Interference-weighted communication signal processing systems and methods

• US 20050135492A1
• Filed: 12/19/2003
• Published: 06/23/2005
• Est. Priority Date: 12/19/2003
• Status: Active Grant

• Current Assignee: Dong-Shen Yu, Ming Jia, Wen Tong
• Original Assignee: Rockstar Bidco LP (Rockstar Consortium Inc.)
• Inventors: Tong, Wen, Jia, Ming, Yu, Dong-Shen
• Granted Patent: US 8,027,417 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 7/0667 of delayed versions of same signal using space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0848 Joint weighting
• CPC Class Codes: H04B 7/0891 Space-time diversity rake receivers H04B1/7115; space-time decoding H04L1/0631
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

A level of interference affecting signal components of received communication signals is estimated and used to weight the signal components. The signal components in a each of a number of groups of signal components are weighted based on respective interference estimates to thereby adjust signal components for coloured interference, which may vary significantly between different groups of signal components. Each group of signal components may include a single component or components within a relatively narrow sub-band of the communication signals, such as a coherence bandwidth of an Orthogonal Frequency Division Multiplexing (OFDM) signal.

Claims

1. A communication signal receiver comprising:

an input for receiving a communication signal, the communication signal comprising signal components; and

a processor adapted to receive the communication signal from the input, to estimate interference in the communication signal, to apply a first weight based on a first interference estimate to a first signal component of the communication signal, and to apply a second weight based on a second interference estimate to a second signal component of the communication signal.

2. The communication signal receiver of claim 1, wherein the first signal component is included in a first group of signal components of the received communication signal, wherein the second signal component is included in a second group of signal components of the received communication signal, and wherein the processor is adapted to apply the first weight to each signal component of the first group of signal components and to apply the second weight to each signal component of the second group of signal components.

3. The communication signal receiver of claim 2, wherein the communication signals comprise Orthogonal Frequency Division Multiplexing (OFDM) signals, and wherein the signal components comprise sub-carrier signals.

4. The communication signal receiver of claim 3, wherein each of the first and second groups of signal components includes sub-carrier signals within a coherence bandwidth of the OFDM signals.

5. The communication signal receiver of claim 1, wherein the input is adapted for connection to an antenna system.

6. The communication signal receiver of claim 5, wherein the antenna system comprises a single antenna.

7. The communication signal receiver of claim 6, wherein the single antenna is configured to receive communication signals from a plurality of transmitting antennas.

8. The communication signal receiver of claim 5, wherein the antenna system comprises a plurality of antennas.

9. The communication signal receiver of claim 8, wherein each of the plurality of antennas is configured to receive communication signals from a plurality of transmitting antennas.

10. The communication signal receiver of claim 1, wherein the processor comprises an interference estimator for estimating interference in the communication signal and a decoder adapted for connection to the interference estimator and to the input, and wherein the input is adapted for connection to an antenna system.

11. The communication signal receiver of claim 10, wherein the processor further comprises a demodulator adapted for connection to the decoder for demodulating decoded communication signal components output from the decoder, and a multiplier connected to the demodulator and to the interference estimator for applying the first and second weights to first and second demodulated communication signal components output from the demodulator.

12. The communication signal receiver of claim 11, wherein the demodulator is selected from the group consisting of a Quadrature. Amplitude Modulation (QAM) demodulator and a Quadrature Phase Shift Keying (QPSK) demodulator.

13. The communication signal receiver of claim 10, wherein the decoder combines weighted signal components of different received communication signals to generate decoded communication signals.

14. The communication signal receiver of claim 13, wherein the decoder is selected from the group consisting of a Space-Time Transmit Diversity (STTD) decoder and a Multiple Input Multiple Output (MIMO) decoder.

15. A method of processing communication signals comprising:

receiving a communication signal, the communication signal comprising a plurality of signal components;

estimating interference affecting the received communication signal; and

applying a respective weight to at least two of the signal components based on respective interference estimates.

16. The method of claim 15, further comprising decoding the weighted signal components.

17. The method of claim 16, wherein decoding comprises combining weighted signal components of different received communication signals.

18. The method of claim 17, wherein receiving comprises receiving a plurality of communication signals.

19. The method of claim 18, wherein the communication signals comprise diversity signals in a Space-Time Transmit Diversity (STTD) system.

20. The method of claim 19, wherein the diversity signals are Orthogonal Frequency Division Multiplexing (OFDM) signals, and wherein the plurality of signal components comprises sub-carrier signals.

21. The method of claim 20, wherein the STTD system is a 2-by-2 STTD system, and wherein combining comprises combining according to

$\begin{array}{c}{\hat{s}}_1\end{array}$

( k ) = ⁢

( 

h 11 ⁡

( k ) 

2 + 

h 12 ⁡

( k ) 

2 σ

1 2 ⁡

( k ) + 

h 21 ⁡

( k ) 

2 + 

h 22 ⁡

( k ) 

2 σ

2 2 ⁡

( k ) ) ⁢

s 1 ⁡

( k ) + ⁢

h 11 * ⁡

( k ) ⁢

n 1 , 1 ⁡

( k ) + h 12 ⁡

( k ) ⁢

n 1 , 2 * ⁡

( k ) σ

1 2 ⁡

( k ) + ⁢

h 21 * ⁡

( k ) ⁢

n 2 , 1 ⁡

( k ) + h 22 ⁡

( k ) ⁢

n 2 , 2 * ⁡

( k ) σ

2 2 ⁡

( k ) ⁢

 

⁢

and s ^ 2 ⁡

( k ) = ⁢

( 

h 11 ⁡

( k ) 

2 + 

h 12 ⁡

( k ) 

2 σ

1 2 ⁡

( k ) + 

h 21 ⁡

( k ) 

2 + 

h 22 ⁡

( k ) 

2 σ

2 2 ⁡

( k ) ) ⁢

s 2 ⁡

( k ) + ⁢

h 12 * ⁡

( k ) ⁢

n 1 , 1 ⁡

( k ) + h 11 ⁡

( k ) ⁢

n 1 , 2 * ⁡

( k ) σ

1 2 ⁡

( k ) + ⁢

h 22 * ⁡

( k ) ⁢

n 2 , 1 ⁡

( k ) + h 21 ⁡

( k ) ⁢

n 2 , 2 * ⁡

( k ) σ

2 2 ⁡

( k )

where

k is a sub-carrier index;

h₁₁, h₁₂, h₂₁, and h₂₂ are elements in a 2-by-2 STTD channel matrix;

σ

₁² and σ

₂² are interference estimates for s₁ and s₂;

s₁ and s₂ are transmitted communication signals; and

n_1,1, n_1,2, n_2,1, and n_2,2 are noise signals.

22. The method of claim 21, wherein the signal combining uses hard-decision estimates of s₁(k) and s₂(k).

23. The method of claim 21, wherein estimating comprises estimating σ

₁² and σ

₂² as

${\mathrm{\sigma <br><br>}}_1^2\approx <br><br>\sum <br><br>\left(\begin{array}{c}{<br><br>\frac{{\hat{s}}_{1,1}<br><br>\left(k\right)}{\left({<br><br>h_{11}<br><br>\left(k\right)<br><br>}^2+{<br><br>h_{12}<br><br>\left(k\right)<br><br>}^2\right)}-s_1<br><br>\left(k\right)<br><br>}^2+\\ {<br><br>\frac{{\hat{s}}_{2,1}<br><br>\left(k\right)}{\left({<br><br>h_{11}<br><br>\left(k\right)<br><br>}^2+{<br><br>h_{12}<br><br>\left(k\right)<br><br>}^2\right)}-s_2<br><br>\left(k\right)<br><br>}^2\end{array}\right)$ ${\mathrm{\sigma <br><br>}}_2^2\approx <br><br>\sum <br><br>\left(\begin{array}{c}{<br><br>\frac{{\hat{s}}_{1,2}<br><br>\left(k\right)}{\left({<br><br>h_{21}<br><br>\left(k\right)<br><br>}^2+{<br><br>h_{22}<br><br>\left(k\right)<br><br>}^2\right)}-s_1<br><br>\left(k\right)<br><br>}^2+\\ {<br><br>\frac{{\hat{s}}_{2,2}<br><br>\left(k\right)}{\left({<br><br>h_{21}<br><br>\left(k\right)<br><br>}^2+{<br><br>h_{22}<br><br>\left(k\right)<br><br>}^2\right)}-s_2<br><br>\left(k\right)<br><br>}^2\end{array}\right),$

where

s_i,j (i=1, 2;

j=1,

     2) represents a communication signal received at antenna j corresponding to a transmitted communication signal s_i; and

the summations are over a coherence bandwidth of the OFDM signals.

24. The method of claim 23, wherein the estimating uses hard-decision estimates of s₁(k) and s₂(k).

25. The method of claim 16, wherein receiving comprises receiving a plurality of communication signals, and wherein the communication signals comprise received communication signals in a Multiple Input Multiple Output (MIMO) system.

26. The method of claim 25, wherein decoding comprises interference-weighted hard-decision decoding according to

$\stackrel{}{\stackrel{\rightharpoonup }{s}}$

^ = min ⁢



r ⇀

- H ⁢

 

⁢

s ⇀

σ

⇀



,

where

{right arrow over (r)} is a vector comprising the received communication signals;

H is a channel matrix of the MIMO system;

{right arrow over (s)} is a vector comprising transmitted communication signals; and

{right arrow over (σ

)} is a vector comprising interference estimates.

27. The method of claim 26, wherein applying comprises applying at least a first weight to each signal component in a first group of signal components and a second weight to each signal component in a second group of signal components, and wherein the interference estimates σ

₁² of {right arrow over (σ

)} are estimated as

$\begin{array}{c}{\mathrm{\sigma <br><br>}}_i^2=<br><br>E<br><br>\left[{<br><br>r_i-H_i<br><br>s<br><br>}^2\right]\approx <br><br>\frac{1}{N_c}<br><br>\underset{k=1}{\overset{N_c}{\sum <br><br>}}<br><br><br><br>r_i<br><br>\left({\mathrm{vN}}_c+k\right)-\\ {<br><br>\underset{j=1}{\overset{M}{\sum <br><br>}}<br><br>h_{\mathrm{ij}}<br><br>\left({\mathrm{vN}}_c+k\right)<br><br>s_j<br><br>\left({\mathrm{vN}}_c+k\right)<br><br>}^2,\end{array}$

where

r_i is the i^th element of {right arrow over (r)};

(ν

N_c+k) is a signal component index;

H_i is the i^th row of H;

ν

is an integer;

N_c is a number of signal components in each of the first and second groups of signal components;

M is a number of transmitted communication signals in the MIMO system;

h_ij is an element of H; and

s_j is the j^th element of {right arrow over (s)}.

28. The method of claim 26, wherein decoding further comprises generating first-cut hard-decision estimates of the transmitted communication signals in {right arrow over (s)} according to {right arrow over (ŝ

)}=min∥

{right arrow over (r)}−

H{right arrow over (s)}∥ and

using the first-cut hard-decision estimates for {right arrow over (s)} in the interference-weighted hard-decision decoding.

31. The method of claim 15, further comprising demodulating the plurality of signal components to generate demodulated signal components, wherein applying a respective weight comprising applying respective weights to at least two of the demodulated signal components.

32. The method of claim 31, wherein receiving comprises receiving a plurality of communication signals, wherein demodulating comprises determining a log likelihood ratio (LLR) {tilde over (Λ

)}(b₁) of each bit b₁ of a modulation symbol {right arrow over (b)} mapped to signal components of transmitted signals respectively corresponding to the plurality of signal components of the received communication signals, and wherein applying respective weights comprises applying respective weights to {tilde over (Λ

)}(b₁) with respective estimates of interference power α

.

33. The method of claim 32, further comprising decoding the received communication signals to generate decoded communication signal components, and wherein demodulating comprises demodulating the decoded signal components.

34. The method of claim 33, wherein the decoded signal components comprise a plurality of decoder output signal components {tilde over (s)}₁(k) and a plurality of decoder output signal components ŝ

₂(k), and wherein demodulating comprises determining the LLR for each decoder output signal component as

$\begin{array}{c}\widetilde{\mathrm{\Lambda <br><br>}}<br><br>\left(b_l\right)=<br><br>\underset{s_i=f<br><br>\left(b\right),b_l=0}{\min }<br><br>{<br><br>\frac{{\tilde{s}}_i<br><br>\left(k\right)}{\left({<br><br>h_1<br><br>\left(k\right)<br><br>}^2+{<br><br>h_2<br><br>\left(k\right)<br><br>}^2\right)}-s_i<br><br>\left(k\right)<br><br>}^2-\\ <br><br>\underset{s_i=f<br><br>\left(b\right),b_l=1}{\min }<br><br>{<br><br>\frac{{\tilde{s}}_i<br><br>\left(k\right)}{\left({<br><br>h_1<br><br>\left(k\right)<br><br>}^2+{<br><br>h_2<br><br>\left(k\right)<br><br>}^2\right)}-s_i<br><br>\left(k\right)<br><br>}^2\end{array}$

and weighting {tilde over (Λ

)}(b₁) with

$\mathrm{\alpha <br><br>}=\frac{{\left({<br><br>h_1<br><br>\left(k\right)<br><br>}^2+{<br><br>h_2<br><br>\left(k\right)<br><br>}^2\right)}^2}{{<br><br>h_1<br><br>\left(k\right)<br><br>}^2<br><br>{\mathrm{\sigma <br><br>}}_1^2+{<br><br>h_2<br><br>\left(k\right)<br><br>}^2<br><br>{\mathrm{\sigma <br><br>}}_2^2},$

where

k is a signal component index;

i=1, 2;

h₁ and h₂ are elements in a channel matrix;

σ

₁² and σ

₂² are interference estimates for s₁ and s₂; and

s₁ and s₂ are transmitted communication signals.

35. The method of claim 34, further comprising estimating α

according to

$\frac{1}{\mathrm{\alpha <br><br>}}\approx <br><br>\underset{i=1}{\overset{N_c}{\sum <br><br>}}<br><br>{<br><br>\frac{\widetilde{s_1}<br><br>\left({\mathrm{vN}}_c+i\right)}{{<br><br>h_1<br><br>\left({\mathrm{vN}}_c+i\right)<br><br>}^2+{<br><br>h_2<br><br>\left({\mathrm{vN}}_c+i\right)<br><br>}^2}-{\hat{s}}_1<br><br>\left({\mathrm{vN}}_c+i\right)<br><br>}^2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}$ $\frac{1}{\mathrm{\alpha <br><br>}}\approx <br><br>\underset{i=1}{\overset{N_c}{\sum <br><br>}}<br><br>{<br><br>\frac{\widetilde{s_2}<br><br>\left({\mathrm{vN}}_c+i\right)}{{<br><br>h_1<br><br>\left({\mathrm{vN}}_c+i\right)<br><br>}^2+{<br><br>h_2<br><br>\left({\mathrm{vN}}_c+i\right)<br><br>}^2}-{\hat{s}}_2<br><br>\left({\mathrm{vN}}_c+i\right)<br><br>}^2,$

where

ν

is an integer;

N_c is a number of signal components in each of the plurality of groups of signal components;

(ν

N_c+i) and (k) denote particular ones of the plurality of signal components; and

ŝ

₁(ν

N_c+i) and ŝ

₂(ν

N_c+i) are hard-decision estimates of s₁(ν

N_c+i) and ŝ

₂(ν

N_c+i).

36. The method of claim 35, wherein the received communication signals comprise signals r_i, i=1, . . . , N, wherein the decoded communication signal components comprise decoder output signals s_i, i=1, . . . , M, each comprising a plurality of decoded signal components, and wherein demodulating comprises determining the LLR as

$\begin{array}{c}\stackrel{}{\Lambda }\end{array}$

~ ⁡

( b l ) = ⁢

min s _ = f ⁡

( b _ ) , b l = 0 ⁢

∑

i = 1 N ⁢



r ⁡

( k ) i - ∑

j = 1 M ⁢

h ij ⁡

( k ) ⁢

s j ⁡

( k ) 

2 - ⁢

min s _ = f ⁡

( b _ ) , b l = 1 ⁢

∑

i = 1 N ⁢



r i ⁡

( k ) - ∑

j = 1 M ⁢

h ij ⁡

( k ) ⁢

s j ⁡

( k ) 

2

and weighting {tilde over (Λ

)}(b₁) with

$\mathrm{\alpha <br><br>}=\frac{1}{{\mathrm{\sigma <br><br>}}^2},$

where

k is a signal component index;

σ

² is an interference estimate; and

h_ij is an element of a channel matrix.

37. The method of claim 36, further comprising estimating α

according to

$\frac{1}{\mathrm{\alpha <br><br>}}={\mathrm{\sigma <br><br>}}^2\approx <br><br>\underset{k=1}{\overset{N_c}{\sum <br><br>}}<br><br>\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>{<br><br>r_i<br><br>\left({\mathrm{vN}}_c+k\right)-H_i<br><br>\left({\mathrm{vN}}_c+k\right)<br><br>\stackrel{\to <br><br>}{s}<br><br>\left({\mathrm{vN}}_c+k\right)<br><br>}^2,$

where

H_i is the i^th row of H;

ν

is an integer;

N_c is a number of signal components in each of the plurality of groups of signal components; and

{right arrow over (s)} is a vector comprising transmitted communication signals.

38. A computer program product comprising a computer-readable medium storing instructions which, when executed by a processor, perform the method of claim 15.

29. The method of claim 29, further comprising determining whether the first-cut hard-decision estimates are within a tolerance of the interference-weighted hard-decision decoding results, and if not, repeating the interference-weighted hard-decision decoding using the interference-weighted hard-decision results for {right arrow over (s)}.

30. The method of claim 29, wherein determining whether the first-cut hard-decision estimates are within a tolerance of the interference-weighted hard-decision decoding results comprises measuring the Euclidean distance between the first-cut hard-decision estimates and the interference-weighted hard-decision decoding results.

39. A communication signal receiver system for Orthogonal Frequency Division Multiplexing (OFDM) communications, comprising:

an antenna system for receiving an OFDM communication signal having a plurality of sub-carrier signal components;

means for estimating interference in the received communication signal;

means for applying respective weights to at least two of the sub-carrier signal components based on respective interference estimates; and

means for processing the weighted signal components.

40. The communication signal receiver system of claim 39, wherein the antenna system comprises at least one antenna for receiving a communication signal from at least one transmitting antenna.

41. The communication signal receiver system of claim 40, wherein the means for processing comprises means for decoding and means for demodulating.

42. The communication signal receiver system of claim 41, wherein the means for decoding combines the weighted sub-carrier signal components from a plurality of received OFDM communication signals.

43. The communication signal receiver system of claim 39, wherein each of the at least two sub-carrier signal components is included in a respective group of sub-carrier signal components within a coherence bandwidth of an OFDM communication signal, wherein each of the respective weights is a group weight, and wherein applying comprises, for each group, applying the respective group weight to each sub-carrier signal component in the group.