Offset Phase Shift Keying Modulation in Multiple-Input Multiple-Output Spatial Multiplexing
The increasing demand for multimedia data transmission in mobile wireless communication poses a challenge to reliable signal reception. In order to have good signal quality, a robust digital modulation scheme is required at the transmitter. However, the conventional M-ary Phase Shift Keying (MPSK) commonly used in multiple-input multiple-output (MIMO) communication systems with non-linear radio frequency (RF) power amplifiers causes a relative increase in intercarrier interference (ICI). This paper presents a development of offset-MPSK (O-MPSK) modulation scheme in MIMO spatial multiplexing over the Rayleigh fading channel.
The O-MPSK modulation schemes were developed for 4, 8, 16, 32 and 64 constellation sizes. The development of the O-MPSK was done by shifting the phase of the conventional QPSK, 8-PSK, 16-PSK, 32-PSK and 64-PSK by an odd multiple of pi (π) to give -QPSK, -8PSK, -16PSK, -32PSK and -64PSK, respectively, with a view to reducing the spectral spreading in the power amplifiers at the receiver of a MIMO system. The MIMO techniques used was MIMO Spatial Multiplexing (MIMO–SM). The system models were developed around these schemes and later simulated using MATLAB application toolkit. The performances of the O-MPSK schemes were evaluated using bit error rate (BER) at signal-to-noise ratio (SNR) range of 0 to 20 dB and compared with the conventional MPSK schemes.
The results obtained for all the SNRs in MIMO-SM showed that mean BER of 0.0024, 0.0040, 0.0085, 0.0183 and 0.036 were obtained for -QPSK, -8PSK, -16PSK, -32PSK and -64PSK respectively as against mean BER of 0.0025, 0.0044, 0.0088, 0.0178 and 0.0358 obtained for conventional QPSK, 8PSK, 16PSK, 32PSK and 64PSK respectively.
The mean BER values obtained reveal that the developed O-MPSK outperforms the conventional MPSK due to the relatively lower BER of O-MPSK schemes compared with the MPSK schemes. This is as a result of the reduction in the amplitude variations and spectral spreading at the receiver of the MIMO system.
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