Dual-layer beam forming in cellular networks

1. A method for transmitting in a downlink channel of a cellular network, the method comprising:

selecting by a base station (eNB) to transmit either one or two transmission layers;

when one transmission layer is selected:

preceding a first transmission layer with a first precoder;

selecting a first demodulation reference signal (DMRS) sequence or a second DMRS sequence and preceding the selected DMRS sequence using the first precoder;

transmitting the first transmission layer with the selected precoded DMRS from the eNB to a user equipment (UE); and

transmitting an indicator to the UE to indicate which DMRS sequence is selected and transmitted.

2. The method of claim 1 , wherein when two transmission layers are selected, comprising:

preceding a first transmission layer with a first precoder, and preceding a first DMRS sequence using the first precoder;

preceding a second transmission layer with a second precoder, and preceding a second DMRS sequence using the second precoder;

transmitting the first transmission layer and the first DMRS sequence to the UE; and

transmitting the second transmission layer and the second DMRS sequence to the UE.

3. The method of claim 1 , wherein the indicator is a one-bit indicator comprised in a downlink grant.

4. Method for receiving in a downlink channel of a cellular network, the method comprising:

receiving at a user equipment (UE) a rank indicator from a base station (eNB) indicating one transmission layer or two transmission layers;

when one transmission layer is indicated:

receiving an indicator from the eNB to indicate which demodulation reference signal (DMRS) sequence was selected by the eNB from a first DMRS sequence or a second DMRS sequence;

receiving a first transmission layer from the eNB with the selected DMRS; and

demodulating the selected DMRS and the first transmission layer, wherein the first transmission layer and the selected DMRS have a same precoding.

5. The method of claim 4 , wherein the indicator is a one-bit indicator comprised in a downlink grant.

6. The method of claim 4 , wherein when two transmission layers are indicated, comprising:

receiving at the UE from the eNB a first transmission layer and a first DMRS having a first sequence;

receiving at the UE from the eNB a second transmission layer and a second DMRS having a second sequence;

demodulating the first DMRS and the first transmission layer, wherein the first transmission layer and the selected DMRS have the same precoding; and

demodulating the second DMRS and the second transmission layer, wherein the second transmission layer and the selected DMRS have the same precoding.

7. A base station for a cellular network, the device comprising;

a transceiver configured to couple to a plurality of antenna, wherein the transceiver is configured to transmit to and receiver from user equipment via the plurality of antenna in the cellular network;

a processor coupled to a memory configured to execute a control program in the memory for controlling the transceiver;

wherein the transceiver is configured to select to transmit either one or two transmission layers;

when one transmission layer is selected, the transceiver is configured to:

precode a first transmission layer with a first precoder;

select a first demodulation reference signal (DMRS) sequence or a second DMRS sequence and precode the selected DMRS sequence using the first precoder;

transmit the first transmission layer with the selected precoded DMRS from the base station to a user equipment (UE); and

transmit an indicator to the UE to indicate which DMRS sequence is selected and transmitted.

8. The base station of claim 7 , wherein when two transmission layers are selected the transceiver is configured to:

precode a first transmission layer with a first precoder, and precode a first DMRS sequence using the first precoder;

precode a second transmission layer with a second precoder, and precode a second DMRS sequence using the second precoder;

transmit the first transmission layer and the first DMRS sequence to the UE; and

transmit the second transmission layer and the second DMRS sequence to the UE.