Method in a wireless communication system

Abstract

A method in a Central Node (CN), a method in a Remote Node (RN), and a method in a wireless communication system for allocating reference signals to be used for uplink transmission are disclosed. According to one aspect reference signals are allocated with a method comprising the steps of: determining in a CN a number of reference signals N to be used for uplink transmission by a Remote Node RN; indicating to the RN the number of reference signals N to be used for uplink transmission by the RN; configuring an uplink transmission by the RN with at most the number of reference signals N; and performing by the RN the uplink transmission with at most the number of reference signals N on transmit antennas comprised in the RN. The present invention further discloses a CN and a RN relating to said methods.

1 . A method for reference signal allocation in a wireless communication system, said method comprising:
 determining the number of reference signals to be used by a remote node for an uplink transmission; and   indicating to said remote node said number of reference signals.   
     
     
         2 . The method according to  claim 1 , wherein said wireless communication system comprises a cellular communication system, and said determining of said number of reference signals is based on cell load. 
     
     
         3 . The method according to  claim 1 , wherein said central node is capable of receiving measurement signals from said remote node, and said determining of said number of reference signals is based on said received measurement signals. 
     
     
         4 . The method according to  claim 3 , wherein said measurement signals comprise Sound Reference Signals, SRS. 
     
     
         5 . The method according to  claim 1 , wherein said indicating is performed implicitly in downlink signalling for indicating said number of reference signals. 
     
     
         6 . The method according to  claim 5 , wherein said indicating is performed by using attributes of a signal format. 
     
     
         7 . The method according to  claim 6 , wherein said attributes of said signal format comprise one of location or size of said signal format. 
     
     
         8 . The method according to  claim 5 , wherein said implicit indication includes a value defining maximum number of reference signals N Max  to be used by said remote node for said uplink transmission, and said number of reference signals is obtained as the smallest of N Max  and N Lim , where N Lim  denotes an upper limit integer value known to both said central node and said remote node. 
     
     
         9 . The method according to  claim 1 , wherein said indicating is performed on a Physical Downlink Control Channel, PDCCH, or a Radio Resource Control, RRC, channel. 
     
     
         10 . The method according to  claim 1 , wherein said wireless communication system is one of 3GPP Long Term Evolution, LTE, or 3GPP Long Term Evolution Advanced. 
     
     
         11 . The method according to  claim 1 , wherein said reference signals are Demodulation Reference Signals, DRS, and the set of said Demodulation Reference Signals, DRS, is finite and limited, and said Demodulation Reference Signals, DRS, are orthogonal to each other. 
     
     
         12 . The method according to  claim 1 , comprising:
 configuring an uplink transmission by a remote node with said number of reference signals; and   performing by said remote node said uplink transmission with said number of reference signals on at least one transmit antenna of the remote node.   
     
     
         13 . A method in a remote node for a wireless communication system, wherein said remote node comprises a least one transmit antenna for uplink transmission, and said method comprising:
 receiving an indication of the number of reference signals N to be used for uplink transmission by said remote node;   configuring an uplink transmission with said number of reference signals N; and   performing said uplink transmission with said number of reference signals N on said at least one transmit antenna.   
     
     
         14 . The method according to  claim 13 , wherein said remote node is capable of providing Sounding Reference Signals, SRS, for said uplink transmission. 
     
     
         15 . The method according to  claim 13 , wherein said received indication is an implicit indication, wherein said received indication includes a value defining maximum number of reference signals N Max  to be used by said remote node for said uplink transmission, and said number of reference signals N is obtained as a minimum value of N Max  and N Lim , where N Lim  denotes an upper limit value known to said remote node. 
     
     
         16 . The method according to  claim 15 , wherein said method before configuring said uplink transmission further comprises:
 receiving an indication of said upper limit value N Lim  on a Radio Resource Control, RRC, channel, wherein said received indication is an explicit indication.   
     
     
         17 . The method according to  claim 13 , wherein each of said reference signals corresponds to an antenna port which is coupled to said at least one transmit antenna. 
     
     
         18 . The method according to  claim 13 , wherein the step of configuring an uplink transmission comprises the step of:
 mapping said number of reference signals N to said at least one transmit antenna.   
     
     
         19 . A central node for allocating reference signals in a wireless communication system comprising:
 circuitry arranged to determine the number of reference signals N to be used by an remote node for an uplink transmission; and   circuitry arranged to indicate to said remote node said number of reference signals.   
     
     
         20 . The central node according to  claim 19  being a configured base station or an eNB of an E-UTRA system. 
     
     
         21 . A remote node in a wireless communication system comprising a least one transmit antenna for uplink transmission and
 circuitry arranged to receive an indication of the number of reference signals to be used for uplink transmission by said remote node;   circuitry arranged to configure an uplink transmission with said number of reference signals; and   circuitry arranged to perform said uplink transmission with said number of reference signals.