System and method for user equipment cooperation
User equipment (UE) cooperation can be improved by relaying partial soft information to target UEs. More specifically, a cooperating UE may relay a subset of log-likelihood ratios (LLRs) to the target UE. The subset of LLRs may correspond to fewer than all resource blocks of the original transmission. This may allow UE cooperation to be effective when the cooperating UE was only able to decode a portion of the original transmission. This may also allow fewer network resources (e.g., bandwidth, etc.) to be used when the target UE does not need all of the soft information to decode the original transmission. Multiple cooperating UEs can provide different subsets of LLRs, and the subsets may or may not overlap with one another.
1. A method for user equipment (UE) cooperation, the method comprising:
receiving, by a cooperating UE from a communications controller, a first message transmitted over a plurality of resource blocks (RBs);
determining a plurality of log-likelihood ratios (LLRs) in accordance with the plurality of RBs;
selecting a first subset of LLRs from the plurality of LLRs, wherein the first subset of LLRs corresponds to fewer than all RBs in the plurality of RBs; and
transmitting, by the cooperating UE, the first subset of LLRs to a target UE.
2. The method of claim 1 , further comprising determining a plurality of signal-to-noise ratios (SNRs) for the plurality of RBs, wherein selecting the first subset of LLRs from the plurality of LLRs comprises selecting the first subset of LLRs in accordance with the plurality of SNRs.
3. The method of claim 2 , wherein selecting the first subset of LLRs in accordance with the plurality of SNRs comprises:
identifying which RBs in the plurality of RBs have SNRs exceeding a threshold; and
selecting, for inclusion in the subset of LLRs, LLRs that correspond to the identified RBs.
4. The method of claim 3 , further comprising receiving, by the cooperating UE from the target UE or a central controller, a second message comprising the threshold.
5. The method of claim 3 , wherein the threshold is determined prior to initiation of a UE cooperation process.
6. The method of claim 2 , further comprising:
transmitting, by the cooperating UE to a central controller, the plurality of SNRs; and
receiving, by the cooperating UE from the central controller, an indication message, wherein the indication message identifies the first subset of LLRs to transmit to the target UE.
7. The method of claim 2 , wherein the plurality of LLRs includes the first subset of LLRs and a second subset of LLRs, wherein the first subset of LLRs correspond to RBs having SNRs that are greater than a threshold, and wherein the second subset of LLRs correspond to RBs having SNRs that are less than or equal the threshold.
8. The method of claim 1 , further comprising receiving, by the cooperating UE from the target UE, an RB index, wherein selecting the first subset of LLRs comprises selecting the first subset of LLRs in accordance with the RB index.
9. The method of claim 1 , further comprising quantizing the first subset of LLRs prior to transmitting the first subset of LLRs.
10. The method of claim 1 , wherein selecting the first subset of LLRs comprises selecting the first subset of LLRs in accordance with a minimization of a utility function.
11. The method of claim 1 , further comprising transmitting, by the cooperating UE to the target UE, a second message identifying the first subset of LLRs.
12. A cooperating user equipment (UE) comprising:
a processor; and
a computer readable storage medium storing programming for execution by the processor, the programming including instructions to:
receive a first message transmitted over a plurality of resource blocks (RBs), from a communications controller;
determine a plurality of log-likelihood ratios (LLRs) in accordance with the plurality of RBs;
select a first subset of LLRs from the plurality of LLRs, wherein the first subset of LLRs correspond to fewer than all RBs in the plurality of RBs; and
transmit the first subset of LLRs to a target UE.
13. A method for user equipment (UE) cooperation, the method comprising:
receiving, by a target UE from a communications controller, a message transmitted over a plurality of resource blocks (RBs); and
receiving, by the target UE from a first cooperating UE, a first subset of log-likelihood ratios (LLRs), the first subset of LLRs corresponding to fewer than all RBs in the plurality of RBs.
14. The method of claim 13 , further comprising:
determining a plurality of signal-to-noise ratios (SNRs) in accordance with the plurality of RBs;
determining an RB index in accordance with the plurality of SNRs; and
broadcasting, by the target UE, the RB index to a plurality of cooperating UEs.
15. The method of claim 14 , wherein the RB index indicates which of the plurality of RBs have SNRs that are less than an SNR threshold.
16. The method of claim 15 , further comprising, receiving by the target UE from a central controller, a message comprising the SNR threshold.
17. The method of claim 13 , further comprising:
determining a second plurality of LLRs in accordance with the plurality of RBs;
adding a first LLR of the first subset of LLRs and a second LLR of the second plurality of LLRs to produce a third LLR; and
performing turbo decoding using the third LLR as a soft input.
18. The method of claim 13 , further comprising:
determining an SNR threshold; and
broadcasting, by the target UE to the plurality of cooperating UEs, the SNR threshold.
19. A method for user equipment (UE) cooperation, the method comprising:
receiving, by a central controller from a first cooperating UE, a first signal-to-noise ratio (SNR) measurement corresponding to at least a first resource block (RB);
receiving, by the central controller from a second cooperating UE, a second SNR measurement corresponding to at least the first RB;
selecting a cooperating UE to transmit a set of log-likelihood ratios (LLRs) corresponding to the first RB in accordance with the first SNR measurement and the second SNR measurement; and
prompting the selected cooperating UE to transmit the set of LLRs corresponding to the first RB.
20. The method of claim 19 , wherein selecting the cooperating UE to transmit the set of LLRs corresponding to the first RB comprises:
selecting the first cooperating UE when the first SNR measurement is greater than the second SNR measurement; and
selecting the second cooperating UE when the second SNR measurement is greater than the first SNR measurement.
21. The method of claim 20 , further comprising receiving, by the central controller from a target UE, an RB index, wherein selecting the cooperating UE to transmit the set of LLRs comprises selecting the cooperating UE in accordance with the RB index.
22. The method of claim 20 , further comprising,
determining an SNR threshold; and
sending, by the central controller, the SNR threshold to a plurality of cooperating UEs and a target UE.
23. A target user equipment (UE) comprising:
a processor; and
a computer readable storage medium storing programming for execution by the processor, the programming including instructions to:
receive, from a communications controller, a message transmitted over a plurality of resource blocks (RBs); and
receive a first subset of log-likelihood ratios (LLRs) from a first cooperating UE, the first subset of LLRs corresponding to fewer than all RBs in the plurality of RBs.