| Increasing demand for bandwidth-hungry applications, along with the bandwidth scarcity, has generated a certain momentum toward designing bandwidth-efficient techniques. Recently, multi-way relay channels (MWRCs) have been proposed to improve the spectral efficiency in wireless systems. The main focus of this dissertation is studying the achievable rates of MWRCs as well as proposing methods to improve it.;In the first part of our work, we focus on the users' bit mapping and propose a new mapping for phase-shift keying modulation which increases the achievable rate and decreases the bit error rate of a pairwise MWRC. Interestingly, our proposed mapping outperforms the well-known Gray mapping in terms of both metrics on an additive white Gaussian noise (AWGN) channel.;Then, the achievable rates of a pairwise MWRC, with a simple memoryless relay, where the communication happens over a fading channel with AWGN is studied. For this setup, we determine what relaying strategy suits best based on the system's signal-to-noise ratio.;Later, we extend our rate analysis to the case where the relay is more complex and has memory. First, a symmetric MWRC with AWGN is considered. For this setup, the capacity gap of different relaying strategies are derived and then they are compared with that of one-way relaying. Second, we consider a pairwise MWRC where the links are asymmetric. We show that the system's achievable rate is dependent on the users' transmission pairing in this case. An optimal pairing to maximize the achievable rate is also found.;In the last part of our contributions, erasure MWRCs are the subject of interest. For such channels, we derive an upper bound on the system's achievable rate and also propose low-latency data sharing schemes based on fountain coding. Further, we define a measure, called end-to-end erasure rate, which is used to compare the performance of our proposed schemes with the rate upper bound and the achievable rate of one-way relaying.;Summarily speaking, in the MWRCs' setups studied in this dissertation, multi-way relaying is beneficial when the number of users and the error (erasure) rate are not large. Otherwise, one-way relaying may provide higher data rates. |
