Improved Orthogonal Frequency Division Multiplexing With Index Modulation Spread Spectrum For Optimized Performance

The thesis is devoted to investigate new improved modulation scheme formulated by encompassing orthogonal frequency division multiplexing with index modulation(OFDM-IM),spread spectrum(SS)and in-phase quadrature(I/Q)to improve bit error rate(BER)performance and spectral efficiency.Firstly,we present a new system model which is a novel variant of OFDM-IM-SS.Index modulation(IM)orthogonal frequency division multiplexing(OFDM)spread spectrum(SS)is a recently proposed scheme which transmits additional bits(in the form of indices)through code domains where multiple spreading codes are selected among a set of spreading codes preset before transmission.We combine OFDM-IM-SS with OFDM-IM-I/Q(orthogonal frequency division multiplexing with in-phase quadrature index modulation)which splits the modulated symbol into in-phase and quadrature domains to double the index of conventional OFDM-IM scheme.Thus,our new modulation scheme termed as OFDM-IM-SS-I/Q first splits the modulated symbol into in-phase and quadrature part after which index bits are used to select the spreading codes to separately transmit in-phase and quadrature parts of the modulated symbol.We present a detailed analysis of spectral efficiency and bit error rate(BER)performance of our OFDM-IM-SS-I/Q system.Further,we compare the result with prior modulation schemes,particularly with OFDM-IM-SS.Also,to reduce the system complexity,a low complexity detector at receiver is proposed whose performance matches with the conventional maximum likelihood(ML)detector.The study shows that our proposed OFDM-IM-SS-I/Q scheme obtains a better BER performance than previous OFDM-IM-SS modulation scheme and achieves a higher diversity order too.Computer simulation in MATLAB supports our claims mentioned above validating the theoretical analysis of outperforming OFDM-IM-SS scheme.