Abstract
The quasi-orthogonal space time block coding (QO-STBC) over orthogonal frequency division multiplexing (OFDM) is investigated. Traditionally, QO-STBC does not achieve full diversity since the detection matrix of QO-STBC scheme is not a diagonal matrix. In STBC, the decoding matrix is a diagonal matrix which enables linear decoding whereas the decoding matrix in traditional QO-STBC does not enable linear decoding. In this paper it is shown that there are some interfering terms in terms of non-diagonal elements that result from the decoding process which limit the linear decoding. As a result, interference from the application of the QO-STBC decoding matrix depletes the performance of the scheme such that full diversity is not attained. A method of eliminating this interference in QO-STBC is investigated by nulling the interfering terms towards full diversity for an OFDM system. It was found that the interference reduction technique permits circa 2dB BER performance gain in QO-STBC. The theoretical and simulation results are presented, for both traditional QO-STBC and interference-free QO-STBC applying OFDM
Highlights
Present days wireless communications systems are in great quest for efficient communications
For four time slots where no column of the encoding matrix is eliminated, the QO-Space Time block coding (STBC) orthogonal frequency division multiplexing (OFDM) symbols will be quasi-static for four time slots
QO-STBC scheme that improve the performance of multi antenna system using diversity over OFDM system has been presented
Summary
Present days wireless communications systems are in great quest for efficient communications. It is possible to deploy the STBC technology in way that full rate power transmission can be achieved. In such case, the codes are rather formed in a special orthogonal way. The BER curves suggest that the codes outperform the codes of orthogonal design only at low SNRs, but worsen at increased SNRs [1] This is due to the fact that the slope of the performance curve depends on the diversity order gain. One of the major problems that limits the BER performance of the QO-STBC system is from the interference incurred in the decoding process If these interferences can be removed, the performance of the QO-STBC scheme will improve towards full diversity gain. The numerical simulation results for QO-STBC OFDM system is discussed in Section VI followed by summarized conclusion
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