Xiuming Shan

CP-TDMA : Coloring-and Probability-Based TDMA Scheduling for Wireless Ad Hoc Networks

This paper addresses the issue of transmission scheduling in wireless ad hoc networks. We propose a Time Division Multiple Access (TDMA) scheduling scheme based on edge coloring and probabilistic assignment, called CP-TDMA. We categorize the conflicts suffered by wireless links into two types: explicit conflicts and implicit conflicts, and utilize two different strategies to deal with them. Explicit conflicts are avoided completely by a simple distributed edge-coloring algorithm μ-M, and implicit conflicts are minimized by applying probabilistic time slot assignments to links. We evaluate CP-TDMA analytically and numerically, and find that CP-TDMA, which requires only local information exhibits a better performance than previous work.

Asynchronous track fusion in a multi-scale sensor environment

Track fusion is an important and attractive part in multisensor multitarget tracking for its robustness and flexibility compared with measurement fusion. Much research on track fusion has been done under the common assumption that the sensors in system are synchronous (with no communication delays) or have similar sensor accuracies. Unfortunately, in many multisensor systems, situations often fall short of the above assumption due to the mobility of targets and/or sensors, the communication restrictions, and the type and resource limitations of the individual sensors. The aim of this paper is to propose an asynchronous approach for track fusion in a multi-scale sensor environment, which we refer to as asynchronous hierarchical track fusion (AHTF). It is shown that the proposed AHTF approach provides a solution to combining tracks reported by multi-scale sensors, which are dissimilar in their data rates and resolving capacities. Simulations in a typical maritime surveillance scenario are presented to validate the performance of the proposed approach.

Covariances of Linear Stochastic Differential Equations for Analyzing Computer Networks

Analyses of dynamic systems with random oscillations need to calculate the system covariance matrix, but this is not easy even in the linear case if the random term is not a Gaussian white noise. A universal method is developed here to handle both Gaussian and compound Poisson white noise. The quadratic variations are analyzed to transform the problem into a Lyapunov matrix differential equation. Explicit formulas are then derived by vectorization. These formulas are applied to a simple model of flows and queuing in a computer network. A stability analysis of the mean value illustrates the effects of oscillations in a real system. The relationships between the oscillations and the parameters are clearly presented to improve designs of real systems.

Guardband analysis for distributed OFDMA with user heterogeneity

This paper presents an in-depth analysis of the interference strength and required guardband width between coexistent users for distributed orthogonal frequency division multiple access (OFDMA).In dynamic spectrum access networks,the cross-band interference between spectrally adjacent users is considered harmful with frequency guardbands inserted between spectrum blocks to eliminate the interference.However,the strength of the cross-band interference depends heavily on the user heterogeneity in different OFDM configurations.The cross-band interference due to the three user heterogeneity artifacts of power heterogeneity,sampling rate heterogeneity,and symbol length heterogeneity is investigated to determine the required guardband width.Analytical and simulation results show that the greater user heterogeneity requires larger guardbands with the sampling rate heterogeneity having the greatest effect.These results can be used to assist the design of spectrum allocation strategies.

Locating highly connected nodes in P2P networks with heterogeneous structures

Peer-to-peer (P2P) networks aggregate enormous storage and processing resources while minimizing entry and scaling costs. Gnutella-like P2P networks are complex heterogeneous networks, in which the underlying overlay topology has a power-law node degree distribution. While scale-free networks have great robustness against random failures, they are vulnerable to deliberate attacks where highly connected nodes are eliminated. Since high degree nodes play an important role in maintaining the connectivity, this paper presents an algorithm based on random walks to locate high degree nodes in P2P networks. Simulations demonstrate that the algorithm performs well in various scenarios and that heterogeneous P2P networks are very sensitive to deliberate attacks.

An Adaptive Resource-Based Probabilistic Search Algorithm for P2P Networks

A novel Adaptive Resource-based Probabilistic Search algorithm (ARPS) for P2P networks is proposed in this paper. ARPS introduces probabilistic forwarding for query messages according to the popularity of the resource being searched. A mechanism is introduced to estimate the popularity and adjust the forwarding probability accordingly such that a tradeoff between search performance and cost can be made. Using computer simulations, we compare the performance of ARPS with several other search algorithms. It is shown that ARPS performs well under various P2P scenarios. ARPS guarantees a success rate above a certain level under all circumstances, and enjoys high and popularity-invariant search success rate. Furthermore, ARPS adapts well to the variation of popularity, resulting in high efficiency and flexibility.

Performance Evaluation of Adaptive Probabilistic Search in P2P Networks

The overall performance of P2P-based file sharing applications is becoming increasingly important. Based on the Adaptive Resource-based Probabilistic Search algorithm (ARPS), which was previously proposed by the authors, a novel probabilistic search algorithm with QoS guarantees is proposed in this letter. The algorithm relies on generating functions to satisfy the users constraints and to exploit the power-law distribution in the node degree. Simulation results demonstrate that it performs well under various P2P scenarios. The proposed algorithm provides guarantees on the search performance perceived by the user while minimizing the search cost. Furthermore, it allows different QoS levels, resulting in greater flexibility and scalability.

A receiver-initiated soft-state probabilistic multicasting protocol in wireless ad hoc networks

A novel receiver-initiated soft-state probabilistic multicasting protocol (RISP) for mobile ad hoc network is proposed in this paper. RISP introduces probabilistic forwarding and soft-state for making relay decisions. Multicast members periodically initiate control packets, through which intermediate nodes adjust the forwarding probability. With a probability decay function (soft-state), routes traversed by more control packets are reinforced, while the less utilized paths are gradually relinquished. In this way, RISP can adapt to node mobility; at low mobility, RISP performs similar to a tree-based protocol; at high mobility, it produces a multicast mesh in the network. Simulation results show RISP has lower delivery redundancy than mesh-based protocols, while achieving higher delivery ratio. Further, the control overhead is lower than other compared protocols.