Communication signal equalization systems and methods

• US 20050041574A1
• Filed: 08/06/2004
• Published: 02/24/2005
• Est. Priority Date: 08/08/2003
• Status: Active Grant

• Current Assignee: Blackberry Limited
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Tong, Wen, Wu, Shiquan, Royer, Claude
• Granted Patent: US 7,319,690 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 2025/03375 Passband transmission
• CPC Class Codes: H04L 2025/03522 Frequency domain
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence

Abstract

Communication signal equalization methods and systems are disclosed. A CDMA signal having a data portion and a known portion including a known or repeated data sequence and received over a multipath communication channel represents a linear convolution between the multipath channel and a transmitted CDMA signal. A channel estimate of the communication channel is determined from the known portion, and the CDMA signal is translated into a new CDMA signal which is a cyclic convolution with the channel estimate. A frequency domain representation of the new CDMA signal is adjusted using the channel estimate to produce a frequency domain representation of an equalized signal.

Claims

1. A method of equalizing a CDMA signal received over a multipath communication channel, the CDMA signal having a data portion and a known portion comprising a known or repeated data sequence and representing a linear convolution between the multipath channel and a transmitted CDMA signal, the method comprising:

determining from the known portion a channel estimate of the communication channel;

translating the CDMA signal into a new CDMA signal which comprises a cyclic convolution with the channel estimate; and

adjusting a frequency domain representation of the new CDMA signal using the channel estimate to produce a frequency domain representation of an equalized signal.

2. The method of claim 1, wherein determining comprises determining a time domain channel estimate from the known portion, and wherein adjusting comprises performing a time domain to frequency domain conversion on the time domain channel estimate to produce a frequency domain channel estimate and adjusting the frequency domain representation of the new CDMA signal using the frequency domain channel estimate.

3. The method of claim 2, wherein translating comprises subtracting the known portion from the CDMA signal to produce the new CDMA signal.

4. The method of claim 2, wherein translating comprises replacing at least some of the known portion with a new portion which converts the CDMA signal to the new CMDA signal which is a cyclic convolution with the time domain channel estimate.

5. The method of claim 2, wherein adjusting comprises:

removing the effect of the channel as represented by the frequency domain channel estimate from the frequency domain representation of the new CDMA signal.

6. The method of claim 2, wherein translating comprises removing ISI (inter-symbol interference) effects from the CDMA signal using the time domain channel estimate to produce the new CDMA signal.

7. The method of claim 1, further comprising;

performing a frequency domain to time domain conversion on the frequency domain representation of an equalized signal to produce a time domain equalized signal.

8. The method of claim 1, wherein the known portion comprises at least one of a preceding known portion preceding the data portion and a succeeding known portion following the data portion.

9. The method of claim 1, wherein the known portion comprises at least one of pilot channel signalling and MAC (Media Access Control) channel signalling.

10. The method of claim 1, wherein the CDMA signal comprises 1024 chips, including two data blocks of 400 chips each as the data portion, preceding and succeeding MAC blocks of 64 chips each which precede and follow the data portion, respectively, and preceding and succeeding pilot blocks of 48 chips each which precede and follow the data portion, respectively, as the known portion.

11. The method of claim 4, further comprising;

generating the new portion of the CDMA signal as

$z<br><br>\left(n\right)=\underset{k=0}{\overset{n}{\sum <br><br>}}<br><br>\mathrm{spn}<br><br>\left(k\right)<br><br>\mathrm{ch}<br><br>\left(n-k\right)+\underset{k=1024-N-n}{\overset{1023}{\sum <br><br>}}<br><br>\mathrm{spn}<br><br>\left(k\right)<br><br>\mathrm{ch}<br><br>\left(1024+n-k\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{for}<br><br>\text{\hspace{1em}<br><br>}<br><br>n=0;<br><br>N-1,$

where

N is selected to cover a targeted delay spread and the interference effects;

spn(k)={spn(0),spn(1), . . . ,spn(47)} and {spn(975),spn(976), . . . ,spn(1023)} comprises pilot scrambling code segments for pilot signalling comprising the known portion; and

ch(k)=ch(0),ch((1), . . . ,ch(N) comprises the time domain channel estimate.

12. The method of claim 7, further comprising:

performing further processing on the time domain equalized signal, the further processing comprising at least one of de-scrambling and normal CDMA decoding.

13. The method of claim 2, wherein determining the time domain channel estimate comprises solving:

$\left[\begin{array}{cccc}s<br><br>\left(K_1\right)& s<br><br>\left(K_1+1\right)& \mathrm{\cdots <br><br>}& s<br><br>\left(K_1+N\right)\\ s<br><br>\left(K_1+1\right)& s<br><br>\left(K_1+2\right)& \mathrm{\cdots <br><br>}& s<br><br>\left(K_1+N+1\right)\\ \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}\\ s<br><br>\left(K_1-N\right)& s<br><br>\left(K_1-N+1\right)& \mathrm{\cdots <br><br>}& s<br><br>\left(K_2\right)\end{array}\right][\text{\hspace{1em}<br><br>}<br><br>\begin{array}{c}\mathrm{ch}<br><br>\left(N\right)\\ \mathrm{ch}<br><br>\left(N-1\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{ch}<br><br>\left(0\right)\end{array}]+<br><br>[\begin{array}{c}n<br><br>\left(K_1\right)\\ n<br><br>\left(K_1+1\right)\\ \mathrm{⋮<br><br>}\\ n<br><br>\left(K_2-N\right)\end{array}<br><br>\text{\hspace{1em}<br><br>}]=\left[\begin{array}{c}y<br><br>\left(K_1+N\right)\\ y<br><br>\left(K_1+N+1\right)\\ \mathrm{⋮<br><br>}\\ y<br><br>\left(K_2\right)\end{array}\right],$

where

s(i) comprises an i^th component of the known portion;

ch(i) comprises an i^th component of the time domain channel estimate;

n(i) comprises an i^th component of noise;

r(i) comprises an i^th component of the CDMA signal;

K₁ is a starting index of the known portion;

K₂ is an end index of the known portion; and

N is a number of components in the frequency domain channel estimate.

14. The method of claim 2, wherein adjusting comprises performing a component-wise division of the frequency domain representation of the new CDMA signal by the frequency domain channel estimate.

15. The method of claim 14, wherein the component-wise division is performed only for values of the frequency domain channel estimate which are sufficiently large so as reduce effects of amplifying noise components of the CDMA signal.

16. The method of claim 14, wherein the component-wise division is performed only for components of the frequency domain channel estimate which have values above a predefined threshold value β

.

17. The method of claim 16, further comprising:

multiplying by β

each component of the frequency domain representation of the new CDMA signal for which the corresponding component of the frequency domain channel estimate has a value below β

.

18. The method of claim 16, further comprising:

determining weights for components of the frequency domain channel estimate which have values less than β

;

multiplying by a respective determined weight each component of the frequency domain representation of the new CDMA for which the corresponding component of the frequency domain channel estimate has a value below β

.

19. The method of claim 18, wherein determining weights comprises determining the weights ω

as

ω

=(E^*_ψ

E_ψ

)<sup>−

1</sup>E^*_ψ

d,

where

$d=\left\{d<br><br>\left(m\right)\right\}=\mathrm{spn}<br><br>\left(m\right)-\underset{k\in <br><br>\mathrm{\Omega <br><br>}}{\overset{\text{\hspace{1em}<br><br>}}{\sum <br><br>}}<br><br>\frac{\mathrm{rf}<br><br>\left(k\right)}{\mathrm{cf}<br><br>\left(k\right)}<br><br>\exp <br><br>\left(\mathrm{jmk}<br><br>\frac{2<br><br>\mathrm{\pi <br><br>}}{b}\right);<br><br>$

m=0,1, . . . ,a_i

a is a length of the known portion;

b is a length of a portion of the CDMA signal to be equalized;

spn(m) comprises an m^th component of the known portion;

rf(k) comprises a k^th component of the frequency domain representation of the new CDMA signal;

cf(k) comprises a k^th component of the frequency domain channel estimate;

E_ψ

comprises a matrix formed by both rf(k) and

$\exp <br><br>\left(\mathrm{jmk}<br><br>\frac{2<br><br>\mathrm{\pi <br><br>}}{b}\right)$

for kε

ψ and

m=0,1, . . . ,a, and ψ

comprises indices of the components of the frequency domain channel estimate having values less than β

.

20. The method of claim 1, wherein the data portion of the CDMA signal comprises frequency domain components.

21. A computer program product comprising instructions which when executed perform the method of claim 1.

22. The method of claim 1, implemented at a receiver, further comprising:

multiplexing the data portion and the known portion into the CDMA signal at a transmitter; and

transmitting the CDMA signal from the transmitter to the receiver.

23. The method of claim 22, wherein multiplexing comprises;

assisting in translating from the linear convolution to the cyclic convolution at the receiver end by;

generating frequency domain components from information to be transmitted;

performing a frequency domain to time domain conversion on the frequency domain components to produce time domain components; and

multiplexing the time domain components into the CDMA signal to form the data portion.

24. The method of claim 23, wherein multiplexing comprises;

generating frequency domain components from information to be transmitted; and

multiplexing the frequency domain components into the CDMA signal to form the data portion.

25. A communication signal processing method comprising:

multiplexing a data portion and a known portion comprising a known or repeated data sequence into a CDMA signal; and

outputting the CDMA signal for transmission to a receiver over a multipath communication channel and equalization at the receiver by determining from the known portion a channel estimate of the communication channel, translating the CDMA signal into a new CDMA signal which comprises a cyclic convolution with the channel estimate, and adjusting a frequency domain representation of the new CDMA signal using the channel estimate to produce a frequency domain representation of an equalized signal.

26. The method of claim 25, wherein multiplexing comprises:

multiplexing frequency domain components representing the data into the CDMA signal.

27. A system for equalizing a portion of a CDMA signal received over a multipath communication channel, the CDMA signal having a data portion and a known portion comprising a known or repeated data sequence and representing a linear convolution between the multipath channel and a transmitted CDMA signal, the system comprising:

an input; and

a processor configured to receive the CDMA signal from the input, to determine from the known portion a channel estimate of the communication channel, to translate the CDMA signal into a new CDMA signal which comprises a cyclic convolution with the channel estimate, and to adjust a frequency domain representation of the new CDMA signal using the channel estimate to produce a frequency domain representation of an equalized signal.

28. The system of claim 27, wherein the processor is configured to determine the channel estimate by determining a time domain channel estimate from the known portion, to perform a time domain to frequency domain conversion on the time domain channel estimate to produce a frequency domain channel estimate, and to adjust the frequency domain representation of the new CDMA signal using the frequency domain channel estimate.

29. The system of claim 28, wherein the processor implements a transform engine for performing the time domain to frequency domain conversion.

30. The system of claim 28, wherein the processor is further configured to translate the CDMA signal by subtracting the known portion from the CDMA signal to produce the new CDMA signal.

31. The system of claim 28, wherein the processor is further configured to translate the CDMA signal by replacing at least some of the known portion with a new portion which converts the CDMA signal to the new CMDA signal which is a cyclic convolution with the time domain channel estimate.

32. The system of claim 28, wherein the processor is configured to adjust the frequency domain representation of the new CDMA signal by removing the effect of the channel as represented by the frequency domain channel estimate from the frequency domain representation of the new CDMA signal.

33. The system of claim 28, wherein the processor is further configured to translate the CDMA signal by removing ISI (inter-symbol interference) effects from the CDMA signal using the time domain channel estimate to produce the new CDMA signal.

34. The system of claim 27, wherein the processor is further configured to perform a frequency domain to time domain conversion on the frequency domain representation of an equalized signal to produce a time domain equalized signal.

35. The system of claim 27, wherein the known portion comprises at least one of a preceding known portion preceding the data portion and a succeeding known portion following the data portion.

36. The system of claim 27, wherein the CDMA signal comprises an 1xEV-DO signal.

37. The system of claim 27, further comprising:

a memory,

wherein the processor is further configured to store a portion of the CDMA signal in the memory.

38. The system of claim 31, wherein the processor is further configured to generate the new portion of the CDMA signal as

$z$

( n ) = ∑

k = 0 n ⁢

spn ⁡

( k ) ⁢

ch ⁡

( n - k ) + ∑

k = 1024 - N + n 1023 ⁢

spn ⁡

( k ) ⁢

ch ⁡

( 1024 + n - k ) ⁢

 

⁢

for ⁢

 

⁢

n = 0 ;

N - 1 ,

where

N is selected to cover a targeted delay spread and the interference effects;

spn(k)={spn(0), spn(1), . . . ,spn(47)} and {spn(975),spn(976), . . . , spn(1023)} comprises pilot scrambling code segments for pilot signalling comprising the known portion; and

ch(k)=ch(0),ch(1), . . . ,ch(N) comprises the time domain channel estimate.

39. The system of claim 28, wherein the processor is configured to determine the time domain channel estimate by solving:

$\left[\begin{array}{cccc}s<br><br>\left(K_1\right)& s<br><br>\left(K_1+1\right)& \mathrm{\cdots <br><br>}& s<br><br>\left(K_1+N\right)\\ s<br><br>\left(K_1+1\right)& s<br><br>\left(K_1+2\right)& \mathrm{\cdots <br><br>}& s<br><br>\left(K_1+N+1\right)\\ \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}& \mathrm{\cdots <br><br>}\\ s<br><br>\left(K_2-N\right)& s<br><br>\left(K_2-N+1\right)& \mathrm{\cdots <br><br>}& s<br><br>\left(K_2\right)\end{array}\right][\text{\hspace{1em}<br><br>}<br><br>\begin{array}{c}\mathrm{ch}<br><br>\left(N\right)\\ \mathrm{ch}<br><br>\left(N-1\right)\\ \mathrm{⋮<br><br>}\\ \mathrm{ch}<br><br>\left(0\right)\end{array}]+<br><br>[\begin{array}{c}n<br><br>\left(K_1\right)\\ n<br><br>\left(K_1+1\right)\\ \mathrm{⋮<br><br>}\\ n<br><br>\left(K_2-N\right)\end{array}<br><br>\text{\hspace{1em}<br><br>}]=\left[\begin{array}{c}y<br><br>\left(K_1+N\right)\\ y<br><br>\left(K_1+N+1\right)\\ \mathrm{⋮<br><br>}\\ y<br><br>\left(K_2\right)\end{array}\right],$

where

s(i) comprises an i^th component of the known portion;

ch(i) comprises an i^th component of the time domain channel estimate;

n(i) comprises an i^th component of noise;

r(i) comprises an i^th component of the CDMA signal;

K₁ is a starting index of the known portion;

K₂ is an end index of the known portion; and

N is a number of components in the frequency domain channel estimate.

40. The system of claim 31, wherein the processor is further configured to adjust the frequency domain representation of the new CDMA signal by performing a component-wise division of the frequency domain representation of the new CDMA signal by the frequency domain channel estimate.

41. The system of claim 40, wherein the processor is further configured to perform the component-wise division only for components of the frequency domain channel estimate which have values above a predefined threshold value.

42. The system of claim 41, wherein the processor is further configured to multiply by the predefined threshold value each component of the frequency domain representation of the new CDMA signal for which the corresponding frequency domain channel estimate has a value below the predefined threshold value.

43. The system of claim 41, wherein the processor is further configured to multiply by a respective weight each frequency domain representation of the new CDMA signal for which the corresponding component of the frequency domain channel estimate which has a value below the predefined threshold value.

44. The system of claim 27, implemented at a receiver in a communication system, the communication system further comprising:

a transmitter comprising an input and a processor configured to receive from the input data for transmission to the receiver, to multiplex the data and the known or repeated data sequence to form the data portion and the known portion of the CDMA signal, and to output the CDMA signal for transmission from the transmitter to the receiver.

45. The system of claim 44, wherein the processor is further configured to assisting in translating from the linear convolution to the cyclic convolution at the receiver end by generating frequency domain components from the data, and to multiplex the frequency domain components to form the data portion of the CDMA signal.

46. A communication signal processing system comprising:

an input for receiving data to be transmitted; and

a processor configured to receive the data from the input, to multiplex the data and a known or repeated data sequence into a CDMA signal to form a data portion and a known portion, and to output the CDMA signal for transmission to a receiver over a multipath communication channel and equalization at the receiver by determining from the known portion a channel estimate of the communication channel, translating the CDMA signal into a new CDMA signal which comprises a cyclic convolution with the channel estimate, and adjusting a frequency domain representation of the new CDMA signal using the channel estimate to produce a frequency domain representation of an equalized signal.

47. The system of claim 46, wherein the processor is configured to multiplex the data into the CDMA signal by multiplexing frequency domain components representing the data into the CDMA signal.

48. A CDMA communication system comprising:

communication equipment comprising a processor configured to receive from an input data to be transmitted, to multiplex the data and a known or repeated data sequence into a CDMA signal to form a data portion and a known portion, and to output the CDMA signal for transmission; and

communication equipment comprising a processor configured to receive the CDMA signal over a multipath communication channel, to determine from the known portion a channel estimate of the communication channel, to translate the CDMA signal into a new CDMA signal which comprises a cyclic convolution with the channel estimate, and to adjust a frequency domain representation of the new CDMA signal using the channel estimate to produce a frequency domain representation of an equalized signal.

49. The communication system of claim 48, wherein at least one network element of the communication system comprises the communication equipment comprising a processor configured to receive from an input data to be transmitted.

50. The communication system of claim 48, wherein at least one network element of the communication system comprises the communication equipment comprising a processor configured to receive the CDMA signal.

51. The communication system of claim 48, wherein at least one communication terminal adapted for operation in the communication system comprises the communication equipment comprising a processor configured to receive the CDMA signal.

52. The communication system of claim 48, wherein at least one communication terminal adapted for operation in the communication system comprises the communication equipment comprising a processor configured to receive from an input data to be transmitted.