Enhanced spectral efficiency schemes for space-time block coded spatial modulation.
Motsa, Sibusiso Thabiso.
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The ever-growing demand for high data rate, low latency and energy efficient transmission schemes has seen an increasing popularity of multiple-input multiple-output (MIMO) scheme. One such scheme is the orthogonal space-time block code (STBC) scheme introduced by Alamouti which provides full diversity without sacrificing its data rate. Introduction of spatial multiplexing to STBC through spatial modulation (SM) improves the performance and spectral efficiency whilst eliminating transmit antenna synchronization and inter-channel interference (ICI) at the receiver. In this dissertation, we investigate and evaluate the error performance of both STBC and SM MIMO schemes. As such, we exploit the advantage of both schemes in space-time block coded spatial modulation (STBC-SM) scheme resulting in a high spectral efficient scheme. Motivated by the requisite for higher data rate transmission schemes, we expand the orthogonal STBC transmission matrix to further improve the spectral efficiency of space-time block coded spatial modulation. The fundamental idea is keeping the size of the amplitude/phase modulator (APM) symbol set of STBC the same. Therefore, unitary matrix transformation technique is introduced to the conventional STBC matrix. This technique prevents an increase in the peak-to-average power ratio of the transmitted symbols. A decrease in the phase angle of the unitary matrix yields an increase in the number of information bits transmitted, subsequently increasing the spectral efficiency of a system. A new system referred to as enhanced spectral efficiency space-time block coded spatial modulation (E-STBC-SM) is proposed. Moreover, a tight closed-form lower-bound is derived to estimate the average BER of the E-STBC-SM system over Rayleigh frequency-flat fading channel and validated with Monte Carlo simulations. Comparisons of the proposed E-STBC-SM scheme and conventional STBC-SM scheme are carried out with four receive antennas in all cases. The E-STBC-SM scheme virtually retains the BER performance of the STBC-SM scheme with a maximum attenuation of 0.6 dB throughout modulation order 16, 32 and 64 of a PSK modulator. An increase of between 2 to 5 information bits are obtained across the motioned modulation orders through altering of the phase angle of the unitary matrix transform incorporated with the conventional STBC-SM scheme thus improving the spectral efficiency. In a rare occurrence of 𝑀=32 and 𝜃=𝜋2 configured E-STBC-SM scheme, an improvement of 0.2 dB in error performance was experienced.