Maximizing Energy Efficiency in Multiple Access Channels by Exploiting Packet Dropping and Transmitter Buffering

Quality of service (QoS) for a network is characterized in terms of various parameters specifying packet delay and loss tolerance requirements for the application. The unpredictable nature of the wireless channel demands for application of certain mechanisms to meet the QoS requirements. Traditionally, medium access control (MAC) and network layers perform these tasks. However, these mechanisms do not take (fading) channel conditions into account. In this paper, we investigate the problem using cross layer techniques where information flow and joint optimization of higher and physical layer is permitted. We propose a scheduling scheme to optimize the energy consumption of a multiuser multi-access system such that QoS constraints in terms of packet loss are fulfilled while the system is able to maximize the advantages emerging from multiuser diversity. Specifically, this work focuses on modeling and analyzing the effects of packet buffering capabilities of the transmitter on the system energy for a packet loss tolerant application. We discuss low complexity schemes which show comparable performance to the proposed scheme. The numerical evaluation reveals useful insights about the coupling effects of different QoS parameters on the system energy consumption and validates our analytical results.Comment: in IEEE trans. Wireless communications, 201

Performance analysis of broadband multimedia wireless communication networks

The designing of broadband multimedia wireless network systems should aim at achieving maximum utilisation of wireless resources through statistical multiplexing, while, at the same time satisfying the Quality of Service(QoS) requirements of multimedia traffic. In this research, we consider a priority based scheduling strategy, suitable to the terrestrial/satellite wireless environment. The multimedia traffic is categorised into real-time (voice and video connections) and non-real-time (data connections) depending on whether it is delay sensitive or loss sensitive. The fixed size packets generated by each of the aggregated voice, video and data sources from all user terminals in an uplink beam, are modeled as a 2-state Markov modulated Poisson Process (MMPP). Using the counting process of real-time traffic, the real-time packet loss probability has been evaluated at the uplink. Based on the equation governing the non-real-time packet queueing process at the epochs of the beginning of each frame and by using an embedded Markov chain analysis, the elements of the transition probability matrix are derived. Using the matrix-geometric technique, the occupancy distribution non-real-time packet queue is evaluated. The illustrative results for different cases of traffic mix are presented. Further, we outline the analytical derivation for obtaining covariance function of number of real-time and non-real-time arrivals to a particular downstream link through the switch. We match the covariance function values at different lags with the covariance function of 2-state MMPP at corresponding lags in order to obtain the parameters of approximating 2-state MMPPs. Based on this, and using the single queue model of the uplink, we describe the procedure for evaluating the performance at the downlink. A simulation model has also been developed in order to assess the effects of the various approximations required for the analytical model

An integrated packet/flow model for TCP performance analysis

Processor sharing (PS) models for TCP behavior nicely capture the bandwidth sharing and statistical multiplexing effect of TCP flows on the flow level. However, these ‘rough’ models do not provide insight into the impact of packet-level parameters (such as round trip time and buffer size) on, e.g., throughput and flow transfer times. This paper proposes an integrated packet/flow-level model: it exploits the advantages of PS approach on the flow level and, at the same time, it incorporates the most significant packet-level effects

Performance Modelling and Optimisation of Multi-hop Networks

A major challenge in the design of large-scale networks is to predict and optimise the total time and energy consumption required to deliver a packet from a source node to a destination node. Examples of such complex networks include wireless ad hoc and sensor networks which need to deal with the effects of node mobility, routing inaccuracies, higher packet loss rates, limited or time-varying effective bandwidth, energy constraints, and the computational limitations of the nodes. They also include more reliable communication environments, such as wired networks, that are susceptible to random failures, security threats and malicious behaviours which compromise their quality of service (QoS) guarantees. In such networks, packets traverse a number of hops that cannot be determined in advance and encounter non-homogeneous network conditions that have been largely ignored in the literature. This thesis examines analytical properties of packet travel in large networks and investigates the implications of some packet coding techniques on both QoS and resource utilisation. Specifically, we use a mixed jump and diffusion model to represent packet traversal through large networks. The model accounts for network non-homogeneity regarding routing and the loss rate that a packet experiences as it passes successive segments of a source to destination route. A mixed analytical-numerical method is developed to compute the average packet travel time and the energy it consumes. The model is able to capture the effects of increased loss rate in areas remote from the source and destination, variable rate of advancement towards destination over the route, as well as of defending against malicious packets within a certain distance from the destination. We then consider sending multiple coded packets that follow independent paths to the destination node so as to mitigate the effects of losses and routing inaccuracies. We study a homogeneous medium and obtain the time-dependent properties of the packet’s travel process, allowing us to compare the merits and limitations of coding, both in terms of delivery times and energy efficiency. Finally, we propose models that can assist in the analysis and optimisation of the performance of inter-flow network coding (NC). We analyse two queueing models for a router that carries out NC, in addition to its standard packet routing function. The approach is extended to the study of multiple hops, which leads to an optimisation problem that characterises the optimal time that packets should be held back in a router, waiting for coding opportunities to arise, so that the total packet end-to-end delay is minimised

The Dynamics of Internet Traffic: Self-Similarity, Self-Organization, and Complex Phenomena

The Internet is the most complex system ever created in human history. Therefore, its dynamics and traffic unsurprisingly take on a rich variety of complex dynamics, self-organization, and other phenomena that have been researched for years. This paper is a review of the complex dynamics of Internet traffic. Departing from normal treatises, we will take a view from both the network engineering and physics perspectives showing the strengths and weaknesses as well as insights of both. In addition, many less covered phenomena such as traffic oscillations, large-scale effects of worm traffic, and comparisons of the Internet and biological models will be covered.Comment: 63 pages, 7 figures, 7 tables, submitted to Advances in Complex System

Protocol-processing overhead on the performance of error recovery schemes in high-speed network environments

This paper investigates the effects of protocol-processing overhead on the performance of error recovery schemes in high-speed network environments. The investigated error recovery schemes are:• an edge-to-edge error recovery scheme, where retransmissions of erred packets only take place between source and destination nodes, and• a link-by-link error recovery scheme, where retransmissions only take place between adjacent switching nodes.For retransmission of erred packets, we consider both Go-Back-N and Selective-Repeat procedures in the analysis.The performance measures we obtain are the distribution of transfer delays and the loss probability of packets across a network. To obtain these measures, this paper develops a tandem queueing network model with feedbacks where each queue represents a protocol layer within a switching node, rather than a switching node as a whole.Numerical results show that for a network with very-high-speed/low-error-rate channels, an edge-to-edge scheme gives the smaller packet transmission delay than a link-by-link scheme for both Go-back-N and Selective-Repeat retransmission procedures, while keeping the packet loss probability sufficiently small

Packet loss characteristics for M/G/1/N queueing systems

In this contribution we investigate higher-order loss characteristics for M/G/1/N queueing systems. We focus on the lengths of the loss and non-loss periods as well as on the number of arrivals during these periods. For the analysis, we extend the Markovian state of the queueing system with the time and number of admitted arrivals since the instant where the last loss occurred. By combining transform and matrix techniques, expressions for the various moments of these loss characteristics are found. The approach also yields expressions for the loss probability and the conditional loss probability. Some numerical examples then illustrate our results