7 research outputs found
A Stochastic Geometric Analysis of Device-to-Device Communications Operating over Generalized Fading Channels
Device-to-device (D2D) communications are now considered as an integral part
of future 5G networks which will enable direct communication between user
equipment (UE) without unnecessary routing via the network infrastructure. This
architecture will result in higher throughputs than conventional cellular
networks, but with the increased potential for co-channel interference induced
by randomly located cellular and D2D UEs. The physical channels which
constitute D2D communications can be expected to be complex in nature,
experiencing both line-of-sight (LOS) and non-LOS (NLOS) conditions across
closely located D2D pairs. As well as this, given the diverse range of
operating environments, they may also be subject to clustering of the scattered
multipath contribution, i.e., propagation characteristics which are quite
dissimilar to conventional Rayeligh fading environments. To address these
challenges, we consider two recently proposed generalized fading models, namely
and , to characterize the fading behavior in D2D
communications. Together, these models encompass many of the most widely
encountered and utilized fading models in the literature such as Rayleigh, Rice
(Nakagami-), Nakagami-, Hoyt (Nakagami-) and One-Sided Gaussian. Using
stochastic geometry we evaluate the rate and bit error probability of D2D
networks under generalized fading conditions. Based on the analytical results,
we present new insights into the trade-offs between the reliability, rate, and
mode selection under realistic operating conditions. Our results suggest that
D2D mode achieves higher rates over cellular link at the expense of a higher
bit error probability. Through numerical evaluations, we also investigate the
performance gains of D2D networks and demonstrate their superiority over
traditional cellular networks.Comment: Submitted to IEEE Transactions on Wireless Communication
A Comprehensive Analysis of 5G Heterogeneous Cellular Systems operating over - Shadowed Fading Channels
Emerging cellular technologies such as those proposed for use in 5G
communications will accommodate a wide range of usage scenarios with diverse
link requirements. This will include the necessity to operate over a versatile
set of wireless channels ranging from indoor to outdoor, from line-of-sight
(LOS) to non-LOS, and from circularly symmetric scattering to environments
which promote the clustering of scattered multipath waves. Unfortunately, many
of the conventional fading models adopted in the literature to develop network
models lack the flexibility to account for such disparate signal propagation
mechanisms. To bridge the gap between theory and practical channels, we
consider - shadowed fading, which contains as special cases, the
majority of the linear fading models proposed in the open literature, including
Rayleigh, Rician, Nakagami-m, Nakagami-q, One-sided Gaussian, -,
-, and Rician shadowed to name but a few. In particular, we apply an
orthogonal expansion to represent the - shadowed fading
distribution as a simplified series expression. Then using the series
expressions with stochastic geometry, we propose an analytic framework to
evaluate the average of an arbitrary function of the SINR over -
shadowed fading channels. Using the proposed method, we evaluate the spectral
efficiency, moments of the SINR, bit error probability and outage probability
of a -tier HetNet with classes of BSs, differing in terms of the
transmit power, BS density, shadowing characteristics and small-scale fading.
Building upon these results, we provide important new insights into the network
performance of these emerging wireless applications while considering a diverse
range of fading conditions and link qualities
Interference modeling and performance analysis of 5G MmWave networks
Doctor of PhilosophyDepartment of Electrical and Computer EngineeringBalasubramaniam NatarajanTriggered by the popularity of smart devices, wireless traffic volume and device connectivity have been growing exponentially during recent years. The next generation of wireless networks, i.e., 5G, is a promising solution to satisfy the increasing data demand through combination of key enabling technologies such as deployment of a high density of access points (APs), referred to as ultra-densification, and utilization of a large amount of bandwidth in millimeter wave (mmWave) bands. However, due to unfavorable propagation characteristics, this portion of spectrum has been under-utilized. As a solution, large antenna arrays that coherently direct the beams will help overcome the hostile characteristics of mmWave signals. Building networks of directional antennas has given rise to many challenges in wireless communication design. One of the main challenges is how to incorporate 5G technology into current networks and design uniform structures that bring about higher network performance and quality of service. In addition, the other factor that can be severely impacted is interference behavior. This is basically due to the fact that, narrow beams are highly vulnerable to obstacles in the environment.
Motivated by these factors, the present dissertation addresses some key challenges associated with the utilization of mmWave signals. As a first step towards this objective, we first propose a framework of how 5G mmWave access points can be integrated into the current wireless structures and offer higher data rates. The related resource sharing problem has been also proposed and solved, within such a framework.
Secondly, to better understand and quantify the interference behavior, we propose interference models for mmWave networks with directional beams for both large scale and finite-sized network dimension. The interference model is based on our proposed blockage model which captures the average number of obstacles that cause a complete link blockage, given a specific signal beamwidth. The main insight from our analysis shows that considering the effect of blockages leads to a different interference profile.
Furthermore, we investigate how to model interference considering not only physical layer specifications but also upper layers constraints. In fact, upper network layers, such as medium access control (MAC) protocol controls the number of terminals transmitting simultaneously and how resources are shared among them, which in turn impacts the interference power level. An interesting result from this analysis is that, from the receiving terminal standpoint, even in mmWave networks with directional signals and high attenuation effects, we still need to maintain some sort of sensing where all terminals are not allowed to transmit their packets, simultaneously. The level of such sensing depends on the terminal density.
Lastly, we provide a framework to detect the network regime and its relation to various key deployment parameters, leveraging the proposed interference and blockage models. Such regime detection is important from a network management and design perspective. Based on our finding, mmWave networks can exhibit either an interference-limited regime or a noise-limited regime, depending on various factors such as access point density, blockage density, signal beamwidth, etc
Performance analysis of relay-aided wireless communication systems
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