Relay-aided networks have been proved to be cost-efficient solutions for wireless communications
in respect of high data rates, enhanced spectrum efficiency and improved signal coverage.
In the past decade, relaying techniques have been written into standards of modern wireless
communications and significantly improve the quality of service (QoS) in wireless communications.
In order to satisfy exponentially increased demands for data rates and wireless connectivities,
various novel techniques for wireless communications have been proposed in recent years,
which have brought significant challenges for the performance analysis of relaying networks.
For the purpose of more practical investigations into relaying systems, researchers should not
only analyse the relays employing novel techniques but also attach more importance to complex
environments of wireless communications. With these objectives in mind, in this thesis, in-depth
investigations into system performance for relay-assisted wireless communications are
detailed.
Firstly, the theoretic reliability of dual-hop amplify-and-forward (AF) systems over generalised
η-μ and κ-μ fading channels are investigated using Gallager’s error exponents. These two versatile
channel models can encompass a number of popular fading channels such as Rayleigh,
Rician, Nakagami-m, Hoyt and one-sided Gaussian fading channels. We derive new analytical
expressions for the probability distribution function (pdf) of the end-to-end signal-to-noise-ratio
(SNR) of the system. These analytical expressions are then applied to analyse the system performance
through the study of Gallager’s exponents, which are classical tight bounds of error
exponents and present the trade-off between the practical information rate and the reliability of
communication. Two types of Gallager’s exponents, namely the random coding error exponent
(RCEE) and the expurgated error exponent, are studied. Based on the newly derived analytical
expressions, we provide an efficient method to compute the required codeword length to achieve
a predefined upper bound of error probability. In addition, the analytical expressions are derived
for the cut-off rate and ergodic capacity of the system. Moreover, simplified expressions
are presented at the high SNR regime.
Secondly, the performance of a dual-hop amplify-and-forward (AF) multi-antenna relaying
system over complex Gaussian channels is investigated. Three classical receiving strategies,
i.e. the maximal-ratio combining (MRC), zero-forcing (ZF) and minimum mean square error
(MMSE) are employed in the relay to mitigate the impact of co-channel interference (CCI),
which follows the Poisson point process (PPP). We derive the exact analytical expressions of
the capacities for this system in the infinite-area interference environment and the asymptotic
analytical expressions for the lower bounds of capacities in the limited-area interference scenario.
By computing the numerical results and the Monte Carlo simulation, we can observe the
effect of relay processing schemes under different interference regimes.
In the end, the non-orthogonal multiple access (NOMA) technique is introduced to relaying
systems, which exploits multiplexing in the power domain. Order statistics are applied in this
part to analyse the performances of ordered users. The randomness of both channel fading
and path loss are taken into consideration. In addition to the exact analytical expressions,
asymptotic expressions at high-SNR regimes are provided, which clearly show the effects of
NOMA techniques using at relaying systems
