No. 1 (2006)
Published:
2006-03-30
ARTICLES FROM THIS ISSUE
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Gaze-J2K: gaze-influenced image coding using eye trackers and JPEG 2000
Abstract
The use of visual content in applications of the digital computer has increased dramatically with the advent of the Internet and world wide web. Image coding standards such as JPEG 2000 have been developed to provide scalable and progressive compression of imagery. Advances in image and video analysis are also making human-computer interaction multi-modal rather than through the use of a keyboard or mouse. An eye tracker is an example input device that can be used by an application that displays visual content to adapt to the viewer. Many features are required of the format to facilitate this adaptation, and some are already part of image coding standards such as JPEG 2000. This paper presents a system incorporating the use of eye tracking and JPEG 2000, called Gaze-J2K, to allow a customised encoding of an image by using a user’s gaze pattern. The gaze pattern is used to automatically determine and assign importance to fixated regions in an image, and subsequently constrain the encoding of the image to these regions.
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Benchmarking image codecs by assessment of coded test images: the development of test images and new objective quality metrics
Abstract
Objective quality measures are required for benchmarking codec performance. Our aim was to develop a simple, accurate method capable of rapidly measuring the degree of blockiness, edge-blur and ringing due to image compression. Two test images were designed to emphasise these artefacts. The efficacy of the new metrics is demonstrated using a JPEG codec at a range of compression levels.
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Application of convolutional interleavers in turbo codes with unequal error protection
Abstract
This paper deals with an application of convolu- tional interleavers in unequal error protection (UEP) turbo codes. The constructed convolutional interleavers act as block interleavers by inserting a number of stuff bits into the interleaver memories at the end of each data block. Based on the properties of this interleaver, three different models of UEP turbo codes are suggested. Simulation results confirm that uti- lizing UEP can provide better protection for important parts of each data block, while significantly decreasing the number of stuff bits.
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An identity-based broadcast encryption scheme for mobile ad hoc networks
Abstract
Dynamic ad hoc networks facilitate interconnections between mobile devices without the support of any network infrastructure. In this paper, we propose a secure identity-based ad hoc protocol for mobile devices to construct a group key for a setup of a secure communication network in an efficient way and support dynamic changing of network topology. Unlike group key management protocols proposed previously in the literature, mobile devices can use our protocol to construct the group key by observing the others’ identity, like the MAC address, which distinguishes the device from the others. In contrast to other interactive protocols, we only need one broadcast to setup the group key and member removal is also highly efficient. Finally, we discuss the security issues and provide security proofs for our protocol.
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An adaptive LQG TCP congestion controller for the Internet
Abstract
This paper addresses the problem of congestion control for transmission control protocol (TCP) traffic in the Internet. The method proposed builds on the ideas of TCP Vegas, a true feedback control approach to congestion management of TCP traffic. The new method is based on an adaptive linear quadratic Gaussian (LQG) formulation which uses an extended least squares system identification algorithm com- bined with optimal LQG control. Simulation experiments indicate that the new technique inherits good equilibrium properties from TCP Vegas, but has much superior transient responses which, the paper argues, is important for good dynamic congestion control.
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Load-balanced route discovery for mobile ad hoc networks
Abstract
This paper presents flow-aware routing protocol (FARP), a new routing strategy designed to improve load balancing and scalability in mobile ad hoc networks. FARP is a hop-by-hop routing protocol, which introduces a flow-aware route discovery strategy to reduce the number of control overheads propagating through the network and distributes the flow of data through least congested nodes to balance the network traffic. FARP was implemented in GloMoSim and compared with AODV. To investigate the load distribution capability of FARP new performance metrics were introduced to measure the data packet flow distribution capability of the each routing protocol. The simulation results obtained illustrate that FARP achieves high levels of throughput, reduces the level of control overheads during route discovery and distributes the network load more evenly between nodes when compared to AODV. This paper also describes a number of alternative strategies and improvements for the FARP.
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Effect of unequal power allocation in turbo coded multi-route multi-hop networks
Abstract
Multi-hop ad hoc networks are promising candidates for next generation mobile communications. They have sufficient channel capacity to achieve high data rate transmission for large number of users. One advantage of multi-hop networks is to realize multi-route transmissions. Since information bit streams can be transmitted over multiple routes, we can obtain route diversity effect. In order to enhance the route diversity effect, we usually introduce forward error correction schemes. Turbo coding is one of suitable coding methods for multi-hop networks. The turbo encoder generates one message stream and two parity streams whilst the message stream is more important than the parity streams for achieving reliable communications. Thus an unequal power allocation to the message and parity streams could be effective in improving the performance. In this paper, the effect of unequal power allocation for turbo coded multi-hop networks is investigated. Assuming the channel as additive white Gaussian and binary symmetric, we will show considerable performance improvement by unequal power allocation in terms of the bit error rate performance in multi-route multi-hop networks.
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An adaptive iterative receiver for space-time coding MIMO systems
Abstract
An adaptive iterative receiver for layered space-time coded (LSTC) systems is proposed. The proposed receiver, based on a joint adaptive iterative detection and decoding algorithm, adaptively suppresses and cancels co-channel interference. The LMS algorithm and maximum a posteriori (MAP) algorithm are utilized in the receiver structure. A partially filtered gradient LMS (PFGLMS) algorithm is also applied to improve the convergence speed and tracking ability of the adaptive detector with a slight increase in complexity. The proposed receiver is analysed in a slow and fast Rayleigh fading channels in multiple input multiple output (MIMO) systems.
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Exact pairwise error probability analysis of space-time codes in spatially correlated fading channels
Abstract
In this paper, we derive an analytical expression for the exact pairwise error probability (PEP) of a space-time coded system operating over a spatially correlated slow fading channel using a moment-generating function-based approach. This analytical PEP expression is more realistic than previously published exact-PEP expressions as it fully accounts for antenna spacing, antenna geometries (uniform linear array, uniform grid array, uniform circular array, etc.) and scattering models (uniform, Gaussian, Laplacian, Von-Mises, etc.). Inclusion of spatial information provides valuable insights into the physical factors determining the performance of a space-time code. We demonstrate the strength of our new analytical PEP expression by evaluating the performance of two space-time trellis codes proposed in the literature for different spatial scenarios.
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CDMA wireless system with blind multiuser detector
Abstract
In this paper we present an approach capable of countering the presence of multiple access interference (MAI) in code division multiple access (CDMA) channels. We develop and implement a blind multiuser detector, based on an independent component analysis (ICA) to mitigate both MAI and noise. This algorithm has been utilized in blind source separation (BSS) of unknown sources from their linear mixtures. It can also be used for estimation of the basis vectors of BSS. The aim is to include an ICA algorithm within a wireless receiver in order to reduce the level of interference in CDMA systems. This blind multiuser detector requires less precise knowledge of the channel than does the conventional single-user receiver. The proposed blind multiuser detector is made robust with respect to imprecise knowledge of the received signature waveforms of the user of interest. Several experiments are performed in order to verify the validity of the proposed learning algorithm
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A highly accurate DFT-based parameter estimator for complex exponentials
Abstract
A highly accurate DFT-based complex exponential parameter estimation algorithm is presented in this paper. It will be shown that for large number of samples and high signal to noise ratio (SNR), the phase estimation error variance performance is only 0.0475 dB above the Cramer-Rao lower bound (CRLB) for phase estimation with unknown frequency and phase. The amplitude estimation error variance performance was found to lay on the CRLB for amplitude estimation. Exact phase and amplitude estimation can be achieved in the noiseless case with this algorithm. The algorithm has low implementation computational complexity and is suitable for numerous real time digital signal processing applications.
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Future automation via ubiquitous communications technologies
Abstract
The telecommunications and Internet technologies have evolved dramatically during the last decade, laying solid foundation for the future generation of the ubiquitous Internet access, omnipresent web technologies and ultimate automated information cyberspace. As a result, current efforts in the research and development in the areas of next generation of Internet and telecommunications technologies promote formation of inter-disciplinary international teams of experts, scientists, researchers and engineers to create a new generation of applications and technologies that will facilitate the fully-automated information cyberspace systems, such as future house 2015. The author discusses the current state of the art in the world of telecommunications and Internet technologies, new technological trends in the Internet and automation industries, as well as the concept of the fully-automated future house 2015, while promoting research and development in the inter-disciplinary projects run by multinational teams world-wide.
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Reliability of line-of-sight radio-relay systems
Abstract
The modern radio transmission systems are specifically designed for catching principally two main objectives: on one side to provide a radio solution for long distance where large configurations are required to fulfill the high capacity transmissions needs, on the other side to guarantee link quality as high as possible. The availability of a radio-relay system is dependent upon many factors and particularly upon: the reliability of equipment and propagation conditions. The article describes the wave propagation and equipment that determine the performance of a radio-relay path. National Institute of Telecommunications (NIT) carried out research on propagation phenomena on terrestrial path and exemplary results are described herewith. The availability of radio equipment based on the mean time between failures for equipment modules is presented too.
