Distributed Base Station with Frequency Domain Interface on Which Signal Subspace Varies According to Frequency Bin

Abstract

A method and apparatus is disclosed for determining a signal subspace in a communications system. A remote apparatus obtains signal streams from antenna elements or signal streams from antenna beams. Based on the obtained signal streams, the apparatus selects a signal subspace for a user, the signal sub-space having a dimension M. Based on the selected signal subspace, the apparatus transmits, via an interface to a central apparatus, M streams of post-fast-Fourier-transform data, the interface being capable of transmitting a different sub-space for different frequency bins.

1 . A method for determining a signal subspace in a communications system, the method comprising
 obtaining, in a remote apparatus, signal streams from antenna elements or signal streams from antenna beams;   based on the obtained signal streams, selecting a signal sub-space for a user, the signal subspace having a dimension M; and   based on the selected signal subspace, transmitting, via an interface to a central apparatus, M streams of post-fast-Fourier-transform data, the interface being capable of transmitting a different signal subspace for different frequency bins.   
     
     
         2 . A method according to  claim 1 , characterized in that said selecting comprises selecting a signal subspace for one or more users. 
     
     
         3 . A method according to  claim 1 , characterized in that said selecting comprises selecting several signal subspaces in a cell. 
     
     
         4 . A method as claimed in  claim 1 , characterized in that the interface is capable of transmitting different signal subspaces for different groups of frequency bins. 
     
     
         5 . A method as claimed in  claim 1 , characterized in that the interface is capable of detecting post-fast-Fourier-transform samples and frequency selective signal subspaces. 
     
     
         6 . A method as claimed in  claim 1 , characterized in that the obtained signal streams comprise signals from individual antenna elements, signals from groups of antenna elements, or signals from separate antenna beams. 
     
     
         7 . A method as claimed in  claim 1 , characterized by selecting the antenna element or antenna beam for the user based on fading conditions. 
     
     
         8 . A method as claimed in  claim 1 , characterized by performing signal subspace determination based on longer term signal properties. 
     
     
         9 . An apparatus comprising at least one processor; and at least one memory including a computer program code, wherein the at least one memory and
 the computer program code are configured to, with the at least one processor, cause the apparatus to   obtain signal streams from antenna elements or signal streams from antenna beams;   based on the obtained signal streams, select a signal subspace for a user, the signal subspace having a dimension M; and   based on the selected signal subspace, transmit, via an interface to a central apparatus, M streams of post-fast-Fourier-transform data, the interface being capable of transmitting a different signal subspace for different frequency bins.   
     
     
         10 . An apparatus according to  claim 9 , characterized in that said selecting comprises selecting a signal subspace for one or more users. 
     
     
         11 . An apparatus according to  claim 9 , characterized in that said selecting comprises selecting several signal subspaces in a cell. 
     
     
         12 . An apparatus as claimed in  claim 9 , characterized in that the interface is capable of transmitting different signal subspaces for different groups of frequency bins. 
     
     
         13 . An apparatus as claimed in  claim 9 , characterized in that the interface is capable of detecting post-fast-Fourier-transform samples and frequency selective signal subspaces. 
     
     
         14 . An apparatus as claimed in  claim 9 , characterized in that the obtained signal streams comprise signals from individual antenna elements, signals from groups of antenna elements, or signals from separate antenna beams. 
     
     
         15 . An apparatus as claimed in  claim 9 , characterized in that the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to select the antenna element or antenna beam for the user based on fading conditions. 
     
     
         16 . An apparatus as claimed in  claim 9 , characterized in that the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform signal sub-space determination based on longer term signal properties. 
     
     
         17 . An apparatus as claimed in  claim 9 , characterized in that it comprises a remote radio head unit or a radio frequency unit. 
     
     
         18 . A base station comprising an apparatus as claimed in  claim 9 . 
     
     
         19 . A computer program product comprising executable code that when executed, causes execution of functions of a method according to  claim 1 .