Guihai Chen

An unequal cluster-based routing protocol in wireless sensor networks

Clustering provides an effective method for prolonging the lifetime of a wireless sensor network. Current clustering algorithms usually utilize two techniques; selecting cluster heads with more residual energy, and rotating cluster heads periodically to distribute the energy consumption among nodes in each cluster and extend the network lifetime. However, they rarely consider the hot spot problem in multihop sensor networks. When cluster heads cooperate with each other to forward their data to the base station, the cluster heads closer to the base station are burdened with heavier relay traffic and tend to die much faster, leaving areas of the network uncovered and causing network partitions. To mitigate the hot spot problem, we propose an Unequal Cluster-based Routing (UCR) protocol. It groups the nodes into clusters of unequal sizes. Cluster heads closer to the base station have smaller cluster sizes than those farther from the base station, thus they can preserve some energy for the inter-cluster data forwarding. A greedy geographic and energy-aware routing protocol is designed for the inter-cluster communication, which considers the tradeoff between the energy cost of relay paths and the residual energy of relay nodes. Simulation results show that UCR mitigates the hot spot problem and achieves an obvious improvement on the network lifetime.

An energy-aware routing protocol in wireless sensor networks.

The most important issue that must be solved in designing a data gathering algorithm for wireless sensor networks (WSNS) is how to save sensor node energy while meeting the needs of applications/users. In this paper, we propose a novel energy-aware routing protocol (EAP) for a long-lived sensor network. EAP achieves a good performance in terms of lifetime by minimizing energy consumption for in-network communications and balancing the energy load among all the nodes. EAP introduces a new clustering parameter for cluster head election, which can better handle the heterogeneous energy capacities. Furthermore, it also introduces a simple but efficient approach, namely, intra-cluster coverage to cope with the area coverage problem. We use a simple temperature sensing application to evaluate the performance of EAP and results show that our protocol significantly outperforms LEACH and HEED in terms of network lifetime and the amount of data gathered.

Coding-Aware Multi-path Routing in Multi-Hop Wireless Networks

To overcome the inherent lossy property of wireless links and increase network throughput, many multi-path routing protocols have been proposed to improve the reliability and latency of packet delivery in wireless networks. Multi-path routing protocols, however, do not take advantage of existing coding opportunities to maximize network throughput. In this paper, we propose a novel coding-aware multi-path routing protocol (CAMP), which forwards packets over multiple paths dynamically based on path reliability and coding opportunity. CAMP employs a route discovery mechanism which returns to the source multiple paths along with ETX (Expected Transmission Count) of all links on each path. Using a novel forwarding mechanism, CAMP splits the traffic among multiple paths and actively creates instead of passively waiting for coding opportunity by switching its path to maximize the switching gain. Experimental results demonstrate that CAMP can achieve much higher throughput than comparable schemes for delivering packets in wireless networks.

A Mobility Prediction-Based Adaptive Data Gathering Protocol for Delay Tolerant Mobile Sensor Network

The basic operation of delay tolerant mobile sensor network (DTMSN) is for pervasive data gathering in networks with intermittent connectivity, where traditional data gathering methods can not be applied. In this paper, an efficient mobility prediction-based adaptive data gathering protocol (MPAD) based on the random waypoint mobility model tailored for DTMSN is proposed. In MPAD, a node independently makes decision to replicate messages and send them to the neighbor sensor nodes with a higher probability of meeting the sink node. MPAD consists of two components for data transmission and queue management. Data transmission makes decisions on when and where to transmit data messages according to the node delivery probability, and the queue management employs the message survival time to decide whether the message should be transmitted or dropped for minimizing the transmission overhead. Simulation results show that the proposed MPAD achieves the longer network lifetime and the higher message delivery ratio with the lower transmission overhead and data delivery delay than some other previous solutions designed for DTMSN, such as direct transmission, flooding and message fault tolerance-based data delivery protocol (FAD).

Towards Location-aware Topology in both Unstructured and Structured P2P Systems

A self-organizing peer-to-peer system is built upon an application level overlay, whose topology is independent of underlying physical network. A well-routed message path in such systems may result in a long delay and excessive traffic due to the mismatch between logical and physical networks. In order to solve this problem, we present a family of Peer-exchange Routing Optimization Protocols (PROP) to reconstruct the overlay. It includes two policies: PROP- G for generic condition and PROP-0 for optimized one. Both theoretical analysis and simulation experiments show that these two protocols greatly reduce the average latency of the overlay and achieve a location-aware topology with low overhead. Their overall performance can be further improved if combined with other recent approaches. Specifically, PROP-G can be easily applied to both structured and unstructured systems without the loss of their primary characteristics, such as efficient routing and anonymity. PROP- O, on the other hand, is more efficient, especially in a heterogeneous environment where nodes have different processing capabilities.

Redundancy schemes for high availability in DHTs

High availability in peer-to-peer DHTs requires data redundancy. This paper takes user download behavior into account to evaluate redundancy schemes in data storage and share systems. Furthermore, we propose a hybrid redundancy scheme of replication and erasure coding. Experiment results show that replication scheme saves more bandwidth than erasure coding scheme, although it requires more storage space, when average node availability is higher than 48%. Our hybrid scheme saves more maintenance bandwidth with acceptable redundancy factor.

Cycloid: a constant-degree and lookup-efficient P2P overlay network

Summary form only given. There are many structured P2P systems that use DHT technologies to map data items onto the nodes in various ways for scalable routing and location. Most of the systems require O(logn) hops per lookup request with O(logn) neighbors per node, where n is the network size. We present a constant-degree P2P architecture, namely Cycloid, which emulates a cube-connected-cycles (CCC) graph in the routing of lookup requests. It achieves a time complexity of O(d) per lookup request by using O(1) neighbors per node, where n = d/spl middot/ 2/sup d/. We compare Cycloid with other two constant-degree systems, Viceroy and Koorde in various architectural aspects via simulation. Simulation results show that Cycloid has more advantages for large scale and dynamic systems that have frequent node arrivals and departures. In particular, Cycloid delivers a higher location efficiency in the average case and exhibits a more balanced distribution of keys and query loads between the nodes.

ContinuStreaming: Achieving high playback continuity of Gossip-based Peer-to-Peer streaming

Gossip-based peer-to-peer (P2P) streaming has been proved to be an effective and resilient method to stream qualified media contents in dynamic and heterogeneous network environments. Because of the intrinsic randomness of gossiping, some data segments cannot be disseminated to every node in time, which seriously affects the media playback continuity. In this paper we describe the design of ContinuStreaming, a gossip-based P2P streaming system which can maintain high resilience and low overhead while bring a novel and critical property - full coverage of the data dissemination. With the help of DHT, data segments which are likely to be missed by the gossip-based data scheduling can be quickly fetched by the on-demand data retrieval so as to guarantee continuous playback. We discuss the results of both theoretical analysis and comprehensive simulations on various real-trace overlay topologies to demonstrate the effectiveness of our system. Simulation results show that ContinuStreaming outperforms the existing representative gossip-based P2P streaming systems by increasing the playback continuity very close to 1.0 with only 4% or less extra overhead.

Survive under high churn in structured P2P systems: evaluation and strategy

In Peer to Peer (P2P) systems, peers can join and leave the network whenever they want. Such “freedom” causes unpredictable network environment which leads to the most complex design challenge of a p2p protocol: how to make p2p service available under churn? What is more, where is the extreme of a system’s resistibility to high churn? A careful evaluation of some typical peer-to-peer networks will contribute a lot to choosing, using and designing a certain kind of protocol in special applications. In this paper we analyze the performance of Chord [1], Tapestry [2], Kelips [3], Kademlia [4] and Koorde [5], then find out the crash point [6] of each network based on the simulation experiment. Finally, we propose a novel way to help nodes survive under high churn.

CFP: Integration of Fountain Codes and Optimal Probabilistic Forwarding in DTNs

There has been much research focusing on the routing problem in delay tolerant networks (DTNs). Much of the work has mainly focused on coding schemes for message distribution, while other work has been done on the probabilistic forwarding. Coding schemes achieve higher delivery rate via redundancy before forwarding, while probabilistic forwarding efficiently limits the abuse of the store and forward scheme, maintaining relatively high performance. Providing a reliable and efficient forwarding scheme proves to be challenging as coding and forwarding schemes should be jointly considered. In our paper, we present an optimal probabilistic forwarding scheme using fountain code, which we name as CFP (Coded Forwarding Protocol), where reliability and efficiency can be achieved at the same time. In CFP, We use fountain codes to encode messages and provide the forwarding rule to decide whether to forward messages to another node. The probabilistic forwarding problem is modeled as an optimal stopping problem, and our forwarding rule also considers the influence of fountain codes. We perform trace-driven simulations and compare CFP with other protocols. Simulation results show that, considering the delivery rate, delay, and number of forwardings, CFP performs better than other implemented protocols - Epidemic, which is the most original protocol, and OPF, which represents the optimal probabilistic forwarding protocol - in our simulation.