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Communications, IEEE Transactions on

Issue 1 • Date Jan. 1998

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Displaying Results 1 - 20 of 20
  • Comment on "Reparable key distribution protocols for Internet environments" [with reply]

    Publication Year: 1998 , Page(s): 20 - 22
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (28 KB)  

    For original paper see Hwang and Ku (IEEE Trans. Commun., vol.43, p.1947-9, 1995 May). The present authors find that the key distribution protocol KDP2 proposed in the original paper is, in fact, not reparable, as was claimed by the original authors. A reparable revised version of this KPD2 is then introduced. In a reply Hwang presents an example to show that the Lin et al. revised reparable KDP2 did not solve the problem which they proposed. View full abstract»

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  • Author's reply

    Publication Year: 1998 , Page(s): 22
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (24 KB)  

    First Page of the Article
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  • Corrections To "differentially Amplitude And Phase-encoded Qam For The Correlated Rayleigh-fading Channel With Diversity Reception"

    Publication Year: 1998 , Page(s): 156
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  • On block-coded modulation using unequal error protection codes over Rayleigh-fading channels

    Publication Year: 1998 , Page(s): 1 - 4
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    This paper considers block-coded 8-phase-shift-keying (PSK) modulations for the unequal error protection (UEP) of information transmitted over Rayleigh-fading channels. Both conventional linear block codes and linear UEP (LUEP) codes are combined with a naturally labeled 8-PSK signal set, using the multilevel construction of Imai and Hirakawa (1977). Computer simulation results are presented showing that, over Rayleigh-fading channels, it is possible to improve the coding gain for the most significant bits with the use of binary LUEP codes as constituent codes, in comparison with using conventional binary linear codes alone View full abstract»

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  • New-user identification in a CDMA system

    Publication Year: 1998 , Page(s): 144 - 155
    Cited by:  Papers (19)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    We present three detector/estimators (DEs) which allow multiuser detection and parameter estimation without a side channel in a dynamic asynchronous code-division multiple-access (CDMA) system in which users are entering and leaving the system. These DEs optimally detect a new user given only the chip rate and the spreading factor of the new user. Two of these DEs, the maximum-likelihood detector/estimator (MLDE) and the generalized maximum-likelihood detector/estimator (GMLDE), produce maximum-likelihood estimates of the new user's signature sequence, delay, and amplitude, which are then incorporated into a multiuser detector. The third DE, the cyclic detector/estimator (CDE), is the most computationally efficient of the three processors. This DE detects the new user by testing for cyclostationarity and then uses suboptimal schemes to estimate the new user's signature sequence, delay, and amplitude. Simulations indicate that all three DEs reliably detect a new user for an Es2 (symbol-energy-to-noise ratio) of 5 dB. The MLDE and GMLDE produce signature sequence and delay estimates with probability of error less than 0.07 for an Es2 of 10 dB, and the CDE produces signature sequence and delay estimates with probability of error less than 0.13 for an Es2 of 15 dB View full abstract»

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  • Blind equalization and multiuser detection in dispersive CDMA channels

    Publication Year: 1998 , Page(s): 91 - 103
    Cited by:  Papers (229)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The problem of blind demodulation of multiuser information symbols in a high-rate code-division multiple-access (CDMA) network in the presence of both multiple-access interference (MAI) and intersymbol interference (ISI) is considered. The dispersive CDMA channel is first cast into a multiple-input multiple-output (MIMO) signal model framework. By applying the theory of blind MIMO channel identification and equalization, it is then shown that under certain conditions the multiuser information symbols can be recovered without any prior knowledge of the channel or the users' signature waveforms (including the desired user's signature waveform), although the algorithmic complexity of such an approach is prohibitively high. However, in practice, the signature waveform of the user of interest is always available at the receiver. It is shown that by incorporating this knowledge, the impulse response of each user's dispersive channel can be identified using a subspace method. It is further shown that based on the identified signal subspace parameters and the channel response, two linear detectors that are capable of suppressing both MAI and ISI, i.e., a zero-forcing detector and a minimum-mean-square-error (MMSE) detector, can be constructed in closed form, at almost no extra computational cost. Data detection can then be furnished by applying these linear detectors (obtained blindly) to the received signal. The major contribution of this paper is the development of these subspace-based blind techniques for joint suppression of MAI and ISI in the dispersive CDMA channels View full abstract»

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  • Asymptotic limits in peak envelope power reduction by redundant coding in orthogonal frequency-division multiplex modulation

    Publication Year: 1998 , Page(s): 5 - 10
    Cited by:  Papers (50)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    This paper uses some computational results to show that the peak envelope power (PEP) of orthogonal frequency-division multiplex (OFDM) waveforms can be reduced very substantially by coding to select only those messages with low peak factor as valid codewords in the scheme. It is shown that the asymptotic limit of the PEP is between two and three, and that only four bits of redundancy are necessary to limit the PEP to within 10% of this optimum value as the number of carriers becomes large View full abstract»

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  • Fractionally spaced blind equalization using polyperiodic linear filtering

    Publication Year: 1998 , Page(s): 16 - 19
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    Performance of fractionally spaced equalizers using polyperiodic linear filtering is depicted. The fractionally sampled version of an arbitrary stable channel's outputs with stationary random inputs exhibit cyclostationarity with cycle frequencies being integer multiples of the reciprocal of the oversampling factor. By optimally polyperiodic linear filtering the oversampled outputs, we can fully utilize the cyclostationary property. With some traditional Bussgang techniques, such as stop-and-go decision-directed method, to adaptively update the filter coefficients, the convergence rate of the fractionally spaced equalizers proposed is improved, while the complexity retains in the same order as original Bussgang ones. Some computer simulation results are shown to demonstrate the improvement we can achieve View full abstract»

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  • Multiplexed ARQ for time-varying channels. I. System model and throughput analysis

    Publication Year: 1998 , Page(s): 41 - 51
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    In this paper, a model is developed for a slotted time-division multiplexing system used for assigning transmissions over a set of time-varying channels. Two schemes, a “round-robin” and an adaptive multiplexing scheme, are studied for use with three standard automatic-repeat-request (ARQ) protocols, namely, stop-and-wait (SW), go-back-N (GBN), and ideal selective repeat (ISR). In round-robin multiplexing, transmission slots are assigned periodically to each channel, With the adaptive scheme, the multiplexer selects at each time slot the channel whose state is estimated to have the lowest retransmission probability. The throughputs of these ARQ protocols under either multiplexing scheme are analyzed and compared. The present paper contains a description of the system model and an analysis of the ARQ protocols under both multiplexing schemes. In Part II, a modification to GBN and selective repeat ARQ for reducing the detrimental effects of feedback errors is discussed and analyzed, followed by a throughput performance comparison of all ARQ and multiplexing schemes View full abstract»

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  • The modified Cramer-Rao bound in vector parameter estimation

    Publication Year: 1998 , Page(s): 52 - 60
    Cited by:  Papers (74)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    In this paper we extend the scalar modified Cramer-Rao bound (MCRB) to the estimation of a vector of nonrandom parameters in the presence of nuisance parameters. The resulting bound is denoted with the acronym MCRVB, where “V” stands for “vector”. As with the scalar bound, the MCRVB is generally looser than the conventional CRVB, but the two bounds are shown to coincide in some situations of practical interest. The MCRVB is applied to the joint estimation of carrier frequency, phase, and symbol epoch of a linearly modulated waveform corrupted by correlated impulsive noise (encompassing white Gaussian noise as a particular case), wherein data symbols and noise power are regarded as nuisance parameters. In this situation, calculation of the conventional CRVB is infeasible, while application of the MCRVB leads to simple useful expressions with moderate analytical effort. When specialized to the case of white Gaussian noise, the MCRVB yields results already available in the literature in fragmentary form and simplified contexts View full abstract»

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  • Packet combining in frequency-hop spread-spectrum communication systems

    Publication Year: 1998 , Page(s): 23 - 33
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The performance of frequency-hop spread-spectrum (FHSS) communication systems using hybrid automatic-repeat-request (ARQ) can be improved by combining current and prior transmissions at the receiver. Two methods for combining packets in systems that employ interleaving and Reed-Solomon (RS) coding are presented and analyzed for the partial-band interference channel. These methods use majority logic combining at the codeword level to make retransmission decisions. Bounded distance errors-and-erasures decoding and erasure generation by means of Viterbi's ratio threshold test (RTT) are incorporated in the analysis. Results of the analysis show that, with comparable packet error probabilities, the packet-combining schemes provide significant gains in throughput when compared with systems that do not employ combining View full abstract»

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  • Performance of a fast frequency-hopped noncoherent MFSK receiver with nonideal adaptive gain control

    Publication Year: 1998 , Page(s): 104 - 114
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    An error probability analysis is performed for an orthogonal noncoherent M-ary frequency-shift keying (MFSK) communication system employing fast frequency-hopped (FFH) spread spectrum with diversity. The signal is assumed to be transmitted through a frequency-nonselective slowly fading channel with partial-band noise interference. The partial-band interference is modeled as a Gaussian process. Both the information signal and the partial-band noise interference signal are assumed to be affected by channel fading; it is assumed that the two fading processes are independent and that channel fading need not necessarily affect the information signal and the interference signal in the same way. Each diversity reception is assumed to fade independently according to a Rician process. Adaptive gain control is employed to minimize partial-band interference effects, and the effect of inaccurate noise measurement on the ability of the adaptive gain control receiver to reject partial-band interference is examined. The effect of thermal noise is included in the analysis View full abstract»

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  • On multidimensional coded modulations having uniform error property for generalized decoding and flat-fading channels

    Publication Year: 1998 , Page(s): 34 - 40
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    We consider the problem of uniform error property (UEP) for a coded modulation with constant energy multidimensional symbols, transmitted over the additive white Gaussian noise (AWGN) or fading channels and received by a broad class of decoders. This class includes coherent, partially coherent, double differential, and noncoherent decoders, decoders designed for fading channels, decoders using one or multiple-symbol observations, and many more. These decoders are described as special cases of a general decoder model. This decoder operates by maximizing an arbitrary likelihood function that its arguments are front-end correlator (matched-filter) outputs, A group code structure that guarantees UEP is developed by using the theory of geometrically uniform codes and applying it to the general decoder. These codes are defined over groups (commonly nonbinary) with isometric mapping to channel symbols. We show the code construction for the specific case of Lth-dimensional M-ary phase-shift keying (MPSK). An additional interesting property of these general uniform error codes is related to the case of noncoherent decoding. We show that when using codes of this family, if a code is noncoherently catastrophic, then it is also rotationally invariant. Then, the use of preceding of the input such that the code becomes rotationally transparent will also make it noncatastrophic View full abstract»

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  • Performance of constrained and unconstrained adaptive multiuser detectors for quasi-synchronous CDMA

    Publication Year: 1998 , Page(s): 135 - 143
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    It has previously been shown that multiuser interference in a quasi-synchronous code-division multiple-access (QS-CDMA) system can be effectively rejected using a nonadaptive decorrelator. However, the QS decorrelator is orthogonal to the inflated subspace spanned by the undesired users with arbitrary delays in the QS uncertainty interval and, hence, does not perform as well as a decorrelator with a priori knowledge of the delays. Here, we consider a constrained adaptive linear suppression filter which implicitly estimates the delays of the QS undesired signals, and thus approaches the ideal decorrelator of Lupas and Verdu (1990). For QS-CDMA, it is shown through analysis and simulations that the constrained recursive least-squares (C-RLS) algorithm converges faster than an unconstrained RLS adaptive filter, and generally outperforms the nonadaptive QS decorrelator. A cellular quasi-synchronous system is discussed in the present paper View full abstract»

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  • Determining parameters to minimize jitter generation in the SRTS method

    Publication Year: 1998 , Page(s): 82 - 90
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    The synchronous residual time stamp (SRTS) method has been recommended by the ITU-T as one approach to the transfer of timing information for continuous bit rate (CBR) services being carried by the asynchronous transfer mode (ATM) adaptation layer 1 (AAL1) of the broadband integrated services digital network (B-ISDN). We give an overview of the SRTS method including a description of service clock recovery at the destination. On the basis of analytical expressions derived, we show that even in an ideal SRTS system, where all clocks are jitter-free, the SRTS method inherently generates jitter. We also show that this jitter is equivalent to the so-called waiting time jitter that is found in conventional timing justification techniques. In other systems where waiting time jitter is generated, parameters are chosen in order to minimize the amount of waiting time jitter produced and in which part of the spectrum it is located. We show that for the SRTS method, the choice of parameters to minimize waiting time jitter is quite restricted. For higher service clock frequencies and clocks with large tolerances, it may be impossible to choose parameters to influence the characteristics of the waiting time jitter produced View full abstract»

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  • Blind adaptation of antenna arrays using a simple algorithm based on small frequency offsets

    Publication Year: 1998 , Page(s): 61 - 70
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    With the development of wireless and personal communication systems, there is considerable interest in using antenna array technology to improve the system capacity in both present and future generation wireless systems. A novel and simple algorithm is proposed for blind adaptive extraction of a binary phase-shift keying (BPSK) signal in the presence of interference by cyclostationary signal processing using an antenna array. The algorithm operates in an interference-limited system in which the desired and interfering signals have identical symbol rates, but are modulated on slightly different carrier frequencies. Compared to existing blind algorithms which also exploit the cyclostationarity of the received signal, the new algorithm provides a simpler and faster converging means to estimate the channel phase for diversity combining. Analytical and simulation results are presented and performances are compared with direct matrix inversion (DMI) and existing blind algorithms. Based on the proposed algorithm and the result obtained by Gardner, Schell and Murphy (1992), a time-division multiple-access (TDMA) system with the new channel assignment scheme called cyclic TDMA (CTDMA) is proposed. The simulation results also show that the proposed algorithm is relatively simple and very promising in applications to indoor wireless communication where interference rejection and increased spectrum efficiency are the objectives. Analysis and simulation results are presented to confirm the interference rejection capabilities. The robustness of existing and proposed algorithms to the perturbation of cyclostationarity is also discussed View full abstract»

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  • Design of a low-complexity adaptive interference-mitigating detector for DS/SS receivers in CDMA radio networks

    Publication Year: 1998 , Page(s): 125 - 134
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Code-division multiple-access (CDMA) with direct-sequence/spread-spectrum (DS/SS) modulated signals has emerged as a strong candidate for the air interface of the universal wireless personal communication network planned for the end of the century. In this paper, we take into consideration a low-complexity blind adaptive interference-mitigating detector (BAID) scheme that minimizes the detrimental effect of the multiple-access interference (MAI) on the bit-error-rate (BER) performance of a CDMA data demodulator. We describe a few modifications to the original algorithm that make it more suitable to a practical implementation with dual-binary phase-shift keying (D-BPSK)-modulated DS/SS signals. Specifically, we show how to make the BAID invariant to a possible carrier phase offset introduced in the front-end of the data demodulator, and we also suggest how to increase the robustness of such detector to asynchronous MAI. The uncoded BER performance of the resulting “extended” detector is then evaluated theoretically and by computer simulation in the case of coherent and differential signal detection View full abstract»

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  • Time-varying versus time-invariant finite-length MMSE-DFE on stationary dispersive channels

    Publication Year: 1998 , Page(s): 11 - 15
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    A time-varying structure and a time-invariant structure for the finite-length minimum-mean-square-error decision feedback equalizer (MMSE-DFE) are presented and their performances are compared on a stationary channel impaired by intersymbol interference (ISI) and additive Gaussian noise. The time-varying structure has an innovations error sequence but incurs a throughput loss on ISI channels because of its block-processing nature. Conditions under which the time-invariant structure exhibits near-optimal performance are described. Both structures converge to the canonical MMSE-DFE of Cioffi et al. (see ibid., vol.43, p.2582-94, 1995 and vol.43, p.2595-2604, 1995) as their filters' lengths become infinite View full abstract»

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  • Adaptive detection of DS/CDMA signals in fading channels

    Publication Year: 1998 , Page(s): 115 - 124
    Cited by:  Papers (51)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    This paper examines the behavior of the minimum mean-squared error (MMSE) receiver in frequency-nonselective-fading channels. It is noted that the MMSE receiver will often lose phase lock on the desired signal when the desired signal dips into a deep fade. A modification to the MMSE receiver is presented which is demonstrated to function quite nicely in flat-fading channels. Analytical results for the modified MMSE receiver are presented and found to agree very well with simulation results. These analytical results are then compared to the theoretical performance of the conventional (i.e., correlator) receiver in terms of both bit-error rate (BER) and capacity. As expected, the modified MMSE receiver was found to offer a substantial improvement in both BER and capacity. Finally, a simple empirically derived formula is given which will give a good approximation to the BER of the modified MMSE receiver in a Rayleigh-fading environment. This formula can also be used to determine the number of users a given system can support. It is noted that as Eb/N0 grows, it is quite feasible to approach 100% channel utilization with the MMSE receiver, whereas a conventional receiver is typically limited to a utilization of 10%-20% View full abstract»

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  • BER expressions for differentially detected π/4 DQPSK modulation

    Publication Year: 1998 , Page(s): 71 - 81
    Cited by:  Papers (35)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    Closed form bit-error rate (BER) expressions for differentially detected π/4-shifted differentially encoded quadrature phase-shift keying (QPSK) modulation (π/4 DQPSK) are derived for both additive white Gaussian noise (AWGN) and Rayleigh-fading channels. The derivations are carried out in an exact and most general manner in that in-phase (I) and quadrature (Q) channel bit-error probabilities Pcl and PcQ are separately obtained in terms of the same-quadrature and cross-quadrature noise Correlation functions, including a measure of noise nonstationarity. We then specialize the general expressions for uncorrelated noise and equal noise powers in successive symbol periods to obtain a useful bit-error probability expression for the AWGN channel in the form Pe≈Q(√(1.1716·Eb/N0)) where Q(·) is the Gaussian distribution Q-function and Eb /N0 is the bit energy-to-noise density ratio. Exact BER expressions for the Rayleigh-fading channel that involve the noise parameters are also given and are extended to the case of L-fold diversity combining 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