Methods and devices for determining precoder parameters in a wireless communication network

Abstract

A method and a device for sending parameters of a precoder in a wireless communication system are disclosed. According to one aspect, the method comprises: sending, to a network node, an indication of a subset of beams selected from a plurality of orthogonal beams and an indication of power levels of the selected subset of beams, for a first frequency granularity; and sending, to the network node, an indication of phases of the selected subset of beams, for a second frequency granularity, wherein the indication of the selected beams, the indication of the power levels of the selected subset of beams and the indication of the phases of the selected subset of beams are part of the parameters of the precoder.

What is claimed is: 
     
         1 . A method in a wireless device for determining a precoder, in a wireless communication system, the method comprising:
 receiving reference signals from a network node; and   determining a precoder for channel state information, based on the received reference signals, the precoder comprising a weighted sum of multiple orthogonal beams selected from a rotated two-dimensional discrete Fourier transform (DFT), wherein a power level and a phase of an orthogonal beam are separated with different frequency granularities.   
     
     
         2 . The method of  claim 1 , further comprising determining a rotation factor from a set of possible values of rotation factors, for rotating the two-dimensional DFT. 
     
     
         3 . The method of  claim 1 , wherein the multiple orthogonal are selected from a set of beams. 
     
     
         4 . The method of  claim 3 , further comprising obtaining power levels of the multiple beams and obtaining phases of the multiple beams. 
     
     
         5 . The method of  claim 4 , further comprising sending to the network node an indication of the selected set of beams, an indication of the power levels of the multiple beams, and an indication of the phases of the multiple beams. 
     
     
         6 . The method of  claim 5 , wherein the indication of the power levels is sent with a first frequency granularity and the indication of the phases is sent with a second frequency granularity. 
     
     
         7 . The method of  claim 6 , wherein the first frequency granularity is a frequency bandwidth and the second frequency granularity is a frequency subband. 
     
     
         8 . The method of  claim 4 , wherein the obtained power levels are for generating a first factor of the precoder. 
     
     
         9 . The method of  claim 4 , wherein the obtained phases are for generating a second factor of the precoder. 
     
     
         10 . A wireless device for determining a precoder, in a wireless communication system, the wireless device comprising a processing circuitry having a processor, a memory and a network interface both connected to the processor, the memory containing instructions that, when executed, cause the processor to:
 receive reference signals from a network node; and   determine a precoder for channel state information, based on the received reference signals, the precoder comprising a weighted sum of multiple orthogonal beams selected from a rotated two-dimensional discrete Fourier transform (DFT), wherein a power level and a phase of an orthogonal beam are separated with different frequency granularities.   
     
     
         11 . The wireless device of  claim 10 , wherein the processor is further configured to determine a rotation factor from a set of possible values of rotation factors, for rotating the two-dimensional DFT. 
     
     
         12 . The wireless device of  claim 10 , wherein the multiple beams are selected from a set of beams. 
     
     
         13 . The wireless device of  claim 12 , wherein the processor is further configured to obtain power levels of the multiple beams and obtain phases of the multiple beams. 
     
     
         14 . The wireless device of  claim 13 , wherein the processor is further configured to send to the network node an indication of the multiple beams, an indication of the power levels of the multiple beams, and an indication of the phases of the multiple beams. 
     
     
         15 . The wireless device of  claim 14 , wherein the indication of the power levels is sent with a first frequency granularity and the indication of the phases is sent with a second frequency granularity. 
     
     
         16 . The wireless device of  claim 15 , wherein the first frequency granularity is a frequency bandwidth and the second frequency granularity is a frequency subband. 
     
     
         17 . The wireless device of  claim 13 , wherein the obtained power levels are for generating a first factor of the precoder. 
     
     
         18 . The wireless device of  claim 13 , wherein the obtained phases are for generating a second factor of the precoder. 
     
     
         19 . A computer program product comprising a non-transitory computer readable storage medium having computer readable program code embodied in the medium, the computer readable program code comprising computer readable program code to:
 receive reference signals from a network node; and   determine a precoder for channel state information, based on the channel estimate, the precoder comprising a weighted sum of multiple orthogonal beams selected from a rotated two-dimensional discrete Fourier transform (DFT), wherein a power level and a phase of an orthogonal beam are separated with different frequency granularities.