By Topic

Communications, IET

Issue 5 • Date March 26 2010

Filter Results

Displaying Results 1 - 11 of 11
  • Implementation of a genetic algorithm-based decision making framework for opportunistic radio

    Page(s): 495 - 506
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (659 KB)  

    The cognitive radio (CR) is known as a radio that can reconfigure its transceiver parameters based on the environmental awareness. The opportunistic radio (OR) is considered in this work, with a narrower definition where the awareness is limited to the spectrum knowledge. The decision making framework is employed as a crucial entity to control the behaviour of the OR. The main purpose is to enable an efficient spectrum usage while avoiding the interference to other users. This study describes the proposed OR decision making framework including the flow of context information as an input process to the decision making engine, the context filtering and the reasoning mechanisms in which the decision optimisation is achieved using a genetic algorithm (GA)-based approach. The system stability of the GA-based reasoning engine is tested through simulations. Then, the experimental study is performed on a test platform for a practical proof of the concept. The test platform is based on the Ettus USRP (Universal Software Radio Peripheral) hardware and the GNU Radio open source software. Several tests were carried out to observe the OR capabilities of the proposed decision making framework. Test environment settings together with the observation results are provided in this study, covering the spectrum sensing and opportunistic channel allocation in the industrial, scientific and medical (ISM) band of 2.4 GHz. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Applying wavelets for the controlled compression of communication network measurements

    Page(s): 507 - 520
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Monitoring and measuring various metrics of high-speed networks produces a vast amount of information over a long period of time making the storage of the metrics a serious issue. Previous work has suggested stream aware compression algorithms, among others, that is, methodologies that try to organise the network packets in a compact way in order to occupy less storage. However, these methods do not reduce the redundancy in the stream information. Lossy compression becomes an attractive solution, as higher compression ratios can be achieved. However, the important and significant elements of the original data need to be preserved. This study proposes the use of a lossy wavelet compression mechanism that preserves crucial statistical and visual characteristics of the examined computer network measurements and provides significant compression against the original file sizes. To the best of authors' knowledge, this is the first study to suggest and implement a wavelet analysis technique for compressing computer network measurements. Here, wavelet analysis is used and compared against the Gzip and Bzip2 tools for data rate and delay measurements. In addition, this study also provides a comparison of eight different wavelets with respect to the compression ratio, the preservation of the scaling behaviour, of the long-range dependence (LRD), of the mean and standard deviation and of the general reconstruction quality. The results show that the Haar wavelet provides higher peak signal-to-noise ratio (PSNR) values and better overall results, than other wavelets with more vanishing moments. Our proposed methodology has been implemented on an online-based measurement platform and compressed data traffic generated from a live network. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • AMNP: ad hoc multichannel negotiation protocol with broadcast solutions for multi-hop mobile wireless networks

    Page(s): 521 - 531
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (653 KB)  

    A multi-hop mobile ad hoc network (MANET) is generally configured as a peer-to-peer network with no centralised hubs or controllers that coordinate channel resources. Nodes in a MANET usually equip one single transceiver for data transmissions. However, the single transceiver architecture will cause a difficulty of being implemented in multichannel environment if the network transmission capacity would be improved by adopting parallel multichannel access. To solve this thorny problem, this study presents a distributed medium access control (MAC) layer protocol called ad hoc multichannel negotiation protocol (AMNP) for multichannel transmissions in the multi-hop MANET. Additionally, two problems, the multichannel hidden terminal problem and the multichannel broadcast transmission problem, caused by single transceiver operations in the multichannel environment, which have not been revealed in academia, is presented and solved in this study. Finally, an enhanced AMNP with channel scheduling (AMNP/s) scheme is introduced to improve the channel utilisation. The author show, via simulations, that AMNP/s provides a higher throughput compared to its single-channel counterpart by promoting simultaneous transmissions in different channels. Simulation results also show that AMNP/s derives higher performance than other multichannel transmission schemes that use multiple transceivers. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Capacity of η-μ fading channels under different adaptive transmission techniques

    Page(s): 532 - 539
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    An analysis for the Shannon channel capacity of digital receivers operating over η-μ fading channels is presented under four adaptive policies: constant power with optimal rate adaptation, optimal power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate. In this context, useful formulae for the average channel capacity for maximal-ratio combining receivers with not necessarily identically distributed branches are derived. The analysis also includes the performance of single-branch receivers. These expressions provide an effective tool to assess the spectral efficiency of the aforementioned adaptive transmission techniques over practical fading channels. Our newly derived expressions include several special cases that arise from the η-μ distribution, namely the Nakagami-m and the Hoyt distribution. Extensive numerical and computer simulation results are also presented that illustrate the proposed mathematical analysis. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Inference of link loss rates by explicit estimation

    Page(s): 540 - 550
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (659 KB)  

    Network tomography has been widely used recently to obtain the network internal characteristics by end-to-end measurement. In this study, the authors consider the problem of estimating link loss rates using network tomography. The existing work based on maximum likelihood estimator (MLE) uses iterative approximation to make the inference, which requires a long execution time for large scale network. To overcome this limitation, the authors propose a fast path-based approach (FPA) by explicit estimation to infer the loss rate of links. Instead of estimating the link loss rates directly, the authors first estimate the path loss rates that are used to derive the link loss rates. In addition, the path loss rates are inferred by a new estimator which is an explicit function of loss observations. The authors evaluate the accuracy of this approach through the analysis of the loss rate estimator and simulation. The estimator is proved to be consistent and have the same asymptotic variance as that of the MLE. The simulation results show that the estimated loss rates using the FPA correctly converge to the real loss rates. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spectrum sharing across multiple service providers via cognitive radio nodes

    Page(s): 551 - 561
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    The rapid growth of wireless industry and continuous emergence of new applications increase the demand for wireless spectrum. However, currently the spectrum assigned to different organisations is not utilised efficiently. Particularly, when an infrastructure of a service provider is overloaded and cannot accommodate more users because of the channel scarcity, the infrastructures of other service providers operating in the same area might be in under-loaded status. However, without a proper spectrum sharing scheme, the overloaded infrastructure cannot use the channels licensed to other service providers. This leads to low spectrum utilisation efficiency and higher call blocking rate of service providers. Significant research has been conducted to study sharing channels between cells within one service provider; however, sharing spectrum across different service providers is still under investigation. This paper proposes deploying a network of fixed cognitive radio (CR) nodes to maintain spectrum sharing across multiple service providers operating in the same geographical area. These CR nodes estimate the spectrum utilisation in a given area, and cooperate to provide the spectrum usage information for the overloaded infrastructures of service providers. This work discusses the implementation of the proposed CR-based spectrum sharing technique, and studies the impact of spectrum sharing on the service provider's performance. It is shown that the proposed technique reduces the call blocking rate and improves the spectrum utilisation efficiency. This technique removes the need of sensing spectrum in each user. Thus, it reduces the cost, complexity and battery power consumption of user devices. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance optimisation of a medium access control protocol with multiple contention slots in multiple-input multiple-output ad hoc networks

    Page(s): 562 - 572
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    The multiple-input multiple-output (MIMO) technique can be used to improve the performance of ad hoc networks. Various medium access control (MAC) protocols with multiple contention slots have been proposed to exploit spatial multiplexing for increasing the transport throughput of MIMO ad hoc networks. However, the existence of multiple request-to-send/clear-to-send (RTS/CTS) contention slots represents a severe overhead that limits the improvement on transport throughput achieved by spatial multiplexing. In addition, when the number of contention slots is fixed, the efficiency of RTS/CTS contention is affected by the transmitting power of network nodes. In this study, a joint optimisation scheme on both transmitting power and contention slots number for maximising the transport throughput is presented. This includes the establishment of an analytical model of a simplified MAC protocol with multiple contention slots, the derivation of transport throughput as a function of both transmitting power and the number of contention slots, and the optimisation process based on the transport throughput formula derived. The analytical results obtained, verified by simulation, show that much higher transport throughput can be achieved using the joint optimisation scheme proposed, compared with the non-optimised cases and the results previously reported. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultra-wideband cognitive interrogator network: adaptive illumination with active sensors for target localisation

    Page(s): 573 - 584
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (593 KB)  

    The authors explore the potential application of cognitive interrogator network (COIN) in remote monitoring of mobile subjects in domestic environments, where the ultra-wideband radio frequency identification (UWB-RFID) technique is considered for accurate target localisation. The authors first present the COIN architecture in which the central base station (BS) continuously and intelligently customises the illumination modes of the distributed interrogators in response to the system's changing knowledge of the channel condition and subject movement. Subsequently, the analytical results of the locating probability and time-of-arrival (TOA) estimation uncertainty for a large-scale COIN with randomly distributed active sensors are derived based upon the implemented cognitive intelligence. As an important component to facilitate the adaptive illumination of the environment, the sequential-hypothesis-testing framework is proposed to estimate the tag antenna orientation. Finally, numerical examples are used to demonstrate the key effects of the proposed cognitive schemes on the system performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance of dual-branch selection combining diversity systems in non-identical Nakagami-q (Hoyt) fading channels

    Page(s): 585 - 595
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (498 KB)  

    Motivated by the low-complexity to implement a dual-branch selection combining system, which is a practical method to improve the performance of a communication system subject to fading, this work studies important performance measures for that system over independent but non-identically distributed Nakagami-q fading channels. In particular, a novel closed-form expression is derived for the moments of the output signal-to-noise ratio (SNR), which is utilised to obtain expressions for the average output SNR, and amount of fading. An expression for the outage probability is also obtained in a closed-form. Furthermore, novel expressions for the channel capacity are derived for two adaptive transmission schemes: the optimal rate adaptation with constant power and channel inversion with fixed rate. The corresponding expressions for one-sided Gaussian and Rayleigh fading are obtained as special cases of Nakagami-q fading. Finally, numerical examples are presented for illustration. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of cooperative diversity with relay selection over non-identically distributed links

    Page(s): 596 - 605
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (771 KB)  

    A performance analysis for cooperative diversity systems with best relay selection over Rayleigh fading channels is presented. The authors obtain analytical expressions for the probability density function (PDF), cumulative density function (CDF) and the moment generating function (MGF) of end-to-end signal-to-noise ratio (SNR) of the system under study for independent and non-identically distributed (i.ni.d.) fading links. Using these expressions the authors derive lower bound closed-form expressions for the average symbol error rate (SER), the outage probability, and an upper bound closed-form expression for the average channel capacity. Using numerical evaluation of the mathematical expressions, system performances of different cases are evaluated and compared for both non-identically and identically distributed links showing the impact of the relay selection in cooperative communication systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of asynchronous multicarrier code division multiple access against direct sequence code division multiple access and long polyphase sequences for uplink powerline communication systems with impulsive noise

    Page(s): 606 - 617
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (605 KB)  

    In this study, the performance of two asynchronous multi-access direct sequence code division multiple access (DS-CDMA) and multicarrier code division multiple access (MC-CDMA) systems with binary and polyphase long sequences is compared. An indoor multipath powerline channel model generated from random impedance networks is used. The powerline background, narrowband and impulsive noise are modelled statistically, based on models and measurements done in previous works. A complete analytical performance study is done for asynchronous MC-CDMA employing an interval guard in the form of a cyclic prefix (CP) and periodic long sequences, which provides a better channel coding than short sequences. The analytical results are completed with Monte Carlo simulations for both, DS-CDMA and MC-CDMA systems. Under impulsive noise an upper bound in the bit error rate (BER) performance for DS-CDMA and MC-CDMA systems is obtained analytically, which is confirmed by the Monte Carlo simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IET Communications covers the theory and practice of systems, networks and applications involving line, mobile radio, satellite and optical technologies for telecommunications, and Internet and multimedia communications.

Full Aims & Scope

Meet Our Editors

IET Research Journals
iet_com@theiet.org