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Communications, IEE Proceedings-

Issue 3 • Date Jun 1997

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Displaying Results 1 - 14 of 14
  • Multirate coding for mobile communications link adaptation

    Publication Year: 1997 , Page(s): 211 - 216
    Cited by:  Patents (24)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    A mobile communication system that uses multirate source and channel coding is capable of trading off the source coder bit rate against the channel coder rate to optimise performance over a wide range of channel conditions. This link adaptation enables a mobile station to maintain reasonable speech quality even during marginal carrier to interference ratio conditions. The paper details the design and evaluation of a quad-rate speech and channel coder optimised to provide wireless link adaptation by seamless rate switching View full abstract»

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  • “Dead reckoning”-a primitive and efficient self-routing protocol for ultrafast mesh networks

    Publication Year: 1997 , Page(s): 135 - 142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    The authors describe a new approach to the problem of self-routing in ultra-high-speed multi-computer interconnection networks. The method is based on the concept of “dead reckoning” (self-navigation without the use of landmarks), and is applicable to networks with a mainly regular mesh topology. The packet header contains, in addition to the usual destination address, a tiny amount of directional information (as little as 2 bits in the case of the Manhattan street network). With this additional data, the algorithm for path selection at the network nodes becomes extraordinarily simple, allowing very fast processing with good routing efficiency and high throughput. Most significantly, with this method it is not necessary to read each binary digit of the destination address of every packet arriving at every intermediate routing node; it is sufficient only to perform a single-stage pattern match between the packet address and the address of the routing node. This feature, and the low latency of this self-routing technique, make it particularly well suited to ultrafast photonic networks View full abstract»

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  • Hidden preamble detector for acquisition of frequency hopping multiple-access communication system

    Publication Year: 1997 , Page(s): 161 - 165
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    The problem of acquisition of frequency hopping multiple-access communication systems is addressed. The receiver uses the hidden preamble detector to accomplish the acquisition process. An upper bound on the mean acquisition time is provided and the results are compared with an active correlator and a matched filter. The results show that the hidden preamble detector is a low-complexity detection scheme and has an acquisition speed that is nearly as fast as the matched filter View full abstract»

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  • Performance analysis based on co-channel interference statistics of indoor CDMA systems with RAKE receiver and power control under multipath fading

    Publication Year: 1997 , Page(s): 173 - 179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The statistical correlation distribution convolution algorithm is introduced to study the performance of DS/CDMA indoor wireless systems. With the help of the algorithm, it is possible to obtain the bit error rate against number of simultaneous interfering transmitters, considering the effects of co-channel interference, Rayleigh multipath fading and power schemes. The performance of two receivers, the conventional correlator and equal-gain RAKE receiver, is compared. It is shown that the RAKE receiver can improve the system performance under the indoor multipath fading. However, its effectiveness under the power control is sensitive to the severity of the multipath interference. When the multipath fading is rampant, a tight power control based on the main paths may not help improve the performance of the RAKE receiver View full abstract»

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  • Threshold decision technique for direct sequence code synchronisation in a fading mobile channel

    Publication Year: 1997 , Page(s): 155 - 160
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    The work presents the performance of a threshold decision technique for direct-sequence spread-spectrum code synchronisation. For received PN codes with different SNR, this scheme is able to detect a desired threshold value for verification in the search mode such that the detection probability of the verification mode is maximised and the false alarm probability of the verification mode is minimised. The proposed serial acquisition system is compared to the conventional serial acquisition system, and a significant improvement of performance is shown. Analysis of system performance in both the search and verification modes is presented, and key quantities such as the false alarm probability, the detection probability, and the mean acquisition time are derived in both nonfading and Rayleigh fading environments View full abstract»

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  • Combined techniques for channel allocation algorithms in mobile radio systems

    Publication Year: 1997 , Page(s): 205 - 210
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Global assignment techniques, comprising the various forms of the dynamic channel allocation algorithms, and local assignment techniques, characterised by the algorithms taking advantage of the traffic available at the overlapping service areas, are combined into a common algorithm for mobile radio applications. The performance analysis is carried out by means of the Monte Carlo simulation having a real cellular network as the system under study. The results show a remarkable traffic performance, substantially better than that attained by the individual techniques. An increase in the complexity due to the combination is certainly expected, but, because the local techniques are reasonably simple to implement, it is believed that the overall complexity is mostly dictated by that inherent to the global technique View full abstract»

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  • Nonuniform traffic analysis on a class of self-routing networks

    Publication Year: 1997 , Page(s): 143 - 149
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    The performance of a class of single-path self-routing networks with 2×2 switching elements has been analysed in several studies with ad hoc models that are applicable only to the specific traffic pattern and network interconnection pattern considered. The paper describes a generic model that can accommodate different nonuniform traffic patterns and network interconnection patterns. It also presents results obtained with this model for several nonuniform traffic patterns on unbuffered and input-buffered banyan, omega and baseline networks View full abstract»

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  • Effect of bandlimiting filters on multidimensional digital communication system in Gaussian noise

    Publication Year: 1997 , Page(s): 150 - 154
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The effect of bandlimiting filters in a receiver only and both transmitter and receiver on the bit error probability of a multidimensional digital communication system in a Gaussian channel is analysed. Numerical results are presented for fourth-order Butterworth filters in the receiver and either a third-order filter or no filter in the transmitter View full abstract»

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  • Calculating the expected synchronisation delay for T-code sets

    Publication Year: 1997 , Page(s): 121 - 128
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (780 KB)  

    When variable-length encoding is used over a noisy communications channel, synchronisation problems typically arise following any sort of error. T-codes have been noted for their inherent self-synchronising behaviour following such a loss of synchronisation. Given a code set and associated source symbol probabilities, one measure of synchronisation performance is the expected synchronisation delay (ESD). The authors present a new analytic method for calculating the ESD for an arbitrary T-code set and associated information source. The method more closely reflects the construction of T-code sets than the earlier symbol-oriented asymptotic calculation of Titchener (1986), and yields better precision than Monte Carlo simulations, which have been typically used with large sets. The new algorithm further accommodates the generalised T-augmentation construction of Titchener (see IEE Proc. E, Digit Tech., vol.143, no.3, p.122-8, 1996) View full abstract»

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  • Performance analysis of noncoherent DS-CDMA systems in a Nakagami fading channel with arbitrary parameters

    Publication Year: 1997 , Page(s): 166 - 172
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Code division multiple access (CDMA) systems are actively being considered for use in mobile environments (such as cellular and personal communications systems). New semianalytical expressions for the bit error rate of an asynchronous direct sequence CDMA system employing noncoherent binary demodulation formats in a Nakagami fading multipath channel are derived. Two binary demodulation schemes are considered, namely, the differential phase shift keying and the square-law demodulation with orthogonal spreading sequences. In each case the analysis assumes that an arbitrary number of independent but nonidentical resolvable paths are combined by the RAKE receiver. The results show that the effect of nonidentical fading on system performance cannot be ignored in such systems View full abstract»

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  • Error performance of circular 16-DAPSK with postdetection diversity reception in Rayleigh fading channels

    Publication Year: 1997 , Page(s): 180 - 190
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (988 KB)  

    There is a growing demand for future mobile radio systems to provide not only speech but also integrated data communications and new forms of digital based services. A closed-form expression for the probability of circular 16-ary differential amplitude and phase shift keying with postdetection diversity combining is obtained for frequency-nonselective Rayleigh fading channels. The effect of random FM noise is also considered in the evaluation. Since both the amplitude and phase are encoded and decoded independently, their detailed performances are analysed separately. System parameters such as the ring ratio and decision thresholds have been optimised for a number of fading conditions. The optimal and suboptimal decision thresholds are evaluated. The optimal ring ratio of the modulation is generally a function of the Doppler frequency. The results have shown that postdetection diversity is a powerful technique for reducing the effects of random FM noise View full abstract»

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  • Small improvements in half-rate convolutional codes with popular constraint lengths for applications in satellite communications

    Publication Year: 1997 , Page(s): 199 - 204
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    Half-rate convolutional coding with constraint length 7 and Viterbi decoding has been widely used on satellite data links for a long time because of the substantial savings in satellite transponder power through the 4-5 dB in coding gain. A variant of the standard convolutional encoder consisting of a parallel- and serial-shift register combination is described which leads to small improvements in coding gains for popular constraint lengths and code rates. For example, it is shown that there is a memory-7 half-rate code, with a dfree of 11 in comparison with the best conventional memory-7 half-rate code which has a dfree of only 10. The parallel- and serial-shift register combination can be used to generate a wide class of k/n rate codes in a straightforward manner and can lead to improved performance in concatenated coding arrangements View full abstract»

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  • Analysis of ATM cell loss for systems with on/off traffic sources

    Publication Year: 1997 , Page(s): 129 - 134
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Cell loss, which occurs when buffers overflow in ATM switches, is a key measure for the performance of an ATM network. An ATM network must be designed for very low and predictable cell loss probabilities to provide adequate quality of service for all users. Many methods have been proposed for allocating bandwidth and determining buffer size requirements to provide quality-of-service guarantees. The probabilistic nature of these methods is subject to overly optimistic allocations (insufficient in the worst case) or overly pessimistic allocations (over specified in the best case). The authors present an exact analysis of cell loss for periodic on/off (bursty) traffic sources. Periodic on/off traffic sources are representative of output traffic from leaky-bucket rate-control mechanisms as used in ATM networks. Closed-form equations for buffer sizing and cell loss probabilities are developed and rigorously proved for a single queue with multiple traffic sources and multiple queues with multiple traffic sources serviced via a round-robin discipline. These closed-form equations can be used in concert with probabilistic methods to ensure that buffer and bandwidth allocations are made between the best- and worst-case requirements View full abstract»

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  • Performance of binary CPM schemes in frequency selective fading channels with pilot symbol assisted detection

    Publication Year: 1997 , Page(s): 191 - 198
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (804 KB)  

    Signals transmitted over a land mobile radio channel are very often subjected to frequency selective fading. A detection technique is proposed for continuous phase modulation (CPM) operating in such an environment. The technique uses embedded pilot symbols for channel impulse response estimation. The estimated channel response is updated from symbol to symbol and is used during the sequence detection of the CPM signal. Unlike pilot symbol assisted linear modulation, the pilot symbols in this CPM system are divided into two groups. The first group of pilot symbols is data dependent and is used to force the modulator to return periodically to a known system state. The second group is not data-dependent and is used to specify a known waveform emanating from the periodic known state, for the purpose of channel estimation. The proper pilot symbol encoding rules, as well as the structure of the companion channel estimator, are presented. It is shown that CPM schemes employing this detection technique exhibit no irreducible error floor even in the presence of fast fading and large delay spread. The modem actually performs better in a heavily frequency selective fading environment, due to the implicit diversity effect provided by the channel. The difference in energy efficiency between frequency selective and flat fading can be as large as 5 dB at a 10-3 bit error rate and 8 dB at a 10-4 error rate. These results suggest that the proposed technique is very suitable for use in a system which employs diversity View full abstract»

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