Novel technique for PAPR reduction in OFDM system using π/4-shifted-DQPSK modulation & turbo code

The proposed SLM scheme transforms an input incoming symbol sequence into a set of OFDM symbols by multiplying the phase sequences to the symbol after a intermediate inverse fast Fourier transform (IFFT) stage. The peak-to-average power ratio (PAPR) of OFDM symbols is calculated & the symbol with least PAPR is sent for transmission. Turbo code is used with OFDM for forward error correction. To achieve better spectral efficiency and high capacity the combination of π/4-shifted DQPSK modulation is used along with Turbo coded OFDM. One of the major reasons behind the provision for differential detection is to achieve low complexity at the receiver. A selective-level-mapping type turbo coded OFDM scheme is proposed with the interleaver of turbo encoder to reduce the associated PAPR (peak to average power ratio) reduction. The current model is used to analyze bit error rate (BER) measurement with π/4-shifted-DQPSK modulation in presence of fading channels. The symbols are perturbed by additive white Gaussian noise (AWGN). The combination of DQPSK with SLM not only reduces the complexity at receiver but also results in reduction in PAPR of OFDM signal. The PAPR of the model is calculated with absence of SLM block initially and later with the addition of SLM block resulting in the difference of PAPR up to 3 dB. The simulink is used to model the performance of turbo encoder and decoder to achieve minimum symbol error rate at the receiver with varying iterations. The minimum symbol error rate of 10^-6 is calculated using the principle of APP decoder.