Apparatus and method for determining beamforming vector in a codebook-based beamforming system

• US 20070206626A1
• Filed: 02/05/2007
• Published: 09/06/2007
• Est. Priority Date: 02/03/2006
• Status: Active Grant

• Current Assignee: Korea Advanced Institute of Science and Technology, Samsung Electronics Co. Ltd.
• Original Assignee: Korea Advanced Institute of Science and Technology, Samsung Electronics Co. Ltd.
• Inventors: Nam, Seung-Hoon, Yun, Jae-Yeun, Chung, Sae-Young, Lee, Yong-Hoon, Lee, Jong-Hyeuk, Cho, Myeon-Kyun, Choi, Jihoon
• Granted Patent: US 7,907,913 B2
• Time in Patent Office: Days
• US Class Current: 370/437
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• 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 7/066 Combined feedback for a number of channels, e.g. over several subcarriers like in orthogonal frequency division multiplexing [OFDM]
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

An apparatus and method for determining a beamforming vector in a codebook-based transmission beamforming system are provided. In a feedback method for a receiver in a codebook-based transmission beamforming system, forthcoming channel values for a forthcoming period are generated using M present and previous channel estimates. Effective channel gains for all transmission beamforming vectors included in a codebook are calculated using the forthcoming channel values. A codebook index corresponding to the maximum effective channel gains is fed back to a transmitter.

Claims

1. A receiver in a codebook-based transmission beamforming system, comprising:

a predictor for generating forthcoming channel values for a forthcoming period using M present and previous channel estimates;

an effective channel gain calculator for calculating effective channel gains for transmission beamforming vectors included in a codebook using the forthcoming channel values generated by the predictor; and

a codebook selector for feeding back a codebook index corresponding to the maximum effective channel gains received from the effective channel gain calculator to a transmitter.

2. The receiver of claim 1, wherein the predictor is a linear Minimum Mean Square Error (MMSE) predictor.

3. The receiver of claim 1, wherein the forthcoming period is a predetermined time-frequency area defined by a plurality of subcarriers and a plurality of frames.

4. The receiver of claim 1, wherein the effective channel gain calculator calculates effective channel gains j_k,d(w) for each transmission beamforming vector w by

J_k,d(w)=w^HR(k,mP+d)w
R(k,mP+d)≡

{circumflex over (H)}_MMSE^H(k,mP+d){circumflex over (H)}_MMSE(k,mP+d)

where Ĥ

_MMSE is a forthcoming channel value, k is a subcarrier index, P is a feedback interval, m is a feedback index, and d is a time offset.

5. The receiver of claim 1, wherein the effective channel gain calculator calculates effective channel gains for each transmission beamforming vector included in the codebook for a forthcoming cluster of size K×

P. where K is a number of subcarriers and P is a number of frames, using the forthcoming channel values and selects a minimum effective channel gains.

6. The receiver of claim 5, wherein the codebook selector compares the minimum effective channel gains for all the beamforming vectors received from the effective channel gain calculator, selects the maximum of the minimum effective channel gains, and feeds back one codebook index corresponding to the maximum effective channel gain to the transmitter.

7. The receiver of claim 1, wherein the effective channel gain calculator linearly interpolates a forthcoming cluster of size 2K×

P, where K is a number of subcarriers and P is a number of frames, using two beamforming vectors included in the codebook, calculates effective channel gains for the beamforming vector pair for the linearly interpolated cluster using the forthcoming channel values, and selects the minimum of the effective channel gains.

8. The receiver of claim 7, wherein the codebook selector compares the minimum effective channel gains for all beamforming vector pairs received from the effective channel gain calculator, selects the maximum of the minimum effective channel gains, and feeds back two codebook indexes corresponding to the maximum effective channel gain to the transmitter.

9. A transmitter in a codebook-based transmission beamforming system, comprising:

a beamforming vector generator for receiving a channel prediction-based codebook index and generating a transmission beamforming vector to be used for a cluster of size K×

P, where K is a number of subcarriers and P is a number of frames, according to the received codebook index; and

a beamformer for beamforming transmission data to be mapped to the cluster with the transmission beamforming vector received from the beamforming vector generator and outputting the beamformed data.

10. A transmitter in a codebook-based transmission beamforming system, comprising:

a beamforming vector generator for receiving two channel prediction-based codebook indexes and generating transmission beamforming vectors to be used for a cluster of size 2K×

P, where K is a number of subcarriers and P is a number of frames, by linear interpolation using two beamforming vectors corresponding to the received codebook indexes; and

a beamformer for beamforming transmission data to be mapped to the cluster with the transmission beamforming vectors received from the beamforming vector generator and outputting the beamformed data.

11. A feedback method for a receiver in a codebook-based transmission beamforming system, comprising the steps of:

generating forthcoming channel values for a forthcoming period using M present and previous channel estimates;

calculating effective channel gains for transmission beamforming vectors included in a codebook using the forthcoming channel values; and

feeding back a codebook index corresponding to the maximum effective channel gains to a transmitter.

12. The feedback method of claim 11, wherein the forthcoming channel values are generated in a linear Minimum Mean Square Error (MMSE) predictor.

13. The feedback method of claim 11, wherein the forthcoming period is a predetermined time-frequency area defined by a plurality of subcarriers and a plurality of frames.

14. The feedback method of claim 11, wherein the calculation step comprises calculating effective channel gains j_k,d(w) for each transmission beamforming vector w by

j_k,d(w)=w^HR(k,mP+d)w
R(k,mP+d)≡

{circumflex over (H)}_MMSE^H(k,mP+d){circumflex over (H)}_MMSE(k,mP)+d)

where Ĥ

_MMSE is a forthcoming channel value, k is a subcarrier index, P is a feedback interval, m is a feedback index, and d is a time offset.

15. The feedback method of claim 11, wherein the calculation step comprises:

calculating effective channel gains for each transmission beamforming vector included in the codebook for a forthcoming cluster of size K×

P, where K is a number of subcarriers and P is a number of frames, using the forthcoming channel values; and

selecting a minimum of the effective channel gains for the each transmission beamforming vector.

16. The feedback method of claim 15, wherein the feedback step comprises:

comparing the minimum effective channel gains for all the beamforming vectors and selecting the maximum of the minimum effective channel gains; and

feeding back one codebook index corresponding to the maximum effective channel gain to the transmitter.

17. The feedback method of claim 11, wherein the calculation step comprises:

linearly interpolating a forthcoming cluster of size 2K×

P, where K is a number of subcarriers and P is a number of frames, using two beamforming vectors included in the codebook;

calculating effective channel gains for the beamforming vector pair for the linearly interpolated cluster using the forthcoming channel values; and

selecting the minimums of effective channel gains for all beamforming vector pairs.

18. The feedback method of claim 17, wherein the feedback step comprises:

comparing the minimum effective channel gains for all the beamforming vector pairs;

selecting the maximum of the minimum effective channel gains; and

feeding back two codebook indexes corresponding to the maximum effective channel gain to the transmitter.

19. A beamforming method for a transmitter in a codebook-based transmission beamforming system, comprising the steps of:

receiving a channel prediction-based codebook index;

generating a transmission beamforming vector to be used for a cluster of size K×

P, where K is a number of subcarriers and P is a number of frames, according to the received codebook index; and

beamforming transmission data to be mapped to the cluster with the transmission beamforming vector.

20. A beamforming method for a transmitter in a codebook-based transmission beamforming system, comprising the steps of:

receiving two channel prediction-based codebook indexes;

generating transmission beamforming vectors to be used for a cluster of size 2K×

P, where K is a number of subcarriers and P is a number of frames, by linear interpolation using two beamforming vectors corresponding to the received codebook indexes; and

beamforming transmission data to be mapped to the cluster with the transmission beamforming vectors.