A Methodology for Analyzing Power Consumption in Wireless Communication Systems

Energy usage has become an important issue in wireless communication systems. The energy-intensive nature of wireless communication has spurred concern over how best systems can make the most use of this non-renewable resource. Research in energy-efficient design of wireless communication systems show that one of its challenges is that the overall performance of the system depends, in a coupled way, on the different submodules of the system i.e. antenna, power amplifier, modulation, error control coding, and network architecture. Network architecture implementation strategies offer protocol software implementors an opportunity of incorporating low-power strategies into the design of the network protocols used for data communication. This dissertation proposes a methodology that would allow a software protocol implementor to analyze the power consumption of a wireless communication system. The foundation of this methodology lies in the understanding of the formal specification of the wireless interface network architecture which can be used to predict the performance of the system. By extending this hypothesis, a protocol implementor can use the formal specification to derive the power consumption behaviour of the wireless system during a normal operation (transmission or reception of data). A high-level formalism like state-transition graphs, can be used to track the protocol processing behaviour and to derive the associated continuous-time Markov chains. Because of their diversity, Markov reward models(MRM) are used to model the power consumption associated with the different states of a specified protocol layer. The models are solved analytically using the Mobius performance and dependability tool. Using the MRM accumulation and utilization measures, a profile of the power consumption is generated. Results from the experiments on the protocol layers show the individual power consumption and utilization of the different states as well as the accumulated power consumption of different protocol layers when compared. Ultimately, the results from the reward model solution can be used in the energy-efficient design of wireless communication systems. Lastly, in order to get an idea of how wireless communication device companies handle issues of power consumption, we consulted with the wireless module engineers at Siemens Communication South Africa and present our findings on current practices in energy efficient protocol implementation

Online QoS/Revenue Management for Third Generation Mobile Communication Networks

This thesis shows how online management of both quality of service (QoS) and provider revenue can be performed in third generation (3G) mobile networks by adaptive control of system parameters to changing traffic conditions. As a main result, this approach is based on a novel call admission control and bandwidth degradation scheme for real-time traffic. The admission controller considers real-time calls with two priority levels: calls of high priority have a guaranteed bit-rate, whereas calls of low priority can be temporarily degraded to a lower bit-rate in order to reduce forced termination of calls due to a handover failure. A second contribution constitutes the development of a Markov model for the admission controller that incorporates important features of 3G mobile networks, such as code division multiple access (CDMA) intra- and inter-cell interference and soft handover. Online evaluation of the Markov model enables a periodical adjustment of the threshold for maximal call degradation according to the currently measured traffic in the radio access network and a predefined goal for optimization. Using distinct optimization goals, this allows optimization of both QoS and provider revenue. Performance studies illustrate the effectiveness of the proposed approach and show that QoS and provider revenue can be increased significantly with a moderate degradation of low-priority calls. Compared with existing admission control policies, the overall utilization of cell capacity is significantly improved using the proposed degradation scheme, which can be considered as an 'on demand' reservation of cell capacity.To enable online QoS/revenue management of both real-time and non real-time services, accurate analytical traffic models for non real-time services are required. This thesis identifies the batch Markovian arrival process (BMAP) as the analytically tractable model of choice for the joint characterization of packet arrivals and packet lengths. As a key idea, the BMAP is customized such that different packet lengths are represented by batch sizes of arrivals. Thus, the BMAP enables the 'two-dimensional', i.e., joint, characterization of packet arrivals and packet lengths, and is able to capture correlations between the packet arrival process and the packet length process. A novel expectation maximization (EM) algorithm is developed, and it is shown how to utilize the randomization technique and a stable calculation of Poisson jump probabilities effectively for computing time-dependent conditional expectations of a continuous-time Markov chain required by the expectation step of the EM algorithm. This methodological work enables the EM algorithm to be both efficient and numerical robust and constitutes an important step towards effective, analytically/numerically tractable traffic models. Case studies of measured IP traffic with different degrees of traffic burstiness evidently demonstrate the advantages of the BMAP modeling approach over other widely used analytically tractable models and show that the joint characterization of packet arrivals and packet lengths is decisively for realistic traffic modeling at packet level

Mobile Ad-Hoc Networks

Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks

Transport Control Protocol Optimisation over Wireless Internet: a Cross-Layer Approach

This thesis presents an analytical model of a cross-layer communication system to enable improvement in the Transport Control Protocol (rCP) over mixed wired and wireless Internet. The focus is on the quantitative performance evaluation of the interactions between TCP and a hybrid Automatic Repeat reQuest protocol (HARQ) in the link layer (LL) with a finite buffer size. TCP evolution is described and a review of the different approaches to im/ r prove its performance is given. A survey of the most relevant TCP analytical proposals is also provided. The operation of a HARQ scheme comprising Forward Error CorreCtion (FEC) convolutional codes and a Selective Repeat (SR) ARQ protocol is analytically charac~erised by a Discrete Time Markov Chain (DTMC). Corruption losses occur in a radio channel and are modelled by a two-state DTMC whilst congestive losses are due to an LL finite buffer size. HARQ performance parameters are computed through the twO-moment approximation of an M/G/K/l analysis. The accuracy and correctness of the HARQ model is assessed as well as its adequacy for multimedia applications. All analytical results are validated through the well known network simulator, ns-2. It is shown that performance improvemen~ is achieved by dynamically selecting optimal HARQ parameters. It is also illustrated that HARQ can provide the required 'QoS as well as reliable transfer to multimedia applications only under certain power' and traffic conditions given that the impact of congestive losses is greater as the transmission quality improves. An existing mathematical representation of TCP Reno is extended in order to model TCP NewReno given its better performance over noisy channels, Continuous Time Markov Chains (CTMC) are used to this end. The NewReno model accuracy is also validated. .A cross-layer TCP-HARQ communication system is developed with these two analytical models. Top down e>.:plicit notification from TCP to HARQ takes place. The advertised TCP state variables are passed to the LL entity which is able to predict NewReno performance and select the optimal HARQ ,. values. These predictions are computed through fixed-point approximations. The joint TCP-HARQ analytical model is validated and its correctness is demonstrated as well as its capacity to provide a significant TCP performance improvement through the selection of HARQ optimal parameters. It is also demonstrated that smaller LL buffer sizes than the typical size provide similar TCP throughput whilst higher buffer capacities do not represent significant performanc'e improvement. LL buffer capacity reduction mainly depends on the quality of the transmission over the radio channel.EThOS - Electronic Theses Online ServiceGBUnited Kingdo