This thesis is primarily concerned with developing new parameter based blind deconvolution algorithms and studying their applications. The blind deconvolution problem for minimum phase (MP) systems is well understood, and in this case the well known predictive schemes can be employed. When systems are nonminimum phase (NMP), however, the predictive deconvolution methods can only generate the spectrally equivalent MP solution. This is because the predictive schemes are based only on autocorrelations, which are completely blind to the phase properties of systems. In order to solve the blind deconvolution problem of NMP systems, higher order cumulant (HOC) analysis is adopted in this thesis. The reason for this is that HOC carry the phase information of systems only to a linear phase shift, the parametric approach is adopted due to its advantages in terms of variance and resolution over nonparametric methods. Both MA and AR based models are studied in this work. A new robust blind deconvolution algorithm for MP systems: variance approximation and series decoupling (VASD), is presented first. It is shown that this algorithm possesses some advantages over the existing ones with the same purpose. Then, based on a MA system model, we proposed a HOC-based two-step relay algorithm, in which the close-form formula for MA parameters are combined with an optimal fitting scheme, and the thorny problem of multimodality is overcome to a very great degree. Thus, the optimal identification of the MA parameters of NMP systems can be obtained. In the study of the AR based model, six new families of HOC based linear equations with respect to the AR parameters are derived. Since the inverse filter coefficients are simply the solution of a set of linear equations, their uniqueness can normally be guaranteed. In comparison with the existing AR based methods, only diagonal slices of cumulants are used in our algorithms, in which simplicity and elegance are fully embodied. It has been shown that our algorithm can offer more accurate results than the existing ones.

A large amount of research has been put into areas of signal processing, medium design, head and servo-mechanism design and coding for conventional longitudinal as well as perpendicular magnetic recording. This work presents some further investigation in the signal processing and coding aspects of longitudinal and perpendicular digital magnetic recording. The work presented in this thesis is based upon numerical analysis using various simulation methods. The environment used for implementation of simulation models is C/C + + programming. Important results based upon bit error rate calculations have been documented in this thesis. This work presents the new designed Asymmetric Decoder (AD) which is modified to take into account the jitter noise and shows that it has better performance than classical BCJR decoders with the use of Error Correction Codes (ECC). In this work, a new method of designing Generalised Partial Response (GPR) target and its equaliser has been discussed and implemented which is based on maximising the ratio of the minimum squared euclidean distance of the PR target to the noise penalty introduced by the Partial Response (PR) filter. The results show that the new designed GPR targets have consistently better performance in comparison to various GPR targets previously published. Two methods of equalisation including the industry's standard PR, and a novel Soft-Feedback- Equalisation (SFE) have been discussed which are complimentary to each other. The work on SFE, which is a novelty of this work, was derived from the problem of Inter Symbol Interference (ISI) and noise colouration in PR equalisation. This work also shows that multi-level SFE with MAP/BCJR feedback based magnetic recording with ECC has similar performance when compared to high density binary PR based magnetic recording with ECC, thus documenting the benefits of multi-level magnetic recording. It has been shown that 4-level PR based magnetic recording with ECC at half the density of binary PR based magnetic recording has similar performance and higher packing density by a factor of 2. A novel technique of combining SFE and PR equalisation to achieve best ISI cancellation in a iterative fashion has been discussed. A consistent gain of 0.5 dB and more is achieved when this technique is investigated with application of Maximum Transition Run (MTR) codes. As the length of the PR target in PR equalisation increases, the gain achieved using this novel technique consistently increases and reaches up to 1.2 dB in case of EEPR4 target for a bit error rate of 10-5.

Spam is becoming a more and more severe problem for individuals, networks, organisations and businesses. The losses caused by spam are billions of dollars every year. Research shows that spam contributes more than 80% of e-mails with an increased in its growth rate every year. Spam is not limited to emails; it has started affecting other technologies like VoIP, cellular and traditional telephony, and instant messaging services. None of the approaches (including legislative, collaborative, social awareness and technological) separately or in combination with other approaches, can prevent sufficient of the spam to be deemed a solution to the spam problem. The severity of the spam problem and the limitations of the state-of-the-Art solutions create a strong need for an efficient anti-spam mechanism that can prevent significant volumes of spam without showing any false positives. This can be achieved by an efficient anti-spam mechanism such as the proposed anti-spam mechanism known as "Spam Prevention using Access Codes", SPAC. SPAC targets spam from two angles i.e. to prevent/block spam and to discourage spammers by making the infrastructure environment very unpleasant for them. In addition to the idea of Access Codes, SPAC combines the ideas behind some of the key current technological anti-spam measures to increase effectiveness. The difference in this work is that SPAC uses those ideas effectively and combines them in a unique way which enables SPAC to acquire the good features of a number of technological anti-spam approaches without showing any of the drawbacks of these approaches. Sybil attacks, Dictionary attacks and address spoofing have no impact on the performance of SPAC. In fact SPAC functions in a similar way (i.e. as for unknown persons) for these sorts of attacks. An application known as the "SPAC application" has been developed to test the performance of the SPAC mechanism. The results obtained from various tests on the SPAC application show that SPAC has a clear edge over the existing anti-spam technological approaches.

Cooperative diversity provides a new paradigm in robust wireless re- lay networks that leverages Space-Time (ST) processing techniques to combat the effects of fading. Distributing the encoding over multiple relays that potentially observe uncorrelated channels to a destination terminal has demonstrated promising results in extending range, data- rates and transmit power utilization. Specifically, Space Time Block Codes (STBCs) based on orthogonal designs have proven extremely popular at exploiting spatial diversity through simple distributed pro- cessing without channel knowledge at the relaying terminals. This thesis aims at extending further the extensive design and analysis in relay networks based on orthogonal designs in the context of Quasi- Orthogonal Space Time Block Codes (QOSTBCs). The characterization of Quasi-Orthogonal MIMO channels for cooper- ative networks is performed under Ergodic and Non-Ergodic channel conditions. Specific to cooperative diversity, the sub-channels are as- sumed to observe different shadowing conditions as opposed to the traditional co-located communication system. Under Ergodic chan- nel assumptions novel closed-form solutions for cooperative channel capacity under the constraint of distributed-QOSTBC processing are presented. This analysis is extended to yield closed-form approx- imate expressions and their utility is verified through simulations. The effective use of partial feedback to orthogonalize the QOSTBC is examined and significant gains under specific channel conditions are demonstrated. Distributed systems cooperating over the network introduce chal- lenges in synchronization. Without extensive network management it is difficult to synchronize all the nodes participating in the relaying between source and destination terminals. Based on QOSTBC tech- niques simple encoding strategies are introduced that provide compa- rable throughput to schemes under synchronous conditions with neg- ligible overhead in processing throughout the protocol. Both mutli- carrier and single-carrier schemes are developed to enable the flexi- bility to limit Peak-to-Average-Power-Ratio (PAPR) and reduce the Radio Frequency (RF) requirements of the relaying terminals. The insights gained in asynchronous design in flat-fading cooperative channels are then extended to broadband networks over frequency- selective channels where the novel application of QOSTBCs are used in distributed-Space-Time-Frequency (STF) coding. Specifically, cod- ing schemes are presented that extract both spatial and mutli-path diversity offered by the cooperative Multiple-Input Multiple-Output (MIMO) channel. To provide maximum flexibility the proposed schemes are adapted to facilitate both Decode-and-Forward (DF) and Amplify- and-Forward (AF) relaying. In-depth Pairwise-Error-Probability (PEP) analysis provides distinct design specifications which tailor the distributed- STF code to maximize the diversity and coding gain offered under the DF and AF protocols. Numerical simulation are used extensively to confirm the validity of the proposed cooperative schemes. The analytical and numerical re- sults demonstrate the effective use of QOSTBC over orthogonal tech- niques in a wide range of channel conditions.

Independent vector analysis (IVA) is studied as a frequency domain blind source separation method, which can theoretically avoid the permutation problem by retaining the dependency between different frequency bins of the same source vector while removing the dependency between different source vectors. This thesis focuses upon improving the performance of independent vector analysis when it is used to solve the audio separation problem in a room environment. A specific stability problem of IVA, i.e. the block permutation problem, is identified and analyzed. Then a robust IVA method is proposed to solve this problem by exploiting the phase continuity of the unmixing matrix. Moreover, an auxiliary function based IVA algorithm with an overlapped chain type source prior is proposed as well to mitigate this problem. Then an informed IVA scheme is proposed which combines the geometric information of the sources from video to solve the problem by providing an intelligent initialization for optimal convergence. The proposed informed IVA algorithm can also achieve a faster convergence in terms of iteration numbers and better separation performance. A pitch based evaluation method is defined to judge the separation performance objectively when the information describing the mixing matrix and sources is missing. In order to improve the separation performance of IVA, an appropriate multivariate source prior is needed to better preserve the dependency structure within the source vectors. A particular multivariate generalized Gaussian distribution is adopted as the source prior. The nonlinear score function derived from this proposed source prior contains the fourth order relationships between different frequency bins, which provides a more informative and stronger dependency structure compared with the original IVA algorithm and thereby improves the separation performance. Copula theory is a central tool to model the nonlinear dependency structure. The t copula is proposed to describe the dependency structure within the frequency domain speech signals due to its tail dependency property, which means if one variable has an extreme value, other variables are expected to have extreme values. A multivariate student's t distribution constructed by using a t copula with the univariate student's t marginal distribution is proposed as the source prior. Then the IVA algorithm with the proposed source prior is derived. The proposed algorithms are tested with real speech signals in different reverberant room environments both using modelled room impulse response and real room recordings. State-of-the-art criteria are used to evaluate the separation performance, and the experimental results confirm the advantage of the proposed algorithms.

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The vast majority of existing Intrusion Detection Systems incorporates static knowledge bases, which contain information about specific attack patterns. Although such knowledge bases can gradually expand, yet they have required the close maintenance of an expert, letting alone the possibility that the knowledge base might overload and tinally run over. Furthermore, most of the existing quantitative methods for intrusion detection require the data records to be processed in offline mode, as a batch. Unfortunately this allows only a snapshot of the actual domain to be analysed. On top of that, should new data records become available they require cost-sensitive calculations due to the fact that re-learning is ineffective for real-time applications. The prospective application of evolving nature-inspired intelligent behavior in conjunction with network intrusion detection is an attractive field which overcomes these problems, but which contains open questions remaining to be answered. A standalone Network Intrusion Detection System, which is capabk of evolving its knowledge structure and parameters in order to prevent both known and novel intrusions. is still not available. Initially, this thesis reviews a methodology for evolving fuzzy classification. which allows data to be processed in online mode by recursively modifying a fuzzy rule base on a per-sample basis. The incremental adaptation is gradually developed by the int1uence of the input data, which arrive from a data stream in succession. Recent studies have shown that the eClass algorithms are a promising elucidation since they have been extensively used for control applications and are also suitable for real-time classification tasks. such as fault detection, diagnosis, robotic navigation ctc. Finally, it is revealed that the relative eClass architecture can be further improved in terms of the predictive accuracy and that it can be effectively applied on behalf of network diagnostics. The improved algorithm is finally compared to others and seems to outperform many well-known methods and to be adequately competent.

The thesis research concerns an integrated framework of terrestrial and satellite networks based on Orthogonal Frequency Division Multiple Access (OFDM) air interface which we call Hybrid Terrestrial-Satellite Mobile System (HTSMS). HTSMS which enables frequency reuse amongst the two networks serves users in urban areas via terrestrial Base Stations whilst satellite links provide service in rural areas in a transparent and seamless manner. The thesis focuses on mitigation of Co-Channel Interference on the uplink of the satellite using Least Mean Squares beamforming onboard the satellite. We propose a preamble transmission strategy based on pilot re-allocation for superior Co-Channel Interference mitigation, specific to HTSMS. Within the preamble framework, we further propose Fully-Dense Preamble, Partially-Dense Preamble and Reduced-Length Preamble as possible schemes and analyse their performance as compared to receiver side alternatives such as Variable Step Size-Least Mean Squares and Normalised-Least Mean Squares beamforming. Results show that the approach not only gives superior convergence but it enables better system performance with less pilot transmissions. Exploiting the susceptibility of the beamforming process to pilots, we further propose Novel Iterative Turbo Beamforming for the HTSMS with a Bit Interleaved Coded Modulation-OFDM. The proposed technique is based on improving a priori information of the soft decoded data and uses both soft data and pilots to perform adaptive beamforming in a turbo-like recursive manner. Results show that proposed approach exhibits significant bit error rate gains with only 1 iteration. Finally, to reduce the associated complexity of onboard beamforming, we first quantify performance advantages of adaptive beamforming against non-adaptive. For the non-adaptive case, we propose onboard based semi-static beamforming where the required beam orientation computed at the ground is transmitted to the satellite at which beamforming weights are calculated. The proposed mechanism is a practical and attractive alternative to existing non-adaptive beamforming approaches, especially for satellite systems offering broadcasting/fixed services. On comparison, results show that adaptive beamforming is superior, however semi-static has comparable performance in specific scenarios. In light of this, we propose a novel-semi adaptive beamformer. The proposed technique is a switch-type beamforming, where a novel switching mechanism enables adaptive and non-adaptive processing to coexist. The algorithm is also robust to both spurious switching as well as other disturbances in the system. For HTSMS, results show that semi-adaptive beamformer can save up to 98% of the filtering computing power without degradation to system performance.

Space and satellite systems are considered to be the most extreme environment to design for and are fraught with engineering difficulty. Performance metrics such as fault tolerance, reliability, pre-determinism and heritage are still high on the list of requirements for all satellite missions. The advent of modem day electronics and miniaturisation, state-of-the-art computing and networking technologies has enabled research into 'distributed satellite systems', where multiple spacecraft work collaboratively to perform a mission using intersatellite connectivity. A satellite can be considered one of many nodes in an autonomous and decentralised system, analogous to a mobile ad-hoc network, enabling opportunities in multiple-point sensing, greater communications capabilities, and spacecraft redundancy. Existing satellite constellations can implement distributed satellite system scenarios but provide unpredictable relative ranges and rates due to various space perturbations. This creates a disconnected environment making it difficult to perform distributed mission operations. Without orbit maintenance, limited onboard resources in power and mass could mean lower processing and networking capabilities which need to rise dramatically to meet requirements for these new missions. This thesis investigates the use of an Agent-based distributed computing platform to enable ad-hoc satellites networking. Agents for real-time systems and their applications conclude that, despite being utilised in complex control systems, most Agent middleware is unsuited for mission critical, real-time, networked, embedded systems. Two constellation scenarios are simulated for distributed satellite missions highlighting orbital issues such as relative distance and mission lifetime. Computing requirements for such distributed computing opportunities using intersatellite connectivity and Agent technologies have led to a novel system-on-a-chip design, including a general purpose processor core and a dedicated Java co-processing core to enable hard real-time Agent functionalities and software Agent applications at minimal overhead. Common Agent middleware platforms are compared and a software configuration is chosen with relevant Agent services. A distributed image compression case study is also presented. A picosatellite testbed is also designed to provide realistic computing and power constraints.

The purpose of this research study was to investigate solutions to degradations in QoS (Quality of Service) for Broadband Internet provision via Geostationary Satellite Systems. Analysis as well as trials using commercial equipment have shown that these can result from certain Radio Resource Management (RRM) schemes, the limited capacity per user as well as atmospheric channel impairments. The latter is being effectively addressed by Fade Mitigation Techniques, leading however in a reduction and variation of the useful capacity. In addition, internet applications and protocols have been developed for terrestrial networks and therefore their adaptation to the satellite architecture characteristics, or the opposite, is often necessary. An important challenge has also been to improve individual application performance while at the same time optimise the overall system performance and maximising the transmission capacity. The optimisation methodology adopted is cross-layer design, a concept based on the exchange of parameters between non adjacent layers of the protocol stack. Six cross-layer mechanisms are proposed as part of this research targeting VoIP (Voice over IP) as well as TCP applications (Transport Control Protocol) using connection splitting. The mechanisms employ optimisation algorithms utilising real-time information from the MAC (Medium Access Control) as well as other non adjacent layers. The performance assessment performed via software simulations demonstrated important improvements in QoS. For VoIP for example, the MOS score which can be achieved even under congestion is above or around 80 in the R factor scale, with a theoretical maximum of 93. Simulations on TCP have also indicated how a cross-layer design allows the beginning of file data transfer at the physical layer to start earlier, which is important for small files. With respect to bigger files, a "cross-layer TCP" version can reduce the transfer delay of a typical file by about 50% with respect to TCP New Reno and 30% compared to TCP Hybla. The principal conclusion from this research is that broadband satellite systems can offer comparable QoS to terrestrial networks for most popular internet applications. This is under the condition that adequate capacity is available and adaptive techniques are implemented across the network, optimising performance jointly over several layers of the protocol stack. To this purpose the cross-layer designs proposed as part of this research become an essential tool.