Multi-user detection method

• US 20020072336A1
• Filed: 08/24/2001
• Published: 06/13/2002
• Est. Priority Date: 09/14/2000
• Status: Active Grant

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubushi Denki Kabushiki Kaisha
• Inventors: Mottier, David
• Granted Patent: US 7,031,671 B2
• Time in Patent Office: Days
• US Class Current: 455/101
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers

Abstract

Multi-user detection method with elimination of interference between users, each user transmitting modulated data in the form of symbols on a transmission channel, each transmission channel (k) comprising at least one propagation path (i) and each propagation path arriving at an array of reception antennae (l) according to a direction of arrival (θ_i,k), the method comprising at least one sequence of steps for each user (k), each sequence comprising:

(a) a reception step (600_k,700_k,800_k,800,900) decomposing each antenna signal into filtered signals (x_l,i,k) issuing from the different paths (i) of the said user (k) and combining the said filtered signals by means of a first plurality of coefficients (b_l,i,k, c_i,k) in order to form an estimation (z_k) of the signal transmitted by the user;

(b) a step of estimating (670_k,770_k,870_k,870,970) the contribution ((x_l,k)l=1 . . . L) of the user to the signals received by the different antennae from the said estimation of the signal transmitted and a second plurality of coefficients (u_i,k, w_l,i,k ) obtained from the said first plurality of coefficients;

(c) a step of eliminating interference (680_k′,780_k,880_k,880,980) subtracting from the antenna signals the contribution estimated at step (b) in order to obtain cleaned antenna signals;

the cleaned antenna signals supplied by at least one first sequence being used as antenna signals by at least one second sequence.

Claims

1. Multi-user detection method with elimination of interference between users, each user transmitting modulated data in the form of symbols on a transmission channel, each transmission channel (k) comprising at least one propagation path (i) and each propagation path arriving at an array of reception antennae ( t ) according to a direction of arrival (θ

_i,k), the method comprising at least one sequence of steps for each user (k), characterised in that each sequence comprises;

(a) a reception step (600_k,700_k,800_k,800,900) decomposing each antenna signal into filtered signals (x_l,i,k) issuing from the different paths (i) of the said user (k) and combining the said filtered signals by means of a first plurality of coefficients (b_l,i,k,c_i,k) in order to form an estimation (z_k) of the signal transmitted by the user;

(b) a step of estimating (670_k,770_k,870_k,870,970) the contribution ((x_l,k)l=1 . . . L) of the user to the signals received by the different antennae from the said estimation of the signal transmitted and a second plurality of coefficients (u_i,k,w_l,i,k) obtained from the said first plurality of coefficients;

(c) a step of eliminating interference (680_k′

,780_k,880_k,880,980) subtracting from the antenna signals the contribution estimated at step (b) in order to obtain cleaned antenna signals;

the cleaned antenna signals supplied by at least one first sequence being used as antenna signals by at least one second sequence.

2. Multi-user detection method according to claim 1, characterised in that the first plurality of coefficients comprises a first set of complex coefficients (b_l,i,k) and a second set of complex coefficients (c_i,k) and in that the filtered signals (x_l,i,k,) are subjected to a channel formation step (420_k) in order to form signals of paths (y_i,k) by means of the said first set, the said path signals then being linearly combined (440_k) by means of the said second set in order to supply the said estimation (z_k) of the signal transmitted, the coefficients of the first set being adapted so as to minimise a plurality of first error signals (ε

′

_i,k) between a reference value (q_k) of the transmitted signal and the said path signals (y_i,k), the coefficients of the said second set being adapted so as to minimise a second error signal (ε

″

_k) between the said estimation (z_k) and the said reference value.

3. Multi-user detection method according to claim 2, characterised in that the said second plurality (w_l,i,k,u_i,k) of coefficients comprises a first set of complex coefficients (w_l,i,k) and a second set of complex coefficients (u_i,k), the coefficients (w_l,i,k) of the said first set of the second plurality being obtained from the arguments of the coefficients (b_l,i,k) of the first set of the first plurality and the coefficients (u_i,k) of the said second set of the second plurality being obtained from coefficients (c_i,k) of the said second set of the first plurality.

4. Multi-user detection method according to claim 3, characterised in that the coefficients (u_i,k) of the said second set of the second plurality are obtained by conjugation of the coefficients (c_i,k) of the second set of the first plurality.

5. Multi-user detection method according to claim 3 or 4, characterised in that the coefficients (w_l,i,k) of the said first set of the second plurality are obtained from a linear regression on the arguments of the coefficients (b_l,i,k) of the first set of the first plurality.

6. Multi-user detection method according to one of claims 2 to 5, characterised in that, at the first sequence,

the coefficients (b_l,i,k) of the first set of the first plurality are initialised by b_l,i,k(0)=δ

(l−

l₀),∀

i where δ

is the Dirac symbol, l₀ is an antenna number;

and in that the coefficients (c_i,k) of the second set of the first plurality are initialised by c_i,k(0)=c,∀

i where c is a given complex coefficient.

7. Multi-user detection method according to one of claims 2 to 5, characterised in that, at the first sequence, the coefficients (b_l,i,k) of the first set of the first plurality are initialised by b_l,i,k(0)=exp(−

j({circumflex over (v)}_i,k(0)+2π

d/λ

·

cos{circumflex over (θ

)}_i,k(0)·

(l−

1))) and in that the coefficients (c_i,k) of the second set of the first plurality are initialised by c_i,k(0)={circumflex over (α

)}_i,k(0) where {circumflex over (θ

)}_i,k(0), {circumflex over (ν

)}_i,k(0), {circumflex over (α

)}_i,k(0) are respectively estimations of the directions of arrival, phase rotations and coefficients of attenuation for the different paths.

8. Multi-user detection method according to claim 1, characterised in that the first plurality of coefficients consist of a set of complex coefficients (b_l,i,k) and in that the filtered signals (x_l,i,k) are linearly combined (520_k) by means of said set in order to supply said estimation (z_k) of the signal transmitted, the coefficients of said set being adapted so as to minimise an error signal (ε

_k) between the said estimation (z_k) and a reference value (q_k).

9. Multi-user detection method according to claim 8, characterised in that the said second plurality (w_l,i,k,u_i,k) of coefficients comprises a first set of complex coefficients (w_l,i,k) and a second set of complex coefficients (u_i,k), the coefficients (u_i,k) of the said second set of the second plurality being obtained by:

u_i,k=g_i,k/g_k where g_i,k is an estimation of the norm of the sub-vector

10. Multi-user detection method according to claim 8 or 9, characterised in that, at the first sequence, the coefficients (b_l,i,k) of the said set of the first plurality are initialised by b_l,i,k(0)=b·

δ

(l−

l₀),∀

i where δ

is the Dirac symbol, l₀ is an antenna number and b a given complex coefficient.

11. Multi-user detection method according to claim 8 or 9, characterised in that, at the first sequence, the coefficients (b_l,i,k) of the said set of the first plurality are initialised by b_l,i,k(0)={circumflex over (α

)}i,k(0)·

exp(−

j({circumflex over (ν

)}_i,k(0)+2π

d/λ

·

cos{circumflex over (θ

)}_i,k(0)·

(l−

1))) where {circumflex over (θ

)}_i,k(0), {circumflex over (ν

)}_i,k(0), {circumflex over (α

)}_i,k(0) are respectively estimations of the directions of arrival, phase rotations and coefficients of attenuation for the different paths.

12. Multi-user detection method according to one of the preceding claims, characterised in that, for a given user (k), the interference is eliminated by subtracting (680_k,880_k,880,980) from the antenna signals of the contributions of all the other users.

13. Multi-user detection method according to claim 12, characterised in that each sequence comprises a step of estimating (610_k,710_k,810_k,810,910) the symbols transmitted from the estimation of the signal transmitted (z_k) in order to obtain first estimated signals (ŝ

_k), a step of demodulating (620_k, 720_k,820_k,820,920) the first estimated symbols (ŝ

_k) in order to obtain estimated data ({circumflex over (d)}_k), a step of channel decoding (630_k,730_k,830_k,830,930) of the said estimated data followed by a channel recoding (640_k,740_k,840_k,840,940) and a remodulation (650_k,750_k,850_k,850,950) in order to obtain second estimated symbols (ŝ

′

_k).

14. Multi-user detection method according to claim 2 or 13, or 8 and 13, characterised in that the reference value (q⁽ⁿ⁾_k) for a transmitted signal, used at the second sequence or at a subsequence sequence (n), is the second estimated symbol (ŝ

′

<sup>(n−

1)</sup>_k) obtained for this signal at the previous sequence.

15. Multi-user detection method according to claim 2 or 14, or 8 and 14, characterised in that the reference value (q⁽ⁿ⁾_k) for a transmitted signal, used at the second sequence or at a subsequent sequence (n), is a combination of the first estimated symbol (ŝ

⁽ⁿ⁾_k) obtained for this signal at the current sequence and of the second estimated symbol (ŝ

′

⁽ⁿ⁻

1)_k) obtained for this signal at the previous sequence.

16. Multi-user detection method according to one of the preceding claims, characterised in that, at the second sequence and at the subsequent sequences, the coefficients of the first plurality of a sequence are initialised from the values of coefficients of the first plurality of the previous sequence.

17. Multi-user detection method according to one of claims 1 to 11, characterised in that the users are classified in order of received power and in that the interference is eliminated by subtracting (780_k), one after the other, the contributions of the different users, commencing with the users with the highest received powers.

18. Multi-user detection method according to claims 6 and 17, characterised in that, for each sequence of a user (k), the coefficients (b_l,i,k) of the first set of the first plurality are initialised by b_l,i,k(0)=δ

(l−

l₀),∀

i where δ

is the Dirac symbol, l₀ is an antenna number;

and in that the coefficients (c_i,k) of the second set of the first plurality are initialised by c_i,k(0)=c,∀

i where c is a given complex coefficient.

19. Multi-user detection method according to claims 7 and 17, characterised in that, for each sequence of a user (k), the coefficients (b_l,i,k) of the first set of the first plurality are initialised by b_l,i,k(0)=exp(−

j({circumflex over (ν

)}_i,k(0)+2π

d/λ

·

cos{circumflex over (θ

)}_i,k(0)·

(l−

1))) and in that the coefficients (c_i,k) of the second set of the first plurality are initialised by c_i,k(0)={circumflex over (α

)}_i,k(0) where {circumflex over (θ

)}_i,k(0), {circumflex over (ν

)}_i,k(0), {circumflex over (α

)}_i,k(0) are respectively estimations of the directions of arrival, phase rotations and coefficients of attenuation for the different paths.

20. Multi-user detection method according to claims 10 and 17, characterised in that, for each sequence of a user (k), the coefficients (b_l,i,k) of the said set of the first plurality are initialised by b_l,i,k(0)=b·

δ

(l−

l₀),∀

i where δ

is the Dirac symbol, l₀ is an antenna number and b a given complex coefficient.

21. Multi-user detection method according to claims 11 and 17, characterised in that, for each sequence of a user (k), the coefficients (b_l,i,k) of the said set of the first plurality are initialised by b_l,i,k(0)={circumflex over (α

)}_i,k(0)·

exp(−

j({circumflex over (ν

)}_i,k(0)+2π

d/λ

·

cos{circumflex over (θ

)}_i,k(0)·

(l−

1))) where {circumflex over (θ

)}_i,k(0), {circumflex over (ν

)}_i,k(0), {circumflex over (α

)}_i,k(0) are respectively estimations of the directions of arrival, phase rotations and coefficients of attenuation for the different paths.

22. Multi-user detection method according to claim 12, characterised in that, the estimations of the transmitted signals of the users being considered to be an estimations vector with K components where K is the number of users, the said vector is subjected to a transverse matrix filtering (805,905).

23. Multi-user detection method according to claim 22, characterised in that, the estimated symbols of the users being considered to be a symbols vector with K components, the said symbols vector is subjected to a postcursor matrix filtering (907) and the output of this filtering is subtracted, vector by vector, from the output of the transverse matrix filtering (905).

24. Multi-user detection device, characterised in that it comprises means adapted to implement the method according to one of the preceding claims.