The direct-sequence code division multiple access (DS-CDMA) is one of the significant techniques for wireless communication systems with multiple simultaneous transmissions. The main concern of this thesis is to propose a new linearly constrained constant modulus modified conjugate gradient (LCCM-MCG) adaptive filtering algorithm to deal with problem of channel mismatch associated with the multiple access interference (MAI) in DS-CDMA system over multipath fading channel. In fact, the adaptive filtering algorithm based on the CM criterion is known to be very attractive for the case when the channel parameters are not estimated perfectly. The proposed LCCM-MCG algorithm is derived based on the so-called generalized sidelobe canceller (GSC). It has the advantage of having better stability and less computational complexity compared with conventional recursive least-squares (RLS) algorithm, and can be used to achieve desired performance for multiuser RAKE receiver. Moreover, with the MCG algorithm it requires only one recursive iteration per incoming sample data for updating the weight vector, but still maintains performance comparable to the RLS algorithm. From computer simulation results, we show that the proposed LCCM-MCG algorithm has fast convergence rate and could be used to circumvent the effect due to channel mismatch. Also, the performance, in terms of bit error rate (BER), is quite close to the LCCM-RLS algorithm suggested in [18], and is superior to the stochastic gradient descent (SGD) algorithm proposed in [7].

<p>Two topics in fading channels with a strict delay constraint and a resolution-constrained feedback link are treated in this thesis.</p><p>First, a multi-layer variable-rate single-antenna communication system with quantized feedback, where the expected rate is chosen as the performance measure, is studied under both short-term and long-term power constraints. Iterative algorithms exploiting results in the literature of parallel broadcast channels are developed to design the system parameters. A necessary and sufficient condition for single-layer coding to be optimal is derived. In contrast to the ergodic case, it is shown that a few bits of feedback information can improve the expected rate dramatically. The role of multi-layer coding, however, reduces quickly as the resolution of the feedback link increases.</p><p>The other part of the thesis deals with partial power control systems utilizing quantized feedback to minimize outage probability, with an emphasis on the diversity-multiplexing tradeoff. An index mapping with circular structure is shown to be optimal and the design is facilitated with a justified Gaussian approximation. The diversity gain as a function of the feedback resolution is analyzed. The results are then extended to characterize the entire diversity-multiplexing tradeoff curve of multiple-antenna channels with resolution-constrained feedback. Adaptive-rate communication is also studied, where the concept of minimum multiplexing gain is introduced. It is shown that the diversity gain of a system increases significantly even with coarsely quantized feedback, especially at low multiplexing gains.</p>

In this thesis we have considered a cognitive radio network (CRN) with a pair of primary user (PU) and secondary user (SU) in spectrum sharing networks in path-loss and without path-loss propagation environments under identically distributed m-Nakagami fading channel. The thesis consists of three parts. In the first part we propose an optimized Takagi-Sugeno Fuzzy Inference System (FIS) based power control strategy in cognitive radio networks (CRN) in spectrum sharing network in without path-loss propagation environment. The second part proposes an optimized Takagi-Sugeno FIS based power control strategy in cognitive radio networks in spectrum sharing network in path-loss propagation environment. For without path-loss propagation environment the proposed FIS takes the interference channel gain ratio between SU transmitter (CUtx) and PU receiver (PUrx) and Signal to Noise Ratio (SNR) towards PU transmitter (PUtx) as antecedents and outputs the power scaling factor for SU. For path-loss propagation environment the proposed FIS takes the relative distance ratio between CUtx and PUrx and SNR towards PUtx as antecedents and outputs the power scaling factor for SU. The output power scaling factor is used to vary the transmit power of SU such that it does not degrade the quality of service (QoS) of PU link. The third part presents an implementation of orthogonal frequency division multiplexing (OFDM) transmission technique in CRN. The OFDM technique has intellectual attractive features like coping with the inter symbol interference (ISI), while providing increasing spectral efficiency and improved performance. This can be used in emergency conditions where transmission requires reliability and high data rate. The OFDM transmission technique is applied towards SU transmitter in CRN, which enables SU to utilize the spectrum efficiently under various fading environments. Spectrum sharing networks in with and without path-loss propagation environments and OFDM transmission were tested for bit error rate (BER) performance after fading effects from m-Nakagami fading channel. We conclude that by applying Takagi-Sugeno Fuzzy Inference System (FIS) based power control strategy we can improve the BER performance of PU when compared with no power control strategy and with other fuzzy based power control technique. OFDM transmission technique gives us better data rate and slightly improved BER in CRN hence making it suitable for use in emergency conditions. / mobile: 0735032048 (Muneeb Goraya)

Ad hoc network is intrinsically autonomous and self-configuring network that does not require any dedicated centralized management. For specialized applications such as, military operations, search-and-rescue missions, security and surveillance, patient monitoring, hazardous material monitoring, 4G (4th Generation) coverage extension, and rural communication; ad hoc networks provide an intelligent, robust, flexible and cost effective solution for the wireless communication needs. As in centralized wireless systems, ad hoc networks are also expected to support high data rates, low delays, and large node density in addition to many other QoS (Quality of Service) requirements. However, due to unique ad hoc network characteristics, spectrum scarcity, computational limit of current state-of-the-art technology, power consumption, and memory; meeting QoS requirements is very challenging in ad hoc networks. Studies have shown cross layer to be very effective in enhancing QoS performance under spectrum scarcity and other constraints. In this dissertation, our main goal is to enhance performance (e.g., throughput, delay, scalability, fairness) by developing novel cross layer techniques in single-hop single channel general ad hoc networks. Our dissertation mainly consists of three main sections. In the first section, we identify major challenges intrinsic to ad hoc networks that affect QoS performance under spectrum constraint (i.e., single channel). In the later parts of the dissertation, we investigate and propose novel distributed techniques for ad hoc networks to tackle identified challenges. Different from our main goal, albeit closely related; in the first section we propose a conceptual cross layer frame work for interaction control and coordination. In this context, we identify various functional blocks, and show through simulations that global and local perturbations through parametric correlation can be used for performance optimization. In the second section, we propose MAC (Medium Access Control) scheduling approaches for omni-directional antenna environment to enhance throughput, delay, scalability and fairness performance under channel fading conditions. First, we propose a novel cooperative ratio-based MAC scheduling scheme for finite horizon applications. In this scheduling scheme, each node cooperatively adapts access probability in every window based on its own and neighbors` backlogs and channel states to enhance throughput, scalability and fairness performance. Further, in the second section, we propose two novel relay based MAC scheduling protocols (termed as 2rcMAC and IrcMAC) that make use of relays for reliable transmission with enhanced throughput and delay performance. The proposed protocols make use of spatial diversity due to relay path(s) provided they offer higher data rates compared to the direct path. Simulation results confirm improved performance compared to existing relay based protocols. In the third section, we make use of directional antenna technology to enhance spatial reuse and thus increase network throughput and scalability in ad hoc networks. In this section, we introduce problems that arise as a result of directional communication. We consider two such problems and propose techniques that consequently lead to throughput, delay and scalability enhancement. Specifically, we consider destination location and tracking problem as our first problem. We propose a novel neighbor discovery DMAC (Directional MAC) protocol that probabilistically searches for the destination based on elapsed time, distance, average velocity and beam-width. Results confirm improved performance compared to commonly used random sector and last sector based directional MAC protocols. Further, we identify RTS/CTS collisions as our second problem which leads to appreciable throughput degradation in ad hoc networks. In this respect, we investigate and propose a fully distributed asynchronous polarization based DMAC protocol. In this protocol, each node senses its neighborhood on both linear polarization channels and adapts polarization to enhance throughput and scalability. Throughput and delay comparisons against the basic DMAC protocol clearly show throughput, scalability and delay improvements.

Not available

No description available.

Quality-of-service (QoS) guarantees have become critically important for the transmission of real-time multimedia traffic in next generation mobile wireless networks. The aim of this dissertation is to investigate the cross-layer design for support of delay bound QoS guarantees over fading channels. Providing diverse QoS guarantees presents a challenge due to the time-varying fading nature of wireless channels. Existing physical layer modelling is inadequate in supporting real time QoS metrics such as delay, hence adaptive techniques need to be extended to the upper-protocol layers. The first objective of this dissertation is to introduce a cross-layer design framework which investigates the impact of the physical layer on the data link delay bound QoS performance. At the physical layer, adaptive modulation and coding (AMC) is utilized for transmission over block fading channels. At the data link layer, the effective capacity approach is used to model the delay bound QoS performance subject to physical layer variations. The effects of varying physical layer parameters, such as average signal-to-noise ratio (SNR), the fading parameter for the kagami- model, and target packet-error rate (PER), on the analytical delay bound performance are investigated and then validated by the simulation of a queuing system. Due to the cross-layer design framework, the system’s throughput has a significant impact on bounded delay at the data link layer. The switching levels of the conventional AMC scheme used in the first objective were fixed, subject to a target PER. However, fixed switching levels results in the system’s throughput limiting the delay bound performance. The second objective of this dissertation is to optimize the switching levels of the AMC scheme employed at the physical layer, by maximizing the average throughput, while maintaining the target PER constraint. The analytical and simulated results show that by optimizing the switching levels, a superior delay bound performance is achieved, when compared to the deterministic switching levels of the conventional AMC scheme used in the first objective. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Fading Points is a piece of music for large wind ensemble. The work is concerned with time perception and is designed to convey to the listener a long temporal progression from slow music to fast music. To this end, the work is written using musical gestures specifically designed for their portrayal of musical time. The work consists of four sections, each of which is described in detail in the analytical part of the thesis. The analysis also describes the rhythmic language, which is created around short rhythmic cells. These cells are based on ratios and are used in all levels of the piece from the surface rhythm to the large formal divisions. The harmonic language is also described. The vertical harmony is derived from a dense chord presented at the beginning of the piece. The horizontal pitch material is created from small pitch cells, also taken from the opening chord. These cells are used in isolation but are also combined to create modes, which are the focus of the latter parts of the piece.

In the first part of this thesis, the information capacity of time-varying fading channels is analysed using finite-state Markov channel (FSMC) models. Both fading channel amplitude and fading channel phase are modelled as finite-state Markov processes. The effect of the number of fading channel gain partitions on the capacity is studied (from 2 to 128 partitions). It is observed that the FSMC capacity is saturated when the number of fading channel gain partitions is larger than 4 to 8 times the number of channel input levels. The rapid FSMC capacity saturation with a small number of fading channel gain partitions can be used for the design of computationally simple receivers, with a negligible loss in the capacity. Furthermore, the effect of fading channel memory order on the capacity is studied (from first- to fourth-order). It is observed that low-order FSMC models can provide higher capacity estimates for fading channels than high-order FSMC models, especially when channel states are poorly observable in the presence of channel noise. To explain the effect of memory order on the FSMC capacity, the capacities of high-order and low-order FSMC models are analytically compared. It is shown that the capacity difference is caused by two factors: 1) the channel entropy difference, and 2) the channel observability difference between the high-order and low-order FSMC models. Due to the existence of the second factor, the capacity of high-order FSMC models can be lower than the capacity of low-order FSMC models. Two sufficient conditions are proven to predict when the low-order FSMC capacity is higher or lower than the high-order FSMC capacity. In the second part of this thesis, a new implicit (blind) channel estimation method in time- varying fading channels is proposed. The information source emits bits ???0??? and ???1??? with unequal probabilities. The unbalanced source distribution is used as a priori known signal structure at the receiver for channel estimation. Compared to pilot-symbol-assisted channel estimation, the proposed channel estimation technique can achieve a superior receiver bit error rate performance, especially at low signal to noise ratio conditions.

Κύριος στόχος της διπλωματικής αυτής εργασίας είναι η διερεύνηση τεχνικών βελτίωσης της προσφερόμενης ποιότητας υπηρεσιών (QoS) σε ένα περιβάλλον συνλειτουργίας πολλαπλών HAPs. Στο περιβάλλον αυτό έχουμε διαφορετικούς τύπους χρηστών που μοιράζονται την περιοχή κάλυψης και το εύρος ζώνης. Παρουσιάζεται το θεωρητικό υπόβαθρο της μελέτης αυτής που περιλαμβάνει τη θεωρία τηλεπικοινωνιακής κίνησης. Αναπτύσσουμε ένα αναλυτικό μοντέλο ώστε να περιγράψουμε το περιβάλλον συνλειτουργίας στο οποίο έχουμε δύο κατηγορίες χρηστών. Η μία κατηγορία αποτελείται από χρήστες που έχουν πλήρη πρόσβαση στα HAPs, ενώ η άλλη κατηγορία αποτελείται από χρήστες με περιορισμένη πρόσβαση στα HAPs. Για να επιτύχουμε αυτή τη βελτίωση του QoS εφαρμόζουμε διάφορους μηχανισμούς περιορισμού. Σκοπός μας είναι να περιοριστεί η πρόσβαση στους πόρους του καναλιού για τους χρήστες με πλήρη πρόσβαση στα HAPs, ώστε να υπάρχει μεγαλύτερη πιθανότητα πρόσβασης για τους χρήστες με περιορισμένη πρόσβαση στα HAPs. Παρουσιάζονται και αναλύονται διάφοροι περιορισμοί με στόχο την εύρεση του καταλληλότερου για την επίτευξη μιας ισορροπημένης και χαμηλής πιθανότητας απόρριψης κλήσης. Αναλύεται, επίσης, και επεξηγείται η παρουσία φαινομένων παρεμβολής και πολυόδευσης στο σύστημά μας καθώς και η εξοικονόμηση συχνοτήτων. / The main objective of this thesis is to investigate techniques for improvement the Quality of Service (QoS) in an environment of multiple HAPs. In this environment there are different user types which share coverage area and radio spectrum. It is presented the theoretical background of this study that includes theory telecommunication traffic. We develop an analytical model to describe system behavior of a coexistence scenario containing two user groups, which have full and limited HAP availability. In order to achieve this improvement of QoS, operate different restrictions. Our aim is to limit access to channel resources to users with full access to HAPs, so that there is a greater probability of access for users with limited access to HAPs. Different types of restriction function are analyzed trying to find the most suitable for achieving a balanced low probability performance to both user groups simultaneously. It is also explained the presence of interference, small-scale fading and saving frequencies.