Uplink power control for MU-MIMO
A method of power control for multi-user multi-input multi-output (MU-MIMO) transmissions between a pair of mobile terminals and a radio base station. The method comprises determining signal-to-interference-noise ratios (SINRs) for the radio channels between the mobile terminals and the radio base station, determining a channel orthogonality between the radio channels, and jointly determining, based on the SINRs and the channel orthogonality, power adjustment values for the mobile terminals. The present invention makes use of an understanding that the system gain resulting from MU-MIMO transmissions may be improved by optimizing the transmission power of the co-scheduled mobile terminals. For instance, the power adjustment values may be determined so as to attain certain SINR targets. Alternatively, the power adjustment values may be determined so as to maximize the throughput while maintaining a power budget constraint. Further, a radio base station for MU-MIMO transmissions is provided.
1. A method of power control for uplink multi-user multi-input multi-output (MU-MIMO) wireless transmissions between a pair of mobile terminals, the pair of mobile terminals comprising a first mobile terminal and a second mobile terminal, and a radio base station, the method comprising:
determining a first single-user signal-to-interference-noise ratio, SU-SINR, S 1 , for a first radio channel between the first mobile terminal and the radio base station,
determining a second SU-SINR, S 2 , for a second radio channel between the second mobile terminal and the radio base station,
determining a channel orthogonality, Δ between the first radio channel and the second radio channel, and
jointly determining, based on the first SU-SINR, the second SU-SINR, and the channel orthogonality, a first power adjustment value, α 1 , for the first mobile terminal and a second power adjustment value, α 2 , for the second mobile terminal, wherein the first power adjustment value and the second power adjustment value are determined based on a power budget constraint, K, while maximizing a transmission sum rate for the pair of mobile terminals.
2. The method according to claim 1 , wherein the first power adjustment value and the second power adjustment value are determined based on a first MU-MIMO-SINR, MU-SINR, target, φ 1 S 1 , for the first radio channel and a second MU-SINR target, φ 2 S 2 , for the second radio channel.
3. The method according to claim 2 , wherein
α 1 =−b 1 +√{square root over ( b 1 2 −4α 1 c 1 )}/2α 1 , where α 1 =−φ 1 φ 2 ( S 2 +1/φ 2 ),
b 1 =φ 1 φ 2 ( S 2 +1/φ 2 )(1/φ 1 − S 1 )+ Δ (φ 1 S 1 −φ 2 S 2 ), c 1 =φ 2 S 1 ( S 2 +1/φ 2 )(1− Δ ), and
α 2 =−b 2 +√{square root over ( b 2 2 −4α 2 c 2 )}/2α 2 , where α 2 =−φ 1 φ 2 ( S 1 +1/φ 1 ),
b 2 =φ 1 φ 2 ( S 1 +1/φ 1 )(1/φ 2 − S 2 )+ Δ (φ 2 S 2 −φ 1 S 1 ), c 2 =φ 1 S 2 ( S 1 +1/φ 1 )(1− Δ ).
4. The method according to claim 1 , wherein α 1 =√{square root over (K S 2 / S 1 )}and α 2 =√{square root over (K S 1 / S 2 )}.
5. The method according to claim 1 , wherein the first SU-SINR, the second SU-SINR, and the channel orthogonality, are determined based on instantaneous conditions of the first radio channel and the second radio channel.
6. The method according to claim 1 , further comprising:
determining, based on the first SU-SINR, the second SU-SINR, the channel orthogonality, the first power adjustment value, and the second power adjustment value, a first MU-SINR, S 1 MU,pc , for the first radio channel and a second MU-SINR, S 2 MU,pc , for the second radio channel, and
evaluating, based on the first MU-SINR and the second MU-SINR, whether to schedule the pair of mobile terminals for MU-MIMO transmissions.
7. A radio base station being arranged for uplink multi-user multi-input multi-output (MU-MIMO) wireless transmissions between a pair of mobile terminals, the pair of mobile terminals comprising a first mobile terminal and a second mobile terminal, and the radio base station, the radio base station comprising:
a channel condition estimation unit being arranged for:
determining a first single-user signal-to-interference-noise ratio, SU-SINR, S 1 for a first radio channel between the first mobile terminal and the radio base station,
determining a second SU-SINR S 2 for a second radio channel between the second mobile terminal and the radio base station, and
determining a channel orthogonality Δ between the first radio channel and the second radio channel, and
a multi-user power control (MUPC) unit being arranged for jointly determining, based on the first SU-SINR, the second SU-SINR, and the channel orthogonality, a first power adjustment value α 1 for the first mobile terminal and a second power adjustment value α 2 for the second mobile terminal, wherein
the MUPC unit is arranged for determining the first power adjustment value and the second power adjustment value based on a power budget constraint K while maximizing a transmission sum rate for the pair of mobile terminals.
8. The radio base station according to claim 7 , wherein the MUPC unit is arranged for determining the first power adjustment value and the second power adjustment value based on a first MU-MIMO-SINR, MU-SINR, target φ 1 S 1 for the first radio channel and a second MU-SINR target φ 2 S 2 for the second radio channel.
9. The radio base station according to claim 8 , wherein
α 1 =−b 1 +√{square root over ( b 1 2 −4α 1 c 1 )}/2α 1 , where α 1 =−φ 1 φ 2 ( S 2 +1/φ 2 ),
b 1 =φ 1 φ 2 ( S 2 +1/φ 2 )(1/φ 1 − S 1 )+ Δ (φ 1 S 1 −φ 2 S 2 ), c 1 =φ 2 S 1 ( S 2 +1/φ 2 )(1− Δ ), and
α 2 =−b 2 +√{square root over ( b 2 2 −4α 2 c 2 )}/2α 2 , where α 2 =−φ 1 φ 2 ( S 1 +1/φ 1 ),
b 2 =φ 1 φ 2 ( S 1 +1/φ 1 )(1/φ 2 − S 2 )+ Δ (φ 2 S 2 −φ 1 S 1 ), c 2 =φ 1 S 2 ( S 1 +1/φ 1 )(1− Δ ).
10. The radio base station according to claim 7 , wherein α 1 =√{square root over (K S 2 / S 1 )} and α 2 =√{square root over (K S 1 / S 2 )}.
11. The radio base station according to claim 7 , wherein the channel condition estimation unit is arranged for determining the first SU-SINR, the second SU-SINR, and the channel orthogonality, based on instantaneous conditions of the first radio channel and the second radio channel.
12. The radio base station according to claim 7 , wherein the channel condition estimation unit is further arranged for:
determining, based on the first SU-SINR, the second SU-SINR, the channel orthogonality, the first power adjustment value, and the second power adjustment value, a first MU-MIMO-SINR, MU-SINR, S 1 MU,pc , for the first radio channel and a second MU-SINR, S 2 MU,pc , for the second radio channel,
and wherein the radio base station further comprises:
a scheduler being arranged for evaluating, based on the first MU-SINR and the second MU-SINR, whether to schedule the pair of mobile terminals for MU-MIMO transmissions.