Multi-user downlink linear MIMO precoding system

1. A method implemented in a base station used for a downlink multi-user (MU) multi-input multi-output (MIMO) system, the method comprising:

receiving an indication of a quantized matrix from each of a plurality of scheduled user equipments;

precoding data streams for the plurality of scheduled user equipments; and

transmitting the precoded data to the plurality of scheduled user equipments,

wherein the precoded data is expressed by equation

x=Gu

where x is the precoded data, u denotes the data streams, and G is a precoder,

wherein each scheduled user equipment corresponds to at least one of the data streams, said at least one of the data streams being precoded with a column of the quantized matrix indicated by said each scheduled user equipment,

wherein the number of the data streams is equal to or greater than the number of the scheduled user equipments,

wherein a set of indications restricts a set of channel conditions for the plurality of scheduled user equipments, and

wherein the precoder is determined by:

(a) initializing initial precoder {tilde over (G)} (0) as a function of {circumflex over ( V )}, where {circumflex over ( V )}=[{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ] T and {circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , and {circumflex over (v)} L are indicated by the plurality of scheduled user equipments;

(b) determining k th precoder G (k) as a function of {tilde over (G)} (k) at a k th iteration;

(c) determining (k+1) th precoder {tilde over (G)} (k+1) as a function of G (k) and a channel matrix of transmission channels to the plurality of scheduled user equipments; and

(d) performing (b) and (c) for a specific number of iteration, where the specific number of iteration >0.

2. The method of claim 1 ,

wherein the indication is a quantization index.

3. A method implemented in a user equipment used for a downlink multi-user (MU) multi-input multi-output (MIMO) system, the method comprising:

transmitting an indication of a quantized vector to a base station; and

receiving precoded data from the base station,

wherein the precoded data is precoded with a precoder from data streams for a plurality of scheduled user equipments,

wherein the precoded data is expressed by equation

x=Gu

where x is the precoded data, u denotes the data streams, and G is a precoder,

wherein each scheduled user equipment corresponds to at least one of the data streams, said at least one of the data streams being precoded with a column of the quantized matrix indicated by said each scheduled user equipment,

wherein the number of the data streams is equal to or greater than the number of the scheduled user equipments,

wherein a set of indications restricts a set of channel conditions for the plurality of scheduled user equipments, and

wherein the precoder is determined by:

(a) initializing initial precoder {tilde over (G)} (0) as a function of {circumflex over ( V )}, where {circumflex over ( V )}=[{circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , {circumflex over (v)} L ] T and {circumflex over (v)} 1 , {circumflex over (v)} 2 , . . . , and {circumflex over (v)} L are indicated by the plurality of scheduled user equipments;

(b) determining k th precoder G (k) as a function of {tilde over (G)} (k) at a k th iteration;

(c) determining (k+1) th precoder {tilde over (G)} (k+1) as a function of G (k) and a channel matrix of transmission channels to the plurality of scheduled user equipments; and

(d) performing (b) and (c) for a specific number of iteration, where the specific number of iteration ≧0.

4. The method of claim 3 ,

wherein the indication is a quantization index.