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Wireless Communications, IEEE Transactions on

Issue 2 • Date February 2012

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Displaying Results 1 - 25 of 46
  • Table of contents

    Page(s): c1 - c5
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  • [Staff List]

    Page(s): c2
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  • Call for Papers

    Page(s): c3
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  • Pre/Post-Rake Diversity Combining for UWB Communications in the Presence of Pulse Overlap

    Page(s): 481 - 487
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB) |  | HTML iconHTML  

    Taking the effect of pulse overlap into account, we address the pre/post-rake technique using rake structure at both transmitter and receiver. Firstly, we propose a single-stream (SS) pre/post-rake, in which the pair of pre-rake and post-rake weighting vectors is optimally derived through generalized eigenvalue decomposition (GEVD). Secondly, by judiciously designing multiple pairs of weighting vectors, we derive multiple-stream (MS) pre/post-rake, which enables parallel subchannel transmission while not requiring multiple antennas at the transmitter or receiver. Finally, we conduct simulations to verify the advantages of the SS pre/post-rake and the MS pre/post-rake over existing rakes. View full abstract»

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  • Analysis of OFDM over Nakagami-m Fading with Nonuniform Phase Distributions

    Page(s): 488 - 492
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (294 KB) |  | HTML iconHTML  

    This paper presents a new mathematical analysis for the performance of orthogonal frequency-division multiplexed (OFDM) signals over multipath Nakagami-m fading channels. In contrast to the previous research, this paper focuses on the effects of the nonuniform phase distribution on the error rate performance. A unified expression is derived for the moment generating function (MGF) of the frequency-domain channel gains on Nakagami-m channels with nonuniform phase distributions. Classical MGF methods can then be straightforwardly employed to obtain accurate error rates expressions for different modulation and diversity formats. View full abstract»

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  • Joint Relay and Antenna Selection for Dual-Hop Amplify-and-Forward MIMO Relay Networks

    Page(s): 493 - 499
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (333 KB) |  | HTML iconHTML  

    Four joint relay and antenna selection strategies for dual-hop amplify-and-forward (AF) multiple-input multiple-output relay networks are studied. Two of them require full channel state information (CSI) whereas the other two require only partial CSI. The relays are either channel-assisted AF or fixed-gain AF type. The first joint selection strategy involves choosing the best relay and the best single transmit antennas at the source and the relay. The second strategy jointly involves choosing the best relay and the best single transmit/receive antenna pairs at the source-to-relay and relay-to-destination channels. Moreover, two partial selection strategies, which can be used when the global CSI is not available, are also proposed and analyzed. In order to quantify the system performance analytically, the exact outage probability of all selection strategies is derived in closed-form. Direct insights into the system-design are obtained by deriving the asymptotic outage probability, asymptotic average symbol error rate, diversity order and array gain. View full abstract»

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  • Performance of Amplify-and-Forward Systems with Partial Relay Selection under Spectrum-Sharing Constraints

    Page(s): 500 - 504
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (250 KB) |  | HTML iconHTML  

    This article focuses on the performance of a relay system in spectrum-sharing context. We consider that a secondary user (SU) is allowed to share the spectrum band with a primary user (PU) as long as it meets predefined interference constraints set by the PU. We suppose that the SU's transmitter and receiver are unable to communicate directly and, thus, are helped by a set of intermediate terminal nodes to deliver the data from the source to the destination. The relay nodes function using amplify-and-forward (AF) and a single "best" intermediate node is selected among a cluster by means of partial relay selection (PRS) technique to relay the information to the destination. Statistics for the end-to-end signal-to-noise ratio (SNR), namely, the probability density function (PDF) and the moment generating function (MGF), are derived and used next to evaluate the bit error rate (BER) of several modulation schemes. Numerical results and interpretations complete the study. View full abstract»

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  • Link Adaptation with Position/Motion Information in Vehicle-to-Vehicle Networks

    Page(s): 505 - 509
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB) |  | HTML iconHTML  

    Wireless communication networks use link adaptation to select physical layer parameters that optimize the transmission strategy as a function of the wireless channel realization. In the vehicle-to-vehicle (V2V) networks considered in this letter, the short coherence time of the wireless channel makes link adaptation based on the impulse response challenging. Consequently, link adaptation in V2V wireless networks may instead exploit the large-scale characteristics of the wireless channel (i.e. path loss) since they evolve slowly and enable less frequent feedback. Large-scale channel information may be captured through channel or position/motion measurements. We show, through the definition of new large-scale coherence expressions, that channel measurements render large-scale coherence as a function of time-change while the position/motion measurements render coherence as a function of velocity-change. This letter is concluded with highway simulations of modeled and measured channels to demonstrate the advantage of position/motion information for feedback reduction in V2V link adaptation. View full abstract»

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  • Fast Global Optimal Power Allocation in Wireless Networks by Local D.C. Programming

    Page(s): 510 - 515
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    Power allocations in an interference-limited wireless network for global maximization of the weighted sum throughput or global optimization of the minimum weighted rate among network links are not only important but also very hard optimization problems due to their nonconvexity nature. Recently developed methods are either unable to locate the global optimal solutions or prohibitively complex for practical applications. This paper exploits the d.c. (difference of two convex functions/sets) structure of either the objective function or constraints of these global optimization problems to develop efficient iterative algorithms with very low complexity. Numerical results demonstrate that the developed algorithms are able to locate the global optimal solutions by only a few iterations and they are superior to the previously-proposed methods in both performance and computation complexity. View full abstract»

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  • Exploiting Negative Feedback Information for One-Bit Feedback Beamforming Algorithm

    Page(s): 516 - 525
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1412 KB) |  | HTML iconHTML  

    In this paper a hybrid one-bit feedback algorithm is proposed to achieve carrier phase alignment at the receiver for distributed transmit beamforming. The proposed iterative algorithm employs two schemes to speed up the convergence process, which exploit negative feedback information in a single time slot (Scheme 1) and in successive time slots (Scheme 2) respectively, whereas previously proposed algorithms in the literature discard this information. We show that the proposed algorithm yields a significant improvement in the convergence speed compared to the original algorithm. Furthermore, we modify the proposed algorithm to be capable of tracking time-varying channels which have variable rates of phase drift. The modified hybrid algorithm has the ability to adjust perturbation sizes adaptively without the knowledge of channel state information and is suited for practical implementations. View full abstract»

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  • Autocorrelation Based Coarse Timing with Differential Normalization

    Page(s): 526 - 530
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (313 KB) |  | HTML iconHTML  

    Two novel differential normalization factors, depending on the severity of carrier frequency offset, are proposed for autocorrelation based coarse timing scheme. Compared with the conventional normalization factor based on signal energy, they improve the robustness of the timing metric to signal-to-noise ratio (SNR), improve the mainlobe sharpness of the timing metric and reduce both missed detection and false alarm probabilities. View full abstract»

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  • Impact of Interference on the Performance of Selection Based Parallel Multiuser Scheduling

    Page(s): 531 - 536
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB) |  | HTML iconHTML  

    In conventional multiuser parallel scheduling schemes, every scheduled user is interfering with every other scheduled user, which limits the capacity and performance of multiuser systems, and the level of interference becomes substantial as the number of scheduled users increases. Based on the above observations, we investigate the trade-off between the system throughput and the number of scheduled users through the exact analysis of the total average sum rate capacity and the average spectral efficiency. Our analytical results can help the system designer to carefully select the appropriate number of scheduled users to maximize the overall throughput while maintaining an acceptable quality of service under certain channel conditions. View full abstract»

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  • New Insights into Optimal Discrete Rate Adaptation for Average Power Constrained Single and Multi-Node Systems

    Page(s): 537 - 543
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (278 KB) |  | HTML iconHTML  

    The throughput-optimal discrete-rate adaptation policy, when nodes are subject to constraints on the average power and bit error rate, is governed by a power control parameter, for which a closed-form characterization has remained an open problem. The parameter is essential in determining the rate adaptation thresholds and the transmit rate and power at any time, and ensuring adherence to the power constraint. We derive novel insightful bounds and approximations that characterize the power control parameter and the throughput in closed-form. The results are comprehensive as they apply to the general class of Nakagami-m (m ≥1) fading channels, which includes Rayleigh fading, uncoded and coded modulation, and single and multi-node systems with selection. The results are appealing as they are provably tight in the asymptotic large average power regime, and are designed and verified to be accurate even for smaller average powers. View full abstract»

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  • Masked Beamforming for Multiuser MIMO Wiretap Channels with Imperfect CSI

    Page(s): 544 - 549
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (257 KB) |  | HTML iconHTML  

    This letter investigates masked beamforming schemes for multiuser multiple-input multiple-output (MIMO) downlink systems in the presence of an eavesdropper. With noisy and outdated channel state information (CSI) at the base station (BS), we aim to maximize the transmit power of an artificial noise, which is broadcast to jam any potential eavesdropper, while meeting individual minimum mean square error (MMSE) constraints of the desired user links. To this end, we adopt a Bayesian approach and derive an average MSE uplink-downlink duality with imperfect CSI. Using the duality, a robust beamforming algorithm is proposed. Simulation results show the effectiveness of the proposed scheme. View full abstract»

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  • Exact Signal Model and New Carrier Frequency Offset Compensation Scheme for OFDM

    Page(s): 550 - 555
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (415 KB) |  | HTML iconHTML  

    Carrier frequency offset (CFO) causes spectrum misalignment of transmitter and receiver filters. This misalignment leads to energy loss and distortion of received signal, resulting in performance degradation of the whole system. However, these issues are often overlooked by existing works. This paper presents an exact signal model for OFDM that takes into account the CFO-induced spectral misalignment and related aliasing effects. Incorporating these practical issues, we also propose a new preamble structure and a new CFO compensation approach to mitigate their negative effects. Theoretical analysis and simulation results substantiate the importance of the exact signal model and the advantage of the proposed CFO compensation scheme. View full abstract»

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  • On the Energy Efficiency-Spectral Efficiency Trade-Off in the Uplink of CoMP System

    Page(s): 556 - 561
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (434 KB) |  | HTML iconHTML  

    In this paper, we derive a generic closed-form approximation (CFA) of the energy efficiency-spectral efficiency (EE-SE) trade-off for the uplink of coordinated multi-point (CoMP) system and demonstrate its accuracy for both idealistic and realistic power consumption models (PCMs). We utilize our CFA to compare CoMP against conventional non-cooperative system with orthogonal multiple access. In the idealistic PCM, CoMP is more energy efficient than non-cooperative system due to a reduction in power consumption; whereas in the realistic PCM, CoMP can also be more energy efficient but due to an improvement in SE and mainly for cell-edge communication and small cell deployment. View full abstract»

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  • Quality-of-Service Analysis of Queuing Systems with Long-Range-Dependent Network Traffic and Variable Service Capacity

    Page(s): 562 - 570
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (417 KB) |  | HTML iconHTML  

    Many high-quality measurement studies have demonstrated that wireless network traffic exhibits the noticeable Long-Range-Dependent (LRD) property. Moreover, the fading nature of wireless channels can lead to variable service capacity. Due to the inherent difficulty and high complexity of modelling the fractal-like LRD traffic, existing analytical models of queuing systems with LRD arrival processes have been primarily limited to the simplified scenarios where the service capacity is assumed to be constant. Given the time-varying nature of wireless channels in the real-world working environments, it is very important and necessary to investigate system performance in the presence of variable service capacity. To this end, this paper presents a comprehensive analytical model for queuing systems subject to LRD traffic and variable service capacity. We extend the application of a Large Deviation Principle and derive the closed-form expressions of Quality-of-Service (QoS) metrics. The accuracy of the model validated through extensive simulation experiments makes it a cost-effective evaluation tool for performance analysis of communication networks. To illustrate its applications, the model is adopted to investigate the effects of LRD traffic and variable service capacity on the system performance and resource configuration. View full abstract»

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  • Broadcasting with an Energy Harvesting Rechargeable Transmitter

    Page(s): 571 - 583
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (421 KB) |  | HTML iconHTML  

    In this paper, we investigate the transmission completion time minimization problem in an additive white Gaussian noise (AWGN) broadcast channel, where the transmitter is able to harvest energy from the nature, using a rechargeable battery. The harvested energy is modeled to arrive at the transmitter during the course of transmissions. The transmitter has a fixed number of packets to be delivered to each receiver. The objective is to minimize the time by which all of the packets are delivered to their respective destinations. To this end, we optimize the transmit powers and transmission rates in a deterministic setting. We first analyze the structural properties of the optimal transmission policy in a two-user broadcast channel via the dual problem of maximizing the departure region by a fixed time T. We prove that the optimal total transmit power sequence has the same structure as the optimal single-user transmit power sequence in . In addition, the total power is split optimally based on a cut-off power level; if the total transmit power is lower than this cut-off level, all transmit power is allocated to the stronger user; otherwise, all transmit power above this level is allocated to the weaker user. We then extend our analysis to an M-user broadcast channel. We show that the optimal total power sequence has the same structure as the two-user case and optimally splitting the total power among M users involves M-1 cut-off power levels. Using this structure, we propose an algorithm that finds the globally optimal policy. Our algorithm is based on reducing the broadcast channel problem to a single-user problem as much as possible. Finally, we illustrate the optimal policy and compare its performance with several suboptimal policies under different settings. View full abstract»

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  • Secure Location Verification Using Simultaneous Multilateration

    Page(s): 584 - 591
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    Substantial effort has been invested on secure location verification in hope to enable mobile wireless systems to optimize system performance or securely confer rights based on the participants' locations. However, most previous studies do not address the impact of, and are often susceptible to, collusion attacks in which adversaries share their private keys. In this paper, we propose a secure multilateration scheme. Given the same processing delay, detection threshold, and assuming zero synchronization error between verifiers, our proposed scheme achieves the highest rate of false-location detection by any verification system based solely on time-of-flight measurements. We also show that our scheme is resilient to collusion attacks if the verification system can detect the distance enlargement attack. We propose using other physical measurements to mitigate the distance enlargement, and thus also the collusion, attacks. To the best of our knowledge, this is the first attempt to prevent collusion attacks by mitigating the distance enlargement attack. View full abstract»

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  • User Partitioning for Less Overhead in MIMO Interference Channels

    Page(s): 592 - 603
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (663 KB) |  | HTML iconHTML  

    This paper presents a study on multiple-antenna interference channels, accounting for general overhead as a function of the number of users and antennas in the network. The model includes both perfect and imperfect channel state information based on channel estimation in the presence of noise. Three low-complexity methods are proposed for reducing the impact of overhead in the sum network throughput by partitioning users into orthogonal groups. The first method allocates spectrum to the groups equally, creating an imbalance in the sum rate of each group. The second proposed method allocates spectrum unequally among the groups to provide rate fairness. Finally, geographic grouping is proposed for cases where some receivers do not observe significant interference from other transmitters. For each partitioning method, the optimal solution not only requires a brute force search over all possible partitions, but also requires full channel state information, thereby defeating the purpose of partitioning. We therefore propose greedy methods to solve the problems, requiring no instantaneous channel knowledge. Simulations show that the proposed greedy methods switch from time-division to interference alignment as the coherence time of the channel increases, and have a small loss relative to optimal partitioning only at moderate coherence times. View full abstract»

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  • OFDM Modulated Cooperative Multiple-Access Channel with Network-Channel Coding

    Page(s): 604 - 613
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (522 KB) |  | HTML iconHTML  

    In this paper, we consider the half-duplex cooperative multiple-access channel (CMAC) with frequency-selective block-fading. Each link employs an orthogonal frequency division multiplexing (OFDM) system, where modulated symbols are drawn from a finite constellation set. We first obtain the diversity order of the CMAC, as a function of the time sharing variables of the users and the rates of the codes. To achieve this rate-diversity tradeoff, we use the principle of network coding where messages of the two sources are jointly encoded. Both separate and joint network-channel coding approaches are considered. Specifically, we design multiple turbo codes that minimize the outage probabilities of these approaches. We also give a code structure for the multiple turbo codes to achieve full diversity of the system. The codes are optimized using the extrinsic information transfer (EXIT) chart analysis with iterative decoding tailored for OFDM modulated CMAC. Numerical examples show that with our proposed design technique, the achieved frame error rate is within 0.5dB from the information outage. Without network-channel coding, the outage probability of distributed coding cannot achieve the diversity order given in the rate-diversity tradeoff. View full abstract»

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  • Uplink Interference Mitigation for OFDMA Femtocell Networks

    Page(s): 614 - 625
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (561 KB) |  | HTML iconHTML  

    Femtocell networks, consisting of a conventional macro cellular deployment and overlaying femtocells, forming a hierarchical cell structure, constitute an attractive solution to improving the macrocell capacity and coverage. However, the inter- and intra-tier interferences in such systems can significantly reduce the capacity and cause an unacceptably high level of outage. This paper treats the uplink interference problem in orthogonal frequency-division multiple-access (OFDMA)-based femtocell networks with partial cochannel deployment. We first propose an inter-tier interference mitigation strategy without the femtocell users power control by forcing the femto-interfering macrocell users to use only some dedicated subcarriers. The non-interfering macrocell users, on the other hand, can use either the dedicated subcarriers, or the shared subcarriers which are also used by the femtocell users. We then propose subcarrier allocation schemes based on the auction algorithm for macrocell users and femtocell users, respectively, to independently mitigate the intra-tier interference. The proposed interference mitigation scheme for femtocell networks offers significant performance improvement over the existing methods by substantially reducing the inter- and intra-tier inferences in the system. View full abstract»

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  • Interference Alignment with Analog Channel State Feedback

    Page(s): 626 - 636
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB) |  | HTML iconHTML  

    Interference alignment (IA) is a multiplexing gain optimal transmission strategy for the interference channel. While the achieved sum rate with IA is much higher than previously thought possible, the improvement comes at the cost of requiring network channel state information at the transmitters. This can be achieved by explicit feedback, a flexible yet potentially costly approach that incurs large overhead. In this paper we propose analog feedback as an alternative to limited feedback or reciprocity based alignment. We show that the full multiplexing gain observed with perfect channel knowledge is preserved by analog feedback and that the mean loss in sum rate is bounded by a constant when signal-to-noise ratio is comparable in both forward and feedback channels. When signal-to-noise ratios are not quite symmetric, a fraction of the multiplexing gain is achieved. We consider the overhead of training and feedback and use this framework to numerically optimize the system's effective throughput. We present simulation results to demonstrate the performance of IA with analog feedback, verify our theoretical analysis, and extend our conclusions on optimal training and feedback length. View full abstract»

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  • An Autonomous Resource Block Assignment Scheme for OFDMA-Based Relay-Assisted Cellular Networks

    Page(s): 637 - 647
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (451 KB) |  | HTML iconHTML  

    Terminal relaying offers an effective means for improving the performance of OFDMA-based wireless networks. However, revrr{with the increase in the number of relaying terminals (RTs), their coordination becomes a cumbersome task.} To address this drawback, in this paper an autonomous scheme is proposed whereby the RTs assign resource blocks (RBs) to incoming wireless terminals (WTs) in a way that minimizes the number of hit occurrences at which the same RB is assigned to multiple WTs. The proposed scheme uses cyclic group generators to determine the sequence of RBs to be assigned by each RT. This scheme is particularly beneficial in terminal relaying systems in which the distribution of the WTs is nonuniform and the channel quality indicators are not available. Simulation results show that the proposed scheme performs significantly better than currently available autonomous assignment schemes. View full abstract»

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  • Group Contention-Based OFDMA MAC Protocol for Multiple Access Interference-Free in WLAN Systems

    Page(s): 648 - 658
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1320 KB) |  | HTML iconHTML  

    In WLAN systems, the difference in propagation delay among stations (STAs) can exceed the predefined cyclic prefix length, leading to multiple access interference (MAI). To solve this MAI problem, it is necessary to use a longer cyclic prefix length for orthogonality between different subchannels; however, this sacrifices system efficiency due to the cyclic prefix overhead. In this paper, we propose a group contention-based OFDMA to solve the MAI problem with an adequate cyclic prefix length and support a larger number of STAs. The STAs within the cyclic prefix duration that are synchronized to an access point (AP), are included in the same contending group and compete with other STAs of the group in transmitting packets. The proposed scheme allows for the adoption of an adequate cyclic prefix length without MAI, and is able to reduce the cyclic prefix overhead. In addition, since no packet errors are induced by MAI in any of the STAs, the STAs can transmit simultaneously without redundant short interframe spaces (SIFSs) and other control packets. Through analysis and simulation, we show that for a large number of STAs, the proposed scheme achieves higher throughput than 802.11 protocols and a conventional CSMA combined with OFDMA. View full abstract»

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