Airsync: enabling distributed multiuser MIMO with full multiplexing gain

• US 8,995,410 B2
• Filed: 05/15/2013
• Issued: 03/31/2015
• Est. Priority Date: 05/25/2012
• Status: Active Grant

• Current Assignee: University of Southern California
• Original Assignee: University of Southern California
• Inventors: Balan, Horia Vlad, Psounis, Konstantinos, Caire, Giuseppe
• Primary Examiner(s): Mew, Kevin
• Application Number:
  US13/895,181
• Publication Number:
  US 20130315211A1
• Time in Patent Office: 685 Days
• Field of Search: 370/336, 370/338, 370345-346, 370/349, 370/389, 370/392, 370400-401, 370/428, 370/442, 370/465, 370/498, 370/500
• US Class Current: 370/336
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2672 Frequency domain
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2692 with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0035 Resource allocation in a cooperative multipoint environment

Abstract

Time and phase synchronization may enable distributed multiuser multiple-input multiple-output (MIMO) architectures and techniques, such as supported by the IEEE 802.11n standard, where several access points are connected to a central server and operate as a large distributed multi-antenna access point. The phase of all access points can be locked using a common reference (e.g., a synchronization tone) broadcasted over the air in conjunction with a predictive filter (e.g., a Kalman filter) which closely tracks the phase drift for each subcarrier channel.

Claims

1. A system for implementing distributed multi-user MIMO with spatial multiplexing, the system comprising:

a main transmitter operative to transmit (i) a plurality of packets with data over a transmission band, and (ii) a reference signal including a pilot tone, wherein each packet includes a format with an initial probing header and a number of channel estimation symbols;

one or more secondary transmitters operative to receive the probing header transmitted by the main transmitter and determine a block timing of the packet; and

a central server operative to select one or more clients that are each operative to receive data over separate channels within the transmission band and to process channel estimation symbols for each of the main and secondary transmitters.

2. The system of claim 1, wherein the pilot tone is out of band relative to the transmission band.

3. The system of claim 1, wherein each secondary transmitter is operative to track the phase of the pilot tone for estimating an associated phase drift from the main transmitter.

4. The system of claim 1, each secondary transmitter includes a synchronization circuit operative to detect the initial probing header and to determine a block timing of the packet.

5. The system of claim 1, wherein the central server is operative to provide precoding for the data transmitted by each of the main transmitter and the one or more secondary transmitters.

6. The system of claim 5, wherein the precoding comprises zero-forcing beamforming (ZFBF).

7. The system of claim 5, wherein, for each of the transmitters, the central server is operative to compute a waveform of the signal to be transmitted in the next downlink slot.

8. A system for implementing distributed multi-user MIMO with spatial multiplexing, the system comprising:

a memory;

a processor having access to the memory and configured to;

cause a main transmitter to transmit (i) a plurality of packets with data over a transmission band, and (ii) a reference signal including a pilot tone, wherein each packet includes a format with an initial probing header and a number of channel estimation symbols;

cause one or more secondary transmitters to receive the probing header transmitted by the main transmitter and determine a block timing of the packet; and

cause a central server to select one or more clients that are each operative to receive data over separate channels within the transmission band and to process channel estimation symbols for each of the main and secondary transmitters.

9. The system of claim 8, wherein the pilot tone is out of band relative to the transmission band.

10. The system of claim 8, wherein each secondary transmitter is operative to track the phase of the pilot tone for estimating an associated phase drift from the main transmitter.

11. The system of claim 8, each secondary transmitter includes a synchronization circuit operative to detect the initial probing header and to determine a block timing of the packet.

12. The system of claim 8, wherein the central server is operative to provide precoding for the data transmitted by each of the main transmitter and the one or more secondary transmitters.

13. The system of claim 12, wherein the precoding comprises zero-forcing beamforming (ZFBF).

14. The system of claim 12, wherein, for each of the transmitters, the central server is operative to compute a waveform of the signal to be transmitted in the next downlink slot.