MOBILE ASSISTED DOWNLINK BEAMFORMING WITH ANTENNA WEIGHT FEEDBACK

• US 20080081671A1
• Filed: 10/03/2006
• Published: 04/03/2008
• Est. Priority Date: 10/03/2006
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Tan, Jun, Ghosh, Amitava, Wang, Fan, Benes, Stanley J.
• Granted Patent: US 7,747,225 B2
• Time in Patent Office: Days
• US Class Current: 455/562.1
• CPC Class Codes: H01Q 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
• CPC Class Codes: H01Q 3/30 varying the relative phase between the radiating elements of an array H01Q3/2605, H01Q3/2658, H01Q3/2682, H01Q3/44 take precedence
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0636 Feedback format
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex

Abstract

A subscriber unit (104) with multiple receive antennas (160, 162) and a single transmit antenna (160) derives beamforming weights to be used at a base station (102) with multiple transmitting antennas (602, 604, 606, and 608). The downlink beamforming weights are derived at the subscriber unit (104) from a prior downlink transmission from the base station (102) to the subscriber device (104) and an uplink sounding signal is used to carry derived downlink beam forming weights to the base station (102). Downlink antenna specific pilots (without weight) are used at the subscriber device (104) to determine the beamforming weights. Decimated sounding signals, where the number of sounding subcarriers is al least the same as the number of antennas at the base station (102), allow multiple users to sound at the same time.

Claims

1. A method on an RF communications receiver, the method comprising:

receiving n downlink pilot signals with at least one receive antenna at a receiver, each of the n downlink pilot signals being associated with a respective one of n downlink transmit antennas at a remote transmitter transmitting the n downlink pilot signals;

determining, based upon the received n downlink pilot signals, a respective RF propagation channel between each respective receive antenna within the at least one receive antenna at the receiver and each respective downlink transmit antenna within n downlink transmit antennas at the remote transmitter;

determining, based upon characteristics of each respective downlink RF propagation channel, n downlink transmit antenna weighting factors for each downlink data stream from the remote transmitter to the receiver, each downlink transmit antenna weighting factor within the n downlink transmit antenna weighting factors corresponding to a respective weighting factor to be applied to one respective downlink transmit antenna within n downlink transmit antennas and one respective downlink data stream being transmitted from the remote transmitter to the receiver within at least one downlink data streams;

modulating a respective modulation signal onto each uplink subcarrier within n uplink subcarriers, wherein each respective modulation signal comprises a respective complex value corresponding to one respective downlink transmit antenna weighting factor within the n downlink transmit antenna weighting factors; and

transmitting the uplink subcarriers through at least one transmitting receive antenna that is within the at least one receive antenna.

2. The method according to claim 1, wherein the modulating comprises:

modulating a respective signal on a first subcarrier within the n uplink subcarriers with a first antenna weight corresponding to at least one respective downlink data stream from the remote transmitter to the receiver; and

modulating an m^th of the n subcarriers with a complex value corresponding to an m^th antenna weight corresponding to the at least one respective downlink data stream from the remote transmitter to the receiver, where each uplink subcarrier is separated from each other uplink subcarrier by a decimation factor, and wherein 1<

m≦

n.

3. The method according to claim 2, wherein the modulation of the first of the n uplink subcarriers comprises:

summing, to produce a first sum, complex values corresponding to the respective RF propagation channel for the first subcarrier between n base station transmit antennas and the at least one transmitting receive antenna at the remote transmitter;

calculating a conjugate of the first sum;

multiplying the first downlink antenna weight by the conjugate of the first sum to produce the respective modulation signal; and

scaling the respective modulation signal for the first subcarrier.

4. The method according to claim 2, where the modulating the first of the n uplink subcarriers comprises:

summing, to produce a first sum, complex values corresponding to the respective RF propagation channel for the first subcarrier between n base station transmit antennas and the at least one transmitting receive antenna at the remote transmitter;

calculating a conjugate of the first sum;

quantizing the first downlink antenna weight;

multiplying the first quantized downlink antenna weight with the conjugate of the first sum to produce the respective modulation signal for the first subcarrier; and

scaling the respective modulation signal for the first subcarrier.

5. The method according to claim 2, where the modulation of the m^th of the n uplink subcarriers comprises:

summing, to produce a m^th sum, complex values corresponding to the respective RF propagation channel for the m^th subcarrier between n base station transmit antennas and the at least one transmitting receive antenna at the remote transmitter;

calculating a conjugate of the m^th sum;

multiplying the m^th downlink antenna weight by the conjugate of the m^th sum to produce the respective modulation signal for the m^th subcarrier; and

scaling the respective modulation signal for the m^th subcarrier.

6. The method according to claim 2, where the modulating the m^th of the n subcarriers comprises:

summing, to produce a m^th sum, complex values corresponding to the respective RF propagation channel for the m^th subcarrier between n base station transmit antennas and the at least one transmitting receive antenna at the remote transmitter;

calculating a conjugate of the m^th sum;

quantizing the m^th downlink antenna weight;

multiplying the m^th quantized downlink antenna weight with the conjugate of the m^th sum to produce the respective modulation signal for the m^th subcarrier; and

scaling the respective modulation signal for the m^th subcarrier.

15. The method according to claim 1, wherein the modulating comprises:

identifying n sets of weight products, each of the n sets of weight products containing a respective n weight products and wherein each set of weight products within the n sets of weight products is to be received by a respective downlink transmit antenna within the n downlink transmit antennas at the remote transmitter;

associating each weight product of the (n*n) weight products with a respective subcarrier,

associating each of the n weight products within each of the n sets of weight products with a respective associated downlink transmit antenna weighting factor within the n downlink transmit antenna weighting factors, wherein each of the n sets of weight products comprise n weight products that are each associated with different respective downlink transmit antenna weighting factors;

associating each set of weight products within the n sets of weight products with a respective associated RF propagation channel;

calculating each of the weight products by determining a respective product of the respective associated downlink transmit antenna weighting factor for that weight product and a complex value evaluation of the respective associated RF propagation channel for the respective associated subcarrier associated with that weight product; and

modulating each of the respective subcarriers with its associated weight product.

16. The method according to claim 15, further comprising:

quantizing, prior to the calculating the n weight products, each of the n downlink transmit antenna weighting factors, and

wherein the calculating the n weight products uses respective associated downlink transmit antenna weighting factors that are quantized downlink transmit antenna weighting factors.

7. A base station, comprising:

a receiver adapted to receive, from a remote transceiver at a local transceiver, a plurality of signals on uplink subcarriers, wherein each uplink signal in the plurality of uplink signals is modulated by a respective complex value comprising a representation of a downlink transmission antenna weight to be applied to a respective downlink transmit antenna at the local transceiver; and

a weight extraction processor adapted to extract, by demodulating the plurality of signals on uplink subcarriers, a plurality of downlink transmission antenna weights comprising each of the respective complex values modulated signal onto each respective uplink subcarrier.

8. The base station according to claim 7, further comprising a weighting unit adapted to apply, to each respective downlink transmission antenna at the local transceiver, a respective downlink transmission antenna weight within the plurality of downlink transmission antenna weights when transmitting a signal to the remote transceiver.

9. The base station according to claim 7, wherein the weight extraction processor is further adapted to extract by deriving the plurality of downlink transmission antenna weights by combining the plurality of received signals on the uplink subcarriers corresponding to modulation signals for antenna weights.

10. The base station according to claim 7, wherein the weight extraction processor is further adapted to extract, by combining the plurality of received signals on uplink subcarriers corresponding to a plurality of downlink transmission antenna weights comprising each of the respective complex values modulated onto each respective uplink subcarrier.

11. The base station according to claim 10, further comprising a weighting unit adapted to apply, to each respective downlink transmission antenna at the local transceiver, a respective downlink transmission antenna weight within the plurality of downlink transmission antenna weights when transmitting a signal to the remote transceiver.

12. The base station according to claim 7, wherein the receiver is further adapted to:

receive, at a first of n antennas on a local transceiver, a first through n uplink subcarriers, wherein each uplink subcarrier in the first through n of uplink subcarriers is separated by a decimation value and modulated by a respective complex value representing a downlink transmission antenna weight to be applied to a respective downlink transmit antenna at the local transceiver; and

receive, at an m^th of n antennas on the local transceiver, signals on an m^th set of m*n-(n-1) through m*n uplink subcarriers, wherein, each uplink subcarrier in the m*n-(n-1) through m*n of uplink subcarriers is separated by the decimation value and carries a symbol modulated by a corresponding one of the respective complex values representing a downlink transmission antenna weight to be applied to the respective downlink transmit antennas at the local transceiver and a first downlink data stream to be transmitted to the receiver within at least one respective downlink data stream to be transmitted to the receiver, and wherein 1<

m≦

n, and

wherein the weight extraction processor is further adapted to extract by extracting a plurality of extracted downlink transmission antenna weights comprising each of the respective complex values modulated onto each respective uplink subcarrier.

13. The base station according to claim 12, further comprising a weighting unit adapted to apply, to each of the respective downlink transmission antennas at the local transceiver, a respective downlink transmission antenna weight within the plurality of extracted downlink transmission antenna weights when transmitting a downlink signal to the remote transceiver.

14. A method of communicating antenna beamforming weighting values, the method comprising:

receiving, at a first transceiver, n downlink pilot signals with at least one receive antenna, each of the n downlink pilot signals being associated with a respective one of n downlink transmit antennas at a second transceiver transmitting the n downlink pilot signals;

determining, based upon the received n downlink pilot signals, a respective RF propagation channel between each respective receive antenna within the at least one receive antenna at the first transceiver and each respective downlink transmit antenna within n downlink transmit antennas at the second transceiver;

determining, based upon characteristics of each respective downlink RF propagation channel, n downlink transmit antenna weighting factors for each downlink data stream from the second transceiver to the first transceiver, each downlink transmit antenna weighting factor within the n downlink transmit antenna weighting factors corresponding to a respective weighting factor to be applied to one respective downlink transmit antenna within n downlink transmit antennas and one respective downlink data stream being transmitted by the second transceiver to the first transceiver within at least one downlink data streams;

modulating a respective modulation signal onto each uplink subcarrier within n uplink subcarriers, wherein each respective modulation signal comprises a respective complex value corresponding to one respective downlink transmit antenna weighting factor within the n downlink transmit antenna weighting factors;

transmitting the uplink subcarriers from the second transceiver;

receiving, from a first transceiver at a second transceiver, the uplink subcarriers, wherein each uplink signal in the plurality of uplink signals is modulated by a respective complex value comprising a representation of a downlink transmission antenna weight to be applied to a respective downlink transmit antenna at the second transceiver; and

extracting, by demodulating the respective modulation signals on each uplink subcarrier within n uplink subcarriers, a plurality of downlink transmission antenna weights comprising each of the respective complex values modulated signal onto each respective uplink subcarrier.

17. The method according to claim 14, further comprising:

estimating, at the second transceiver, uplink channel characteristics, and wherein the modulating comprises;

modulating a respective signal on a first subcarrier within the n uplink subcarriers with a complex value corresponding to a first antenna weight corresponding to at least one respective downlink data stream from the remote transmitter to the receiver; and

modulating an m^th of the n subcarriers with a complex value corresponding to an m^th antenna weight corresponding to the at least one respective downlink data stream from the remote transmitter to the receiver, where each uplink subcarrier is separated from each other uplink subcarrier by a decimation factor, and wherein 1<

m≦

n and wherein the extracting is based at least in part on the uplink channel characteristics.