Pilots for MIMO communication systems

Patent metadata

Field	Value
Publication number	US-9967005-B2
Application number	US-201514836620-A
Country	US
Kind code	B2
Filing date	Aug 26, 2015
Priority date	Oct 25, 2002
Publication date	May 8, 2018
Grant date	May 8, 2018

Abstract

Pilots suitable for use in MIMO systems and capable of supporting various functions are described. The various types of pilot include—a beacon pilot, a MIMO pilot, a steered reference or steered pilot, and a carrier pilot. The beacon pilot is transmitted from all transmit antennas and may be used for timing and frequency acquisition. The MIMO pilot is transmitted from all transmit antennas but is covered with different orthogonal codes assigned to the transmit antennas. The MIMO pilot may be used for channel estimation. The steered reference is transmitted on specific eigenmodes of a MIMO channel and is user terminal specific. The steered reference may be used for channel estimation. The carrier pilot may be transmitted on designated subbands/antennas and may be used for phase tracking of a carrier signal. Various pilot transmission schemes may be devised based on different combinations of these various types of pilot.

First claim

What is claimed is:

1. A method for wireless multiple-input multiple-output (MIMO) communication utilizing orthogonal frequency division multiplexing (OFDM) comprising:
obtaining a set of pilot symbols for each antenna in a plurality of antennas;
obtaining an orthogonal sequence for each antenna in the plurality of antennas, wherein the plurality of antennas are assigned different orthogonal sequences;
covering the set of pilot symbols for each antenna with the orthogonal sequence for the antenna to obtain a set of sequences of covered pilot symbols for the antenna, wherein the set of pilot symbols are covered so as to reduce an amount of overhead associated with pilot transmission;
processing the set of sequences of covered pilot symbols for each antenna to obtain a sequence of OFDM symbols for the antenna; and
transmitting the plurality of sequences of OFDM symbols from the plurality of antennas.

2. The method of claim 1 , wherein the pilot symbols correspond to one or more of a beacon pilot, a MIMO pilot, a steered pilot and a carrier pilot.

3. The method of claim 1 , wherein the pilot symbols correspond to a MIMO pilot and wherein covering the set of pilot symbols comprises covering the set of pilot symbols using an orthogonal code corresponding to one or more of an M-sequence or a time-shifted version of an M-sequence.

4. The method of claim 1 , wherein the pilot symbols correspond to a MIMO pilot and wherein covering the set of pilot symbols comprises covering the set of pilot symbols using a plurality of Walsh sequences scaled by a complex multipliers using complex correction factors.

5. The method of claim 1 , wherein the set of pilot symbols are for transmission on a set of subbands and wherein transmitting the plurality of sequences of symbols comprises transmitting a plurality of pilot sequences on corresponding principal eigenmodes of respective subbands.

6. The method of claim 5 , wherein the pilot symbols correspond to a carrier pilot and wherein transmitting the plurality of sequences of symbols comprises transmitting the carrier pilot on the principal eigenmodes while using a steering vector for spatial processing.

7. The method of claim 1 , wherein the pilot symbols correspond to a steered pilot and wherein transmitting the plurality of sequences of symbols comprises:
obtaining a set of steered reference pulses for each of a plurality of eigenmodes; and
transmitting the sets of steered reference pulses using time-domain multiplexing.

8. The method of claim 1 , wherein the pilot symbols correspond to a steered pilot and wherein transmitting the plurality of sequences of symbols comprises:
isolating a single multipath component for a wideband channel;
processing the multipath component as a narrowband channel to obtain a single steering vector for the multipath component for each of a plurality of eigenmodes; and
transmitting the steering vector.

9. The method of claim 1 , wherein the pilot symbols correspond to a beacon pilot and a MIMO pilot and wherein transmitting the plurality of sequences of symbols comprises:
transmitting symbols corresponding to the beacon pilot with information sufficient to permit a user terminal to achieve timing and frequency acquisition; and
transmitting symbols corresponding to the MIMO pilot with information sufficient to permit a user terminal to obtain one or more of (a) an estimate of a downlink MIMO channel, (b) a steering vector for an uplink transmission and (3) a matched filter for a downlink transmission.

10. The method of claim 1 , further comprising:
receiving MIMO pilot signals from a user terminal; and
estimating a calibrated uplink channel response from the received MIMO pilot signals.

11. The method of claim 1 , wherein transmitting the plurality of sequences of symbols comprises:
transmitting data on a plurality of wideband eigenmodes in accordance with spatial multiplexing; and
transmitting data on a principal wideband eigenmode in accordance with one or more of beam-steering or beam-forming.

12. The method of claim 1 , wherein the pilot symbols correspond to a steered reference and wherein transmitting the plurality of sequences of symbols comprises transmitting a set of symbols on one wideband eigenmode in a given symbol period while performing spatial processing with a set of eigenvectors for that wideband eigenmode.

13. The method of claim 1 , wherein the pilot symbols correspond to a steered reference and wherein transmitting the plurality of sequences of symbols comprises transmitting multiple sets of the symbols on multiple wideband eigenmodes in a same symbol period by performing spatial processing with multiple sets of eigenvectors for the wideband eigenmodes.

14. The method of claim 1 , wherein the pilot symbols correspond to a steered pilot and wherein transmitting the plurality of sequences of symbols comprises transmitting a steered pilot generated using a set of normalized eigenvectors for a principal wideband eigenmode with information sufficient to permit a user terminal to derive a matched filter for a beam-steering mode.

15. The method of claim 14 , wherein the steered pilot is transmitted in one or more of a preamble or a pilot portion of a forward channel protocol data unit.

16. The method of claim 1 , wherein the set of pilot symbols is for transmission on a set of subbands and wherein a number of subbands used in each set is selected based on a signal to noise ratio (SNR) of a wideband eigenmode associated with the set.

17. The method of claim 16 , wherein subband multiplexing is used to reduce an amount of overhead needed to transmit a steered pilot.

18. The method of claim 1 , wherein the pilot symbols correspond to a steered pilot and wherein the method further comprises:
receiving a steered reference pilot; and
deriving an estimate of an input vector so that a mean square error between the received pilot and the transmitted pilot symbols is minimized.

19. The method of claim 1 , wherein the pilot symbols correspond to a steered pilot and wherein the method further comprises:
receiving a steered reference pilot for one wideband eigenmode in any particular symbol period; and
obtaining an estimate of one eigenvector for each subband of that wideband eigenmode for use in one or more of matched filtering and spatial processing.

20. The method of claim 1 , wherein the pilot symbols correspond to a carrier pilot and wherein the method further comprises selectively resetting pilot sequences for each of a plurality of transport channels for transmission.

21. A device for wireless multiple-input multiple-output (MIMO) communication utilizing orthogonal frequency division multiplexing (OFDM) comprising:
a plurality of antennas;
a processing circuit configured to
obtain a set of pilot symbols for each antenna in the plurality of antennas,
obtain an orthogonal sequence for each antenna in the plurality of antennas, wherein the plurality of antennas are assigned different orthogonal sequences,
cover the set of pilot symbols for each antenna with the orthogonal sequence for the antenna to obtain a set of sequences of covered pilot symbols for the antenna, wherein the set of pilot symbols are covered so as to reduce an amount of overhead associated with pilot transmission, and
process the set of sequences of covered pilot symbols for each antenna to obtain a sequence of OFDM symbols for the antenna; and

a transmitter configured to
transmit the plurality of sequences of OFDM symbols from the

Assignees

• Qualcomm Inc

Inventors

• Ketchum John
• Wallace Mark
• Walton J Rodney
• Howard Steven

Classifications

• H04L1/0618

  Space-time coding · CPC title

• H04L25/0226

  sounding signals per se · CPC title

• H04B7/0421 Primary

  utilizing implicit feedback, e.g. steered pilot signals · CPC title

• H04L5/0023

  Time-frequency-space · CPC title

• H04B7/0684

  using different training sequences per antenna · CPC title