Design & Implementation for Combination of QPSK & BPSK Modulation Techniques

Modulation techniques have concerned increasing attention in optical wireless communications. Downlink transmission (base station to mobile terminal) using high data rate Mary Quadrature Amplitude Modulation (QAM), Quadrature Phase Shift Keying (QPSK) and Binary Phase Shift Keying (BPSK) modulation schemes are considered in a Wideband-Code Division Multiple Access (W-CDMA) system. QPSK or Quadrature Phase-Shift Keying is a higher order modulation scheme used in digital modulation. It is a widely used digital modulation technique in wireless communication, such as TDMA cellular telephone, OFDM, Bluetooth, Satellite communication etc. due to its advanced noise immunity, bandwidth efficiency and simpler circuitry. In this paper, we will be implementing a BPSK plus QPSK modulator for a communication link. In this, this system separately modulates the BPSK and QPSK signals with same input information and then combines in adder. Then it can demodulate with a common detector and we get the same output as input. We can analysis the performance of these modulation techniques when system is subjected to AWGN and fading are consider in the channel. Subsequently, a comparison study is carried out to obtain BER performance for each PSK-based transmission scheme. The design will be simulated by MATLAB tool. We will use MATLAB R2013a for simulation and evaluation of BER and SNR for system models. The output signal waveform will be measured and tested to find signal quality and the SNR or Signal to Noise Ratio. The comparison study showed that BER for BPSK + QPSK is higher than BPSK but lower than half of QPSK’s BER . KeywordsModulation techniques, Communication system performance, optical signal processing, capacity.