Pi-Chung Wang

A Reliable Transmission Protocol for ZigBee-Based Wireless Patient Monitoring

Patient monitoring systems are gaining their importance as the fast-growing global elderly population increases demands for caretaking. These systems use wireless technologies to transmit vital signs for medical evaluation. In a multihop ZigBee network, the existing systems usually use broadcast or multicast schemes to increase the reliability of signals transmission; however, both the schemes lead to significantly higher network traffic and end-to-end transmission delay. In this paper, we present a reliable transmission protocol based on anycast routing for wireless patient monitoring. Our scheme automatically selects the closest data receiver in an anycast group as a destination to reduce the transmission latency as well as the control overhead. The new protocol also shortens the latency of path recovery by initiating route recovery from the intermediate routers of the original path. On the basis of a reliable transmission scheme, we implement a ZigBee device for fall monitoring, which integrates fall detection, indoor positioning, and ECG monitoring. When the triaxial accelerometer of the device detects a fall, the current position of the patient is transmitted to an emergency center through a ZigBee network. In order to clarify the situation of the fallen patient, 4-s ECG signals are also transmitted. Our transmission scheme ensures the successful transmission of these critical messages. The experimental results show that our scheme is fast and reliable. We also demonstrate that our devices can seamlessly integrate with the next generation technology of wireless wide area network, worldwide interoperability for microwave access, to achieve real-time patient monitoring.

A memory-efficient Huffman decoding algorithm

To reduce the memory size and fasten the process of searching for a symbol in a Huffman tree, we exploit the property of the encoded symbols and propose a memory-efficient data structure to represent the Huffman tree, which uses memory nd bits, where n is the number of source symbols and d is the depth of the Huffman tree. Based on the proposed data structure, we present an O(log n)-time Huffman decoding algorithm. An adaptive version for single-side growing Huffman tree is also addressed. This version could improve the average performance from log n to /spl Sigma//sub i//sup n//spl lceil/i/(h - 1)/spl rceil/ /spl times/ w/sub i/log h//spl Sigma/w/sub i/, where w/sub i/ is the frequency for i/sub th/ symbol and h is a pre-defined value.

Tcam-based multi-match packet classification using multidimensional rule layering

Ternary content addressable memory (TCAM) has superior performance for single-match packet classification but not the case for multi-match packet classification. The limitation is caused by TCAM architecture that reports only the first matching rule. To cope with the limitation, previous algorithms use extra TCAM entries or accesses, or both, to fulfill multi-match packet classification. These algorithms also reorder rules; thus, a multi-match classifier based on these algorithms cannot maintain performance for single-match packet classification. In other words, all matching rules must be yielded to determine the highest priority matching rule. In this paper, we present a TCAM-based scheme for multi-match packet classification without single-match penalty. Our scheme partitions a rule set based on range layering, which can be applied to achieve range encoding. The rule partitioning generates rule subsets which satisfy that the rules in a subset are mutually disjoint. Each rule is then tagged a bitmap for subset identification to fulfill multi-match packet classification. Two approaches, loose coupling and tight coupling, are derived with different search procedures while incorporating range encoding. Both approaches can maintain original rule order, but with different performance tradeoff. We also present a refinement which uses all available TCAM entries to improve the performance of multi-match packet classification. The experimental results show that combining range encoding with multi-match packet classification has advantages of storage efficiency and speed superiority. The capability of supporting single-match packet classification also provides better flexibility of applying different packet actions.

Shortcut Anycast Tree Routing in MANETs

In hierarchical tree-based routing for service discovery in a MANET, all routes form a tree infrastructure. Therefore, the transmitted packets from a node may go up to the tree root and down to the leaf node. The routing overhead of the tree-based routing algorithm cannot be avoided if the packet forwarding is based on parent-child relationships, even the destination node may be located near the source node. In order to improve such problem, each node should consider its neighbor nodes as next hop nodes in their routing tables. In this work, we present a shortcut any cast tree routing in MANETs. We minimize control overhead by establishing the routing tables only for certain nodes on an any cast tree. Our scheme can reduce the volume of query messages as well as the reply messages. It also reduces the transmission latency. We also improve the information accuracy of the routing tables by periodically transmitting update messages. The simulation results show that the performance of our shortcut any cast tree routing algorithm is fast and efficient for MANETs.

Performance enhancement of XCP for high bandwidth-delay product networks

It has been demonstrated that as the per-flow product of bandwidth delay increases, TCP becomes inefficient and unstable, regardless of the queuing discipline. By decoupling utilization control from fairness control, the explicit control protocol (XCP) outperforms TCP in both conventional and high bandwidth-delay environments. In this article, we present an efficient flow control scheme based on XCP for high bandwidth-delay product networks. It can shorten the response time and improve the performance of XCP. Simulation results show the effectiveness of our proposed scheme in several performance aspects. Moreover, its implementation is simple enough to fulfill the required criteria of high bandwidth-delay product networks

A New Service Level Agreement Model for Best-Effort Traffics in IP over WDM

In this paper, we propose a new SLA model for best effort IP traffic over WDM networks. This model jointly considers two QoS metrics, workable traffic volume and availability, as SLA parameters. We devise an algorithm of integer programming to minimize operation cost for the incremental traffic.

A scalable hardware solution for packet classification

One of interesting hardware solutions proposed to solve the packet classification problem is bit-vector algorithm. Different from other hardware solutions such as ternary CAM, it efficiently utilizes the memories to achieve an excellent performance in medium size policy database; however, it cannot scale up with the policy number increases. In this paper, we proposed an improved bit-vector algorithm named bit vector condensation, which can be adapted to large policy databases. Experiments showed that our proposed algorithm drastically improves in the storage requirements and search speed as compared to the original algorithm

Performance improvement of vector quantization by using threshold

Vector quantization (VQ) is an elementary technique for image compression. However, the complexity of searching the nearest codeword in a codebook is time-consuming. In this work, we improve the performance of VQ by adopting the concept of THRESHOLD. Our concept utilizes the positional information to represent the geometric relation within codewords. With the new concept, the lookup procedure only need to calculate Euclidean distance for codewords which are within the threshold, thus sifts candidate codewords easily. Our scheme is simple and suitable for hardware implementation. Moreover, the scheme is a plug-in which can cooperate with existing schemes to further fasten search speed. The effectiveness of the proposed scheme is further demonstrated through experiments. In the experimental results, the proposed scheme can reduce 64% computation with only an extra storage of 512 bytes.

Fast hierarchical FLP model for VoD server deployment

Video on demand (VoD) is an important service for the next generation networks. In the VoD servers. it is not efficient to preserve all copies of videos. The videos could be divided into the popular ones and less popular ones according to their playing ratios. Since the popular videos are accessed frequently, they should be placed on every server, the cache server. Oppositely, the unpopular one are placed on the central server. In this work, we propose a detailed mathematical model for the hierarchical facility location problem (FLP) encountered in the cache/central server deployment. A linear model for hierarchical FLP is presented and could obtain the feasible solution easily. The experimental results demonstrate the effectiveness.

A hybrid MAC protocol for wireless sensor networks

Energy efficiency is an important issue for wireless sensor networks (WSNs). A MAC protocol for WSNs may tolerate higher packet latency in order for minimizing energy consumption, but such a MAC protocol may not accommodate real-time applications. In this paper, we present a hybrid MAC protocol that minimizes both energy consumption and packet latency simultaneously. The protocol utilizes a cross-layer approach that dynamically switches the MAC behavior between TDMA and CSMA based on the routing information of AODV. The nodes which are not involved in data transmission are kept in TDMA mode to minimize their energy consumption. When a node receives a routing request message, it switches to CSMA mode for receiving subsequent data packets promptly. We evaluate the performance of our protocol with various network density. The simulation results show that our protocol can improve both energy efficiency and packet latency of WSNs.