Distributed Antenna Diversity Transmission Method

• US 20090202020A1
• Filed: 02/11/2008
• Published: 08/13/2009
• Est. Priority Date: 02/11/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Hafeez, Abdulrauf
• Granted Patent: US 8,213,533 B2
• Time in Patent Office: Days
• US Class Current: 375/299
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/0426 Power distribution
• CPC Class Codes: H04B 7/0465 taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account
• CPC Class Codes: H04W 88/085 Access point devices with remote components
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A Distributed Antenna System employs a downlink transmission method that requires limited channel information feedback and less coherency between signals than is required for information broadcast. Distributed antennas are treated as diversity antennas with a given power allocation. Each antenna can transmit to multiple UEs by transmitting a weighed sum of their signals, and multiple antennas can transmit to one UE by transmitting weighed space-time (or space-frequency) coded signals. The power allocation weights are determined as an optimum power allocation policy with per-antenna power constraints.

Claims

1. A method of transmitting information signals to two or more User Equipment (UE) from a Distributed Antenna System comprising:

assigning a non-zero power allocation weight to each of two or more distributed antennas;

encoding information signals to two or more UEs using a space-time or space-frequency code; and

transmitting the encoded information signals to each of the two or more UEs from each of the two or more antennas, the information signals weighted at each antenna by the non-zero power allocation weight assigned to that antenna.

2. The method of claim 1 wherein assigning a non-zero power allocation weight to each of two or more antennas comprises calculating power allocation weights that maximize the minimum UE information rate under per-antenna power constraints.

3. The method of claim 2 further comprising receiving instantaneous channel power information from each UE, and calculating power allocation weights in response to the instantaneous channel power information.

4. The method of claim 3 further comprising transmitting to each UE the calculated non-zero power allocation weight of each antenna and the UE information rate.

5. The method of claim 4 further comprising decoding, in each UE, the space-time or space-frequency code by using an estimate of the channel impulse response coefficients and the weight information.

6. The method of claim 2 wherein the non-zero power allocation weights are selected on the basis of the criterion

$\underset{w_{k,l,m}}{\max }$

min k 

∑

l = 1 L 

R k , l 

( w k , l , m )

such that the constraints

$\underset{k=1}{\overset{K}{\sum <br><br>}}<br><br>\underset{l=1}{\overset{L}{\sum <br><br>}}<br><br>w_{k,l,m}=1<br><br><br><br>\forall <br><br>m$

∀

m and w_k,l,m≧

0 ∀

k,l,m are satisfied, where

m is the antenna index,

k is the UE index,

l is the index of the independent flat-fading channel comprising the propagation medium between each antenna and each UE,

w_k,l,m is the power allocation weight for the l-th channel between UE k and antenna m, and

R_k,l(w_k,l,m) is the information rate in bits/s/Hz that can be allocated to UE k.

7. The method of claim 6 wherein L=1, and the non-zero power allocation weights are selected on the basis of the criterion

$\underset{w_{k,0,m}}{\max }$

( min k 

∑

m = 1 M 

w k , 0 , m 

p _ k , 0 , m ) 1 + ∑

i = 1 K 

∑

m = 1 M 

w i , 0 , m 

p i , 0 , m

such that the constraints

$\underset{k=1}{\overset{K}{\sum <br><br>}}<br><br>w_{k,0,m}=1<br><br><br><br>\forall <br><br>m$

∀

m and w_k,0,m≧

0 ∀

k, m are satisfied, where p_k,l,m is the instantaneous channel power reported by UE k to antenna m for the single channel l=0.

8. The method of claim 7 wherein the non-zero power allocation weights are selected on the basis of the equivalent criterion

$\underset{w_{k,0,m}}{\max }$

min k 

∑

m = 1 M 

w k , 0 , m 

p k , 0 , m

such that the constraints

$\underset{k=1}{\overset{K}{\sum <br><br>}}<br><br>w_{k,0,m}=1<br><br><br><br>\forall <br><br>m$

∀

m and w_k,0,m≧

0 ∀

k,m are satisfied.

9. The method of claim 1 wherein assigning a non-zero power allocation weight to each of two or more antennas comprises calculating power allocation weights that maximize the minimum UE average SINR under per-antenna power constraints.

10. The method of claim 9 further comprising receiving average received signal power information from each UE, and calculating power allocation weights in response to the average received signal power information.

11. The method of claim 9 further comprising:

transmitting to each UE the calculated non-zero power allocation weight of each antenna;

receiving from each UE estimates of the channel impulse response coefficients for each antenna with non-zero power allocation weights; and

determining the information rates that may be allocated to the channels of each UE in response to the instantaneous channel power information; and

wherein encoding information signals to two or more UEs comprises encoding the information signals using appropriately-dimensioned space-time or space-frequency codes at the determined information rates.

12. The method of claim 11 further comprising decoding, in each UE, the space-time or space-frequency code by using an estimate of the channel impulse response coefficients and the weight information.

13. The method of claim 9 wherein the average SINR for the k-th UE is

${\stackrel{}{S}}_{}$



I 



N 



R _ k = ∑

m = 1 M 

w k , m 

p _ k , m 1 + ∑

i ≠

k 

∑

m = 1 M 

w i , m 

p _ i , m

where

m is the antenna index,

k is the UE index,

w_k,m is the power allocation weight between UE k and antenna m, and

p_k,m=E_h[p_k,l,m] is the average signal power received by the k-th UE from the antenna m.

14. A Distributed Antenna System (DAS), comprising:

a plurality of antennas, each operative to transmit independent, power-weighted, space-time or space-frequency encoded signals to a plurality of User Equipment (UE); and

a controller in data transfer relationship with the plurality of antennas, the controller operative to calculate power allocation weights for each antenna as an optimum power allocation policy with per-antenna power constraints.

15. The DAS of claim 14 wherein the antennas are each further operative to transmit their respective power allocation weights to the plurality of UE.

16. The DAS of claim 14, wherein the controller is operative to calculate power allocation weights that maximize the minimum UE data rate under per-antenna power constraints.

17. The DAS of claim 16, wherein the controller receives instantaneous channel power information from each UE, and calculates the power allocation weights in response to the instantaneous channel power information.

18. The DAS of claim 14, wherein the controller is operative to calculate power allocation weights that maximize the minimum UE average SINR under per-antenna power constraints.

19. The DAS of claim 18, wherein the controller receives average received signal power information from each UE, and calculates the power allocation weights in response to the average received signal power information.