Shih-Lin Wu

A Multi-channel MAC Protocol with Power Control for Multi-hop Mobile Ad Hoc Networks

1Department of Electrical Engineering, Chang Gung University, Tao-Yuan, 333, Taiwan 2Department of Computer Science and Information Engineering, National Chiao-Tung University, Hsin-Chu, 300, Taiwan 3Department of Computer Science and Information Engineering, National Central University, Chung-Li, 32054, Taiwan Email: slwu@mail.cgu.edu.tw, yctseng@csie.nctu.edu.tw, neel@csie.ncu.edu.tw, sheujp@csie.ncu.edu.tw

Intelligent medium access for mobile ad hoc networks with busy tones and power control

In mobile ad hoc networks (MANETs), one essential issue is how to increase channel utilization while avoiding the hidden-terminal and the exposed-terminal problems. Several MAC protocols, such as RTS/CTS-based and busy-tone-based schemes, have been proposed to alleviate these problems. In this paper, we explore the possibility of combining the concept of power control with the RTS/CTS-based and busy-tone-based protocols to further increase channel utilization. A sender will use an appropriate power level to transmit its packets so as to increase the possibility of channel reuse. The possibility of using discrete, instead of continuous, power levels is also discussed. Through analyses and simulations, we demonstrate the advantage of our new MAC protocol. This, together with the extra benefits such as saving battery energy and reducing cochannel interference, does show a promising direction to enhance the performance of MANETs.

Location awareness in ad hoc wireless mobile networks

Networks composed of dynamically repositioning mobile hosts require location awareness to provide new geographic services and to maximize routing efficiency and quality of service. Because wireless networks can operate in a 3D physical environment, exploiting mobile hosts location information is both natural and inevitable. Emerging geographic services based on mobile ad-hoc networks (manets) must confront several challenges, including how to increase positioning accuracy and how to establish a connection from location information to the vast body of Web data, as in a tour-guide system for example.

A priority MAC protocol to support real-time traffic in ad hoc networks

Carrier sense multiple access and its variants have been widely used in mobile ad hoc networks. However, most existing access mechanisms cannot guarantee quality for real-time traffic. This paper presents a distributed medium access control protocol that provides multiple priority levels for stations to compete for the wireless channel. One common channel is assumed to be shared by all stations. Stations are assumed to be able to hear each other (i.e., the network is fully connected). The channel is accessed by stations according to their priorities, and for stations with the same priority, they send frames in a round robin manner. The channel access procedure is divided into three stages: priorities classification period, ID initialization period, and transmission period. Simulation results indicate that our protocol provides high channel utilization and bounded delays for real-time frames.

Code placement and replacement strategies for wideband CDMA OVSF code tree management

The use of OVSF codes in WCDMA systems has offered opportunities to provide variable data rates to flexibly support applications with different bandwidth requirements. Two rarely addressed issues in such environments are the code placement problem and code replacement problem. The former may have significant impact on code utilization and thus code blocking probability, while the latter may affect the code reassignment cost if dynamic code assignment is to be conducted. The general objective is to make the OVSF code tree as compact as possible in order to support new calls, either with less blocking or with less reassignment cost. This paper is perhaps the first one which addresses these issues in WCDMA. Three simple strategies, which can be adopted by both code placement and code replacement, are proposed: random, leftmost, and crowded-first. Among them the crowded-first strategy looks most promising, which is shown to be able to reduce, for example, the code blocking probability by 77% and the number of reassignments by 81% as opposed to the random strategy when the system is 80% fully loaded and the max SF=256.

A multi-channel MAC protocol with power control for multi-hop mobile ad hoc networks

In a mobile ad-hoc networks (MANET), one essential issue is medium access control (MAC) which addresses how to utilize the radio spectrum efficiently and to resolve potential contention and collision among mobile hosts on using the medium. Existing work is dedicated to using multiple channels and power control to improve the performance of MANET. We investigate the possibility of bringing the concepts of power control and multi-channel medium access together in the MAC design problem in a MANET. Existing protocols only address one of these issues independently. The proposed protocol is characterized by the following features: it follows an on-demand style to assign channels to mobile hosts; the number of channels required is independent of the network topology and degree; it flexibly adapts to host mobility; no form of clock synchronization is required; and power control is used to exploit frequency reuse. Power control may also extend battery life and reduce signal interference, both of which are important in wireless communication. Through simulations, we demonstrate the advantage of our new protocol.

Route Maintenance in a Wireless Mobile Ad Hoc Network

A mobile ad-hoc network (MANET) is formed by a cluster of mobile hosts, without the infrastructure of base stations. To deal with the dynamic changing topology of a MANET, many routing protocols have been proposed. In this paper, we consider the route maintenance problem, which includes two parts: route deterioration and route breakage. In a MANET, a route may suddenly become broken because only one host roams away. Even if a route remains connected, it may become worse due to host mobility or a better route newly being formed in the system. Existing protocols, however, will stick with a fixed route once it is discovered, until it is expired or broken. In this paper, we show how to enhance several existing protocols with route optimization and local route recovery capability. So the routing paths can be adjusted on-the-fly while they are still being used for delivering packets and can be patched in minimum wireless bandwidth and delay while route errors occur.

Increasing the throughput of multihop packet radio networks with power adjustment

The packet radio network (PRN) is an attractive architecture to support mobile and wireless communication. Although the code assignment problem has been studied extensively on PRN, we observe that the power control problem has been ignored by most works, but may have significant impact on performance. By power control, we mean that the transmission ranges of stations are tunable. We show, given a PRN in which each host already received a code, how to adjust the powers of stations to control/improve the topology of the PRN without violating the original code assignment. Several schemes are proposed. Through simulations, we demonstrate that although the code assignment problem is NP-complete and thus computationally very expensive, using our power adjustment schemes can easily improve the network performance by about 20% with polynomial costs.

Dynamic channel allocation with location awareness for multi-hop mobile ad hoc networks

The wireless mobile ad hoc network (MANET) has received a lot of attention recently. This paper considers the channel assignment problem in a MANET which has access to multiple channels. Although a MANET does not have the infrastructure of base stations, interestingly its channel assignment can be conducted efficiently in a way very similar to that in cellular systems (such as GSM). In this paper, we propose a new location-aware channel assignment protocol called GRID-B (read as GRID with Channel Borrowing), which is a sequel of our earlier GRID protocol [Location-aware channel assignment for a multi-channel mobile ad hoc network, Technical Report NCU-HSCCL-2000-02, 2000]. The protocol assigns channels to mobile hosts based on the location information of mobile hosts that might be available from the positioning device (such as GPS) attached to each host. According to our knowledge, no location-aware channel assignment protocol has been proposed before for MANETs. Several channel borrowing strategies are proposed to dynamically assign channels to mobile hosts so as to exploit channel reuse and resolve the unbalance of traffic loads among different areas (such as hot and cold spots). We then propose a multi-channel MAC protocol, which integrates GRID-B. Extensive simulation results are presented to show the advantage of the new GRID-B protocol.

Distributed power management protocols for multi-hop mobile ad hoc networks

The power management scheme in IEEE 802.11 protocol has three severe challenges: beacon contention, timing synchronization, and reliable neighbor maintenance. These challenges are more serious in large and dense multi-hop mobile ad hoc networks (MANETs). To overcome these challenges and improve the energy efficiency as well as network throughput, we propose three new power management protocols. Especially, our solutions offer the network designers full flexibility in trading energy, latency, and neighbor maintenances accuracy versus each other by appropriately tuning system parameters. Analyses and simulations show that the proposed protocols attain both the better energy efficiency and throughput than existing protocols.