Cunqing Hua

Optimal routing and data aggregation for maximizing lifetime of wireless sensor networks

An optimal routing and data aggregation scheme for wireless sensor networks is proposed in this paper. The objective is to maximize the network lifetime by jointly optimizing data aggregation and routing. We adopt a model to integrate data aggregation with the underlying routing scheme and present a smoothing approximation function for the optimization problem. The necessary and sufficient conditions for achieving the optimality are derived and a distributed gradient algorithm is designed accordingly. We show that the proposed scheme can significantly reduce the data traffic and improve the network lifetime. The distributed algorithm can converge to the optimal value efficiently under all network configurations.

Prefix-Randomized Query-Tree Protocol for RFID Systems

In this paper we present a new tree search-based protocol for the anti-collision problem of RFID systems. This protocol builds a binary search tree according to the prefixes chosen randomly by tags rather than using their ID-based prefixes. Therefore, the tag identification time of the proposed protocol is no longer limited by the tag ID distribution and ID length as the conventional tree search protocol. The time complexity of the protocol is derived and shown that it can identify tags faster than the Query-Tree protocol.

Asynchronous random sleeping for sensor networks

Sleeping scheduling is a common energy-conservation solution for sensor networks. For application whereby coordination of sleeping among sensors is not possible or inconvenient, random sleeping is the only option. In this article, we study the asynchronous random sleeping(ARS) scheme whereby sensors (i) do not need to synchronize with each other, and (ii) do not need to coordinate their sleeping schedules. The stationary coverage probability and the expected coverage periods for ARS are derived. For surveillance application, we derive in addition the detection probability and detection delay distribution. The correctness of our results is validated through extensive simulations. We compare ARS with other synchronous and asynchronous sleeping scheduling algorithms and show that ARS offers better performance in terms of detection delay in the lower duty-cycle regime. We also conduct simulations to demonstrate that our results can be a good approximation for clock drifting case.

Data aggregated maximum lifetime routing for wireless sensor networks

In this paper, we present a data aggregated maximum lifetime routing scheme for wireless sensor networks. We address the problem of jointly optimizing data aggregation and routing so that the network lifetime can be maximized. A recursive smoothing method is adopted to overcome the non-differentiability of the objective function. We derive the necessary and sufficient conditions for achieving the optimality of the optimization problem and design a distributed gradient algorithm accordingly. Extensive simulations are carried out to show that the proposed algorithm can significantly reduce the data traffic and improve the network lifetime. The convergence property of the algorithm is studied under various network configurations.

Channel Assignment and User Association Game in Dense 802.11 Wireless Networks

In densely deployed IEEE 802.11 wireless networks, the transmission delay experienced by a user depends not only on the traffic load of the associated AP, but also the contention level of other APs operating on the same channel. However, due to the random distribution of users and inappropriate allocation of AP channels, the traffic loads of different APs are often uneven, leading to unfair delay experience to different users. In this paper, we consider the problem of channel assignment and user association for balancing the traffic load of APs operating on different channels, which is modeled as a non-cooperative game. We prove the existence of Nash equilibrium (NE) for this game, and derive the price of anarchy and the fairness index at NE. Simulation results are provided to compare the performance of the proposed algorithm with the theoretical bounds.

A Game Theoretical Approach for Load Balancing User Association in 802.11 Wireless Networks

In the multi-cell IEEE 802.11 wireless networks, the traffic loads of access points(APs) are often uneven, which leads to inefficient use of network resources and unfair service to users. To alleviate such imbalance, different user association schemes have been proposed that use different metrics for measuring the congestion level of APs. In this paper, we propose a game theoretical model for the user association problem using the {\it airtime cost} as the congestion metric. The centralized and localized algorithms are designed for achieving the airtime- balancing Nash equilibrium. Simulation results show that the proposed algorithms outperform the existing scheme in terms of fairness and load balance.

Maximum lifetime routing and data aggregation for wireless sensor networks

In this paper we solve the maximum lifetime routing (MLR) problem for a sensor network by joint optimizing routing and data aggregation. We present a smoothing method to overcome the nondifferentiability of the objective function. By exploiting the special structure of the network, we derive the necessary and sufficient conditions to achieve the optimality. Based on these conditions, a gradient descent algorithm is designed for its solution. The proposed algorithm is shown to converge to the optimal value efficiently under all network configurations. The incorporation of optimal routing and data aggregation is shown via many examples to provide significant improvement of the network lifetime.

Robust Topology Engineering in Multiradio Multichannel Wireless Networks

Topology engineering concerns with the problem of automatic determination of physical layer parameters to form a network with desired properties. In this paper, we investigate the joint power control, channel assignment, and radio interface selection for robust provisioning of link bandwidth in infrastructure multiradio multichannel wireless networks in presence of channel variability and external interference. To characterize the logical relationship between spatial contention constraints and transmit power, we formulate the joint power control and radio-channel assignment as a generalized disjunctive programming problem. The generalized Benders decomposition technique is applied for decomposing the radio-channel assignment (combinatorial constraints) and network resource allocation (continuous constraints) so that the problem can be solved efficiently. The proposed algorithm is guaranteed to converge to the optimal solution within a finite number of iterations. We have evaluated our scheme using traces collected from two wireless testbeds and simulation studies in Qualnet. Experiments show that the proposed algorithm is superior to existing schemes in providing larger interference margin, and reducing outage and packet loss probabilities.

A robust relay placement framework for 60GHz mmWave wireless personal area networks

Multimedia streaming applications with stringent QoS requirements in 60GHz mmWave wireless personal area networks (WPANs) demand high rate and low latency data transfer as well as low service disruption. In this paper, we consider the problem of robust relay placement in 60GHz WPANs. Relays forward traffic from transmitter devices to receiver devices facilitating i) the primary communication path for non-line-of-sight (NLOS) transceiver pairs, and ii) secondary (backup) communication path for line-of-sight (LOS) transceiver pairs. We formulate the robust minimum relay placement problem and the robust maximum utility relay placement problem with the objective to minimize the number of relays deployed and maximize the network utility, respectively. Efficient algorithms are developed to solve both problems and have been shown to incur less service disruption in presence of moving subjects that may block the LOS paths in the environment.

Cluster-based cooperative communications and relay selection in wireless networks

In the conventional dual-hop cooperative communications, the relays with imbalanced channel gain to the source and the destination cannot be efficiently utilized since one of these two hops can become the bottleneck of the overall transmission. In this paper, we propose a cluster-based cooperative communication (CBCC) scheme to address this problem. In this scheme, relays are divided into two clusters, and the cooperative transmissions consist of three stages. In this way, the bottleneck between the relay and the source or the destination can be potentially broken through the relay-to-relay transmissions. We focus on the relay selection problem for this cluster-based cooperation scheme, which turns out to be difficult due to the coupling of the relays between two clusters. We then resort to the design of heuristic algorithm and provide simulation results to show the performance of the proposed scheme.