No description available.

A multilevel modulation format, namely absolute added correlative coding (AACC) is proposed to overcome the effect of fibre dispersion. A novel modulation and demodulation systems are proposed along with bit-error rate (BER) estimation technique. Transmission properties and system applications are also discussed. The research topics are categorised according to the type of the proposed multilevel signalling. It is worth mentioning that AACC can also be implemented with both NRZ and RZ pulse coding based upon the applications in order to optimise their performance.

vii, 100 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 1981

No description available.

In order to support increasing traffic loads, mobile operators need cost-effective solutions to improve the spectral efficiency of their cellular networks, or to off-load them by diverting some of the load to other networks. Advances in the radio resource management may to some extent reduce the need for costly new deployments. The resource management should not only focus on spectrum efficiency—it should try to meet the service requirements of applications that are expected to contribute large data volumes, such as video streaming. Many of those applications are multicast/broadcast in nature (e.g., mobile TV, data podcasting). Our focus in this thesis is on resource allocation mechanisms that exploit the mobility of users. The mobility induces channel quality fluctuations and creates intermittent connectivity, which both can be used to improve the resource efficiency of wireless multimedia systems. The thesis concentrates on two areas: link-layer resource allocation for video streaming in cellular networks and mobility-assisted content distribution in hybrid cellular/ad-hoc networks. In the area of wireless video streaming, we study bit-rate allocation, statistical multiplexing, and channel-aware scheduling. The bit-rate allocation should provide a distortion-optimal assignment of source, channel, and pilot bit-rates under link capacity constraints. We derive an analytical model that captures the video distortion as a function of the bit-rates and, based on it, we study various bit-rate allocation strategies and their robustness to varying radio conditions. The statistical multiplexing can be used to smooth out the burstiness of video streams and avoid over-provisioning of transport channels. We study the statistical multiplexing gains of H.264 video streams, both in terms of bit-rate requirements and video quality. When multiple flows are multiplexed on a shared transport channel, multi-user scheduling becomes crucial for the performance. Channel-aware scheduling exploits fluctuations in radio conditions to optimize the assignment of channel resources. We study the impact of channel-aware scheduling on the performance of delay-sensitive applications and possible extensions of channel-aware schemes to multicast scenarios. In the area of mobility-assisted content distribution, we study the resource efficiency of mobility-assisted podcasting and we propose an analytical model for pedestrian content distribution. The mobility-assisted podcasting exploits random encounters of mobile terminals equipped with short range radios to forward the podcast episodes, thereby relieving the strain on cellular networks. We provide results on the achievable spectrum and energy savings of such scheme. Finally, we introduce the “street model”, the first building block in a conceived library of analytical models that would be used to study the performance of pedestrian content distribution in some common case scenarios of urban mobility. Based on the “street model”, we study how various system parameters and node mobility affect the efficiency of content distribution in a grid of streets that represents a part of Stockholm’s downtown area. / QC20100618

This thesis considers the joint design of bit loading, precoding and receive filters for a multiple-input multiple-output (MIMO) digital communication system. Both the transmitter and the receiver are assumed to know the channel matrix perfectly. It is well known that, for linear MIMO transceivers, orthogonal transmission (i.e., diagonalization of the channel matrix) is optimal for some criteria such as maximum mutual information. It has been shown that if the receiver uses the linear minimum mean squared error (MMSE) detector, the optimal transmission strategy is to perform bit loading on orthogonal subchannels. In the first part of the thesis, we consider the problem of designing the transceiver in order to minimize the probability of error given maximum likelihood (ML) detection. A joint bit loading and linear precoder design is proposed that outperforms the optimal orthogonal transmission. The design uses lattice invariant operations to transform the channel matrix into a lattice generator matrix with large minimum distance separation at a low price in terms of transmit power. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere-packing properties. An algorithm for this power minimization is presented along with a lower bound on the optimization. Apparently, given the optimal ML detector, orthogonal subchannels are (in general) suboptimal. The ML detector may suffer from high computational complexity, which motivates the use of the suboptimal but less complex MMSE detector. An intermediate detector in terms of complexity and performance is the decision feedback (DF) detector. In the second part of the thesis, we consider the problem of joint bit loading and precoding assuming the DF detector. The main result shows that for a DF MIMO transceiver where the bit loading is jointly optimized with the transceiver filters, orthogonal transmission is optimal. As a consequence, inter-symbol interference is eliminated and the DF part of the receiver is actually not required, only the linear part is needed. The proof is based on a relaxation of the discrete set of available bit rates on the individual subchannels to the set of positive real numbers. In practice, the signal constellations are discrete and the optimal relaxed bit loading has to be rounded. It is shown that the loss due to rounding is small, and an upper bound on the maximum loss is derived. Numerical results are presented that confirm the theoretical results and demonstrate that orthogonal transmission and the truly optimal DF design perform almost equally well. An algorithm that makes the filter design problem especially easy to solve is presented. As a byproduct from the work on decision feedback detectors we also present some work on the problem of optimizing a Schur-convex objective under a linearly shifted, or skewed, majorization constraint. Similar to the case with a regular majorization constraint, the solution is found to be the same for the entire class of cost functions. Furthermore, it is shown that the problem is equivalent to identifying the convex hull under a simple polygon defined by the constraint parameters. This leads to an algorithm that produces the exact optimum with linear computational complexity. As applications, two unitary precoder designs for MIMO communication systems that use heterogenous signal constellations and employ DF detection at the receiver are presented. / QC 20100624

Future wireless communication systems will utilize the spatialproperties of the wireless channel to improve the spectralefficiency and thus increase capacity. This is realized bydeploying multiple antennas at both the transmitter and receiver.Development and analysis of communication systems utilizing thespatial properties of the channel requires channel models thatproperly reflect these characteristics. Due to the unpredictable nature of the wireless channel, a commonapproach is to model its effects statistically. A few largeworld-wide cooperations, like the third generation partnershipproject (3GPP) or wireless world initiative new radio (WINNER)project, have developed channel models intended for reference andstandardization use. These models are partly based on some bulkparameters that describe the characteristics of the channel overlarger areas of several wavelengths. Such parameters includeshadow fading, angle spread, and delay spread, among others, andare within the WINNER project called large-scale (LS) parameters.In the spatial channel model (SCM) and the WINNER model, theselarge-scale parameters are, however, assumed independent betweenseparate links, i.e., between channels modelling the propagationbetween one mobile and several base stations, or between one basestation and several mobiles. Such assumptions may be valid forsingle-link, singe-cell systems, where each communication link issufficiently separated in either time or frequency. In practice,dependencies between parameters describing separate wirelesschannels is expected. Future systems will allow a dense frequencyreuse, and results from system evaluations based on models withindependent links may be inaccurate. Examples of this may be insystems that exploit the spatial nature of the channel, likemulti-user scheduling using a single carrier, or macro-diversitysystems deploying several base stations. Therefore, it isimportant to analyze multi-node measurements in order to extractand characterize this channel dependence. This thesis focuses on representing the wireless channelstatistically. Through unique multi-site channel measurements andanalysis, key parameters describing the channel namely shadowfading, delay spread and angle spread at both the base station andthe mobile station are extracted. For these parameters, the firstand the second order statistics are derived, and plausibledistributions and models are proposed. Further, the spatial andcorrelation properties of these parameters are analyzed. Moreover,a study highlighting the effect of the independent channelassumption is given, showing the importance of modelling thespatial dependence between the LS parameters when analyzingsystems that utilize the channel's spatial properties.Incorporating the models and correlation properties found hereinfor the LS parameters results in channel models appropriate formulti-node communication analysis and evaluation. / QC20100720 / ACCESS

In the last few years we have been witnessing the beginning of a revolution in the world of wireless communication. The recent launch of advanced smartphones in the mobile market has been welcomed by mobile operators as an opportunity to finally fulfill the promises of 3G and increase the uptake of mobile services. Driven by unprecedented user experience and flat rate pricing, the success of novel mobile platforms for accessing multimedia content and applications has gone far beyond the most optimistic of expectations. Data-hungry services are currently creating significant capacity limitations in many networks, and projections on future content consumption anticipate that with the next generation of mobile devices the stress on cellular infrastructures will increase. Rolling-out additional capacity is not the most profitable of solutions given the current cost structure of mobile infrastructures. Instead, a significant cost reduction can be achieved by revolutionizing the current content provision paradigm. Accordingly, this thesis proposes solutions for making future services and infrastructures more affordable. From an operator perspective, terminal-to-terminal information forwarding has the potential to increase both coverage and capacity, however it introduces opportunity costs and energy losses at the user side. Resource delegation, together with an energy reimbursement scheme, is presented in this thesis to induce user cooperation. The results show that this approach is successful in fostering significant cooperation among users and can create a simultaneous improvement in user utility, data rates and operator revenues. Opening up for public access privately deployed WLANs might radically lower the cost of wireless services. However, since these networks are deployed in an uncoordinated manner, only discontinuous coverage can be provided. To hide the sparsity of the infrastructure to the end-user perception we propose the adoption of opportunistic schemes for content pre-fetching. Results show that already with moderate AP densities a set of archetypical services, including web-browsing, can be provided with sufficient user perceived quality. Epidemic exchange of popular content, and inter-AP cooperation are also shown to further decrease the required AP density. Moreover, to support informed access selection decisions when performing vertical handovers to WLANs, we propose “Word-of-Mouth”, a reputation-based scheme for revealing the QoS of different networks. By epidemically exchanging grades on their experienced service quality, we show that terminal agents can collectively improve their decision making, avoiding selecting networks not meeting the required QoS. Context-based content delivery is presented in this thesis as means to improve the utilization of wireless resources in cellular systems. Since networks are typically dimensioned for peak hour traffic, the BSs are underutilized for significant portions of the day. By adopting context-based architectures, capable of opportunistically utilizing the instantaneous excess of resources for content pre-fetching, we show that a significant amount of additional traffic can be served in already existing networks. The gains introduced by this content provision paradigm over the current “on-demand” solutions are further expressed in terms of lower requirements on BS density, more users in the system and larger files served while reaching the same level of user experience. / QC20100716

The use of multiple transmit antennas is considered a key ingredient to significantly improve the spectral efficiency of wireless communication systems beyond that of currently employed systems. Transmit beamforming schemes have been proposed to exploit the spatial characteristics of multi-antenna radio channels; that is, multiple-input single-output (MISO) channels. In multiuser communication systems, the downlink throughput can be significantly increased by simultaneously transmitting to several users in the same timefrequency slot, by means of spatial-division multi-access (SDMA). Several SDMA beamforming algorithms are available for joint optimal beamforming and power control for the downlink. Such optimal beamforming minimizes the total transmission power, while ensuring an individual target quality of service (QoS) for each user; alternatively the weakest QoS is maximized, subject to a transmit power constraint. In this thesis, both of these formulations are considered and some of the available algorithms are generalized to enable quadratic shaping constraints on the beamformers. By imposing additional constraints, the QoS measure can be extended to take factors other than the customary signal to interference-plus-noise ratio (SINR) into account. Alternatively, other limitations such as interference requirements or physical constraints may be incorporated in the optimization. The proposed beamforming algorithms are also based on a more general SINR expression than previously analyzed in this context. The generalized SINR expression allows for more accurate modeling; for example, non-zero self interference can be modeled in code-division multi-access (CDMA) systems. A major limiting factor for downlink resource allocation is the amount of channel-state information (CSI) available at the base station. In most cases, CSI can be estimated only at the receivers, and then fed back to the base station. This procedure typically constrains the amount of CSI that can be conveyed. In this thesis, a minimum mean squared-error (MMSE) SINR estimation framework is proposed, which combines partial CSI with channel-distribution information (CDI); the CDI varies slowly and is assumed to be known at the transmitter. User selection (scheduling) and beamforming techniques, suitable for the MMSE SINR estimates, are also proposed. Special attention is given to the feedback of a scalar channel-gain information (CGI) parameter. The CSI provided by CGI feedback is studied in depth for correlated Rayleigh and Ricean fading channels. It is shown, using asymptotic analysis, that large realizations of the CGI parameter convey additional spatial CSI at the transmitter; the proposed scheme is thus ideal for multiuser diversity transmission schemes, where resources are allocated only to users experiencing favorable channel conditions. It is shown by numerical simulations that, in wide-area scenarios, feeding back a single scalar CGI parameter per user, provides sufficient information for the proposed downlink resource-allocation algorithms to perform efficient SDMA beamforming and user selection / QC 20100712

Wireless access to the Internet is expected to be very valuable for both individuals and the society. However, advances in transmission technology alone may not be sufficient to support the anticipated demand for higher data rates and greater traffic volumes. Fortunately, a low cost means of increasing capacity is to match wireless infrastructures to the non-uniform spatial distribution of traffic. Multiple radio access standards and base station classes, having different cost and performance, could be combined to create a heterogeneous wireless access network which provides the required data rates and capacities where needed (or desired). In the case of a non-uniform spatial distribution of traffic, the traditional technical performance measures of coverage and capacity are no longer adequate for comparing the cost effectiveness of different network configurations. Therefore in this dissertation, we propose a general methodology to evaluate the total cost and capacity of heterogeneous networks. Moreover, a few promising capacity expansion paths, including multiple cellular standards as well as wireless local area network technologies, have been evaluated for urban scenarios. While results show that macro cellular systems are the most cost effective solution for a uniform spatial traffic distribution, a complementary hot spot layer is for non-uniform traffic distributions required even at a moderate average traffic density. The incremental cost, which is modest as compared to current revenues for operators, is shown to be quite insensitive to the choice of technology used in the hot spot layer. Moreover, if high data rates are demanded on the uplink, then dedicated indoor solutions are required. Which in turn implies that network providers should exploit existing broadband infrastructures to provide the required backhaul connectivity. In order to address non-urban scenarios, especially in sparsely populated areas, where there is insufficient revenue to support multiple independent networks, a multi-operator network sharing network architecture should be employed. This dissertation proposes a priority queuing method to achieve fair sharing of radio resources between operators in such an architecture. / QC 20100730