Weihuang Fu

Gaussian versus Uniform Distribution for Intrusion Detection in Wireless Sensor Networks

In a Wireless Sensor Network (WSN), intrusion detection is of significant importance in many applications in detecting malicious or unexpected intruder(s). The intruder can be an enemy in a battlefield, or a malicious moving object in the area of interest. With uniform sensor deployment, the detection probability is the same for any point in a WSN. However, some applications may require different degrees of detection probability at different locations. For example, an intrusion detection application may need improved detection probability around important entities. Gaussian-distributed WSNs can provide differentiated detection capabilities at different locations but related work is limited. This paper analyzes the problem of intrusion detection in a Gaussian-distributed WSN by characterizing the detection probability with respect to the application requirements and the network parameters under both single-sensing detection and multiple-sensing detection scenarios. Effects of different network parameters on the detection probability are examined in detail. Furthermore, performance of Gaussian-distributed WSNs is compared with uniformly distributed WSNs. This work allows us to analytically formulate detection probability in a random WSN and provides guidelines in selecting an appropriate deployment strategy and determining critical network parameters.

Hops-based Sleep Scheduling Algorithm for Enhancing Lifetime of Wireless Sensor Networks

In this paper, we study the node sleep scheduling scheme in the commonly used static disk model for sensor networks, where homogenous sensors are uniformly distributed in a circular area with a stationary sink located at the center. Then, we introduce and analyze a hops-based sleeping scheduling algorithm (HSS) for enhancing the lifetime and energy efficiency of the sensor networks. The HSS divides the circular sensor network into several levels according to the average hop distance based on certain network parameters. By assigning hops-based sleeping probabilities to each sensor, and the network lifetime as well as energy efficiency can be greatly improved. Simulations are performed to compare our proposed HSS scheme with the traditional randomized sleeping scheduling (RSS) scheme, where all the nodes have the uniform sleeping probability. The results demonstrate that our HSS scheme can enhance network lifetime greatly, provide desired QoS requirement effectively, and drastically outperform the RSS scheme

Differentiable Spectrum Partition for Fractional Frequency Reuse in Multi-Cell OFDMA Networks

To mitigate inter-cell interference (ICI) and achieve higher spectrum efficiency, fractional frequency reuse (FFR) has been widely adopted by the next generation wireless systems, wherein different frequency reuse factors are applied to cell center and cell edge zones. In such conventional FFR, a contiguous radio spectrum is partitioned in a fixed fashion across all cells for edge and cell center zones. This approach evidently lacks the flexibility of inter-cell and/or intra-cell resource allocation adjustment and the capability of dealing with traffic load fluctuation and quality of service (QoS) requirements variations. This paper models the implementation of FFR in a multi-cell network environment and proposes a scheme called D-FFR that can adaptively partition radio spectrum in a distributed manner to achieve different FFR configuration among different cells. Resource demands and various inter-cell/intracell allocation constraints are accounted in D-FFR to enable differentiable inter-cell and/or intra-cell throughput and deliver higher spectrum efficiency. Analytical and extensive simulation results are provided in the paper to validate the effectiveness of our proposed scheme.

Capacity of Hybrid Wireless Mesh Networks with Random APs

In conventional Wireless Mesh Networks (WMNs), multihop relays are performed in the backbone comprising of interconnected Mesh Routers (MRs) and this causes capacity degradation. This paper proposes a hybrid WMN architecture that the backbone is able to utilize random connections to Access Points (APs) of Wireless Local Area Network (WLAN). In such a proposed hierarchal architecture, capacity enhancement can be achieved by letting the traffic take advantage of the wired connections through APs. Theoretical analysis has been conducted for the asymptotic capacity of three-tier hybrid WMN, where per-MR capacity in the backbone is first derived and per-MC capacity is then obtained. Besides related to the number of MR cells as a conventional WMN, the analytical results reveal that the asymptotic capacity of a hybrid WMN is also strongly affected by the number of cells having AP connections, the ratio of access link bandwidth to backbone link bandwidth, etc. Appropriate configuration of the network can drastically improve the network capacity in our proposed network architecture. It also shows that the traffic balance among the MRs with AP access is very important to have a tighter asymptotic capacity bound. The results and conclusions justify the perspective of having such a hybrid WMN utilizing widely deployed WLANs.

Clustering Based Fractional Frequency Reuse and Fair Resource Allocation in Multi-Cell Networks

Fractional frequency reuse (FFR), using different frequency reuse factors for cell center and edge regions, is able to effectively improve spectrum efficiency in multi-cell OFDMA networks. However, optimal performance is hard to achieve in practice as the efficiency of resource allocation could drop drastically due to the constraint from the frequency partitions formed by FFR. Since the radio resource is pre-partitioned for cell edge and center, fair resource allocation in a cell is also difficult to implement. Conventional frequency partition adjustment either has high complexity due to global optimization or suffers from heavy performance degradation due to absence of effective control on inter-cell interference (ICI). To solve this issue, we create models for analyzing geographical distribution of interference in multi-cell networks. Based on the observed non-uniform distributed ICI, we redefine the zones for fractional reuse and propose clustering based FFR, which offers resource allocation higher flexibility and better fairness with additional spatial dimension. Extensive simulation has been performed to validate practicality and effectiveness of our proposed scheme.

Intrusion detection in Gaussian distributed Wireless Sensor Networks

Intrusion detection in a Wireless Sensor Network (WSN) is of significant importance in many applications to detect malicious or unexpected intruder(s). The intruder can be an enemy in a battlefield, or a unusual environmental change in a chemical industry etc. With uniform distribution, the detection probability is the same for any point in a WSN. However, some applications may require different degrees of detection probability at different locations in the deployment area. Gaussian distributed WSNs (i.e., normal distribution) can provide differentiated detection capabilities at different locations and are widely deployed in practice. In view of this, this paper analyzes the problem of intrusion detection in a Gaussian distributed WSN, by characterizing intrusion detection probability with respect to intrusion distance and network deployment parameters. Two detection models are considered: single-sensing detection and multiple-sensing detection. Effects of different network parameters on the intrusion detection probability are examined in details. This work allows us to analytically formulate the intrusion detection probability within a certain intrusion distance under various application scenarios, therefore provides insight for directing the application-specific WSN deployment such as intrusion detection.

Flow-Based Channel Assignment in Channel Constrained Wireless Mesh Networks

Wireless mesh network (WMN) technology extends the service coverage by supporting multi-hop communication and enhances the network capacity by utilizing multi-radio and multichannel. The number of multiple channels is essential for the implementation and the efficiency of channel assignment. While the number of channels is not sufficient, channel assignment needs to consider the channel sharing at certain mesh routers (MRs). The distribution of traffic flows in the network greatly affects the channel assignment. Different to a mobile ad hoc network (MANET), the traffic in a WMN is predominated by the Internet traffic. In this paper, we analyze the number of channels for a feasible conflict free channel assignment in such a network. We also propose a flow-based channel assignment in the channel constrained situation by implementing channel mergence algorithm so that MRs can appropriately share the channel resource. Extensive simulations are performed to illustrate the effectiveness of our proposed scheme.

Delay and Capacity Optimization in Multi-radio Multi-channel Wireless Mesh Networks

The technology of wireless mesh network (WMN) provides a flexible Internet access service in a wide region by employing multi-hop wireless routing and enhances the network performance by utilizing multi-radio and multi-channel. Delay analysis is a fundamental issue for delay-sensitive application such as VoIP and video conference, and delay constrained capacity is essential for a network to provide satisfied service. This paper models such a network and obtains the packet delay and network capacity by considering a queueing network formed by multi-radio mesh routers (MRs) and carrier sense multiple access (CSMA) mechanism is assumed for packet transmissions over links between MRs. We investigate the problems of intercluster dominated traffic, study the impact of the number of radios and channels to the delay and the capacity, and optimize the network performance by adjusting the MR deployment and the transmission power.

Error Control Strategies for WiMAX Multi-Hop Relay Networks

Next generation wireless system such as advanced WiMAX (i.e., IEEE802.16m) and LTE advanced will fully embrace multi-hop relay architecture. The conventional Automatic Repeat reQuest (ARQ) and the more recent Hybrid ARQ (HARQ) are two simple yet highly effective error control techniques designed for single hop system. Nevertheless, extending them in a synergistic manner to support multi-hop relay networks is by no means a trivial undertaking. This paper explores a variety of multi-hop error control techniques such as hop-by-hop ARQ, 2-link ARQ and end-to-end ARQ, and various possible combinations with HARQ. We further establish an analytical framework for each of these key techniques and evaluate the performance. Based on the analysis and comparison, we propose a low complexity error control mechanism tailored for the multi-hop transmission features. Extensive simulation results compare the performance and validate our analytical framework.

A Tree-based Channel Assignment Scheme for Wireless Mesh Networks

Unlike ad hoc networks where traffic is randomly distributed among every pair of nodes, the traffic in wireless mesh networks (WMNs) is predominantly toward or from the Internet Gateways (IGWs)for Internet services. Due to this, interference and collision are more serious in the Mesh Router (MRs) closer to the IGWs and the Internet throughput of the network is limited by the number of orthogonal channels and radios of the IGW. In this paper, we propose a channel assignment scheme which exploits a tree-based topology in WMNs and implements a heuristic channel assignment algorithm, aiming to achieve the maximal Internet throughput. The channels are sequentially assigned level by level in the tree, starting from the IGW. The simulation results show that the network using this scheme achieve the Internet throughput close to the maximal capacity of IGW.