Precoding and scheduling for a cellular communication system using a large number of base stations antennas
For an infinite number of transmit antennas at a base station (BS), matched filter (MF) precoding (a type of precoding used to perform SU-MIMO transmission) becomes optimal for performing spatial multiplexing. But observations have shown that precoding types for performing MU-MIMO transmission can perform significantly better than MF precoding for a realizable number of transmit antennas at the BS, even while using the simplest precoding types for MU-MIMO transmission. For large inter-cell interference typically encountered by user terminals (UTs) at or near the boundary of the cell served by the BS, MF precoding can still be used to eliminate or reduce the need for coordination among cells, which consumes network and back-haul resources.
1. A base station for switching between a single-user multiple-input multiple-output (SU-MIMO) transmission mode and a multiple-user multiple-input multiple-out (MU-MIMO) transmission mode, the base station comprising:
a data source configured to provide a plurality of data streams;
a scheduler configured to control the data source to provide as output a first set of the plurality of data streams intended for transmission to interior user terminals and a second set of the plurality of data streams intended for transmission to one or more edge user terminals; and
a precoder configured to precode the first set of the plurality of data streams in accordance with the MU-MIMO transmission mode and to precode the second set of the plurality of streams in accordance with the SU-MIMO transmission mode,
wherein the precoder is configured to precode the second set of the plurality of data streams using matched filter precoding and is configured to select a precoding type, other than the matched filter precoding, to precode the first set of the plurality of data streams based on the number of data streams in the first set of the plurality of data streams as compared to a threshold.
2. The base station of claim 1 , wherein the scheduler is further configured to classify each of a plurality of user terminals as being a part of the interior user terminals or the one or more edge user terminals based on channel quality indication metrics received from the plurality of user terminals.
3. The base station of claim 1 , wherein the precoding type is a zero-forcing precoding.
4. The base station of claim 1 , wherein the precoding type is a minimum mean square error precoding.
5. The base station of claim 1 , wherein each data stream in the first set of the plurality of data streams includes a symbol.
6. The base station of claim 1 , wherein the scheduler is configured to control the data source such that the number of data streams in the first set of the plurality of data streams is less than the threshold.
7. The base station of claim 1 , wherein the threshold is determined based on a number of transmit antennas configured to transmit the first set of the plurality of data streams to the interior user terminals.
8. The base station of claim 1 , wherein the precoder is configured to select the precoding type to precode the first set of the plurality of data streams to be zero-forcing precoding based on the number of data streams in the first set of the plurality of data streams being less than the threshold.
9. The base station of claim 1 , wherein the precoder is configured to select the precoding type to precode the first set of the plurality of data streams to be minimum mean square error precoding based on the number of data streams in the first set of the plurality of data streams being less than the threshold.
10. The base station of claim 9 , wherein the threshold is determined based on a number of transmit antennas configured to transmit the first set of the plurality of data streams to the interior user terminals.
11. An apparatus, comprising:
a scheduler configured to control a data source to provide as output a first set data streams intended for transmission to interior user terminals of a cell in a cellular network and a second set of data streams intended for transmission to one or more edge user terminals of the cell in the cellular network; and
a precoder configured to precode the first set of data streams in accordance with a multiple-user multiple-input multiple-out (MU-MIMO) transmission mode and to precode the second set of data streams in accordance with a single-user multiple-input multiple-out (SU-MIMO) transmission mode,
wherein the precoder is configured to precode the second set of the plurality of data streams using matched filter precoding and is configured to select a precoding type, other than the matched filter precoding, to precode the first set of data streams based on the number of data streams in the first set of data streams as compared to a threshold.
12. The apparatus of claim 11 , wherein the precoding type is a zero-forcing precoding.
13. The apparatus of claim 11 , wherein the precoding type is a minimum mean square error precoding.
14. The apparatus of claim 11 , wherein each data stream in the first set of data streams includes a symbol.
15. The apparatus of claim 11 , wherein the scheduler is configured to control the data source such that the number of data streams in the first set of data streams is less than the threshold.
16. The apparatus of claim 11 , wherein the threshold is determined based on a number of transmit antennas configured to transmit the first set of data streams to the interior user terminals.
17. A method, comprising:
controlling a data source to provide as output a first set of data streams intended for transmission to interior user terminals of a cell in a cellular network;
controlling the data source to provide a second set of data streams intended for transmission to one or more edge user terminals of the cell in the cellular network;
precoding the first set of data streams in accordance with a multiple-user multiple-input multiple-out (MU-MIMO) transmission mode;
precoding the second set of data streams, using matched filter precoding, in accordance with a single-user multiple-input multiple-out (SU-MIMO) transmission mode; and
selecting a precoding type, other than the matched filter precoding, to precode the first set of data streams based on the number of data streams in the first set of data streams as compared to a threshold.
18. The method of claim 17 , wherein the threshold is determined based on a number of transmit antennas to be used to transmit the first set of data streams to the interior user terminals.
19. The method of claim 17 , wherein the precoding type is a zero-forcing precoding.
20. The method of claim 17 , wherein the precoding type is a minimum mean square error precoding.