Method, apparatus and computer program for relay selection

• US 20090296626A1
• Filed: 05/30/2008
• Published: 12/03/2009
• Est. Priority Date: 05/30/2008
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Hottinen, Ari, Viterbo, Emanuele
• Granted Patent: US 8,331,280 B2
• Time in Patent Office: Days
• US Class Current: 370/315
• CPC Class Codes: H04B 7/155 Ground-based stations H04B7/204 takes precedence

Abstract

First are determined which relays are available between at least one source and at least one destination, and from them are selected a subset of those relays for an activation interval under a constraint of equal transmit energy per selected relay across the activation interval. A matrix is formed, using CSI received from the relays, to evaluate each effective channel between source and destination that goes through each of the relays, including multi-relay hops, and the relays are selected from that matrix. Utility of source-relay pairing is evaluated in view of the relay-destination channel and the pairing enables relays to multiplex multiple sources where feasible.

Claims

1. A method comprising:

determining a plurality of relays that are available between at least one source and at least one destination;

selecting a subset of the plurality of relays for an activation interval under a constraint that comprises relay transmit energy per activation interval; and

causing at least one of the relays of the subset to relay between the at least one source and the at least one destination during the activation interval.

2. The method of claim 1, wherein the constraint that comprises relay transmit energy per activation interval is equal transmit energy per selected relay across the activation interval.

3. The method of claim 1, wherein selecting the subset of the plurality of relays further comprises evaluating an effective channel from the at least one source to the at least one destination via multiple feasible subsets of the plurality of relays.

4. The method of claim 3, wherein evaluating the effective channel comprises using channel state information received at the at least one destination from each of the plurality of relays that are available.

5. The method of claim 4, wherein evaluating the effective channel comprises evaluating a two-hop multi-input multi-output capacity equation.

6. The method of claim 1, wherein the at least one source comprises a plurality of sources, and wherein selecting the subset of the plurality of relays comprises selecting individual relays and source-relay pairs.

7. The method of claim 6, executed by a scheduling node and wherein causing at least one of the relays of the subset to relay between the at least one source and the at least one destination during the activation interval comprises signaling by the scheduling node each of the selected relays to relay from its paired source or sources.

8. The method of claim 6, wherein the activation interval spans at least two consecutive slots and the source-relay pairing is not identical across the activation interval while the relay transmission energy per activation interval constraint is satisfied.

9. The method of claim 1, wherein selecting the subset of the plurality of relays comprises forming a matrix of effective channel from each of the at least one source to destination through each of the plurality of relays that are available to the destination, and selecting the subset from the effective channel matrix.

10. The method of claim 9, wherein there are at least two sources and wherein selecting the subset of the plurality of relays further comprises selecting whether and which of the sources to pair to the subset of relays by evaluating utility for pairing each individual source k1 to an individual relay k2 according to

${\gamma }_{}$

k 



1 , k 



2 = { γ

k 



1 

( 2 ) + γ

k 



2 

( 2 ) 



ifk 1 ≠

k 2 , γ

k 



2 

( 1 ) 



ifk 1 = k 2

wherein γ

is a signal to noise ratio.

11. The method of claim 10, wherein the utility for pairing further depends on evaluating performance of a multiple-input-multiple-output channel between two of the relays and the at least one destination.

12. The method of claim 10, wherein selecting the subset of the plurality of relays comprises solving

${\max }_{\mathrm{xk},j}$

∑

k 

∑

j 

γ

k , j 

x k , j ,

wherein x_k,j is an element of a permutation matrix X=(x_k,j) for user k and relay j.

13. The method of claim 1, executed by the at least one of the relays without control signaling from a scheduling network node that informs of relay selection, and wherein causing the at least one of the relays of the subset to relay comprising transmitting to the at least one destination during the activation interval data that was received from the at least one source.

14. A device comprising:

a processor configured to determine from received transmissions a plurality of relays that are available between at least one source and at least one destination;

the processor further configured to select a subset of the plurality of relays for an activation interval under a constraint that comprises relay transmit energy per activation interval; and

a transmitter configured to cause at least one of the relays of the subset to relay between the at least one source and the at least one destination during the activation interval.

15. The device of claim 14, wherein the constraint that comprises relay transmit energy per activation interval is equal transmit energy per selected relay across the activation interval.

16. The device of claim 14, wherein the processor is configured to select the subset of the plurality of relays by evaluating an effective channel from the at least one source to the at least one destination via multiple feasible subsets of the plurality of relays.

17. The device of claim 16, wherein the processor is configured to evaluate the effective channel by using channel state information that is received from each of the plurality of relays that are available.

18. The device of claim 17, wherein the processor is configured to evaluate the effective channel using a two-hop multi-input multi-output capacity equation.

19. The device of claim 14, wherein the at least one source comprises a plurality of sources, and wherein the processor is configured to select the subset of the plurality of relays by selecting individual relays and source-relay pairs.

20. The device of claim 19, wherein the device comprises a scheduling node and the transmitter causes at least one of the relays of the subset to relay between the at least one source and the at least one destination by signaling each of the selected relays to relay from its paired source or sources.

21. The device of claim 19, wherein the activation interval spans at least two consecutive slots and the source-relay pairing is not identical across the activation interval while the relay transmission energy per activation interval constraint is satisfied.

22. The device of claim 14, wherein the processor is configured to select the subset of the plurality of relays by forming a matrix of effective channel from each of the at least one source to destination through each of the plurality of relays that are available to the destination, and to select the subset from the effective channel matrix.

23. The device of claim 22, wherein there are at least two sources and wherein the processor is configured to select the subset of the plurality of relays by selecting whether and which of the sources to pair to the subset of relays by evaluating utility for pairing each individual source k1 to an individual relay k2 according to

${\gamma }_{}$

k 



1 , k 



2 = { γ

k 



1 

( 2 ) + γ

k 



2 

( 2 ) 



ifk 1 ≠

k 2 , γ

k 



2 

( 1 ) 



ifk 1 = k 2

wherein γ

is a signal to noise ratio.

24. The device of claim 23, wherein the utility for pairing further depends on evaluating performance of a multiple-input-multiple-output channel between two of the relays and the at least one destination.

25. The device of claim 23, wherein the processor is configured to select the subset of the plurality of relays by solving

${\max }_{\mathrm{xk},j}$

∑

k 

∑

j 

γ

k , j 

x k , j ,

wherein x_k,j is an element of a permutation matrix X=(x_k,j) for user k and relay j.

26. The device of claim 14, wherein the device comprises the at least one of the relays of the subset that relays between the at least one source and the at least one destination during the activation interval

27. A computer readable memory embodying a program of instructions for causing a processor to take actions directed toward selecting relays, the actions comprising:

determining a plurality of relays that are available between at least one source and at least one destination;

selecting a subset of the plurality of relays for an activation interval under a constraint that comprises relay transmit energy per activation interval; and

causing at least one of the relays of the subset to relay between the at least one source and the at least one destination during the activation interval.

28. The computer readable memory of claim 27, wherein the constraint that comprises relay transmit energy per activation interval is equal transmit energy per selected relay across the activation interval.

29. The computer readable memory of claim 27, wherein selecting the subset of the plurality of relays further comprises evaluating an effective channel from the at least one source to the at least one destination via multiple feasible subsets of the plurality of relays.

30. The computer readable memory of claim 29, wherein evaluating the effective channel comprises using channel state information received at the at least one destination from each of the plurality of relays that are available.

31. The computer readable memory of claim 27, wherein the at least one source comprises a plurality of sources, and wherein selecting the subset of the plurality of relays comprises selecting individual relays and source-relay pairs.

32. The computer readable memory of claim 27, wherein selecting the subset of the plurality of relays comprises forming a matrix of effective channel from each of the at least one source to destination through each of the plurality of relays that are available to the destination, and selecting the subset from the effective channel matrix.

33. The computer readable memory of claim 32, wherein there are at least two sources and wherein selecting the subset of the plurality of relays further comprises selecting whether and which of the sources to pair to the subset of relays by evaluating utility for pairing each individual source k1 to an individual relay k2 according to

${\gamma }_{}$

k 



1 , k 



2 = { γ

k 



1 

( 2 ) + γ

k 



2 

( 2 ) 



ifk 1 ≠

k 2 , γ

k 



2 

( 1 ) 



ifk 1 = k 2

wherein γ

is a signal to noise ratio,

wherein the utility for pairing further depends on evaluating performance of a multiple-input-multiple-output channel between two of the relays and the at least one destination;

and wherein selecting the subset of the plurality of relays comprises solving

${\max }_{\mathrm{xk},j}<br><br>\underset{k}{\sum <br><br>}<br><br>\underset{j}{\sum <br><br>}<br><br>{\mathrm{\gamma <br><br>}}_{k,j}<br><br>x_{k,j},$

wherein x_k,j is an element of a permutation matrix X=(x_k,j) for user k and relay j.