Wei Kuang Lai

Adaptive backup routing for ad-hoc networks

The network topology changes frequently in ad-hoc networks. Some on-demand protocols with multi-paths or backup routes have been proposed to improve the performance in ad-hoc networks. AODV-BR scheme improves AODV routing protocols by constructing a mesh structure and providing multiple alternate routes. The algorithm establishes the mesh and multi-path using the RREP of AODV, which does not transmit many control messages. In this paper, we propose two schemes: AODV-ABR and AODV-ABL to increase the adaptation of routing protocols to topology changes by modifying AODV-BR. In AODV-ABR, the alternative route can be created by overhearing not only RREP packets but also data packets. AODV-ABL combines the benefits of AODV-ABR and Local repair. Finally, we evaluate the performance improvement by simulations.

Channel assignment for initial and handoff calls to improve the call-completion probability

The paper focuses on how to assign channels for initial and handoff calls. Previous schemes give priority to handoff calls by queuing handoff calls, reserving some channels for handoff calls, or subrating existing calls for handoff calls. We queue both initial and handoff calls. We take this idea from derivations of the optimal value for an approximation to the call-completion probability. Our goal is to have higher call-completion probability and still keep forced-termination probability low. We propose four schemes: SFTT (single-queue, FIFO, timeout, average timeout), SPTT (single-queue, priority, timeout, average timeout), DFTS (dual-queues, FIFO, timeout, statistical TDM), and DPTS (dual-queues, priority, timeout, statistical TDM). The four schemes, along with the NPS and FIFO schemes, were simulated and compared. For the SFTT scheme, we also simulated different average timeouts for initial calls. All four proposed schemes have better call-completion probabilities than the NPS and FIFO schemes. Call-completion probabilities can be improved by implementing a priority scheme which serves the waiting call with the least remaining time first. The implementation of statistical multiplexing also has the effect of increasing call-completion probability when the average new-call arrival rates are high. However, both the priority scheme and statistical multiplexing may increase forced-termination probability.

Application of support vector machines to bandwidth reservation in sectored cellular communications

Many mechanisms based on bandwidth reservation have been proposed in the literature to decrease connection dropping probability for handoffs in cellular communications. The handoff events occur at a much higher rate in sectored cellular networks than in traditional cellular systems. An efficient bandwidth reservation mechanism for the neighboring cells is therefore critical in the process of handoff during the connection of multimedia calls to avoid the unwillingly forced termination and waste of limited bandwidth in the sectored cellular communications, particularly when the handoff traffic is heavy. In this paper, a self-adaptive bandwidth reservation scheme, which adopts support vector machines technique, is proposed to reduce the forced termination probability. Meanwhile, a channel-borrowing technique is used to decrease the new call-blocking probability of real-time traffic. The simulation results show that the proposed scheme can achieve superior performance than the representative bandwidth-reserving schemes in sectored cellular networks in the literature when performance metrics are measured in terms of the forced termination probability and the new call- blocking probability.

A self-adaptive zone routing protocol for Bluetooth scatternets

This work presents a routing protocol that utilizes the characteristics of Bluetooth technology for Bluetooth-based mobile ad hoc networks. The routing tables are maintained in the master devices, and the routing zone radius for each table is adjusted dynamically via a fuzzy inference system. Given that some useless routing packets exist which increase the network loads in the existing ad hoc routing protocols, this work selectively employs multiple unicasts or a single broadcast when the destination device moves beyond the routing zone radius coverage of the routing table. The simulation results demonstrate that the dynamic adjustment of the routing table size in each master device results in considerably faster routing request reply time, as well as fewer request packets and useless packets compared with two representative protocols, Zone Routing Protocol (ZRP) and Dynamic Source Routing.

Bus Assisted Connectionless Routing Protocol for Metropolitan VANET

The rapid development of the wireless communications lets more and more people are used to access network services via various wireless technologies. Users expect the ubiquitous network environments to acquire information they needed anytime and anywhere. How to provide an efficient routing protocol is one of major challenges in VANETs to improve the performance in terms of packet delivery ratio, end-to-end delay with less control overheads. In this paper, we propose two schemes: (1) The footmark leaving scheme. It can pursue the target vehicle automatically in compliance with its moving trajectory without route recalculation and the aid of GPS during transmission. It only maintains a table of passed vehicles in each road segment to efficiently seek out target vehicles. (2) The bus-assisted transmission protocol. By benefiting from the predictability and regularity of buses, packets can be transmitted by switching between common vehicles and buses so that routes would be more feasible and scalable. It can greatly improve the reliability of transmitting packets in VANET.

Adaptive resource reservation schemes for proportional DiffServ enabled fourth-generation mobile communications system

Many mechanisms based on bandwidth reservation have been proposed in the literature to decrease connection dropping probability for handoffs in cellular communications. The handoff events occur at a much higher rate in packet-switched fourth generation mobile communication networks than in traditional cellular systems. An efficient bandwidth reservation mechanism for the neighboring cells is therefore critical in the process of handoff during the connection of multimedia calls to avoid the unwillingly forced termination and waste of limited bandwidth in fourth generation mobile communication networks, particularly when the handoff traffic is heavy. In this paper, two self-adaptive bandwidth reservation schemes, which adopt support vector regression and swarm intelligence techniques, respectively, are proposed to reduce the forced termination probability of multimedia handoffs. Meanwhile, a proportional differentiated service model is incorporated into our schemes to accommodate new metrics used in processing handoffs in next generation networks. The simulation results show that both the proposed schemes can achieve superior performance than the representative bandwidth-reserving schemes in the literature when performance metrics are measured in terms of the forced termination probability for the handoffs, the call blocking probability for the new connections and bandwidth utilization.

A flow control scheme on ATM networks with max-min fairness

Asynchronous Transfer Mode does not guarantee Quality of Service for Available Bit Rate (ABR) service type during connection establishment. The remaining bandwidth for ABR traffics varies. Without adequate flow control, congestion can cause the degradation of network performance. In this article, we propose an Explicit Rate calculating Algorithm with Max-Min fairness (ERAMM) for rate-based flow control. From analysis and simulation results, we know the ERAMM has the advantages of fast convergence, low oscillations, little parameter sensitivity, and high link bandwidth utilization with less buffer requirements.

Improving handover performance by switching between unicast and multicast addressing

With increased popularity and pervasiveness, mobile networking has become a definite trend for future networks. Users strongly demand that the connectivity of ongoing services be retained while roaming across different points of attachment. Efficient handover schemes are essential to the aforementioned vision. However, there are time-consuming procedures in the process. Various research has been devoted to the acceleration of movement detection and registration. However, a time-consuming operation, i.e., duplicate-address detection (DAD), was overlooked by most studies. One novel scheme that features anycast technique is developed and presented in this paper. The proposed approach switches to anycast addressing during handover and switches back to normal unicast addressing after all required operations are completed. By switching to anycast addressing, a mobile node can continue the reception of packets from its corresponding node before its new care-of address is actually validated. Thus, transmission disruption can effectively be minimized. In addition, a simple but effective buffer-control scheme is designed to reduce possible packet loss and prevent the out-of-order problem. Analytical study reveals that improved performance can be guaranteed, as reflected in the simulation results.

A Dynamic Alternate Path QoS Enabled Routing Scheme in Mobile Ad hoc Networks

A mobile ad hoc network (MANET) is a collection of self-organized mobile nodes that are capable of communicating with each other without the aid of any established infrastructure or centralized administration. Routing algorithm has been a challenge task in the wireless ad hoc network for a long time due to the dynamic nature of network topology. A recent trend in ad hoc network routing is the reactive on-demand philosophy where routes are established only when required. The on-demand routing protocol for ad hoc network is appealing because of its low routing overhead and its effectiveness when the frequency of route re-establishment and the demand of route queries are not high. However, considering the increasing demand of Quality-of-Service (QoS) requirements in many applications, the current on-demand routing protocols used for ad-hoc network should be adapted appropriately to effectively meet the stringent QoS requirements of specific multimedia traffic. We thus propose a routing protocol which tries its best to satisfy QoS requirements of specific multimedia traffic in the volatile environments of a MANET. The results of a series of simulations exhibit the practicability and feasibility of our approaches.

A cluster-based routing protocol for wireless sensor networks with adjustable cluster size

A cluster-based routing scheme for wireless sensor networks featuring adjustable cluster size is proposed in this article. Aimed at the reduction of power consumption, the proposed scheme is designed to adjust cluster sizes on the fly such that communication loads can be evenly shared by individual nodes, and consequently extend the lifetime of an entire sensor network. In the proposed scheme, named ACRP, sensor nodes form clusters automatically. Cluster heads assign time slots to sensor nodes for data transmission. Cluster heads then aggregate received data and forward them to the base station along established routing paths. In particular, based on received cluster information, the base station periodically adjusts the cluster membership of sensor nodes such that each clusters have comparable size, and pick up new head with most residual energy for each cluster. By doing so, the communication load can be shared by participant nodes and the data transmission schedules for each cluster will have similar duration. Both contribute to faster data transmission and extended lifetime for wireless sensor networks. Simulation result reveals that the proposed scheme is effective and outperforms the well-known LEACH in most scenarios.