Apparatus and method for providing transmit diversity in a mobile communication system using multiple antennas

• US 20050286650A1
• Filed: 06/17/2005
• Published: 12/29/2005
• Est. Priority Date: 06/18/2004
• Status: Abandoned Application

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Dae-gyun, Mun, Cheol, Han, Jin-Kyu, Lee, Myoung-Won, Kim, Youn-Sun, Kim, Dong-Hee, Kwon, Hwan-Joon, Park, Han-Kyu
• Application Number:
  US11/154,530
• Publication Number:
  US 20050286650A1
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/061 using feedback from receiving side
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0639 Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04L 1/0001 Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/0625 Transmitter arrangements
• CPC Class Codes: H04L 1/0643 block codes

Abstract

A transmit diversity apparatus and method are provided for adaptively providing a transmit diversity gain or a beamforming gain depending on changes in a radio channel undergoing multipath fading in a mobile communication system using multiple antennas. A transmitter forms as many fixed beams as the number of transmit antennas and a receiver selects a fixed beam having relatively high power among received fixed beams or linearly combines the received fixed beams. This common eigen space transmit diversity scheme improves the link performance between the transmitter and the receiver.

Claims

1. A diversity apparatus for a transmitter having a plurality of transmit antennas in a mobile communication system, comprising:

a plurality of fixed beamformers for forming fixed beam signals using a plurality of common eigen bases, each for one fixed beam signal; and

the plurality of transmit antennas for receiving the fixed beam signals from the fixed beamformers and transmitting the fixed beam signals over a radio network.

wherein each of the fixed beam signals is receivable in every part of a cell area.

2. The diversity apparatus of claim 1, wherein each of the fixed beam signals is receivable in every part of a cell area.

3. The diversity apparatus of claim 1, wherein the number of the common eigen bases is equal to the number of the transmit antennas.

4. The diversity apparatus of claim 1, wherein the plurality of common eigen bases are mutually orthogonal.

5. The diversity apparatus of claim 1, wherein the plurality of common eigen bases are time-invariant.

6. The diversity apparatus of claim 1, wherein each of the fixed beam signals is transmitted with the same transmit power.

7. The diversity apparatus of claim 1, wherein the common eigen bases are the eigen vectors of a transmit spatial correlation matrix R expressed as

$R={\int }_{}^{}$

- Δ

/ 2 Δ

/ 2 ⁢

p ⁡

( θ

) ⁢

a H ⁡

( θ

) ⁢

a ⁡

( θ

) ⁢

 

⁢

ⅆ

θ

where Δ

is a sector radius of the transmit antennas, p(θ

) is a radiation pattern of the transmit antennas, a(θ

) is a response vector of the transmit antennas, a(θ

)=[1,exp(j2π

d_T sin θ

/λ

. . . exp(j2π

(n_T−

1)d_T sin θ

/λ

)], n_T is a number of the transmit antennas, d_T is an antenna spacing, and λ

is a wavelength of a carrier.

8. The diversity apparatus of claim 1, further comprising a switch for receiving feedback information about a selected common eigen basis from a receiver and switching the selected common eigen basis to a fixed beamformer using the selected common eigen basis as a beamforming weight.

9. The diversity apparatus of claim 8, wherein the feedback information is determined by

${\gamma }_{}$

STD = max ⁡

( E b N o ⁢



h 1 

2 , E b N o ⁢



h 2 

2 , …

⁢

 

, E b N o ⁢



h n 

2 )

where E_b is signal energy, N_o is noise energy, and h_n is a multipath fading channel coefficient from an n^th transmit antenna to a receive antenna of the receiver.

10. The diversity apparatus of claim 1, further comprising a space-time block code (STBC) encoder for STBC-encoding a plurality of signals demultiplexed from data symbols and providing STBC-coded signals to the plurality of fixed beamformers.

11. The diversity apparatus of claim 10, wherein the STBC encoder STBC-encodes the signals using an Alamouti code.

12. The diversity apparatus of claim 1, further comprising an adaptive beamformer for receiving feedback information about a transmit weight estimated by the receiver from the receiver, generating an adaptive beam signal according to the feedback information, and providing the adaptive beam signal to the plurality of fixed beamformers.

13. The diversity apparatus of claim 12, wherein the adaptive beamformer performs a primary beamforming using a transmit weight and the plurality of fixed beamformers perform secondary fixed beamforming using the common eigen bases.

14. The diversity apparatus of claim 12, wherein the transmit weight is computed by

w={tilde over (h)}/∥

{tilde over (h)}∥

where {tilde over (h)} is a vector comprising estimated fading channel coefficients of the fixed beam signals from the transmit antennas to the receive antenna and ∥

∥

is an norm operator that computes the value of a vector.

15. A diversity apparatus for a receiver in a mobile communication system, the receiver receiving radio data symbols from a transmitter that has a plurality of transmit antennas and forms fixed beams in a common eigen space using common eigen bases corresponding to the transmit antennas as weights, comprising:

an antenna for transmitting and receiving data over a radio network;

a fading estimator for estimating at least one of fading channels formed by a plurality of fixed beams; and

a basis selector for measuring the instantaneous power levels of the estimated fading channels and feeding back information about the common eigen basis of a fading channel having the highest instantaneous power level to the transmitter.

16. The diversity apparatus of claim 15, wherein the feedback information is determined by

${\gamma }_{}$

STD = max ⁡

( E b N o ⁢



h 1 

2 , E b N o ⁢



h 2 

2 , …

⁢

 

, E b N o ⁢



h n 

2 )

where E_b is signal energy, N_o is noise energy, and h_n is a multipath fading channel coefficient from an n^th transmit antenna to the antenna of the receiver.

17. A diversity apparatus for a receiver in a mobile communication system, the receiver receiving radio data symbols from a transmitter that has a plurality of transmit antennas and forms fixed beams in a common eigen space using common eigen bases corresponding to the transmit antennas as weights, comprising:

an antenna for transmitting and receiving data over a radio network;

a fading estimator for estimating at least one of fading channels formed by a plurality of fixed beams;

a space-time block code (STBC) encoder for STBC-encoding data symbols received on the at least one estimated fading channel; and

a multiplexer for multiplexing STBC-encoded signals.

18. The diversity apparatus of claim 17, wherein the STBC encoder STBC-encodes the signals using an Alamouti code.

19. A diversity apparatus for a receiver in a mobile communication system, the receiver receiving radio data symbols from a transmitter that has a plurality of transmit antennas and forms fixed beams in a common eigen space using common eigen bases corresponding to the transmit antennas as weights, comprising:

an antenna for transmitting and receiving data over a radio network;

a fading estimator for estimating at least one of fading channels formed by a plurality of fixed beams; and

a transmit weight estimator for estimating a transmit weight from the at least one estimated fading channel, for use in beamforming in the transmitter and feeding back information about the transmit weight estimate to the transmitter.

20. The diversity apparatus of claim 19, wherein the transmit weight is estimated by

w={tilde over (h)}/∥

{tilde over (h)}∥

where {tilde over (h)} is a vector comprising estimated fading channel coefficients of the fixed beam signals from the transmit antennas of the transmitter to the antenna of the receiver and ∥

∥

is an operator that computes the value of a vector.

21. A method of providing transmit diversity to a receiver in a transmitter having a plurality of transmit antennas, comprising the steps of:

receiving from the receiver feedback information about a common eigen basis of a fading channel estimated at the receiver among a plurality of common eigen bases;

selecting at least one of a plurality of fixed beamformers based on the feedback information and inputting data symbols for transmission to the selected fixed beamformer;

forming a fixed beam signal using the common eigen basis using a weight through the selected fixed beamformer; and

transmitting the fixed beam signal through the transmit antennas over a radio network.

22. The method of claim 21, wherein each of fixed beam signals from the fixed beamformers is receivable in every part of a cell area.

23. The method of claim 21, wherein the number of the common eigen bases is equal to the number of the transmit antennas.

24. The method of claim 21, wherein the common eigen bases are time-invariant and common to all receivers.

25. The method of claim 21, wherein each of fixed beam signals formed using the common eigen bases is transmitted with the same transmit power.

26. The method of claim 21, wherein the common eigen bases are the eigen vectors of a transmit spatial correlation matrix R expressed as

$R={\int }_{}^{}$

- Δ

/ 2 Δ

/ 2 ⁢

p ⁡

( θ

) ⁢

a H ⁡

( θ

) ⁢

a ⁡

( θ

) ⁢

ⅆ

θ

where Δ

is a sector radius of the transmit antennas, p(θ

) is a radiation pattern of the transmit antennas, a(θ

) is a response vector of the transmit antennas, a(θ

)=[1,exp(j2π

d_T sin θ

/λ

) . . . exp(j2π

(n_T−

1)d_T sin θ

/λ

)], n_T is a number of the transmit antennas, d_T is an antenna spacing, and λ

is a wavelength of a carrier.

27. The method of claim 21, wherein the feedback information is determined by

${\gamma }_{}$

STD = max ⁡

( E b N o ⁢



h 1 

2 , E b N o ⁢



h 2 

2 , …

⁢

 

, E b N o ⁢



h n 

2 )

where E_b is signal energy, N_o is noise energy, and h_n is a multipath fading channel coefficient from an n^th transmit antenna to a receive antenna of the receiver.

28. A method of providing transmit diversity to a receiver in a transmitter having a plurality of transmit antennas, comprising the steps of:

space-time block code (STBC)-encoding data symbols for transmission;

providing STBC-coded signals to a plurality of fixed beamformers;

forming the STBC-coded signals into fixed beam signals using common eigen bases through the fixed beamformers; and

transmitting the fixed beam signals through the transmit antennas over a radio network.

29. The method of claim 28, wherein each of the fixed beam signals from the fixed beamformers is receivable in every part of a cell area.

30. The method of claim 28, wherein the number of the common eigen bases is equal to the number of the transmit antennas.

31. The method of claim 28, wherein the common eigen bases are time-invariant and common to all receivers.

32. The method of claim 28, wherein the transmission step comprises the step of transmitting each of the fixed beam signals formed using the common eigen bases with the same transmit power.

33. The method of claim 28, wherein the common eigen bases are the eigen vectors of a transmit spatial correlation matrix R expressed as

$R={\int }_{}^{}$

- Δ

/ 2 Δ

/ 2 ⁢

p ⁡

( θ

) ⁢

a H ⁡

( θ

) ⁢

a ⁡

( θ

) ⁢

ⅆ

θ

where Δ

is a sector radius of the transmit antennas, p(θ

) is the radiation pattern of the transmit antennas, a(θ

) is the response vector of the transmit antennas, a(θ

)=[1,exp(j2π

d_T sin θ

/λ

) . . . exp(j2π

(n_T−

1)d_T sin θ

/λ

)], n_T is the number of the transmit antennas, d_T is an antenna spacing, and λ

is the wavelength of a carrier.

34. The method of claim 28, wherein the STBC encoding step comprises the step of STBC-encoding the data symbols using an Alamouti code.

35. A method of providing transmit diversity to a receiver in a transmitter having a plurality of transmit antennas, comprising the steps of:

receiving from the receiver feedback information about a transmit weight estimated at the receiver for use in beamforming in the transmitter;

performing a primary beamforming using the transmit weight;

providing the primary beamformed signal to a plurality of fixed beamformers;

performing a secondary beamforming using common eigen bases through the fixed beamformers and outputting fixed beam signals; and

transmitting the fixed beam signals over a radio network through the transmit antennas.

36. The method of claim 35, wherein each of the fixed beam signals from the fixed beamformers is receivable in every part of a cell area.

37. The method of claim 35, wherein the number of the common eigen bases is equal to the number of the transmit antennas.

38. The method of claim 35, wherein the common eigen bases are time-invariant and common to all receivers.

39. The method of claim 35, wherein the transmission step comprises the step of transmitting each of the fixed beam signals formed using the common eigen bases with the same transmit power.

40. The method of claim 35, wherein the transmit weight for the primary beamforming is determined by

w={tilde over (h)}/∥

{tilde over (h)}∥

where {tilde over (h)} is a vector comprising estimated fading channel coefficients of the fixed beam signals from the transmit antennas of the transmitter to a receive antenna of the receiver and ∥

∥

is an norm operator that computes the value of a vector.

41. The method of claim 35, wherein the common eigen bases are the eigen vectors of a transmit spatial correlation matrix R expressed as

$R={\int }_{}^{}$

- Δ

/ 2 Δ

/ 2 ⁢

p ⁡

( θ

) ⁢

a H ⁡

( θ

) ⁢

a ⁡

( θ

) ⁢

ⅆ

θ

where Δ

is a sector radius of the transmit antennas, p(θ

) is a radiation pattern of the transmit antennas, a(θ

) is a response vector of the transmit antennas, a(θ

)=[1,exp(j2π

d_T sin θ

/λ

) . . . exp(j2π

(n_T−

1)d_T sin θ

/λ

)], n_T is a number of the transmit antennas, d_T is an antenna spacing, and λ

is a wavelength of a carrier.