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Communications, IET

Issue 9 • Date June 2011

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Displaying Results 1 - 17 of 17
  • Error probability performance and ergodic capacity of l-branch switched and examine combining in weibull fading channels

    Page(s): 1173 - 1181
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (543 KB)  

    In this study, we consider a switched and examine combining (SEC) diversity scheme over independent and identically distributed (i.i.d.) L-branch Weibull fading channels and evaluate its performance in terms of ergodic capacity and the bit error rate (BER) for a class of coherent modulation schemes. The authors use the probability density function (pdf) of the effective signal-to-noise ratio (SNR) at the output of the SEC combiner in evaluating the BER and ergodic capacity for the considered model. The results are presented in closed-form expressions that are shown to generalise some special cases that are known in the literature. The general expressions are also shown to reduce to some other novel cases that are not reported in the literature. Numerical results and simulations are provided to verify the derived expressions. View full abstract»

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  • Lower bounds on mobile terminal localisation in an urban area

    Page(s): 1182 - 1191
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    Lower bounds on localisation errors serve as a performance indicator of how close a localisation system is to providing optimal performance. In this study, localisation of mobile terminals for urban areas is performed using received signal strength (RSS)-based techniques with maximum likelihood (ML) and linear kernel (LK) estimators. Simulations are performed with and without buildings in an urban area cell to illustrate the effect of discontinuities in the RSS profiles, on radio location accuracy. Results show that a localisation error is higher when buildings are absent as compared to the scenario when buildings are present. Buildings add extra features to the RSS measurement space which, if known to the localisation system, improve radio location accuracy. A comparison is made between the root mean-square error of the ML and LK estimators with the Cramer-Rao bound (CRB), the Bayesian Cramer-Rao bound (BCRB) and the Weiss-Weinstein bound (WWB). These comparisons show that the previously used CRB and BCRB do not provide realistic lowers bounds in the presence of buildings. In such cases bounds, such as WWB, which are capable of handling RSS discontinuities provide more realistic lower bounds on the accuracy of radio location. View full abstract»

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  • Ant-system-based location management scheme for wireless cellular networks

    Page(s): 1192 - 1198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (750 KB)  

    The current era of mobile networks allow users to communicate while they are moving. These network facilities are dealt by the location management (LM). In this article, the authors are proposing a nature-inspired LM technique based on ant system. The bottom line of proposed scheme is to follow the route of ahead entities and perform the LM based on it. The performance evaluation is carried out and is compared with existing LM scheme. It is observed that the signalling cost, network traffic and overheads are reduced, as compared to traditional LM scheme, in the communication network. View full abstract»

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  • Switch-and-stay partial relay selection over rayleigh fading channels

    Page(s): 1199 - 1203
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    In this study, a switch-and-stay partial relay selection (SS-PRS) scheme is analysed, where only a single relay from two cooperating open-form decode-and-forward (DF) relays is active in each transmission time slot. The performance of the proposed relay selection scheme is presented in terms of the outage probability and the average bit error rate (ABER). In this study, closed-form expressions are derived for the outage probability and the ABER of the system. In addition, an optimum threshold for the relay switching is found in a minimum ABER sense for the binary phase-shift keying modulation. The numerical and analytical results show that the SS-PRS scheme and the conventional PRS scheme give almost the same performance, whereas the SS-PRS has the advantage of notably lower complexity. View full abstract»

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  • Novel framework for proactive handover with seamless multimedia over WLANs

    Page(s): 1204 - 1212
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (769 KB)  

    Supporting multimedia applications over 802.11 wireless LANs requires low latency and seamless handover between multiple access points. However, the existing handover process in 802.11 products suffers from very high delay and frequent service disruption, which are not acceptable for streaming multimedia applications. In order to reduce this high delay and service disruption, the authors have designed and implemented a new proactive handover strategy over 802.11. The strategy intelligently issues proactive scan and handover triggers to reduce the effective channel scanning delay. Subsequently, it reserves resources in advance, to reduce the handoff reconnection delay and provide necessary QoS guarantee. Using actual implementation and simulation study, the authors demonstrate that their proposed strategy is capable of achieving magnitudes of latency, jitter and throughput improvements during the 802.11 handover operations, thereby providing seamless multimedia transmission. View full abstract»

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  • Anti-uniform huffman codes

    Page(s): 1213 - 1219
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (157 KB)  

    In this study, the authors consider the class of anti-uniform Huffman (AUH) codes. The authors derived tight lower and upper bounds on the average codeword length, entropy and redundancy of finite and infinite AUH codes in terms of the alphabet size of the source. These bounds are tighter than similar bounds. Also a tight upper bound on the entropy of AUH codes is presented in terms of the average cost of the code. The Fibonacci distribution is introduced, which plays a fundamental role in AUH codes. It is shown that such distributions maximise the average length and the entropy of the code for a given alphabet size. The authors also show that the minimum average cost of a code is achieved by an AUH codes in a highly unbalanced cost regime. View full abstract»

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  • Genetic algorithm-assisted joint quantised precoding and transmit antenna selection in multi-user multi-input multi-output systems

    Page(s): 1220 - 1229
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1236 KB)  

    This study presents a simple and efficient genetic algorithm-assisted approach for joint quantised precoding and transmit antenna selection based on the criterion of maximum capacity. The objective is to alleviate the effect of multi-user interference and to reduce hardware costs, such as the cost of radio frequency chains associated with antennas in the downlink of multi-input multi-output systems with limited feedback. To avoid the enormous search effort required by existing approaches, the authors propose a novel variant of the conventional genetic algorithm, called the hybrid genetic algorithm, in which each chromosome is divided into a bit string for precoding vector selection and an integer string for transmit antenna selection. In addition, new crossover and mutation operations are employed to accommodate these new chromosomes. The results of simulations show that the performance of the proposed approach is close to that of the exhaustive search method, but its computational complexity is substantially lower. View full abstract»

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  • Capacity of multiuser multiple input multiple output-orthogonal frequency division multiplexing systems with doubly correlated channels for various fading distributions

    Page(s): 1230 - 1236
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (883 KB)  

    In this article, the capacity of multiuser multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system is analysed under Rayleigh, Rician, Lognormal and Weibull fading channels, and compared with each other under both semi- and doubly correlated channels. The distribution of the complex Wishart matrix is utilised to derive closed-form expressions of ergodic capacity of MIMO-OFDM systems under doubly correlated channels when the transmitter has no channel state information (CSI) and the receiver has perfect CSI. The capacity of MIMO-OFDM systems is plotted for various fading channels under different system specifications, such as number of transmit and receive antennas, number of subcarriers and different power levels. The obtained results are used to study the impact of channel correlation on capacity. View full abstract»

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  • Finite-state Markov channel modelling under jointly varying amplitude and phase in time-varying flat fading channels

    Page(s): 1237 - 1245
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1226 KB)  

    In this study, the authors investigate the first-order finite-state Markov chain modelling of time-varying flat fading channels. The scope of this work is to consider the joint effects of unknown channel phase and amplitude on the received signal. Performance measures such as level crossing rate, steady-state probability, state transition probability and state time duration of the fading models are derived, plotted and analysed. Comparison of the performance measures are made for Rician, Lognormal and Weibull fading distributions. View full abstract»

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  • Single-field programmable gate array simulator for geometric multiple-input multiple-output fading channel models

    Page(s): 1246 - 1254
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (798 KB)  

    The authors propose a compact and fast fading channel simulator for the baseband verification and prototyping of multiple-input multiple-output (MIMO) wireless communication systems. The simulator accurately and efficiently implements models of both single-bounce and multiple-bounce geometric propagation conditions. Fading samples are generated at a low rate, comparable to the Doppler frequency, and then interpolated to match the desired sample rate. Bit-true simulations verify the accuracy of the hardware simulator. As an example, when implemented on a Xilinx XC5VLX110 field-programmable gate array (FPGA), the 4×4 MIMO geometric fading channel simulator occupies only 6.6× of the configurable slices while generating more than 16×324 million samples per second. The geometric MIMO fading channel simulator is well suited for use in an FPGA-based error rate performance verification system. View full abstract»

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  • Improved multi-stage clustering-based blind equalisation

    Page(s): 1255 - 1261
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (491 KB)  

    A new blind equalisation algorithm is presented for multi-level quadrature amplitude modulation schemes. The presented technique provides faster convergence and improved performance in terms of mean square error, which is demonstrated through various simulations. A mathematical analysis is also presented for the steady-state mean square error, which verifies the better performance of the proposed scheme over the conventional ones. The performance is also compared on the basis of inter-symbol interference metric. A computationally efficient implementation of the proposed algorithm is also presented. Simulations are done with various types of fading channels ranging from highly degrading Hoyt fading channels to moderate Rayleigh fading channels. View full abstract»

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  • Further results on the capacity of free-space optical channels in turbulent atmosphere

    Page(s): 1262 - 1267
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (254 KB)  

    In recent studies, the average capacity for optimal rate adaptation (ORA) of free-space optical channels in turbulent atmosphere has been derived in closed form, mainly based on the application of Meijer's G-function. To this end, the channel was assumed to be memoryless, stationary and ergodic, with independent and identically distributed fading statistics. It was also assumed that scintillations follow a gamma'gamma distribution so as to appropriately describe moderate-to-strong turbulence conditions. In the current contribution, the author will extend this work in two aspects: (i) using the properties of Meijer's G-function, it is shown that the average capacity provides also a closed-form solution for adaptation policies other than ORA, namely optimal power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate; (ii) if the additional loss caused by a misalignment between transmitter and receiver (pointing error) is taken into account, it is demonstrated that the developed analytical framework applies straightforwardly. View full abstract»

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  • Identification of true-static predistorter using a sine wave and accurate quantification of memory effects in broadband wireless transmitters

    Page(s): 1268 - 1274
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (387 KB)  

    This study proposes a new technique for the extraction of static non-linearities in wideband transmitters by launching a simple sinusoidal wave within the bandwidth of the system. The transmitter is first characterised under a two-carrier wideband code division multiple access (WCDMA) drive signal and modelled using a memory polynomial model. Two types of memoryless digital predistorters are then synthesised and applied to the amplifier model. The first predistorter is derived from the averaging of the measured data under the two-carrier WCDMA signal, while the second is derived using a sinusoidal wave signal excitation. Discrepancies between the two predistortion functions are illustrated, demonstrating that the predistorter using the averaging technique is biased by the presence of linear memory effects. The results show that the residual distortions at the output of the linearised power amplifier are different and more present when using the sine wave excitation technique compared with the averaging technique. This finding indicates that the sine wave-based technique is more rigorous for de-embedding the static non-linearity from the overall non-linear behaviour, which corroborates the validity of the proposed approach in extracting the true static behaviour of the system and its pertinence for the accurate extraction and quantification of memory effects. View full abstract»

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  • Look-ahead sphere decoding: algorithm and VLSI architecture

    Page(s): 1275 - 1285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    Multiple-input-multiple-output (MIMO) systems are recognised as a key enabling technology in high-performance wireless communications; however, the implementation of high-throughput MIMO detectors still is a critical task. Among known MIMO detectors, sphere decoder algorithm (SDA) is capable of optimal performance with acceptable processing complexity. The study presents an improved SDA, which enables significant throughput increase at a very limited additional complexity and with no degradation in terms of bit error rate performance. The modified detection method, called LASDA (look-ahead SDA), is based on formal algorithm transformations, namely look-ahead, retiming and pipelining, and requires a modified tree search strategy. The VLSI design of LASDA detector supporting a 4 × 4 MIMO channel with 16 QAM modulation is detailed in the study for a 130 nm CMOS standard cell technology: synthesis results show that the proposed solution achieves an average throughput of 380 Mbps at a signal-to-noise ratio of 22 dB (Rayleigh fading channel), with an occupied silicon area of 0.18 mm2. Comparisons with a number of previous implementations are also provided. View full abstract»

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  • Relay selection with transmit precoding design for multiple-input multiple-output amplify-and-forward relay network

    Page(s): 1286 - 1294
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (699 KB)  

    By employing the amplify-and-forward relaying strategy, a relay selection method with simplified precoding is proposed for two-hop multi-relay channels. The proposed method consists of two parts. In the first part, the authors present an optimal beamforming scheme with full channel state information (CSI) and derive a simplified and analytic expression for the output SNR through each relay, thereby selecting the best relay. The second part considers the transmit precoding problem with the CSI known to the receiver only and provide a selection strategy with Grassmannian beamforming. The new algorithm chooses only one relay based on the maximal received SNR to assist in transmission. It can significantly reduce the system consumption, achieve excellent bit-error-rate and average throughput and maintain full diversity order. Simulation results demonstrate that the performance of the proposed schemes with low complexity approaches towards the optimal iteration method. For practical situations with a distance attenuation factor, the performance gain of the authors schemes is also evident. View full abstract»

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  • Improving playout rate of streaming service with power efficiency over wireless multihop networks

    Page(s): 1295 - 1302
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (325 KB)  

    There is a trade-off problem between power consumption and streaming service quality over the wireless multihop networks. If the transmission power increases to overcome the bad link condition, the quality of streaming service can improve, but it can stress the other links and deplete the battery power of nodes. However, since the existing algorithms for streaming services do not consider this trade-off problem, streaming service quality cannot be guaranteed with the high power efficiency. In this study, the authors formulate the optimisation problem to solve the trade-off problem. Then, the authors propose a new cross-layer algorithm to achieve the derived optimal solution. The proposed cross-layer approach covers three layers: application layer, transport layer and physical layer. The newly proposed cross-layer algorithm not only avoids the underflow and the overflow of the decoder buffer, but also achieves the high playout rate and the high power efficiency. Through simulation results, it is shown that the proposed algorithm achieves the high and smooth playout rate with the high power efficiency. View full abstract»

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  • Super-low-complexity qr decomposition-M detection scheme for MIMO-OFDM systems

    Page(s): 1303 - 1307
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (406 KB)  

    This study proposes a super-low-complexity detection scheme to control the surviving symbols at each stage of near-maximum-likelihood detection for MIMO-OFDM systems. The new scheme can reduce not only the number of surviving symbol replica candidates at each stage, but also the number of Euclidian distance calculations required for selecting each surviving symbol replica candidate. The former is implemented by adaptively controlling the number of survived candidates according to the estimated level of interference plus noise while the latter is performed by a quadrant detection method. Simulation results show that the proposed scheme has a much lower complexity than that of conventional approaches. View full abstract»

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