Improved Analysis of Co-Channel Interference Suppression for WHT-STC-OFDM Systems

Abstract

OFDM technology combined with STC has been used widely in modern communication systems, due to offering many advantages such as improving system capacity. Meanwhile it faces the mutual interference, such as CCI, which generated by multi-antenna transmitting at the receiver. Based on those advantages coming from the combination of STC-OFDM with WHT and the combination of STC-OFDM with ABF, an algorithm is proposed to suppress co-channel interference. Theoretical analysis and computer simulation showed the proposed algorithm could improve Symbol Error Rate performance and suppress CCI in STC-OFDM communication systems. Keywords-OFDM; STC; Adaptive Beamforming; Walsh Hadamard Transform. ⅠINTRODUCTIONIt is expected that future wireless communication standards would introduce multiple antenna to improving system performance including increasing capacity and reliability. Recently, Multiple Input Multiple Output (MIMO) has been extensively studied for high transmission data rate and spectrum efficiency required for the 4 th generation mobile communication systems.Alamouti proposed that Space Time Coding (STC) should be applied to adapting MIMO in wireless communication systems [1] , due to the combination can obtain higher coding gain without any bandwidth loss while reducing the influence of multi-path and improving the capacity. Simultaneously, the combination of STC and OFDM modulation not only alleviate drawbacks of each other, but also improve the high speed transmission performance limited to two fundamental impairments, multi-path fading and ISI. However, multi-antenna transmission may be result in interference such as Co-Channel Interference (CCI) each other at receiver by signals transmitted from different antennas of either the same transmitter or other transmitters. According to that, suppressing interference in STC-OFDM systems is important [2] .Adaptive Beamforming(ABF) can effectively suppress CCI and cancel multi-path fading [3] ; in addition, the combination of ABF and Null Deepening (ND) based on Minimum Mean Square Error (MMSE) of pilot signals also can effectively suppress CCI [4] , and there are plenty of literatures about improving the performance of OFDM systems [5][6] ; furthermore, combining STC-OFDM with Walsh Hadamard Transform (WHT) can reduce the Peak-to-Average Power Ratio (PAPR) and improve the performance of systems [7] .Based on the previous researches, the combination of WHT and ABF-ND suppressing CCI in STC-OFDM systems was proposed. Accordingly, the combination of WHT-STC-OFDM and ABF could enhance the ability to suppressing CCI to a certain extent.In this paper, the certain organization is followed as below:The section 2 describes the proposed combination of WHT and ABF-ND as a CCI canceller in the STC-OFDM system. As the section 3 evaluated a theoretical expression to estimate the system performance, besides, theoretical and simulation curves are presented for comparison and validation. Finally, section 4 presents the conclusions.