The main motivation of this thesis is to design low-complexity high-efficiency pulse-based ultrawide bandwidth (UWB) systems with reasonable bit-error-rate (BER) performance. The thesis starts with proposing a new pulse-based UWB system, namely the hybrid direct-sequence time-hopping (DS-TH) UWB system. This novel pulse-based UWB system is capable of inheriting the advantages of both the pure direct-sequence (DS)-UWB and pure time-hopping (TH)-UWB systems, while avoiding their disadvantages. Furthermore, this hybrid DS-TH UWB scheme can be easily converted to the pure DS-UWB or pure TH-UWB scheme. The BER performance of the hybrid DS-TH UWB systems employing either correlation or minimum mean-square error (MMSE) detection is investigated. From our studies it can be found that both the correlation and MMSE detectors have the capability to make use of the multipath diversity. The correlation detector does not have the capability to remove multiuser interference (MUI) and inter-symbol interference (ISI), while the MMSE detector is capable of mitigating efficiently both the ISI and MUI. While for single-user scenario the correlation detector is near-optimum and has low-complexity, it is shown that for multi-user scenarios theMMSE detector must be employed in order to achieve a reasonable BER performance. However, in this case the complexity of the hybrid DS-TH UWB system is found to be extreme. Furthermore, in order to implement MMSE detection, the signature waveforms, delays and complete channel knowledge of all the active users are required to be known by the receiver, which make the MMSE detection impractical. In practical channels obtaining the channel knowledge is highly challenging, since the received UWB signals usually consist of a huge number of resolvable multipaths and the energy conveyed by each resolvable multipath is usually very low. In order to mitigate the above mentioned problems of the MMSE detection, then, in this thesis a range of training-based adaptive detectors are investigated in the context of the hybrid DS-TH UWB systems. In detail, in this thesis a brief introduction to the literature of adaptive detection is first provided, followed by the philosophies of least mean-square (LMS), normalised least-mean squares (NLMS) and recursive least square (RLS) algorithms. In our study decision directed (DD) approaches are also introduced to the adaptive detectors to improve the BER performance and spectral-efficiency of the hybrid DS-TH UWB systems. Our studies show that the complexity of the adaptive LMS and adaptive NLMS detectors may be even lower than that of the conventional correlation detector. For the RLS adaptive detector, our studies show that, if it is initialised properly, it is capable of attaining a faster convergence rate than the LMS and NLMS adaptive detectors. In this case, the RLS adaptive detector requires less number of training bits, and hence provides higher spectral-efficiency than the LMS and NLMS adaptive detectors for the hybrid DS-TH UWB systems. Furthermore, the RLS adaptive detector is more robust and has more degrees of freedom than the LMS and NLMS adaptive detectors. However, the complexity of the RLS adaptive detector is still too high to be implemented in practical UWB systems. In order to further reduce the complexity of the RLS adaptive detector, rank-reduction techniques are introduced. With the aid of reduced-rank techniques, the filter size can be efficiently reduced, which in turn reduces the number of parameters required to be estimated. Consequently, the convergence speed, tracking ability and robustness of the RLS adaptive detector can be improved. In this thesis, three classes of reduced-rank techniques are investigated associated with the RLS adaptive detector, which are derived based on the principles of principal components analysis (PCA), crossspectral metric (CSM) and Taylor polynomial approximation (TPA), respectively. Our study and simulation results show that, given a sufficient rank of the detection subspace on which the RLS adaptive detector is operated, the reduced-rank RLS adaptive detector is capable of achieving a similar BER performance as the corresponding full-rank RLS adaptive detector, while with a detection complexity that is significantly lower than that of the fullrank RLS adaptive detector. Furthermore, our studies shown that the TPA-based reduced-rank RLS adaptive detector constitutes one of the highly efficient detection schemes for the pulse-based UWB systems. The TPA-based reduced-rank RLS adaptive detector is usually capable of attaining the full-rank BER performance with a very low rank, which is typically in the range of 5 − 8, regardless of the system size in terms of the spreading factor, number of resolvable multipaths and the number of users supported by the UWB systems. Finally, in this thesis we summarise our discoveries and provide discussion on the possible future research issues.

In this thesis, we have explored self-concatenated coding schemes that are designed for transmission over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels. We designed both the symbol-based Self-Concatenated Codes considered using Trellis Coded Modulation (SECTCM) and bit-based Self- Concatenated Convolutional Codes (SECCC) using a Recursive Systematic Convolutional (RSC) encoder as constituent codes, respectively. The design of these codes was carried out with the aid of Extrinsic Information Transfer (EXIT) charts. The EXIT chart based design has been found an efficient tool in finding the decoding convergence threshold of the constituent codes. Additionally, in order to recover the information loss imposed by employing binary rather than non-binary schemes, a soft decision demapper was introduced in order to exchange extrinsic information with the SECCC decoder. To analyse this information exchange 3D-EXIT chart analysis was invoked for visualizing the extrinsic information exchange between the proposed Iteratively Decoding aided SECCC and soft-decision demapper (SECCC-ID). Some of the proposed SECTCM, SECCC and SECCC-ID schemes perform within about 1 dB from the AWGN and Rayleigh fading channels’ capacity. A union bound analysis of SECCC codes was carried out to find the corresponding Bit Error Ratio (BER) floors. The union bound of SECCCs was derived for communications over both AWGN and uncorrelated Rayleigh fading channels, based on a novel interleaver concept. Application of SECCCs in both UltraWideBand (UWB) and state-of-the-art video-telephone schemes demonstrated its practical benefits. In order to further exploit the benefits of the low complexity design offered by SECCCs we explored their application in a distributed coding scheme designed for cooperative communications, where iterative detection is employed by exchanging extrinsic information between the decoders of SECCC and RSC at the destination. In the first transmission period of cooperation, the relay receives the potentially erroneous data and attempts to recover the information. The recovered information is then re-encoded at the relay using an RSC encoder. In the second transmission period this information is then retransmitted to the destination. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated encoder. At the destination a Distributed Binary Self-Concatenated Coding scheme using Iterative Decoding (DSECCC-ID) was employed, where the two decoders (SECCC and RSC) exchange their extrinsic information. It was shown that the DSECCC-ID is a low-complexity scheme, yet capable of approaching the Discrete-input Continuous-output Memoryless Channels’s (DCMC) capacity. Finally, we considered coding schemes designed for two nodes communicating with each other with the aid of a relay node, where the relay receives information from the two nodes in the first transmission period. At the relay node we combine a powerful Superposition Coding (SPC) scheme with SECCC. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second transmission period after re-encoding it, again, using a SECCC encoder. At the destination, the amalgamated block of Successive Interference Cancellation (SIC) scheme combined with SECCC then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput.

Detailed wireless video structures employing novel channel coding schemes for enhancing the achievable performance are designed. Although there is a plethora of papers on both robust video transmission, iterative detection and video telephony, there is a paucity of up-to-date research studies on the unified treatment of the topic of near capacity multimedia communication systems using iterative detection aided joint source-channel decoding employing sophisticated transmission techniques. Therefore in this thesis we focus our attention not only on the source and channel coding but also on their iterative decoding and transmission. Initially, we investigated the H.264 codec’s error sensitivity. The perceptually more important bits were provided with more strong protection relative to less important bits using Unequal Error Protection (UEP) by applying different-rate Recursive Systematic Convolutional (RSC) codes. We then further improved the attainable performance of a Data-Partitioned (DP) H.264 coded video transmission system using UEP based IrRegular Convolutional Codes (IRCC). An iterative detection aided combination of IRCC and a rate-1 precoder was used to improve the overall BER performance and to enhance the objective video quality expressed in terms of the Peak Signal-to-Noise Ratio (PSNR)1. More specifically, we exploited the innate UEP capability and high design flexibility of IRCCs, which are constituted by different-rate subcodes capable of maintaining an excellent iterative decoding performance. In contrast to regular convolutional codes, which encode the entire segment of the source signal using the same code, the IRCCs introduced encode the source signal by splitting it into segments having specifically designed lengths, each of which is encoded by a code having an appropriately designed code-rate. A novel Extrinsic Information Transfer (EXIT) chart matching procedure was used for the design of our specific IRCC which allowed us to design near-capacity schemes. Additionally, we developed a novel Unequal Source-Symbol Probability Aided (USSPA) design, which is capable of further enhancing the subjective video quality by exploiting the residual redundancy that remains in the source-coded stream after encoding. Furthermore, we proposed a family of Short Block Codes (SBCs) designed for guaranteed convergence in Iterative Source-Channel Decoding (ISCD). The DP H.264 source coded video stream was used to evaluate the performance of our system using SBCs in conjunction with RSCs for transmission over correlated narrowband Rayleigh fading channels. The effect of different SBC schemes having diverse minimum Hamming distances (dH,min) and code rates on the attainable system performance was quantified, when using iterative SBSD and channel decoding, while keeping the overall bit-rate budget constant by appropriately partitioning the total available bit rate budget between the source and channel codecs. EXIT charts were used for analysing the attainable system performance and it was observed from the EXIT-chart analysis that the convergence behaviour of ISCD is substantially improved with the aid of SBCs. The above-mentioned investigations evolved further by designing more sophisticated non-coherent-detection aided space time coding based Multiple-Input Multiple-Output (MIMO) schemes for near-capacity video transmissions without the need for any high-complexity MIMO channel estimation. Space time coding constitutes an effective transmit diversity technique of compensating the effects of wireless channels by exploiting the independent fading of the signal transmitted from multiple antennas. Space-time coding is capable of achieving a substantial diversity and power gain relative to its single-input and single-output counterpart, which is attained without any bandwidth expansion. More specifically, we proposed a new near-capacity Sphere Packing (SP) modulation aided Differential Space Time Spreading (DSTS) design for the transmission of the video coded stream. SP modulation is a specific scheme, which maintains the highest possible Euclidean distance of the modulated symbols, while constitutes DSTS a low-complexity MIMO technique that does not require any channel estimation, since it relies on non-coherent detection. Finally, in order to circumvent the BER floor imposed by conventional two-stage turbo-detection schemes, we considered jointly optimised three-stage source and channel decoding arrangements employing serially concatenated and iteratively decoded SBCs combined with a URC and multi-dimensional SP modulation. The mutual information between the SBC, URC and SP constituent components is iteratively exploited in a turbo process in order to improve the overall BER and objective video quality in terms of the PSNR. The resultant coded signal was transmitted using a non-coherently detected DSTS MIMO-aided transceiver designed for near capacity JSCD. The performance of the system was evaluated by considering interactive video telephony using the H.264/AVC source codec. Again, the convergence behaviour of the MIMO transceiver advocated was investigated with the aid of EXIT charts.

This thesis examines the notion of the long term robust stability of iterative learning control (ILC) systems engaged in trajectory tracking, using a robust stability theorem based on a biased version of the nonlinear gap metric. This is achieved through two main results: The first concerns the establishment of a nonlinear robust stability theorem, where signals are measured relative to a given trajectory. Although primarily motivated by ILC, the theorem provided is applicable to a wider range of problems. This is due to its development being made independently of any particular signal space, provided the space is furnished with a definition of causality. The theorem's formulation therefore permits its implementation on single- or multi-dimensional problems in a variety of different settings. Necessitated by an ILC constraint concerning reference signals, the trajectory that stability is measured relative to must often lie outside the signal space that is chosen. The robust stability theorem is therefore devised to address signals that lie in extended signal spaces throughout. Additionally, the theorem is applicable to nonlinear systems, and it is shown that the biased gap measure collapses to the standard nonlinear gap measure when the bias is set to zero. It is also shown to collapse to the classical linear gap when restricting the analysis to certain linear systems. The second result applies the robust stability theorem to ILC using a 2D signal space. Initially the subject of ILC is reviewed and some of the problems associated with controllers are described; in particular the issues of long-term stability and the criteria for convergence. ILC algorithms expressed in the `lifted system' or `supervector' formulation are discussed and then analysed using the biased robust stability theorem. Results are presented regarding the use of filtering in ILC algorithms to aid robustness, and also the robustness of inverse model-based techniques. The robust stability tool applied to ILC in this thesis is not restricted in its analysis to algorithms which are `causal' (in an ILC sense); and is based on a general unstructured uncertainty model in contrast to the existing literature, whereby uncertainties are typically constrained to additive, multiplicative or parametric models.

The practical use of temporal multimedia has increased markedly in recent years as enabling technologies for the distribution and streaming of media have become available. As a part of this trend, hypermedia systems and models have adapted accordingly to incorporate such distributed multimedia for presentation. Structured interpretation of information has long been a fundamental feature of both open hypermedia systems and knowledge systems. Metadata, in its many forms, has become the cornerstone for providing this structured knowledge above and beyond basic data and information. This thesis presents the rationale and requirements for continuous metadata, which supports the metadata accompanying distributed multimedia throughout the lifecycle of streamed media, from generation, through distribution, to presentation. Throughout this process it is the temporal and continuous nature of the metadata which is paramount. A conceptual framework for continuous metadata is proposed to encapsulate these principles and ideas. Continuous metadata and the associated framework enable the development, in particular, of real-time, collaborative, semantically enriched distributed multimedia applications. Experience building one such system using continuous metadata is evaluated within the framework. An ontology is developed for the system to enable the collation, distribution, and presentation of structure aiding navigation of multimedia, and it is shown how continuous metadata utilising the ontology can be distributed using multicast

New approaches are essential to improve the inference of semantic relationships from low-level features for image annotation and retrieval. Current research on image annotation sometimes represents images in terms of regions and objects, but pays little attention to the spatial relationships between those regions or objects. Annotations are most frequently assigned at the global level, and even when assigned locally the extraction of relational descriptors is often neglected. To enrich the semantic description of the visual information, the use of spatial relationships offers one way to describe objects in an image more richly and often captures a relevant part of information in the image. In this thesis, new approaches for enhancing image annotation and retrieval by capturing spatial relationships between labelled objects in images are developed. Starting with an assumption of the availability of labelled objects, algorithms are developed for automatically extracting absolute object positional terms and relative terms describing the relative positions of objects in the image. Then, by using order of magnitude height information for objects in the domain of interest, relative distance of objects from the camera position in the real world are extracted, together with statements about nearness of objects to each other in the image and nearness in the real world. A knowledge-based representation is constructed using spatial and domain specific ontologies, and the system stores the asserted spatial statements about the images, which may then be used for image retrieval. The resulting Spatial Semantic Image System is evaluated using precision, recall and F-scores to test retrieval performance, and a small user trial is employed to compare the system’s spatial assertions with those made by users. The approach is shown to be capable of handling effectively a wide range of queries requiring spatial information and the assertions made by the system are shown to be broadly in line with human perceptions.

A variety of cooperative relaying schemes are designed for the single-carrier frequency-division multiple-access (SC-FDMA) uplink, when communicating over broadband wireless channels. Our goal is to reduce the battery power dissipated both by transmission and signal processing, so that the overall energy-efficiency may be increased. We assume that there are a number of inactive mobile terminals acting as potential relays, which have either fixed or time-variant positions in a cell. Our investigations are focused on the optimum exploitation of all the resources, when considering relay selection, power allocation and channel-quality-aided adaptive subband allocation. We exploit the benefits of combining the path-loss reduction and diversity gains arising from both fixed and opportunistic relaying, user cooperation and from all the propagation paths, as well as from multiple antennas. Novel frequency-domain equalisation and diversity combining approaches are also conceived. Specifically, we firstly conceive two single-relay assisted topologies for the sake of exploiting the achievable cooperative diversity, namely the single-dedicated-relaying (SDR), where each relay is dedicated to a single user, and the single-shared-relaying (SSR), when a single relay assists multiple users. In order to eliminate both the multi-user interference and for the sake of mitigating the noise-amplification imposed by amplify-and-forward (AF) relaying, we propose an efficient subband-based AF scheme, which is benchmarked against the conventional AF regime in the context of both the SDR and SSR topologies. Furthermore, by assuming that the channel state information (CSI) is available at the base station (BS)’s receiver, a joint frequency-domain equalisation and diversity-combining scheme is proposed for the sake of increasing the achievable cooperative diversity gain. In this case, when considering the different number of available relays that are geographically dispersed across a large-scale environment subject to both path-loss and shadowing, we propose three different dynamic relay selection schemes, namely single-user relay selection (SU-RS), multi-user relay selec-tion (MU-RS), and multiple-access relay selection (MA-RS), combined with source/relay vi power allocation in the context of opportunistic cooperation (OC) for the sake of increasing the multi-user system’s throughput. By contrast, when the source-to-destination (S-D)direct links are of low quality and hence are deemed to be unavailable, we exploit the relays which are roaming within each other’s vicinity in geographically localised manner in a cluster. Therefore, by assuming that these cooperating relays are capable of exchanging their channel quality information (CQI), we propose two first-hop-quality-aware (FHQA)joint dynamic resource allocation (DRA) schemes for opportunistic relaying (OR) based SCFDMA uplink, which beneficially combines channel-quality-aware subband allocation with efficient relay selection. The FHQA joint DRA schemes optimise the multi-user multi-relay networks relying on whether it is the source-to-relay (S-R) or the relay-to-destination (R-D) link, which dominates the attainable performance, when the BS’s receiver employs either single or multiple antennas. Additionally, the benefits of OR are quantified in the context of interleaver-aided decode-and-forward (DF) relaying for transmission over correlated fading channels. Therefore, the length of the interleavers combined with channel coding may be shortened. As a result, we benefit from a reduced interleaving delay and/or from a total transmit power reduction. In comparison to the benchmark schemes considered in the literature, the reliability and energy-efficiency of our proposed systems are significantly improved.

Anatomy of the fitness landscape for a group of well known combinatorial optimisation problems is studied in this research and the similarities and the differences between their landscapes are pointed out. In this research we target the analysis of the fitness landscape for MAX-SAT, Graph-Colouring, Travelling Salesman and Quadratic Assignment problems. Belonging to the class of NP-Hard problems, all these problems become exponentially harder as the problem size grows. We study a group of properties of the fitness landscape for these problems and show what properties are shared by different problems and what properties are different. The properties we investigate here include the time it takes for a local search algorithm to find a local optimum, the number of local and global optima, distance between local and global optima, expected cost of found optima, probability of reaching a global optimum and the cost of the best configuration in the search space. The relationship between these properties and the system size and other parameters of the problems are studied, and it is shown how these properties are shared or differ in different problems. We also study the long-range correlation within the search space, including the expected cost in the Hamming sphere around the local and global optima, the basin of attraction of the local and global optima and the probability of finding a local optimum as a function of its cost. We believe these information provide good insight for algorithm designers.

As a highly effective physical-layer interference management technique, the joint detection of a vector of non-orthogonal information-bearing symbols simultaneously transmitted over multiple-input multiple-output (MIMO) channels is of fundamental importance for high throughput digital communications. This is because the generic mathematical model of MIMO detection underpins a wide range of relevant applications including (but not limited to) the equalization of dispersive band-limited channels imposing intersymbol interference (ISI), the multiuser detection (MUD) in code-division multiple-access (CDMA) systems and the multi-stream detection for multiple-antenna based spatial-division multiplexing (SDM) systems. With the evolution of wireless networks, the “virtual MIMO” concept was conceived,which is also described by the generic mathematical MIMO model. MIMO detection becomes even more important, because the achievable performance of spectrum-efficient wireless networks is typically interference-limited, rather than noise-limited. In this thesis, a pair of detection methods that are well-suited for large-scale MIMO systems are investigated. The first one is the probabilistic data association (PDA) algorithm, which is essentially an interference-modelling approach based on iterative Gaussian approximation. The second one is the semidefinite programming (SDP) relaxation based approach, which approximates the optimal maximum likelihood (ML) detection problem to a convex optimization problem. The main advantage of both methods is that they impose a moderate computational complexity that increases as a polynomial function of the problem size, while providing competitive performance. The contributions of this thesis can be broadly categorized into two groups. The first group is related to the design of virtually antipodal (VA) detection of rectangular M-ary quadrature amplitude modulation (M-QAM) symbols transmitted in SDM-MIMO systems. As a foundation, in the first parts of Chapter 2 and Chapter 3 the rigorous mathematical relationship between the vector space of transmitted bits and that of transmitted rectangular M-QAM symbols is investigated. Both linear and nonlinear bit-to-symbol mappings are considered. It is revealed that the two vector spaces are linked by linear/quasi-linear transformations, which are explicitly characterized by certain transformation matrices. This formulation may potentially be applicable to many signal processing problems of wireless communications. For example, when used for detection of rectangular M-QAM symbol vector, it enables us to transform the conventional three-step “signal-to-symbol-to-bits” decision process to a direct “signal-to-bits” decision process. More specifically, based on the linear VA transformation, in Chapter 2 we propose a unified bit-based PDA (B-PDA) detection method for linear natural mapping aided rectangular M-QAM symbols transmitted in SDM-MIMO systems. We show that the proposed linear natural mapping based B-PDA approach attains an improved detection performance, despite dramatically reducing the omputational complexity in contrast to the conventional symbol-based PDA detector. Furthermore, in Chapter 3 a quasi-linear VA transformation based generalized low-complexity semidefinite programming relaxation (SDPR) detection approach is proposed for Gray-coded rectangular M-QAM signalling over MIMO channels. Compared to the linear natural mapping based B-PDA of Chapter 2, the quasi-linear VA transformation based SDPR method is capable of directly deciding on the information bits of the ubiquitous Gray-mapping aided rectangular M-QAM by decoupling the M-QAM constellation into several 4-QAM constellations. Moreover, it may be readily combined with the low-complexity bit-flipping based “hill climbing” technique for exploiting the unequal error protection (UEP) property of rectangular M-QAM, and the resultant VA-SDPR detector achieves the best bit-error rate (BER) performance among the known SDPR-based MIMO detectors conceived for high-order QAM constellations, while still maintaining the same order of polynomial-time worst-case computational complexity. Additionally, we reveal that the linear natural mapping based VA detectors attain the same performance provided by the binary reflected Gray mapping based VA detectors, but the former are simpler for implementation. Therefore, only if there are other constraints requiring using the nonlinear Gray mapping, it is preferable to use the linear natural mapping rather than the Gray mapping, when the VA detectors are used in uncoded MIMO systems. The second group explores the application of the PDA-aided detectors in some more sophisticated systems that are of great interest to the wireless research community. In particular, the design of iterative detection and decoding (IDD) schemes relying on the proposed low complexity PDA methods is investigated for the turbo-coded MIMO systems in Chapter 4 and 5. It has conventionally been regarded that the existing PDA algorithms output the estimated symbol-wise a posteriori probabilities (APPs) as soft information. In Chapter 4 and 5, however, we demonstrate that these probabilities are not the true APPs in the rigorous mathematical sense, but a type of nominal APPs, which are unsuitable for the classic architecture of IDD receivers. Moreover, our study shows that the known methods of calculating the bit-wise extrinsic logarithmic likelihood ratios (LLRs) are no longer applicable to the conventional PDA based methods when detecting M-ary modulation symbols. Additionally, the existing PDA based MIMO detectors typically operate purely in the probabilistic domain. Therefore, the existing PDA methods are not readily applicable to IDD receivers. To overcome this predicament, in Chapter 4 and Chapter 5 we propose the approximate Bayes’ theorem based logarithmic domain PDA (AB-Log-PDA) and the exact Bayes’ theorem based logarithmic domain PDA (EB-Log-PDA) detectors, respectively. We present the approaches of calculating the bit-wise extrinsic LLRs for both the AB-Log-PDA and the EB-Log-PDA, which makes them well-suited for IDD receivers. Furthermore, we demonstrate that invoking inner iterations within the PDA algorithms – which is common practice in PDA-aided uncoded MIMO systems – would actually degrade the IDD receiver’s performance, despite significantly increasing its overall computational complexity. Additionally, we investigate the relationship between the extrinsic LLRs of the proposed EB-Log-PDA and of the AB-Log-PDA. It is also shown that both the proposed AB-Log-PDA- and the EB-Log-PDA-based IDD schemes dispensing with any inner PDA iterations are capable of achieving a performance comparable to that of the optimal maximum a posteriori (MAP) detector based IDD receiver in the scenarios considered, despite their significantly lower computational complexity. Finally, in Chapter 6, a base station (BS) cooperation aided distributed soft reception scheme using the symbol-based PDA algorithm and soft combining (SC) is proposed for the uplink of multiuser multicell MIMO systems. The realistic 19-cell hexagonal cellular model relying on radical unity frequency reuse (FR) is considered, and local cooperation based message passing is used instead of a global message passing chain for the sake of reducing the backhaul traffic. We show that despite its moderate complexity and backhaul traffic, the proposed distributed PDA (DPDA) aided SC (DPDA-SC) reception scheme significantly outperforms the conventional non-cooperative benchmarkers. Furthermore, since only the index of the quantized converged soft information has to be exchanged between collaborative BSs for SC, the proposed DPDA-SC scheme is relatively robust to the quantization errors of the soft information exchanged. As an appealling benefit, the backhaul traffic is dramatically reduced at a negligible performance degradation.

In the past year, there has been an advancement in the development of optical active and passive Silicon-On-Insulator for Photonic Integrated Circuits (PICs) applications. Following the continuous miniaturisation trend in this technology the study of the loss performance of these devices also become an attractive subject. Among the many components silicon based optical modulators are specifically important for low loss and high bandwidth short reach interconnects. The general aim of this thesis is to design and computationally investigate the performance of a multilayer hybrid silicon modulator. The design involves a heterojunction structure that operates based on plasma dispersion effect taking the effect of surface roughness and scattering loss into account. For this purpose a novel numerical approach is developed to estimate scattering loss due to the roughness in general waveguide structures and also the proposed silicon based optical waveguide modulator in this work. The applicability can be however extended towards wider range of optical waveguide based devices including multilayer configurations. The method is based on 2D Fourier transform technique that is widely used in Magneto Resonance Imaging technique. Firstly, the effect of three forms of roughness is investigated in a general strip waveguide structure; isotropic, anisotropic and the mixture of isotropic and anisotropic. In each case the generated sidewall roughness is implemented in various SOI high contrast refractive index waveguides. The waveguide dimensions have been chosen to cover a large variety of waveguide sizes to evaluate the accuracy of the modelling technique. Two SOI waveguide samples have been fabricated. The first sample is 100nm, 1200nm and 1400nm in width and 500nm in height which are single mode in Mid Infra Red (MIR) region. The second sample contains waveguide with 220nm height and 330nm widths that is single mode in Near Infra Read (NIR) wavelength. Other dimensions are chosen from several published works. The calculated losses using FDTD show good agreement with all measured fabricated waveguide and the referred experimental works in the literature. The three dimensional model successfully explains the scattering loss dependence on the width of a high aspect ratio waveguide when the result is compared with a published work. While the measurement shows the loss reduces from 32dB/cm to 0.8dB/cm, the simulation results varies from 44dB/cm to 1dB/cm. The interdependence of scattering loss is also investigated against other theoretical approaches when the correlation length varies from 0 to 1000nm. The relatively low aspect ratio waveguide is chosen to have a fixed dimension of 220nm by 330nm and 5nm value. In order to study the scattering loss caused by roughness the roughness model is applied in the proposed modulator structure. The design involves a multimode strip like p doped silicon material wrapped by transparent ZnO as a naturally n doped active material. This forms a pn heterojunction that is implemented in one arm of a Mach Zehnder interferometer. The switch is designed to operate at 1.55µm and in depletion mode to avoid minority carrier life time effect in switching speed. The calculated capacitance switching speed of a pulse were less than 1 pf=cm and 90ps respectively. The resistivity v is higher compared to a general form of heterojunction due to the relativity larger ZnO/Si contact area of the device. The phase shifter is implemented in Mach Zehnder structure to change from phase modulation to amplitude modulation using a MMI structure. The calculated extinction ratio was as high as 23.7dB with the insertion loss of 2.5dB. Further simulation results shows that the 100nm change in the ZnO thickness can alter the effective index of refraction and loss performance of the devices. In an ideal situation, as the thickness increases from 50nm to 150nm the loss changes from 2 to 8dB/cm for TE mode. The involvement of sidewall roughness results higher insertion loss by at least by 0.2dB when the rms of the sidewall roughness increases by 7nm. As the ZnO coating thickness increases, the roughness effect is counterbalanced by almost 50%.