Conference Paper

Space-Frequency OFDM System with Null-Steering Beamformer

Sch. of Inf. Sci. & Technol., Southwest Jiaotong Univ., Chengdu
DOI: 10.1109/ITST.2006.288908 Conference: ITS Telecommunications Proceedings, 2006 6th International Conference on
Source: IEEE Xplore

ABSTRACT The system employing space-frequency OFDM (SF-OFDM) transmitter diversity suffers enhanced co-channel interference (CCI) due to the use of multiple transmitters at each mobile. A beamforming for the cancellation of CCI in SF-OFDM system is proposed. The performance of the beamformer based on null-steering has been investigated. Simulation results show that the proposed method has a good CCI cancellation ability. Meanwhile, the system performance can be enhanced by using the time delays of the signals from different direction of arrivals (DOAs)

0 Bookmarks
 · 
150 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: A simple extended orthogonal space-frequency coded multiple input single output (MISO) orthogonal frequency division multiplexing (OFDM) transmitter diversity technique for wireless communications over frequency selective fading channels is presented. The proposed technique utilizes OFDM to transform frequency selective fading channels into multiple flat fading sub-channels on which space-frequency coding is applied. A four-branch transmitter diversity system is implemented without bandwidth expansion and with only one receive antenna. The associated simulations verify that the four-branch transmitter diversity scheme achieves a significant improvement in average bit-error rate (BER) performance. The proposed scheme also outperforms the previously reported scheme due to Yu et. al. with only single phase feedback, and that improvement is retained with quantized feedback. Since the angle feedback is on a per tone basis, the feedback information would be too large for any practical OFDM system. However, we adopt a method which exploits the correlation among the feedback terms for the subcarriers, i.e. a group based quantization technique to reduce the feedback overhead significantly, rendering this scheme attractive to broadband wireless access systems.
    Sarnoff Symposium, 2008 IEEE; 05/2008
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Combined with space-time coding, the orthogonal frequency division multiplexing (OFDM) system explores space diversity. It is a potential scheme to offer spectral efficiency and robust high data rate transmissions over frequency-selective fading channel. However, space-time coding impairs the system ability to suppress interferences as the signals transmitted from two transmit antennas are superposed and interfered at the receiver antennas. In this paper, we developed an adaptive beamforming based on least mean squared error algorithm and null deepening to combat co-channel interference (CCI) for the space-time coded OFDM (STC-OFDM) system. To illustrate the performance of the presented approach, it is compared to the null steering beamformer which requires a prior knowledge of directions of arrival (DOAs). The structure of space-time decoders are preserved although there is the use of beamformers before decoding. By incorporating the proposed beamformer as a CCI canceller in the STC-OFDM systems, the performance improvement is achieved as shown in the simulation results. Comment: Journal of Telecommunications,Volume 1, Issue 1, pp6-13, February 2010
    02/2010;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A simple extended orthogonal space-frequency coded multiple input single output (MISO) orthogonal frequency division multiplexing (OFDM) transmitter diversity technique for wireless communications over frequency selective fading channels is presented. The proposed technique utilizes OFDM to transform frequency selective fading channels into multiple flat fading sub-channels on which space-frequency coding is applied. A four-branch transmitter diversity system is implemented without bandwidth expansion and with only one receive antenna. The associated simulations verify that the four-branch transmitter diversity scheme achieves a significant improvement in average bit-error rate (BER) performance. The proposed scheme also outperforms the previously reported scheme due to Yu, Keroueden, and Yuan with only single phase feedback, and that improvement is retained with quantized feedback. Since the angle feedback is on a per tone basis, the feedback information would be too large for any practical OFDM system. However, we adopt a method which exploits the correlation among the feedback terms for the subcarriers, i.e. a group based quantization technique to reduce the feedback overhead significantly, rendering this scheme attractive to broadband wireless access systems. The performance improvement of convolutionally concatenated space-frequency block coding (CCSBC) schemes is also investigated.
    Broadband Communications, Networks and Systems, 2008. BROADNETS 2008. 5th International Conference on; 10/2008