Showing papers in "IEEE Communications Letters in 2008"
TL;DR: The optimal detector for the so-called spatial modulation (SM) system introduced by Mesleh et al. in 2006 is derived, and it is shown that SM with the optimal detector achieves performance gains over popular multiple antenna systems, making it an excellent candidate for future wireless communication standards.
Abstract: In this letter, we derive the optimal detector for the so-called spatial modulation (SM) system introduced by Mesleh et al. in (Mesleh, 2006). The new detector performs significantly better than the original (~ 4 dB gain), and we support our results by deriving a closed form expression for the average bit error probability. As well, we show that SM with the optimal detector achieves performance gains (~ 1.5 - 3 dB) over popular multiple antenna systems, making it an excellent candidate for future wireless communication standards.
875 citations
TL;DR: ACO-OFDM requires less optical power for a given data rate than DCO- OFDM for all but the largest constellations and is better suited to adaptive systems as the same structure is optimum for all constellation.
Abstract: We present theoretical and simulation results for the performance of asymmetrically-clipped optical OFDM (ACO-OFDM) and DC-biased optical OFDM (DCO-OFDM) in AWGN for intensity-modulated direct-detection systems. Constellations from 4 QAM to 1024 QAM are considered. For DCO-OFDM, the optimum bias depends on the constellation size which limits its performance in adaptive systems. ACO-OFDM requires less optical power for a given data rate than DCO-OFDM for all but the largest constellations and is better suited to adaptive systems as the same structure is optimum for all constellations.
638 citations
TL;DR: This work demonstrates the performance advantages of polar codes over RM codes under belief-propagation decoding in binary-input channels with certain symmetries.
Abstract: Polar coding is a code construction method that can be used to construct capacity-achieving codes for binary-input channels with certain symmetries. Polar coding may be considered as a generalization of Reed-Muller (RM) coding. Here, we demonstrate the performance advantages of polar codes over RM codes under belief-propagation decoding.
474 citations
TL;DR: The probability density function of the received signal-to-noise ratio for the considered relaying link is approximated in closed form, and an asymptotic exponential expression is proposed to simplify performance estimation.
Abstract: This letter offers a statistical analysis of the basic two-hop Amplify-and-Forward link, where the relay node is selected based on instantaneous and partial knowledge of the channel. In contrast with previously reported work, where relay selection requires global knowledge (2 hops) of the relaying link, the problem considered is interesting in practical ad-hoc systems, where only neighboring (1 hop) channel information is available to the nodes. The probability density function of the received signal-to-noise ratio for the considered relaying link is approximated in closed form, and an asymptotic exponential expression is proposed to simplify performance estimation.
430 citations
TL;DR: The average bit-error rate in closed form of a FSO system operating in this channel environment, assuming intensity modulation/direct detection with on-off keying, is evaluated.
Abstract: In this letter, we investigate the error rate performance of free-space optical (FSO) links over strong turbulence fading channels together with misalignment (pointing error) effects. First, we present a novel closed-form expression for the distribution of a stochastic FSO channel model which takes into account both atmospheric turbulence-induced fading and misalignment-induced fading. Then, we evaluate the average bit-error rate in closed form of a FSO system operating in this channel environment, assuming intensity modulation/direct detection with on-off keying. Numerical examples are further provided to collaborate on the derived analytical expressions.
351 citations
TL;DR: Under average power constraint at the relay station, it is shown that the optimal relay-precoder always loads power across channel eigenvectors and then decomposes the equivalent MIMO channel into a set of parallel SISO channels.
Abstract: In this letter, we address the problem of transceiver design in a non-regenerative MIMO relay system, where linear processing is applied at both the relay and destination to jointly minimize the mean-squared error (MSE) of symbol estimations. Under average power constraint at the relay station, we show that the optimal relay-precoder always loads power across channel eigenvectors and then decomposes the equivalent MIMO channel into a set of parallel SISO channels. Simulation results demonstrate that our method outperforms other relaying schemes in terms of both BER and MSE.
294 citations
TL;DR: This letter proposes an efficient frequency assignment technique for femtocells considering practical issues such as hand-off, coverage, and interference, and calculates interference-limited coverage area (ILCA) of a co-channel femtocell base station.
Abstract: Successful deployment of femtocells requires intelligent cell planning and introduces some unique challenges. In this letter, an efficient frequency assignment technique is proposed for femtocells considering practical issues such as hand-off, coverage, and interference. Moreover, interference-limited coverage area (ILCA) of a co-channel femtocell base station is calculated based on parameters such as the distance to the macrocell BS, path loss exponents, and transmission power levels.
266 citations
TL;DR: This Letter proposes a simple and efficient data compression algorithm particularly suited to be used on available commercial nodes of a WSN, where energy, memory and computational resources are very limited.
Abstract: Power saving is a critical issue in wireless sensor networks (WSNs) since sensor nodes are powered by batteries which cannot be generally changed or recharged. As radio communication is often the main cause of energy consumption, extension of sensor node lifetime is generally achieved by reducing transmissions/receptions of data, for instance through data compression. Exploiting the natural correlation that exists in data typically collected by WSNs and the principles of entropy compression, in this Letter we propose a simple and efficient data compression algorithm particularly suited to be used on available commercial nodes of a WSN, where energy, memory and computational resources are very limited. Some experimental results and comparisons with, to the best of our knowledge, the only lossless compression algorithm previously proposed in the literature to be embedded in sensor nodes and with two well- known compression algorithms are shown and discussed.
241 citations
TL;DR: A new method for orthogonal frequency division multiplexing (OFDM) sidelobe suppression is introduced that is added to OFDM symbols that is calculated using optimization methods to minimize adjacent channel interference (ACI) while keeping the extension power at an acceptable level.
Abstract: In this letter, we introduce a new method for orthogonal frequency division multiplexing (OFDM) sidelobe suppression. An extension is added to OFDM symbols that is calculated using optimization methods to minimize adjacent channel interference (ACI) while keeping the extension power at an acceptable level. Using this technique, interference to adjacent signals is reduced significantly at the cost of a small decrease in the useful symbol energy. The proposed method can be used by cognitive radio (CR) systems to shape the spectrum of OFDM signals and to minimize interference to licensed users (LU), or to reduce the size of guard bands used in conventional OFDM systems.
233 citations
TL;DR: Information-guided channel-hopping is introduced, a new scheme for high data rate communication over Rayleigh fading channel using multiple transmit antennas, and the capacity behavior is better than that of the space-time block coding for more than two transmit antennas.
Abstract: In this letter, we introduce information-guided channel-hopping, a new scheme for high data rate communication over Rayleigh fading channel using multiple transmit antennas. This scheme is proposed based on the fact that the independence character of multi-channel can be used as an additional information transmitting channel, and the maximum likelihood decoding can be achieved in a simple way by decoupling of the signals conveyed by different methods. The analysis results prove that the capacity behavior of this scheme is better than that of the space-time block coding for more than two transmit antennas.
209 citations
TL;DR: This paper will discuss a few problems found in the enhanced scheme and then propose how to overcome them, regarding the properties of anonymity and backward secrecy.
Abstract: Recently, a new authentication scheme with anonymity for wireless communications has been proposed, and then some security problems have been demonstrated. In this paper, we will discuss a few problems found in the enhanced scheme and then propose how to overcome them, regarding the properties of anonymity and backward secrecy.
TL;DR: A handover decision method based on the prediction of traveling distance within an IEEE 802.11 wireless local area network (WLAN) cell that successfully keeps the number of failed or unnecessary handovers low is proposed.
Abstract: We propose a handover decision method based on the prediction of traveling distance within an IEEE 802.11 wireless local area network (WLAN) cell. The method uses two thresholds which are calculated by the mobile terminal (MT) as it enters the WLAN cell. The predicted traveling distance is compared against these thresholds to make a handover decision in order to minimize the probability of handover failures or unnecessary handovers from a cellular network to a WLAN. Our analysis shows that the proposed method successfully keeps the number of failed or unnecessary handovers low.
TL;DR: By employing the MGF-based approach one can easily evaluate average bit error rates (ABERs) in fading radio channels characterized statistically by the eta - mu and re k - mu distributions either in terms of elementary functions or in Terms of finite-range integrals of elementary function.
Abstract: In this letter, we prove that in contrast with earlier reported results the moment generating functions (MGFs) of the generalized eta - mu and re k - mu distributions are expressed in terms of elementary functions. Thus by employing the MGF-based approach one can easily evaluate average bit error rates (ABERs) in fading radio channels characterized statistically by the eta - mu and re k - mu distributions either in terms of elementary functions or in terms of finite-range integrals of elementary functions.
TL;DR: An approximation for the Gaussian Q-function is proposed that enables simpler evaluation of important communication system performance metrics and the usefulness of the approximation is demonstrated by obtaining a simple closed form expression for the average symbol error probability of differentially encoded QPSK in Nakagami-m fading.
Abstract: In this letter we propose an approximation for the Gaussian Q-function that enables simpler evaluation of important communication system performance metrics. The approximation enables derivation of closed-form expressions for metrics such as average symbol, bit and block error probabilities which are known to be analytically involved as they require computation of the expectation of Q-function and its integer powers, for any m of Nakagami-m fading. The tightness of the approximation is verified by simulations. The usefulness of the approximation is demonstrated by obtaining a simple closed form expression for the average symbol error probability of differentially encoded QPSK in Nakagami-m fading.
TL;DR: This work proposes an enhanced synchronization algorithm to calculate the asymmetric ratio of the communication link, and the proposed algorithm enhances an accuracy of the time synchronization.
Abstract: IEEE 1588 is a standard to synchronize independent clocks running on separate nodes of a distributed measurement and control system. In IP based cellular network, it is considered as a key technology to synchronize base stations. Especially, interests for the low-cost and very-small home cellular base station called the Femtocell is increasing, and it is connected to the cellular core network using an asymmetric communication link such as xDSL. However, the conventional IEEE 1588 synchronization algorithm assumes symmetrical links, and makes errors for asymmetric links for the calculation of the time difference between the master clock (a clock source) and the slave clock (a clock consumer). We propose an enhanced synchronization algorithm to calculate the asymmetric ratio of the communication link, and the proposed algorithm enhances an accuracy of the time synchronization.
TL;DR: The exact symbol error probability (SEP) of cooperative diversity with opportunistic amplify-and-forward (AF) relaying with maximal ratio combining of orthogonal multiple AF relay transmissions is analyzed.
Abstract: We analyze the exact symbol error probability (SEP) of cooperative diversity with opportunistic amplify-and-forward (AF) relaying. The benefit of this opportunism to the SEP is assessed by comparing with maximal ratio combining of orthogonal multiple AF relay transmissions.
TL;DR: This paper converts an unknown signal symbol to an address of the look-up table (LUT), loads the pre-calculated values of the test functions for the likelihood ratio test, and produces the estimated modulation scheme in real-time.
Abstract: This paper describes a likelihood test based modulation classification method for identifying the modulation scheme of a software-defined radio (SDR) in real-time without pilot symbols between transmitters and receivers. Unlike the prior art, the paper converts an unknown signal symbol to an address of the look-up table (LUT), loads the pre-calculated values of the test functions for the likelihood ratio test, and produces the estimated modulation scheme in real-time. The statistical performance of the LUT based classifier is studied. Simulation results are presented to confirm the theoretical analysis.
TL;DR: Close-form expressions for the average bit error probability of BPSK, QPSK and M-QAM of an amplify-and-forward average power scaling dual-hop relay transmission over non-identical Nakagami-m fading channels are presented.
Abstract: We present closed-form expressions for the average bit error probability (ABEP) of BPSK, QPSK and M-QAM of an amplify-and-forward average power scaling dual-hop relay transmission, over non-identical Nakagami-m fading channels, with integer values of m. Additionally, we evaluate in closed-form the ABEP under sufficiently large signal-to-noise ratio for the source-relay link, valid for arbitrary rn. Numerical and simulation results show the validity of the proposed mathematical analysis and point out the effect of the two hops unbalanced fading conditions on the error performance.
TL;DR: Judicious modulation of non-data subcarriers renders a transmitted OFDM signal and a few of its higher-order derivatives continuous at the OFDM symbol boundaries, which results in reduced out-of-band emission.
Abstract: In this letter we show that judicious modulation of non-data subcarriers renders a transmitted OFDM signal and a few of its higher-order derivatives continuous at the OFDM symbol boundaries. This novel approach results in reduced out-of-band emission: typically, it achieves over 30 dB power suppression at adjacent-channel center-frequencies.
TL;DR: A simple mathematical model of IEEE 802.15.4 unslotted CSMA/CA by busy cycle of M/G/l queueing system is provided to obtain several performance measures that can be used for determining the optimal number of devices while supporting the required QoS constraints.
Abstract: We provide a simple mathematical model of IEEE 802.15.4 unslotted CSMA/CA by busy cycle of M/G/l queueing system to obtain several performance measures. Our performance measures can be used for determining the optimal number of devices while supporting the required QoS constraints on the average packet delay and the packet loss probability, and also for calculating battery lifetime.
TL;DR: The analysis and the preliminary experiments indicate that the proposed method- can discriminate mimicking flooding attacks from legitimate accessing efficiently and effectively.
Abstract: DDoS is a spy-on-spy game between attackers and detectors. Attackers are mimicking network traffic patterns to disable the detection algorithms which are based on these features. It is an open problem of discriminating the mimicking DDoS attacks from massive legitimate network accessing. We observed that the zombies use controlled function(s) to pump attack packages to the victim, therefore, the attack flows to the victim are always share some properties, e.g. packages distribution behaviors, which are not possessed by legitimate flows in a short time period. Based on this observation, once there appear suspicious flows to a server, we start to calculate the distance of the package distribution behavior among the suspicious flows. If the distance is less than a given threshold, then it is a DDoS attack, otherwise, it is a legitimate accessing. Our analysis and the preliminary experiments indicate that the proposed method- can discriminate mimicking flooding attacks from legitimate accessing efficiently and effectively.
TL;DR: A closed-form expression is derived for the outage probability of the destination signal-to-noise ratio (SNR) in terms of the confluent hypergeometric function of two variables in a Rayleigh flat-fading environment.
Abstract: We investigate the performance of a cooperative multiple-input multiple-output (MIMO) relay channel in which the source and relay use the same orthogonal space-time block code (OSTBC) for transmission whereas the relay and destination use maximum-ratio-combining (MRC) for reception. Considering that perfect channel state information is available at the relay and destination, we derive a closed-form expression for the outage probability of the destination signal-to-noise ratio (SNR) in terms of the confluent hypergeometric function of two variables in a Rayleigh flat-fading environment. The validity of the closed-form expression is confirmed with the numerical results.
TL;DR: Analytic performance of IEEE 802.11 distributed coordination function that takes into account hidden node problem and unsaturated traffic condition is presented for symmetric networks and it is shown that the presence of hidden nodes barely affects the network performance in low traffic conditions, but it causes 33% performance loss in moderate traffic scenarios.
Abstract: Analytic performance of IEEE 802.11 distributed coordination function that takes into account hidden node problem and unsaturated traffic condition is presented for symmetric networks. This enables us to estimate the performance of practical wireless local area networks more accurately. It is shown that the presence of hidden nodes barely affects the network performance in low traffic conditions, but it causes 33% performance loss in moderate traffic scenarios. Analytical results presented in the paper are backed by simulation results.
TL;DR: A generalization of the progressive edge-growth (PEG) algorithm is proposed with the aim of designing LDPC code graphs with substantially improved approximated cycle extrinsic message degree (ACE) properties.
Abstract: In this letter, we propose a generalization of the progressive edge-growth (PEG) algorithm with the aim of designing LDPC code graphs with substantially improved approximated cycle extrinsic message degree (ACE) properties. The proposed realization of generalized PEG algorithm outperforms original PEG algorithm and its subsequent modification proposed by Xiao and Banihashemi.
TL;DR: It is shown that it is possible to take advantage of the periodic redundancy induced by the cyclic prefix to get an accurate NDA SNR estimator.
Abstract: This letter deals with the problem of non data aided (NDA) signal to noise ratio (SNR) estimation of OFDM signals transmitted through unknown multipath fading channel. Most of existing OFDM SNR estimators are based on the knowledge of pilot sequences which is not applicable in some contexts such as cognitive radio for instance. We show that it is possible to take advantage of the periodic redundancy induced by the cyclic prefix to get an accurate NDA SNR estimator. Numerical simulations highlight the benefit of the proposed method compared with the state of the art.
TL;DR: Simulation results confirm that the new MASVH algorithm improves the system performance in terms of higher throughput and lower dropping probability, as well as reduces the user traffic cost for accessing the integrated wireless networks.
Abstract: Vertical handoff in next generation heterogeneous wireless networks is a multi-dimensional issue. In this article we propose a multi-dimensional adaptive SINR based vertical handoff algorithm (MASVH) which uses the combined effects of SINR, user required bandwidth, user traffic cost and utilization from participating access networks to make handoff decisions for multi-attribute QoS consideration. Simulation results confirm that the new MASVH algorithm improves the system performance in terms of higher throughput and lower dropping probability, as well as reduces the user traffic cost for accessing the integrated wireless networks.
TL;DR: It is shown that the optimum number of secondary users decreases when the weighting coefficient of the usage efficiency increases, the sample correlation increases, or the SNR increases.
Abstract: The optimum number of secondary users in collaborative spectrum sensing is derived for lognormal shadowing channels, static additive white Gaussian noise channels and Rayleigh fading channels, when the efficiency of resources usage is considered in the system design. By weighting the detection performance and the usage efficiency in a target function that is maximized with respect to the number of secondary users, it is shown that the optimum number of secondary users decreases when the weighting coefficient of the usage efficiency increases, the sample correlation increases, or the SNR increases.
TL;DR: An improved method for estimating the frame/symbol timing offset in preamble-aided OFDM systems is presented, which combines autocorrelation techniques with restricted crosscorrelation to achieve a near-ideal timing performance without significant increase in complexity.
Abstract: An improved method for estimating the frame/symbol timing offset in preamble-aided OFDM systems is presented. It uses a conventional preamble structure and combines autocorrelation techniques with restricted crosscorrelation to achieve a near-ideal timing performance without significant increase in complexity. Computer simulations show that the method is robust in both AWGN and fading multipath channels, achieving better performance than the existing methods.
TL;DR: A series of structured LDPC codes suitable for use in quantum error correction, belonging to the class of dual-containing Calderbank-Shor-Steane (CSS) codes, are presented.
Abstract: We present a series of structured LDPC codes suitable for use in quantum error correction. Those codes belong to the class of dual-containing Calderbank-Shor-Steane (CSS) codes. The component CSS code is designed using the combinatorial object known as balanced incomplete block design (BIBD) with an even index. The quantum LDPC codes have the rate around 0.9. Several examples of quantum LDPC codes from BIBDs from unity index, extended by addition of an all- ones column, are introduced as well. To improve the BER performance, we employed the method of removing the cycles
TL;DR: This letter proposes some improvements in the PEG algorithm which greatly improve the girth properties of the resulting graphs, and focuses on regular column-weight two graphs (dv = 2), although the algorithm can be applied to any graph connectivity.
Abstract: The progressive edge-growth (PEG) construction is a well known algorithm for constructing bipartite graphs with good girth properties. In this letter, we propose some improvements in the PEG algorithm which greatly improve the girth properties of the resulting graphs: given a graph size, they increase the girth g achievable by the algorithm, and when the girth cannot be increased, our modified algorithm minimizes the number of cycles of length g. As a main illustration, we focus on regular column-weight two graphs (dv = 2), although our algorithm can be applied to any graph connectivity. The class of dv = 2 graphs is often used for non-binary low density parity check codes that can be seen as monopartite graphs: for a given target girth gt, this new instance of the PEG algorithm allows to construct cages, i.e. graphs with the minimal size such that a graph of girth gt exists, which is the best result one might hope for.