Showing papers in "IEEE Communications Letters in 2007"
TL;DR: This letter analyzes the performance of cooperative diversity wireless networks using amplify-and-forward relaying over independent, non-identical, Nakagami-m fading channels and shows that the derived error rate and outage probability are tight lower bounds particularly at medium and high SNR.
Abstract: This letter analyzes the performance of cooperative diversity wireless networks using amplify-and-forward relaying over independent, non-identical, Nakagami-m fading channels. The error rate and the outage probability are determined using the moment generating function (MGF) of the total signal-to-noise-ratio (SNR) at the destination. Since it is hard to find a closed form for the probability density function (PDF) of the total SNR, we use an approximate value instead. We first derive the PDF and the MGF of the approximate value of the total SNR. Then, the MGF is used to determine the error rate and the outage probability. We also use simulation to verify the analytical results. Results show that the derived error rate and outage probability are tight lower bounds particularly at medium and high SNR
513 citations
TL;DR: This paper introduces and analyzes relaying techniques that increase the achievable throughput in multi-hop wireless networks by applying network coding over bi-directional traffic flows by introducing a relaying method based on amplify-and-forward (AF), where the relay node utilizes the inherent combining of packets provided by simultaneous transmissions over a multiple access channel.
Abstract: This paper introduces and analyzes relaying techniques that increase the achievable throughput in multi-hop wireless networks by applying network coding over bi-directional traffic flows. We term each such technique as bi-directional amplification of throughput (BAT)-relaying. While network coding is normally performed by combining decoded packets, here we introduce a relaying method based on amplify-and-forward (AF), where the relay node utilizes the inherent combining of packets provided by simultaneous transmissions over a multiple access channel. Under low noise levels, AF BAT-relaying offers a superior throughput performance. The unconventionality of AF BAT relaying opens many possibilities for further research.
381 citations
TL;DR: A channel reservation scheme for cognitive radio spectrum handoff allows the tradeoff between forced termination and blocking according to QoS requirements and can greatly reduce forced termination probability at a slight increase in blocking probability.
Abstract: A Markov chain analysis for spectrum access in licensed bands for cognitive radios is presented and forced termination probability, blocking probability and traffic throughput are derived. In addition, a channel reservation scheme for cognitive radio spectrum handoff is proposed. This scheme allows the tradeoff between forced termination and blocking according to QoS requirements. Numerical results show that the proposed scheme can greatly reduce forced termination probability at a slight increase in blocking probability
343 citations
TL;DR: A novel, simple and tight approximation for the Gaussian Q-function and its integer powers is presented, and an accuracy improvement is achieved over the whole range of positive arguments.
Abstract: We present a novel, simple and tight approximation for the Gaussian Q-function and its integer powers. Compared to other known closed-form approximations, an accuracy improvement is achieved over the whole range of positive arguments. The results can be efficiently applied in the evaluation of the symbol error probability (SEP) of digital modulations in the presence of additive white Gaussian noise (AWGN) and the average SEP (ASEP) over fading channels. As an example we evaluate in closed-form the ASEP of differentially encoded QPSK in Nakagami-m fading.
242 citations
TL;DR: A channel access protocol for ad-hoc underwater acoustic networks which are characterized by long propagation delays and unequal transmit/receive power requirements is proposed, which achieves a throughput several times higher than that of the slotted FAMA, while offering similar savings in energy.
Abstract: This paper proposes a channel access protocol for ad-hoc underwater acoustic networks which are characterized by long propagation delays and unequal transmit/receive power requirements. The protocol saves transmission energy by avoiding collisions while maximizing throughput. It is based on minimizing the duration of a hand-shake by taking advantage of the receiver's tolerance to interference when the two nodes are closer than the maximal transmission range. Nodes do not need to be synchronized, can move, are half-duplex, and use the same transmission power. This protocol achieves a throughput several times higher than that of the slotted FAMA, while offering similar savings in energy. Although carrier sensing ALOHA offers a higher throughput, it wastes much more power on collisions.
229 citations
TL;DR: The performance degradation of collaborative sensing due to correlated shadowing is characterized by deriving a lower-bound on the probability of missing the opportunities for unlicensed access by evaluating the effective number of collaborating users in terms of the distance spread of the sensing network and the characteristics of the propagation environment.
Abstract: Collaborative spectrum sensing enables opportunistic unlicensed access to the unused portions of the licensed spectrum. We characterize the performance degradation of collaborative sensing due to correlated shadowing by deriving a lower-bound on the probability of missing the opportunities for unlicensed access. Moreover, we evaluate the effective number of collaborating users in terms of the distance spread of the sensing network and the characteristics of the propagation environment. This has practical implications in terms of protocol design as having a few number of users collaborate over a large distance may be more effective than a dense sensing network confined to a small area
206 citations
TL;DR: It is shown that optimal selection and transmission of a single relay among a set of multiple amplify-and-forward (AF) candidates minimize the outage probability and outperform any other strategy that involves simultaneous transmissions from more than one AF relay under an aggregate power constraint.
Abstract: In this paper, we show that optimal selection and transmission of a single relay among a set of multiple amplify-and-forward (AF) candidates minimize the outage probability (i.e., outage-optimal) and outperform any other strategy that involves simultaneous transmissions from more than one AF relay under an aggregate power constraint. This outage optimality demonstrates that cooperation benefits are maximized with intelligent scheduling among AF relays.
179 citations
TL;DR: A fairness-aware adaptive resource allocation scheme for the downlink of multihop OFDMA systems and an efficient heuristic algorithm composed of subchannel-allocation, load-balancing and power-distribution steps are proposed.
Abstract: We investigate a fairness-aware adaptive resource allocation scheme for the downlink of multihop OFDMA systems. Assuming that the base station has all the channel information, we formulate an optimization problem for an adaptive subchannel-, path- and power-allocation scheme that maximizes system capacity while guaranteeing minimum resources for each user. Since the optimization should be performed in real time, we propose an efficient heuristic algorithm composed of subchannel-allocation, load-balancing and power-distribution steps. The proposed algorithm is simple in that the iterative computations are removed, and accurate in that it performs similarly to the optimum solution
150 citations
TL;DR: It is shown that the performance loss due to using a less complex combiner is not substantial and a closed- form expression for the outage probability of a system with an arbitrary number of relay nodes is derived.
Abstract: Distributed spatial diversity systems utilize multiple communication nodes to create independent signal replicas that are combined at the destination. Practical diversity receivers often employ simple combining techniques especially if comparable performance to more complex optimum combining can be achieved. The performance of decode-and-forward relaying that uses selection combining is investigated. In particular, a closed- form expression for the outage probability of a system with an arbitrary number of relay nodes is derived. By comparing the performance of a system that uses selection combining to one that uses optimum maximal ratio combining, it is shown that the performance loss due to using a less complex combiner is not substantial.
123 citations
TL;DR: Simulations for the uplink of a synchronous DS-CDMA system show that the proposed methods significantly outperform the best known IC schemes.
Abstract: This letter proposes a unified approach to joint iterative parameter estimation and interference cancellation (IC) for uplink CDMA systems in multipath channels. A unified framework is presented in which the IC problem is formulated as an optimization problem of an IC parameter vector for each stage and user. We also propose detectors based on a least-squares (LS) joint optimization method for estimating the linear receiver filter front-end, the IC, and the channel parameters. Simulations for the uplink of a synchronous DS-CDMA system show that the proposed methods significantly outperform the best known IC schemes.
119 citations
TL;DR: Novel expressions for the average channel capacity (ACC) of single-branch receivers operating in generalized fading channels, namely eta-mu and kappa-mu, are derived and it is shown that, for any given fading condition, the Nakagami-m ACC defines regions of capacity.
Abstract: Novel expressions for the average channel capacity (ACC) of single-branch receivers operating in generalized fading channels, namely eta-mu and kappa-mu, are derived. The expressions are written in terms of the well-known Meijer's G-functions, which are easily implemented in the most popular computing softwares. In addition, it is shown that, for any given fading condition, the Nakagami-m ACC defines regions of capacity: it lowerbounds the eta-mu ACC and it upperbounds the kappa-mu ACC. In the same way, it lowerbounds the alpha-mu ACC for alpha m, and it upperbounds the alpha-mu ACC for alpha > 2 and mu < m.
TL;DR: According to the simulation results, the proposed protocol requires less time consumption for tag identification than the present tag anti-collision protocols implemented in EPC Class 0, Class 1, and Class 1 Gen.
Abstract: Since the tree based RFID tag anti-collision protocol achieves 100% read rate, and the slotted ALOHA based tag anti-collision protocol allows simple implementation and good performance in small amount of tags, we consider how to take the advantages of each algorithm. This paper presents query tree based reservation for efficient RFID tag anti-collision. According to the simulation results, the proposed protocol requires less time consumption for tag identification than the present tag anti-collision protocols implemented in EPC Class 0, Class 1, and Class 1 Gen. 2
TL;DR: This work proposes a novel method that improves the embedding efficiency of binary covering functions by fully exploiting the information contained in the choice of addition or subtraction in theembedding.
Abstract: In image steganography, each pixel can carry a ternary message by choosing adding/subtracting one to/from the gray value. Although ternary covering functions can provide embedding efficiency higher than binary ones, it is necessary to convert the binary message into a ternary format. We propose a novel method that improves the embedding efficiency of binary covering functions by fully exploiting the information contained in the choice of addition or subtraction in the embedding. The improved scheme can perform equally well with, or even outperform, ternary covering functions without ternary conversion of the message.
TL;DR: Performance analysis and simulation results show that the proposed estimation and anti-collision algorithm consumes 10-15% less time slots than the binary tree protocol and dynamic framed slotted ALOHA (DFSA).
Abstract: In RFID systems, tag collision resolution is significantly important for fast tag identification. In this letter, we propose an accurate and robust tag estimation method and an effective tag anti-collision protocol. Performance analysis and simulation results show that the proposed estimation and anti-collision algorithm consumes 10-15% less time slots than the binary tree protocol and dynamic framed slotted ALOHA (DFSA). The proposed algorithm has also tolerance to the inaccuracy of tag estimation
TL;DR: This paper presents a full-rate full-diversity 2x2 STC design leading to substantially lower complexity of the optimum detector than existing schemes, which makes the implementation of high performance full- rate codes realistic in practical systems.
Abstract: Multiple-input multiple-output (MIMO) techniques have become an essential part of broadband wireless communications systems. For example, the recently developed IEEE 802.16e specifications for broadband wireless access include three MIMO profiles employing 2x2 space-time codes (STCs) and two of those are mandatory on the downlink of Mobile WiMAX systems. Conventional approaches to STC design are based on performance criteria such as coding gain, diversity gain, multiplexing gain, and ignore the decoder complexity. In this paper, we take an alternative approach and present a full-rate full-diversity 2x2 STC design leading to substantially lower complexity of the optimum detector than existing schemes. This makes the implementation of high performance full-rate codes realistic in practical systems.
TL;DR: This work proposes to use hierarchical modulation to solve the dilemma of adjusting the modulation scheme to the relay or to the destination link and shows with simulation results that the proposed system achieves a significant gain compared to reference systems.
Abstract: We consider a relay communication with distributed channel coding. The source broadcasts channel encoded and modulated information to the relay and to the destination. In a second time slot, the relay sends additional redundancy to the destination. The broadcast from the source leads to the dilemma of adjusting the modulation scheme to the relay or to the destination link. We propose to use hierarchical modulation to solve this dilemma. We show with simulation results that the proposed system achieves a significant gain compared to reference systems.
TL;DR: Two mechanisms are proposed to enhance throughput and energy efficiency of IEEE 802.15.4 CSMA-CA by adjusting the backoff exponent based on both consecutive clear channel assessment busy results and a packet transmission.
Abstract: Two mechanisms are proposed to enhance throughput and energy efficiency of IEEE 802.15.4 CSMA-CA. The first one is an enhanced collision resolution (ECR) mechanism that adjusts the backoff exponent (BE) based on both consecutive clear channel assessment (CCA) busy results and a packet transmission. The second one is an enhanced backoff (EB) mechanism that shifts the range of backoff counters by utilizing the CCA outcome. The simulation results demonstrate that the proposed mechanisms significantly enhance both throughput and energy efficiency of IEEE 802.15.4
TL;DR: An analytical model is proposed for the contention based bandwidth request scheme for best-effort and non-real time polling services in point-to-multipoint (PMP) architecture and simulations validate its high accuracy.
Abstract: IEEE 802.16 standard specifies a contention based bandwidth request scheme for best-effort and non-real time polling services in point-to-multipoint (PMP) architecture. In this letter we propose an analytical model for the scheme and study how the performances of bandwidth efficiency and channel access delay change with the contention window size, the number of contending subscriber stations, the number of slots allocated for bandwidth request and data transmission. Simulations validate its high accuracy.
TL;DR: It is shown that using separate reader antennas and multiple RF transponder antennas will decrease link envelope correlation effects and a near maximum bit-error-rate can be achieved with link envelope correlations less than 0.6.
Abstract: High-frequency backscatter radio systems operate in the dyadic backscatter channel, a pinhole channel whose envelope probability density function and bit-error-rate performance are strongly affected by link envelope correlation - the envelope correlation between the forward and backscatter links of the dyadic backscatter channel. This paper shows that link envelope correlation is most detrimental for backscatter radio systems using co-located reader transmitter and receiver antennas and a single RF transponder antenna. It is shown that using separate reader antennas and multiple RF transponder antennas will decrease link envelope correlation effects and a near maximum bit-error-rate can be achieved with link envelope correlation less than 0.6.
TL;DR: In this letter, a BER study is presented for decode-and-forward (DF) relaying in independent but not identically distributed Rayleigh fading channels and it is shown that the analytic results are perfectly matched with the simulated ones.
Abstract: In this letter, a BER study is presented for decode-and-forward (DF) relaying in independent but not identically distributed Rayleigh fading channels. For an arbitrary number of relays, exact and closed-form expressions of the BER are provided for M-ary PAM, QAM and PSK, respectively. It is also shown that the analytic results are perfectly matched with the simulated ones
TL;DR: A new non-data-aided estimate is proposed, which makes use of the sixth-order moment of the received data, and which can be tuned for a particular constellation in order to extend the usable range of SNR values.
Abstract: Signal-to-noise ratio (SNR) estimation is an important task in many digital communication systems. With nonconstant modulus constellations, the performance of the classical second- and fourth-order moments estimate is known to degrade with increasing SNR. A new non-data-aided estimate is proposed, which makes use of the sixth-order moment of the received data, and which can be tuned for a particular constellation in order to extend the usable range of SNR values. The advantage of the new method is especially significant for constellations with two different amplitude levels, e.g. 16-amplitude-and-phase-shift keying (16-APSK)
TL;DR: A distributed version of switch and stay combining is proposed for relaying systems that utilize a single decode and forward relay, andumerical results show that these systems achieve the beneficial effects of diversity, although they do not employ any diversity combiner at the destination terminal.
Abstract: A distributed version of switch and stay combining is proposed for relaying systems that utilize a single decode and forward relay. The performance analysis of such system is presented, along with that of a simplified version of the so-called incremental relaying protocol. Numerical results show that these systems achieve the beneficial effects of diversity, although they do not employ any diversity combiner at the destination terminal
TL;DR: It is shown that the stability region derived from traditional Nyquist analysis is not an accurate representation of the actual stability region, and that the use of switched linear system models with time delay and new Lyapunov tools can provide sound sufficient stability conditions.
Abstract: In the context of explicit congestion control protocols like XCP and RCP where the equilibrium queue lengths are zero, we show that the stability region derived from traditional Nyquist analysis is not an accurate representation of the actual stability region, and that the use of switched linear system models with time delay and new Lyapunov tools can provide sound sufficient stability conditions.
TL;DR: A novel technique for accurately estimating the proportions of packet losses arising from collisions and from other sources of loss (channel noise, hidden nodes etc) is presented.
Abstract: We present a novel technique for accurately estimating the proportions of packet losses arising from collisions and from other sources of loss (channel noise, hidden nodes etc). Our approach is robust, makes use of local station-level measurements and requires no message passing. The required measurements are available in standard hardware as they are required for CSMA/CA operation. No channel quality probing is required which ensures energy efficiency
TL;DR: Experimental results show that the approach based on nonextensive entropy outperforms previous ones based on classical entropy while providing enhanced flexibility, which is enabled by the possibility of fine-tuning the sensitivity of the detection mechanism.
Abstract: Detection is a crucial step towards efficiently diagnosing network traffic anomalies within an autonomous system (AS). We propose the adoption of nonextensive entropy - a one-parameter generalization of Shannon entropy - to detect anomalies in network traffic within an AS. Experimental results show that our approach based on nonextensive entropy outperforms previous ones based on classical entropy while providing enhanced flexibility, which is enabled by the possibility of fine-tuning the sensitivity of the detection mechanism.
TL;DR: Numerical simulations show that the Type IV Pearson distribution can accurately approximate distribution of the sum of lognormal random variables in a wide probability range.
Abstract: In this paper, the Type IV Pearson distribution is proposed to approximate the distribution of the sum of lognormal random variables, and the parameters of the Type IV Pearson distribution are derived through matching the mean, variance, skewness and kurtosis of the two distributions. Numerical simulations show that the Type IV Pearson distribution can accurately approximate distribution of the sum of lognormal random variables in a wide probability range.
TL;DR: A parallel weighted bit-flipping decoding algorithm for low-density parity-check (LDPC) codes is proposed and it is demonstrated through examples that the proposed PWBF decoding converges in about 5 iterations with performance very close to that of the standard belief-propagation decoding.
Abstract: A parallel weighted bit-flipping (PWBF) decoding algorithm for low-density parity-check (LDPC) codes is proposed. Compared to the best known serial weighted bit-flipping decoding, the PWBF decoding converges significantly faster but with little performance penalty. For decoding of finite-geometry LDPC codes, we demonstrate through examples that the proposed PWBF decoding converges in about 5 iterations with performance very close to that of the standard belief-propagation decoding.
TL;DR: Simulation results demonstrate that the EHRP reduces routing overhead and route discovery delay of ZigBee mesh networks significantly compared with the hierarchical routing protocol (HRP) defined in ZigBee v1.1.0.
Abstract: This letter proposes the enhanced hierarchical routing protocol (EHRP) for ZigBee mesh networks. The EHRP finds the shortest hierarchical path based on the ZigBee hierarchical addressing scheme. The EHRP provides efficient and reliable routing paths. In addition, the EHRP is completely compatible with ZigBee v.1.0 standard. Simulation results demonstrate that the EHRP reduces routing overhead and route discovery delay of ZigBee mesh networks significantly compared with the hierarchical routing protocol (HRP) defined in ZigBee v1.0.
TL;DR: A very accurate estimation of the capacity of a single-input single-output system operating in a log-normal environment is provided and the analytical expressions obtained match perfectly the capacity given by simulations.
Abstract: In this paper, we first provide a very accurate estimation of the capacity of a single-input single-output system operating in a log-normal environment. Then, hinging on the fact that the sum of log-normal Random Variables (RV) is well approximated by another log-normal RV, we apply the obtained results to find the capacity of Maximum Ratio Combining and Equal Gain Combining in a log-normal environment. The capacity in an interference-limited environment is also investigated in this paper. The analytical expressions obtained match perfectly the capacity given by simulations.
TL;DR: A finite load, large buffer model for the WLAN medium access protocol IEEE 802.11 is developed that gives throughput and delay predictions and it is shown that increased buffering can help this inequity, but only at the expense of possibly significantly increased delays.
Abstract: A finite load, large buffer model for the WLAN medium access protocol IEEE 802.11 is developed that gives throughput and delay predictions. This enables us to investigate the impact of buffering on resource allocation. In the presence of heterogeneous loads, 802.11 do not allocate transmission opportunities equally. It is shown that increased buffering can help this inequity, but only at the expense of possibly significantly increased delays