On Media-Based Modulation for Wireless Communications
Traditionally, symbols chosen from complex modulation alphabets such as QAM and PSK are used to convey information bits, and complex fades introduced by the channel are viewed as detrimental effects that cause amplitude and phase distortion to the transmitted symbols. An alternative and interesting approach is to consider the complex channel fade coefficients themselves to constitute a modulation alphabet (referred to as `channel alphabet'). An example of this approach is a recently proposed `media-based modulation (MBM)' scheme, which uses digitally controllable parasitic elements (called as radio frequency mirrors) near the transmit antenna(s) to create the channel alphabet. Each radio frequency (RF) mirror can be either ON or OFF. A mirror allows the incident RF signal to pass through it transparently when it is ON, and reflects back the incident RF signal when it is OFF. The ON/OFF status of the mirrors is called as `mirror activation pattern (MAP)'. The channel alphabet needs to be known only at the receiver and not at the transmitter. MBM has been shown to achieve significant performance gains compared to conventional modulation schemes. In this thesis, we investigate the performance of MBM in various scenarios like transmission with feedback, differential transmission, imperfect channel state information, full-duplex communications, and cooperative relaying. The contributions in this thesis are three-fold. In the first part, we investigate the performance of some interesting physical layer techniques when applied to MBM. First, we combine MBM with generalized spatial modulation (GSM), and investigate its performance. Next, we study the performance of feedback based mirror activation pattern (MAP) selection (analogous to transmit antenna selection in multi-antenna systems), and phase compensation and constellation rotation (PC-CR) techniques in MBM. We also analyze the diversity orders achieved by the ED-based MAP selection scheme and the PC-CR scheme. In the second part, we deal with channel estimation aspects in MBM. First, we present a differential MBM (DMBM) scheme which does not require estimation of channel modulation alphabet at the receiver for detection. We also propose a low-complexity maximum-likelihood (ML) detection algorithm for DMBM. Next, we analyze the effect of imperfect channel estimation on the bit error performance of MBM. We analyze the performance for two types of detectors, namely, i) the commonly studied mismatched detector, and ii) the true ML detector that maximizes the likelihood by taking the statistics of the channel estimate into account. In the final part, we investigate the performance of full-duplex (FD) communication using MBM, and compare it with that of FD with conventional modulation schemes. First, we investigate the FD communication using MBM and DMBM in a point-to-point setting, and present detectors for signal detection. Next, we analyze the performance of a two-hop three-node FD relay network, where the source and relay nodes transmit using MBM. The relay uses decode-and-forward (DF) relaying protocol. Next, we investigate the performance of MBM in a two-way relaying network, where two FD nodes exchange information with the help of a FD relay node using DF protocol.