By Topic

Communications, IET

Issue 8 • Date September 2008

Filter Results

Displaying Results 1 - 12 of 12
  • REEP: data-centric, energy-efficient and reliable routing protocol for wireless sensor networks

    Page(s): 995 - 1008
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (827 KB)  

    Owing to the growing demand for low-cost 'networkable' sensors in conjunction with recent developments of micro-electro mechanical system (MEMS) and radio frequency (RF) technology, new sensors come with advanced functionalities for processing and communication. Since these nodes are normally very small and powered with irreplaceable batteries, efficient use of energy is paramount and one of the most challenging tasks in designing wireless sensor networks (WSN). A new energy-aware WSN routing protocol, reliable and energy efficient protocol (REEP), which is proposed, makes sensor nodes establish more reliable and energy-efficient paths for data transmission. The performance of REEP has been evaluated under different scenarios, and has been found to be superior to the popular data-centric routing protocol, directed-diffusion (DD) (discussed by Intanagonwiwat et al. in 'Directed diffusion for wireless sensor networking' IEEE/ACM Trans. Netw., 2003, 11(1), pp. 2-16), used as the benchmark. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Logarithmic cyclic frequency domain profile for automatic modulation recognition

    Page(s): 1009 - 1015
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (314 KB)  

    Cyclostationary techniques have been applied widely to the problem of recognising communication modulation schemes. As these techniques are processing intensive, much effort has been invested in researching algorithms that can reduce the number of computational steps required, with fast Fourier transform approaches predominating. A novel approach to improve the extent of the cyclic frequency (alpha) is proposed. By using the constant Q transform (COT), a logarithmic form of the spectral correlation function (SCF) can be produced. This allows the alpha-axis to be extended, which can be advantageous when the receiver bandwidth cannot be well matched to the signal frequency and bandwidth using a priori knowledge of spectrum allocation. It is found that a CQT- based SCF can form the basis of a logarithmic cyclic frequency domain profile algorithm without loss of sensitivity compared with the conventional, linear form. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Robust phased array receiver for multipath code-division multiple access communication systems

    Page(s): 1016 - 1022
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (186 KB)  

    The problem of estimating information symbols transmitted through non-Gaussian multipath CDMA wireless channels with a phased array is considered. First, a robust detector based on the minimax robust estimation theory is proposed. This proposed robust technique has a decreased sensitivity of the estimates with respect to an actually unknown distribution of random noises and interferences. Then, the estimation accuracy of information signals is analysed by Monte Carlo simulation of this direction-of-arrival estimation- based robust detector in multipath scenario. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scheduling advance reservation requests for wavelength division multiplexed networks with static traffic demands

    Page(s): 1023 - 1033
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    Telecommunication and grid computing applications demand high bandwidth data channels that offer guarantees with respect to service availability. Such applications include: remote surgery, remote experimentation, video on-demand, teleconferencing and bulk transfers. Furthermore, by forecasting traffic patterns Internet service providers attempt to optimise network resources in order to lower operational costs during peak periods of bandwidth consumption. Advance reservation for wavelength division multiplexed networks can address some of these issues by reserving high volume communication channels (i.e. lightpaths) beforehand. The authors develop a mathematical model to solve the problem of scheduling lightpaths in advance. The optimal solution is presented as a mixed integer linear program with the assumption that all traffic is static and the network is centrally controlled. Furthermore, we have developed two novel meta-heuristics based on: 1) a greedy implementation (local search) and 2) simulated annealing. The meta-heuristics have shown to produce good approximate solutions in a reasonable amount of time. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Concatenated peak-to-average power ratio reduction scheme with threshold limited selection for coded orthogonal frequency-division multiplexing

    Page(s): 1034 - 1042
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (314 KB)  

    The authors propose a concatenated scheme to reduce the peak-to-average power ratio (PAPR) in coded orthogonal frequency-division multiplexing (OFDM) systems. First, they employ a label-bits-inserted encoder of a random-like code to achieve selected mapping (SLM). Then they set a threshold at the selector to limit the number of candidate sequences. Both analytical and numerical results show that the complexity of the SLM implemented by the label-bit-inserted encoder can be significantly reduced by threshold limited selection. With the same complexity, the performance of PAPR reduction is improved. The proposed concatenated PAPR reduction scheme enjoys many advantages including low-complexity, small overhead, no side information transmission and no performance loss or additional complexity at the receiver. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detection and avoidance scheme for direct-sequence ultra-wideband system: a step towards cognitive radio

    Page(s): 1043 - 1050
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    Detection and avoidance (DAA) is a soft-spectrum-based adaptation scheme proposed for multi-band ultra-wideband (MB-UWB) radio as a measure of co-existence between UWB devices and existing radio systems in overlapped bands. However, the principle of DAA in the direct-sequence UWB (DS-UWB) is very different from that in MB-UWB method. In DS-UWB, re-design of transmission pulses is required each time a new set of allowed bandwidths is discovered, as opposed to the turning-off-carrier-tone way in MB-UWB. Therefore the re-design of DS-UWB pulses in a cognitive radio environment must be easily reconfigurable. The problem of synthesising DS-UWB pulses conforming to arbitrary spectrum masks is addressed. In the proposed method, the masks are expanded by orthonormal functions chosen to be Hermite-Gaussian functions (HGFs). As the HGFs are eigenfunctions to the fractional Fourier transform, of which the inverse Fourier transform is a particular case, the set of the HGFs constitutes both a time-domain and a frequency-domain basis, that is, a co-basis, and therefore the transmission pulses can be easily obtained from the expansion of the specified spectrum masks. The co-basis-expansion-based DAA scheme for DS-UWB is evaluated through computer simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Channel estimation for time-hopping pulse position modulation ultra-wideband communication systems

    Page(s): 1051 - 1060
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (223 KB)  

    Ultra-wideband (UWB) communication systems are used in indoor environments with dense multi-path characteristics. Therefore channel estimation has an important role in the receiver of these systems. A new approach for data-aided (DA) and non-data-aided (NDA) channel estimation is proposed, which is called the pulse compression (PC) method. This method is useful for UWB systems employing time-hopping pulse position modulation. The PC method requires only some basic operations such as sampling, overlap-add and finite impulse response filtering. The PC method, in both DA and NDA scenarios, in spite of its low complexity, outperforms the maximum-likelihood (ML) method in channel parameters estimation. The bit error rate (BER) of the DA method, in single-user scenario, performs as well as the ML method, and in multi-user scenario, in the worst case, there is only 0.5 dB loss compared with the ML method. In the case of NDA scenario, the proposed method outperforms the NDA-ML method, that is, in the single-user scenario about 4 dB gain at the BER of 10-3 is observed. In multi-user scenario, it outperforms significantly the NDA-ML method, and its performance loss in comparison with the perfect channel knowledge scenario is about 3 dB at the BER of 10-3. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improved low-complexity low-density parity-check decoding

    Page(s): 1061 - 1068
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (518 KB)  

    A practical low-complexity decoding of low-density parity-check codes is studied. A fast decoding scheme for weighted bit-flipping (WBF) based algorithms is first proposed. Then, an optimised 2 bit decoding scheme and its VLSI architecture are presented. It is shown that the new approach has significantly better decoding performance while having comparable hardware complexity compared with WBF-based algorithms. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Joint maximum-likelihood frequency offset and channel estimation for multiple-input multiple-output-orthogonal frequency-division multiplexing systems

    Page(s): 1069 - 1076
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (373 KB)  

    The problem of joint maximum-likelihood estimation of the carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output orthogonal frequency-division multiplexing systems is investigated, assuming that a training sequence is available. The exact solution to this problem turns out to be too complex for practical purposes. To overcome this difficulty, the authors resort to the expectation-maximisation (EM) algorithm and propose an iterative scheme which iterates between estimating the channel parameters and the frequency offset. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications. Moreover, the Cramer-Rao bounds (CRB) for both CFO and channel estimators are developed to evaluate the performance of the proposed scheme. Simulation results show that the proposed algorithm achieves almost ideal performance compared with the CRBs in all ranges of signal-to-noise ratio for both channel and frequency offset estimates. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of rectangular quadrature amplitude modulation with combined arbitrary transmit antenna selection and receive maximal ratio combining in nakagami-m fading

    Page(s): 1077 - 1088
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (265 KB)  

    The average symbol error probability (SEP) performance of arbitrary rectangular quadrature amplitude modulation in the context of arbitrarily ordered transmit antenna selection and receive maximal ratio combining diversity system is analysed. The channel gains are assumed to follow Nakagami-m fading distribution with in general arbitrary fading parameters. Exact expressions for the average SEP performance are derived for the general case of unequal in-phase and quadrature decision distances as well as distinct in-phase and quadrature modulation orders. The results generalise many previous case studies, and can be used to investigate the impact of various diversity-combining schemes and different modulation and channel parameters on the system average SEP performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Distributed source coding using symbol-based and non-binary turbo codes - applications to wireless sensor networks

    Page(s): 1089 - 1097
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (197 KB)  

    A simple but powerful scheme for distributed source coding (DSC) based on the concept of binning and syndromes and non traditional turbo codes is proposed. The previous works on the compression with side information using turbo codes and the binning technique are focused on binary turbo codes. The source is considered to be binary or is converted to a binary stream. This conversion, however, reduces the redundancy that could be exploited by the compression algorithm. To achieve higher compression efficiency, the authors propose using a scheme based on a turbo decoder that decides over symbols rather than bits. In the same direction and for further performance improvement, at the cost of increased encoder complexity, they also present a DSC scheme based on non-binary turbo codes. The results demonstrate improved performance. Based on the suggested algorithms, a scheme for gathering real data in wireless sensor networks and assess the corresponding energy savings is proposed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • WLAN smart antenna with Bluetooth interference reduction

    Page(s): 1098 - 1107
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (483 KB)  

    Because of the coexistence of wireless local area network (WLAN) and Bluetooth at the same ISM band, WLAN systems cannot eliminate the interference by Bluetooth in the physical layer by carrier sense multiple access/collision avoidance. A novel smart antenna system for the WLAN systems to suppress the Bluetooth interference is proposed. The proposed smart antenna system employs the property of multi-carrier transmission of an orthogonal frequency-division multiplexing (OFDM) system to eliminate the correlation among the multi-path components, and the direction of arrival (DOA) estimation algorithm can estimate the correct DOAs. In the simulation, we apply the proposed smart antenna to the 802.11 system using OFDM. The simulation results demonstrate a superior performance under Bluetooth interference. 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