1,721,032 research outputs found
Minimum cell size for information capacity increase in cellular wireless network
Full text linkIn conventional cellular wireless communication system, interference modelling has focused on the six primary co-channel interfering cells (first tier co-channel cells). In the current accepted interference model, co-channel interfering cells beyond the first tier (subsequent tier co-channel cells) are neglected. This currently accepted interference models is suitable for cellular wireless communication systems operating at carrier frequencies, f c = 0.9 and 1.8 GHz, cell size radii R > 1 km and basic path loss exponent α ≥ 2. The future and emerging wireless communication systems are expected to be operating at frequencies f c > 2 GHz (3.35 - 15.75 GHz), cell size radii R≤ 1 km and basic path loss exponent α ≤ 2. This, makes the current acceptable co-channel interference model unsuitable for information capacity analysis of the future cellular systems. Therefore, a co-channel interference model suitable for future and emerging wireless communication system becomes necessary.
In this thesis a new and modified interference model is proposed. The proposed interference model includes the first and subsequent tier co-channel interfering cells. The proposed interference model will be suitable for cellular wireless communication systems operating at carrier frequencies f c > 2 GHz, cell size radii R≤ 1 km and basic path loss exponent α ≤ 2. A mathematical analysis, supported by computer simulation is used, to study the uplink information capacity performance for the conventional and proposed interference model. The analysis and simulation results of the proposed interference model show that at carrier frequencies f c > 2 GHz, co-channel interfering cells beyond the first tier become active as cell size radius R, reduces. As an example for a carrier frequency f c = 15.75 GHz, cell size radius R = 100 m at a normalized reuse distance Ru = 4, there was a 15.32 % decrease in the information capacity between the conventional and proposed interference model.
An information capacity - cost analysis is used to find a minimum cell size for information capacity increase in cellular wireless network, thus a theoretical limit to cell size reduction. The results show that as the cell size radius R reduces to 300 m and less, the proposed interference model show a 5.76 - 18.89 % decrease in the information capacity per unit cost (£, $, etc) at microwave carrier frequencies f c > 3.35 GHz. This result illustrates that there is a theoretical limit to cell size reduction in relation to information capacity performance and cost.
An inductive approach is used to generate a formula for calculating the number of co-channel interfering cells Nn in a cellular wireless site layout. Such a formula allows one to calculate the number of co-channel interfering cells in subsequent tiers of a cellular wireless site layout. The geometric derivation shows that the number of co-channel interfering cell Nn in a subsequent tier is the product of the number of co-channel interfering cells in the first tier NI and the tier number n. Thus, the number of co-channel interfering cell in a subsequent tier Nn = NI × n. This formula enables subsequent tier co-channel interference to be included in the information capacity analysis of future and emerging, and finding the minimum cell size for information capacity increase in a cellular wireless communication system
Spectrum aggregation for dynamic spectrum access based cognitive networks
Full text linkTelecommunication standards bodies and vendors all over the world are seeking ways of continuing the evolution of mobile communication technology on to its next generation. Providing ubiquitous broadband access to all mobile users distributed in a given area with a fragmented spectrum remains a challenging task. This thesis contributes to the global efforts by extending bandwidth by means of Spectrum Aggregation (SA) in Next Generation Mobile Networks (NGMN).
First of all, the motivation behind SA for NGMN is investigated. SA is introduced to create large virtual carrier bandwidths for data hungry users by aggregating fragmented segments of spectrum. By using SA, multiple carriers with different bandwidths, dispersed within intra or inter-bands, can be simultaneously utilised to provide higher data rates, better coverage and simplified multi-band traffic management, resulting in an enhanced user quality of experience. However, SA functionality introduces new challenges for transceiver architecture and Radio Resource Management (RRM) functionality of the network.
Secondly, spectrum assignment for cognitive radio networks with SA is investigated. For this purpose, an aggregation-based spectrum assignment is formulated as an integer optimisation problem. The problem is solved using a genetic algorithm to exploit the discontinuity of the available spectrum and to achieve higher capacity gains. The formulation not only considers interference to primary users but also takes into account co-channel interference among secondary users and maximum aggregation span. Simulation results clearly show that the proposed algorithm outperforms state-of-the-art solutions in terms of spectrum utilisation and higher convergence rate.
Thirdly, RRM in Long-Term Evolution (LTE) networks with SA is considered. It is shown that the optimal solution of RRM in different scenarios can be achieved by solving the relaxed optimisation problem. The optimum RRM algorithm with reduced complexity is proposed and compared with the current solutions in literature. The proposed algorithm optimally assigns component carriers, resource blocks, modulation and coding scheme values based on users' channel state information and SA capabilities. Simulation results clearly show that the proposed algorithm outperforms current solutions in terms of cell throughput and user throughput fairness.
Last but not least, resource allocation with SA for orthogonal frequency-division multiplexing based networks is studied. A joint resource allocation problem with SA functionality is formulated and sub-optimal solutions with low computational complexity are proposed. Simulation results verify that the proposed algorithms achieve near optimum throughput and exploit the multi-carrier diversity of wireless systems
Adaptive MMSE multiuser receivers in MIMO OFDM wireless communication systems
Full text linkIn a bid to cope with challenges of increasing demand for higher data rate, better quality of service, and higher network capacity, there is a migration from Single Input Single Output (SISO) antenna technology to a more promising Multiple Input Multiple Output (MIMO) antenna technology. On the other hand, Orthogonal Frequency Division Multiplexing (OFDM) technique has emerged as a very popular multi-carrier modulation technique, thus it is considered as a promising solution to enhance the data rate of future broadband wireless communication systems.
The first contribution of this thesis is the development of a low complexity adaptive algorithm that is robust against slow and fast fading channel scenarios, in comparison to the conventional individual parameter estimation by E. Teletar in his famous paper of 1999. Implementing the Adaptive MMSE Receivers in MIMO OFDM systems which I refer to (AMUD MIMO OFDM), combines the adaptive minimum mean square error multiuser receiver's scheme with prior information of the channel and interference cancelation in the spatial domain, achieves enhanced joint channel estimation and signal detection which makes the new technique effectively mobile.
A mathematical analysis and simulation results to estimate the Information Capacity of Mobile Communication system with MMSE DFE and OFDM receivers were investigated. The capacity of a stationary channel with ISI is achievable by both the single carrier MMSE DFE and multicarrier modulation over narrow sub channels with OFDM receivers. The achieved capacity result shows that in both techniques single carrier and multicarrier, apart from different implementations are essentially identical when it comes to achievable criteria for information channel capacity.
Lastly, AMUD MIMO OFDM were compared with both adaptive vector pre-coding and iterative system and their performance were fantastic, results shows that it will assure transmission over a high channel capacity
Power conservation and performance analysis of mobile ad hoc wireless networks
Full text linkMobile ad-hoc network (MANET) have emerged as a new systems and the most promising fields for research and development of wireless network. As the popularity of mobile device and wireless networks significantly increased over the past years, MANET has now become one of the most vibrant and active field of communication and networks. Due to severe challenges such as the open medium, unpredicted mobility of mobile nodes, distributed and cooperative communication and inherently constrained capabilities, which manifest exhaustible sources of power. Due to the increasing demand for high-speed data services, the limited and high cost of licensed, and the future MANETs are expected to be operating at frequencies greater than 2 GHz and most of the research work in the area has been done in the frequency range of 1-2 GHz.
In this thesis, a power conservation model is proposed. The proposed model is based on the conventional on-demand ad hoc routing protocols with the addition of a power model without incurring additional complexity on the existing MANET characteristics. The mobile nodes are able to computes their power their power status adaptively to decide if they are fit for packet forwarding and reception. The research illustrates the power conserving behaviour of the new technique using an analytical approach and also by computer simulations. The results have shown that power savings of more than 15% were achieved with not much delay in the network. The performance of the routing protocols in the presence of ambient noise in the network was analyzed as well as the sensitivity of MAANETs at a carrier frequencies above 2 GHz using the free space and two slope path loss model. Results show that at carrier frequency greater than 2 GHz the break point distance affects the throughput performance of the network, whilst at frequency less than 2 GHz, the throughput performance for the free space and two slope model was the same
Time varying channel models for 5G mobile communication systems
Full text linkResearchers all over the world are looking for ways of continuing the evolution of mobile communication technology to its fifth generation (5G). Providing high data rate information transfer to highly mobile users over time varying communication channels remains a shared obstacle. In this thesis, we contribute to these global efforts by providing further fundamental understanding of time varying channels in 5G mobile communication systems and overcome the obstacle.
First, we reopen the door of research in the field of time varying communication channels. The door has almost been closed before by a well-accepted conclusion related to the types of channels. It was ‘proven’ that mutual information rate of the uniformly symmetric variable noise finite state Markov channel (USVNFSMC) was maximized by input signals of maximum information entropy. The result means time varying channels and time invariable channels are identical, regarding information rate maximization over input signal probability distribution. We provide evidence that assumptions for the results are not valid for time varying channels and replace them with more practical ones. We confirm, via input signals of non-uniform independent distribution and first order Markov chain, that the mutual information rate of the USVN-FSMC is maximized by input signals with information redundancy.
Second, we provide a solution which dramatically reduces the waste of communication resources in estimating channel state information of time varying mobile communication channels. The orthodox method in dealing with time varying channels is that, the channel is “cut” to pieces in time domain to look like a sequence of time invariable channels for the purpose of state estimation. By doing this the capacity loss is staggering for n-times higher carrier frequency channels and
n-dimensional multiple input and multiple output channels, eliminating almost entirely the capacity gain of these two most promising capacity-increasing techniques for 5G. We define the simplest finite state Markov model for time varying channels to explain the essential difference between information processing of time varying channels and time invariable channels. We prove that the full information capacity of the model can be achieved by the differential type encoding/decoding scheme without employing any conventional channel state estimator
Turbo coding and equalization for wireless communication systems
Full text linkTurbo coding, a forward error correcting coding (FEC) technique, has made near Shannon Limit performance possible when Iterative decoding algorithms are used. Intersymbol interference (ISI) is a major problem in communication systems when information is transmitted through a wireless channel. Conventional approaches implement an equalizer to remove the ISI, but significant performance gain can be achieved through joint equalization and decoding.
In this thesis, the suitability of turbo equalization as a means of achieving low bit error rate for high data communication systems over channels with intersymbol interference was investigated. A modified decision feedback equalizer algorithm (DFE) that provides significant improvement when compared with the conventional DFE is proposed. It estimates the data using the a priori information from the SISO channel decoder and also a priori detected data from previous iteration to minimize error propagation.
Investigation was also carried out with Iterative decoding with imperfect minimum mean square error (MMSE) decision feedback equalizer, assuming soft outputs from the channel decoder that are independent identically distributed Gaussian random variables. The prefiltering method is considered in this thesis, where an all-pass filter is employed at the receiver before equalization to create a minimum phase overall impulse response.
The band limited channel suffers performance degradation due to impulsive noise generated by electrical appliances. This thesis analysed a set of filter design criteria based on minimizing the bit error probability of impulse noise using digital smear filter
Optimisation and algorithms in wireless networks for mission critical applications
Full text linkThe focus of this dissertation is to present novel algorithms and techniques in wireless network systems aiming at performance optimisation. This thesis provides contribution to knowledge on the following topics: (a) sum rate maximisation of two interfering users in an Orthogonal Frequency Division Multiple Access (OFDMA)-based cooperative base stations and (b) event-region detection in Wireless Sensor Networks (WSNs).
The first area of work makes contribution on problem of maximising the sum rate of two interfering users, while limiting the received interference at each user. An OFDMA-based system operating in downlink is considered. Comparisons between achieved average spectral efficiency of proposed interference power constraint resource allocation scheme as opposed to achieved average spectral efficiency by non-cooperative Time Division Multiple Access (TDMA) method is provided to prove that the proposed cooperative Base Stations (BSs) scheme outperforms non-cooperative TDMA.
The second area of work makes contribution on problem of event region and event boundary detection in WSNs. A new method for classifying randomly deployed sensor nodes over an area of interest into distinctive categories is provided. In this work, a network of spatially distributed and wirelessly connected sensor nodes commissioned to detect two different phenomena, occurring in distant parts of an area of interest, is considered. Analysis on correlation between statistical attributes of received signal distribution at each node and the node’s regional position with respect to two events is provided. Simulation results proves that each node can acknowledge its regional position based only on the statistical attributes of its own environmental readings. This is a promising approach because if only the nodes placed in the close by region of each phenomena report back their reading to the Base Station (BS), as opposed to transmitting entire readings from all nodes, the required bandwidth reduces to be proportional to the size of that event-region only
Adaptive signal combining and detection in cooperative wireless networks
Full text linkIn this research adaptive algorithms were developed for multiuser detection and signal combining in cooperative wireless networks. Some of the key contributions and works of this research thesis are: 1. A computationally simple Adaptive Minimum Mean Square Error Multiuser Detection scheme was proposed to eliminate multiple access interference in uplink communication of an asynchronous cooperative CDMA wireless network, where users cooperate in a relaying mode while they exchange data and channel information with the destination node. The proposed scheme provides better interference resistance than optimum multiuser detection Maximum Likelihood Sequence Estimation in cooperative wireless networks. The performance was examined under Amplify-and-Forward and Decode-and-Forward cooperative protocols in flat fading Rayleigh wireless channels. 2. Adaptive signal combining was proposed for cooperative wireless networks and its performance was analysed by using Least Mean Square and Recursive Least Square algorithms. The other classical non-adaptive techniques Maximal Ratio Combining and Wiener were also examined. It was also shown that adaptive signal combining achieves Wiener's solution in cooperative wireless networks with added benefit of computational simplicity over classical combining schemes. 3. Weighted Least Square Error Method of signal combining was proposed for wireless signal combining, where estimates of inverse of the channel noise variance was used as weight of the combiner. The proposed method was a receiver with noise estimation filters at each received branch for the noise estimation. The reciprocal of the estimate of the channels noise variance were used as weights of combiner to achieve Wiener’s solution of signal combining. The proposed algorithm was used in cooperative, non cooperative wireless networks and multiple antennas system. It was also shown that un weighted least square error method is equivalent to equal gain combining scheme. The performance of the proposed mathematical algorithms were examined with computer simulations in various wireless channel models
Requirement driven knowledge management system design to support automotive product development
Full text linkNowadays, New Product Development (NPD) has become a business priority in manufacturing companies due to international competition in terms of meeting higher and changing customer requirements, generating high profit at low cost, and maintaining sustainable development and growth. Through literature review and industrial investigations, it has been recognised that NPD is an information and knowledge intensive process. However, in current practice, enterprise knowledge is not properly managed or easily accessible. Many service providers have not followed the good practice of considering business objectives and end users’ requirements as main drivers of knowledge management system development and implementation.
This doctoral thesis presents a methodology for the design and development of Knowledge Management (KM) systems to support NPD based on Enterprise Architecture Frameworks (EAFs). The project focuses on IT system specifications
generation driven by business and knowledge users’ requirements in the automotive industry. Current EAFs have been developed by researchers and practitioners to help enterprises to design their information systems based on business objectives and user requirements. However, these frameworks are mainly proposed to manage information and data such as finances, resources, management and engineering
documents, not for the increasingly important enterprise knowledge, especially tacit and unstructured knowledge.
This project aims to extend the capabilities of the latest enterprise architecture frameworks so that not only data and information, but also enterprise knowledge can be managed. A guideline in the form of a flowchart has been developed, which provides a process that can be followed and used by system developers and implementation. The extended EAF has been implemented as easy-to-use folders for the development of a structured knowledge base. A case study in an automotive company proved that the methodology can be used to produce the functional specifications of their IT systems to include knowledge management capability. The system specification can then be used, either to assess a company’s existing information systems and direct its future system development and implementation; or to develop/implement a complete new information system from scratch
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