By Topic

Communications, IEE Proceedings-

Issue 1 • Date Feb 1999

Filter Results

Displaying Results 1 - 11 of 11
  • Performance comparison of spread-spectrum methods on an interference-limited HF channel

    Page(s): 23 - 28
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A severe problem with radio communication in the high-frequency range is the large amount of typically narrowband, interfering signals from other users. A statistical description of the interfering signals is employed in evaluating different spread-spectrum HF radio systems. In particular, when a frequency-hopping (FH) and a direct-sequence (DS) system are compared, the FH system performs better than the DS system under the author's assumptions. The FH system is inherently well suited for the HF environment with its predominantly narrowband interfering signals. The interference rejection capability that the DS systems normally possess is not sufficient to handle the large dynamic range of the HF interfering power. Additional narrowband interference rejection would be required to create useful DS systems for the HF channel. Furthermore, the author demonstrates the dramatic gain connected with adaptive frequency-hopping, which uses an adaptively selected pool of the channels with least interference for the communication View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive multilevel code selection and MUI cancellation for DS/CDMA over fading channel

    Page(s): 35 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    For transmission of speech or multimedia information in a time-varying mobile channel, fixed rate codes are normally used designed for average or worst channel conditions. However, fixed rate codes fail to explore the time-varying nature of the mobile channel. In their previous work the authors have shown that a multilevel code, when used in conjunction with multiuser interference (MUI) cancellation in cascade, yields better performance than a conventional coded modulation scheme applied to CDMA. They show that, when multilevel codes are changed with varying channel conditions (i.e. are chosen adaptively according to the channel state information (CSI)), the throughput (average number of information bits per symbol duration) can be increased without too much performance degradation. Code selection criteria as well as some codes with appropriate thresholds are also presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Novel group-based spreading code protocol: hierarchy schedule sensing protocol for CDMA wireless networks

    Page(s): 15 - 21
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    An efficient hierarchy schedule sensing (HSS) spreading code protocol is proposed for wireless DS/CDMA networks. It uses a central pilot frame to schedule request transmissions to avoid collisions. To reduce the scheduling time, hierarchical group-based spreading codes are employed. A two-dimensional continous time Markov chain is used to model the behaviour of the HSS protocol. The performance is evaluated under various channel traffic loads. The results show that the HSS protocol offers a robust performance without much extra hardware cost if compared with conventional receiver-based spreading code protocols View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Blind adaptive algorithm for demodulation of DS/CDMA signals with mismatch

    Page(s): 29 - 34
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The minimum mean-squared error (MMSE) linear detector is known to be a near-far resistant strategy for direct-sequence code-division multiple access systems. The MMSE linear detector can be implemented adaptively by the MOE adaptation algorithm or the Griffiths (1969) adaptation algorithm, which utilises the desired signal vector for initial adaptation instead of training sequences. The performance loss caused by the imprecise knowledge of the desired signal vector is investigated. A new blind adaptive algorithm is presented to mitigate the effect of the mismatch caused by the timing error in acquisition. Several numerical results show that the new algorithm can provide a resistance to the effect of mismatch compared to the MOE and Griffiths algorithms View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New quasi-analytic BER estimation technique on the nonlinear satellite communication channels

    Page(s): 68 - 72
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    A novel quasi-analytic (QA) simulation technique to estimate bit error rate (BER) over nonlinear satellite communication channels is introduced. Generally, QA simulation is performed by assuming that the noise probability density function (PDF) at the receiver is known, and that, in most cases, the noise entering the receiver is considered to be additive white Gaussian noise (AWGN). However, because of the nonlinear characteristics of a high power amplifier such as a travelling wave tube amplifier (TWTA) in the satellite, the noise PDF present in the down-link cannot be assumed to be a Gaussian PDF any longer. An efficient QA technique which finds a non-Gaussian noise PDF at the output of the TWTA and hence estimates BER accurately, is introduced. Simulation has been performed using a QPSK satellite system, and BERs are estimated using various methods including the Monte Carlo (MC) method, classical QA methods, and the proposed method. Simulation results showed that the proposed QA technique produces BER values approximating to those of the MC technique View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Minimum cost wavelength-path routing and wavelength allocation using a genetic-algorithm/heuristic hybrid approach

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    Minimum cost wavelength-path routing and wavelength allocation of multiwavelength all-optical transport networks using a genetic-algorithm (GA)/heuristic hybrid approach is described. A cost model is adopted which incorporates a dependency on link wavelength requirements. The hybrid algorithm developed uses an object-oriented representation of networks, and incorporates four operators: path mutation, single-point crossover, reroute and shift-out. In addition, an operator-probability adaptation mechanism is employed to improve operator productivity. Experimental results from seven fifteen-node test networks, obtained using a tool for optical network optimisation, modelling and design (NOMaD), suggest the GA/heuristic hybrid approach provides superior results compared to three other wavelength-allocation heuristics, except when the network cost depends most heavily on wavelength requirement View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Co-channel interference analysis for mobile radio suffering lognormal shadowed Nakagami fading

    Page(s): 49 - 54
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    Determination of the outrage performance of a cellular mobile system in lognormal shadowed Nakagami (1960) fading environments has been the focus of many researchers. However, general results are not available in the literature. The difficulty arises from the philosophy which attempts to determine first the outage probability for Nakagami fading and then average it over lognormal distributions. The consequence is outage expressions in the form of an intractable multi-fold integral. By formulating the problem in the framework of characteristic functions and naturally combining the two separated steps in a single one, the author obtains an expression for outage probability always in the form of a two-fold integral no matter how many co-channel users are in operation. The outage probability so obtained can be accurately and efficiently evaluated by using the Hermite and Gaussian quadrature. It thereby provides a general analysis tool for lognormal shadowed Nakagami channels with arbitrary parameters. Numerical results are also presented to illustrate the theory View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cell loss probability of a finite ATM buffer queue

    Page(s): 9 - 14
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    Various formulations have been proposed to analyse the statistical behaviour of multimedia traffic over an ATM switch of infinite capacity. The authors present different approaches for calculating the cell loss probability of a finite buffer queue. They first model an ATM traffic source using a two-state Markov-modulated Bernoulli process (MMBP), and then calculate the cell loss probability of a finite ATM buffer queue fed with N such traffic sources using different approaches. Numerical comparison confirms that all these approaches yield similar results. The first two approaches are based on the matrix geometric formulation. The authors derive the queue length distribution of a finite ATM buffer and solve for the probability. The cell loss probability is approximated by the saturation probability (i.e. the probability that the buffer is full, in the first approach). In the second approach, having obtained the state probability, the authors derive the exact expression for the cell loss probability using conditional probability. The third approach is based on an approximation for the buffer content of a queueing buffer. The cell loss probability is formulated using a generating function and solved by examining the smallest pole of its function View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Availability and performance of satellite links suffering from interference by an adjacent satellite and rain fades

    Page(s): 61 - 67
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    An analysis is presented relating rain attenuation statistics to BEP performance of Earth-space links subjected to interference by an adjacent satellite operating in the same frequency band. A systematic design method is proposed that takes into account the BER objectives specified by the ITU for the design of satellite links. Numerical results based on the proposed method have been obtained to investigate the combined effect of rain and interference for the Ku and Ka bands and for various data rates and climatic zones View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive equalisation of frequency selective multipath fading channels based on sample selection

    Page(s): 55 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The behaviour of the frequency selective multipath fading channel has been studied for normalised RMS delay spread over the range from 0.01 to 1.0. This corresponds to 1 ns-100 ns RMS delay spread for a system operating at 10 Mb/s. Over this range, occur in bursts because of fading, intrasymbol interference (IaSI) when the channel spread is low and intersymbol interference (ISI) when the channel spread is high. When the SNR is sufficiently high, the channel is rarely in deep fade, and equalisers in such channels may improve the system performance. It is shown that conventional decision feedback equalisers (DFE) with fixed midpoint sampling do not perform well in the range of RMS delay spread considered for realising a BER⩽10-3. A new equalisation technique is introduced, namely, the sample-diversity (SD) DFE. To realise sample diversity at the DFE input, N samples are taken from each symbol and these samples are used to drive N different DFEs. A simple selection mechanism is introduced to select the best sampling phase and DFE to be used in the tracking mode. Through simulations, the SDDFE is shown to have much better performance than conventional DFE. The SD technique is also applied to coherent-QPSK (CQPSK) detection where N parallel detectors are used. Being a combination of diversity and equalisation, the SD approach is shown as a promising technique for symbol detection in multipath fading channels View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of an FFT-based FFH/BFSK product-combining receiver with partial-band jamming

    Page(s): 43 - 48
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The performance analysis of a fast frequency-hopped binary frequency-shift-keying (FFH/BFSK) spread-spectrum (SS) system in conjunction with a fast Fourier transform (FFT) processor is presented. Under the conditions of partial-band jamming (PBJ) and additive white Gaussian noise (AWGN), the bit-error rate (BER) expressions of the proposed FFT-based product-combining receiver (PCR) are derived in terms of the characteristic functions of the decision statistics. The BER expressions, validated by simulation results, are applicable to any arbitrary diversity level. The BER results show that there is an optimum diversity level for the FFT-based PCR. The FFT-based PCR is also shown to perform better than the well known square-law linear-combining receiver View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.