SYSTEM AND METHODS TO COMPENSATE FOR DOPPLER EFFECTS IN DISTRIBUTED-INPUT DISTRIBUTED-OUTPUT WIRELESS SYSTEMS

• US 20120314570A1
• Filed: 05/04/2012
• Published: 12/13/2012
• Est. Priority Date: 04/02/2004
• Status: Active Grant

• Current Assignee: Rearden, LLC
• Original Assignee: Rearden, LLC
• Inventors: Forenza, Antonio, Perlman, Stephen G.
• Granted Patent: US 9,312,929 B2
• Time in Patent Office: Days
• US Class Current: 370/230
• CPC Class Codes: H04B 7/01 Reducing phase shift
• 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 7/0617 for beam forming
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04W 28/0236 radio quality, e.g. interference, losses or delay
• CPC Class Codes: H04W 72/121 for groups of terminals or users
• CPC Class Codes: H04W 72/51 based on terminal or device properties
• CPC Class Codes: H04W 72/541 using the level of interference
• CPC Class Codes: H04W 88/085 Access point devices with remote components

Abstract

A system and methods are described which compensate for the adverse effect of Doppler on the performance of DIDO systems. One embodiment of such a system employs different selection algorithms to adaptively adjust the active BTSs to different UEs based by tracking the changing channel conditions. Another embodiment utilizes channel prediction to estimate the future CSI or DIDO precoding weights, thereby eliminating errors due to outdated CSI.

Claims

1. A multiuser (MU) multiple antenna system (MAS) that adaptively reconfigures to compensate for Doppler effects due to user mobility or changes in the propagation environment.

2. The system as in claim 1 wherein the MU-MAS system is a distributed-input distributed-output (DIDO) wireless system comprising one or more sets of user equipment (UE), base transceiver stations (BTSs), controllers (CTRs), centralized processors (CPs) and base station networks (BSNs).

3. The system as in claim 1 employing distributed antennas that exploits spatial, polarization and/or pattern diversity to enhance data rate and/or coverage to one or multiple users in wireless systems.

4. The system as in claim 1 wherein the UEs are located around or in between the distributed antennas or surrounded by the distributed antennas.

5. The system as in claim 1 wherein MU-MAS employs complex weights at the receiver of the uplink channel to demodulate independent streams (e.g. data or CSI) from the UEs.

6. The system as in claim 5 wherein the complex weights of the uplink receiver are derived from the downlink precoding weights or computed via maximum ratio combining receiver.

7. The system as in claim 2 wherein the CP and the BTSs are equipped with encoders/decoders to compress/decompress information exchanged among them over the BSN.

8. The system in claim 7 wherein the precoded baseband data streams are compressed, before being transmitted from/to the BTS to/from the DIDO distributed antennas, to reduce overhead over the BSN.

9. The system as in claim 2 wherein the CP adaptively selects the BTSs to be used for low- or high-mobility UEs based on latency over the BSN.

10. The system as in claim 9 wherein the adaptation is based on the type of high versus low data rate BSN, or QoS, or average traffic statistics (e.g., daytime or nighttime use of different networks), or instantaneous traffic statistics (e.g., temporary network congestions) over the BSN.

11. The system as in claim 2 wherein the CP adaptively selects the BTSs to be used for low- or high-mobility UEs based on the Doppler velocities of every BTS-UE link.

12. The system as in claim 2 wherein linear prediction is employed to estimate the CSI or DIDO precoding weights in the future, thereby eliminating the adverse effect of Doppler on the performance of the DIDO system.

13. The system as in claim 12 wherein the prediction is employed in the time, frequency and/or space domains.

14. A method implemented within a multiuser (MU) multiple antenna system (MAS) to compensate for Doppler effects comprising:

measuring Doppler velocity of a first mobile user relative to a plurality of base transceiver stations (BTSs); and

dynamically assigning the first mobile user to a first BTS of the plurality of BTSs based on the measured Doppler velocity for the first BTS relative to other BTSs.

15. The method as in claim 14 wherein if the first mobile user has a measured Doppler velocity which is relatively higher than a second mobile user, then dynamically assigning comprises assigning the first mobile user to a first BTS and assigning the second mobie user to a second BTS, the first BTS having a relatively lower latency associated therewith than the second BTS.

16. The method as in claim 14 wherein the latency includes (a) time taken to transmit a first training signal from the first mobile user to a BTS, (b) round-trip delay over a base station network (BSN) connecting the BTSs to a centralized processor (CP), and (c) time taken buy the CP to process channel state information (CSI) for the wireless channel between the BTSs and the first mobile user, generate precoded data streams for the first mobile user based on the CSI, and schedule transmissions to different mobile users including the first user for the current transmission.

17. The method as in claim 16 wherein the latency further includes time taken to transmit a second training signal from the BTS to the first mobile user.

18. The method as in claim 14 wherein dynamically assigning further comprises assigning based on a combination of link quality of a communication channel between each BTS and the first mobile user and the measured Doppler velocity associated with each BTS with respect to the first user.

19. The method as in claim 18 wherein, for a given Doppler velocity, the BTS having the relatively higher link quality is selected.

20. The method as in claim 18 wherein for a given link quality, the BTS having the relatively lower Doppler velocity is selected.

21. The method as in claim 14 further comprising:

estimating future complex channel coefficients based on past complex channel coefficients to compensate for the adverse effect of Doppler on communication between the BTSs and the first mobile user.

22. The method as in claim 21 wherein linear prediction is employed for estimation.

23. The method as in claim 14 wherein the first mobile user is dynamically assigned to the first BTS based on both the Doppler Velocity and channel state information (CSI) defining quality of communication channels between the mobile user and each of the BTSs within the plurality.

24. The method as in claim 23 further comprising:

building a matrix of Doppler velocities and link qualities for each of the BTSs within the plurality with respect to the first mobile user; and

selecting a BTS which has a Doppler velocity below a specified threshold and link quality above a specified threshold.

25. A multiuser (MU) multiple antenna system (MAS) to compensate for Doppler effects comprising:

a plurality of base transceiver stations (BTSs);

a first mobile user establishing a communication link with each of the BTSs;

a centralized processor (CP) measuring Doppler velocity of a first mobile user relative to each of the BTSs and dynamically assigning the first mobile user to a first BTS of the plurality of BTSs based on the measured Doppler velocity for the first BTS relative to other BTSs.

26. The system as in claim 25 wherein if the first mobile user has a measured Doppler velocity which is relatively higher than a second mobile user, then dynamically assigning comprises assigning the first mobile user to a first BTS and assigning the second mobie user to a second BTS, the first BTS having a relatively lower latency associated therewith than the second BTS.

27. The system as in claim 25 wherein the latency includes (a) time taken to transmit a first training signal from the first mobile user to a BTS, (b) round-trip delay over a base station network (BSN) connecting the BTSs to a centralized processor (CP), and (c) time taken buy the CP to process channel state information (CSI) for the wireless channel between the BTSs and the first mobile user, generate precoded data streams for the first mobile user based on the CSI, and schedule transmissions to different mobile users including the first user for the current transmission.

28. The system as in claim 27 wherein the latency further includes time taken to transmit a second training signal from the BTS to the first mobile user.

29. The system as in claim 25 wherein dynamically assigning further comprises assigning based on a combination of link quality of a communication channel between each BTS and the first mobile user and the measured Doppler velocity associated with each BTS with respect to the first user.

30. The system as in claim 29 wherein, for a given Doppler velocity, the BTS having the relatively higher link quality is selected.

31. The system as in claim 29 wherein for a given link quality, the BTS having the relatively lower Doppler velocity is selected.

32. The system as in claim 25 wherein the CP estimates future complex channel coefficients based on past complex channel coefficients to compensate for the adverse effect of Doppler on communication between the BTSs and the first mobile user.

33. The system as in claim 32 wherein linear prediction is employed for estimation.

34. The system as in claim 25 wherein the first mobile user is dynamically assigned to the first BTS based on both the Doppler Velocity and channel state information (CSI) defining quality of communication channels between the mobile user and each of the BTSs within the plurality.

35. The system as in claim 34 wherein the CP performs the additional operations of:

building a matrix of Doppler velocities and link qualities for each of the BTSs within the plurality with respect to the first mobile user; and

selecting a BTS which has a Doppler velocity below a specified threshold and link quality above a specified threshold.