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US6549585B2
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Combined interference cancellation and maximum likelihood decoding of space-time block codes
Assignee: AT&T Inc
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Filing: 2001-01-22
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Granted: 2003-04-15
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Expires: 2021-01-22
Abstract
Abstract Block-encoded transmissions of a multi-antenna terminal unit are effectively detected in the presence of co-channel interfering transmissions from other multi-antenna terminal units, when the base station has a plurality of antennas, and interference cancellation is combined with maximum likelihood decoding. The signals received in one base station antenna are employed in processing the signals received in a second base station antenna so as to cancel the signals of one terminal unit, while decoding the signals transmitted by the other terminal unit. Zero-forcing and MMSE approaches are presented. In another embodiment of this invention the basic decoding approach is used to obtain an initial estimate for the symbols from each terminal. Assuming that the signals of the first terminal unit has been decoded correctly, the receiver employs this initial decoded signal of the first terminal unit to cancel their contribution to the signals received at the base station antennas while decoding the signals of the second terminal unit. This process is then repeated assuming that the signals of the second terminal unit has been decoded correctly, the receiver employs this initial decoded signal of the second terminal unit to cancel their contribution to the signals received at the base station antennas while decoding the signals of the first terminal unit. The above disclosed techniques are viable for any number K of terminal units concurrently transmitting over a given channel, where each terminal unit is using a space-time block code with N transmit antennas, and a base station has at least K receive antennas.
Inventors
- 👤 Ayman F. Naguib
- 👤 Nambirajan Seshadri
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 15:11
CPC Classifications
H; H04; H04B; H04B1/00; H04B1/69; H04B1/707; H04B1/7097; H04B1/7103; H04B1/7105; H04B1/71055; H04B1/71057; H04B7/00; H04B7/02; H04B7/04; H04B7/06; H04B7/0613; H04B7/0667; H04B7/0669; H04B7/12; H04L; H04L1/00; H04L1/02; H04L1/04; H04L1/06; H04L1/0618; H04L1/08; H04B7/08; H04B7/0837; H04B7/0842; H04B7/0845; H04B7/0848; H04B7/0857; Y; Y02; Y02D; Y02D30/00; Y02D30/70
Claims Analysis
Total Claims: 26
Claim 1
Independent Claim
105 words
A method for decoding signals received at M receiving antennas, where M≧2, from K synchronized terminal units, each of which employs N transmitting antennas, comprising the steps of: processing said M signals, received over L time intervals, where L is an integer, with signals having components related to channel coefficients between transmitting points of said terminal units and an input interface, to detect signals transmitted from each of said K terminal units by canceling interference from K−1 of said terminal units, where M and K are integers such that M≧2 and K≦M, and identifying probable signals transmitted by said terminal units through maximum likelihood detection.
Claim 2
Independent Claim
105 words
A method for decoding signals received at M receiving antennas, where M≧2, from K synchronized terminal units, each of which employs N transmitting antennas, comprising the steps of: processing said M signals, received over L time intervals, where L is an integer, with signals having components related to channel coefficients between transmitting points of said terminal units and an input interface, to detect signals transmitted from each of said K terminal units by canceling interference from K−1 of said terminal units, where M and K are integers such that M≧2 and K≦M, and identifying probable signals transmitted by said terminal units through maximum likelihood detection.
Claim 3
Dependent Claim
13 words
The method of claim 1 where transmissions of said terminal units are synchronized.
Claim 4
Dependent Claim
26 words
The method of claim 1 where each of the K terminal units employs at least two transmitting antennas, and said input interface includes M receiving antennas.
Claim 5
Dependent Claim
31 words
The method of claim 1 where each of the K terminal units employs N transmitting antennas, where N is greater than 1 , and said input interface includes M receiving antennas.
Claim 6
Dependent Claim
59 words
The method of claim 4 , where said interference canceling involves algebraic operations carried out on said M received signals with said signals having components related to channel coefficients between transmitting points of said terminal units, to form a plurality of signals, each of which is substantially unrelated to signals sent by all but one of the terminal units.
Claim 7
Dependent Claim
10 words
The method of claim 4 where said K=M=2 and 1≦N≦2.
Claim 8
Dependent Claim
170 words
The method of claim 6 where said processing comprises multiplying said vector of received signals by conditioning matrix [ I - G 1 G 2 - 1 - H 2 H 1 - 1 I ] , where H 1 = [ h 11 h 12 h 12 * - h 11 * ] , G 1 = [ g 11 g 12 g 12 * - g 11 * ] , H 2 = [ h 21 h 22 h 22 * - h 21 * ] , G 2 = [ g 21 g 22 g 22 * - g 21 * ] , I is the diagonal matrix, h ij is a channel coefficient estimate between a transmitting antenna i of a first transmitting unit and a receive antenna j of said M receiving antennas, and g ij is a channel coefficient estimate between a transmitting antenna i of a second transmitting unit and a receive antenna j of said M receiving antennas.
Claim 9
Dependent Claim
7 words
The method of claim 7 where L=2.
Claim 10
Dependent Claim
58 words
The method of claim 7 where said maximum likelihood detection minimizes a metric ∥{tilde over (r)} 1 −{tilde over (H)}·ê∥ 2 over all potential code vectors ĉ, where {tilde over (r)} 1 is one of said plurality of signals formed by said step of multiplying, and {tilde over (H)}=H 1 −G 1 G 2 −1 H 2 .
Claim 11
Dependent Claim
14 words
The method of claim 9 where said maximum likelihood detection develops an uncertainty measure.
Claim 12
Dependent Claim
23 words
The method of claim 10 where the uncertainty measure is given by Δ c ∥{tilde over (r)} 1 −{tilde over (H)}·ĉ∥ 2 .
Claim 13
Dependent Claim
294 words
The method of claim 6 where said processing executes a subroutine ZF.DECODE(r x ,r y ,H x ,H y ,G x ,G y ) which returns an output ĉ by executing the following calculations {tilde over (r)}=r x −G x G y −1 r y , {tilde over (H)}=H x −G x G y −1 H y , c ^ = argmin c ∈ C r ~ - H ~ · c x 2 , where r x is the first argument of the ZF.DECODE subroutine and corresponds to a vector of signals received over said L time intervals at receiving antenna x, r y is the second argument of the ZF.DECODE subroutine and corresponds to a vector of signals received over said L time intervals at receiving antenna y, H x is the third argument of the ZF.DECODE subroutine and corresponds to a matrix comprising channel coefficients between transmitting antenna x of a first terminal unit and said M receiving antennas, H y is the fourth argument of the ZF.DECODE subroutine and corresponds to a matrix comprising channel coefficients between transmitting antenna y of said first terminal unit and said M receiving antennas, G x is the fifth argument of the ZF.DECODE subroutine and corresponds to a matrix comprising channel coefficients between transmitting antenna x of a second terminal unit and said M receiving antennas, G y is the sixth argument of the ZF.DECODE subroutine and corresponds to a matrix comprising channel coefficients between transmitting antenna y of said second terminal unit and said M receiving antennas, and ĉ is a selected code vector c from a set of code vectors C as the code transmitted by the terminal related to the second and third arguments of the ZF.DECODE subroutine.
Claim 14
Dependent Claim
63 words
The method of claim 12 where said processing comprises executing the ZF.DECODE subroutine a first time with argument (r 1 , r 2 , H 1 , H 2 , G 1 , G 2 ),and executing the ZF.DECODE subroutine a second time with argument (r 2 , r 1 , H 2 , H 1 , G 2 , G 1 ).
Claim 15
Dependent Claim
31 words
The method of claim 12 where said subroutine ZF.DECODE also returns an uncertainty measure output Δ c by carrying out the calculation Δ c =∥{tilde over (r)}−{tilde over (H)}·ĉ∥ 2 .
Claim 16
Dependent Claim
199 words
The method of claim 14 where said processing comprises the steps of: executing the ZF.DECODE subroutine a first time, with argument (r 1 , r 2 , H 1 , H 2 , G 1 , G 2 ), to obtain a first version of a probable vector signal of a first terminal unit, ĉ 0 , and a measure of uncertainty, Δ c,0 ; obtaining a first version of a probable vector signal of a second terminal unit, ŝ 0 , and a measure of uncertainty Δ s,0 ; executing the ZF.DECODE subroutine a second time, with argument (r 2 , r 1 , G 2 , G 1 , H 2 , H 1 ), to obtain a second version of a probable vector signal of the second terminal unit, ŝ 0 , and a measure of uncertainty, Δ s,1 ; obtaining a second version of a probable vector signal of a first terminal unit, ĉ 0 , and a measure of uncertainty Δ c,1 ; selecting said first version of said probable vector signals if (Δ c,0 +Δ s,0 )<(Δ x,1 +Δ s,1 ), and selecting said second version of said probable vector signal based otherwise.
Claim 17
Dependent Claim
118 words
The method of claim 1 where M≧2 and K≧2, and where said processing comprises the steps of: combining said M received signals for form a signal that is essentially independent of transmissions of all but one of the terminal units, performing a maximum likelihood detection to identify a probably signal vector transmitted by said one of the terminal units, modifying remaining ones of said M received signals to account for contribution of the probable signals vector, and returning to said step of combining as long as there is a terminal unit whose transmission is to be detected, to select another one of said terminal units whose signal is to be detected with said step of maximum likelihood detection.
Claim 18
Dependent Claim
398 words
The method of claim 1 where M≧2 and K≧2, and where said processing comprises executing a subroutine ( c ^ , Δ ) = G_ZDECODE ( { r m } 1 ≤ m ≤ M , { H km } 1 ≤ k ≤ K , 1 ≤ m ≤ M ) { r m ( 0 ) = r m , 1 ≤ m ≤ M H k , m ( 0 ) = H k , m , 1 ≤ m ≤ M , 1 ≤ k ≤ K for j = 1 → K - 1 M j = M - j , K j = K - j for i = 1 → M j r i ( j ) = r i ( j - 1 ) - H j , i ( j - 1 ) ( H K j , M j ( j - 1 ) ) + r M j ( j - 1 ) H k , i ( j ) = H k , i ( j - 1 ) - H K j , m ( j - 1 ) ( H K j , M j ( j - 1 ) ) + r k , M j ( j - 1 ) , 1 ≤ k ≤ K j end end c ^ = argmin c ^ 1 ∈ C ∑ m = 1 M - K + 1 r m ( K - 1 ) - H 1 , m ( K - 1 ) · c ^ 2 Δ = ∑ m = 1 M - K + 1 r m ( K - 1 ) - H 1 , m ( K - 1 ) · c ^ 2 } where r m (a) is a received signal at antenna m, as modified in step (a); H k,m (a) is a matrix of channel coefficients between terminal unit k and receive antenna m, at step a; and (H k,m (a) ) + is the generalized inverse of H k,m (a) .
Claim 19
Dependent Claim
35 words
The method of claim 1 where said processing form a vector of signals from said M signals and said processing includes pre-multiplying said vector by a preconditioning matrix having components related to said channel coefficients.
Claim 20
Dependent Claim
20 words
The method of claim 18 where said components of the conditioning matrix are related to estimates of said channel coefficients.
Claim 21
Dependent Claim
27 words
The method of claim 1 , further comprising the step of: post-processing signals developed in said of identifying, to create detected signals adapted for delivery to users.
Claim 22
Dependent Claim
162 words
A detector responsive to M received signals, where M≧2 from a plurality of terminal units, for canceling interference from K of said terminal units, where K N, comprising: a processor for transforming said M received signals through algebraic operations involving data related to channel coefficients between transmitting antennas of said terminal units and said M received signals, to form a plurality of signals, to each of which is substantially unrelated to signals sent by all but one of the terminal units, where M, N, and K are positive integers, and to perform maximum likelihood detection calculations on said plurality of signals; a memory coupled to said processor for storing information for controlling said processor; and a subroutine stored in said memory and executed by said processor, which subroutine performs said transforming of said M received signals, where each execution of said subroutine develops one of said signals that is substantially unrelated to signals sent by all but one of the terminal units.
Claim 23
Dependent Claim
162 words
A detector responsive to M received signals, where M≧2 from a plurality of terminal units, for canceling interference from K of said terminal units, where K N, comprising: a processor for transforming said M received signals through algebraic operations involving data related to channel coefficients between transmitting antennas of said terminal units and said M received signals, to form a plurality of signals, to each of which is substantially unrelated to signals sent by all but one of the terminal units, where M, N, and K are positive integers, and to perform maximum likelihood detection calculations on said plurality of signals; a memory coupled to said processor for storing information for controlling said processor; and a subroutine stored in said memory and executed by said processor, which subroutine performs said transforming of said M received signals, where each execution of said subroutine develops one of said signals that is substantially unrelated to signals sent by all but one of the terminal units.
Claim 24
Dependent Claim
16 words
A The detector of claim 21 where said subroutine is executed not less than K times.
Claim 25
Dependent Claim
166 words
The detector of claim 21 where said data is [ I - G 1 G 2 - 1 - H 2 H 1 - 1 I ] , where H 1 = [ h 11 h 12 h 12 * - h 11 * ] , G 1 = [ g 11 g 12 g 12 * - g 11 * ] , H 2 = [ h 21 h 22 h 22 * - h 21 * ] , G 2 = [ g 21 g 22 g 22 * - g 21 * ] , I is the diagonal matrix, h ij is a channel coefficient estimate between a transmitting antenna i of a first transmitting unit and a receive antenna j of said M receiving antennas developing said M received signals, and g ij is a channel coefficient estimate between a transmitting antenna i of a second transmitting unit and a receive antenna j of said M receiving antennas.
Claim 26
Dependent Claim
18 words
The detector of claim 23 where said processor also performs maximum likelihood detection on said plurality of signals.
References Cited (Backward Citations)
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