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Due to the increasing demand of traffic, mobile networks requires flexibility to modify the area of service at any time. The use of antenna tilt is a crucial element in the design of modern networks as this element can modify the area of served cell and affects several parameters like coverage capacity or energy. The tilt of antennas automatically with remote electrical tilt (RET) is particularly relevant due to new smart networks that require the control of the system remotely. However, RET has limitations as a result of the imperfections of the design of real antennas. This is due to the fact that the whole pattern can vary for each tilt iteration. This study proposes a system level simulation of two real antennas with similar characteristics like gain, beam width and frequency, in order to evaluate the results in terms of coverage and capacity for different degrees of tilt. The results show that remote electrical tilt improves both coverage and capacity up to 32% and 50% respectively. However the performance of both the antennas differ. For example, different sizes of networks are simulated and different degree of optimum tilt is obtained for each antenna, which is explained by the comparison of the radiation patterns. The difference between the angles of the optimum tilt for different sizes of the network also affects to the energy efficiency metrics that have been simulated. One type of antenna shows better effects when tilt is applied and the energy efficiency improves up to 13% with respect to the other antenna. Through the comparison of the radiation pattern, it is possible to conclude which elements are the most important for different areas of coverage of the network. The high gain and the roll off of the main beam play an important role for cell edge coverage. In addition, sharp roll-off inclination and higher gain are the elements which have the strongest influence on tilt. Finally, the effect of side lobe levels on other parameters of the network is shown in this study. Lower side lobe level affects the areas closer to the base station and upper side lobe level interfere the adjacent cell. This study shows how these levels change for each tilt iteration and, thus, explains the difference in the performance of both antennas.

This thesis focuses on the issues in transport protocol performance in wireless ad-hoc networks.From the review of existing research we identify the following three main factors contributing to the poor performance of transport protocols such as TCP. These are: the inability of transport protocol to detect/identify and respond to network events in wireless ad-hoc networks; the inability of TCP window-based flow control mechanism to avoid overloading the wireless channel; and the frequent route failures due to mobility, causing interruptions in transmission. / We focus on 2 mechanisms to improve the performance of transport protocols. Recognising the many benefits of multipath routing in wireless ad-hoc networks, we propose a multipath transport design framework, incorporating a number of transport protocol components that are suitable for wireless ad-hoc networks, with different degrees of cross-interference. We first consider the use of independent multiple paths, and show that the throughput performance of multiple paths is no more than 55-60%, due to a spatial reuse of the wireless channel at the source. We then show that the overall improvement resulting from the use of independent multiple paths is further limited by the scarcity of independent multiple paths between a given pair of source and destination nodes. We conclude that independent multipaths are worth consideration only in sufficiently dense and large networks. Then we propose metrics to characterise node-disjoint multipaths with different degrees of cross-interference, and investigate correlation of these metrics with the throughput performance of multipath. / Our simulation results show that the throughput performance of multiple paths is determined by both the number of cross-interference links between paths and the local density of cross path links. These observations can be used in selecting multiple paths for good throughput performance of multipath transport. / The second mechanism we focus on is the rate-based flow control over a multi-hop path. Recognising the lack of suitable bandwidth estimation techniques for multi-hop wireless networks, we propose a new bandwidth estimation technique (termed Saturation Throughput Estimate or STE) suitable for wireless ad-hoc networks. It is based on a nearly linear relationship between channel occupancy (a local measurement of the channel activity level) and throughput available to a node. It also accounts for the traffic forwarded by the neighbouring nodes on behalf of the node in question. We show that our estimation technique is capable of providing good estimates of bandwidth available to a node in small to medium size ad-hoc networks, over a broad range of traffic loads. We also develop and verify an analytical model of IEEE 802.11 suitable for studying 802.11 performance under limited load conditions. Our analytical studies confirm the key assumption of a nearly linear relationship between channel occupancy and throughput underlying the proposed STE bandwidth estimation technique, and provide useful insights into selecting a suitable operating point to achieve high channel utilisation and avoid congestion in the wireless channel. Subsequently, the proposed STE bandwidth estimation technique is fine-tuned to meet the requirements of rate-based flow control over a multi-hop path. Finally, we present and develop a design of a feedback rate-based flow control framework to evaluate the merit of our STE technique and other rate estimation techniques proposed in the subject literature. We show that ATP (Ad-Hoc Transport Protocol) rate estimation technique tends to saturate the network, resulting in long queuing delay. In contrast, the rate-based flow control scheme using our STE rate estimate as rate feedback is effective in regulating and maintaining traffic just below the congestion point, thus achieving high network utilisation in static and low mobility networks. / Thesis (PhDTelecommunications)--University of South Australia, 2006.

Multicast is an efficient way of disseminating information to a group of receivers on the Internet and other computer networks. To combat losses, transmission repetition is common in both best effort and reliable multicast protocols. In the latter, repetition is performed by an automatic repeat request (ARQ) scheme. In either case, forward error correction (FEC) coding can be used to replace repetition, which may result in remarkably improved performance in terms of user throughput. This improvement is especially significant for wireless networks where bandwidth is valuable and loss rate is high. The main goal of this research is to find efficient FEC and hybrid FEC/ARQ (known as HARQ) schemes for a class of message-based multicast protocols, which are compatible with the protocols operating in a wireless environment. / In this thesis, firstly, general multicast and error control techniques are reviewed and examined. A message-based multicast protocol P_Mul is used as a base for performance studies and protocol modifications. P_Mul is designed to handle receivers operating in responsive and silent (no feedback) operational modes. An OPNET model of the standard P_Mul error recovery scheme, originally based on ARQ, is developed. Various schemes such as an ideal (rateless) FEC, Reed-Solomon and LDPC codes are incorporated in the model and their behaviours simulated, discussed and compared with the standard P_Mul performance. / Novel message-based mathematical models are derived that allow accurate estimation of P_Mul performance in the case of finite-length message multicast. The mathematical models take into account certain scenarios and schemes, e.g. when loss is random and all receivers non-responsive or responsive with error recovery based on ARQ or its hybrid with ideal FEC. / Furthermore, the simulation model is expanded so that P_Mul can efficiently manage complex traffic with different priorities; seamlessly serve multicast groups whose members may change operational modes frequently; and adapt to the channel conditions without saturating the network with an excessive number of packets. The performance of the P_Mul model with various enhancements is progressively simulated, compared and argued, pointing to the influence of the various protocol and network parameters. / Finally, a novel method for improving the performance of short messages at high error rates is proposed and the preliminary performance analysed. The method applies erasure decoding on smaller payload portions, called packet segments, to better match with the high error rates, yet without shortening the packet to the lower layer. With some increase in processing complexity and error detection overhead, the chance of short message reception improves considerably / Thesis (PhDTelecommunications)--University of South Australia, 2005.

Thesis (MEng)--University of South Australia, 1996

Thesis (PhD)--University of South Australia, 1999

Bibliography: p. 343-355. / xxiv, 355 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Based on a comprehensive review of past techniques and power combining structures, a class of spatial power combiners compatible with the requirements of millimetre wave operation are identified. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1999?

Bibliography : p. 275-283. / xii, 283 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / 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. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1999

Thesis (M.S.)--George Mason University, 2007. / Title from PDF t.p. (viewed Jan. 17, 2008). Thesis director: Brian L. Mark Submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. Vita: p. 60. Includes bibliographical references (p. 58-59). Also available in print.