Shun-Te Wang

Survivable and delay-guaranteed backbone wireless mesh network design

Backbone wireless mesh networks (BWMNs) consisting of wireless mesh routers are emerging alternatives to implementations of metropolitan area networks (MANs). In a BWMN, gateways connect to the Internet via wireline links and provide Internet access services for users. Due to the limited wireless channel bit rate, multiple gateways are usually required in a BWMN, which costs budget and takes time to set up. In this paper, we study the network topology design and the gateway arrangement so that the construction cost of a BWMN is minimal. Two algorithms, namely, the Predefined Gateway Set Algorithm (PGSA) and the Self-Constituted Gateway Algorithm (SCGA), are proposed for the BWMN design. A genetic algorithm and a proposed enhanced Djikstras algorithm are employed to search for the low-cost network configuration with constraints such as survivability, link capacity, degree limitation and maximum tolerable delay. Computational results show that the PGSA can give an acceptable network configuration rapidly. In case the gateway cost is high, using the SCGA can lower the network construction cost at the expense of more computational time.

Finding stable routes in mobile ad hoc networks

A mobile ad hoc network (MANET) is an infrastructureless and highly dynamic network. Routes in such a network may fail frequently because of node mobility or other issues. Stability therefore can be an important element in the design of routing protocols. Stable routes, also called long-lived routes, can be discovered and used to reduce the overhead resulted from route maintenance in ad hoc networks. We propose the long-lived route prediction (LRP) scheme to discover stable routes. The LRP scheme is distributed and predicts long-lived routes based on the history of link lifetime. Furthermore, we apply the LRP scheme to both the open area and urban area using simulation. Simulation results show that the LRP scheme can indeed discover stable routes to reduce route rediscovery, and can be much more efficient and scalable.

Support of Efficient Route Discovery in Mobile Ad Hoc Access Networks

SUMMARY The Public Wireless Local Area Network (PWLAN) is an emerging service for wireless access to the Internet. However, the service coverage of the PWLAN is limited by the deployment of access points (APs) because only those who stay near the AP can access the PWLAN. A feasible way of extending the service coverage of a PWLAN is to deploy mobile ad hoc access networks (MAHANs) so that users who are not in an AP’s radio coverage area can send their packets to the AP in a multihop manner. However, in a MAHAN, mobile nodes that intend to access the Internet have to discover routes to the AP first, which may result in considerable bandwidth cost. In this paper, we propose the Appointed BrOadcast (ABO) method to reduce the cost of route discovery in MAHANs. Using the ABO method can achieve this goal on the basis of packet overhearing. Functions that are necessary for network and data link layers to employ the ABO method are also discussed. Simulation results show that using the ABO method can significantly reduce the cost on route discoveries. Due to the widespread use of legacy IEEE 802.11 nodes, the problem of how ABO-enhanced and legacy IEEE 802.11 nodes can coexist in a MAHAN is also discussed.

Software downloading in reconfigurable networks of open wireless architecture using SDR technology

The remarkable advances of practical software-defined radios that use programmable digital devices and radio architectures will enable people with different kinds of equipment running on different frequencies to communicate with one another by proper reconfigurations of their communication devices. In the future fourth-generation mobile communication systems, various access technologies will be integrated into a common platform called the open wireless architecture. SDR technology can be used to implement an OWA system. In a multihop SDR reconfigurable network that follows OWA standards, nodes may be reconfigured while they are working; however, if an error occurs during software dissemination, some nodes may not receive the software correctly, and the network is thus partitioned. Hence, it is very important to ensure that every node in the network can receive the software and update itself correctly. This article proposes a download scheme for real-time software download, application software upgrades, or radio protocol change of wireless nodes in multihop reconfigurable networks. In addition, related enabling hardware techniques are reviewed

Comparison of power saving schemes for sink nodes in wireless sensor networks

We provide an extensive analysis of the MAC state operation for energy conservation and introduce both channel release and setup schemes regarding the uplink data traffic for wireless sensor networks. The introduction of a release timer has already been applied to some power saving schemes in the literature. In this paper, however, an additional release timer is used to let sink nodes go back to inactive state at time-out. Instead of using randomly distributed release timers as in the literature, we use Erlang-k distributed release timers here in order to improve the inaccuracy in the analysis. We find that a longer release time period can be a better design choice for arrival traffics with deterministic packet length.

SABAGAR: A Simple Attribute-Based Addressing and GPS-Aided Routing Protocol for Applications in Wireless Sensor Networks

We propose in this paper a data-centric routing protocol for wireless sensor network applications. This protocol, called SABAGAR, is designed to be implemented easily to provide the basis for commercially successful products, and to await more vendors in wireless products. Sensor nodes may have no global identifications because the number of sensors can be large, hence, attribute-based addressing and broadcast communication paradigm can be used to facilitate data acquisition. However, broadcasting simply by flooding usually results in serious redundancy and endlessly looping packets, and thus degrades the network performance. To deal with this problem, we present a position-vector-based (PVB) algorithm for the SABAGAR protocol. This paper also provides detailed simulation results to support the proposed protocol design.

An adaptation scheme for quick response to fluctuations in IEEE 802.11 link quality

We propose in this paper a cross-layer link adaptation (CLLA) scheme that uses the number of successful transmissions, the number of transmission failures, and the channel information from the physical layer to determine proper transmission parameters for subsequent medium accesses. In order to improve the throughput of a wireless local area network, dynamic link adaptation schemes can be applied so that the signal and protocol parameters can be adjusted as the radio link conditions change, according to the quality of a wireless channel. Receivers signal-to-noise ratio (SNR) and received signal level (RSL) are two critical performance parameters that vary with time due to path loss, shadowing effect, multi-path fading and interference. Hence, according to the SNR and RSL of the latest received frame, a link adaptation scheme can quickly respond to the channel variation and suitably adjust parameters for transmissions. The CLLA scheme lets frames be transmitted at the highest available data rate using proper medium access methods to achieve high throughput. Simulation results show that the CLLA scheme performs well in throughput in practical mobile environments.

A One-Dimensional Probabilistic Model of Wireless Multihop Internet Access

Wireless multihop access networks, where clients can access the Internet through Internet gateways by direct or multihop transmissions, are potential for future wireless data services and vehicular network applications. In the context of multihop transmissions, less number of gateways is required for Internet access while a certain level of Internet connectivity still holds. In this paper, we investigate the Internet connectivity, which is the probability that all clients are Internet-reachable, in one-dimensional multihop wireless access networks. We show the relationship between the Internet connectivity and the deployment of Internet gateways. These results are useful for network operators and service providers to deploy Internet gateways, manage clients, design protocols and develop wireless-based software for future mobile network applications.

Capacity upgrading in mobile ad hoc access networks (MAHANs) using CSMA/CAPA

From recent trends, mobile ad hoc access networks (MAHANs) have attracted high attention to be adopted in future 4G networks. The gateway in a typical MAHAN provides Internet access service for mobile nodes. In order to guarantee ubiquitous Internet accessibility, mobile nodes should cooperate to relay packets for nodes lying behind the radio coverage of the gateway. The carrier sense multiple access with collision avoidance (CSMA/CA) protocol is commonly used as the MAC protocol in ad hoc networks. However, CSMA/CA suffers from contentions and is not suitable for MAHANs where traffic flows are aggregated at the gateway. In this paper, we propose the CSMA protocol with collision avoidance, packing and accompanying (CSMA/CAPA) for MAHANs. The packing scheme allows more packets to be transmitted in a frame while the accompanying scheme allows nodes with more opportunities to transmit their frames. The feasible queueing strategy for CSMA/CAPA protocol is discussed. Simulation results show that CSMA/CAPA can significantly upgrade the capacity of MAHANs even when the channel error rate is high.

Design of a resource advertisement and discovery protocol for large and dense manets

Abstract With remarkable advances in wireless technologies, applications of mobile ad hoc networks will be in widespread use in the near future. Thus, the geographical network environments may become large and dense. In such network environments, a large number of resource discovery queries may be generated when specific resources or services are needed. In order to effectively utilize the limited bandwidth of the networks, and reduce power used by mobile devices, the design for resource discovery protocols should take both the operational cost and the network performance into account. Moreover, the results of resource discoveries may further be used in later route discovery processes of certain ad hoc routing protocols. In this paper we propose a simple resource advertisement and discovery (SRAD) protocol for mobile ad hoc networks. The SRAD protocol self‐organizes a proximity network and works in a fully distributed architecture without centralized control or management to prevent performance bottleneck. In addition, a resource description and management scheme is also devised to share loads among mobile nodes. The simulation results show that the SRAD protocol can achieve the same level of performance as in broadcast‐based protocols while generating fewer transmitted messages in large and dense mobile ad hoc networks.