In today's increasingly advancing communication technologies, a variety of modulation techniques have been used, such as Pulse Amplitude Modulation(PAM), Pulse Code Modulation(PCM), Phase-Shift Keying(PSK), Differential Phase-Shift Keying(DPSK), Frequency-Shift Keying(FSK), Amplitude-Shift Keying(ASK), Quadrature Amplitude Modulation (QAM). Each modulation technique has its advantages and disadvantages and its designed working environment. As each technique is not perfect, there is always room to improve for every technology, for example, to improve error performance, or increase bandwidth efficiency, or reduce the transmission cost.
QAM is a widely used modulation and demodulation technique due to its high bandwidth efficiency. On the other hand, its error performance is worse than binary PSK (BPSK) and quadrature PSK (QPSK). Each constellation size has an optimal constellation design with the lowest symbol error rate (SER). QAM constellations often used in practice, e.g. QPSK, 16 square QAM, are usually not optimal, due to implementation complications.
This thesis introduces the concept of QAM, system diagram, its advantages and disadvantages, and SER performance analysis over additive white Gaussian channels (AWGN). We obtain SER performance of various 16QAM constellations via MATLAB simulation and find the optimal one. Conventional Gray coding is not possible for the optimal constellation. Therefore, we again used MATLAB simulation to obtain and compare bit error rate (BER) of various mappings.
Another contribution of this thesis is that we standardized the simulation program such that an arbitrary constellation of 16QAM can be inputted for SER/BER performance simulation. We also constructed a user-friendly MATLAB graphics user interface (GUI) that allows for easy input of trial constellation coordinates, and convenient comparison of simulation results.
Keywords: 16QAM,MATLAB,SER,BER,Optimal constellation.