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Communications, IET

Issue 2 • Date Jan. 21 2011

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Displaying Results 1 - 12 of 12
  • Performance analysis of signal-to-interferenceplus- noise ratio-based selection diversity over correlated rayleigh fading channels

    Publication Year: 2011 , Page(s): 127 - 134
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    In wireless communications systems, desired signal can be exposed to fading, cochannel interference (CCI) and noise. Diversity combining, such as space diversity, is a well-known method that can be used to alleviate the effects of these degradations. L-branch selection combining (SC) receiver which uses signal-to-interference-plus-noise ratio (SINR) power algorithm over correlated Rayleigh fading channels in the presence of Rayleigh distributed CCI and Gaussian noise is considered. The outage probability as significant performance criteria is analytically derived. The main contribution of this paper is that the analysis is carried out including the noise as a stochastic process, not only its average power value. The proposed mathematical analysis is complemented by various evaluation results showing the effects of the fading correlation as well as the number of diversity branches on the system's performance. In addition, SC performance in interference-plus-noise environment is compared with performance in noise- and interference-limited environments. View full abstract»

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  • Performance of interference-limited dual-hop non-regenerative relays over rayleigh fading channels

    Publication Year: 2011 , Page(s): 135 - 140
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (359 KB)  

    This paper studies the performance of a dual-hop non-regenerative relay fading channel in an interference-limited environment. The relay and destination nodes are corrupted by co-channel interference. New closed-form expressions for the probability density function and cumulative distribution function of the output signal-to-interference ratio are derived. Analytical expressions for the outage probability of both the channel-state-information-assisted relay and the fixed-gain relay channels are derived and the obtained numerical results are compared. Monte-Carlo simulations are performed to verify the obtained theoretical results. View full abstract»

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  • Efficient soft decoding of reed-solomon codes based on sphere decoding

    Publication Year: 2011 , Page(s): 141 - 153
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (990 KB)  

    A novel soft-decision decoding method motivated by the idea of sphere decoding is proposed for Reed-Solomon (RS) codes. Sphere decoding reduces the complexity of finding the closest lattice point to a given point by confining the search to points that fall inside a sphere around the given point. In the authors- proposed scheme, in order to reduce the search even further, the search effort is concentrated on the most probable lattice points. To do so, they first find the most reliable positions of the codeword. Then a sphere decoder is used to select symbol values for these positions. The proposed sphere decoder chooses the acceptable symbol values for each position from a pre-determined ordered set of most probable transmitted symbols. Each time the most reliable code symbols are selected, they are used to find the rest of RS symbols. If the resulting codeword is within the search radius, it is saved as a candidate transmitted codeword. The ordering used in the algorithm helps finding the candidate codewords quickly resulting in an efficient decoding method. Simulation results indicate considerable coding gains over hard decision decoding with a feasible complexity. The performance is also superior to the soft decision Koetter-Vardy method. View full abstract»

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  • Implementation of low-complexity companding technique for efficient peak-toaverage power ratio reduction in orthogonal frequency division multiplexing systems

    Publication Year: 2011 , Page(s): 154 - 162
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (679 KB)  

    Orthogonal frequency division multiplexing (OFDM) system has become an extremely popular wireless communication system in recent years. However, since the OFDM system is limited by a high peak-to-average power ratio (PAPR), companding techniques are often used to reduce PAPR. A uniformly distributed non-linear companding scheme offers efficient PAPR reduction with a low bit error rate (BER). However, such a scheme is difficult to implement. This work presents the referred companding scheme, expanded as a Taylor polynomial. Further, a novel low-complexity companding technique is developed to simplify the Taylor polynomial scheme by using the Padé approximation. Simulation results indicate that the performance of the proposed scheme is nearly the same as that of the referred scheme and the Taylor polynomial scheme over the additive white Gaussian noise (AWGN) channel or the multipath fading channel. Furthermore, the results of the hardware implementation demonstrate that the proposed scheme has lower complexity and computational time than the referred and Taylor polynomial schemes. View full abstract»

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  • Using two global positioning system satellites to improve wireless fidelity positioning accuracy in urban canyons

    Publication Year: 2011 , Page(s): 163 - 171
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (757 KB)  

    It is well known that a global positioning system (GPS) receiver needs to `see` at least four satellites to provide a three-dimensional fix solution. But in difficult environments such as an urban canyon, the number of `visible` satellites is often not enough. Wireless fidelity (WiFi) signals have been utilised for positioning mainly based on the fingerprinting technology. However, the accuracy of WiFi positioning outdoors is from several tens of metres to more than one hundred metres. This study proposes a new methodology to integrate WiFi positioning technology and GPS to improve positioning accuracy in urban canyons. When only two GPS satellites are visible, the pseudorange observations can be used to generate a time difference of arrival (TDOA) measurement. The TDOA generates a hyperboloid surface which can be intersected with the surface of the Earth and shows the possible location of the user on that line of position. Integrating this method with the WiFi fingerprinting technology can increase the positioning performance significantly. The test results show that the positioning accuracy can be improved by more than 50% if the new method can be applied. View full abstract»

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  • Agent-driven backbone ring-based reliable multicast routing in mobile ad hoc networks

    Publication Year: 2011 , Page(s): 172 - 189
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (909 KB)  

    Routing in mobile ad hoc networks (MANETs) for groups should aim at providing reliable and robust multicast routes to the group members against link failures, node failures and mobility conditions. The authors propose an agent-based multicast routing scheme in MANET that builds a backbone in the form of a reliable ring and finds multicast routes. The authors use the convex hull algorithm to find the outer boundary of the network area that helps in creating a reliable ring at an optimum distance between the centroid and outer boundary. The reliability of such a backbone is modelled by using reliable links based on the probabilistic measure of link failures. Later, a mesh of multicast routes are found by connecting: (i) source to source's nearest ring node and (ii) destination to destination's nearest ring node. The scheme consists of a set of static and mobile agents, which coordinate through knowledge base and identify links to form a reliable ring at an optimal distance from the centre of MANET area. Agents are also used to recover routes against link failures, node failures and mobility of nodes with local patching of failed links/nodes. The results show that there is an improvement in control overheads, packet delivery ratio, group reliability and packet delivery latency as compared to two protocols: (i) on demand multicast routing protocol and (ii) agent-based multicast routing scheme in MANETs. View full abstract»

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  • Stable throughput and delay performance in cognitive cooperative systems

    Publication Year: 2011 , Page(s): 190 - 198
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (583 KB)  

    The cognitive cooperative system with coexisting scenario of multiple primary users and one secondary capable of relaying is considered in this study. The primary users transmit packets in orthogonal subchannels. According to the cognitive principle, the secondary activity cannot interfere with the primary performance. Therefore in this study, the secondary user makes use of the spectrum when sensed idle. Based on the proposed media access control (MAC) protocol, the authors derive the stable throughput and delay slots expressions of each primary user with secondary relaying. They also achieve the stable network constraints of relaying probability ε, the feasible range of primary arrival rates and the maximum allowed secondary transmitting power which is to make a tradeoff between the stable throughput of the primary and secondary user. Simulation results show that secondary relaying can increase the primary and secondary throughput and also reduce the delay slots when designing an appropriate ε. View full abstract»

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  • Kalman smoothing-based adaptive frequencydomain channel estimation for uplink multiple-input multiple-output orthogonal frequency division multiple access systems

    Publication Year: 2011 , Page(s): 199 - 208
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    This study investigates Kalman smoothing (KS)-based frequency-domain channel estimation for uplink multiple-input multiple-output (MIMO) orthogonal frequency division multiple access (OFDMA) systems with time-varying channels. The proposed KS channel estimation scheme significantly outperforms the recursive least squares (RLS) channel estimation in the high signal-to-noise ratio (SNR) range, because of more effective exploitation of the signal information. In addition, channel interpolation is employed to improve the channel estimation accuracy by exploiting the correlation between adjacent subcarriers. The proposed KS channel estimator can also achieve a bit error rate (BER) performance which is close to the case with perfect channel state information (CSI) with a training overhead of only 5%. View full abstract»

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  • Improved superimposed training-based channel estimation method for closed-loop multiple input multiple output orthogonal frequency division multiplexing systems

    Publication Year: 2011 , Page(s): 209 - 221
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (706 KB)  

    This study pertains to the use of superimposed training (ST) in closed-loop multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. A novel method consisting of a technique to refine the channel estimate at the transmitter in an ST-based closed-loop MIMO-OFDM system is proposed. The estimate is refined at the transmitter by making use of the previous data that was transmitted. This significantly reduces the data interference in the channel estimate and hence improves performance. The mean squared estimation error (MSEE) of the refined channel estimate is mathematically analysed and it is shown that in the limit, the accuracy of the refined channel estimate is identical to the pilot-assisted case with the additional advantage of the bandwidth efficiency inherent in ST-based systems. Two factors in general affect all transmitter side techniques that make use of the fed back channel coefficients. One is the quantisation error affecting the channel estimate. The other is the channel variations that may render the fed back channel coefficients outdated for further use. The effect of these factors on the proposed refined channel estimation scheme is discussed in detail. Simulation results are presented in terms of the MSEE and the bit error rate performance demonstrating the usefulness of the proposed scheme. View full abstract»

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  • Efficient construction of irregular codes with midterm block length and near-shannon performance

    Publication Year: 2011 , Page(s): 222 - 230
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (862 KB)  

    In this study, the authors propose a new method for constructing irregular low-density parity-check codes (LDPC codes) with midterm or short block lengths. It is a Monte-Carlo simulation-based optimisation procedure called downhill simplex which uses progressive edge growth method for Tanner graph construction in cost function evaluations. It outperforms the density evolution (DE) method in both efficiency and performance. The efficiency of the authors' proposal mostly depends on the Monte-Carlo simulation time which owing to the midterm block lengths is relatively small compared to the time delay of the conventional DE method. Simulation results show that for block length of 3200 and a relatively low code rate 3/8, LDPC codes constructed using the authors' proposal noticeably outperform those constructed with DE method by more than 0.2 dB in the entire signal to noise ratio (SNR) range under AWGN channel. View full abstract»

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  • Design and performance analysis of non-data-aided carrier phase estimators for amplitude and phase shift keying signals

    Publication Year: 2011 , Page(s): 231 - 239
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    This study studies the feedforward (FF) non-data-aided (NDA) carrier phase estimation of the amplitude and phase shift keying (APSK) signals. The true Cramer-Rao bounds (CRBs) for NDA phase estimation of APSK signals are derived and evaluated numerically using Gauss-Hermite quadrature. The jitter variance of the FF Viterbi-Viterbi (V&V) algorithm is analysed assuming the absence of data pattern noise. It is proved that, when the design parameter μ=-2, the jitter variance is able to converge asymptotically to the modified CRB (MCRB) at high signal-to-noise ratios (SNRs). For practical application, the parameter μ is also optimised for 16/32/64-APSK signals at different SNRs. The analytical results of the jitter variance are verified by Monte-Carlo evaluations. It is shown that, for 32/64-APSK signals, the plain V-algorithm cannot approach the CRBs due to the data pattern noise. A modified V-algorithm based on the constellation partition and a linear combination of the sub-estimators is proposed to eliminate the divergence. Simulation results show that the jitter variance of the proposed estimator is very close to the CRB at the SNRs of interest and converges to the MCRB at high SNRs. View full abstract»

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  • Green modulations in energy-constrained wireless sensor networks

    Publication Year: 2011 , Page(s): 240 - 251
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    Owing to the unique characteristics of sensor devices, finding the energy-efficient modulation with a low-complexity implementation (refereed to as green modulation) poses significant challenges in the physical layer design of wireless sensor networks (WSNs). Towards this goal, the authors present an in-depth analysis on the energy efficiency of various modulation schemes using realistic models in the IEEE 802.15.4 standard to find the optimum distance-based scheme in a WSN over Rayleigh and Rician fading channels with path loss. The authors describe a proactive system model according to a flexible duty-cycling mechanism utilised in practical sensor apparatus. The present analysis includes the effect of the channel bandwidth and the active mode duration on the energy consumption of popular modulation designs. Path-loss exponent and DC-DC converter efficiency are also taken into consideration. In considering the energy efficiency and complexity, it is demonstrated that among various sinusoidal carrier-based modulations, the optimised non-coherent M-ary frequency shift keying (NC-MFSK) is the most energy-efficient scheme in sparse WSNs for each value of the path-loss exponent, where the optimisation is performed over the modulation parameters. In addition, the authors show that the on-off keying displays a significant energy saving as compared to the optimised NC-MFSK in dense WSNs with small values of path-loss exponent. View full abstract»

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