By Topic

Communications, IEE Proceedings-

Issue 3 • Date Jun 2000

Filter Results

Displaying Results 1 - 11 of 11
  • Efficient digital predistortion in radio relay links with nonlinear power amplifiers

    Page(s): 175 - 179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    An adaptive digital predistortion scheme, based on the amplitude-and-phase predistortion concept, is considered for the linearisation of microwave power amplifiers in high-data-rate radio relay links. The algorithm is thoroughly assessed and compared to a digital predistortion scheme previously proposed in the literature, assuming linearisation accuracy, adaptation speed and implementation complexity as merit criteria. The proposed predistorter proves to be considerably faster than the other scheme, though exhibiting approximately the same accuracy and a reduced complexity View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Tamed frequency modulation detection analysis with NEC receivers

    Page(s): 149 - 154
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    Various PSK modulations as well as minimum shift keying (MSK) have achieved great improvements in the signal-to-noise ratio by utilising the nonredundant error correction (NEC) technique. The cost for this improvement is neither an increase in bandwidth nor an increase in transmission power, but some extra complexity in the receiver. The receiver is only equipped with a bank of differential detectors and a simple error detection/correction circuit, whose complexity depends on the correction capability that the transmit-receive system must have. Here, it is proved that it is possible to differentially detect correlative, nonsymmetric continuous-phase frequency modulations such as tamed frequency modulation (TFM) with NEC receivers. TFM has not been used as much as MSK until now owing to its generation difficulties, but its main advantages of constant envelope and of very high spectrum efficiency make it a perfect candidate to work upon. Hence, TFM is first contaminated with additive white Gaussian noise and is subsequently detected through a single-error-correcting NEC receiver. Both the theoretical analysis and the computer simulations show that substantial error probability reduction is achieved over differentially detected TFM systems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bit-error probabilities for 2- and 4-DPSK in general Nakagami fading channels with correlated Gaussian noise

    Page(s): 155 - 162
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Exact bit-error probability (BEP) expressions are derived for 2- and 4-ary differential phase shift keying (2- and 4-DPSK) with post-detection equal gain combining (EGC) in arbitrarily correlated slow Nakagami fading channels. Unlike previous work, the effect of noise correlation between adjacent symbol intervals is considered and shown explicitly in the BEP expressions. The characteristic function method is used to give a BEP expression in a general form for 2- and 4-DPSK. Furthermore, closed-form BEP expressions are derived for 2-DPSK with coloured noise, and for 4-DPSK with white noise and integer fading parameter m. The theoretical result is demonstrated by analysing two antenna configurations, giving some interesting findings View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Iterative soft-decision decoding of linear block codes

    Page(s): 133 - 136
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    The authors show that for linear block codes defined over extensions of GF(2) a variant of the sub-optimal soft-decision Dorsch (1974) algorithm offers very good performance with low complexity. Furthermore, we show that, owing to the nature of the algorithm, it can easily be adapted to produce a soft-decision output. This is then exploited in an iterative decoding scheme for product codes which is based on a decoding algorithm first proposed by Pyndiah (see IEEE Trans. Commun., vol.46, no.8, p.1003-10, 1998 and by Aitsab and Pyndiah (see Proceedings of the IEEE Globecom'96 conference, vol.1/3 p.121-5, 1996). Two different interleaver structures are presented yielding different performances both in terms of coding delay and bit-error-rate for a given signal-to-noise ratio. Reed Solomon codes are used in the simulations. For reasons of complexity, only codes defined over GF(16) are considered. Simulations were carried out for the AWGN channel View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptable Viterbi detector for a decomposed CPM model over rings of integers

    Page(s): 137 - 143
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    A novel, practical and flexible way of implementing continuous phase modulation (CPM) using a decomposed model and a Viterbi detector is presented. The decomposed CPM modulator, comprising a continuous phase encoder (CPE) and a memoryless modulator (MM), is implemented and can be concatenated with a ring convolutional encoder (CE) such that the detector may be readily adapted to the ring of integers over which the CE/CPE operates, A partial-response CPM system is simulated over additive white Gaussian noise (AWGN) and Rayleigh flat fading (RFF) channels, and results, in terms of the bit error rate (BER) against the signal to noise ratio (SNR) are presented, discussed and evaluated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Decomposition technique for fixed channel assignment problems in mobile radio networks

    Page(s): 187 - 194
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The paper is concerned with the possibility of using a decomposition technique to solve fixed channel assignment (FCA) problems. The main idea is first to transform and then to decompose the original large FCA problem into a number of smaller-size connected integer linear programming (ILP) sub-problems. A sequential branch-and-bound algorithm is then used to solve optimally and efficiently the sub-problems. The computational results obtained when the technique is applied to a number of different benchmark problems confirm that the proposed technique is computationally efficient in solving large-scale FCA problems and that it is capable of significantly reducing the computation time involved. The technique also makes it possible in some cases to solve large-scale FCA problems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiple-symbol differential detection of π/4-DQPSK in land mobile satellite communication channels

    Page(s): 163 - 168
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    Multiple-symbol detection of π/4-DQPSK in land mobile satellite communications (modelled as correlated Rician fading) is studied. Metrics for maximum likelihood detection are derived. For the no channel-information case. The generation of the metric can be implemented as a multiple-symbol differential detector. For the ideal channel-information case, however, the generation of the metric cannot be implemented as a multiple-symbol differential detector. The BER performances of this scheme are evaluated through the union bounds of pairwise bit error probabilities and Monte Carlo simulation for both cases. It has been found that in light or medium fading Rician channels, about 1.0 dB gain for Eb/N0 at a BER=104 can be achieved by using four-symbol detection instead of conventional two-symbol detection. The gain is greater than 1 dB when the BER is lower. It is also demonstrated that multiple-symbol differential detection actually increases the BER for severe fading Rician channels (K<10.5 dB) or Rayleigh channels if no channel information is available. However, with ideal channel information, the multiple-symbol detection can reduce the BER at high Eb/N0. The influence of different fading rates on the BER performance is also evaluated, showing a lower BER at a lower fading rate, as expected View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Traffic performance analysis of integrated dual-band cellular radio networks

    Page(s): 180 - 186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The teletraffic performance of integrated dual-band networks is evaluated. This type of network links two cellular radio systems which have different sets of frequency bands and the same cell size to a single base station. Dual-band mobile stations use handoff to establish calls on the better system. The multidimensional birth-death process is used to characterise the system state and evaluate the performance of dual-band networks in a given cell. The analytical results show that an integrated dual-band network can provide higher offered traffic load than a heterogeneous network, which can only handle roaming between two cellular radio systems. The blocking probability and the offered traffic load of the integrated dual-band network are also calculated by the Erlang-B formula to validate the results View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Planar approximation for the least reliable bit log-likelihood ratio of 8-PSK modulation

    Page(s): 144 - 148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    The optimum decoding of component codes in block coded modulation (BCM) schemes requires the use of the log-likelihood ratio (LLR) as the signal metric. An approximation to the LLR for the least reliable bit (LRB) in an 8-PSK modulation based on planar equations with fixed-point arithmetic is developed that is both accurate and easily realisable for practical BCM schemes. Through an error power analysis and an example simulation it is shown that the approximation results in less than 0.06 dB in degradation over the exact expression at an Es/N0 of 10 dB. It is also shown that the approximation can be realised in combinatorial logic using roughly 7300 transistors. This compares favourably to a look-up table approach in typical systems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Simulation of reflection effects for a dedicated short range microwave communication system

    Page(s): 195 - 199
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Reflection effects can severely degrade the performance of electronic road pricing systems in which communication must take place between a fixed road side system and an on-board unit in a moving vehicle. This degradation is caused by destructive and constructive interference between the direct-path signal and reflected signals. Such interference will also occur in systems using circularly polarised waves. Depolarisation will also have a negative influence on the communication. Both problem areas, which are closely related, are investigated by numerical simulations. The degradation is determined and a solution to overcome this problem is suggested View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Quasi-deterministic space-time second-order blind sequence estimation

    Page(s): 169 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    A fast, robust, second-order, blind space-time algorithm is presented for identifying the symbols from a transmitting mobile source, received at the base station of a wireless uplink channel, by estimating the effective inverse channel via a quasi-deterministic approach. This technique achieves a trade-off between speed and robustness in the presence of increasing additive channel noise by using estimates of the additive-noise variance and short-term temporally averaged estimates of an analogue of the ensemble averaged autocorrelation of the received sequence. Using these psuedo-autocorrelations provides a faster sequence-estimation procedure than existing deterministic techniques which merely seek to use the properties of the signal subspace, ignoring the correlation between successive received symbols-an approach that has been confined to statistical techniques. Likewise, inclusion of the additive noise variance (which needs to be computed less frequently than the block-processing rate) lends robustness to the sequence estimation procedure. Since no other statistical averages are computed, the proposed technique is sufficiently fast in both time- and frequency-selective fading environments. Further, no assumptions are made regarding the distribution of the received signal, the dimensionality of the signal subspace, or other properties of the symbol alphabet. Compared with existing blind identification techniques, this approach has mild identifiability conditions, low computational requirements and superior performance characteristics View full abstract»

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