PAPR Reduction for MIMO-OFDM System using Integrated Modified PTS Technique

Abstract

The progression in age and its growing demands, there has been rapid development in the field of communication system. The combined multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) called (MIMO-OFDM) systems. It has been receiving a great attention, for achieving high speed, high quality of service (QOS) and robustness to frequency selective fading channels by changing it in to parallel flat fading channels. It also increases range and reliability of wireless communications system. Beside those advantages high peak to average power ratio (PAPR) is a major drawback of multicarrier transmission system. It leads power amplifier at transmitter enters into saturation region instead of being in linear region. It also increase the complexity in the analog to digital (ADC) and digital to analog conversion(DAC). Partial Transmit Sequence (PTS) algorithm is used to provide low PAPR and mitigates the out of band radiation in MIMO-OFDM system. However, the use of conventional PTS (C-PTS) technique requires excessive searching in order to find optimal phase sequence out of all permissible combinations, leading to sharp increment in computational complexity. The integrated modified PTS scheme based on single inverse fast Fourier transform (IFFT) in contrast to the C-PTS require reduced IFFT blocks and iterations. These characteristics considerably decrease processing time and less computation following in decreased complexity. This thesis used a local searching algorithm to optimize the set of phase factors that decrease the searching complexity. The performance of MIMO-OFDM system based on integrated modified PTS scheme using Quadrature Phase Shift Keying Modulation (QPSK) has been evaluated with different factor. There is a significant improvement in PAPR reduction for the integrated modified PTS that can be quantified as 5.5 dB. when 64 sub carriers, 4 sub-blocks, 4 phase, 4 oversampling factor and 0.6 roll-off factor for 102 complimentary cumulative distribution function (CCDF) value variables have been used and it can further increase as number sub blocks increase. In comparison with the C-PTS the integrated modified PTS give better trade off PAPR reduction and computational complexity reduced by 6%. The bit error rate (BER) is evaluated and analyzed with the theoretical value