Apparatus and method for erasure detection and soft-decision decoding in cellular system receiver

• US 20050278609A1
• Filed: 11/29/2004
• Published: 12/15/2005
• Est. Priority Date: 06/09/2004
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kim, Yun-Hee, Lee, Sang-Hyun, Kim, Kwang-Soon, Ahn, Jae-Young
• Granted Patent: US 7,453,959 B2
• Time in Patent Office: Days
• US Class Current: 714/780
• CPC Class Codes: H03M 13/11 using multiple parity bits
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/31 combining coding for error detection or correction and efficient use of the spectrum without error detection or correction H03M5/14 , H03M5/145
• CPC Class Codes: H03M 13/3723 using means or methods for the initialisation of the decoder
• CPC Class Codes: H03M 13/455 using a set of erasure patterns or successive erasure decoding, e.g. generalized minimum distance [GMD] decoding
• CPC Class Codes: H03M 13/612 Aspects specific to channel or signal-to-noise ratio estimation H03M13/63 takes precedence
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Dislosed is an apparatus and method for erasure detection and soft-decision decoding in a cellular system receiver. In the present invention, a complex channel gain and a noise variance of a received symbol from a cellular system transmitter are estimated, and an erasure symbol (a symbol with high power interference) is detected by comparing a threshold value according to the estimated complex channel gain or noise variance with power of the received symbol. Log-likelihood ratios corresponding to constituent bits of the detected erasure symbols are allowed to be 0, and the log-likelihood ratios of the constituent bits of the other received symbols are calculated. A soft-decision decoding operation of received bits is performed with the calculated log-likelihood ratios.

Claims

1. An apparatus for erasure detection and soft-decision decoding in a cellular system receiver for decoding a code block received from a cellular system transmitter, comprising:

a channel gain and noise variance estimator for estimating a complex channel gain and a noise variance of the received code block;

an erasure detector for detecting an erasure symbol (a received symbol with high power interference) by comparing a threshold value based on the estimated complex channel gain or the noise variance with power of the received symbol;

a soft-decision decoding metric calculator for setting log-likelihood ratios of constituent bits of the erasure symbols to be 0 and computing the log-likelihood ratios of the constituent bits of other received symbols; and

a soft-decision channel decoder for decoding the received code block with the calculated log-likelihood ratios.

2. The apparatus of claim 1, wherein the erasure detector detects the received symbol as the erasure symbol when the power of the received symbol is greater than the threshold value.

3. The apparatus of claim 2, wherein the threshold value includes a constant multiple of the power of the fading channel gain of the received symbol.

4. The apparatus of claim 2, wherein the threshold value includes a value which is represented by a sum of the power of the fading channel gain of the received symbol and a constant multiple of an average noise variance.

5. The apparatus of claim 1, wherein the channel gain and noise variance estimator calculates an average noise variance in a physical data channel and estimates the noise variance, and the average noise variance is given by the equation

${\sigma }_{}^{}$

w , a 2 = 1 L p ⁢

∑

p ∈

PILOT ⁢



r p - h ^ p ⁢

x p 

2

where r_p denotes a pilot receive symbol, x_p denotes a pilot transmission symbol, ĥ

_p denotes a complex channel fading gain which is estimated with a pilot channel through filtering or interpolating the tentative pilot channel estimates, and L_p denotes the number of the pilot symbols in a slot.

6. The apparatus of claim 1, wherein the channel gain and noise variance estimator calculates the average noise variance in the physical data channel and estimates the noise variance, and the average noise variance is given by the equation

${\sigma }_{}^{}$

w , a 2 = 1 L p ⁢

∑

l = 0 L - 1 ⁢



r l - h ^ l ⁢

x ^ l 

2

where r_l denotes a received symbol in a physical channel to be denoted, ĥ

_l denotes a channel estimate of the I^th data of a receive physical channel estimated by the pilot channel, {circumflex over (x)}_l, is given by an estimate of a transmission symbol estimated from r_l/ĥ

_l, and L denotes the number of the receive symbols configuring the physical channel.

7. The apparatus of claim 5, wherein the soft-decision decoding metric calculator uses the calculated average noise variance as the noise variance of the received symbols in computing the log-likelihood ratio.

8. The apparatus of claim 1, further comprising a noise variance re-estimate unit for re-estimating the noise variance by using other received symbols which are not detected as the erasure symbol.

9. The apparatus of claim 8, wherein the erasure detector detects the erasure symbols by comparing a new threshold value based on the re-estimated noise variance with the power of the received symbol.

10. The apparatus of claim 9, wherein the re-estimated noise variance is given by the equation

${\sigma }_{}^{}$

w , u 2 = 1 

U 

⁢

∑

l ∈

U ⁢

( 

r 1 

2 - 

h ^ 1 

2 )

in which U denotes an index set of the receive symbols which are not detected as the erasure symbol, |U| denotes the total number of elements of the set of U, |r_l|² denotes the receive power of the received symbol, and ĥ

₁ denotes the complex channel gain estimate.

11. The apparatus of claim 9, wherein the re-estimated noise variance is given by the equation

${\sigma }_{}^{}$

w , u 2 = 1 

U 

⁢

∑

l ∈

U ⁢



r 1 - h ^ l ⁢

x ^ l 

2

in which U denotes an index set of the receive symbols which are not detected as the erasure symbol, |U| denotes the total number of elements of the set of U, r_l denotes the received symbol, ĥ

₁ denotes the complex channel gain estimate, and {circumflex over (x)}_l denotes the estimate of the transmission symbol.

12. The apparatus of claim 8, wherein the soft-decision decoding metric calculator uses the re-estimated noise variance as the noise variance of the received symbols in computing the log-likelihood ratio.

13. The apparatus of claim 9, wherein the threshold value includes a value which is represented by a sum of the power of complex channel gain of the received symbol and a constant number multiple of an average noise variance.

14. A method for erasure detection and soft-decision decoding in a cellular system receiver for decoding a received code block from a cellular system transmitter, comprising:

a) estimating complex channel gains and a noise variance of the received code block;

b) detecting an erasure symbol (a received symbol with high power interference) by comparing a threshold value based on the estimated complex channel gain or the noise variance with power of the received code block;

c) establishing log-likelihood ratios of constituent bits of the detected erasure symbols to be 0 and computing the log-likelihood ratios of the constituent bits of other received symbols; and

d) decoding the received code block with the calculated log-likelihood ratios.

15. The method of claim 14, further comprising e) re-estimating the noise variance by using other received symbols which are not detected as the erasure symbol.

16. The method of claim 14, wherein b) comprises detecting the received symbol as the erasure symbol when the power of the received symbol is greater than the first threshold value.

17. The method of claim 15, wherein b) comprises detecting the erasure symbols by comparing a new threshold value based on the re-estimated noise variance with the power of the received symbol.

18. The method of claim 17, wherein c) uses the re-estimated noise variance as the noise variance of the received symbols in computing the log-likelihood ratios.

19. The method of claim 14, wherein c) uses an average noise variance of the received symbol as the noise variance of the received symbols in computing the log-likelihood ratios.