporary information bit {circumflex over (b)}(0,q) is performing an interference suppression process;generating a modified signal sq′ of the qth sub-carrier according to the modified received signal vector rq and the plurality of training bits b(n,q) of the qth sub-carrier;generating a modified detection vector vq,EMICT according to the modified autocorrelation matrix Rq and the transpose matrix (sq′)H of the signal sqH of the qth sub-carrier; andgenerating a desired information bit bEMIC%(0,q) of the qth sub-carrier according to the modified detection vector vq,EMICT, the modified received signal vector rq;wherein the interference suppression process is performed by subtract the interference item

20. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the received signal vector r is generated according to a first equation: r=[r1Tr2TKrMT]T wherein, r1T represents a first received signal of each received signal; r2T represents a second received signal of each received signal; rMT represents an Mth received signal of each received signal, wherein M represents the number of the antennas.

21. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the autocorrelation matrix R is generated according to a second equation: R=E[rrH]

22. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the signal sq of the qth sub-carrier is generated according to a third a third equation: sq=E[r×b(n,q)]wherein the received signal vector r and the plurality of the plurality of training bits b(n,q) of the qth sub-carrier is used for cross-correction.

23. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the detection vector vq,LMMSET is generated according to a fourth equation: vq,LMMSET=sqHR−1

24. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the temporary information bit {circumflex over (b)}(0,q) is generated according to a fifth equation: {circumflex over (b)}(0,q)=vq,LMMSETr

25. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the modified received signal vector rq is generated according to a sixth equation:

26. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the modified autocorrelation matrix Rq is generated according to a seventh equation: Rq=E[rqrqH]

27. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the modified signal sq′ of the qth sub-carrier is generated according to an eighth equation: sq′=E[rq×b(n,q)]wherein the received signal vector r and the plurality of the plurality of training bits b(n,q) of the qth sub-carrier is used for cross-correction.

28. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the modified detection vector vq,EMICT is generated according to a ninth equation: vq,EMICT=sqHRq−1

29. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the desired information bit bEMIC%(0,q) of the qth sub-carrier is generated according to an eighth equation: bEMIC%(0,q)=vq,EMICTrq

30. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 19, wherein the interference suppression process is a multistage interference cancellation.

31. The method for co-channel interference suppression in OFDM systems with multiple receiving antennas as claimed in claim 28, wherein the generation of the desired information bit bEMIC%(0,q) of the qth sub-carrier is a signal detection of a multistage interference cancellation.