244 research outputs found
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Intelligent genetic algorithms for next-generation broadband multi-carrier CDMA wireless networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This dissertation proposes a novel intelligent system architecture for next-generation broadband multi-carrier CDMA wireless networks. In our system, two novel and similar intelligent genetic algorithms, namely Minimum Distance guided GAs (MDGAs) are invented for both peak-to-average power ratio (PAPR) reduction at the transmitter side and multi-user detection (MUD) at the receiver side. Meanwhile, we derive a theoretical BER performance analysis for the proposed MC-CDMA system in A WGN channel. Our analytical results show that the theoretical BER performance of synchronized MC-CDMA system is the same as that of the synchronized DS-CDMA system which is also used as a theoretical guidance of our novel MUD receiver design. In contrast to traditional GAs, our MDGAs start with a balanced ratio of exploration and exploitation which is maintained throughout the process. In our algorithms, a new replacement strategy is designed which increases significantly the convergence rate
and reduces dramatically computational complexity as compared to the conventional GAs. The simulation results demonstrate that, if compared to those schemes using exhaustive search and traditional GAs, (1) our MDGA-based P APR reduction scheme achieves 99.52% and 50+% reductions in computational complexity, respectively; (2)
our MDGA-based MUD scheme achieves 99.54% and 50+% reductions in computational complexity, respectively. The use of one core MDGA solution for both issues can ease the hardware design and dramatically reduce the implementation cost in practice
Low delay video coding
Analogue wireless cameras have been employed for decades, however they have not become an universal solution due to their difficulties of set up and use. The main problem is the link robustness which mainly depends on the requirement of a line-of-sight view between transmitter and receiver, a working condition not always possible. Despite the use of tracking antenna system such as the Portable Intelligent Tracking Antenna (PITA [1]), if strong multipath fading occurs (e.g. obstacles between transmitter and receiver) the picture rapidly falls apart. Digital wireless cameras based on Orthogonal Frequency Division Multiplexing (OFDM) modulation schemes give a valid solution for the above problem. OFDM offers strong multipath protection due to the insertion of the guard interval; in particular, the OFDM-based DVB-T standard has proven to offer excellent performance for the broadcasting of multimedia streams with bit rates over 10 Mbps in difficult terrestrial propagation channels, for fixed and portable applications. However, in typical conditions, the latency needed to compress/decompress a digital video signal at Standard Definition (SD) resolution is of the order of 15 frames, which corresponds to ≃ 0.5 sec. This delay introduces a serious problem when wireless and wired cameras have to be interfaced. Cabled cameras do not use compression, because the cable which directly links transmitter and receiver does not impose restrictive bandwidth constraints. Therefore, the only latency that affects a cable cameras link system is the on cable propagation delay, almost not significant, when switching between wired and wireless cameras, the residual latency makes it impossible to achieve the audio-video synchronization, with consequent disagreeable effects. A way to solve this problem is to provide a low delay digital processing scheme based on a video coding algorithm which avoids massive intermediate data storage. The analysis of the last MPEG based coding standards puts in evidence a series of problems which limits the real performance of a low delay MPEG coding system. The first effort of this work is to study the MPEG standard to understand its limit from both the coding delay and implementation complexity points of views. This thesis also investigates an alternative solution based on HERMES codec, a proprietary algorithm which is described implemented and evaluated. HERMES achieves better results than MPEG in terms of latency and implementation complexity, at the price of higher compression ratios, which means high output bit rates. The use of HERMES codec together with an enhanced OFDM system [2] leads to a competitive solution for wireless digital professional video applications
Effect of Data Flow Architecture on Programming Language Design
This study is concerned with the aspects of data flow architecture. A survey of data flow processors is presented. The two broad classes of languages, procedural and applicative, are considered for the language design for the data flow architecture. Starting from the basic data flow program representation, the study extendends to the high level languages. Method for translating the conventional presented. language to data flow representation is Consideration is given to the conventional structured languages. A general discussion of usage of appli.cative language classes are presented, without considering specific syntax. The material presented can be extended to specific syntax design and its practical use can be studied from the given general discussions.Computing and Information Sciences
Computer architectures for functional and logic languages
PhD ThesisIn recent years interest in functional and logic languages has
grown considerably. Both classes of language offer advantages for programming
and have an influential group of people promoting them. As yet
no consensus has formed as to which class is best, and such a consensus
may never form. Future general-purpose computer architectures may well
be required to support both classes of language efficiently. Novel
architectures designed to support both classes of languages could even
add impetus to the area of hybrid functional/logic languages.
Treleaven et al[68] have proposed a classification of computational
mechanisms which they believe underly several types of novel computer
architecture (i.e. control flow, data flow and reduction). The classification
partitions novel general-purpose architectures into the following
classes: control driven - where a statement is executed when it is
selected by flow(s) of control, data driven - where a statement is executed
when some combination of its arguments are available, and demand
driven - where a statement is executed when the result it produces is
needed by another, already active instruction.
This thesis investigates the efficient support of both functional
and logic languages using an architecture that attempts to be general
purpose by embodying all the mechanisms that underly the above classification.
A novel packet communication architecture is presented which intergrates
the control driven, data driven and demand driven computational
mechanisms. A software emulator for the machine was used as the basis
for separate implementations of functional and logic languages, which
were in turn used to evaluate the effectiveness of the computational
mechanisms described in the classification. These mechanisms allowed
functional languages to be implemented wi th ease, but caused severe
problems when used to support logic languages. The difficulties with
these mechanisms are taken as signifying that they do not provide adequate
support for logic languages. The problems encountered led to the
development of a novel implementation technique for logic languages,
which also proved to be a good basis for a combined functional and logic
model. This model is believed to provide a sound foundation for a
parallel computer system that would support functional and logic
languages with equal elegance and efficiency, and would therefore also
support hybrid languages. The design for such a computer is described
at the end of this thesis.the Science and Engineering Research Council, Great Britain
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