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Wireless Communications, IEEE Transactions on

Issue 8 • Date Aug. 2006

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  • IEEE Transactions on Wireless Communications - Table of contents

    Page(s): 1
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  • A cost-function based technique for design of good prunable interleavers for turbo codes

    Page(s): 1953 - 1958
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (431 KB) |  | HTML iconHTML  

    This paper addresses the design of semi-random, prunable interleavers for parallel concatenated convolutional codes (PCCC). The proposed technique is iterative and is based on the growth of a smaller interleaver up to the desired length N. The optimization is achieved via a minimization using a cost-function strictly related to both the correlation properties of the extrinsic information and the concept of spread of an interleaver. Performance of the designed interleavers are given in terms of bit error rate (BER) and frame error rate (FER). Comparisons are given with respect to other prunable and ad-hoc interleaver design techniques already proposed in literature. The designed interleavers are prunable and have a behavior very similar to the interleavers designed with techniques which maximize the spread of the permutation View full abstract»

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  • Optimum and reduced complexity multiuser detectors for asynchronous CPM signaling

    Page(s): 1959 - 1965
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (493 KB) |  | HTML iconHTML  

    Maximum likelihood detector algorithms are developed for the matrix of transmitted symbols in a multiuser system in which the received signal is the sum of K cochannel continuous phase modulated (CPM) signals and additive white Gaussian noise. We illustrate that the maximum likelihood matrix detector, which provides optimum detector performance, consists of K sets of front-end matched filters followed by a Viterbi algorithm. We also derive two reduced complexity receivers, demonstrating through simulation that they perform within 1-2 dB of the optimal while substantially reducing complexity. The paper demonstrates how performance can be traded off against complexity, giving particular attention to cochannel Gaussian minimum shift keyed (GMSK) signals View full abstract»

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  • Low complexity iterative decoding for bit-interleaved coded modulation

    Page(s): 1966 - 1970
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (313 KB) |  | HTML iconHTML  

    Bit-interleaved coded modulation with iterative decoding (ID) is an effective scheme for both AWGN and fading channels because it simultaneously realizes large Euclidean distance and high diversity. In the literature, ID schemes with hard-decision feedback (HDF), as well as soft-decision feedback (SDF), have been investigated. While HDF/ID exhibits a performance inferior to SDF/ID, it is much simpler to implement. To enhance the performance of HDF/ID with moderate additional complexity, we propose a uniform soft-decision feedback ID (USF/ID) scheme. The proposed scheme is applicable in both single antenna and multiple antenna communication systems. The simulation results verify that it achieves impressive performance gain over HDF/ID and has a practically more attractive implementation than SDF/ID, especially for complexity-constrained wireless applications View full abstract»

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  • Measurement-based TFRC: improving TFRC in heterogeneous mobile networks

    Page(s): 1971 - 1975
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (914 KB) |  | HTML iconHTML  

    As a well-known multimedia stream transport protocol, TFRC provides smooth transfer rate under stable network conditions, and achieves good fairness to TCP. However, it is not flexible in heterogeneous mobile networks because the available bandwidth varies rapidly. This paper proposes a measurement based TFRC (MBTFRC) protocol, which uses passive bandwidth measurements at the receiver to improve the flexibility of TFRC. In addition, a window-based EWMA filter with two weights is used to achieve stability and fairness simultaneously. Simulation results verify the flexibility, stability and fairness of MBTFRC View full abstract»

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  • Iterative demodulation/decoding methods based on Gaussian approximations for lattice based space-time coded systems

    Page(s): 1976 - 1983
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (415 KB) |  | HTML iconHTML  

    In this letter, we study iterative demodulation and decoding methods for lattice based space-time coded systems concatenated with convolutional codes. We first apply the optimal MAP demodulation and the suboptimal linear MMSE methods to lattice based space-time demodulation and decoding. We then propose two other methods based on the idea of soft interference cancellation and in one method vector Gaussian approximation is used and in the other method scalar Gaussian approximation is used. We also present the EXIT chart analyses for the performance analyses for these iterative methods. Both theoretical and simulation results show that the performance of the vector Gaussian approximation method is the same as that of the linear MMSE method but in some cases the vector Gaussian approximation method has lower complexity. The complexity of the scalar Gaussian approximation method is the lowest among these different methods and grows linearly with the transmission rate while it still has an acceptable performance. Full diversity and full rate lattice based space-time coding is compared with the BLAST scheme and simulations show that the former has a better performance than the later even with the proposed suboptimal iterative demodulation and decoding methods View full abstract»

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  • Analysis of a secure conference scheme for mobile communication

    Page(s): 1984 - 1986
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    Dynamic participation is a feature of the secure conference schemes that allows new conferees to join and the old conferees to leave. The conferees who have left should not be able to decrypt the secure conference communication anymore. A secure conference scheme with dynamic participation was proposed in M.S. Hwang and W.P. Yang (1995) and later it was modified with the self-encryption mechanism in K.F. Hwang and C.C. Chang (2003) for a better performance. In this paper we analyze both the original scheme and the modified version. We show that both of them are subject to the active and passive attacks presented in this paper. Our active attack works in the way that a colluding group of attackers can still obtain the conference key even after they all leave the conference. The passive attack does not need any attacker to ever participate the conference. The conference key can be compromised with a large probability as long as the number of conferees is large View full abstract»

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  • Effects of the BS power and soft handoff on the outage and capacity in the forward link of an SIR-based power-controlled CDMA system

    Page(s): 1987 - 1992
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1003 KB) |  | HTML iconHTML  

    In the forward link of a signal-to-interference ratio (SIR)-based fast power-controlled CDMA system, the fraction of base station (BS) power allocated to a mobile station (MS) is considered as a key factor affecting the system performance. By using our proposed macrodiversity non-orthogonality factor, we establish a unified analytical model to characterize the distribution of the fraction of BS power allocated to an MS in either the non-soft handoff mode or the soft handoff mode. By using that distribution and limiting the maximum fraction of BS power available to an MS, a closed-form expression of the capacity at a certain outage probability is obtained. The effects of system parameters, such as the available Rake fingers, the soft handoff threshold, the unbalance of the BS power, and the power control error, on the capacity are investigated from the viewpoint of the limitation on the fraction of BS power allocated to an MS. Simulation results show that soft handoff does not always improve capacity and the capacity gain may result depending on the choice of the system parameters View full abstract»

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  • A cross-layer approach to transmit antenna selection

    Page(s): 1993 - 1997
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (347 KB) |  | HTML iconHTML  

    In this paper, we investigate a cross-layer approach to transmit antenna selection capable of adapting the number of active antennas to varying channel conditions. We address a cross-layer methodology in the sense that the criterion for the selection of antenna subsets is the maximization of link layer throughput which takes into account characteristics both at the physical and link layers. In order to enhance system performance, adaptive modulation is included to jointly perform antenna selection and rate adaptation. Performance assessment is conducted in terms of link layer throughput and transmission delay View full abstract»

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  • SIR-optimized weighted linear parallel interference canceller on fading channels

    Page(s): 1998 - 2003
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (438 KB) |  | HTML iconHTML  

    In this letter, we present a weighted linear parallel interference canceller (LPIC) where the multiple access interference (MAI) estimate in a stage is weighted by a factor before cancellation on Rayleigh fading and diversity channels. We obtain exact expressions for the average signal-to-interference ratio (SIR) at the output of the cancellation stages which we maximize to obtain the optimum weights for different stages. We also obtain closed-form expressions for the optimum weights for the different stages. We show that this SIR-optimized weighted LPIC scheme clearly outperforms both the matched filter (MF) detector as well as the conventional LPIC (where the weight is taken to be unity for all stages), in both near-far as well as non-near-far conditions on Rayleigh fading and diversity channels View full abstract»

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  • A performance study of MIMO detectors

    Page(s): 2004 - 2008
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (186 KB) |  | HTML iconHTML  

    Several approaches have recently been proposed for the efficient optimum or approximate solution of the detection problem in multiple-input multiple-output transmission systems. These are, however, difficult to compare. In the present work we briefly summarize the most popular and promising of these approaches and offer a way to visualize the tradeoff between complexity of the detection and the achievable power efficiency using "complexity-power diagrams". We conclude that the so-called sphere decoder algorithm is very attractive in terms of average complexity, while for low and constant processing delay lattice reduction with subsequent simple linear or nonlinear detection is more favorable View full abstract»

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  • Performance of decorrelating receivers in multipath Rician fading channels

    Page(s): 2009 - 2016
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (543 KB) |  | HTML iconHTML  

    This letter focuses on the performance analysis of the decorrelating receiver in multipath Rician faded CDMA channels. M-ary QAM scheme is employed to improve the spectral efficiency. Approximate expressions are first derived for the two performance indexes: the average symbol error rate (SER) and the average bit error rate (BER) when the decorrelating-first receiver perfectly knows the channel information of the user of interest. To achieve desirable closed-form expressions of the SER and the BER, we exploit results in large system analysis and make assumptions of a high signal-to-interference ratio (SIR) and/or a small Rician K-factor. To measure the receiver performance in the practical scenario, we further derive expressions to approximate the average SER and BER of the decorrelating-first scheme with channel uncertainty. Simulation results demonstrate that the analytical results can also be employed to evaluate the performance of the combining-first receiver View full abstract»

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  • Cyclic prefixed single carrier transmission in ultra-wideband communications

    Page(s): 2017 - 2021
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (335 KB) |  | HTML iconHTML  

    This letter proposes cyclic prefixed single carrier transmission with frequency domain equalization (SC-FDE) as an alternative physical layer solution for UWB communications. The performance of SC-FDE over IEEE 802.15.3a UWB channel models is analyzed, simulated and compared with that of impulse based single carrier UWB (SC-UWB) and multicarrier UWB employing orthogonal frequency division multiplexing (OFDM-UWB). The impact of channel coding on the performance of OFDM and SC-FDE in UWB is also studied. Our results demonstrate performance advantage of the SC-FDE scheme, especially when implementation issues such as low complexity and low power consumption for UWB are taken into consideration. The performance of SC-FDE with diversity combining using oversampling is also investigated View full abstract»

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  • Novel diversity receivers in the presence of Gaussian channel estimation errors

    Page(s): 2022 - 2025
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    Novel diversity receivers that operate in the presence of Gaussian channel estimation errors are proposed for L independent and identically distributed fading channels. Previous work concerned with channel estimation errors has mainly examined the performance of maximal ratio combining (MRC) with estimation errors. It is shown here that MRC is not optimal when estimation errors occur. Moreover, it is shown that better diversity receivers that operate in the presence of Gaussian channel estimation errors can be obtained by using knowledge of the channel estimate statistics. Numerical results show that the derived new diversity receivers can perform as much as 2.0 dB in signal-to-noise ratio better than the conventional MRC receiver in some cases View full abstract»

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  • Improved autocorrelation demodulation receivers based on multiple-symbol detection for UWB communications

    Page(s): 2026 - 2031
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (365 KB) |  | HTML iconHTML  

    The autocorrelation demodulation (ACD) has potential for use in medium-range low-cost UWB communications, however, its weak performance is a bottle neck. To improve ACD's performance, it is proposed to combine the multiple-symbol detection with ACD to form a multiple-symbol-based ACD receiver. In contrast to ordinary ACD scheme that uses symbol-by-symbol decision, the proposed structure uses block-based multiple-symbol joint decision. Performance of the new scheme is evaluated analytically for arbitrary block sizes employing Gaussian approximation approach. The accuracy of the method is verified by computer simulation. The evaluation shows that the proposed scheme offers several dB improvement in performances with only a moderate increase in complexity View full abstract»

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  • Impact of signal constellation expansion on the achievable diversity of pragmatic bit-interleaved space-time codes

    Page(s): 2032 - 2037
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (443 KB) |  | HTML iconHTML  

    This letter studies the effect of signal constellation expansion on the achievable diversity of pragmatic bit-interleaved space-time codes in quasistatic multiple antenna channels. Signal constellation expansion can be obtained either by increasing the size of the constellation in the complex plane or by using multidimensional linear mappings. By means of two simple constructions, we provide a comparison of the two options with message passing decoding. We show that multidimensional expansion achieves some performance advantage over complex-plane expansion at the cost of significantly higher decoding complexity and larger peak-to-average power ratio of the transmitted signals View full abstract»

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  • On the capacity of frequency-flat and frequency-selective Rician MIMO channels with single-ended correlation

    Page(s): 2038 - 2043
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (363 KB) |  | HTML iconHTML  

    This paper considers the ergodic capacity of spatially-correlated Rician MIMO channels. We address the case where the Rician component has a single dominant path and where the correlation occurs at one end of the MIMO link. We derive upper bounds which are tight for all signal to noise ratios (SNR), and lower bounds which converge to the exact capacity at high SNR. For frequency-flat channels we investigate the capacity variation with Rician K-factor and correlation. For frequency-selective channels we also examine the effect of the total angle spread View full abstract»

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  • Correlatively coded OFDM

    Page(s): 2044 - 2049
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    A class of correlative codes is proposed to significantly improve the spectral performance of the rectangularly pulsed orthogonal frequency-division multiplexing (OFDM) signal with or without cyclic prefix or zero padding. It is analytically shown that the correlatively coded OFDM signal can achieve very high spectral efficiency while yielding an extremely small fractional out-of-band power View full abstract»

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  • Performance analysis of a CDMA network with fixed overlapping sectors in nonuniform angular traffic

    Page(s): 2050 - 2060
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (746 KB) |  | HTML iconHTML  

    The problem of base station antenna assignment (BSAA) with minimum mobile transmit power (MTP) is studied for CDMA networks with fixed overlapping sector antenna architecture (FOSAA) where more than one co-located antenna is used to cover any space in the network. It is first noted that the non-FOSAA has limitations in switching users between in-cell sectors and also out-of-cell sectors in moderately-loaded networks. It is then shown that by employing overlapping sectors in FOSAA, we can exploit the flexibility of assigning a user to one of possibly many potential antenna to effectively support the nonuniform azimuthal traffic. It is also shown that the BSAA problem with minimum MTP is a special case of a general problem that was solved by Hanly and Yates. The process of dynamic cell sectoring is differentiated twofold as cell-breathing (CB) and cell-slicing (CS) and the latter can be viewed as being azimuthal discrete counterpart of the former radial scheme. The hybrid scheme, CB+CS, offers better performance in terms of minimum total MTP in a FOSAA system. Simulation results demonstrate the flexibility and effectiveness of the FOSAA system in nonuniform angular traffic View full abstract»

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  • On the capacity of mobile ad hoc networks with delay constraints

    Page(s): 2061 - 2071
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (833 KB) |  | HTML iconHTML  

    Previous work on ad hoc network capacity has focused primarily on source-destination throughput requirements for different models and transmission scenarios, with an emphasis on delay tolerant applications. In such problems, network capacity enhancement is achieved as a tradeoff with transmission delay. In this paper, the capacity of ad hoc networks supporting delay sensitive traffic is studied. First, a general framework is . proposed for characterizing the interactions between the physical and the network layer in an ad hoc network. Then, CDMA ad hoc networks, in which advanced signal processing techniques such as multiuser detection are relied upon to enhance the user capacity, are analyzed. The network capacity is characterized using a combination of geometric arguments and large scale analysis, for several network scenarios employing matched filters, decorrelators and minimum-mean-square-error receivers. Insight into the network performance for finite systems is also provided by means of simulations. Both analysis and simulations show a significant network capacity gain for ad hoc networks employing multiuser detectors, compared with those using matched filter receivers, as well as very good performance even under tight delay and transmission power requirements View full abstract»

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  • Capacity losses in wireless CDMA networks using imperfect decorrelating space-time Rake receiver in fading multipath channel

    Page(s): 2072 - 2081
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB) |  | HTML iconHTML  

    In this paper we analyze the impact of system imperfections on the overall cellular code-division multiple access (CDMA) radio network performance. The theory is general and some examples of practical sets of channel and system parameters are used as illustration. A flexible signal model, based on the complex signal format, is used enabling us to model all wideband CDMA standards. For such a signal, we first derive a complex decorrelator structure. In the next step imperfections in the operation of a decorrelating space-time Rake combiner are modeled and analyzed. Relative capacity losses and the network sensitivity function are used as performance measures. Simulations are also performed to confirm some of the key assumptions made in the analysis. Numerical results show that the user capacity varies significantly depending on the multipath profile, diversity order, fading rate, and code crosscorrelations. It is shown that up to 97 % of the system capacity can be lost due to the system imperfections. More, advanced and robust parameter estimators and/or multiuser detectors are needed to alleviate these degradations at the cost of increased complexity View full abstract»

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  • Spatial scheduling in multiuser wireless systems: from power allocation to admission control

    Page(s): 2082 - 2091
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (563 KB) |  | HTML iconHTML  

    Given a zero forcing transmit beamforming, we focus on how the multi-antenna access point distributes the scarce resource (power) among the single-antenna terminals. Since there is a clear trade-off between the satisfaction of the individual needs and the global performance of the cell, several criteria are proposed, ranging from a classical physical layer point of view of capacity (rate) maximization to bit error rate (BER)-based cost functions, which are closer to the second layer of the protocol stack. Between two traditional techniques, namely the uniform power allocation and the equal BER and rate, a new one is proposed, which ultimately provides an intermediate performance. Then, we add BER (or signal to noise ratio) constraints so that the admission control problem has to be solved. Among traditional options, we propose a new mechanism to balance the above-mentioned trade-off between the total performance and the particular user behavior. The results in terms of fairness are presented by a mean vs. variance plot and by the Gini plot View full abstract»

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  • Cyclic delay diversity with bit-interleaved coded modulation in orthogonal frequency division multiple access

    Page(s): 2092 - 2100
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (542 KB) |  | HTML iconHTML  

    We consider cyclic delay diversity in OFDMA. Cyclic delay diversity is an elegant way to obtain spatial diversity in an FEC coded OFDM system without exceeding the guard interval. We first address the problem of choosing the cyclic delays and propose a new robust design rule which enables to pick up the full spatial and frequency diversity which is inherent in a frequency-selective MIMO channel. Our choice of cyclic delays has consequences for the interleaving and multiple access scheme since the spatial diversity appears to be transformed into frequency diversity between neighbouring subcarriers. Therefore, a system with a conventional block frequency interleaver will fail to exploit the spatial diversity. We propose an interleaving and multiple access strategy which guarantees that all users obtain the maximum possible diversity advantage using FEC codes with a limited constraint length. Furthermore, we provide a performance comparison to transmit diversity from orthogonal designs View full abstract»

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  • Noncoherent block detection in the presence of DC offset

    Page(s): 2101 - 2110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (582 KB) |  | HTML iconHTML  

    In this paper, we deal with noncoherent detection of a digitally phasor block-modulated signal in the additive white Gaussian noise channel when a direct-current (DC) offset is present in the receiver baseband processing. By processing the received baseband signal block by block, a generalized linear transform is used to remove the offset prior to data detection, thereby releasing the succeeding detection process from the threat of DC offset. Operating on transform output blocks, a generalized maximum-likelihood scheme is developed for noncoherent data detection without a priori knowledge of channel amplitude and phase. When all the signaling blocks are confined within the space expanded by the basis vectors obtained from the onset-removal transform matrix, the proposed detection scheme can exploit the advantage of performing data detection and estimation on channel amplitude and phase jointly in the maximum-likelihood sense. It is analytically shown that the block detection scheme provides the bit error performance asymptotically approaching that of the corresponding ideal coherent phase-shift-keyed (PSK) detection in the absence of DC offset when the block length is increased. An iterative detection scheme is also modified from the block detection scheme to simplify the realization complexity. Both block and iterative detection schemes are shown to outperform the conventional training-sequence-aided PSK detection scheme under the same transmission throughput efficiency View full abstract»

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  • Performance analysis of macrodiversity, voice/data CDMA systems

    Page(s): 2111 - 2118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1052 KB) |  | HTML iconHTML  

    A performance analysis is presented for macrodiversity integrated voice/data CDMA systems. Macrodiversity with maximal ratio combining (MMRC) is ideal for such voice/data systems since it allows robust resource sharing between the two users while removing uncertainties in estimating the system capacity. Our analytical model allows the systems to dynamically allocate additional channels to data users to increase throughput when the necessary resource is available. The data users are characterized by arrival rates and average data size, and the resulting data user quality of service (QoS) performances are evaluated by using a simple birth-and-death Markov process. Our analytical results are fully verified by computer simulation. We show how various system QoS measures such as blocking and outage probabilities can be obtained and used in call admission control (CAC) decisions View full abstract»

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Aims & Scope

The IEEE Transactions on Wireless Communications publishes high-quality manuscripts on advances in the state-of-the-art of wireless communications.

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Meet Our Editors

Editor-in-Chief
Jeff Andrews
Cullen Trust for Higher Education Endowed Professor of Engineering