Multi-user multiple input multiple output wireless communications

1. A method implemented in a user equipment used in a multi-user multiple input multiple output (MU-MIMO) wireless communications system, the method comprising:

receiving from a base station an indication of a first modulation type for the user equipment;

receiving a first data signal and a first precoded pilot for the user equipment;

receiving a second data signal and a second precoded pilot for a co-scheduled user equipment, where a second modulation type for the co-scheduled user equipment is unknown to the user equipment;

comparing with a threshold a norm of a channel estimate determined from the second precoded pilot for the co-scheduled user equipment;

if the norm exceeds the threshold, deciding the second modulation type through modulation classification algorithm exploiting an assumption that the second modulation type remains constant within a resource block;

processing the first data signal and the second data signal by using the first modulation type and the second modulation type to perform interference cancellation; and

generating a log-likelihood ratio (LLR) for the user equipment,

wherein each of the first modulation type and the second modulation type is any one of 4-QAM (quadrature amplitude modulation), 16-QAM, or 64-QAM, and

wherein the modulation classification algorithm is responsive to probabilities assigned to the three choices for the second modulation type.

2. The method as in claim 1 , wherein the processing comprises:

jointly demodulating the first data signal and the second data signal by using the first modulation type and the second modulation type.

3. A user equipment used in a multi-user multiple input multiple output (MU-MIMO) wireless communications system, the user equipment comprising:

a receiver to receive from a base station an indication of a first modulation type for the user equipment, to receive a first data signal and a first precoded pilot for the user equipment, and to receive a second data signal and a second precoded pilot for a co-scheduled user equipment, where a second modulation type for the co-scheduled user equipment is unknown to the user equipment; and

a processor to compare with a threshold a norm of a channel estimate determined from the second precoded pilot for the co-scheduled user equipment and, if the norm exceeds the threshold, to decide the second modulation type through modulation classification algorithm exploiting an assumption that the second modulation type remains constant within a resource block,

wherein each of the first modulation type and the second modulation type is any one of 4-QAM (quadrature amplitude modulation), 16-QAM, or 64-QAM,

wherein the modulation classification algorithm is responsive to probabilities assigned to the three choices for the second modulation type,

wherein the processor processes the first data signal and the second data signal by using the first modulation type and the second modulation type to perform interference cancellation, and

wherein the processor generates a log-likelihood ratio (LLR) for the user equipment.

4. The user equipment as in claim 3 ,

wherein the processor jointly demodulates the first data signal and the second data signal by using the first modulation type and the second modulation type.

5. A method implemented in a multi-user multiple input multiple output (MU-MIMO) wireless communications system, the method comprising:

transmitting to a user equipment an indication of a first modulation type for the user equipment;

transmitting to the user equipment a first data signal and a first precoded pilot for the user equipment;

transmitting to the user equipment a second data signal and a second precoded pilot for a co-scheduled user equipment, where a second modulation type for the co-scheduled user equipment is unknown to the user equipment;

comparing, at the user equipment, with a threshold a norm of a channel estimate determined from the second precoded pilot for the co-scheduled user equipment;

if the norm exceeds the threshold, deciding, at the user equipment, the second modulation type through modulation classification algorithm exploiting an assumption that the second modulation type remains constant within a resource block;

processing, at the user equipment, the first data signal and the second data signal by using the first modulation type and the second modulation type to perform interference cancellation; and

generating a log-likelihood ratio (LLR) for the user equipment,

wherein each of the first modulation type and the second modulation type is any one of 4-QAM (quadrature amplitude modulation), 16-QAM, or 64-QAM, and

wherein the modulation classification algorithm is responsive to probabilities assigned to the three choices for the second modulation type.

6. The method as in claim 5 , wherein the processing comprises:

jointly demodulating the first data signal and the second data signal by using the first modulation type and the second modulation type.