Wireless communication apparatus and method

• US 7,167,526 B2
• Filed: 01/18/2002
• Issued: 01/23/2007
• Est. Priority Date: 06/07/2001
• Status: Expired due to Fees

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Chin, Francois Po Shin, Liang, Ying-Chang
• Primary Examiner(s): Tran; Khai
• Assistant Examiner(s): WARE, CICELY Q
• Application Number:
  US10/054,543
• Publication Number:
  US 20040071222A1
• Time in Patent Office: 1,831 Days
• Field of Search: 375/310, 375/299, 375/267, 325148-267, 455/69
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/0673 using feedback from receiving side

Abstract

A method and apparatus for achieving combined beamforming and transmit diversity for frequency selective fading channels in a communication system having a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of: providing a signal to be transmitted; space-time encoding the signal to produce at least two separate signals, each on a respective output; feeding each output signal to a multiple access transmit processor to produce an output signal; applying respective selected transmit beamforming weights to each output signal; feeding the respective weighted signals to a signal combiner to perform a summing function of the signals and produce a signal for transmission; feeding the summed signal to each of the multiple transmit antennae for transmission; transmitting the signals over respective physical channels; receiving the transmitted signal at at least a single receive antenna; feeding the transmitted signal to a multiple access receive processor to produce an output signal; and space-time decoding the received signal.

Claims

1. A method of achieving transmit diversity gain for frequency selective fading channels in a communication system that is a time-division duplex system and has a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of:

providing a signal to be transmitted s(n);

space-time encoding the signal s(n) to produce at least two separate signals s₁(n),s₂(n), each on a respective output;

feeding each output signal s₁(n),s₂(n) to a zero-forcing pre-equaliser having a respective function g₁(k), g₂(k) to produce an output signal x₁(n), x₂(n);

feeding the output signal x₁(n), x₂(n) of each pre-equaliser to a transmit antenna;

transmitting the output signals x₁(n), x₂(n) over respective physical channels h₁(k), h₂(k);

receiving the output signals x₁(n), x₂(n) at at least a single receive antenna; and

space-time decoding the received signals, wherein

the functions g₁(k), g₂(k) of the zero-forcing pre-equalisers are selected such that the channel responses g₁(k)*h₁(k), g₂(k)*h₂(k) of the respective physical channels h₁(k), h₂(k) are flat fading channels; and

deriving real channel coefficients from uplinik channel coefficients for use in selecting the functions g₁(k), g₂(k) of the pre-equalisers.

2. A method according to claim 1, wherein the step of deriving the real channel coefficients from uplinik channel coefficients uses training symbols from the uplinik channel.

3. A method according to claim 1, wherein the step of deriving the real channel coefficients from uplinik channel coefficients uses blind techniques.

4. A method according to claim 1, wherein the communications system is a frequency-division duplex system and the method includes the further step of deriving the real channel coefficients by sending a set of training symbols to the receive antenna of the mobile terminal, the mobile terminal estimating the real channel coefficients and feeding back channel coefficient information to the base station.

5. A base station with multiple transmit antennae for communicating with a mobile terminal having at least a single receive antenna over physical channels h₁(k), h₂(k), the base station comprising:

a space-time encoder having an input of a signal to be transmitted s(n) and at least two outputs each producing a separate signal s₁(n),s₂(n);

at least two zero-forcing pre-equalisers, each fed by a respective output signal s₁(n),s₂(n) and having a respective function g₁(k), g₂(k) to produce an output signal x₁(n), x₂(n), wherein real channel coefficients are derived from uplinik channel coefficients for use in selecting the functions g₁(k), g₂(k) of the pre-equalisers; and

at least two transmit antennae, each being fed by the output signal x₁(n), x₂(n) of a respective one of the pre-equalisers, wherein the functions g₁(k), g₂(k) of the zero-forcing pre-equalisers are selected such that the channel responses g₁(k)*h₁(k), g₂(k)*h₂(k) of the respective physical channels h₁(k), h₂(k) are flat fading channels.

6. A communications system comprising the base station of claim 5 and a

mobile terminal having at least a single receive antenna and a space-time decoder to decode the signals received from the base station.

7. A method of achieving combined beamforming and transmit diversity for frequency selective fading channels in a communication system having a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of:

providing a signal to be transmitted S(n;

k);

space-time encoding the signal S(n;

k) to produce at least two separate signals S₁(n;

k),S₂(n;

k), each on a respective output;

feeding each output signal S₁(n;

k),S₂(n;

k) to a transmit processor to produce an output signal X₁(n;

k), X₂(n;

k);

applying respective selected transmit beamforming weights to each output signal X₁(n;

k),

feeding the respective weighted signals to a signal combiner to perform a summing function of the signals and produce a signal X(n;

k) for transmission;

feeding the summed signal X(n;

k) to each of the multiple transmit antennae for transmission;

transmitting the signals X(n;

k) over physical channel h(n;

k) wherein the physical channel h(n;

k) consists of two time-delayed rays, h₁(n;

k) and h₂(n;

k), with delay Δ

τ

;

receiving the received signal Y(n;

k) at at least a single receive antenna;

feeding the received signal Y(n;

k) to a receive processor to produce an output signal; and

space-time decoding the received signal;

wherein

the transmit processors do not add cyclic prefixes and one of the output signals from the transmit processors is delayed by Δ

τ

before the respective selected transmit beamforming weight is applied thereto.

8. A method according to claim 7, wherein the respective transmit beamforming weights are selected as the eigenvectors corresponding to the two largest eigenvalues of the downlinik channel covariance matrix (DCCM) of the physical channels h(n;

k).

10. A method according to claim 7, wherein the physical channel h(n;

k) consists of two time-delayed rays, h₁(n;

k) and h₂(n;

k), with delay Δ

τ

, the beamforming weights being chosen such that the average transmit SINR function at the base station is maximized for each ray.

11. A method according to claim 7, wherein the physical channel h(n;

k) consists of two time-delayed rays, h₁(n;

k) and h₂(n;

k), with delay Δ

τ

, the beamforming weights being chosen such that the average receive SINR function at the mobile terminal is maximized.

13. A method according to claim 7, wherein the physical channel h(n;

k) consists of two time-delayed rays, h₁(n;

k) and h₂(n;

k), with delay Δ

τ

, the beamforming weights for each ray are chosen as the principal eigenvector of the downlinik channel covariance matrix (DCCM) corresponding to that ray.

23. A method according to claim 7, wherein the transmit and receive processors are selected from the group consisting of:

OFDM, MC-CDMA MC-DS-CDMA and a single carrier system with cyclic prefix.

9. A method of achieving combined beamforming and transmit diversity for frequency selective fading channels in a communication system having a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of:

providing a signal to be transmitted S(n,k);

space-time encoding the signal S(n,k) to produce at least two separate signals S₁(n;

k),S₂(n;

k), each on a respective output;

feeding each output signal S₁(n;

k),S₂(n;

k) to a transmit processor to produce an output signal X₁(n,k), X₂(n;

k);

applying respective selected transmit beamforming weights to each output signal X₁(n,k), X₂(n;

k);

feeding the respective weighted signals to a signal combiner to perform a summing function of the signals and produce a signal X(n;

k) for transmission;

feeding the summed signal X(n;

k) to each of the multiple transmit antennae for transmission;

transmitting the signals X(n;

k) over physical channel h(n;

k);

receiving the received signal Y(n;

k) at at least a single receive antenna;

feeding the received signal Y(n;

k) to a receive processor to produce an output signal; and

space-time decoding the received signal;

wherein the physical channel h(n;

k) consists of two time-delayed rays, h₁(n;

k) and h₂(n;

k), with delay Δ

τ

, the beamforming weights being chosen such that the delayed signal or its inverse fast Fourier transform (IFFT) only goes through one channel h₁(n;

k) between the base station multiple transmit antennae and the receive antenna, whilst the undelayed signal or its IFFT only goes through another channel h₂(n;

k) between the base station multiple transmit antennae and the receive antenna, thereby creating two different channels which can be space-time decoded to recover the transmitted signal.

12. A method according to claim 9, wherein the respective transmit beamforming weights are selected as the eigenvectors corresponding to the two largest eigenvalues of the downlinik channel covariance matrix (DCCM) of the physical channels h(n;

k).

14. A method of achieving combined beamforming and transmit diversity for frequency selective fading channels in a communication system having a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of:

providing a signal to be transmitted S(n;

k);

space-time encoding the signal S(n,k) to produce at least two separate signals S₁(n;

k),S₂(n;

k), each on a respective output;

feeding each output signal S₁(n;

k),S₂(n;

k) to a transmit processor to produce an output signal X₁(n,k), X₂(n;

k);

applying respective selected transmit beamforming weights to each output signal X₁(n,k), X₂(n;

k);

feeding the respective weighted signals to a signal combiner to perform a summing function of the signals and produce a signal X(n;

k) for transmission;

feeding the summed signal X(n;

k) to each of the multiple transmit antennae for transmission;

transmitting the signals X(n;

k) over physical channel h(n;

k);

receiving the received signal Y(n;

k) at at least a single receive antenna;

feeding the received signal Y(n;

k) to a receive processor to produce an output signal; and

space-time decoding the received signal

wherein the physical channel h(n;

k) consists of two time-delayed clustered rays, h₁(n;

k) and h₂(n;

k), with delay ψ

, and maximum excess delay for the clusters Δ

ψ

, the transmit processors have a cyclic prefix length of Δ

ψ and

one of the output signals from the transmit processors is delayed by ψ

before the respective selected transmit beamforming weight is applied thereto.

15. A method according to claim 14, wherein the respective transmit beamforming weights are selected as the eigenvectors corresponding to the two largest eigenvalues of the downlinik channel covariance matrix (DCCM) of the physical channels h(n;

k).

16. A method according to claim 14, wherein the beamforming weights are chosen such that the delayed signal or its inverse fast Fourier transform (IFFT) only goes through one channel h₁(n;

k) between the base station multiple transmit antennae and the receive antenna, whilst the undelayed signal or its IFFT only goes through another channel h₂(n;

k) between the base station multiple transmit antennae and the receive antenna, thereby creating two different channels which can be space-time decoded to recover the transmitted signal.

17. A method according to claim 14, wherein the beamforming weights being chosen such that the average transmit SINR function at the base station is maximized for each clustered ray.

18. A method according to claim 14, wherein the beamforming weights being chosen such that the average receive SINR function at the mobile terminal is maximized.

19. A method according to claim 14, wherein the beamforming weights for each clustered ray are chosen as the principal eigenvector of the downlinik channel covariance matrix (DCCM) corresponding to that clustered ray.

20. A method according to claim 14, comprising the further steps of:

estimating a power-delay-DOA profile for channel h(n;

k); and

, based on the profile;

determining the cyclic prefix, Δ

ψ

, to be added by the transmit processors;

determining the delay ψ

;

diversity order and modulation scheme; and

determining the transmit beamforming weights.

21. A method according to claim 20, comprising the further step of estimating the downlinik channel covariance matrix (DCCM) from the uplinik channel covariance matrix (UCCM) to construct transmit beamforming weights.

22. A method according to claim 21, comprising the further step of determining the diversity order and modulation scheme based on the profile.

30. A base station according to claim 14, wherein the transmit and receive processors are selected from the group consisting of:

OFDM, MC-CDMA MC-DS-CDMA and single carrier system with cyclic prefix.

24. A base station with multiple transmit antennae for communicating with a mobile terminal having at least a single receive antenna over physical channel h(k), the base station comprising:

a space-time encoder having an input of a signal to be transmitted and at least two outputs each producing a separate signal;

at least two transmit processors each receiving one of the outputs from a respective space-time encoder;

at least two transmit beamformers each receiving an output from a respective transmit processor and applying a transmit beamforming weight thereto;

a signal combiner receiving signals from the beamformers and operable to perform a summing function of the signals from the beamformers and produce a signal for transmission by the multiple transmit antennae;

wherein the physical channel h(n;

k) consists of two time-delayed rays, h₁(n;

k) and h₂(n;

k), with delay Δ

τ

, further comprising a delay of Δ

τ

interposed between one of the multiple access transmit processor outputs and a beamformer to delay the signal output from the transmit processor by Δ

τ

before the respective selected transmit beamforming weight is applied thereto, wherein the transmit processors do not add cyclic prefixes.

31. A communications system comprising the base station of claim 24 and a

mobile terminal having at least a single receive antenna, a receive processor to produce an output signal and a space-time decoder to decode the output signal.

35. A communications system comprising the base station of claim 24 and a

mobile terminal having at least a single receive antenna and a space-time decoder to decode the received signal.

25. A base station with multiple transmit antennae for communicating with a mobile terminal having at least a single receive antenna over physical channel h(k), the base station comprising:

a space-time encoder having an input of a signal to be transmitted and at least two outputs each producing a separate signal;

at least two transmit processors each receiving one of the outputs from a respective space-time encoder;

at least two transmit beamformers each receiving an output from a respective transmit processor and applying a transmit beamforming weight thereto;

a signal combiner receiving signals from the beamformers and operable to perform a summing function of the signals from the beamformers and produce a signal for transmission by the multiple transmit antennae;

wherein the physical channel h(n;

k) consists of two time-delayed clustered rays, h₁(n;

k) and h₂(n;

k), with delay ψ

, and maximum excess delay for the clusters Δ

ψ

, further comprising a delay of ψ

interposed between one of the multiple access transmit processor outputs and a beamformer to delay the signal output from the transmit processor by ψ

before the respective selected transmit beamforming weight is applied thereto, the transmit processors having a cyclic prefix length of Δ

ψ

.

26. A communications system comprising the base station of claim 25 and a

mobile terminal having at least a single receive antenna, a receive processor to produce an output signal and a space-time decoder to decode the output signal.

27. A base station with multiple transmit antennae for communicating with a mobile terminal having at least a single receive antenna over physical channel h(k), the base station comprising:

a space-time encoder having an input of a signal to be transmitted and at least two outputs each producing a separate signal;

at least two transmit processors each receiving one of the outputs from a respective space-time encoder;

at least two transmit beamformers each receiving an output from a respective transmit processor and applying a transmit beamforming weight thereto;

a signal combiner receiving signals from the beamformers and operable to perform a summing function of the signals from the beamformers and produce a signal for transmission by the multiple transmit antennae; and

a first processor to determine a power-delay-DOA profile estimate for channel h(n;

k); and

, based on the profile, determine;

the length, Δ

ψ

, of the cyclic prefix to be added by the transmit processors;

the delay ψ

;

diversity order and modulation scheme; and

the transmit beamforming weights.

28. A communications system comprising the base station of claim 27 and a

mobile terminal having at least a single receive antenna, a receive processor to produce an output signal and a space-time decoder to decode the output signal.

29. A base station according to claim 27, further comprising a second processor to estimate a downlinik channel covariance matrix (DCCM) from the uplinik channel covariance matrix (UCCM) to construct transmit beamforming weights.

32. A method of achieving combined beamforming and transmit diversity for frequency selective fading channels in a communication system having a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of:

providing a signal to be transmitted s(n);

space-time encoding a signal to be transmitted s(n) to produce at least two separate signals s₁(n),s₂(n), each on a respective output;

delaying one of the space-time encoded output signals by Δ

τ

;

applying respective selected transmit beamforming weights to the delayed and undelayed signals;

feeding the respective weighted signals to a signal combiner to perform a summing

function of the signals and produce a signal for transmission;

feeding the summed signal to each of the multiple transmit antennae for transmission;

transmitting the summed signals over the physical channel h(k);

receiving the major components of the transmitted signals at at least a single receive antenna at substantially the same time; and

space-time decoding the received signal;

wherein the physical channel h(k) consists of two time-delayed rays h₁(k), h₂(k) with delay Δ

τ

, the beamforming weights are chosen such that the delayed signal only goes through one ray h₁(k) between the base station multiple transmit antennae and the receive antenna, whilst the undelayed signal only goes through another ray h₂(k) between the base station multiple transmit antennae and the receive antenna.

33. A method of achieving combined beamforming and transmit diversity for frequency selective fading channels in a communication system having a base station with multiple transmit antennae and a mobile terminal with at least a single receive antenna, the method comprising the steps of:

providing a signal to be transmitted s(n);

space-time encoding a signal to be transmitted s(n) to produce at least two separate signals s₁(n),s₂(n), each on a respective output;

delaying one of the space-time encoded output signals by Δ

τ

;

applying respective selected transmit beamforming weights to the delayed and undelayed signals;

feeding the respective weighted signals to a signal combiner to perform a summing function of the signals and produce a signal for transmission;

feeding the summed signal to each of the multiple transmit antennae for transmission;

transmitting the summed signals over the physical channel h(k);

receiving the major components of the transmitted signals at at least a single receive antenna at substantially the same time; and

space-time decoding the received signal

wherein the physical channel h(k) consists of multiple rays with two major rays h₁(k), h₂(k) delayed by Δ

τ

, the beamforming weights are chosen such that the delayed signal only goes through one ray h₁(k) between the base station multiple transmit antennae and the receive antenna, whilst the undelayed signal only goes through another ray h₂(k) between the base station multiple transmit antennae and the receive antenna.

34. A base station with multiple transmit antennae for communicating with a mobile terminal having at least a single receive antenna over physical channel h(k) having two time-delayed rays, h₁(k) and h₂(k), the base station comprising:

a space-time encoder having an input of a signal to be transmitted and at least two outputs each producing a separate signal;

at least two transmit beamformers each receiving an output from the space-time encoder and applying a transmit beamforming weight thereto;

a signal combiner receiving signals from the beamformers and operable to perform a summing function of the signals from the beamformers and produce a signal for transmission by each of the multiple transmit antennae, wherein a delay of Δ

τ

is interposed between the space-time encoder and one of the beamformers such that the major components of the transmitted signals are received at at least a single receive antenna at substantially the same time.