Book Description

The ubiquitous wireless networks in the next generation of communication systems have motivated advanced techniques with diverse ranges of connectivity, coverage, reliability, and throughput. The massive connectivity in the context of the heterogenous networks has conveyed to different sorts of challenges including inter-cell and intra-cell originated interferences. The complications aggravate due to the sporadic nature of the traffic generated by large-scale and low-powered networks over limited spectrum resources. In this thesis, different techniques in enhancing the reliability, as well as spectral and power efficiency in the future generations of the multi-point communication networks have been investigated. Our proposed schemes are based on the coordination of the transmitters in sharing the source information followed by the joint transmission and the iterative detection. in the context of the cooperative source and channel coding. The Non-Orthogonal Multiple Access (NOMA), Coordinated Multi-Point (CoMP) transmission and the Iterative Joint Detection and Decoding (IJDD) receivers are the frameworks that we have used to validate our proposed improvements. We have initially investigated the cooperative NOMA as the physical layer network coding scheme in the downlink of wireless communication systems. It is proposed to benefit from the so-called interference received from adjacent cells instead of ignoring or cancelling them, as in the state-of-the-art systems. The application of cooperative NOMA is evaluated in a system-level information theoretic framework to optimize the user-pairing strategy. The results show the cell edges with the strongest interference are the optimal vicinity for the NOMA applications. Further, we have evaluated the NOMA for the uplink in the dense Internet of Things (IoT) systems, where the sensor elements observe the correlated sources. Realizing that the separation of source coding from channel coding in NOMA systems with correlated sources is suboptimal, we propose our scheme based on the cooperative source and channel coding. The transmitters are assumed to be privy to the whole data through a high-rate and low-latency background connection. The cooperative source coding is then followed by the transmission over the non-orthogonal multiple access (NOMA) channel. As the transmit signals experience different delay-spreads through the channel, the data streams are received asynchronously, resulting in inter-symbol interference (ISI) at the receiver. We show that the correlated nature of the asynchronous channels can be exploited as the extra source of information, provided that a proper detection technique is adopted. The capacity region is developed, where the sum-rate exceeds that of the synchronous NOMA. The potency of the successive interference cancellation (SIC) receivers, as the main block in NOMA receivers, is investigated. By applying water-filling and geometric power allocation, we show that the NOMA performance degradation in asynchronous channels is caused by the nature of SIC. We have proposed our iterative joint detection and decoding (IJDD) receiver that outperforms SIC in asynchronous NOMA receivers. Moreover, we have addressed two key challenges in Coordinated Multi-point (CoMP) networks. The asynchronous downlink and imperfect channel state information (CSI) are jointly considered in an information theoretical framework. We assume delays from the Transmission and Reception Points (TRP) to the target user, in general, may exceed cyclic prefix (CP) length, causing symbol-asynchronous reception at the receiver. We characterize an accurate mathematical model for the asynchronous Rayleigh fading channel with imperfect CSI for multi-TRP schemes. We have derived the capacity region for asynchronous CoMP systems and have generalized it to the multi-TRP schemes. We propose a low-complexity iterative detection scheme targeting minimizing the mean square error (MMSE) in our asynchronous fading channel model. Finally, we have associated the coordinated multi-point transmission with NOMA methodology. We have considered the downlink CoMP in a Single-Frequency Network (SFN) of Digital Terrestrial Television (DTT) broadcasting network. The coordinated transmit signals are assumed to have embedded Layered-Division Multiplexing (LDM) to enhance the coverage, reliability, and spectral efficiency in multi-content broadcasting. We have extended the MMSE-IJDD receiver to higher order modulation formats and have evaluated the order of the computational complexity for our proposed receiver to be in a decent range. Our extensive simulations validate the proposed scheme providing a considerable boost in the channel reliability, while enhancing the spectral and power efficiency, even as the number of TRPs increases.