Dexiang Wang

Residual energy aware channel assignment in cognitive radio sensor networks

We investigate the channel assignment problem in a cluster-based multi-channel cognitive radio sensor network in this paper. Due to the inherent power and resource constraints of sensor networks, energy efficiency is the primary concern for network design. An R-coefficient is developed to estimate the predicted residual energy using sensor information (current residual energy and expected energy consumption) and channel conditions (primary user behavior). We examine three channel assignment approaches: Random pairing, Greedy channel search and Optimization-based channel assignment. The last two exploit R-coefficient to obtain a residual energy aware channel assignment solution. Simulation results show that R-coefficient-based approaches lead to better performance in terms of energy consumption and residual energy balance. Optimization-based channel assignment outperforms the other two approaches with respect to network lifetime.

A Fault-Tolerant Backbone Network Architecture Targeting Time-Critical Communication for Avionic WDM LANs

In this paper, we focus on the design and analysis of a torus-based backbone architecture which targets to meet both the low delay and high reliability requirements of avionic time-critical communications. Reliable optical connection between arbitrary source-destination pairs is proposed by enabling four non-overlapping lightpaths between the source and destination, which makes the network tolerant to at least three arbitrary link failures without losing connectivity. A greedy algorithm is introduced to set up the four non-overlapping lightpaths with the aim of maximizing two-terminal reliability (TTR), as well as minimizing signal attenuation and propagation delay. A wavelength assignment and reuse (WAR) method is used to reduce by half the wavelength requirement for all-to-all communication in a case study of 4×4 torus. Both probabilistic analysis and a packet-level simulation reveal that the proposed architecture can provide efficient communication with a 3-fault reliability guarantee.

Circulant-Graph-Based Fault-Tolerant Routing for All-Optical WDM LANs

High demands in data delivery latency and communication reliability encourage the use of fault-tolerance-enhanced all-optical WDM networks. Low latency is satisfied by setting up a direct lightpath between any communication pair to enable one-shot transmission. High reliability is met by establishing multiple disjoint lightpaths from the source to the destination. In this paper, we explore the fault-tolerance potential in circulant graphs, which offer good flexibility in the number of supported nodes and network connectivity. We propose a circulant-graph-based all-optical network architecture together with a fault-tolerant routing algorithm. Network resource utilization is analytically calculated and results show that increasing network connectivity helps reduce the required number of wavelengths for simultaneous all-node communications. A connection reliability model is developed combining both node and link failure effects. The reliability benefit obtained from the proposed algorithm grows almost linearly with network connectivity increase in a logarithmic scale.

On the Accuracy of Maximum Likelihood Estimation for Primary User Behavior in Cognitive Radio Networks

The primary user (PU)s busy/idle behavior in a cognitive radio network is conventionally modeled using a two-state Markov chain. Maximum likelihood (ML) estimation is widely applied to estimate the state transition probabilities. This letter derives a precise expression of the probability mass function (PMF) for the ML estimator, which has not been reported in the literature. By leveraging the exact PMF expression, the essential relation among the number of samples, transition probabilities, and estimation accuracy is revealed.

A Torus-Based 4-Way Fault-Tolerant Backbone Network Architecture for Avionic WDM LANs

In this paper, we leverage the torus topology to design a wavelength division multiplexing (WDM) backbone network for operation in hazardous avionic environments. The proposed WDM local area network offers efficient data delivery and fast fault recovery via establishing four non-overlapping lightpaths for any source-destination pair. First, we describe a torus-based architecture and propose an efficient non-overlapping lightpath setup algorithm: FOLD (Four-way Optimal Disjoint Routing). The algorithm is proved to achieve optimal link utilization. Second, based on the proposed lightpath setup algorithm, a wavelength allocation and reuse (WAR) scheme enforcing wavelength continuity is proposed to minimize the wavelength utilization for all-to-all communication. An analytical calculation on wavelength utilization shows that the proposed WAR performs very close to an ideal wavelength assignment scheme without wavelength continuity being enforced. Lastly, the probabilistic and capacity analysis demonstrates vast reliability improvement via applying the proposed network architecture in terms of network-failure-induced impact on connection reliability and network capacity degradation.

A Smart-NIC-Based Power-Proxy Solution for Reduced Power Consumption during Instant Messaging

The major challenge to achieving efficient power management for local computers that serve as edge devices of the Internet is to achieve long sleeping times while at the same time maintaining network connectivity. By modifying the network interface card (NIC) with a low-weight proxy module that can handle a certain amount of network protocol semantics and hence still keep the local computer alive on the Internet, a longer host sleeping time can be achieved, while keeping many of the components, including CPU, memory, motherboard, hard drive, etc, remain in a very-low-energy mode. In this paper, we pursue a power-proxy solution to the widely-used Instant Messenger (IM) applications. Yahoo! Messenger® is selected for a case study to investigate its communication protocol YMSG. Furthermore, the decision on inactivity time-out values is a crucial factor for energy savings, but the random nature of idle periods makes the decision another challenge. We formulate the decision problem into a stochastic program and propose an adaptive algorithm to set up appropriate inactivity time-out values. Simulations show that the proposed power-proxy solution combined with the inactivity time-out setup algorithm can efficiently reduce the power consumption of an edge computer.

Stability region adaptation using transmission power control for transport capacity optimization in IEEE 802.16 wireless mesh networks

Transmission power control in multihop wireless networks is a challenging problem due to the effects that different node transmission powers have across the layers of the protocol stack. In this paper, we study the problem of transmission power control in IEEE 802.16 mesh networks with distributed scheduling. We consider the effects of transmission power control on the link-scheduling performance when a set of end-to-end flows established in the network are given. The problem is approached by means of the stability region of the link-scheduling policy. Specifically, the stability region is adapted using transmission-power control to the paths of the flows. This adaptation enables the flows to support higher levels of data traffic under lower levels of end-to-end delay. To the best of our knowledge, the approach of stability-region-based transmission power control has not been studied before. We propose a heuristic transmission-power-control algorithm for solving the problem of adapting the stability region to the flows. It is shown, by means of simulation, that the algorithm outperforms the transmission power control based on spatial reuse, which is a widely used approach. Also, it is shown that the solution of the algorithm has performance close to the optimal solution for moderate-sized networks, i.e., networks with no more than 25 nodes and 25 flows.

Primary user behavior estimation with adaptive length of the sample sequence

Modeling and estimating the primary user (PU) behavior is critical to implement dynamic spectrum access in cognitive radio networks. In this paper, we investigate the estimation accuracy of the PU behavior based on the Markov model. Maximum Likelihood (ML) estimation is employed to estimate the transition probabilities of the Markov model based on the sample sequence of PU idle/busy states. An approximate distribution of the ML estimator is derived to evaluate the estimation accuracy specified by the confidence level. To meet the requirement of estimation accuracy while reducing the unnecessary sensing time, we propose a learning algorithm which refines the estimation results iteratively. It dynamically estimates the required length of the sample sequence which is adaptive to the changing PU behavior. Numerical results show that the proposed estimation algorithm well tracks the variation of the PU behavior. Compared to the estimation method using fixed length of sample sequence, the proposed algorithm achieves the same requirement of the estimation accuracy with less number of samples.

Effect of traffic patterns on optical time-division-multiplexed/WDM networks for avionics

Communication systems for use in commercial aircrafts are becoming increasingly complex and bandwidth intensive to meet the needs of multimedia users, as well as perform system management functions. The various avionics sub-systems have varied requirements for services that generate a wide range of traffic patterns. Wavelength Division Multiplexing (WDM) provides a robust way to offer such services, but measures have to be taken to make sure that the bandwidth is effectively utilized. Using Optical Time Division Multiplexing (OTDM) with WDM increases the bandwidth usage per wavelength in the WDM system, thereby increasing the effective utilization of the system capacity. This paper analyzes the effect of three different traffic patterns generated at the sub-systems, on an OTDM/WDM network.

Multi-Layer Simulation Design and Validation for a Two-Tier Fault-Tolerant WDM LAN

In this paper, we report our progress on the development of a simulation framework for optical local area networks, which enables a multi-layer network simulation and hence bridges the gap between the traditional signal-level and traffic-level simulators. The framework, called DRAGON (discrete-model register for Artifex-based general-purpose optical local area network simulation), is built upon the Artifex modeling platform, and it models a wide register of fiber-optic components, emulating features at multiple network layers, spanning over signal and noise power monitoring, bit error rate (BER) estimation, packet collision detection, and propagation/transmission delay emulation. We demonstrate the effectiveness of DRAGON by modeling a novel two-tier fault-tolerant wavelength division multiplexing local area network (WDM LAN) architecture, and we show the impact of the proposed WDM LAN architecture on the quality of service requirements of WDM traffic.