Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Bibliography : p. 275-283. Investigates the characteristics of the handover algorithm; how the handover request response time affects the call quality or call drop; and, studies a linear highway model to examine handover performance at the system level in which heavy new call and handover traffic occurs.

Satellites will play an indispensable role in the deployment of commercial networks to meet an increasing demand for supporting multimedia services at high data rates. Next generation satellite systems, operating at high frequency bands offer large bandwidth and are able to provide broadband services. To interface satellite links with existing terrestrial networks for providing communication access to a variety of users directly, several performance issues need to be addressed. Current thesis presents a technically viable satellite-integrated network model that is efficient in carrying broadband services to users over a wide scattered area. Accurate prediction of attenuation level is necessary for a reliable network model to operate with required service availability. Long term rainfall data has been analysed to characterise attenuation level at a selected region such as Dhaka. It is shown that rainfall is highly seasonal and attenuation level is quite high during monsoon. However, the seasonal behaviour of rainfall can be exploited to improve the link availability. Radar and rain gauge measurements at Sparsholt are also used to find rain cell size distribution, which is an important factor in site diversity implementation to combat severe rain fade. It is found that convective rain cell has extension in the region of 10 km. The network model is designed with dimensioning the effective bandwidth to support a number of users over the satellite link by taking into account the multimedia traffic characteristics. Concatenated coding, a robust coding scheme is implemented to improve the link quality at a level required to deliver broadband services. The ITU-T performance objectives of 7.5×10 for CLR and 1.4×10 for CER over satellite links are met at a required Eb/No of 2.95 dB and 2.88 dB respectively. Different enhancement mechanisms for optimum TCP performance are implemented to combat the large propagation delay associated with a satellite link. It is revealed through the simulation that TCP performance over a satellite link is as efficient as terrestrial links with these enhancement mechanisms Finally, the overall performance of the designed network is evaluated through link budget analysis and simulation. An innovative downlink power control strategy has been implemented to maintain the link during the rainiest months. The interference level due to high power satellite transmission in the designed system is also calculated to protect other existing communication links sharing the same frequency bands. A feasible broadband network designed with characterising propagation as well as networking issues will efficiently deliver broadband communication services to a large population promptly and in a cost-effective manner. Such a network solution will be in the realm of current R & D towards broadband satellite networks.

Mobile communication systems have continued to evolve beyond the currently deployed Third Generation (3G) systems with the main goal of providing higher capacity. Systems beyond 3G are expected to cater for a wide variety of services such as speech, data, image transmission, video, as well as multimedia services consisting of a combination of these. With the air interface being the bottleneck in mobile networks, recent enhancing technologies such as the High Speed Downlink Packet Access (HSDPA), incorporate major changes to the radio access segment of 3G Universal Mobile Telecommunications System (UMTS). HSDPA introduces new features such as fast link adaptation mechanisms, fast packet scheduling, and physical layer retransmissions in the base stations, necessitating buffering of data at the air interface which presents a bottleneck to end-to-end communication. Hence, in order to provide end-to-end Quality of Service (QoS) guarantees to multimedia services in wireless networks such as HSDPA, efficient buffer management schemes are required at the air interface. The main objective of this thesis is to propose and evaluate solutions that will address the QoS optimization of multimedia traffic at the radio link interface of HSDPA systems. In the thesis, a novel queuing system known as the Time-Space Priority (TSP) scheme is proposed for multimedia traffic QoS control. TSP provides customized preferential treatment to the constituent flows in the multimedia traffic to suit their diverse QoS requirements. With TSP queuing, the real-time component of the multimedia traffic, being delay sensitive and loss tolerant, is given transmission priority; while the non-real-time component, being loss sensitive and delay tolerant, enjoys space priority. Hence, based on the TSP queuing paradigm, new buffer managementalgorithms are designed for joint QoS control of the diverse components in a multimedia session of the same HSDPA user. In the thesis, a TSP based buffer management algorithm known as the Enhanced Time Space Priority (E-TSP) is proposed for HSDPA. E-TSP incorporates flow control mechanisms to mitigate congestion in the air interface buffer of a user with multimedia session comprising real-time and non-real-time flows. Thus, E-TSP is designed to provide efficient network and radio resource utilization to improve end-to-end multimedia traffic performance. In order to allow real-time optimization of the QoS control between the real-time and non-real-time flows of the HSDPA multimedia session, another TSP based buffer management algorithm known as the Dynamic Time Space Priority (D-TSP) is proposed. D-TSP incorporates dynamic priority switching between the real-time and non-real-time flows. D-TSP is designed to allow optimum QoS trade-off between the flows whilst still guaranteeing the stringent real-time component’s QoS requirements. The thesis presents results of extensive performance studies undertaken via analytical modelling and dynamic network-level HSDPA simulations demonstrating the effectiveness of the proposed TSP queuing system and the TSP based buffer management schemes.

M.Ing. / In general, error control coding is absolutely necessary for reliable data transmission. However, the performance of error control codes depends on the statistical structure of the error process on the communication channel. The mobile radio channel, which has been investigated, is subject to path loss effects, a variety of noise effects and interferences and various types of scattering and multipath fading. All these effects contribute to the error processes on the radio channel when transmitting data over it. Any meaningful analytical description of the error process in terms of the characteristics of the individual physical causes of errors are difficult to undertake. Consequently, alternative ways of modelling real communication. channels are being presented. It is more convenient to include the above mentioned perturbations in a discrete inner communication channel consisting of the modem, radio equipment and the mobile radio medium, which are then modelled with a discrete partitioned Markov chain. The partitioned Markov chain inner channel models also give a more accurate description of a real communication channel than does a binary symmetric channel model. However, in order to model a communication channel, the complete statistical structure of the bit error sequence on the channel must be known. In the first instance the memory effective recording of the error sequence of discrete inner communications channels has been considered. This has led to an implementation, where a portable recording system has been developed for mobile .radio channels or any other communication channel with a data rate of up to 4800 bits per second. Programs have been developed to determine all the important statistical distributions which are necessary to be able to model the channel. A channel modelling system has been developed, which fits a channel model to the real channel and then determines the important statistical distributions of the channel model to enable comparison with the real channel. The channel modelling system is versatile and can be used with any future communication system. A number of different mobile VHF and UHF inner channels have been investigated experimentally and the associated discrete models have been developed. In addition to the above mentioned discrete inner communications channels, some "outer channels" have been developed. The "outer channels" comprise of an inner channel and the block error detection, correction and misdetection events, associated with the code words of an error control system. It has been shown that the underlying statistical structure of these events on a discrete renewal inner channel can be represented with outer channel models, i.e. simple partitioned Markov processes, similar to the inner channel models. Analytical procedures to determine the parameters of these outer channel models are being presented. The inner channel parameters and the characteristics of the error control event have been used to develop the outer channel models, i.e. the simple partitioned Markov chains, representing the underlying statistical structure of the block error detection, decoding error in error correction and misdetection (undetected error) events of a block code on the discrete renewal inner channel. Finally it is shown that these outer channel models can be used to evaluate error control codes and systems. Forward-error control and automatic-repeat-request systems have been evaluated and compared with each other.

The use of satellites for mobile communication applications has become a global issue. The use of handheld, vehicle mounted and transportable terminals is a key feature of Satellite Personal Communication Networks (S-PCNs). Due to the higher eirp requirements on the Earths surface and also because of their inherent delay, geostationary (GEO) satellites are not considered suitable for such applications. Instead, constellations of satellites at lower altitudes have been proposed for use in what are termed 2nd generation mobile satellite communication systems. Low intensity regions in the Earths surrounding trapped radiation bands, have resulted in two altitude bands of specific interest, resulting in two constellation types - LEO (Low Earth Orbit) constellations at around 1,000 km and MEO (Medium Earth Orbit) constellations at around 10,000 km. A satellite constellation consists of a number of satellites orbiting at the same altitude and inclination and phased in a specific way. The work reported in this thesis proposes a network control architecture for LEO or MEO based S-PCN systems. Air-interface signalling aspects are then considered for mobility management and call setup signalling. LEO and MEO constellation design aspects and properties are initially considered. Important implications on the control network are drawn based on constellation coverage and connectivity properties. Other system constraints such as terrestrial network interworking considerations as well as user, network operator and regulator requirements are also considered. Finally network and more specifically satellite control signalling is examined before a S-PCN architecture is proposed. The reference architecture results in constellation control being distributed globally with individual satellite control, at any one time, being located at a specific earth station. The use of two earth station types allows network administration to be separated from traffic channel carrying aspects. In order to reduce system setup cost and delay, the reuse of network related standards from the GSM terrestrial mobile communication system is envisaged. An equivalence is made between the S-PCN architecture and the GSMs terrestrial architecture. Network implementation aspects are considered for a 14 satellite MEO constellation. Network implications resulting from the use of LEO and MEO constellations are considered. After an examination of S-PCN traffic demand on a MEO constellation, mobility management signalling is considered. A new approach is proposed based on the use of a positioning system. The performance of this approach is examined from a system signalling viewpoint for both LEO and MEO constellations and a method to minimise the required amount of signalling is described. The air interface signalling procedure for location update, based on a modified GSM network layer protocol, is simulated from a delay point of view for both LEO and MEO constellations. User-originated, user-terminated and user-to-user call setup signalling were also simulated and their delay performance examined. The importance of random access channel delay and of user cooperation with the link were highlighted as aspects which have a significant influence on the average signalling delay. Finally, the effect of common and dedicated control channel system signalling on satellite power consumption, based on busy hour call setup and mobility management signalling estimates, was examined for a MEO constellation. From this, conclusions can be made on the signalling power efficiency of S-PCN systems.

M.Ing. (Electrical and Electronic Engineering) / Please refer to full text to view abstract

M.B.A. / The first mobile cellular telephone was established In St. louis (Missouri. USA) in 1946. In a few years time Europe followed with a similar service. These systems were based on technology developed during the World War 2 (Vodacom Corporate Profile:1999/2000:1). Between 1950 and 1960, cellular radio evolved to become automatic and Its costs dropped due to the Introduction of transistor technology. During the 1970's large scale integration and development of micro-processors enabled more complex systems development (Vodacom Corporate Profile :1999/2000:1 ). In 1988 the European Telecommunications Standard Institute (ETSI) was created. This Institute enabled network operators and telecommunications equipment manufacturers to become Involved In the specification of Global System for Mobile Communications (GSM) (Vodacom Corporate Profile :199~/2000:1 ). The GSM standard of communication was launched In Europe in 1992. This standard Is widelyused In European and African countries...

The frequency spectrum allocated to cellular mobile telephone systems is very limited. Efficient channel assignment schemes can significantly increase the utilization of the available frequency channels. Virtually Fixed Channel Assignment (VFCA) is a dynamic channel assignment method. The idea behind it is simple: each cell is allocated a set of nominal channels. A call request generated in a cell is assigned a nominal channel if one is available. Otherwise, a channel from an adjacent cell is borrowed to serve this call as long as frequency interference constraints are satisfied. VFCA is a promising method because (i) it is efficient in channel assignment, and (ii) it is relatively easy to implement compared to other dynamic channel assignment methods. VFCA has been analyzed based primarily on simulation studies in the past twenty years. In this thesis, we focus our study on development of new channel borrowing strategies and analytical models for VFCA. The contribution of this work is summarized as follows. (1) Development of an queuing model for performance analysis of VFCA. This model may also be used to conduct sensitivity analysis on some system parameters when VFCA is used. (2) Proposed a new channel reservation scheme for handoffs. (In a cellular system, when a call using a channel crosses a cell boundary, it needs to be handed off to a new channel in the new cell. This is called a handoff.) An optimization model for this channel reservation scheme is developed. (3) Applied the fluid-flow approach to modeling an integrated mobile cellular system that uses VFCA to estimate the distribution of data queue length in a cell of the system. These results are useful in the design, performance analysis and optimization of VFCA schemes.

Thesis (Ph. D.)--Faculty of Science, University of Oulo, Finland, 2006. / Includes bibliographical references (p. 218-236).