Method and apparatus for performing distributed computation of precoding estimates
A method and apparatus for performing distributed computation of precoding estimates within a DAS. An RRH comprises a receiver component arranged to receive uplink signals from active user devices. The RRH further comprises a processing component arranged to perform channel estimation for each active user device m, based on the received uplink signals, to obtain channel estimates H m,i between each active user device m and the RRH, compute intra-RRH interference precoding estimates F m for each active user device m based on the channel estimates H m,i , and solve interference-free conditions to obtain inter-RRH interference precoding estimates for each RRH j within the DAS.
1. A remote radio head apparatus (RRH) within a distributed antenna system (DAS), the RRH configured to perform distributed computation of precoding estimates within the DAS and comprising:
a receiver component arranged to receive uplink signals from active user devices; and
a processing component arranged to:
perform channel estimation for each active user device m, based on the received uplink signals, to obtain channel estimates H m,i between each active user device m and the RRH;
compute intra-RRH interference precoding estimates F m for each active user device m based on the channel estimates H m,i ;
solve interference-free conditions to obtain inter-RRH interference precoding estimates for each RRH j within the DAS, wherein the interference-free conditions comprise one of
H m,i F m P j,(i+k)modN RRH =0; and
P j,(i+k)modN RRH =argmin(| H ij F j P j,(i+k)modN RRH | F ).
2. The RRH of claim 1 further arranged to communicate the inter-RRH interference precoding estimates to a base station controller of the DAS.
3. The RRH of claim 1 , wherein the processing component is arranged to perform the channel estimation using one of:
a different pilot subcarrier in the uplink transmission from each transmit antenna of the user device;
a different cyclic shift for the uplink channel from each transmit antenna of the user device; and
orthogonal cover codes for the uplink channels from the transmit antennas of the user device.
4. The RRH of claim 1 , wherein the processing component is arranged to compute intra-RRH interference precoding estimates F m using one of:
singular value decomposition;
maximum ratio combining/transmit;
zero forcing; and
minimum mean square error.
5. The RRH of claim 1 further arranged to apply the estimated intra-RRH interference precoding F m to downlink data streams for the user devices.
6. A distributed antenna system (DAS) comprising:
a base station controller; and
a plurality of remote radio head apparatuses (RRH) coupled to the base station controller, wherein
each RRH is arranged to perform distributed computation of precoding estimates within the DAS;
each RRH comprises a receiver component arranged to receive uplink signals from active user devices;
each RRH further comprises a processing component arranged to:
perform channel estimation for each active user device m, based on the received uplink signals, to obtain channel estimates H m,i between each active user device m and the RRH;
compute intra-RRH interference precoding estimates F m for each active user device m based on the channel estimates H m,i ;
solve interference-free conditions to obtain inter-RRH interference precoding estimates for each RRH j within the DAS, wherein the interference-free conditions comprise one of
H m,i F m P j,(i+k)modN RRH =0; and
P j,(i+k)modN RRH =argmin(| H ij F j P j,(i+k)modN RRH | F ).
7. The DAS of claim 6 , wherein each RRH is further arranged to communicate the inter-RRH interference precoding estimates to a base station controller of the DAS.
8. The DAS of claim 7 , wherein the base station controller is arranged to combine inter-RRH interference precoding estimates received from each of the plurality of RRHs to obtain an inter-RRH interference precoding matrix P, and to apply inter-RRH interference precoding P to downlink data streams for the user devices.
9. The DAS of claim 6 , wherein the processing component of each RRH is arranged to perform the channel estimation using one of:
a different pilot subcarrier in the uplink transmission from each transmit antenna of the user device;
a different cyclic shift for the uplink channel from each transmit antenna of the user device; and
orthogonal cover codes for the uplink channels from the transmit antennas of the user device.
10. The DAS of claim 6 , wherein the processing component of each RRH is arranged to compute intra-RRH interference precoding estimates F m using one of:
singular value decomposition;
maximum ratio combining/transmit;
zero forcing; and
minimum mean square error.
11. The DAS of claim 6 , wherein each RRH is further arranged to apply the estimated intra-RRH interference precoding F m to downlink data streams for the user devices.
12. A method of performing distributed computation of precoding estimates within a distributed antenna system, DAS; the method comprising:
receiving, by a remote radio head apparatus (RRH), uplink signals from active user devices;
performing, by the RRH, channel estimation for each active user device m, based on the received uplink signals, to obtain channel estimates H m,i between each active user device m and the RRH;
computing, by the RRH, intra-RRH interference precoding estimates F m for each active user device m based on the channel estimates H m,i ;
solving, by the RRH, interference-free conditions to obtain inter-RRH interference precoding estimates for each RRH j within the DAS, wherein the interference-free conditions comprise one of
H m,i F m P j,(i+k)modN RRH =0; and
P j,(i+k)modN RRH =argmin(| H ij F j P j,(i+k)modN RRH | F ).
13. The method of claim 12 further comprising communicating the inter-RRH interference precoding estimates to a base station controller of the DAS.
14. The method of claim 13 further comprising, at the base station controller, combining inter-RRH interference precoding estimates received from each of a plurality of RRHs to obtain an inter-RRH interference precoding matrix P, and applying inter-RRH interference precoding P to downlink data streams for the user devices.
15. The method of claim 12 , wherein the channel estimation is performed using a different pilot subcarrier in the uplink transmission from each transmit antenna of the user device.
16. The method of claim 12 comprising computing intra-RRH interference precoding estimates F m using one of:
singular value decomposition;
maximum ratio combining/transmit;
zero forcing; and
minimum mean square error.
17. The method of claim 12 further comprising applying the estimated intra-RRH interference precoding F m to downlink data streams for the user devices.