Fulu Li

Lightweight deployment-aware scheduling for wireless sensor networks

Wireless sensor networks consist of a large number of tiny sensors that have only limited energy supply. One of the major challenges in constructing such networks is to maintain long network lifetime as well as sufficient sensing areas. To achieve this goal, a broadly-used method is to turn off redundant sensors. In this paper, the problem of estimating redundant sensing areas among neighbouring wireless sensors is analysed. We present simple methods to estimate the degree of redundancy without the knowledge of location or directional information. We also provide tight upper and lower bounds on the probability of complete redundancy and on the average partial redundancy. With random sensor deployment, our analysis shows that partial redundancy is more realistic for real applications, as complete redundancy is expensive, requiring up to 11 neighbouring sensors to provide a 90 percent chance of complete redundancy. Based on the analysis, we propose a scalable Lightweight Deployment-Aware Scheduling (LDAS) algorithm, which turns off redundant sensors without using accurate location information. Simulation study demonstrates that the LDAS algorithm can reduce network energy consumption and provide desired QoS requirement effectively.

Analysis on the redundancy of wireless sensor networks

Wireless sensor networks consist of a large number of tiny sensors that have only limited energy supply. One of the major challenges in constructing such networks is to maintain long network lifetime as well as sufficient sensing area. To achieve this goal, a broadly-used method is to turn off redundant sensors. In this paper, the problem of estimating redundant sensing areas among neighbouring wireless sensors is analysed. We present an interesting observation concerning the minimum and maximum number of neighbours that are required to provide complete redundancy and introduce simple methods to estimate the degree of redundancy without the knowledge of location or directional information. We also provide tight upper and lower bounds on the probability of complete redundancy and on the average partial redundancy. With random sensor deployment, our analysis shows that partial redundancy is more realistic for real applications, as complete redundancy is expensive, requiring up to 11 neighbouring sensors to provide a 90 percent chance of complete redundancy. Our results can be utilised in designing effective sensor scheduling algorithms to reduce energy consumption and in the mean time maintain a reasonable sensing area.

Energy-efficient cooperative routing in multi-hop wireless ad hoc networks

We study the routing problem for multi-hop wireless ad hoc networks based on cooperative transmission. We prove that the minimum energy cooperative path (MECP) routing problem, i.e., using cooperative radio transmission to find the best route with the minimum energy cost from a source node to a destination node, is NP-complete. We thus propose a cooperative shortest path (CSP) algorithm that uses the Dijkstras algorithm as the basic building block and reflects the cooperative transmission properties in the relaxation procedure. Simulation results show that with more nodes added in the network, our approach achieves more energy saving compared to traditional non-cooperative shortest path algorithms. Another interesting observation is that the proposed algorithm achieves better fairness among different nodes with denser networks. Implementation issues are also discussed

Minimum Energy Cooperative Path Routing in Wireless Networks: An Integer Programming Formulation

We study the problem of minimum energy cooperative path (MECP) routing in wireless networks. The joint problem of cooperative routing in wireless networks that combines route selection and the transmit diversity was recently presented in A. Khandani et al. (2003). Several heuristic algorithms were also proposed in A. Khandani et al. (2003) to approximate the minimum energy cooperative path, while it has not been possible to judge the quality of the solutions with respect to the optimal. In this paper, we present an integer programming formulation of the MECP problem towards an optimal solution for a network where the locations of the nodes are known a priori and fixed

Minimum energy cooperative path routing in all-wireless networks: NP-completeness and heuristic algorithms

We study the routing problem in all-wireless networks based on cooperative transmissions. We model the minimum-energy cooperative path (MECP) problem and prove that this problem is NP-complete. We hence design an approximation algorithm called cooperative shortest path (CSP) algorithm that uses Dijkstras algorithm as the basic building block and utilizes cooperative transmissions in the relaxation procedure. Compared with traditional non-cooperative shortest path algorithms, the CSP algorithm can achieve a higher energy saving and better balanced energy consumption among network nodes, especially when the network is in large scale. The nice features lead to a unique, scalable routing scheme that changes the high network density from the curse of congestion to the blessing of cooperative transmissions.

A networking perspective of cooperative spectrum sharing in wireless networks: Analysis and experiments

In this paper, we present a networking perspective of cooperative spectrum sharing in wireless networks. For unlicensed band like WiFi, e.g., 2.4 GHz, it is particularly critical that network nodes share the same spectrum cooperatively and efficiently. We discuss several cooperative techniques for spectrum sharing in wireless networks including strategies to cooperatively reduce the transmitting power, and approaches to cooperatively reduce transmission interference. We also formulate the spectrum sharing problem as a cooperative game. Finally, we conduct extensive experiments to demonstrate techniques and phenomena for cooperative spectrum sharing in wireless networks. In one set of experiments, we demonstrate the wireless broadcast advantage (WBA) by attaching radio modules to cameras, in which automatic photography synchronization is achieved among a group of cameras wirelessly. In another set of experiments, we show that TV band can be shared with commodity network nodes cooperatively.

Information processing for live photo mosaic with a group of wireless image sensors

Photo tourism [11] is a platform that allows users to transform unstructured online digital photos into a 3D experience. Nowadays, image sensors are being extensively used to allow images to be taken automatically and remotely, which facilitates the opportunity for live update of photo mosaics. In this paper, we present a novel framework for live photo mosaic with a group of wireless image sensor nodes, where the image data aggregation is accomplished in an efficient and distributed way. Essentially, we propose to conduct clustering and data compression at wireless image sensor network level while conserving the completeness of the feature point information [9] for reconstruction. Toward the realization of the whole system, we have built image sensor prototypes with commodity cameras and we validated our approach by indepth analysis, extensive simulations and field experiments.

Collaborative storage with mobile devices in wireless networks for P2P media sharing

Information storage and storage sharing are key components of modern networked computer systems. Mobile devices such as PDAs and cell phones normally have very limited storage capacities compared with PCs or laptops, while storing a large number of media objects (such as e-books, pictures and videos, etc.) on mobile devices could take a lot of space. In this paper, we study collaborative storage with mobile devices, where contributory storage infrastructure is constructed among a group of mobile devices for P2P (peer-to-peer) media sharing. We analyze the design tradeoffs of the collaborative storage system with mobile devices via concrete application examples in different settings. In this study, we focus on two main performance metrics: (1) the availability rate for a stored data object in the collaborative storage system when a peer node tries to access the given item, and (2) the uploading and retrieval delay for a stored data object of different sizes in a variety of circumstances. We experimentally verify the performance and feasibility of the constructed prototype of a shared e-library with a collection of e-books, pictures and videos based upon the paradigm of collaborative storage with mobile devices.

NASC: Network-Aware Source Coding for Wireless Broadcast Channels with Multiple Sources

In this paper, we present a network-aware source coding (NASC) approach for wireless broadcast channels with multiple sources. The proposed NSAC approach takes into account the information of the network topology during the source coding process and the cross-layer design approach may be beneficial for wireless networks. We derive the optimal bounds using network-aware source coding in wireless networks for two scenarios: the minimization of the total traffic load and the minimization of the total required energy. Implementation issues are also discussed.

Analysis on errors due to photon noise and quantization process with multiple images

In the scenes with deflective and/or reflective medium such as fogs or mirrors, where the contrast levels among the intensity values of the pixels in the image are very small, even a small estimation improvement on the intensity value of each pixel could make a big difference for the perceptual quality of the final image if we want to subtract the interference components from the original image. In this paper we analyze the average quantization error, total error and photon noise from multiple images with fixed and varied exposure time. We observe that by properly controlling and varying exposure time with multiple images, one can obtain an image with better performance than that of the conventional wisdom, where multiple images are taken repeatedly with the same exposure time.