Patent ID: 8208952

Claim:
Method for allocating a minimum downlink power from a transmitter ( 1 ) of a cellular multi-user multi-antenna communications system with N users ( 30 - 1 , 30 - 2 , . . . , 30 -N) attached to said transmitter ( 1 ), wherein the transmitter ( 1 ) comprises n t transmit antennas ( 10 - 1 , 10 - 2 , . . . , 10 -n t ), and each of the N users comprises at least one antenna ( 30 - 1 1 . . . , 30 - 1 Z1 , 30 - 2 1 . . . , 30 - 2 Z2 , . . . 30 -N 1 . . . , 30 -N ZN ), the method comprising the steps of, at a certain time instant t: generating at said transmitter ( 1 ) a plurality of M random beams (b 1 . . . b M ), wherein 2≦M≦n t ; sending each one of said M random beams through all the said n t transmit antennas ( 10 - 1 , 10 - 2 , . . . , 10 -n t ); calculating at each one of said N users ( 30 - 1 , 30 - 2 , . . . , 30 -N) a signal-to-noise-interference-ratio for each one of said M random beams sent by said transmitter ( 1 ); sending back to said transmitter ( 1 ) said calculated values of signal-to-noise-interference-ratio, said signal-to-noise-interference-ratio representing a partial channel state information; selecting at said transmitter ( 1 ) the M best users which correspond to the M best values of signal-to-noise-interference-ratio per beam; assuming at the transmitter ( 1 ) that there exists uncertainty in said partial channel state information; characterised in that the method further comprises the steps of: allocating a minimum amount of power to said M beams (b 1 . . . b M ), wherein said minimum amount of power is dependent on said best values of signal-to-noise-interference-ratio per beam (b 1 . . . b M ), on a predetermined quality of service requirement per user ( 30 - 1 , 30 - 2 , . . . , 30 -N) and on a predefined allowed outage in the quality of service requirement per user, said power allocation being robust to said assumed uncertainty in said partial channel state information.