Showing papers in "IEEE Communications Letters in 2010"

Direction of Departure (DOD) and Direction of Arrival (DOA) Estimation in MIMO Radar with Reduced-Dimension MUSIC

Abstract: This letter discusses the problem of direction of departure (DOD) and direction of arrival (DOA) estimation for multi-input multi-output (MIMO) radar, and derives a reduced-dimension multiple signal classification (MUSIC) algorithm therein. The proposed algorithm, which only requires one-dimension search, can avoid the high computational cost within two-dimension MUSIC (2D-MUSIC) algorithm. We illustrate that the algorithm has better performance ESPRIT algorithm, and has very close performance to 2D-MUSIC algorithm. Further our algorithm requires no pair matching. Simulation results verify the usefulness of our algorithm.

Nested Polar Codes for Wiretap and Relay Channels

Abstract: We show that polar codes asymptotically achieve the whole capacity-equivocation region for the wiretap channel when the wiretapper's channel is degraded with respect to the main channel, and the weak secrecy notion is used. Our coding scheme also achieves the capacity of the physically degraded receiver-orthogonal relay channel. We show simulation results for moderate block length for the binary erasure wiretap channel, comparing polar codes and two edge type LDPC codes.

Performance Analysis of Two Hop Amplify-and-Forward Systems with Interference at the Relay

Abstract: We analyze the performance of a two hop channel state information (CSI)-assisted amplify-and-forward system, with co-channel interference at the relay. The system's outage probability and the average bit error rate (BER) in the presence of Rayleigh faded multiple interferers are investigated. We derive an exact expression for the outage probability and an accurate bound for the system's average BER. Simulation results show the validity of the analysis and point out the effect of interference.

Reputation-based cooperative spectrum sensing with trusted nodes assistance

Abstract: Existing cooperative spectrum sensing (CSS) schemes are typically vulnerable to attacks where misbehaved cognitive radios (CRs) falsify sensing data. To ensure the robustness of spectrum sensing, this letter presents a secure CSS scheme by introducing a reputation-based mechanism to identify misbehaviors and mitigate their harmful effect on sensing performance. Encouraged by the fact that such secure CSS is sensitive to the correctness of reputations, we further present a trusted node assistance scheme. This scheme starts with reliable CRs. Sensing information from other CRs are incorporated into cooperative sensing only when their reputation is verified, which increases robustness of cooperative sensing. Simulations verify the effectiveness of the proposed schemes.

Multiple output selection-LAS algorithm in large MIMO systems

Abstract: We present a low-complexity algorithm for detection in large MIMO systems based on the likelihood ascent search (LAS) algorithm. The key idea in our work is to generate multiple possible solutions or outputs from which we select the best one. We propose two possible approaches to achieve this goal and both are investigated. Computer simulations demonstrate that the proposed algorithm, Multiple Output Selection-LAS, which has the same complexity order as that of conventional LAS algorithms, is superior in bit error rate (BER) performance to LAS conventional algorithms. For example, with 20 antennas at both the transmitter and receiver, the proposed MOS-LAS algorithm needs about 4 dB less SNR to achieve a target BER of 10-4 for 4-QAM.

Performance of PPM on terrestrial FSO links with turbulence and pointing errors

Abstract: In recent work, the error performance of on-off keying has been investigated for free-space optical (FSO) links impaired by both turbulence and pointing loss. In the current letter, the analytical framework is extended to M-ary pulse-position modulation (PPM), providing exact results for M = 2. Since the approach is not directly applicable to PPM signals with M > 2, a closed-form approximation of the average symbol error probability is derived for this case, which is shown via simulation to be tight over a wide SNR range of interest.

Evaluating the Impact of Social Selfishness on the Epidemic Routing in Delay Tolerant Networks

Abstract: To cope with the uncertainty of transmission opportunities between mobile nodes, Delay Tolerant Networks (DTN) routing exploits opportunistic forwarding mechanism. This mechanism requires nodes to forward messages in a cooperative and altruistic way. However, in the real world, most of the nodes exhibit selfish behaviors such as individual and social selfishness. In this paper, we investigate the problem of how social selfishness influences the performance of epidemic routing in DTN. First, we model the message delivery process with social selfishness as a two dimensional continuous time Markov chain. Then, we obtain the system performance of message delivery delay and delivery cost by explicit expressions. Numerical results show that DTN is quite robust to social selfishness, which increases the message delivery delay, but there is more reducing of delivery cost.

Improving the performance of space shift keying (SSK) modulation via opportunistic power allocation

Abstract: In this Letter, we show that the performance of Space Shift Keying (SSK) modulation can be improved via opportunistic power allocation methods. For analytical tractability, we focus on a 2 × 1 Multiple-Input-Multiple-Output (MIMO) system setup over correlated Rayleigh fading channels. A closed-form solution of the optimal power allocation problem is derived, and it is shown that the transmit-power of each transmit-antenna should be chosen as a function of the power imbalance ratio and correlation coefficient of the transmit-receive wireless links. Numerical results are shown to substantiate the analytical derivation and the claimed performance improvement.

A Channel Rendezvous Scheme for Cognitive Radio Networks

Abstract: Cognitive radio networks need to utilize available spectrum in a dynamic and opportunistic fashion without causing interference to co-located primary nodes. Before data transmission begins, secondary nodes must establish a link on a channel which is not occupied by primary nodes. Unfortunately, in cognitive radio networks, the set of available channels can be different for each node, since it is determined by the relative locations of nodes to primary nodes. We are the first to present a distributed channel rendezvous scheme which finds a commonly available channel between any two nodes in a bounded time without synchronization. Our scheme determines the order, in which two nodes visit channels to find a common channel, if any, within a bounded time.

Random-Restart Reactive Tabu Search Algorithm for Detection in Large-MIMO Systems

Abstract: We present a low-complexity algorithm based on reactive tabu search (RTS) for near maximum likelihood (ML) detection in large-MIMO systems. The conventional RTS algorithm achieves near-ML performance for 4-QAM in large-MIMO systems. But its performance for higher-order QAM is far from ML performance. Here, we propose a random-restart RTS (R3TS) algorithm which achieves significantly better bit error rate (BER) performance compared to that of the conventional RTS algorithm in higher-order QAM. The key idea is to run multiple tabu searches, each search starting with a random initial vector and choosing the best among the resulting solution vectors. A criterion to limit the number of searches is also proposed. Computer simulations show that the R3TS algorithm achieves almost the ML performance in 16 × 16 V-BLAST MIMO system with 16-QAM and 64-QAM at significantly less complexities than the sphere decoder. Also, in a 32 × 32 V-BLAST MIMO system, the R3TS performs close to ML lower bound within 1.6 dB for 16-QAM (128 bps/Hz), and within 2.4 dB for 64-QAM (192 bps/Hz) at 10-3 BER.

An Efficient Anti-Collision Protocol for RFID Tag Identification

Abstract: In this paper, an efficient anti-collision protocol, named collision tree protocol (CT), is proposed, and a collision tree is put forward to capture the complete communications between the reader and tags in an execution of CT. The main novelty of CT is that both the generating of prefixes and the splitting of tag group are according to the collided bit directly. Both the properties of collision tree and the results of experiments show that the proposed protocol improves the efficiency of tags identification up to 50% and achieves the best performance of the tree-based tags identification protocols.

Investigation on multiuser diversity in spectrum sharing based cognitive radio networks

Abstract: A new form of multiuser diversity, named multiuser interference diversity, is investigated for opportunistic communications in cognitive radio (CR) networks by exploiting the mutual interference between the CR and the existing primary radio (PR) links. The multiuser diversity gain and ergodic throughput are analyzed for different types of CR networks and compared against those in the conventional networks without the PR link.

Fractional bit encoded spatial modulation (FBE-SM)

Abstract: In this Letter, we introduce fractional bit encoded (FBE)-spatial modulation (SM), which is a novel and more versatile SM scheme that allows the transmitter to be equipped with an arbitrary number of antennas. The solution is based on the theory of modulus conversion, and is especially useful for compact mobile devices where cost and space constraints pose fundamental limits on the achievable bit rate. Numerical results will show that FBE-SM can offer design flexibility and the desired trade-off in terms of attainable performance and capacity.

Computationally Tractable Model of Energy Detection Performance over Slow Fading Channels

Abstract: Energy detection (ED) has been widely used for detecting unknown deterministic signals in many wireless communication applications, e.g., cognitive radio, and ultra-wideband (UWB). However, the performance analysis of ED over slow fading channels is cumbersome, because it is difficult to derive closed-form expressions for the average probability of detection involving the generalised Marcum Q-function and the log-normal distribution. In this letter, we derive an approximation of the average probability of detection over a slow fading channel by replacing the log-normal distribution with a Wald distribution. In addition, we analyze the detection performance of the ED using a square-law combining scheme over multiple independent and identically distributed slow fading channels.

RRED: robust RED algorithm to counter low-rate denial-of-service attacks

Abstract: The existing Random Early Detection (RED) algorithm and its variants are found vulnerable to emerging attacks, especially the Low-rate Denial-of-Service (LDoS) attacks. In this letter we propose a Robust RED (RRED) algorithm to improve the TCP throughput against LDoS attacks. The basic idea behind the RRED is to detect and filter out attack packets before a normal RED algorithm is applied to incoming flows. We conduct a set of simulations to evaluate the performance of the proposed RRED algorithm. The results show that, compared to existing RED-like algorithms, the RRED algorithm nearly fully preserves the TCP throughput in the presence of LDoS attacks.

Capacity Analysis of Opportunistic Relaying in Cooperative Systems with Outdated Channel Information

Abstract: In this paper, we analyze the Shannon capacity of the opportunistic relaying technique in amplify-and-forward cooperative systems over Rayleigh fading channels under outdated channel information. Closed-form expressions are derived for the average channel capacity and outage probability. Using numerical evaluations the performances of different cases are compared to evaluate and quantify the effects of outdated channel information on the channel capacity and the outage performance.

Enhanced ARP: preventing ARP poisoning-based man-in-the-middle attacks

Abstract: In this letter, an enhanced version of Address Resolution Protocol (ARP) is proposed to prevent ARP poisoning-based Man-in-the-Middle (MITM) attacks. The proposed mechanism is based on the following concept. When a node knows the correct Media Access Control (MAC) address for a given IP address, if it retains the IP/MAC address mapping while that machine is alive, then MITM attack is impossible for that IP address. In order to prevent MITM attacks even for a new IP address, a voting-based resolution mechanism is proposed. The proposed scheme is backward compatible with existing ARP and incrementally deployable.

Adaptive congestion control for DSRC vehicle networks

Abstract: Dedicated short range communications (DSRC) was proposed for collaborative safety applications (CSA) in vehicle communications. In this article we propose two adaptive congestion control schemes for DSRC-based CSA. A cross-layer design approach is used with congestion detection at the MAC layer and traffic rate control at the application layer. Simulation results show the effectiveness of the proposed rate control scheme for adapting to dynamic traffic loads.

A handover authentication using credentials based on chameleon hashing

Abstract: This letter proposes a handover authentication scheme using credentials based on chameleon hashing. The main challenges in handover authentication are to provide robust security and efficiency. The main idea of this letter is that credentials generated using the collision resistant hash function provide an authenticated ephemeral Diffie-Hellman key exchange only between a mobile node and an access point without communicating with an authentication server whenever a handover authentication occurs. Our scheme supports robust key exchange and efficient authentication procedure.

New companding transform for PAPR reduction in OFDM

Abstract: High peak-to-average power ratio (PAPR) is a major drawback of orthogonal frequency division multiplexing (OFDM) systems. Among the various PAPR reduction techniques, companding transform appears attractive for its simplicity and effectiveness. This paper proposes a new companding algorithm. Compared with the others, the proposed algorithm offers an improved bit error rate and minimized out-of-band interference while reducing PAPR effectively. Theoretical analysis and numerical simulation are presented.

Optimal joint source and relay beamforming for MIMO relays with direct link

Abstract: In this letter, we investigate the optimal structure of the source precoding matrix and the relay amplifying matrix for non-regenerative multiple-input multiple-output (MIMO) relay communication systems with the direct source-destination link. We show that both the optimal source precoding matrix and the optimal relay amplifying matrix have a beamforming structure. Based on this structure, an iterative joint source and relay beamforming algorithm is developed to minimize the mean-squared error (MSE) of the signal waveform estimation. Numerical example demonstrates an improved performance of the proposed algorithm.

An optimal coding strategy for the binary multi-way relay channel

Abstract: We derive the capacity of the binary multi-way relay channel, in which multiple users exchange messages at a common rate through a relay. The capacity is achieved using a novel functional-decode-forward coding strategy. In the functional-decode-forward coding strategy, the relay decodes functions of the users' messages without needing to decode individual messages. The functions to be decoded by the relay are defined such that when the relay broadcasts the functions back to the users, every user is able to decode the messages of all other users.

Performance versus overhead for fountain codes over F q

Abstract: Fountain codes for packet erasure recovery are investigated over Galois fields of order q ? 2. It is shown through development of tight upper and lower bounds on the decoding failure probability under maximum likelihood decoding, that the adoption of higher order Galois fields is beneficial, in terms of performance, for linear random fountain codes. Moreover, it is illustrated how Raptor codes can provide performances very close to those of random fountain codes, with an affordable encoding and decoding complexity. Non-binary Raptor codes turn out to represent an appealing option for applications requiring severe constraints in terms of performance versus overhead, especially for small source block sizes.

Adaptive active constellation extension algorithm for peak-to-average ratio reduction in OFDM

Abstract: For PAR reduction in OFDM systems, the clipping-based Active Constellation Extension (ACE) technique is simple and attractive for practical implementation. However, we observe it cannot achieve the minimum PAR when the target clipping level is set below an initially unknown optimum value. To overcome this low clipping ratio problem, we propose a novel ACE algorithm with adaptive clipping control. Simulation results demonstrate that our proposed algorithm can reach the minimum PAR for severely low clipping ratios. In addition, we present the tradeoff between PAR and the loss in Eb/No over an AWGN channel in terms of the clipping ratio.

A Novel Decoding-and-Forward Scheme with Joint Modulation for Two-Way Relay Channel

Abstract: In this letter, a novel decode-and-forward (DF) strategy for the two-way relay over Rayleigh fading channels is presented and analyzed. By encoding the two messages jointly at the relay node, the proposed scheme (termed DF-JM) can effectively handle matched or unmatched data rates from the two sources. In addition, it is possible to design optimal constellation labeling maps at the relay node, so that the minimum Euclidean distance among the desired points can be maximized for side-information based demodulation at the destinations. Simulation results indicate that the DF-JM approach performs better than existing DF schemes and the denoise-and-forward (DNF) scheme in terms of the end-to-end bit error rate (BER).

Accurate tag estimation for dynamic framed-slotted ALOHA in RFID systems

Abstract: Dynamic framed-slotted ALOHA (DFSA) is one of the most popular algorithms to resolve tag collision in RFID systems. In DFSA, it is widely known that the optimal performance is achieved when the frame size is equal to the number of tags. So, a reader dynamically adjusts the next frame size according to the current number of tags. Thus it is important to estimate the number of tags accurately. In this paper, we propose a novel tag estimation method for DFSA. We compare the performance of the proposed method with those of other existing methods. And, simulation results show that our scheme improves the accuracy of tag estimation and the speed of tag identification.

Energy-Efficient Coverage Based on Probabilistic Sensing Model in Wireless Sensor Networks

Abstract: Network coverage is one of the most critical issues to implement Wireless Sensor Networks (WSNs). It is important to find out a sensor set with maximal residual energy to cover all points of interest (PoIs). This issue was named as minimum weight sensor coverage problem (MWSCP) based on a boolean disc model and a probabilistic sensing model in the literature. In this paper, we introduce intelligent algorithms to solve this problem, yielding a better solution to MWSCP to extend network lifetime. Simulation results are conducted to demonstrate the effectiveness of our proposed algorithm in terms of network lifetime over existing algorithms.

A New SLNR-Based Linear Precoding for Downlink Multi-User Multi-Stream MIMO Systems

Abstract: Signal-to-leakage-and-noise ratio (SLNR) is a promising criterion for linear precoder design in multi-user (MU) multiple-input multiple-output (MIMO) systems. It decouples the precoder design problem and makes closed-form solution available. In this letter, we present a new linear precoding scheme by slightly relaxing the SLNR maximization for MU-MIMO systems with multiple data streams per user. The precoding matrices are obtained by a general form of simultaneous diagonalization of two Hermitian matrices. The new scheme reduces the gap between the per-stream effective channel gains, an inherent limitation in the original SLNR precoding scheme. Simulation results demonstrate that the proposed precoding achieves considerable gains in error performance over the original one for multi-stream transmission while maintaining almost the same achievable sum-rate.

Outage probability analysis for η-μ fading channels

Abstract: In this Letter we derive exact closed-form expressions for the outage probability (OP) in η-μ fading channels. First, a general expression in terms of the confluent Lauricella function is derived for arbitrary values of μ. Next, we restrict the analysis to physical η-μ channel models, i.e. to integer values of 2μ, and obtain exact closed-form expressions for the OP in terms of Marcum Q, Bessel and elementary functions. The results in this Letter are applicable to the OP analysis of maximal ratio combining (MRC) over i.i.d. η-μ or Hoyt fading channels.

QoS aware relay selection and subcarrier allocation in cooperative OFDMA systems

Abstract: Most existing works on resource allocation in cooperative OFDMA systems have focused on homogeneous users with same service and demand. In this letter, we investigate relay selection and subcarrier allocation in a cooperative OFDMA system with considerations of QoS guarantees and service support. By introducing QoS price, this combinatorial problem with exponential complexity is converted into a convex one, and a dual based QoS-aware schedule (QAS) algorithm is proposed to tackle the problem. Simulation results reveal that our proposed algorithm significantly outperforms previous works in terms of both services support and QoS satisfaction.