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Communications, IEEE Transactions on

Issue 9 • Date Sept. 1998

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Displaying Results 1 - 18 of 18
  • Comments on "Comparison of diversity combining techniques for Rayleigh-fading channels"

    Publication Year: 1998 , Page(s): 1109 - 1110
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (73 KB)  

    The authors comment that the probability density function (PDF) of the signal-to-noise ratio (SNR) for third-order selection combining (SC3) given by Eng, Kong and Milstein (see ibid., vol.44, p.1117-29, 1996) is incorrect. A correction is given by presenting a more efficient method of deriving the generalized PDF of the SNR essential in the analysis of Nth-order selection combining. View full abstract»

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  • Correction to "Comparison of diversity combining techniques for Rayleigh-fading channels"

    Publication Year: 1998
    Cited by:  Papers (17)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (47 KB)  

    Based on the observation of Kim, Kwon, Hong and Whang (see ibid., vol.46, no.9, p.1109-10, 1998), we discovered that in our derivation (see ibid., vol.44, p.1117-29, 1996), a factor of one-half in the exponent of one of three exponentials was inadvertently dropped and this, in turn, affected two other equations. View full abstract»

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  • Simultaneous broadcasting of analog FM and digital audio signals by means of adaptive precanceling techniques

    Publication Year: 1998 , Page(s): 1233 - 1242
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    A method for broadcasting digital audio simultaneously with existing analog frequency modulation (FM) radio is presented. The method is based on precomputing the response of the host analog FM signal at the digital receiver and precanceling it at the transmitter. As a result, the digital transmission is free from interference from analog FM. We select the rate and power level of the digital transmission in a manner that the interference the digital data incur on the analog FM signal remains at acceptably low levels. The digital transmission is based on adaptive orthogonal frequency-division multiplexing (OFDM) (adaptive multicarrier). The frequencies and number of carriers of the digital multicarrier modem are judiciously selected in a time-varying fashion so as to cause a negligible distortion in a standard receiver for analog FM. Simulations based on conservative nonoptimized signal design indicate that data rates up to about 130 kb/s inside the 200-kHz FM channel are achievable for acoustic test signals. We present a number of numerical examples where the average digital data use up to 50% of the 200-kHz power spectrum with digital signal power levels 25-35 dB below the analog signal. Due to the resulting variable-rate digital transmission, a control channel is required. A method of precanceling with multiple orthogonal direct-sequence spread-spectrum schemes is also presented View full abstract»

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  • Fast adaptive equalization/diversity combining for time-varying dispersive channels

    Publication Year: 1998 , Page(s): 1146 - 1162
    Cited by:  Papers (22)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    We examine adaptive equalization and diversity combining methods for fast Rayleigh-fading frequency selective channels. We assume a block adaptive receiver in which the receiver coefficients are obtained from feedforward channel estimation. For the feedforward channel estimation, we propose a novel reduced dimension channel estimation procedure, where the number of unknown parameters are reduced using a priori information of the transmit shaping filter's impulse response. Fewer unknown parameters require a shorter training sequence. We obtain least-squares, maximum-likelihood, and maximum a posteriori (MAP) estimators for the reduced dimension channel estimation problem. For symbol detection, we propose the use of a matched filtered diversity combining decision feedback equalizer (DFE) instead of a straightforward diversity combining DFE. The matched filter form has lower computational complexity and provides a well-conditioned matrix inversion. To cope with fast time-varying channels, we introduce a new DFE coefficient computation algorithm which is obtained by incorporating the channel variation during the decision delay into the minimum mean square error (MMSE) criterion. We refer to this as the non-Toeplitz DFE (NT-DFE). We also show the feasibility of a suboptimal receiver which has a lower complexity than a recursive least squares adaptation, with performance close to the optimal NT-DFE View full abstract»

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  • A generalized suboptimum unequally spaced channel allocation technique. II. In coherent WDM systems

    Publication Year: 1998 , Page(s): 1186 - 1193
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    For pt.I see ibid., vol.46, no.8, p.1027-37 (1998). Four-wave mixing (FWM) in dispersion-shifted optical fiber is a major problem associated with low optical input power levels in optical wavelength-division multiplexed (WDM) systems. To reduce the crosstalk caused by FWM, a generalized suboptimum unequally spaced channel allocation (S-BISCA) technique has been proposed. While the S-USCA technique reduces the PWM power substantially, it also reduces the minimum channel spacing compared to conventional equal channel spacing (ECS) systems when the same number of carrier channels are accommodated in a fixed optical bandwidth. This results in more interchannel interference (ICI) when employing the S-USCA scheme. The power penalty of the ECS and the S-USCA systems caused by crosstalk and frequency drift are investigated and compared in this paper. The superior system performance region, where S-USCA systems out perform ECS systems, is also quantified. For 20-channel systems using an amplitude-shift keying (ASK) heterodyne detection scheme, for instance, results show that the S-USCA technique pays less power penalty up to bit rates of 5.5, 7.5, and 9.5 Gb/s, when all channels have identical states of polarization and the launched input power per channel Pin, equals to -6, -3, and 0 dBm, respectively View full abstract»

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  • On the power spectral density of digital pulse streams generated by M-ary cyclostationary sequences in the presence of stationary timing jitter

    Publication Year: 1998 , Page(s): 1135 - 1145
    Cited by:  Papers (19)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The spectral occupancy and composition of a chosen digital signaling technique when the data pulse stream is nonideal, due, for instance, to implementation imperfections, are important considerations in the design of a practical communication system. One source of imperfection is timing jitter where the rising and falling transitions do not occur at the nominal data transition time instants; nevertheless, the time instants are offset by random amounts relative to the nominal one. The amount of timing shift per transmission interval is random and is typically characterized by a discrete stationary random process (independent of the data sequence) with known statistical properties. The purpose of this paper is to characterize the power spectral density (PSD) of baseband signaling schemes in the presence of arbitrary timing jitter. Although general PSD results are first obtained for arbitrary timing jitter statistics, specific results are then given for the cases of practical interest, namely, uniform and Gaussian-distributed jitter. Examples of an uncorrelated data pulse stream, an independent identically distributed data stream, and a Markov source are given. Interesting results emerge when the generating sequence {an} is uncorrelated. For generating sequences {an} that are nonzero-mean, timing jitter has the effect of widening the main lobe of the spectrum and increasing the sidelobes. When the generating sequence is zero-mean and uncorrelated, a rather surprising result is that the timing jitter does not affect the PSD. Simulation results are also presented to verify the analysis View full abstract»

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  • Performance analysis of CFDAMA-PB protocol for packet satellite communications

    Publication Year: 1998 , Page(s): 1206 - 1214
    Cited by:  Papers (19)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Combined free/demand-assignment multiple-access (CFDAMA) schemes are suitable for broad-band packet satellite communications systems serving a finite number of bursty data sources. The performance analysis of the CFDAMA using piggy-backed (PB) reservation is presented. The probability generating function (PGF) of the packet delay is developed. The performance is evaluated in terms of three performance measures: average packet delay, variance of packet delay, and cumulative probability distribution of packet delay. Performance comparison with other pertinent schemes shows CFDAMA-PB to be superior for a wide range of user population sizes View full abstract»

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  • The condition for the applicability of the Viterbi algorithm with implications for fading channel MLSD

    Publication Year: 1998 , Page(s): 1112 - 1116
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    The general condition for the optimality of the Viterbi algorithm (VA) as a method for implementing maximum-likelihood sequence detection (MLSD) is described. It is shown that this folding condition is not met for the fading linear Gaussian channel. This clarifies previously published results and allows approaches for approximate MLSD to be viewed as an attempt to force the VA as a suboptimal solution View full abstract»

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  • Narrow-band-interference suppression in multiuser CDMA systems

    Publication Year: 1998 , Page(s): 1163 - 1175
    Cited by:  Papers (17)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    This paper handles the simultaneous suppression of narrow-band and multiaccess interference in code division multiple-access (CDMA) direct-sequence spread-spectrum (DSSS) systems. The basic structure we refer to is reminiscent of the decorrelating detector, but here the design strategy relies on the concept of combating jointly the two interference sources-precisely, a decision as to the bit transmitted by each user is made based on the projection of the observables onto the orthogonal complement to the subspace spanned by the other users' signatures and the narrow-band interference. We focus on several different implementations of such a strategy, assuming a different degree of prior knowledge as to the narrow-band interference. An important side result of the proposed approach is that, in general, complete suppression of data-like interference may be achieved through periodically time-varying processing. An adaptive version of such a receiver is also presented, wherein the projection direction is estimated based on suitable estimates of the covariance properties of the observables. The value of this method is also assessed by studying the rate of convergence of the estimated direction to the true projection direction View full abstract»

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  • An in-band power-saving protocol for mobile data networks

    Publication Year: 1998 , Page(s): 1194 - 1205
    Cited by:  Papers (26)  |  Patents (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A new alternative is proposed for reducing the power consumption of the portable (battery-powered) units operating in a mobile packet-data network. First, a review of the current power-saving protocols is given. It is shown that the most common means for conserving power is the intermittent operation of the receivers (at the portable units) and a central administration authority that synchronizes the receivers. Some drawbacks of the synchronous operation lead us to the introduction of an asynchronous power-saving protocol, where no central synchronization is necessary and where each terminal may control its power consumption relative to its current needs. According to the proposed power-saving page-and-answer protocol, an acknowledgment paging procedure is preceding every packet transmission in order to alert mobile terminals with pending traffic. Steady-state performance is evaluated with the aid of simulation. The relationship between the achieved power-saving and the mean packet delay degradation is presented. Finally, we express some notable implementation issues and some considerations regarding the employment of this protocol as a supplementary power-saving service in microcellular mobile data networks and wireless local area networks View full abstract»

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  • Analysis and optimization of pilot-channel-assisted BPSK for DS-CDMA systems

    Publication Year: 1998 , Page(s): 1122 - 1124
    Cited by:  Papers (30)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    Pilot-channel-assisted binary phase-shift keying (PCA-BPSK) in direct-sequence code-division multiple-access (DS-CDMA) systems is investigated. The loss due to imperfect channel estimation is calculated, and the pilot-to-data channel power ratio is optimized analytically. The results show the effects of the various parameters and provide a suitable tool for system design View full abstract»

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  • Direct sequence spread spectrum Walsh-QPSK modulation

    Publication Year: 1998 , Page(s): 1227 - 1232
    Cited by:  Papers (6)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    We present Walsh-quadrature phase-shift keying (Walsh-QPSK) pseudonoise (PN) modulation schemes for both coherent and noncoherent direct-sequence code-division multiple-access (DS-CDMA) systems, wherein the PN spreading sequences for in-phase and quadrature data in a conventional QPSK PN modulation scheme are coded by Walsh sequences indexed by a special rule to reduce the envelope variation of the transmitted signal. The signal characteristics of the two schemes are analyzed when a rectangular-shaped PN chip pulse is used, and it is shown that the proposed coherent DS-CDMA system has a constant envelope even in the presence of a transmitted phase reference. We simulate the signals to obtain the envelope variations when a spectrally efficient shaped PN chip pulse is used, and compare the results with those of conventional QPSK and orthogonal QPSK (OQPSK) PN modulation schemes. The results show that both the noncoherent and coherent Walsh-QPSK schemes have smaller envelope variations than the conventional noncoherent QPSK and OQPSK PN modulation schemes, even though in the coherent Walsh-QPSK scheme the pilot channel is added to the signal channel View full abstract»

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  • Design of ATM AAL1 SAR for circuit emulation

    Publication Year: 1998 , Page(s): 1117 - 1121
    Cited by:  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    The asynchronous transfer mode (ATM) adaptation layer type 1 (AAL1) segmentation and reassembly (SAR) are designed and implemented by the field programmable gate array (FPGA). The SAR header is generated and processed in the FPGA and the SAR payload is stored in an external first-in-first-out (FIFO) device. A method to recover the source clock, called synchronous residual time stamp (SRTS), is implemented. The designed AAL1 SAR FPGA is properly tested in a prototype circuit board View full abstract»

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  • A search for good convolutional codes to be used in the construction of turbo codes

    Publication Year: 1998 , Page(s): 1101 - 1105
    Cited by:  Papers (69)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    Recursive systematic convolutional encoders have been shown to play a crucial role in the design of turbo codes. We recall some properties of binary convolutional encoders and apply them to a search for good constituent convolutional codes of turbo codes. Tables of the “best” recursive systematic convolutional encoders found are presented for various rates, together with the average bit-error probability performances of some turbo codes using them View full abstract»

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  • Bit-error probability for an adaptive diversity receiver in a Rayleigh-fading channel

    Publication Year: 1998 , Page(s): 1106 - 1108
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    The bit-error probability is determined for a binary antipodal diversity system with an adaptive receiver using decision-directed channel estimation. The diversity channels are assumed to be nonselective Rayleigh-fading channels with additive white Gaussian noise (AWGN). The analysis is valid for all linear estimators which use a finite-impulse-response (FIR)-type estimation filter. Numerical results are presented for a minimum mean-square error (MMSE) filter and a moving average (MA) filter View full abstract»

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  • Objective picture quality scale (PQS) for image coding

    Publication Year: 1998 , Page(s): 1215 - 1226
    Cited by:  Papers (123)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    A new methodology for the determination of an objective metric for still image coding is reported. This methodology is applied to obtain a picture quality scale (PQS) for the coding of achromatic images over the full range of image quality defined by the subjective mean opinion score (MOS). This PQS takes into account the properties of visual perception for both global features and localized disturbances. The PQS closely approximates the MOS, with a correlation coefficient of more than 0.92, as compared to 0.57 obtained using the conventional weighted mean-square error (WMSE). Extensions and applications of the methodology and of the resulting metric are discussed View full abstract»

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  • Performance limits of Reed-Solomon coded CDMA with orthogonal signaling in a Rayleigh-fading channel

    Publication Year: 1998 , Page(s): 1125 - 1134
    Cited by:  Papers (16)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    The asymptotic performance of Reed-Solomon (RS)-coded M-ary orthogonal signaling with ratio-threshold test (RTT) type demodulation in a Rayleigh-fading channel is considered. We show that the minimum E¯b/N0 needed for error-free communication is eln2 (2.75 dB) with RTT, and 4.79 (6.8 dB) with hard decisions. The optimum code rate that minimizes the required E¯b/N0 is e-1 with RTT and 0.46 with hard decision, and the optimum ratio threshold approaches 1 for large M. Next, we investigate the fundamental limit in a direct-sequence spread-spectrum multiple-access (DS/SSMA) system employing an M-ary orthogonal code of length N=Mm, which is obtained by spreading every row of an M×M Hadamard matrix with a user-specific random sequence of length N. We derive the minimum E¯b/N0 for error-free communication as a function of the number of users, the optimum code rate that minimizes E¯B/N0, and the maximum limit on the total information transmission rate. Then, we consider a multirate DS/SSMA system, where a population of users simultaneously transmit at different power levels a variety of traffic types of different information rates. We derive the minimum required E¯B/n0 and the optimum code rate for each traffic type View full abstract»

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  • Performance enhancement of spectral-amplitude-coding optical CDMA using pulse-position modulation

    Publication Year: 1998 , Page(s): 1176 - 1185
    Cited by:  Papers (135)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    Spectral-amplitude-coding optical code-division multiple-access (OCDMA) systems are limited by interference between incoherent sources. A detailed analysis of this limit for a system with a balanced receiver is presented. Additional pulse-position modulation (PPM) coding is proposed as a method to improve the system performance beyond this limit. A simple and robust PPM decoding structure is proposed, and the performance analysis of the whole PPM-OCDMA system is presented. The interference-limited performance of the PPM-OCDMA system is found to be superior to that of the original system when the number of simultaneous users is of the order of the PPM word length or larger. In particular, for a PPM word length of two, an increase in spectral efficiency of up to 100% is possible with no change in the signaling rate, data rate, or bit-error rate (BER) 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