BER and PAPR Analysis of OFDM System for π⁄4-DQPSK and GMSK

Abstract

In the last few years wireless communications have seen a fast growth due to the high mobility that they allow.With promising technology and ever-increasing wireless devices, the spectrum is becoming scarcer day by day. In this case, using Orthogonal Frequency Division Multiplexing (OFDM) for spectrally efficient transmission is an alternative solution. OFDM is a bandwidth efficient multicarrier modulation scheme where the available spectrum is divided into subcarriers, with each subcarrier data modulated at low rate. OFDM has gained a tremendous interest in recent years because of its spectral efficiency and robustness in the presence of severe multipath channel conditions with simple equalization, robustness against Inter-Symbol Interference (ISI), multipath fading, in addition to its high spectral efficiency. However, the Peak to Average Power Ratio (PAPR) is a major drawback of multicarrier transmission system such as OFDM. As power amplifier is used at the transmitter side, OFDM signal forced the amplifier to work in the nonlinear regiondue to the high PAPR which leads to in-band distortion and out-band radiation. This can be avoided by increasing the dynamic range of power amplifier which leads to high cost and high consumption of power at the base station. To reduce PAPR number of techniques has been proposed in literature. In this dissertation, MPSK, π⁄4-DQPSK, GMSK modulation schemes are implemented in OFDM system. GMSK is Continuous Phase Modulation (CPM), which can give higher bandwidth efficiency than QPSK and higher-order MPSK.Andπ⁄4-DQPSK gives much smaller fluctuations of the envelope than that of QPSK.Bit Error Rate or Bit Error Ratio (BER) performance analysis is done for MPSK, π⁄4-DQPSK, GMSK modulation schemes with OFDM system under AWGN channel, Rayleigh fading channel, Rician fading channel. In case of GMSK-OFDM, BER decreases more rapidly with respect to SNR when compared with 64PSK. This dissertation presents analysis of PAPR for above described OFDM system. An efficient PAPR reduction technique i.e the Selected Mapping (SLM) is implemented. The PAPR is analysed usingComplementaryCumulative Distribution Function (CCDF),which is the one of the most regularly used parameter to measure the efficiency of any PAPR technique.Reduction in PAPR is obtained for OFDM system with above mentioned modulation techniques.