BEAMFORMING METHODS AND SYSTEMS EMPLOYING MEASURED POWER AT A RECEIVER TO PERFORM CHANNEL ESTIMATION

• US 20100285752A1
• Filed: 03/16/2010
• Published: 11/11/2010
• Est. Priority Date: 05/11/2009
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Laboratories America Inc (NEC Corporation)
• Inventors: Lakshmanan, Sriram, Sundaresan, Karthikeyan
• Granted Patent: US 8,380,133 B2
• Time in Patent Office: Days
• US Class Current: 455/63.1
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0691 using subgroups of transmit antennas
• CPC Class Codes: H04B 7/0874 using subgroups of receive antennas

Abstract

Beamforming methods and systems are described in which differential channel estimation can be computed based on measured power at receiver. Simultaneous activation of antennas in separate pairs can be used to determine relative phases of antennas with respect to a reference antenna based on the power measurements. In turn, the beam forming signals can be weighted in accordance with the relative phases to adapt the signals to a multipath environment. Existing power measurement capabilities of conventional receivers can be employed to achieve approximate channel estimates.

Claims

1. An adaptive beamforming method comprising:

successively activating different pairs of antenna elements, wherein one of the antenna elements is a reference antenna element that is included in each pair and is activated in tandem with the other antenna element in each pair;

receiving indications of relative phases, at a receiver, of the antennae elements with respect to the reference antenna element; and

weighting beamforming signals transmitted from the antenna elements based on the relative phases to adapt the beamforming signals to a multipath environment and thereby improve a signal to noise ratio, wherein the relative phases are computed from powers of the signals received from tandem activation of each of the pairs of antenna elements measured at the receiver.

2. The method of claim 1, further comprising:

activating each antenna element in isolation; and

receiving indications of the magnitude of each signal from each of the isolated activations, wherein the weighting is further based on the magnitudes of the signals, at the receiver, received from the isolated activations and wherein the magnitudes are computed from the powers of the signals received from the isolated activations measured at the receiver.

3. The method of claim 2, wherein the relative phases are computed by calculating

4. The method of claim 3, wherein the weighting further comprises determining a beamforming weight for beamforming signals of each corresponding antenna element (i) by calculating

5. The method of claim 4, wherein the successively activating the different pairs of antenna elements includes applying equal weights on signals transmitted from the pairs of antenna elements and wherein the method further comprises:

successively activating the pairs of antenna elements, where antenna elements of a pair are activated in tandem, by applying different sets of weights on transmitted signals to resolve ambiguity of the relative phases, wherein each pair of the antenna elements is allocated a different set of weights, where each given set includes different weights within the given set that are based on a relative phase computed from the tandem, equal weight activation of the pair of antenna elements to which the given set is allocated; and

receiving indications of precise relative phases, at the receiver, of the antenna elements with respect to the reference antenna element,

wherein the weighting is based on the precise relative phases and wherein the precise relative phases are determined by selecting, for each pair of antenna elements, the relative phase corresponding to the weights applied to the signals transmitted from the pair of antenna elements having the highest power at the receiver among the signals transmitted from the tandem, different weight activations of the pair of antenna elements.

6. The method of claim 5, wherein the set of weights for the given pair of antenna elements (i,1) comprises φ

_i1, −

φ

_i1, π

−

φ

_i1, −

(π

−

φ

_i1), where φ

_i1 is the relative phase computed from powers of signals received from the tandem, equal weight activation of the given pair of antenna elements (i,1), and wherein the magnitudes of the signals transmitted from the tandem, different weight activations of the given pair of antenna elements (i,1) is

7. The method of claim 1, wherein the indications of the relative phases are the powers of the signals received from tandem activations of each of the pair of antenna elements measured at the receiver and wherein the relative phases are computed by a transmitter including the antenna elements.

8. The method of claim 1, wherein the relative phases are computed by and transmitted from the receiver.

9. The method of claim 1, wherein the powers of the signals received from tandem activations of each of the pair of antenna elements measured at the receiver are received signal strength indications (RSSI) and wherein the relative phases are computed solely from powers of the signals received from activations of the antenna elements.

10. A method for receiving beamforming signals comprising:

receiving signals generated by successive activation of different pairs of antenna elements at a transmitter, wherein one of the antenna elements is a reference antenna element that is included in each pair and is activated in tandem with the other antenna element in each pair;

measuring the power of each of the signals;

transmitting indications of relative phases of the antennae elements with respect to the reference antenna element; and

receiving beamforming signals transmitted from the antenna elements that are weighted based on the relative phases to adapt the beamforming signals to a multipath environment and thereby improve a signal to noise ratio, wherein the relative phases are computed from the powers of the signals received from tandem activation of each of the pair of antenna elements.

11. The method of claim 10, further comprising:

receiving signals generated by successive activation of each of the antenna elements in isolation;

measuring the power of each of the signals received from the activation of each of the antenna elements in isolation; and

transmitting indications of the magnitude of each signal received from each of the isolated activations, wherein the weighting of the beamforming signals is further based on the magnitudes of the signals, and wherein the magnitudes are computed from the powers of the signals received from the isolated activations.

12. The method of claim 11, wherein the relative phases are computed by calculating

13. The method of claim 12, wherein the weighting of the beamforming signals comprises determining a beamforming weight for beamforming signals of each corresponding antenna element (i) by calculating

14. The method of claim 13, wherein the signals received from the successive activation of the different pairs of antenna elements are weighted with equal weights and wherein the method further comprises:

receiving signals that are generated by successive activation of the pairs of antenna elements, where antenna elements of a pair are activated in tandem, and are weighted by different sets of weights to resolve ambiguity of the relative phases, wherein each pair of the antenna elements is allocated a different set of weights, where each given set includes different weights within the given set that are based on a relative phase computed from the tandem, equal weight activation of the pair of antenna elements to which the given set is allocated;

measuring the power of each of the signals received from the tandem, different weight activation of each of the pair of antenna elements; and

transmitting indications of precise relative phases of the antennae elements with respect to the reference antenna element,

wherein the weighting of the beamforming signals is based on the precise relative phases and wherein the precise relative phases are determined by selecting, for each pair of antenna elements, the relative phase corresponding to the weights applied to the signals transmitted from the pair of antenna elements having the highest power among the signals transmitted from the tandem, different weight activations of the pair of antenna elements.

15. The method of claim 14, wherein the set of weights for the given pair of antenna elements (i,1) comprises φ

_i1, −

φ

_i1, π

−

φ

_i1, −

(π

−

φ

_i1), wherein φ

_i1 is the relative phase computed from powers of signals received from the tandem, equal weight activation of the given pair of antenna elements (i,1) and wherein the magnitudes of the signals transmitted from the tandem, different weight activations of the given pair of antenna elements (i,1) is

16. The method of claim 10, wherein the indications of the relative phases are the powers of the signals received from tandem activations of each of the pair of antenna elements and wherein the relative phases are computed by the transmitter.

17. The method of claim 10, wherein the relative phases are computed by and transmitted from a receiver implementing the method.

18. The method of claim 10, wherein measuring the power of each of the signals constitutes determining received signal strength indications (RSSI) and wherein the relative phases are computed solely from powers of the signals received from activations of the antenna elements.

19. A adaptive beamforming system comprising:

a transmitter configured to successively activate pairs of antenna elements to generate signals, wherein one of the antenna elements is a reference antenna element that is included in each pair and is activated in tandem with the other antenna element in each pair; and

a receiver configured to receive and measure the powers of the signals and to transmit indications of relative phases of the antennae elements with respect to the reference antenna element to the transmitter,

wherein the transmitter is further configured to weight beamforming signals transmitted from the antenna elements to the receiver based on the relative phases to adapt the beamforming signals to a multipath environment and thereby improve a signal to noise ratio, and wherein the relative phases are computed, by the transmitter or the receiver, from the powers of the signals received from tandem activation of each of the pair of antenna elements.

20. The method of claim 19,

wherein equal weights are applied to the generated signals,

wherein the transmitter is further configured to successively activate the pairs of antenna elements, where antenna elements of a pair are activated in tandem, by applying different sets of weights on other transmitted signals to resolve ambiguity of the relative phases, wherein each pair of the antennas is allocated a different set of weights, where each given set includes different weights within the given set that are based on a relative phase computed from the tandem, equal weight activation of the pair of antenna elements to which the given set is allocated,

wherein the receiver is further configured to measure the power of each of the signals received from the tandem, different weight activations of each of the pair of antenna elements and to transmit indications of precise relative phases of the antennae elements with respect to the reference antenna element, and

wherein the transmitter is configured to weight the beamforming signals based on the precise relative phases determined by selecting, for each pair of antenna elements, the relative phase corresponding to the weights applied to the signals transmitted from the pair of antenna elements having the highest power among the signals transmitted from the tandem, different weight activations of the pair of antenna elements.