Using antenna arrays in multipath environment

• US 7,184,492 B2
• Filed: 02/10/2003
• Issued: 02/27/2007
• Est. Priority Date: 02/10/2003
• Status: Active Grant

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Primary Examiner(s): Kim; Kevin
• Application Number:
  US10/361,244
• Publication Number:
  US 20040156443A1
• Time in Patent Office: 1,478 Days
• Field of Search: 375/299, 375/267, 375/260
• US Class Current: 375/299
• CPC Class Codes: H04B 7/0408 using two or more beams, i.e. beam diversity
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/0695 using beam selection

Abstract

The invention comprises using beamforming antenna to coherently transmit an information signal to a receiver using two or more directional beams. In one embodiment, the phase and timing of the information signals carried by each directional beams are adjusted such that the signals arrive synchronously at the mobile terminal. Time synchronization may be obtained by delaying signals transmitted on selected directional beams to compensate for different propagation delays, or by preconditioning and filtering the signals using a channel coefficient matrix.

Claims

1. A method of transmitting an information signal to a first mobile terminal comprising:

forming a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay;

selecting two or more directional beams to use for transmitting the information signal to the first mobile terminal;

for each selected directional beam, generating a transmit signal derived from the information signal for transmission to the first mobile terminal;

transmitting the transmit signals to the first mobile terminal over respective ones of the selected directional beams; and

compensating for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein compensating for differences in propagation delay between the selected directional beams comprises delaying transmit signals transmitted on at least one of the selected directional beams; and

,

wherein forming a transmit signal for a selected directional beam comprises;

determining a channel coefficient polynomial describing the estimated amplitude and phase attenuation associated with the selected directional beam; and

prefiltering the information signal using the channel coefficient polynomial.

2. The method of claim 1 wherein prefiltering the information signal using the channel coefficient polynomial comprises prefiltering the information signal with a time reverse conjugate of the channel coefficient polynomial.

3. The method of claim 2 wherein the channel coefficient polynomial includes complex coefficients encoding phase and amplitude attenuation associated with the directional beam and propagation delay values.

4. The method of claim 3 wherein compensating for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal comprises adjusting the propagation delay values in the channel coefficient polynomial to compensate for the differences in propagation delay between selected directional beams.

5. The method of claim 2 wherein forming a transmit signal for a selected directional beam further comprises filtering the information signals using a pulse shaping filter.

6. The method of claim 1, wherein forming a transmit signal for a selected directional beam comprises pre-filtering the information signal in a transmit signal generator to compensate for inter-symbol interference in the selected directional beams.

7. The method of claim 1, wherein forming a transmit signal for a selected directional beam comprises pre-filtering the information signal in a transmit signal generator to compensate for interference between the at least two directional beams.

8. A method of transmitting an information signal to a first mobile terminal comprising:

forming a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay;

selecting two or more directional beams to use for transmitting the information signal to the first mobile terminal;

for each selected directional beam, generating a transmit signal derived from the information signal for transmission to the first mobile terminal;

transmitting the transmit signals to the first mobile terminal over respective ones of the selected directional beams; and

compensating for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein selecting at two or more directional beams to use for transmitting an information signal to the first mobile terminal comprises estimating path loss associated with the plurality of directional beams and selecting directional beams from the plurality of directional beams based on the estimated path loss.

9. A method of transmitting an information signal to a first mobile terminal comprising:

forming a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay;

selecting two or more directional beams to use for transmitting the information signal to the first mobile terminal;

for each selected directional beam, generating a transmit signal derived from the information signal for transmission to the first mobile terminal;

transmitting the transmit signals to the first mobile terminal over respective ones of the selected directional beams; and

compensating for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein selecting at two or more directional beams to use for transmitting an information signal to the mobile terminal comprises measuring the strength of signals received from the first mobile terminal on the plurality of directional beams and selecting directional beams from the plurality of directional beams based on the strength of the received signals.

10. A method of transmitting an information signal to a first mobile terminal comprising:

forming a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay;

selecting two or more directional beams to use for transmitting the information signal to the first mobile terminal;

for each selected directional beam, generating a transmit signal derived from the information signal for transmission to the first mobile terminal;

transmitting the transmit signals to the first mobile terminal over respective ones of the selected directional beams; and

compensating for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein selecting at two or more directional beams to use for transmitting an information signal to the first mobile terminal comprises;

estimating multi-path propagation channel characteristics between the transmitter and the first mobile terminal for the plurality of directional beams; and

choosing the selected directional beams based on the estimated multipath propagation channel characteristics.

11. The method of claim 10 wherein estimating multipath propagation channel characteristics comprises determining the multipath channel characteristics based on a loopback signal from the first mobile terminal.

12. A method of transmitting an information signal to a first mobile terminal comprising:

forming a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay;

selecting two or more directional beams to use for transmitting the information signal to the first mobile terminal;

for each selected directional beam, generating a transmit signal derived from the information signal for transmission to the first mobile terminal;

transmitting the transmit signals to the first mobile terminal over respective ones of the selected directional beams; and

compensating for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

further comprising reselecting at least one directional beam responsive to path loss variations.

13. A communication system to transmit an information signal to a first mobile terminal comprising:

one or more beamforming antennas to form a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay, where each beamforming antenna comprises a plurality of antenna elements;

a controller to select two or more directional beams from at least one beamforming antenna for transmitting the information signal to the first mobile terminal;

a transmit signal generator coupled to each of said beamforming antenna and said controller to derive a transmit signal from the information signal for each selected directional beam; and

a delay element to compensate for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein the delay element compensates for differences in the propagation delay between the selected directional beams by delaying the transmit signal on at least one of the selected directional beams; and

,

wherein the transmit signal generator determines a channel coefficient polynomial describing the estimated amplitude and phase attenuation associated with the selected directional beams.

14. The communication system of claim 13 wherein the delay element adjusts the propagation delay in the channel coefficient polynomial to compensate for the differences in propagation delay between selected directional beams.

15. The communication system of claim 13 wherein the transmit signal generator includes a filter to pre-filter the information signal using the channel coefficient polynomial.

16. The communication system of claim 15 wherein the filter comprises a finite impulse response filter to pre-filter the information signal with a time reverse conjugate of the channel coefficient polynomial.

17. The communication system of claim 16 wherein the channel coefficient polynomial determined by the transmit signal generator further includes complex coefficients encoding phase and amplitude attenuation associated with the directional beams and propagation delay.

18. A communication system to transmit an information signal to a first mobile terminal comprising:

one or more beamforming antennas to form a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay, where each beamforming antenna comprises a plurality of antenna elements;

a controller to select two or more directional beams from at least one beamforming antenna for transmitting the information signal to the first mobile terminal;

a transmit signal generator coupled to each of said beamforming antenna and said controller to derive a transmit signal from the information signal for each selected directional beam; and

a delay element to compensate for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein the controller estimates path loss associated with the plurality of directional beams and selects directional beams from the plurality of directional beams based on the estimated path loss.

19. A communication system to transmit an information signal to a first mobile terminal comprising:

one or more beamforming antennas to form a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay, where each beamforming antenna comprises a plurality of antenna elements;

a controller to select two or more directional beams from at least one beamforming antenna for transmitting the information signal to the first mobile terminal;

a transmit signal generator coupled to each of said beamforming antenna and said controller to derive a transmit signal from the information signal for each selected directional beam; and

a delay element to compensate for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein the controller measures the strength of signals received from the first mobile terminal on the plurality of directional beams and selects directional beams from the plurality of directional beams based on the strength of the received signals.

20. A communication system to transmit an information signal to a first mobile terminal comprising:

one or more beamforming antennas to form a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay, where each beamforming antenna comprises a plurality of antenna elements;

a controller to select two or more directional beams from at least one beamforming antenna for transmitting the information signal to the first mobile terminal;

a transmit signal generator coupled to each of said beamforming antenna and said controller to derive a transmit signal from the information signal for each selected directional beam; and

a delay element to compensate for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein the controller estimates multi-path propagation channel characteristics between the transmitter and the first mobile terminal for the plurality of directional beams and chooses the selected directional beams based on the estimated multi-path propagation channel characteristics.

21. The communication system of claim 20 wherein the controller estimates the multipath propagation channel characteristics by determining the multi-path channel characteristics based on a loopback signal from the first mobile terminal.

22. A communication system to transmit an information signal to a first mobile terminal comprising:

one or more beamforming antennas to form a plurality of directional beams, each directional beam oriented in a different direction and having a propagation delay, where each beamforming antenna comprises a plurality of antenna elements;

a controller to select two or more directional beams from at least one beamforming antenna for transmitting the information signal to the first mobile terminal

a transmit signal generator coupled to each of said beamforming antenna and said controller to derive a transmit signal from the information signal for each selected directional beam; and

a delay element to compensate for differences in propagation delay between the selected directional beams such that the transmit signals arrive time aligned at the first mobile terminal;

wherein the controller further reselects at least one directional beam responsive to path loss variations.