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Communications, IEEE Transactions on

Issue 11 • Date Nov 1988

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Displaying Results 1 - 13 of 13
  • Statistical distribution of PCM framing times

    Publication Year: 1988 , Page(s): 1236 - 1241
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The authors evaluate a robust framing technique which incorporates sufficient memory to simultaneously evaluate all bits in a candidate synchronizing codeword. Three performance measures are identified and the distribution function and mean value are developed in closed form for each measure. Predicted search and maintenance time distributions have been verified by measurements on a laboratory model. The authors present graphs of search time distributions which illustrate the effect of system parameters and variations in the channel error rate View full abstract»

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  • Interference suppression to aid acquisition in direct-sequence spread-spectrum communications

    Publication Year: 1988 , Page(s): 1200 - 1207
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The acquisition and tracking systems of a spread-spectrum receiver are probably the most critical components of the receiver, since if they fail to function properly, it is doubtful that the desired signal can be successfully detected. This means that the affect of interference (such as jamming) on the receiver while it is attempting to learn the correct phase position of the incoming code might be especially harmful, since the interference might not allow the receiver to acquire the signal. To address this problem, a narrow-band interference suppression filter is used to enhance the performance of a serial search acquisition scheme for a direct-sequence spread-spectrum receiver. Analytical expressions for the probabilities of error in both the search and lock modes are derived, and numerical results are used to illustrate the sensitivity of the receiver to various system parameters. It is shown that the presence of the rejection filter can be significantly improves the performance of the acquisition system View full abstract»

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  • Asymptotic performance of M-ary orthogonal modulation in generalized fading channels

    Publication Year: 1988 , Page(s): 1246 - 1248
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    The asymptotic (M→∞) probability of symbol error Pe,m for M-ary orthogonal modulation in a Nakagami-m fading channel is given by the incomplete gamma function P(m, mx) where x=In 2/(Eb/N0) and Eb is the average energy per bit. For large signal-to-noise ratio this leads to a channel where the probability of symbol error varies as the inverse mth power of Eb/N0. These channels exist for all m⩾1/2. The special case of m=1 corresponds to Rayleigh fading, an inverse linear channel View full abstract»

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  • PSK and DPSK trellis codes for fast fading, shadowed mobile satellite communication channels

    Publication Year: 1988 , Page(s): 1242 - 1246
    Cited by:  Papers (50)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    The performance of 8-PSK and 8-DPSK trellis codes is presented for a class of fast fading, land mobile satellite communication channels. The fading model is Rician but, in addition, the line-of-sight path is subjected to a fast lognormal attenuation that represents tree shadowing. The fading parameters used in this study represent the degree of shadowing and are based on measured data. The primary application considered is for digital speech transmission and thus, bit error probabilities in the order of 10-3 are emphasized. Sensitivity of the bit error probability to amplitude fading, amplitude and phase fading, and decoding delay is presented. Performance is determined via digital computer simulation. Optimal four- and eight-state codes are determined and optimality is found to be dependent on the presence of lognormal shadowing View full abstract»

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  • Optimum quantization for detection

    Publication Year: 1988 , Page(s): 1254 - 1258
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Vector quantization is a procedure widely used in communications. The problem has been solved for the basic detection situation using the locally optimal procedure and with some constraints on the quantization scheme. It is stated in its widest sense, which consists of finding the partition of the observation space and the values associated with it in such a way that the detection performance is optimal. It is solved completely with the deflection criterion, and the solution introduces the concept of quantization by a likelihood ratio procedure View full abstract»

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  • Analysis of strategies for serial-search spread-spectrum code acquisition-direct approach

    Publication Year: 1988 , Page(s): 1208 - 1220
    Cited by:  Papers (45)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1064 KB)  

    A `direct' approach to obtain statistics of the code acquisition time for serial-search spread-spectrum receivers is presented, which combines the idea of algebraic characterization of the search with transform domain methods. This is a very general unified technique, yielding many other known results as special cases. One of the major advantages of the direct approach is that the effect of the search strategy on moments of the acquisition times can be isolated from the effect of the detection/verification logic. This fact will permit one both to analyze all known search strategies-confirming several conclusions regarding their comparative performance-and to propose two novel strategies (alternate search) which outperform the conventional ones when the code rewinding time is small in comparison to the dwell times. Optimum search strategy based on the maximum a posteriori criterion (MAP) is analyzed, thus ensuring an absolute and uniform basis of comparison. The two new strategies perform well by this measure View full abstract»

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  • Gaussian approximation versus nearly exact performance analysis of optical communication systems with PPM signaling and APD receivers

    Publication Year: 1988 , Page(s): 1185 - 1192
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    A 25 Mbit/s direct-detection optical communication system that used Q=4 PPM signaling was constructed and its performance measured under laboratory conditions. The system used a single mode AlGaAs laser diode (λ=834 nm) and low-noise silicon avalanche photodiode (APD). A procedure is given to numerically compute system performance which uses the nearly exact Webb's approximation of the true Conradi distribution for the APD output that does not require excessive amounts of computer time (a few CPU minutes on VAX 8600 per system operating point). Comparison revealed that modeling the APD output as a Gaussian process under conditions of negligible background radiation and low (less than 10-12A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain and overestimates of system bit error probability. Examples are given which illustrate the breakdown of the Gaussian approximation in assessing system performance. The measured performance of the system was found to be in excellent agreement with the performance predicted by the nearly exact computational procedure. This system achieved a bit error probability of 10-6 at a received signal energy corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700 View full abstract»

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  • Performance of 16-state SQAM in a nonlinearly amplified multichannel interference environment

    Publication Year: 1988 , Page(s): 1263 - 1267
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    The performance of 16-state SQAM (superposed-QAM) system, in a nonlinearly amplified multichannel environment, in the presence of additive white Gaussian noise (AWGN), intersymbol interference (ISI), and adjacent channel interference (ACI), is experimentally analyzed via computer simulation. Various channel conditions, such as channel spacings between the main and adjacent channels, and fade depth on the desired main channel, are examined. Baseband signal waveshape of 16-SQAM as well as the receive low-pass filter bandwidth are optimized to achieve a good P(e) performance. The result shows that 16-SQAM system is more efficient than MAMSK (multiamplitude MSK) in the frequency utilization View full abstract»

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  • Fast single-element PN acquisition for the TDRSS MA system

    Publication Year: 1988 , Page(s): 1226 - 1235
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (828 KB)  

    The authors present a description and performance analysis of a new PN code acquisition approach for the tracking and data relay satellite system with multiple access (TDRSS MA) return subsystem. The MA subsystem uses a phased array on-board the TDRS with 30 elements whose received signals are each independently retransmitted to the ground for beam forming. In the current operational system, acquisition is performed by using a serial search of the possible PN epochs on the beam-formed 30-element signal. In contrast, the new approach performs acquisition on a single (arbitrary) element signal using a parallel (i.e., simultaneous) search of all possible PN epochs. Since only one element signal is used, no beam forming is required prior to PN acquisition. The approach is based on sampling and digital processing of the received signal. The new method also incorporates techniques which counteract the effects of Doppler and asynchronous data modulation. The probability of correct acquisition as a function of acquisition time, signal-to-noise ratio, data rate, and user satellite Doppler is analyzed View full abstract»

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  • On the performance of digital detectors with dependent samples

    Publication Year: 1988 , Page(s): 1248 - 1254
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The asymptotic performances of three digital detectors operating with dependent samples are examined. Analytic expressions for the performances when the number of dependent samples M is large are obtained. Examples are also given which indicate how the performances vary with M. It is shown that the performances of hard-limiting detectors may be improved by processing more dependent samples. The amount of the hard-limiting loss that is recoverable depends upon the detector prefilter. A simple expression is derived which gives the irretrievable hard-limiting loss as a function of the noise autocorrelation, View full abstract»

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  • Novel structure for high-speed multihighway serial-to-parallel converter

    Publication Year: 1988 , Page(s): 1221 - 1225
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    The authors propose a novel structure for a high-speed multihighway serial-to-parallel converter for future high-speed digital switching systems. The proposed structure consists of a two-dimensional shift register array which can shift both horizontally and vertically. The shift direction is changed at the frame periods. The calculated results confirmed the superiority of the proposed structures over conventional ones, namely, faster operating speed and fewer gates View full abstract»

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  • Error performance of a digitally processed binary ESK frequency hopping receiver in the presence of large Doppler

    Publication Year: 1988 , Page(s): 1258 - 1262
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    Analysis is made of the effects of Doppler on the error rate performance of a low data rate binary FSK frequency hopping receiver, employing a discrete Fourier transform (DFT) technique for baseband detection. Bit detection decision is made by locating the maximum of the DFT outputs which, in the frequency domain, are assumed to be separated by 1/T where T is the bit period. Both the worst case and average error performances are obtained and presented as a function of Eb/N0 for various values of M where Eb/N0 is the signal bit energy-to-noise density ratio and M is the degree of freedom associated with the Doppler uncertainty window. The E b/N0 degradation as a function of M is also presented View full abstract»

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  • The design of a hybrid adaptive quantizer for speech coding applications

    Publication Year: 1988 , Page(s): 1193 - 1199
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    A new adaptive quantizer which uses a combination of instantaneous and syllabic adaptation is presented for use in speech codecs. It can be designed to adapt to changes in the mean, variance, and pdf shape of its input signal, and to quantize the signal using one or more bits/sample. It is therefore called the generalized hybrid adaptive quantizer (GHAQ). An efficient procedure for optimizing the GHAQ using a training sequence of signal samples is described, and the effects on the performance of the GHAQ of varying the memory length and the syllabic compandor time constant are investigated. It is found that an optimized version of the two-bit GHAQ offers improved signal-to-noise ratio over Jayant's adaptive quantizer with a one-word memory when it is used in a predictive speech codec with a zero-, first-, or second-order fixed predictor View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia