Showing papers in "IEEE Communications Letters in 2006"
TL;DR: A novel method of steganographic embedding in digital images is described, in which each secret digit in a (2n+1)-ary notational system is carried by n cover pixels and, at most, only one pixel is increased or decreased by 1.
Abstract: A novel method of steganographic embedding in digital images is described, in which each secret digit in a (2n+1)-ary notational system is carried by n cover pixels and, at most, only one pixel is increased or decreased by 1. In other words, the (2n+1) different ways of modification to the cover pixels correspond to (2n+1) possible values of a secret digit. Because the directions of' modification are fully exploited, the proposed method provides high embedding efficiency that is better than previous techniques
616 citations
TL;DR: An asymptotic analysis of the symbol error rates of a selection AF network is presented, and it is compared with the conventional all-participate scheme.
Abstract: Cooperative diversity schemes significantly improve the performance of wireless networks by transmitting the same information through several nodes. The amplify-and-forward (AF) relaying method is one of the most attractive cooperative diversity schemes due to its low complexity. Selection AF relaying has recently been proven to achieve the same diversity order as and lower outage probability than all-participate relays. In this letter, we present an asymptotic analysis of the symbol error rates of a selection AF network, and compare it with the conventional all-participate scheme
446 citations
TL;DR: The performance of digital communication systems over generalized-K (K/sub G/) fading channels is analyzed and evaluated and novel closed form expressions for the SNR statistics, the average Shannon's channel capacity and the bit error rate are derived.
Abstract: The performance of digital communication systems over generalized-K (K/sub G/) fading channels is analyzed and evaluated. Novel closed form expressions for the SNR statistics, the average Shannon's channel capacity and the bit error rate (BER) are derived. These expressions are used to study important performance criteria such as the outage performance, the average capacity and the BER for a great variety of modulation formats in K/sub G/ fading channels. The proposed mathematical analysis is accompanied with various performance evaluation results, which demonstrate the usefulness of the proposed approach.
379 citations
TL;DR: A model for the error in estimated distance as measured from the estimated TOA of the direct path (DP) in a typical multipath indoor environment is introduced and relates the behavior of the two components of the TOA estimation error to the bandwidth of the system.
Abstract: Time of arrival (TOA) estimation used with ultra wideband (UWB) transmission is currently the most popular technique for accurate indoor geolocation. Due to severe indoor multipath conditions, these techniques often suffer from significant inaccuracy in location estimation. In this paper, we introduce a model for the error in estimated distance as measured from the estimated TOA of the direct path (DP) in a typical multipath indoor environment. The TOA estimation error has two components, (1) the errors caused by the multipath dispersion affecting any signal path and (2) the errors caused by undetected direct path (UDP) conditions. The statistical behavior of this error is also a function of the system bandwidth. The empirical data from UWB indoor measurements in an office building are used to design a model for the distance measurement error. This model relates the behavior of the two components of the TOA estimation error to the bandwidth of the system.
349 citations
TL;DR: The performance of decode-and-forward relaying in channels with dissimilar fading parameters is investigated and a closed-form expression for the outage probability of a system with an arbitrary number of relays is derived.
Abstract: Decode-and-forward relaying has been shown to be a viable transmission protocol for wireless networks incorporating distributed spatial diversity. Practical systems may employ relay channels that experience statistically different signal fading. The performance of decode-and-forward relaying in channels with dissimilar fading parameters is investigated. In particular, a closed-form expression for the outage probability of a system with an arbitrary number of relays is derived
326 citations
TL;DR: This letter investigates a new method for sidelobe suppression characterized by the insertion of a few so-called cancellation carriers at both sides of the OFDM spectrum that achieves a significant reduction of out-of-band radiation.
Abstract: Orthogonal frequency-division multiplexing (OFDM) suffers from high out-of-band radiation. In this letter, we investigate a new method for sidelobe suppression characterized by the insertion of a few so-called cancellation carriers (CCs) at both sides of the OFDM spectrum. These special carriers are modulated with complex weighting factors which are optimized such that the sidelobes of the CCs cancel the sidelobes of the transmit signal. With this technique a significant reduction of out-of-band radiation is achieved at the cost of a small degradation in system performance
313 citations
TL;DR: The proposed method is based on the multiplication of the used subcarriers with subcarrier weights, which reduces OFDM sidelobes by more than 10 dB in the average without requiring the transmission of any side information.
Abstract: In this letter, a method for sidelobe suppression in OFDM systems is proposed and investigated. The proposed method is based on the multiplication of the used subcarriers with subcarrier weights. The subcarrier weights are determined in such a way that the sidelobes of the transmission signal are minimized according to an optimization algorithm which allows several optimization constraints. As a result, sidelobe suppression by subcarrier weighting reduces OFDM sidelobes by more than 10 dB in the average without requiring the transmission of any side information
271 citations
TL;DR: A novel tag anti-collision scheme called adaptive binary splitting (ABS) is presented, which assigns distinct timeslots to tags by using information obtained from the last identification process.
Abstract: Tag collision arbitration for passive RFID tags is a significant issue for fast tag identification. This letter presents a novel tag anti-collision scheme called adaptive binary splitting (ABS). For reducing collisions, ABS assigns distinct timeslots to tags by using information obtained from the last identification process. Our performance evaluation shows that ABS outperforms other tree based tag anti-collision protocols.
256 citations
TL;DR: An implementation using fountain codes is simulated, demonstrating that such a scheme has advantages in efficiency, reliability and robustness over conventional fixed-rate codes, particularly when channel state information is not available at the transmitter.
Abstract: We propose a framework for communication over fading channels utilizing rateless codes. An implementation using fountain codes is simulated, demonstrating that such a scheme has advantages in efficiency, reliability and robustness over conventional fixed-rate codes, particularly when channel state information is not available at the transmitter.
206 citations
TL;DR: This letter presents the first successful method for iterative stochastic decoding of state-of-the-art low-density parity-check (LDPC) codes and has a significant potential for high-throughput and/or low complexity iterative decoding.
Abstract: This letter presents the first successful method for iterative stochastic decoding of state-of-the-art low-density parity-check (LDPC) codes. The proposed method shows the viability of the stochastic approach for decoding LDPC codes on factor graphs. In addition, simulation results for a 200 and a 1024 length LDPC code demonstrate the near-optimal performance of this method with respect to sum-product decoding. The proposed method has a significant potential for high-throughput and/or low complexity iterative decoding.
184 citations
TL;DR: The comparison between the result and the simulation shows that the analytical model is accurate in evaluating the energy consumption and hence provides a potential guidance in efficiently managing energy.
Abstract: Energy management is an important component for the emerging standard IEEE 802.16e supporting mobility. In this paper, we characterize the standardized sleep mode in IEEE 802.16e. The comparison between our result and the simulation shows that our analytical model is accurate in evaluating the energy consumption and hence provides a potential guidance in efficiently managing energy.
TL;DR: Simulation results reveal that the proposed algorithm achieves the tradeoff between system throughput and fairness.
Abstract: In this letter, we formulate a downlink packet scheduling problem for proportional fairness in orthogonal frequency division multiple access with frequency division multiple access (OFDMA) systems to derive necessary conditions for optimality, which results in efficient subcarrier and power allocation algorithms. Simulation results reveal that our proposed algorithm achieves the tradeoff between system throughput and fairness
TL;DR: In this letter, a closed-form solution for the outage probability behaviour of a relay network in Nakagami-m fading channels is derived and the results are applicable for Rayleigh fading.
Abstract: It is well known that the cooperation among nodes can improve the performance of a wireless network. In this letter we analyze the outage probability behaviour of a relay network in Nakagami-m fading channels. A closed-form solution for the outage probability is derived. When m=1, the results are applicable for Rayleigh fading. Computer simulations confirm the presented mathematical analysis
TL;DR: Through the derivation of symbol error rate expressions, it is demonstrated that the maximum achievable diversity orders under APS and IPS constraints are N+1 and 2N, respectively.
Abstract: In this letter, we investigate the impact of receive diversity on the error rate performance of a relay-assisted cooperative scheme in which the relay terminal is operating in amplify-and-forward (AF) mode under the so-called average power scaling (APS) and instantaneous power scaling (IPS) constraints We assume that the source and relay terminals are each equipped with one antenna, while the destination terminal is equipped with N receive antennas Through the derivation of symbol error rate expressions, we demonstrate that the maximum achievable diversity orders under APS and IPS constraints are N+1 and 2N, respectively
TL;DR: Despite the inherent difficulties of non-convexity and non-separability of the optimization problem, it is shown that, with readily-verifiable sufficient conditions, a distributed algorithm is developed that converges to the globally and jointly optimal rate allocation and persistence probabilities.
Abstract: We study joint end-to-end congestion control and per-link medium access control (MAC) in ad-hoc networks. We use a network utility maximization formulation, in which by adjusting the types of utility functions, we can accommodate multi-class services as well as exploit the tradeoff between efficiency and fairness of resource allocation. Despite the inherent difficulties of non-convexity and non-separability of the optimization problem, we show that, with readily-verifiable sufficient conditions, we can develop, a distributed algorithm that converges to the globally and jointly optimal rate allocation and persistence probabilities.
TL;DR: The probability that a one-dimensional stationary ad hoc wireless network is composed of at most C clusters is presented and the probability of network connectivity, i.e. the case of C=1, can be derived as a special case.
Abstract: The probability that a one-dimensional stationary ad hoc wireless network is composed of at most C clusters is presented. The probability of network connectivity, i.e. the case of C=1, can be derived as a special case. A very simple approximate formula is also presented for the probability of network connectivity. We also explain our approximation heuristically, which confirms the analytical result. The analysis is validated by computing the probability of network connectivity and comparing it with the Monte Carlo simulation results.
TL;DR: A priority-based scheme, comprising frame tailoring and priority toning, is proposed, in order to relax such a problematic delay and guarantee time-bounded delivery of high priority packets in event-monitoring networks.
Abstract: IEEE 802.15.4 slotted carrier-sense multiple access with collision avoidance (CSMA-CA) adopts periodic sleeping for energy efficiency support. However, such a periodic sleeping mechanism, especially with contention-based medium access, tends to cause additional sleep delay due to heavy contention. In this letter, we propose a priority-based scheme, comprising frame tailoring and priority toning, in order to relax such a problematic delay and guarantee time-bounded delivery of high priority packets in event-monitoring networks.
TL;DR: An exact expression for the pairwise error probability (PEP) of space-time trellis codes over the cascaded Rayleigh fading channel is derived in the form of a simple single finite-range integral.
Abstract: Cascaded Rayleigh distribution is used to model multipath fading in mobile-to-mobile communication scenarios and provides a better fit to experimental data in such scenarios compared to the conventional Rayleigh channel model. In this letter, we derive an exact expression for the pairwise error probability (PEP) of space-time trellis codes over the cascaded Rayleigh fading channel, which is in the form of a simple single finite-range integral. Through the derived PEP expression, we present the maximum diversity order achievable over such channels and demonstrate the performance degradation in comparison to conventional Rayleigh channels. Monte-Carlo simulations are further demonstrated to confirm the analytical results.
TL;DR: The use of hexagonal constellation is proposed as a method to achieve PAPR reduction without increasing signal power in the TI technique.
Abstract: One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the OFDM signal. Tone injection (TI) technique is a promising candidate for the reduction of the PAPR of an OFDM signal. But this technique requires the increase of the transmit signal power because of the injected signal. In this paper, we propose the use of hexagonal constellation as a method to achieve PAPR reduction without increasing signal power in the TI technique
TL;DR: Based on nonuniform pilot tone placement, optimal pilot sequences are derived, which can achieve the minimum mean square error of the least squares estimate for multiple-input multiple-output (MIMO) OFDM systems.
Abstract: In orthogonal frequency division multiplexing (OFDM) systems, since virtual subcarriers are not used for transmission, approach of conventional uniformly placed pilot tones is not applicable in some situations. In this letter, based on nonuniform pilot tone placement, we derive optimal pilot sequences, which can achieve the minimum mean square error of the least squares estimate for multiple-input multiple-output (MIMO) OFDM systems. Simulation results demonstrate the effectiveness of the proposed approach.
TL;DR: Two-dimensional (2-D) correction schemes are proposed to improve the performance of conventional min-sum (MS) decoding of irregular low density parity check codes and the proposed method provides a comparable performance as belief propagation (BP) decoding while requiring less complexity.
Abstract: Two-dimensional (2-D) correction schemes are proposed to improve the performance of conventional min-sum (MS) decoding of irregular low density parity check codes. An iterative procedure based on parallel differential optimization is presented to obtain the optimal 2-D factors. Both density evolution analysis and simulation show that the proposed method provides a comparable performance as belief propagation (BP) decoding while requiring less complexity. Interestingly, the new method exhibits a lower error floor than that of BP decoding. With respect to conventional MS and 1-D normalized MS decodings, the 2-D normalized MS offers a better performance. The 2-D offset MS decoding exhibits a similar behavior.
TL;DR: Analysis of the average number of retransmissions and throughput of collaborative hybrid-ARQ Type I ( i.e., without memory) and chase combining (i.e, with memory) protocols is provided for any number of relays.
Abstract: According to collaborative hybrid automatic-repeat-request (ARQ) protocols, relay stations that have been able to decode the original message from previous transmissions, collaborate with the source in future retransmissions by jointly sending a space-time codeword. In this letter, analysis of the average number of retransmissions and throughput of collaborative hybrid-ARQ Type I (i.e., without memory) and chase combining (i.e., with memory) protocols is provided for any number of relays.
TL;DR: In this letter, cyclic-prefix based noise-variance and power-delay-profile estimators for Orthogonal Frequency Division Multiplexing (OFDM) systems are presented and a heuristic estimator and a class of approximate maximum likelihood (ML) estimators are proposed.
Abstract: In this letter, we present cyclic-prefix (CP) based noise-variance and power-delay-profile estimators for Orthogonal Frequency Division Multiplexing (OFDM) systems. Signal correlation due to the use of the CP is exploited without requiring additional pilot symbols. A heuristic estimator and a class of approximate maximum likelihood (ML) estimators are proposed. The proposed algorithms can be applied to both unitary and non-unitary constellations. These algorithms can be readily used for applications such as minimum mean-square error (MMSE) channel estimation.
TL;DR: A simple method to find the probability density function of a sum of independent exponential random variables by using characteristic function is proposed and successfully applied to formulate the closed-form BER expression of 2 Tx-J Rx transmit diversity as well as the outage probability of repetition coding.
Abstract: In order to evaluate exactly the performance of some diversity schemes, the probability density function (pdf) of a sum of independent exponential random variables (r.v.'s) must be known. This paper proposes a simple method to find it by using characteristic function., The resultant pdf is successfully applied to formulate the closed-form BER expression of 2 Tx-J Rx transmit diversity as well as the outage probability of repetition coding.
TL;DR: A new early stopping criterion is proposed for low density parity check (LDPC) codes to reduce the number of decoding iterations while preserving a good decoding performance.
Abstract: A new early stopping criterion is proposed for low density parity check (LDPC) codes to reduce the number of decoding iterations while preserving a good decoding performance. The new criterion is based on the convergence of the mean magnitude (CMM) of the log-likelihood ratio messages at the output of each decoding iteration. Information-theoretic support and extensive simulations are provided to demonstrate the efficiency of the criterion
TL;DR: A sensor network packet traffic model is derived and analyzed for intrusion detection applications and validated using simulations.
Abstract: Performance evaluation of wireless sensor network (WSN) protocols requires realistic data traffic models since most of the WSNs are application specific. In this letter, a sensor network packet traffic model is derived and analyzed for intrusion detection applications. Presented analytical work is also validated using simulations.
TL;DR: An enhanced binary search with cut-through operation to minimize the anti-collision cost and the analytic results show that the proposed scheme achieves low delay in the collision resolution with low power consumption.
Abstract: RFID systems allow contactless identification of objects using radio frequency. When there is more than one transponder within the interrogation area of a reader, all the transponders may send data (or tags) at the same time which may lead to mutual interference. This event causes data loss and is referred to as a collision. In this letter, we propose an enhanced binary search with cut-through operation to minimize the anti-collision cost. The analytic results show that the proposed scheme achieves low delay in the collision resolution with low power consumption.
TL;DR: The throughput obtainable by each node for broadcasting to-all-of the other nodes in a network consisting of n nodes with- fixed transmission ranges and C bits per second channel capacity is bounded by O(C/n), which is equivalent to the upper bound for per node capacity of a fully connected single-hop network.
Abstract: We present an upper bound on the broadcast capacity of arbitrary ad hoc wireless networks. The throughput obtainable by each node for broadcasting to-all-of the other nodes in a network consisting of n nodes with- fixed transmission ranges and C bits per second channel capacity is bounded by O(C/n), which is equivalent to the upper bound for per node capacity of a fully connected single-hop network
TL;DR: Simple and precise closed-form approximations to the probability density function and cumulative distribution function of the sum of independent identically distributed Weibull variates are derived and find applicability in several wireless communications issues.
Abstract: Simple and precise closed-form approximations to the probability density function and cumulative distribution function of the sum of independent identically distributed Weibull variates are derived. The new approximations find applicability in several wireless communications issues such as equal-gain combining, signal detection, linear equalizers, outage probability, intersymbol interference, and phase jitter
TL;DR: This paper proposes the channel estimation for multiple input multiple output (MIMO)-OFDM with time varying channels based on the grouped and equispaced pilot tones to approximate theTime varying channels to the polynomials.
Abstract: Time varying channels will degrade the performance of orthogonal frequency division multiplexing (OFDM) due to the interchannel interference (ICI). In this paper, we propose the channel estimation for multiple input multiple output (MIMO)-OFDM with time varying channels based on the grouped and equispaced pilot tones. Specifically, we approximate the time varying channels to the polynomials. Additionally, we propose the detection method for the OFDM with ICI.