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Communications, IET

Issue 10 • Date July 2 2013

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Displaying Results 1 - 15 of 15
  • Dual-antenna-based blind joint hostile jamming cancellation and multi-user detection for uplink of asynchronous direct-sequence code-division multiple access systems

    Publication Year: 2013 , Page(s): 911 - 921
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    The authors investigate the problem of blind multi-user detection (MUD) for uplink of asynchronous direct-sequence code-division multiple access (DS-CDMA) systems with hostile jamming. To cope with the lack of prior knowledge of spread signals, hostile jamming and channel state information, the authors propose a scheme based on blind source separation (BSS) to solve this problem. Dual receive antennas are used in the proposed scheme. By exploiting the structure of the two received signals, a BSS model with dependent sources is formed, and then blind hostile jamming cancellation and MUD are obtained by solving this BSS problem. The proposed scheme does not require to know any information about the hostile jamming, and can work well under multiple kinds of hostile jamming. Simulation results further demonstrate that if such proposed approach is used to cancel hostile jamming and make MUD, then the bit-error-rate performance can be substantially improved as compared with earlier detectors. View full abstract»

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  • Relay selection in cognitive radio networks with interference constraints

    Publication Year: 2013 , Page(s): 922 - 930
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (482 KB)  

    In this study, the authors investigate the outage probability of underlay cognitive radio systems with relay selection. In particular, they consider a secondary multi-relay network operating in the amplify-and-forward (AF) mode and only the `best' relay is selected, which satisfies an index of merit. The proposed selection strategy takes into consideration the effect of primary user (PU) interference. That is, the authors assume that the secondary multi-relay network is exposed to unwanted interference from a neighboring PU network. They derive a closed-form outage probability expression and further present a thorough asymptotic diversity order analysis of the underlying scenario. A simulation study is presented to corroborate the analytical results and to have further insight into the performance of the proposed selection strategy. View full abstract»

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  • Approximate distribution of log2(A + x2)

    Publication Year: 2013 , Page(s): 931 - 941
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (827 KB)  

    This study concerns the approximate distribution of the random variable log2(A + χ2) and its applications in the performance analysis of communication systems where A is 0 or 1 and χ2 a chi-square distributed random variable. The authors prove that log2(A + χ2) is approximately Gaussian distributed and derive the expressions of the mean and variance of the approximate distribution. The approximate Gaussian distribution provides a new way to simplify the derivation of performance metrics and obtain analytical results. Then the authors utilise the approximate results in two applications, which are the approximation of the Gaussian Q-function and capacity analysis, respectively. For one thing, the approximate distribution can be explored to deduce a new approximate equivalent expression of the Q-function on the basis of which an accurate approximation of the Gaussian Q-function can be developed. For another, the approximate Gaussian distribution provides an intuitive approach to analyse the channel capacity of Rayleigh-fading multiple antenna systems. The approximate statistical distributions of the channel capacities of orthogonal space-time block codes, single-input multiple-output, multiple-input single-output, transmit antenna selection with maximal-ratio combining and multiple-input multiple-output systems are presented. The applicability of the approximate distribution can be demonstrated through simulation results in both applications. View full abstract»

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  • Joint beamforming design and base-station assignment in a coordinated multicell system

    Publication Year: 2013 , Page(s): 942 - 949
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (267 KB)  

    This study is concerned with the downlink beamforming designs in a coordinated multicell system with dynamic base-station (BS) assignment. At each cell, a multiple-antenna BS employs linear beamforming to send multiple data streams to its assigned mobile-stations (MSs). Exploiting multicell coordination, the multiple BSs jointly optimise the beamformers and the BS-MS assignments to enhance the overall system performance. With per-BS power constraints, considered are the coordinated beamforming problems under the following two design criteria: (i) minimising the transmit power margin at the BS with a set of target signal-to-interference-plus-noise ratios (SINR) at the MSs and (ii) jointly maximising the minimum SINR margin at the MSs. As the original problem formulations are shown to be non-convex integer programs, which are combinatorially hard, the authors propose an efficient convex relaxation approach to solve the problems with low complexity. Simulations show that the convex relaxation-based assignment schemes significantly outperform heuristic fixed assignment schemes. View full abstract»

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  • Joint sector identity and integer part of carrier frequency offset detection by phase-difference in long term evolution cell search process

    Publication Year: 2013 , Page(s): 950 - 959
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1013 KB)  

    In the Long Term Evolution (LTE) system, the initial cell search needs not only to achieve the timing synchronisations of symbols, slots and frames, but also to detect the sector identity (ID), the cell ID group and the carrier frequency offset (CFO), which includes an integer part (ICFO) and a fractional part. To accomplish this cell search process, two synchronisation signals, the primary synchronisation signal (PSS) and the secondary synchronisation signal, are periodically broadcasted from base stations in the LTE system. The PSS is mainly used for sector ID detection. In this study, an innovative algorithm for detecting the sector ID and ICFO together via the PSS-matching process is presented. In the proposed scheme, the phases of the differential correlation instead of the absolute values are adopted to determine the ICFO. Furthermore, a new set of PSS is proposed in order to improve the success probability of ICFO detection. Compared with conventional schemes, the proposed scheme can detect both the sector ID and ICFO with higher accuracy and much lower complexity. View full abstract»

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  • Proof on the maximal rates of space-time block codes from complex orthogonal design

    Publication Year: 2013 , Page(s): 960 - 965
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (170 KB)  

    In this study, the authors present a novel proof on the maximal rates of space-time block codes from complex orthogonal design (COD). The method of the proof is derived from an observation about the CODs, which reveals some inherent laws of their structure. The proof is applicable to any CODs, rather than to some specific designs, and does not need any auxiliary matrix or matrix transformation. The conclusion in this study also indicates that the upper bound of the CODs' rate conjectured by the authors is tight and achievable. View full abstract»

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  • Soft-decision decoding of convolutional codes with square-law detectors

    Publication Year: 2013 , Page(s): 966 - 972
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (691 KB)  

    In this study, the authors investigate the performance of soft-decision decoding of convolutional codes in receivers that employ square-law detection. Traditionally, soft-decision decoding has been considered only in coherent or differentially-coherent receivers. Over the past few years, the emergence of ultra-wideband (UWB) communication has brought energy detectors to prominence. In this study, the authors derive low-complexity approximations for the log-likelihood ratio (LLR) with a class of square-law detectors in UWB radios. The authors then show that performance improvements, similar to those achievable in coherent detectors, can be obtained even with energy detectors when soft-decisions are employed in a maximum-likelihood decoding algorithm. The authors also investigate the complexity and accuracy of the proposed approximations when the LLR is computed using fixed point arithmetic. An expression for the bit error probability with soft-decision decoding is derived. Several simulation results, including the error rate performance of hard- and soft-decision decoding schemes with the exact and approximate LLR values, are presented. View full abstract»

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  • Distributed turbo coded cooperative networks under imperfect channel state information in Rayleigh fading channels

    Publication Year: 2013 , Page(s): 973 - 979
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (502 KB)  

    In this study, under imperfect channel state information in Rayleigh fading channels, the authors analyse a previously proposed distributed turbo coded cooperative scheme based on parallel concatenated convolutional codes and soft-decode-and-forward mode. For coherent binary phase shift keying over independent Rayleigh fading channels, the authors assume that the imperfect estimation errors are Gaussian distributed having a variance equal to a fraction of the variance of normalised Rayleigh distribution. Using the transfer function approach, the authors define an upper bound of the pairwise error probability to compute the average union upper bound for the bit error probability. View full abstract»

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  • Low-complexity channel estimation and turbo equalisation for high frequency channels

    Publication Year: 2013 , Page(s): 980 - 987
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (553 KB)  

    A low-complexity channel estimation algorithm is proposed to improve performance of two high frequency standardised waveforms: MIL-STD-188-110B Appendix C standard and STANAG 4285. In the proposed estimation algorithm, the channel impulse response is modelled as a linear-time function within a frame and the least square criterion is adopted. With the estimated CIRs, the authors study and compare bit-error-rate (BER) performance and complexity of three turbo equalisation (TEQ) schemes, including the minimum mean-square error (MMSE), the MMSE with decision feedback equalisation (DFE) (MMSE-DFE) and the soft-feedback interference-cancellation (SFIC) turbo receivers. The authors then propose a hybrid TEQ scheme that uses the MMSE-DFE equaliser for the first iteration and the SFIC equaliser for the rest. Simulation results show that the proposed channel estimation algorithm performs well and the TEQ schemes realise a significant performance improvement as compared with a non-iterative receiver. Moreover, the proposed hybrid TEQ scheme achieves the best trade-off between BER and complexity for the MIL-STD-188-110B Appendix C standard, whereas the SFIC-TEQ scheme is optimal for the STANAG 4285 standard. View full abstract»

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  • Maximum euclidean distance network coded modulation for asymmetric decode-and-forward two-way relaying

    Publication Year: 2013 , Page(s): 988 - 998
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (771 KB)  

    Network coding (NC) compresses two traffic flows with the aid of low-complexity algebraic operations, hence holds the potential of significantly improving both the efficiency of wireless two-way relaying, where each receiver is collocated with a transmitter and hence has prior knowledge of the message intended for the distant receiver. In this contribution, network coded modulation (NCM) is proposed for jointly performing NC and modulation. As in classic coded modulation, the Euclidean distance between the symbols is maximised, hence the symbol error probability is minimised. Specifically, the authors first propose set-partitioning-based NCM as an universal concept which can be combined with arbitrary constellations. Then the authors conceive practical phase-shift keying/quadrature amplitude modulation (PSK/QAM) NCM schemes, referred to as network coded PSK/QAM, based on modulo addition of the normalised phase/amplitude. To achieve a spatial diversity gain at a low complexity, a NC oriented maximum ratio combining scheme is proposed for combining the network coded signal and the original signal of the source. An adaptive NCM is also proposed to maximise the throughput while guaranteeing a target bit error probability (BEP). Both theoretical performance analysis and simulations demonstrate that the proposed NCM can achieve at least 3 dB signal-to-noise ratio gain and two times diversity gain. View full abstract»

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  • Pilot-aided estimation and equalisation of a radio-over-fibre system in wideband code division multiple access

    Publication Year: 2013 , Page(s): 999 - 1007
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (719 KB)  

    In this study, the impact of a Radio-over-Fibre (RoF) subsystem on the capacity performance of wideband code division multiple access is evaluated. This study investigates the use of pilot-aided channel estimation to compensate for the optical subsystem non-linearities for different channel conditions, estimation intervals and coding schemes. The results show that pilot-aided channel estimation is an effective method for compensating the composite impairments of the optical subsystem and the radio frequency (RF) channel. It is found that there is always a suitable pilot power level which maximises the system capacity performance regardless of coding scheme and channel condition. Also, the peak capacity is only slightly affected by a decrease in the estimation interval. View full abstract»

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  • Development of rain attenuation model for Southeast Asia equatorial climate

    Publication Year: 2013 , Page(s): 1008 - 1014
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (389 KB)  

    Statistical distribution of rain attenuation is essential for development of microwave and millimeter-wave communication links. Therefore rain-related statistics are very important for a commercialisation system designer. This study proposes modifications to the International Telecommunication Union (ITU-R P.618-10) model and an appropriate rain attenuation prediction model for tropical countries. The model was developed based on data obtained from tropical and equatorial regions. The proposed model uses rainfall rate and rain attenuation at 0.01% of the time, R0.01 and A0.01, elevation angle θ and altitude of site hs, respectively, as input parameters. The proposed model showed remarkable agreement with existing rain attenuation measured data in terms of prediction errors for mean square, standard deviation and root-mean square. The proposed rain attenuation model was used for validation by comparing the model with measured data collected from Nigeria, Kenya and Papua New Guinea, whereby the proposed model gave a percentage error below 12%. View full abstract»

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  • Joint bit loading and power allocation for downlink minimum mean square error combining based multi-carrier code division multiple access systems

    Publication Year: 2013 , Page(s): 1015 - 1023
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (742 KB)  

    The performance of a downlink multi-carrier code-division multiple-access (MC-CDMA) system heavily depends on the receiver type at the user side. The minimum mean square error-combining scheme possesses the finest performance. However, the resource allocation problem becomes a highly complex task because of multiple access interference. This study investigates a realistic scenario, where the base station determines the bit loading and power for all downlink users with both the power and bit error rate (BER) constraints to maximise the overall system throughput. The authors first derive the instantaneous signal to interference and noise ratio (SINR) and then approximate data transmission as an equivalent M-QAM system with a signal-to-noise ratio (SNR) equal to the instantaneous SINR of that user. Combined with accurate BER formulas of M-QAM system, the authors estimate the BER for each user given a set of power and bit loading configuration. Finally, the authors develop an iterative joint bit loading and power allocation algorithm to maximise the system throughput. The simulation results show that the proposed solution achieves performance close to the optimal one and maintains the BER close to the desired target. View full abstract»

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  • Performance comparison of chaotic spreading sequences generated by two different classes of chaotic systems in a chaos-based direct sequencecode division multiple access system

    Publication Year: 2013 , Page(s): 1024 - 1031
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (929 KB)  

    In the world of wireless communications, achieving a highly secure transmission at the lowest possible performance degradation has presented a major challenge and a number of conventional direct-sequence-code division multiple access (DS-CDMA)-based solutions have been put forward that deals with the issue. This study aims to overcome the challenge by introducing a new approach that employs a chaotic sequence in DS-CDMA system over fading channels. The proposed algorithm, which assumes a perfect sync between the transmitter and the receiver, generates a binary code by using a three-dimensional (3D) chaotic system. Simulations based on a flat-fading channel with additive white Gaussian noise and inter-user interference reveal that the new approach outperforms codes generated by other classes of chaotic systems, that is, the 1D chaotic system. The results also proved the proposition's performance is comparable to conventional pseudo-noise spreading codes, the Gold code, in several key aspects including security of transmission, bit-error rate, code generation speed and the number of possible code sequences. View full abstract»

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  • Cross-layer channel selection and reward-based power allocation for increasing system capacity and reward in multiple-input-multiple-output wireless communications

    Publication Year: 2013 , Page(s): 1032 - 1041
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (579 KB)  

    For increasing network bandwidth and guaranteeing quality of service in WiMAX, IEEE 802.16 m proposes the multiple-input-multiple-output (MIMO) technique that offers compatible specifications with the existing IEEE 802.16 family specifications. However, the performance of the IEEE 802.16 MIMO specification is significantly degraded in the high-mobility environment and high communication interference. As a result, a sender easily uses inaccurate modulation and coding scheme (MCS) and improper power allocation for different-priority users having different received signal-to-noise ratios. The system capacity is thus affected significantly. Additionally, the multiuser MIMO systems seldom consider that different-priority users and different-class traffic bring different rewards to the system. This study thus proposes a cross-layer reward-based approach (namely CLR) that consists of three schemes: adaptive modulation and coding determination, cross-layer dynamic channel selection, and reward-based weighting power allocation. The proposed CLR approach achieves accurate channel state information determination, optimal channel selection, and adaptive reward power allocation. Numerical results demonstrate that the proposed approach significantly outperforms the other approaches in system reward, system capacity, and the accuracy of the MCS determination. View full abstract»

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