Performance of the transmission control protocol (TCP) over wireless with quality of service.

Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.The Transmission Control Protocol (TCP) is the most widely used transport protocol in the Internet. TCP is a reliable transport protocol that is tuned to perform well in wired networks where packet losses are mainly due to congestion. Wireless channels are characterized by losses due to transmission errors and handoffs. TCP interprets these losses as congestion and invokes congestion control mechanisms resulting in degradation of performance. TCP is usually layered over the Internet protocol (lP) at the network layer. JP is not reliable and does not provide for any Quality of Service (QoS). The Internet Engineering Task Force (IETF) has provided two techniques for providing QoS in the Internet. These include Integrated Services (lntServ) and Differentiated Services (DiffServ). IntServ provides flow based quality of service and thus it is not scalable on connections with large flows. DiffServ has grown in popularity since it is scalable. A packet in a DiffServ domain is classified into a class of service according to its contract profile and treated differently by its class. To provide end-to-end QoS there is a strong interaction between the transport protocol and the network protocol. In this dissertation we consider the performance of the TCP over a wireless channel. We study whether the current TCP protocols can deliver the desired quality of service faced with the challenges they have on wireless channel. The dissertation discusses the methods of providing for QoS in the Internet. We derive an analytical model for TCP protocol. It is extended to cater for the wireless channel and then further differentiated services. The model is shown to be accurate when compared to simulation. We then conclude by deducing to what degree you can provide the desired QoS with TCP on a wireless channel

Predictive relay-selection cooperative diversity in land mobile satellite systems

Cooperative diversity protocols promise a new dimension of diversity that provides better communication by engaging nearby relays in forming a ‘virtual’ array of antennas for combined signal transmission. The current incremental cooperative diversity algorithms incrementally select best relay(s) to cooperate based on the channel quality reported by the relays. However, the algorithms do not take into consideration the fact that the chosen best relay(s) at estimation may not always be best at the time of communication. This is due to the time delay between the relay selection and its transmission of signal (problem of outdated Channel Quality Information). To solve this problem, the concept of channel prediction is introduced and employed whereby each relay determines a predicted value of its Channel Quality Information (CQI) based on its past measurements. The paper therefore develops a novel predictive relay-selection (PRS) cooperative diversity model which seeks to improve Land Mobile Satellite (LMS) communication through prediction protocols. In the model, the chosen best relay is the one with the best predicted CQI value instead of the traditional outdated one. Performance analysis of outage probability and average bit error probability for the newly developed PRS cooperation shows that the PRS cooperation is better than direct and outdated CQI relay communication.http://onlinelibrary.wiley.com/doi/10.1002/sat.11182017-03-31hb2016Electrical, Electronic and Computer Engineerin

Traffic modelling and analysis of next generation networks.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2008.Wireless communication systems have demonstrated tremendous growth over the last decade, and this growth continues unabated worldwide. The networks have evolved from analogue based first generation systems to third generation systems and further. We are envisaging a Next Generation Network (NGN) that should deliver anything anywhere anytime, with full quality of service (QoS) guarantees. Delivering anything anywhere anytime is a challenge that is a focus for many researchers. Careful teletraffic design is required for this ambitious project to be realized. This research goes through the protocol choices, design factors, performance measures and the teletraffic analysis, necessary to make the project feasible. The first significant contribution of this thesis is the development of a Call Admission Control (CAC) model as a means of achieving QoS in the NGN’s. The proposed CAC model uses an expanded set of admission control parameters. The existing CAC schemes focus on one major QoS parameter for CAC; the Code Division Multiple Access (CDMA) based models focus on the signal to interference ratio (SIR) while the Asynchronous Transfer Mode (ATM) based models focus on delay. A key element of NGN’s is inter-working of many protocols and hence the need for a diverse set of admission control parameters. The developed CAC algorithm uses an expanded set of admission control parameters (SIR, delay, etc). The admission parameters can be generalized as broadly as the design engineer might require for a particular traffic class without rendering the analysis intractable. The second significant contribution of this thesis is the presentation of a complete teletraffic analytical model for an NGN. The NGN network features the following issues; firstly, NGN call admission control algorithm, with expanded admission control parameters; secondly, multiple traffic types, with their diverse demands; thirdly, the NGN protocol issues such as CDMA’s soft capacity and finally, scheduling on both the wired and wireless links. A full teletraffic analysis with all analytical challenges is presented. The analysis shows that an NGN teletraffic model with more traffic parameters performs better than a model with less traffic parameters. The third contribution of the thesis is the extension of the model to traffic arrivals that are not purely Markovian. This work presents a complete teletraffic analytical model with Batch Markovian Arrival (BMAP) traffic statistics unlike the conventional Markovian types. The Markovian traffic models are deployed for analytical simplicity at the expense of realistic traffic types. With CAC, the BMAP processes become non-homogeneous. The analysis of homogeneous BMAP process is extended to non-homogeneous processes for the teletraffic model in this thesis. This is done while incorporating all the features of the NGN network. A feasible analytical model for an NGN must combine factors from all the areas of the protocol stack. Most models only consider the physical layer issues such as SIR or the network layer issues such as packet delay. They either address call level issues or packet level issues on the network. The fourth contribution has been to incorporate the issues of the transport layer into the admission control algorithm. A complete teletraffic analysis of our network with the effects of the transport layer protocol, the Transmission Control Protocol (TCP), is performed. This is done over a wireless channel. The wireless link and the protocol are mathematically modeled, there-after, the protocols effect on network performance is thoroughly presented