Receiving device and transmission device for wireless communication

1. A receiving device for use in a wireless OFDM communication system, said receiving device comprising:

two or more receive antennas for receiving OFDM signals received over a channel from a transmission device having two or more transmit antennas and applying transmit beamforming, and

circuitry configured to

perform channel estimation to estimate the channel,

generate transmit beamforming information based on the channel estimation, said transmit beamforming information comprising beamforming information per subcarrier or time domain tap,

determine a reduced set of transmit beamforming information from said transmit beamforming information, wherein said reduced set comprises beamforming information for a reduced set of subcarriers in a frequency domain or for a reduced set of taps in a time domain, and

feed back the reduced set of transmit beamforming information to the transmission device.

2. The receiving device of claim 1 , wherein

the circuitry is further configured to compress the generated transmit beamforming information and to determine the reduced set of transmit beamforming information from said compressed transmit beamforming information.

3. The receiving device of claim I, wherein

the reduced set of transmit beamforming information comprises a beamforming information value or matrix per subcarrier of said reduced set of subcarriers in the frequency domain or a beamforming information value or matrix per tap of said reduced set of taps in the time domain.

4. The receiving device of claim 3 , wherein

the circuitry is further configured to feed back the reduced set of beamforming information values or matrices and associated subcarrier values or indices indicating their position in the frequency domain or associated tap positions or delays of taps indicating their position or delay in the time domain.

5. The receiving device of claim 1 , wherein

the circuitry is further configured to determine the reduced set of transmit beamforming information by one or more of

differential processing of beamforming information between subcarriers or taps,

grouping of beamforming information for two or more subcarriers or taps,

interpolation or regression over groups beamforming information for a fixed or dynamic number of two or more subcarriers or taps, and

reduction of channel state information in time domain.

6. The receiving device of claim 1 , wherein

the circuitry is further configured to determine the reduced set of transmit beamforming information comprising beamforming information for a reduced set of subcarriers in the frequency domain by

determining, starting with a reduced set of subcarriers containing a single subcarrier, an additional subcarrier, whose associated beamforming information should be included in the reduced set of transmit beamforming information, by computing an accumulated error between approximate beamforming information reconstructed using the reduced set of transmit beamforming information and the complete transmit beamforming information within a subcarrier interval, and

including the beamforming information or its gradient, associated with said additional subcarrier position or with said subcarrier interval length, in the reduced set of beamforming information if the computed accumulated error exceeds a predetermined error threshold.

7. The receiving device of claim 1 , herein

the circuitry is further configured to determine the reduced set of transmit beamforming information comprising beamforming information for all the reduced set of taps in the time domain by

determining, starting with a reduced set of taps containing a single tap, an additional tap, whose associated beamforming information should be included in the reduced set of transmit beamforming information, by computing an accumulated error between approximate beamforming information reconstructed using the reduced set of transmit beamforming information and the complete transmit beamforming information within a tap interval, and

including the beamforming information or its gradient, associated with said additional tap position or with said tap interval length, in the reduced set of beamforming information if the computed accumulated error exceeds a predetermined error threshold.

8. The receiving device of claim 7 , wherein

the circuitry is further configured to compute the accumulated error by use of approximate beamforming information determined for the taps in a tap interval from the beamforming information associated with said additional tap and the preceding tap of the beamforming interval.

9. The receiving device of claim 8 , wherein

the circuitry is further configured to compute the accumulated error by

determining a distance metric, per tap in the tap interval, between the approximate beamforming information and the beamforming information of the complete transmit beamforming information,

computing, per tap in the tap interval, a square of an absolute value of said distance metric, and

summing, for all taps in the tap interval, said squares.

10. The receiving device of claim 1 , wherein

the circuitry is further configured to determine the reduced set of transmit beamforming information comprising beamforming information for all the reduced set of taps in the time domain by

selecting, based on the obtained or estimated channel information in the time domain, taps having a strongest magnitude or a magnitude over a predetermined magnitude threshold,

computing for each selected channel information beamforming information, and

including the beamforming information of the selected taps in the reduced set of transmit beamforming information.

11. A receiving method for use in a wireless OFDM communication system, said receiving method comprising:

receiving OFDM signals received over a channel from a transmission device having two or more transmit antennas and applying transmit beamforming, and

performing channel estimation to estimate the channel,

generating transmit beamforming information based on the channel estimation, said transmit beamforming information comprising beamforming information per subcarrier or time domain tap,

determining a reduced set of transmit beamforming information from said transmit beamforming information, wherein said reduced set comprises beamforming information for a reduced set of subcarriers in frequency domain or for a reduced set of taps in a time domain, and

feeding back the reduced set of transmit beamforming information to the transmission device.

12. The receiving device of claim 1 , wherein

the circuitry is configured to determine the reduced set of transmit beamforming information based on the channel estimation.

13. The receiving device of claim 1 , wherein

the reduced set of transmit beamforming information comprises beamforming information for the reduced set of subcarriers in the frequency domain.

14. The receiving device of claim 13 , wherein

the circuitry is configured to determine the reduced set of subcarriers for which the transmit beamforming information is to be ted back based on the channel estimation.

15. The receiving device of claim 13 , wherein

the circuity is configured to determine a spacing between subcarriers in the frequency domain for the reduced set of subcarriers for which the transmit beamforming information is to be fed back based on the channel estimation.