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Wireless Communications, IEEE Transactions on

Issue 3 • Date March 2009

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Displaying Results 1 - 25 of 66
  • Table of contents

    Page(s): i - iii
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    Freely Available from IEEE
  • Pilot-symbol-assisted detection scheme for distributed orthogonal space-time block coding

    Page(s): 1057 - 1061
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    In this letter, we investigate the effect of imperfect channel estimation on the performance of distributed space-time block codes (DSTBCs) with amplify-and-forward relaying. Exploiting the orthogonality of the underlying code, we derive a maximum likelihood metric conditioned on the channel estimate acquired through the insertion of pilot symbols. For a large number of pilot symbols, we demonstrate that the proposed decoding rule coincides with the so-called mismatched receiver. On the other hand, as the number of pilot symbols decreases, the proposed decoder converges to a non-coherent detector. Through Monte-Carlo simulations, we further demonstrate that the performance of the proposed scheme lies within 0.8 dB of the genie receiver performance bound. View full abstract»

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  • Adaptive differentially coherent orthogonally multiplexed orthogonal phase modulation over flat fading channels

    Page(s): 1062 - 1066
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    A constant-power adaptive transmission technique adopting differentially coherent orthogonally multiplexed orthogonal phase modulation (DOMOPM) signals is studied for flat fading channels. Numerical results show that the constant-power adaptive DOMOPM system significantly outperforms the constant-power adaptive noncoherent frequency shift keying system in average spectral efficiency. View full abstract»

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  • Robust beamforming in the MISO downlink with quadratic channel estimation and optimal training

    Page(s): 1067 - 1072
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    Estimation of the channel state information (CSI) in quadratic form (i.e., quadratic channel estimation) in the downlink can be performed at the base station by using the relayed signals from the mobile users, which facilitates optimization with transmitter CSI. In this letter, the condition for the optimal training sequence for quadratic channel estimation in a multiuser multiple-input single-output (MISO) antenna system in the downlink is first obtained. The mean-square-error (MSE) in the CSI estimate is then analyzed. Based on the quadratic CSI estimates, a robust beamforming optimization algorithm to minimize the base station power while achieving individual users' quality-of-service (QoS) constraints, measured by the MSE in data reception, is proposed. View full abstract»

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  • Utility-optimal random access without message passing

    Page(s): 1073 - 1079
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    Random access has been studied for decades as a simple and practical wireless medium access control (MAC). Some of the recently developed distributed scheduling algorithms for throughput or utility maximization also take the form of random access, although extensive message passing among the nodes is required. In this paper, we would like to answer this question: is it possible to design a MAC algorithm that can achieve the optimal network utility without message passing? We provide the first positive answer to this question through a simple Aloha-type random access protocol. We prove the convergence of our algorithm for certain sufficient conditions on the system parameters, e.g., with a large enough user population. If each wireless node is capable of decoding the source MAC address of the transmitter from the interferring signal, then our algorithm indeed converges to the global optimal solution of the NUM problem. If such decoding is inaccurate, then the algorithm still converges, although optimality may not be always guaranteed. Proof of these surprisingly strong performance properties of our simple random access algorithm leverages the idea from distributed learning: each node can learn as much about the contention environment through the history of collision as through instantaneous but explicit message passing. View full abstract»

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  • Performance analysis of maximum ratio combining with imperfect channel estimation in the presence of cochannel interferences

    Page(s): 1080 - 1085
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    In this paper, we analyze the performance of maximum ratio combining (MRC) systems with imperfect channel estimation in the presence of cochannel interference (CCI) with an arbitrary power interference-to-noise ratio (INR). The maximum combining weights are the imperfect estimates of the desired user's fading channel coefficients and are assumed to be complex Gaussian distributed. The quantified measure for estimation error is the correlation coefficient between the true fading channel coefficients and their estimates. Exact closedform expressions are derived for the probability density function(pdf) of the signal-to-interference-plus-noise ratio (SINR), as well as performance metrics including outage probability and the average symbol error probability (ASEP) for some modulation formats. Simulation results demonstrate the accuracy of our theoretic analysis. View full abstract»

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  • Two-factor user authentication in wireless sensor networks

    Page(s): 1086 - 1090
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    Wireless sensor networks (WSN) are typically deployed in an unattended environment, where the legitimate users can login to the network and access data as and when demanded. Consequently, user authentication is a primary concern in this resource-constrained environment before accessing data from the sensor/gateway nodes. In this letter, we present a two-factor user authentication protocol for WSN, which provides strong authentication, session key establishment, and achieves efficiency. View full abstract»

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  • Preamble sampling MAC protocols with persistent receivers in wireless sensor networks

    Page(s): 1091 - 1095
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    We provide an analytical framework for preamble sampling techniques for MAC protocols in wireless sensor networks, from which we derive closed-form formulas for lifetime and reliability calculations. In addition to take into account transmitter behavior that controls the form and the content of the transmitted preamble, our model also considers receiver behavior that controls the duration of preamble reception in case of successful and failed reception. Along with both transmitter and receiver behavior, our model considers a non-perfect channel and thus takes into account the impacts of transmission errors and retransmissions on lifetime and reliability of preamble sampling protocols. Numerical results show that no protocol is universally optimal; that is, each protocol has its own optimal operation point that depends on the given channel and load conditions. View full abstract»

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  • Mean acquisition time analysis of fixed-step serial search algorithms

    Page(s): 1096 - 1101
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    In this paper, mean acquisition time (MAT) analysis of fixed-step serial search (FSSS) algorithms is presented. First, it is shown that the MAT of an FSSS algorithm can be obtained from that of a conventional serial search (CSS) algorithm after a certain mapping of the uncertainty region. Then, a generic formula for the MAT of FSSS algorithms is derived, which is valid for both dense and sparse channel environments. In addition, MAT formulas for high signal-to-noise ratio scenarios, for large uncertainty regions, and for dense channels are obtained as special cases of the generic solution. Finally, simulation results are presented to verify the analysis and to investigate the factors that affect the optimal step size for FSSS algorithms. View full abstract»

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  • Efficient power allocation for decentralized distributed space-time block coding

    Page(s): 1102 - 1106
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    In this paper, we propose two ad-hoc, yet efficient, power allocation strategies for a decentralized distributed space-time block coding (Dis-STBC) system where knowledge about the channel state information (CSI) is not available at the transmitter(s). The first is an open-loop strategy which requires no control signaling; the second is a feedback-assisted strategy which requires some control signaling, but which can achieve better power-efficiency. Focusing on a particular decentralized Dis-STBC scheme (m-group), the asymptotic outage probability is derived and the power-efficiency advantages of the proposed strategies over a uniform-power strategy are illustrated by evaluating the outage and link failure probabilities. View full abstract»

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  • On physically-based normalization of MIMO channel matrices

    Page(s): 1107 - 1112
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (214 KB) |  | HTML iconHTML  

    Various normalizations of the MIMO channel matrix are discussed from a physical perspective. It is demonstrated that the physics of antenna arrays and propagation channel should be taken into account when normalization is chosen, so that SNR has proper physical meaning, the conclusions are physical and correspond to realistic systems. The antenna array geometry and the transmission strategy (coherent/non-coherent) limits the choice of normalization and determines how the capacity and other performance metrics scale with the number of antennas, which is more pronounced for densely-populated antenna arrays. This is especially important for an asymptotic analysis, when the number of antennas increases to infinity. Limitations of such analysis from the physical perspective are pointed out. View full abstract»

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  • Source and channel coding for homogeneous sensor networks with partial cooperation

    Page(s): 1113 - 1117
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    A sensor networks in which two nodes communicate a remote measurement to an access point is investigated (CEO problem). The focus is on assessing the performance advantages of cooperative encoding strategies as enabled by out-of-band and finite-capacity communication links between the sensors. The analysis assumes Gaussian source and observation noises, a quadratic (MSE) distortion metric and homogeneous sensors. With rate-constrained links between each sensor and the access point, an achievable rate-distortion trade-off is derived that reduces to known rate-distortion characterizations in the cases without and with perfect cooperation. This result is then extended to a Gaussian multiple access channel scenario by deriving achievable distortions with separate or joint source-channel coding. It is concluded that, for both scenarios, even modest values of the capacity of the inter-sensor links enable the optimal performance with full sensor cooperation to be approached. View full abstract»

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  • On the existence of the Mazo-limit on MIMO channels

    Page(s): 1118 - 1121
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    Mazo, in 1975, showed that the signaling rate of a linear modulation can be significantly higher than the maximum rate for orthogonal signaling without any loss of minimum square Euclidean distance. In subsequent literature the highest such rate is referred to as the Mazo-limit. In this letter we ask whether there exists a Mazo-limit also on MIMO channels. The answer is yes, but it applies to the largest pairwise error probability rather than to minimum square Euclidean distance. Moreover, it occurs at exactly the same rate as in the AWGN case. As a special case results for single-input single-output fading channels are obtained. View full abstract»

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  • A novel CDD-OFDM scheme with pilot-aided channel estimation

    Page(s): 1122 - 1127
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    Cyclic delay diversity (CDD) is a low-complexity standard-conformable transmit diversity scheme for coded orthogonal frequency division multiplexing (OFDM) systems. However, it makes channel estimation more challenging due to the increased frequency-selectivity of the equivalent single-input single-output channel. In this paper, we propose a novel CDD-OFDM scheme with pilot-aided channel estimation for any number of transmit antennas. By alternating and optimizing the cyclic delay parameter over adjacent OFDM symbols, we design a simple yet efficient channel estimation scheme and illustrate its excellent performance for the DVB-T application. View full abstract»

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  • Analysis of pilots for residual frequency offset estimation in MIMO OFDM systems

    Page(s): 1128 - 1132
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    This paper analyses the estimation of residual frequency offset in MIMO OFDM systems using pilot subcarriers embedded in the data payload. A closed-form expression for the MSE is derived and it shows how the frequency and spatial correlation influence performance. It is also shown that an orthogonal design ensures robust performance, which is independent of the frequency correlation of the channel. View full abstract»

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  • Smooth beamforming for OFDM

    Page(s): 1133 - 1138
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    This paper investigates the combination of beamforming and channel state information (CSI) smoothing for OFDM. While both can offer significant performance gains, care must be taken when using both of them at the same time. Two different sets of beamforming weights can produce the same beamforming gains but be unsuitable for CSI smoothing due to sudden changes in the frequency domain. By using orthogonal iterations to compute the beamforming weights, it is shown that a smooth beamformer is produced which is suitable for CSI smoothing at the receiver. An additional benefit of this technique is that the beamforming weights are easy to compute by exploiting the frequency correlation of the channel. The performance is evaluated for an OFDM system based on the IEEE 802.11n draft standard for which the gains are quantified. We also present results obtained from a hardware test bed, which verify the performance of the proposed smooth beamforming technique. View full abstract»

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  • Empirical comparison of MIMO and beamforming schemes for outdoor-indoor scenarios

    Page(s): 1139 - 1143
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    We present an empirically based comparative study of spectral efficiency for a variety of transmission systems applicable to a fixed or repositionable wireless environment, in the context of Wi-Fi, WiMAX or MuniNet systems. A narrowband 4times4 multiple input multiple output (MIMO) channel sounder was constructed and a series of outdoor to indoor measurements were carried out, in multiple locations and with different array configurations. The channel measurements were used to compute the efficiency of different systems that could be deployed in such scenarios, ranging from a full MIMO system with perfect channel state information (CSI) at both ends to simple diversity schemes such as classical beamforming. We show comparisons of efficiency for the different transmit/receive configurations operating in a representative variety of locations. Our results indicate that for low values of signal to noise ratio (SNR), in the range of 5 dB, such as found in strong interference scenarios, simple schemes can achieve median spectral efficiencies as high as 80% of that of MIMO with complete CSI. View full abstract»

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  • Synchronous CDMA based on the cyclical translations of a CAZAC sequence

    Page(s): 1144 - 1147
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    A new scheme of synchronous CDMA is introduced in the paper. The new scheme is based on a code made by all the cyclical translations of a basic sequence having constant amplitude and white discrete spectrum. Such a code is proposed here for the first time as a code for CDMA. According to the proposed scheme, a cyclic prefix is appended to the multiplexed signal. The proposed scheme has a property that none of the known CDMA schemes has: in a multipath environment, it allows multiuser interference to become cyclic intersymbol interference. Noticeably, the memory of the finite state machine that describes the ISI model is equal to memory of the multipath channel. The main advantage of our proposed scheme is that optimal and suboptimal detectors can be obtained from detectors proposed in the past for the ISI channel, which are much easier to implement than conventional multiuser detectors of classical CDMA schemes. Another advantage of our scheme is that it leads naturally to a signal processing architecture similar to that of OFDM systems, hence based on the efficient FFT/IFFT algorithm. View full abstract»

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  • Rate optimization for IDMA systems with iterative joint multi-user decoding

    Page(s): 1148 - 1153
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    In this letter, we develop a rate allocation scheme for interleave-division multiple-access (IDMA) systems with iterative decoding. We use a fully-analytical approach to predict the performance of the scheme. Then, we propose a modified linear programming method to find the best rate profile for the scheme. Numerical results show that with just repetition coding and optimal rate allocation, the performance of the scheme is only about 5 dB away from the capacity for a wide range of SNR, provided that the number of users is sufficiently large. Compared with power allocation schemes for IDMA, the proposed rate allocation scheme achieves a similar performance at a moderate spectral efficiency and the requirement of sophisticated power amplifiers can be relaxed. View full abstract»

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  • Measurement-based frame error model for simulating outdoor Wi-Fi networks

    Page(s): 1154 - 1158
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    We present a measurement-based model of the frame error process on a Wi-Fi channel in rural environments. Measures are obtained in controlled conditions, and careful statistical analysis is performed on the data, providing information which the network simulation literature is lacking. Results indicate that most network simulators use a frame loss model that can miss important transmission impairments even at a short distance, particularly when considering antenna radiation pattern anisotropy and multi-rate switching. View full abstract»

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  • An extension to the ordered subcarrier selection algorithm (OSSA)

    Page(s): 1159 - 1163
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    In this letter, we propose an extension to the ordered subcarrier selection algorithm (OSSA) for orthogonal frequency division multiplexing (OFDM) systems. The result is a simple algorithm for minimizing the bit error rate of the OFDM system at a fixed throughput. The proposed algorithm employs multiple modulations (non-uniform bit loading) within an OFDM symbol. However, unlike existing bit loading algorithms that have a very high computational complexity, the proposed algorithm is based only on the ordered statistics of the subcarrier gains and is consequently very simple. After ordering the subcarriers based on their gains, progressively higher order modulations are used with increasing gains. The key aspect here that greatly simplifies the algorithm is that the modulation used on a subcarrier depends only on the position of its gain in the ordered set and not on the actual values of the gains. We show an analytical approach for determining the parameters of the algorithm. View full abstract»

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  • Error performance of transmit beamforming with delayed and limited feedback

    Page(s): 1164 - 1170
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    Feedback delay can severely affect the performance of transmit beamforming (TB) and the analytical quantification of the performance degradation has attracted much research interest recently. In this letter, we study the effect of delayed and limited-rate codebook index feedback on the error rate performance of TB systems over Rayleigh fading channels. We derive closed-form expressions for the moment generating function (MGF) and the probability density function (PDF) of the receiver output signal-to-noise ratio (SNR) including the effects of outdated and finite-rate feedback and further provide accurate analytical error rate expressions, which are verified by simulation results. The coding gain gap between the full-rate and limited-rate feedback and the coding gain advantage of multiple transmit antennas to the single antenna are analyzed, for limited and delayed feedback. These results are simple and concise and provide new analytical insight into the achievable diversity and combining gains and the loss caused by feedback delay for different system parameters and modulation formats. View full abstract»

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  • Combined synchronization and power control for differentially-encoded di-symbol time-division multiuser impulse radio

    Page(s): 1171 - 1176
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    The differentially-encoded, di-symbol time-division multiuser impulse radio (d2TD-IR) with delay-sum autocorrelation receivers is a low complexity, high efficiency short range wireless communication technology for infrastructure networks. The d2TD-IR system is designed with the assumption that the users are perfectly synchronized. In this letter, we propose a recursive algorithm of combined synchronization and power control. Computer simulation results show that the proposed algorithm has significant performance improvement over the algorithm, in which synchronization and power control are performed separately. View full abstract»

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  • Optimizing antenna configuration for MIMO systems with imperfect channel estimation

    Page(s): 1177 - 1181
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    We study the optimal antenna configuration (i.e. number of transmit and receive antennas) for multiple-input multiple-output systems in pilot-symbol-assisted modulation schemes with imperfect channel estimation. We assume block flat-fading channels and focus on a practical range of high signal-to-noise ratio. An ergodic capacity lower bound is used as the objective function to be maximized. We analytically study the capacity gain from adding extra antennas to the transmitter or to the receiver in two different scenarios. Our numerical results show that the optimal antenna configuration under imperfect channel estimation can be significantly different from that under perfect channel estimation assumption. In addition, we investigate the capacity gain from optimizing antenna configuration and find that the gain can be larger than that achieved by optimizing transmit power over pilot and data symbols, particularly for large block lengths. View full abstract»

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  • Connection-based scheduling for supporting real-time traffic in wireless mesh networks

    Page(s): 1182 - 1187
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    Packet transmission scheduling for supporting real-time traffic in a WMN is difficult, and one of the main challenges is to coordinate temporal operations of the mesh access points (APs) in order to provide strict latency guarantee while efficiently utilizing the radio resources. In this paper a connection-based scheduling (CBS) scheme is proposed. Connections with more hops are given a higher priority, and connections with a lower priority can only use resources remaining from serving all higher priority ones. For each multihop connection, the scheduling minimizes latency between successive hops. A connection-based optimization problem is formulated with an objective to minimize the amount of required AP resources, subject to the latency requirement of the connections. Numerical results show that the proposed scheduling scheme achieves close-to-optimum performance at both the connection and packet levels. 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