SYSTEMS AND METHODS FOR RADIO FREQUENCY CALIBRATION EXPLOITING CHANNEL RECIPROCITY IN DISTRIBUTED INPUT DISTRIBUTED OUTPUT WIRELESS COMMUNICATIONS

• US 20140269502A1
• Filed: 03/15/2013
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Rearden, LLC
• Original Assignee: Rearden, LLC
• Inventors: Forenza, Antonio, Saibi, Fadi, Pitman, Timothy A., Perlman, Stephen G.
• Granted Patent: US 10,547,358 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04B 17/12 of transmit antennas, e.g. of the amplitude or phase
• CPC Class Codes: H04B 7/024 Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0456 Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04L 25/0224 using sounding signals

Abstract

Systems and methods are described for radio frequency (RF) calibration in a multiple antenna system (MAS) with multi-user (MU) transmissions (“MU-MAS”) exploiting uplink/downlink channel reciprocity. The RF calibration is used to compute open-loop downlink precoder based on uplink channel estimates, thereby avoiding feedback overhead for channel state information as in closed-loop schemes. For example, a MU-MAS of one embodiment comprises a wireless cellular network with one or multiple beacon stations, multiple client devices and multiple distributed antennas operating cooperatively via precoding methods to eliminate inter-client interference and increase network capacity.

Claims

1. A multiple antenna system (MAS) with multiuser (MU) transmissions (“

MU-MAS”

) that employs radio frequency (RF) calibration and exploits reciprocity between downlink (DL) and uplink (UL) channels, comprising of multiple distributed antennas, multiple client devices and one or multiple beacon stations.

2. The system as in claim 1 comprising of a plurality of distributed antennas interconnected to a centralized processor (CP) via the base stations network (BSN) and employing precoding to communicate with a plurality of client devices.

3. The system as in claim 2 wherein the CP is aware of the channel state information (CSI) between the distributed antennas and the client devices, and utilizes the CSI to precode data sent over the DL or UL channels.

4. The system as in claim 3 wherein the CSI is estimated at the client devices and fed back to the distributed antennas.

5. The system as in claim 4 wherein the DL-CSI is derived at the distributed antennas from the UL-CSI using radio frequency (RF) calibration and exploiting UL/DL channel reciprocity.

6. The system as in claim 1 wherein RF calibration is employed to compute the DL MU-MAS precoding weights from the UL channel.

7. The system as in claim 6 wherein precoding weights are computed to pre-cancel inter-client interference to every UE.

8. The system as in claim 6 wherein precoding weights are computed from linear precoding methods (e.g., zero forcing or block diagonalization, matrix inversion, etc.).

9. The system as in claim 6 wherein precoding weights are computed from non-linear precoding methods (e.g., dirty-paper coding, Tomlinson-Harashima, lattice trellis, vector perturbation, etc.).

10. The system as in claim 9 wherein Round-Robin or proportional fair scheduling or other types of scheduling methods are used to guarantee similar symbol error rate (SER) performance to all UEs in the MU-MAS.

11. The system as in claim 6 wherein the MU-MAS dynamically switches between linear and non-linear precoding techniques to minimize the computational complexity of the precoder, depending on the number of distributed antennas and/or UEs in every user-cluster.

12. The system as in claim 1 wherein RF calibration is obtained by preconditioning the matrix of UL channel estimates with the complex RF calibration matrix.

13. The system as in claim 12 wherein RF calibration matrix is obtained from the effective DL and UL channels between the distributed antennas and one or multiple beacon stations.

14. The system as in claim 13 wherein the effective DL and UL channels are estimated via training signals sent from/to the distributed antennas to/from the beacon station.

15. The system as in claim 1 wherein the beacon station is any of the distributed antennas.

16. The system as in claim 1 wherein the beacon station is any of the client devices.

17. The system as in claim 2 wherein the RF calibration information is sent from the beacon to the CP via wireless or wireline feedback channel

18. The system as in claim 17 wherein quantization or codebook-based limited feedback techniques are employed to feedback the RF calibration information from the beacon to the CP.

19. The system as in claim 1 wherein the MU-MAS is a cellular network such as the long-term evolution (LTE) network, the client devices are LTE user equipments (UEs), the distributed antennas are LTE enhanced NodeBs (eNodeBs) or mobility management entities (MMES), the CP is the LTE gateway (GW), the BSN is the S1 or X1 interface.

20. The system as in claim 19 wherein the UL demodulation reference signal (DMRS) is employed at the NodeBs to estimate the UL channels from all UEs.

21. The system as in claim 19 wherein the DL cell-specific reference signal (CRS), or CSI reference signal (CSI-RS), demodulation reference signal (DM-RS) are employed to estimate the DL channel from the eNodeBs to the beacon station used for RF calibration.

22. The system as in claim 19 wherein the PUSCH physical channel is used to feedback the RF calibration information from the beacon to the CP.