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Selected Areas in Communications, IEEE Journal on

Issue 2 • Date Feb 2003

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Displaying Results 1 - 12 of 12
  • A Bluetooth scatternet-route structure for multihop ad hoc networks

    Publication Year: 2003 , Page(s): 229 - 239
    Cited by:  Papers (35)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (505 KB) |  | HTML iconHTML  

    Bluetooth scatternets, integrating polling, and frequency hopping spread-sprectrum in their medium access control protocol, provide a contention-free environment for Bluetooth devices to access the medium and communicate over multihop links. Currently, most available scatternet formation protocols tend to interconnect all Bluetooth devices at the initial network startup stage and maintain all Bluetooth links thereafter. Instead of this "big scatternet" approach, we propose a scatternet-route structure to combine the scatternet formation with on-demand routing, thus eliminating unnecessary link and route maintenances. To the best of our knowledge, this is the first effort to address on-demand scatternet formation with every detail. We introduce an extended ID (EID) connectionless broadcast scheme, which, compared with original Bluetooth broadcast mechanism, achieves very much shortened route discovery delay. We also propose to synchronize the piconets along each scatternet route to remove piconet switch overhead and obtain even better channel utilization. Furthermore, we present a route-based scatternet scheduling scheme to enable fair and efficient packet transmissions over scatternet routes. Network performance analysis and simulations show that scatternet routes can provide multihop wireless channels with high network utilization and extremely stable throughput, being especially useful in the transmission of large batches of packets and real time data in wireless environment. View full abstract»

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  • A framework for optimal battery management for wireless nodes

    Publication Year: 2003 , Page(s): 179 - 188
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (791 KB) |  | HTML iconHTML  

    The focus of this paper is to extend the lifetime of a battery powered node in wireless context. The lifetime of a battery depends on both the manner of discharge and the transmission power requirements. We present a framework for computing the optimal discharge strategy which maximizes the lifetime of a node by exploiting the battery characteristics and adapting to the varying power requirements for wireless operations. The complexity of the optimal computation is linear in the number of system states. However, since the number of states can be large, the optimal strategy can only be computed offline and executed via a table lookup. We present a simple discharge strategy which can be executed online without any table lookup and attains near maximum lifetime. View full abstract»

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  • MMSE techniques for space diversity receivers in OFDM-based wireless LANs

    Publication Year: 2003 , Page(s): 151 - 160
    Cited by:  Papers (13)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    This paper studies the application of the minimum mean square error (MMSE) beamformer to orthogonal frequency division multiplexing (OFDM)-based wireless local area networks. The questions here addressed are mainly the design with finite-length data and the choice of the OFDM signal domain where the beamformer is applied, either frequency or time. As OFDM signals need more samples than other modulations to stabilize the estimation of the signal statistics, how to exploit the finite-length training sequence provided for the design of equalizers becomes an important issue. The paper also shows that the usual frequency processing in OFDM is not always the best choice for the spatial beamforming, mainly for channels with a very high delay spread. Then, time processing turns out to be the best suited approach in terms of the tradeoff between performance and complexity. Additionally, novel modifications of the MMSE spatial filter are proposed to improve the raw bit-error rate performance: 1) a temporal semiblind approach that exploits the cyclic prefix and 2) windowing in the frequency domain. View full abstract»

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  • A new statistical wideband spatio-temporal channel model for 5-GHz band WLAN systems

    Publication Year: 2003 , Page(s): 139 - 150
    Cited by:  Papers (95)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1541 KB) |  | HTML iconHTML  

    In this paper, a new statistical wideband indoor channel model which incorporates both the clustering of multipath components (MPCs) and the correlation between the spatial and temporal domains is proposed. The model is derived based on measurement data collected at a carrier frequency of 5.2 GHz in three different indoor scenarios and is suitable for performance analysis of HIPERLAN/2 and IEEE 802.11a systems that employ smart antenna architectures. MPC parameters are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization (FD-SAGE) algorithm and clusters are identified in the spatio-temporal domain by a nonparametric density estimation procedure. The description of the clustering observed within the channel relies on two classes of parameters, namely, intercluster and intracluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions (pdfs) derived from the measured data. The correlation properties are incorporated in two joint pdfs for cluster and MPC positions, respectively. The clustering effect also gives rise to two classes of channel power density spectra (PDS)-intercluster and intracluster PDS-which are shown to exhibit exponential and Laplacian functions in the delay and angular domains, respectively. Finally, the model validity is confirmed by comparison with two existing models reported in the literature. View full abstract»

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  • Bridges of Bluetooth county: topologies, scheduling, and performance

    Publication Year: 2003 , Page(s): 240 - 258
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1329 KB) |  | HTML iconHTML  

    The performance of two Bluetooth piconets linked through a shared device is analyzed using the tools of queueing theory. We analyze both possible topologies: the master/slave (MS) bridge, in which the shared device is the master in one of the piconets and a slave in the other, and the slave/slave (SS) bridge, where the shared device is the slave in both piconets. Two scheduling policies, limited service and exhaustive service, are considered. Analytical results are derived for the probability distribution of access delay (i.e., the time that a packet has to wait before being serviced) and end-to-end delay for both intrapiconet and interpiconet bursty traffic. The SS bridge has been found to offer lower access delays and local end-to-end delay than its MS counterpart, which provides lower end-to-end delay for nonlocal traffic due to the smaller number of hops (three, instead of four) for such traffic. In both topologies, exhaustive service scheduling was found to provide lower delays than the limited service one. All analytical results have been confirmed through simulations. View full abstract»

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  • An adaptive spatio-temporal coding scheme for indoor wireless communication

    Publication Year: 2003 , Page(s): 161 - 170
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (589 KB) |  | HTML iconHTML  

    Systems that employ multiple antennas in both the transmitter and the receiver of a wireless system have been shown to promise extraordinary spectral efficiency. With full channel knowledge at the transmitter and receiver, Raleigh and Cioffi (1998) proposed a spatio-temporal coding scheme, discrete matrix multitone (DMMT), to achieve asymptotically optimum multiple-input-multiple-output (MIMO) channel capacity. The DMMT can be regarded as an extension of the discrete multitone for a digital subscriber lines (DSL) system to the MIMO wireless application. However, the DMMT is basically impracticable in nonstationary wireless environments due to its high-computational complexity. Exploring second-order statistics, we develop an efficient adaptive blind coding scheme for a high-capacity time-division duplexing (TDD) system with slow time-varying frequency-selective MIMO channels. With this method, neither a training sequence nor feedback of channel information is required in the proposed blind approach. Besides, the computational complexity of the proposed scheme is significantly lower than that of the coding scheme described by Raleigh and Cioffi. Simulation results show that the proposed architecture works efficiently in indoor wireless local area network applications. View full abstract»

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  • TCP Veno: TCP enhancement for transmission over wireless access networks

    Publication Year: 2003 , Page(s): 216 - 228
    Cited by:  Papers (124)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (729 KB) |  | HTML iconHTML  

    Wireless access networks in the form of wireless local area networks, home networks, and cellular networks are becoming an integral part of the Internet. Unlike wired networks, random packet loss due to bit errors is not negligible in wireless networks, and this causes significant performance degradation of transmission control protocol (TCP). We propose and study a novel end-to-end congestion control mechanism called TCP Veno that is simple and effective for dealing with random packet loss. A key ingredient of Veno is that it monitors the network congestion level and uses that information to decide whether packet losses are likely to be due to congestion or random bit errors. Specifically: (1) it refines the multiplicative decrease algorithm of TCP Reno-the most widely deployed TCP version in practice-by adjusting the slow-start threshold according to the perceived network congestion level rather than a fixed drop factor and (2) it refines the linear increase algorithm so that the connection can stay longer in an operating region in which the network bandwidth is fully utilized. Based on extensive network testbed experiments and live Internet measurements, we show that Veno can achieve significant throughput improvements without adversely affecting other concurrent TCP connections, including other concurrent Reno connections. In typical wireless access networks with 1% random packet loss rate, throughput improvement of up to 80% can be demonstrated. A salient feature of Veno is that it modifies only the sender-side protocol of Reno without changing the receiver-side protocol stack. View full abstract»

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  • Combined equalization and decoding for IEEE 802.11b devices

    Publication Year: 2003 , Page(s): 125 - 138
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1849 KB) |  | HTML iconHTML  

    Receivers for wireless local area networks based on the IEEE 802.11b standard are required to operate well in heavy multipath, as well as additive noise impairments. This paper discusses a practical approach to combined equalizing and decoding for IEEE 802.11b systems, based on the Fano sequential decoding algorithm. Simulation results are presented demonstrating the greatly improved performance attained using this algorithm to the performance obtained using separate equalization and decoding blocks. This method has been implemented in TI's ACX100 chip. Measured laboratory results are presented that demonstrate superior throughput results obtained from this device compared with throughputs obtained by competitive devices available on the market. View full abstract»

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  • Bluetooth and IEEE 802.11b coexistence: analytical performance evaluation in fading channels

    Publication Year: 2003 , Page(s): 259 - 269
    Cited by:  Papers (52)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1092 KB) |  | HTML iconHTML  

    In this paper, the issue of Bluetooth and IEEE802.11b coexistence in a heterogeneous environment is addressed by means of an integrated analytical approach. The methodology proposed carefully takes both physical (i.e., thermal noise, propagation, interference, modulation formats, and coding techniques) and medium access control (frequency hopping, packet structures, traffic loads) aspects into account. This model can be easily implemented when developing network simulators, thus avoiding the need of extensive bit level Monte Carlo simulations at the physical level. The mean packet error probability is evaluated as a function of the relative distance between the two systems for different conditions (e.g., propagation, packet type, traffic loading, etc). In particular, how the presence or absence of line-of-sight propagation significantly affects the coexistence distance is emphasized. Furthermore, for a fixed quality-of-service level we derive the coexistence domain of the two considered systems in terms of relative distance. View full abstract»

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  • Transmit power adaptation for multiuser OFDM systems

    Publication Year: 2003 , Page(s): 171 - 178
    Cited by:  Papers (595)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (473 KB) |  | HTML iconHTML  

    In this paper, we develop a transmit power adaptation method that maximizes the total data rate of multiuser orthogonal frequency division multiplexing (OFDM) systems in a downlink transmission. We generally formulate the data rate maximization problem by allowing that a subcarrier could be shared by multiple users. The transmit power adaptation scheme is derived by solving the maximization problem via two steps: subcarrier assignment for users and power allocation for subcarriers. We have found that the data rate of a multiuser OFDM system is maximized when each subcarrier is assigned to only one user with the best channel gain for that subcarrier and the transmit power is distributed over the subcarriers by the water-filling policy. In order to reduce the computational complexity in calculating water-filling level in the proposed transmit power adaptation method, we also propose a simple method where users with the best channel gain for each subcarrier are selected and then the transmit power is equally distributed among the subcarriers. Results show that the total data rate for the proposed transmit power adaptation methods significantly increases with the number of users owing to the multiuser diversity effects and is greater than that for the conventional frequency-division multiple access (FDMA)-like transmit power adaptation schemes. Furthermore, we have found that the total data rate of the multiuser OFDM system with the proposed transmit power adaptation methods becomes even higher than the capacity of the AWGN channel when the number of users is large enough. View full abstract»

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  • Performance analysis of ad hoc wireless LANs for real-time traffic

    Publication Year: 2003 , Page(s): 204 - 215
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (834 KB) |  | HTML iconHTML  

    Compelling features of wireless local area networks (WLANs), put a variety of wireless service demands in place. In order to adjust system parameters to fulfill specific needs of different applications, a mathematical description of the system turns to be helpful. The inherent complexity of the wireless access, makes this description very challenging. We propose a new performance model for the IEEE 802.11 WLAN in ad hoc mode. The ad hoc mode has been chosen since we eventually aim at interconnected WLAN clusters where no base station exists. The model is based on the presentation of the system with a pair of one-dimensional state diagrams which can easily accommodate variations of many input parameters. The corresponding state variables are contention window size and buffer occupancy of each user in the system. The input parameters considered are: packet fragmentation factor, buffer size, and maximum allowable number of retransmissions. However, the approach taken is capable of ingesting many other probable parameters of interest. System performance criteria under study are: throughput, delay, and probability of fail to deliver. The last two are crucial for real-time applications. View full abstract»

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  • On the impact of IEEE 802.11 MAC on traffic characteristics

    Publication Year: 2003 , Page(s): 189 - 203
    Cited by:  Papers (52)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB) |  | HTML iconHTML  

    IEEE 802.11 medium access control (MAC) is gaining widespread popularity as a layer-2 protocol for wireless local-area networks. While efforts have been made previously to evaluate the performance of various protocols in wireless networks and to evaluate the capacity of wireless networks, very little is understood or known about the traffic characteristics of wireless networks. In this paper, we address this issue and first develop an analytic model to characterize the interarrival time distribution of traffic in wireless networks with fixed base stations or ad hoc networks using the 802.11 MAC. Our analytic model and supporting simulation results show that the 802.11 MAC can induce pacing in the traffic and the resulting interarrival times are best characterized by a multimodal distribution. This is a sharp departure from behavior in wired networks and can significantly alter the second order characteristics of the traffic, which forms the second part of our study. Through simulations, we show that while the traffic patterns at the individual sources are more consistent with long-range dependence and self-similarity, in contrast to wired networks, the aggregate traffic is not self-similar. The aggregate traffic is better classified as a multifractal process and we conjecture that the various peaks of the multimodal interarrival time distribution have a direct contribution to the differing scaling exponents at various timescales. View full abstract»

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Aims & Scope

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

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Meet Our Editors

Editor-in-Chief
Muriel Médard
MIT