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Online ISSN 1751-8636 Print ISSN 1751-8628

IET Communications

Volume 2, Issue 10, November 2008

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Volume 2, Issue 10

November 2008

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    • Robust chaotic communications exploiting waveform diversity. Part 1: Correlation detection and implicit coding
      • Author(s): C. Williams
      • Source: IET Communications, Volume 2, Issue 10, p. 1213 –1222
      • DOI:  10.1049/iet-com:20070467
      • Type: Article
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      • p. 1213 –1222 (10)
        A correlation receiver is presented for communication using the symbolic dynamics of a chaotic system. A chaotic system offers the potential for power efficient transmitters but many proposals to date have either been susceptible to noise and distortion in the channel, or are spectrally inefficient. The proposed system has a spectrum efficiency equivalent to conventional BPSK and offers a 2 dB performance improvement in AWGN. This is achieved by exploiting diversity in the transmitted signal, whereby each data symbol influences the transmitted pulse shape for the preceding symbols. Correlation detection over multiple symbols allows full exploitation of this diversity. In addition, each symbol can be detected multiple times and so a decoding gain is possible without the need for parity symbols. The diversity mechanism is investigated and the performance gains demonstrated.
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      Robust chaotic communications exploiting waveform diversity. Part 2: Complexity reduction and equalisation
      • Author(s): C. Williams
      • Source: IET Communications, Volume 2, Issue 10, p. 1223 –1229
      • DOI:  10.1049/iet-com:20070468
      • Type: Article
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      • p. 1223 –1229 (7)
        The symbolic dynamics method of communication using chaotic systems has previously been shown to offer performance better than conventional binary phase shift keying (BPSK), while also providing similar spectrum efficiency. This is achieved by exploiting diversity in the waveform, through a mechanism similar to partial response signalling. In order to achieve this performance, a correlation method for detection has been proposed, but complexity was high and only performance in additive white Gaussian noise (AWGN) channels has been considered. It is demonstrated that the complexity can be reduced from requiring 1024 correlations per symbol down to only 32, while degrading performance only by 0.6 dB. The ability to further reduce the occupied bandwidth is investigated. Spectrum occupancy equivalent to a root-raised cosine-filtered BPSK signal is demonstrated, and performance is maintained when the reference waveforms are similarly filtered to maintain the signal match. Finally, a novel equalisation technique that incorporates a decision feedback structure into the correlation detector is proposed. Performance in multipath channels is investigated and shown to be effective.
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      New union bound on the error probability of bit-interleaved space–time codes with finite interleaver sizes
      • Author(s): S.A. Zummo ; P.-C. Yeh ; W.E. Stark
      • Source: IET Communications, Volume 2, Issue 10, p. 1230 –1238
      • DOI:  10.1049/iet-com:20080051
      • Type: Article
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      • p. 1230 –1238 (9)
        A new union bound on the bit error probability of bit-interleaved space–time (BI-ST) coded systems is derived. Unlike existing performance analysis tools for BI-ST systems, the new bound provides a general framework for analysing the performance of BI-ST systems employing finite interleaver sizes. The derivation is based on the uniform interleaving assumption of the coded sequence prior to transmission over multiple antennas. The new bound is a function of the distance spectrum of the code, the signal constellation used and the space–time (ST) mapping scheme. The bound is derived for a general BI-ST coded system and applied to two specific examples, namely, the BI space–time coded modulation and the BI space–time block codes. Results show that the analysis provides a close approximation to the BI-ST performance for a wide range of signal-to-noise ratios. The analysis can also accurately characterise the performance differences between different interleaver sizes, which is a breakthrough in the analysis of BI-ST coded systems.
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      Application-controlled handover for heterogeneous multiple radios over fibre networks
      • Author(s): S.R. Chaudhry  and  H.S. Al-Raweshidy
      • Source: IET Communications, Volume 2, Issue 10, p. 1239 –1250
      • DOI:  10.1049/iet-com:20060384
      • Type: Article
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      • p. 1239 –1250 (12)
        The wired-wireless integration network can be categorised as fixed mobile convergence (FMC). FMC means the convergence of the existing wired network and wireless network. Therefore a mobile device needs the function of connection and control to the FMC infrastructure. An application-controlled handover is developed, which keeps channel continuity in the wired-wireless synergy network environment that consists of 3G (UMTS)+WLAN+WPAN (UWB) and optical fibre network. A handover mechanism transmits and receives data by using the proposed application selection criteria. It maintains the channel and the seamless transmission from mobile device to the remote optical fibre network, to provide real-time service continuity for multimedia traffic. The results show that application-controlled handover has a reduction up to 83% in packet drop, 74% reduction in bit error rate, 85% reduction in power consumption and 100% enhancement in application response time (delay) as compared with the network without handover technique.
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      Maximum-girth slope-based quasi-cyclic (2, k≥5) low-density parity-check codes
      • Author(s): M. Esmaeili  and  M. Gholami
      • Source: IET Communications, Volume 2, Issue 10, p. 1251 –1262
      • DOI:  10.1049/iet-com:20080013
      • Type: Article
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      • p. 1251 –1262 (12)
        A class of maximum-girth geometrically structured regular (n, 2, k≥5) (column-weight 2 and row-weight k) quasi-cyclic low-density parity-check (LDPC) codes is presented. The method is based on cylinder graphs and the slope concept. It is shown that the maximum girth achieved by these codes is 12. A low-complexity algorithm producing all such maximum-girth LDPC codes is given. The shortest constructed code has a length of 105. The minimum length n of a regular (2, k) LDPC code with girth g=12 determined by the Gallager bound has been achieved by the constructed codes. From the perspective of performance these codes outperform the column-weight 2 LDPC codes constructed by the previously reported methods. These codes can be encoded using an erasure decoding process.
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      Two-dimensional indexing polynomial-based pre-distorter for power amplifiers with memory effects
      • Author(s): B. Ai ; Z.D. Zhong ; G. Zhu ; R.T. Xu ; Z.Q. Li
      • Source: IET Communications, Volume 2, Issue 10, p. 1263 –1271
      • DOI:  10.1049/iet-com:20080209
      • Type: Article
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      • p. 1263 –1271 (9)
        An improved segmented polynomial-based pre-distortion method and a novel memory polynomial-based pre-distortion method with two-dimensional indexing are proposed in digital baseband power amplifier pre-distortion systems. Through computer simulations and corresponding analysis, the feasibility and reliability of the proposed methods are verified with three different polynomial formats in the evaluation of relative mean square error, the convergence speed, the random access memory storage units and the power spectral density.
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      Two incremental relaying protocols for cooperative networks
      • Author(s): Q.F. Zhou  and  F.C.M. Lau
      • Source: IET Communications, Volume 2, Issue 10, p. 1272 –1278
      • DOI:  10.1049/iet-com:20080117
      • Type: Article
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      • p. 1272 –1278 (7)
        The authors investigate a cooperative network with three terminals. By exploiting a simple two-bit feedback message from the destination, two incremental relaying protocols are proposed, namely incremental selection amplify-and-forward (ISAF) and joint incremental selection relaying (JISR) with an aim to balance the load between the source and the relay. The authors derive the asymptotic outage probabilities of the two new protocols and find them to be lower than that of the incremental amplify-and-forward (IAF) protocol, which has been identified as the best protocol so far. Moreover, the spectral efficiencies of ISAF and JISR match that of IAF. Simulation results have verified the asymptotic performance of the protocols and have shown that JISR outperforms ISAF and IAF over all signal-to-noise ratio values.
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      Precoding in downlink multi-carrier code division multiple access systems using expectation maximisation algorithm
      • Author(s): A. Haghbin  and  P. Azmi
      • Source: IET Communications, Volume 2, Issue 10, p. 1279 –1288
      • DOI:  10.1049/iet-com:20080046
      • Type: Article
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      • p. 1279 –1288 (10)
        The presence of multiple access interference and hardware complexity of the mobile terminal are two major burdens for multi-carrier code division multiple access schemes. Both burdens can be overcome in downlink by precoding the transmitted signal using the knowledge of the channel state information. In multi-user precoding techniques, the transmitter is optimised to combat channel impairments through the use of new spreading sequences that are obtained by solving an optimisation problem based on some criterion. Among these optimisation problems, the problem based on maximum likelihood is hard and complex to solve. In the proposed precoding scheme, the well-suited expectation maximisation algorithm is used to solve this problem. The proposed precoding technique is simulated and its performance is analysed and compared with some other precoding and detecting techniques. The results show that the proposed scheme considerably outperforms the previous precoding schemes.
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      Diversity–multiplexing trade-off performance of linear dispersive codes
      • Author(s): H. Yang ; G. Li ; L. Tang
      • Source: IET Communications, Volume 2, Issue 10, p. 1289 –1292
      • DOI:  10.1049/iet-com:20070600
      • Type: Article
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      • p. 1289 –1292 (4)
        The diversity–multiplexing trade-off function provides a complete view to evaluate both the diversity-based and the multiplexing-based space–time schemes. The trade-off performance of the linear dispersive codes (LDCs) over both the block fading and the fast fading channels is analysed. Results show that LDCs can achieve better trade-off performance than some of the existing space–time schemes over block fading channels. For fast fading channels, the time factor is clearly expressed in the trade-off function, and the analysis shows that LDCs can achieve both the space diversity and the time diversity simultaneously.
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      Restricting the orthogonal frequency division multiplexing peak-to-mean envelope power ratio by a new set of sequences of length 16
      Communication system model for information rate evaluation of differential detection over time-varying channels
      • Author(s): Z.B. Krusevac ; P.B. Rapajic ; R.A. Kennedy
      • Source: IET Communications, Volume 2, Issue 10, p. 1301 –1310
      • DOI:  10.1049/iet-com:20070610
      • Type: Article
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      • p. 1301 –1310 (10)
        A communication system model for mutual information performance analysis of multiple-symbol differential M-phase shift keying over time-correlated, time-varying flat-fading communication channels is developed. This model is a finite-state Markov (FSM) equivalent channel representing the cascade of the differential encoder, FSM channel model and differential decoder. A state-space approach is used to model channel phase time correlations. The equivalent model falls in a class that facilitates the use of the forward–backward algorithm, enabling the important information theoretic results to be evaluated. Using such a model, one is able to calculate mutual information for differential detection over time-varying fading channels with an essentially finite time set of correlations, including the Clarke fading channel. Using the equivalent channel, it is proved and corroborated by simulations that multiple-symbol differential detection preserves the channel information capacity when the observation interval approaches infinity.
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      Trusted virtual machine monitor-based group signature architecture
      • Author(s): D. Zou ; H. Jin ; J.H. Park ; H.-C. Chao ; Y. Li
      • Source: IET Communications, Volume 2, Issue 10, p. 1311 –1319
      • DOI:  10.1049/iet-com:20080010
      • Type: Article
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      • p. 1311 –1319 (9)
        Group communication is an important technique for many network computing applications. In group communication, a member in a group sends a message to others normally by multicast. Group signature guarantees the integrity of the exchanged data and provides source authentication. In a virtual machine (VMs) based computing system, a virtual machine monitor (VMM) allows applications to run in different VMs strongly isolated from each other. A trusted VMM (TVMM) based platform can provide stronger security protection for group signature systems than traditional computing platforms can. The authors first introduce a TVMM-based group signature architecture and a TVMM security protection mechanism for group signature components. Then, the authors propose a group signature scheme using the function of message checking based on the discrete logarithm problem. Finally, the authors prove the correctness of the group signature scheme and analyse its security in virtual computing environments.
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