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No description available.

Within the last few years, improving the future W-CDMA systems by producing advanced detectors with interference suppression ability has attracted much attention. It is because in an interference-limited multiple access scheme such as W-CDMA, suppression of interference from other users in the detection of each individual user is a significant means to achieving higher capacity and enhanced quality of system performance. Although the use of highly orthogonal spreading codes and employing effective channel estimation and power control techniques mitigate the impact of interferers to a considerable extent, the growing need for further improvement in capacity and QoS in the presence of inter-cell interference and other unknown interferers forces the use of improved interference cancellation detectors at the receiver. This thesis first carries out a survey on significant existing multiuser detection and interference cancellation methods, and provides an evaluation of their performances through computer simulation of a W-CDMA uplink model which is based on UMTS standards. Then, the subject of interference cancellation is considered in this thesis from a rather different point of view. That is, narrow-band interference cancellation is examined for the purpose of studying the overlay of a W-CDMA signal by GSM carriers. In particular application of notch filters in a W-CDMA receiver is simulated and the performance of a spread spectrum system in the presence of overlaid GSM signals is evaluated in various circumstances. The impact of imperfect power control on the performance of various interference cancellation schemes is then studied through the above-mentioned UMTS-based simulation environment.

This thesis analyses the effects caused by the introduction of convolutional coding schemes over the power spectral density (PSD) of impulse radio (IR) based ultra wideband (UWB) communication systems. This is an important topic since UWB emissions are expected to comply with spectral masks imposed by various regulatory bodies. The spectral analysis of convolutionally codedlMarkov-driven IR-based UWB signals is carried out by assuming that the data stream at the encoder input is generated by a binary Markov source (BMS). The signal model covers a wide variety of IR-based modulation schemes such as pulse position modulation (PPM), binary phase shift keying (BPSK), pulse amplitude modulation (P AM), biorthogonal PPM (BOPPM), PAMlPPM and pulse shape modulation (PSM), combined with periodic or random time hopping (TH) and/or direct sequence (DS) multiplication. In addition the inclusion of attenuation and random jitter has been accounted for in the signal model. Novel closed form PSD expressions for convolutionally codedlMarkov-driven IR-based UWB signals are obtained by performing the spectral analysis of the signal model. The formulas provided clearly identifY. the relative contributions of different parameters allowing enhanced design of UWB systems. It is shown that convolutional encoders can be used to generate IR-based UWB signals with advantageous PSD characteristics. The analysis presented in this dissertation focuses on spectral line suppression/elimination. Novel maximum free distance (MFD) binary to M-ary convolutional encoders with spectral line suppression capabilities for M-ary PPM based UWB systems are presented. Moreover, novel MFD binary convolutional encoders which generate BPSKlQ-BOPPM IR-based UWB signals whose PSD is spectral line-free are introduced. Results show that for IRbased UWB systems these convolutional encoders offer improved PSD characteristics when compared to the standard non-coded case and the best convolutional encoders known. As well, it is demonstrated that by using these convolutional encoders improved PSD characteristics and improved bit error rates (BER) can be achieved simultaneously.

The thesis investigates techniques for the adjustment of pre-detection filters employed by high speed serial digital modems operating over both time-invariant and timevarying channels. Various techniques for the adjustment of these pre-detection filters have been considered in previous investigations. The more recent ones enable such filters to be adjusted in a simple and accurate way using an estimate of the sampled impulse response of the linear baseband channel, together with a prior knowledge of the roots that lie outside the unit circle in the z-plane. A root finding algorithm is an integral part of these techniques. Algorithms for the location of the required roots are presented here, and compared with previous ones in an attempt to optimise the operational speed and accuracy of the adjustment of these filters. Alternative algorithm have also been considered, that operate directly on the sampled impulse response of the linear baseband channel, without the need for locating any roots, thus enabling a faster and more accurate adjustment of the pre-detection filter. The relative performances of all the algorithms are then evaluated over different telephone channels, at transmission rates of 9600 and 19200 bits/sec. The algorithms are also tested over fading channels (such as HF radio links), so as to select the one which offers the best compromise between performance and complexity for hardware implementation. Finally, various aspects of the hardware implementation of the selected algorithm have been considered.

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As computing devices become increasingly portable, it is becoming necessary to support Mobility as a core network functionality. The availability of devices such as smartphones, tablets, laptops as well as wireless network infrastructure is opening up the possibility of using Network Mobility to cater for multiple mobile nodes simultaneously. Network mobility may be useful in a number of mobile scenarios, where a large number of mobile nodes are moving in unison. A number of operational benefits stand to be gained by aggregating these nodes into a single mobile unit. Unfortunately, the current state for network mobility support, especially in terms of network layer protocols, is limited. This is in part due to the inherent complexity of mobile network scenarios, the high cost of testing mobile network protocols in operational environments and the difficulties in implementing such protocols. This thesis looks at how network mobility support may be better enabled by making experimentation with mobile networks more accessible. It shows this by first showing how analytical approaches can be useful in mobile network applications, as they abstract away from experimental details and allow for more straight forward protocol comparisons. It then goes on to look at the tools available to study mobile network protocols, where it introduces and extends an existing tool that uses virtual machines to allow for the study of mobile network protocols. Finally, it demonstrates a practical method in which mobile network support may be easily enabled in a practical setting.

Multi-hop wireless ad hoc networks consist of terminals that can communicate without the support of fixed infrastructure. Nodes may communicate directly from source to or can use other nodes in the network as relays to facilitate a path from source to destination. These networks can be rapidly deployed and are therefore well suited to emergency service applications where fixed infrastructure has become unavailable or in situations where a temporary network is required. This thesis studies the optimum design of a multi-hop ad hoc network.

In this research, novel meta material structures based on microstrip integrated circuit technology have been investigated for filter application in the next generation of microwave wireless communication systems. A number of novel microstrip planar filter structures have been developed that are able to meet the stringent requirements for high-performance systems and subsystems, such as sharp-cutoff frequency response, low passband insertion-loss and high return-Joss, high out-af-band rejection, compact size, low cost and ease of integration. The filters are approximately 70% smaller than their conventional counterparts. Analysis and mathematical modeling of these microstrip devices involved the use of transmission-line theory and EM simulation tools which were based on the method of moments and finite element analyses. Measured results were used to validate the predicted behavior and performance of these devices. In fact there was good agreement with the theory and simulation modeling. A Composite right/left-handed (CRLH) metamaterial unit-cell whose ground-plane is defected with a rectangular dielectric slot was used to develop a single and multi-pole bandpass filters. The unit-cell comprises of serial inter-digital capacitors whose junction is connected to a short-circuited inductive stub. By defecting the ground-plane of the unit-cell 's structure with a dielectric slot, which is located immediately below the unit-cell, enables substantial tuning of the filter's centre frequency in the order of 26.5%. This was achieved with minimal effect on the unitcell's insertion- and return-loss performance as well as its selectivity. The filters were fabricated on conventional dielectric substrate and their performance measured to verify the design methodology. The proposed technique eases the trade-off constraints that plague conventional filter designs and makes possible the realization of challenging filter specifications constituted from CRLH unit-cells using distributed transmission-lines. A novel multilayer technique is presented that enables (i) the control of the filter's bandwidth, (ii) significantly improves its passband selectivity, and (iii) enhances its out-of-band rejection without affecting the filter's overall dimensions. The technique involves implementation of identical filter structures on both sides of the dielectric substrate that are interconnected through vias. The filter circuit is laid on top of another identical substrate with a ground-plane. This structure results in a device that exhibits a sharp selectivity that is substantially smaller than traditional filter constructions. The sharpness of the filter is due to the upper and lower transmission zeros present on either side of the filter's passband being shifted closer together which causes reduction in its bandwidth. This effect is opposite to that encountered in conventional multilayer filter structures. It is shown the filter's bandwidth can be controlled while maintaining a good passband insertion- and return-loss performance, i.e. <1.2 dB and >10 dB, respectively. Furthermore, the proposed filter is relatively easy to fabricate using conventional technology. A diplexer was developed based on the proposed multilayer technique and was shown to yield a high out-af-band rejection and high isolation between the two very closely spaced channels. Normally isolators are used to provide isolation between channels in order to prevent inter-channel interference. The technique is relatively simple to realize and cost effective to manufacture. Design methodology and experimental results are presented that show good correlation between the measured and simulation results. This diplexer should find application in multi band wireless communication systems. A triplexer deSign is also presented whose multiband performance was created using CRLH unit-cell structures. The three passband channels of the triplexer have a common input splitter and transmission-line matching network is used to ensure high isolation between the channels is maintained in order to prevent undesired interaction between the channels which would otherwise adversely affect the triplexer's passband response. This was achieved using stepped impedance lines (SIL). No isolators were necessary using the proposed technique. It is also shown that by curving the SIL can provide enhancement in the triplexer's loss performance, bandwidth, and suppression of high order spurii. The design analysis and performance of the triplexer was verified via fabrication and measurement. A novel compact microstrip wideband bandpass filter was presented for wideband application that possesses good insertion- and return-loss, sharp frequency selectivity and high out-of-band rejection. The proposed filter comprises of two inter-digital capacitors with four inductive stubs. It employs a T-shaped open stub that is inserted between the symmetrical unitcell structures.

The increasing demand for terrestrial and satellite delivered digital multimedia services has precipitated the problem of spectrum scarcity in recent years. This has resulted in deployment of spectral efficient technologies such as MIMO for terrestrial systems. However, MIMO cannot be easily deployed for the satellite channel using conventional spatial multiplexing as the channel conditions here are very different from the terrestrial case, and it is often dominated by line of sight fading. Orthogonal circular polarization, which has long been used for increasing both frequency reuse and the power spectral density available to earth-bound satellite terminals, has recently been recommended for directly increasing the throughput available to such devices. Following that theme, this thesis proposes a novel dual circular polarisation multiplexing (DCPM) technique, which is aimed at the burgeoning area of throughput-hungry digital video broadcasting via satellite to handheld devices (DVB-SH) and digital video broadcast to the next generation of hand held (DVB-NGH) systems. In determining the working limits of DCPM, a series of measurement campaigns have been performed, from which extensive dual circular polarised land mobile satellite (LMS) channel data has been derived. Using the newly available channel data and with the aid of statistical channel modelling tools found in literature, a new dual circular polarised LMS MIMO channel model has been developed. This model, in contrast with previously available LMS MIMO channel models, is simpler to implement since it uses a distinct state-based empirical-stochastic approach. The model has been found to be robust and it easily lends itself to rapid implementation for system level MIMO and DCPM analysis. Finally, by way of bit error rate (BER) analysis in different channel fading conditions, it has been determined when best to implement polarisation multiplexing or conventional . MIMO techniques for DVB-type land mobile receivers. It is recommended that DCPM be used when the channel in predominantly Ricean, with eo-polar channel Rice factors and sub-channel cross correlation values greater than 1dB and 0.40 respectively. The recommendations provided by this research are valuable contributions, which may help shape the evolving DVB-NGH standardisation process.