Chih-Shun Hsu

Power-saving protocols for IEEE 802.11-based multi-hop ad hoc networks

Power-saving is a critical issue for almost all kinds of portable devices. In this paper, we consider the design of powersaving protocols for mobile ad hoc networks (MANETs) that allow mobile hosts to switch to a low-power sleep mode. The MANETs being considered in this paper are characterized by unpredictable mobility, multi-hop communication, and no clock synchronization mechanism. In particular, the last characteristic would complicate the problem since a host has to predict when another host will wake up to receive packets. We propose three power management protocols, namely dominating-awake-interval, periodically-fully-awake-interval, and quorum-based protocols, which are directly applicable to IEEE 802.11-based MANETs. As far as we know, the power management problem for multihop MANETs has not been seriously addressed in the literature. Existing standards, such as IEEE 802.11, HIPERLAN, and bluetooth, all assume that the network is fully connected or there is a clock synchronization mechanism. Extensive simulation results are presented to verify the effectiveness of the proposed protocols.

A Distributed Localization Scheme for Wireless Sensor Networks with Improved Grid-Scan and Vector-Based Refinement

Localization is a fundamental and essential issue for wireless sensor networks (WSNs). Existing localization algorithms can be categorized as either range-based or range-free schemes. Range-based schemes are not suitable for WSNs because of their irregularity of radio propagation and their cost of additional devices. In contrast, range-free schemes do not need to use received signal strength to estimate distances and only need simple and cheap hardware, and are thus more suitable for WSNs. However, existing range-free schemes are too costly and not accurate enough or are not scalable. To improve previous work, we present a fully distributed range-free localization scheme for WSNs. We assume that only a few sensor nodes, called anchors, know their locations, and the remaining (normal) nodes need to estimate their own locations by gathering nearby neighboring information. We propose an improved grid-scan algorithm to find the estimated locations of the normal nodes. Furthermore, we derive a vector-based refinement scheme to improve the accuracy of the estimated locations. Analysis, simulation, and experiment results show that our scheme outperforms the other range-free schemes even when the communication radius is irregular.

A distributed location estimating algorithm for wireless sensor networks

The location estimation is a fundamental and essential issue for wireless sensor networks( WSNs). In this paper, we assume that only a few sensor nodes (named as beacon nodes) get their locations by Global Positioning System (GPS) and the remaining nodes without GPS (named as normal nodes) need to estimate their own locations by gathering the nearby neighboring information. Existing works are either too costly or not accurate enough. To improve previous works, we propose a distributed location estimation algorithm for WSNs. In our algorithm, each node without location information only needs to collect the location information of neighboring nodes and use simple computation to estimate its location. Besides, we improve the accuracy of the normal nodes estimative region by discarding the communication area of the beacon node (named as the farther neighboring beacon node), which does not cover the normal node, from the original estimative region. We derive some rules to adjust the estimative region according to the relative location of the normal node and the farther neighboring beacon node. Simulation results show that the proposed algorithm achieves better accuracy of estimative locations

Minimize waiting time and conserve energy by scheduling transmissions in IEEE 802.11-based ad hoc networks

The mobile ad hoc network (MANET) has attracted lots of attention recently. Most of the researches assume that every mobile host in the MANET uses a fixed data rate and follows a distributed coordination function (DCF) to transmit messages. As we know that none of the research has combined multiple data rates and transmission scheduling to minimize waiting time and conserve energy for a MANET with power-saving (PS) mode hosts. IEEE 802.11 has already supported multiple data transmission rate. However, how to decide the transmission rate is still an open question. Here, we propose a data rate selection protocol to select the best available data rate to transmit messages. After the data transmission rate has been selected, we can schedule each transmission according to the data transmission rate and the packet size. Our goal is to minimize the average waiting time of each transmission and thus the PS hosts can switch back to power-saving mode as soon as possible. Therefore, we follow the shortest job first policy to let the transmission with shortest transmission time to access the channel first. Simulation results show that our scheduling protocol can achieve high packet delivery rate, reduce waiting time and conserve lots of energy.

An efficient reliable broadcasting protocol for wireless mobile ad hoc networks

The mobile ad hoc network (MANET) has recently been recognized as an attractive network architecture for wireless communication. Reliable broadcast is an important operation in MANET (e.g., giving orders, searching routes, and notifying important signals). However, using a naive flooding to achieve reliable broadcasting may be very costly, causing a lot of contention, collision, and congestion, to which we refer as the broadcast storm problem. This paper proposes an efficient reliable broadcasting protocol by taking care of the potential broadcast storm problem that could occur in the medium-access level. Existing protocols are either unreliable, or reliable but based on a too costly approach. Our protocol differs from existing protocols by adopting a low-cost broadcast, which does not guarantee reliability, as a basic operation. The reliability is ensured by additional acknowledgement and handshaking. Simulation results do justify the efficiency of the proposed protocol.

Efficient broadcasting protocols for regular wireless sensor networks

The wireless sensor network (WSN) has attracted lots of attention recently. Broadcast is a fundamental operation for all kinds of networks and it has not been addressed seriously in the WSN. Therefore, we propose two types of power and time efficient broadcasting protocols, namely one-to-all and all-to-all broadcasting protocols, for five different WSN topologies. Our one-to-all broadcasting protocols conserve power and time by choosing as few relay nodes as possible to scatter packets to the whole network. Besides, collisions are carefully handled such that our one-to-all broadcasting protocols can achieve 100% reachability. By assigning each node a proper channel, our all-to-all broadcasting protocols are collision free and efficient. Numerical evaluation results compare the performance of the five topologies and show that our broadcasting protocols are power and time efficient. Copyright

An On-Demand Bandwidth Reservation QoS Routing Protocol for Mobile Ad Hoc Networks

QoS routing is the key to support multimedia services in mobile ad hoc networks (MANETs). It is known that resource reservation is one of the best technique to guarantee QoS in MANETs. Lots of the reservation-based QoS routing protocols have been proposed before. However, the effective bandwidth calculation problem and the bandwidth reservation problem have not been addressed seriously. Here, we proposed an on-demand bandwidth reservation QoS routing protocol for TDMA-based multihop MANETs. We propose an algorithm to guide the destination to choose the route that is most likely to satisfy the QoS requirement and an algorithm to reserve the proper time slot and thus keeps more free time slots for other requests. Simulation results show that our protocol can achieve high route establishment probability and low packet loss rate

Design and performance analysis of leader election and initialization protocols on ad hoc networks

Leader election and initialization are two fundamental problems in mobile ad hoc networks (MANETs). The leader can serve as a coordinator in the MANETs and the initialization protocol can assign each host a sequential, unique, and short ID. As we know, no research on initialization for IEEE 802.11-based MANETs has been done. Here, we propose two contention-based leader election and initialization protocols for IEEE 802.11-based single-hop MANETs. We also provide an efficient approach to evaluate the performance of the proposed protocols, such that the performance can be evaluated in polynomial time. The evaluation results provide a guideline to set the size of the contention window and thus improve the performance of the proposed leader election and initialization protocols. The results can also be used as a guideline to set the size of the contention window for any contention-based protocol. Simulation results justify that the evaluation results provide a good guideline to set the size of the contention window. Copyright

Initialization protocols for IEEE 802.11-based ad hoc networks

Leader election and initialization are two fundamental problems in mobile ad hoc networks (MANETs). The leader can serve as a coordinator in the MANETs and the initialization protocol can assign each host a unique and short id. We know that none of the research on initialization for IEEE 802.11-based MANETs has been done. Here, we propose two contention-based leader election and initialization protocols for IEEE 802.11-based single-hop MANETs. Simulation results show that our protocols are efficient.

Power management protocol for regular wireless sensor networks

Most of the existing power saving protocols are designed for irregular networks. These protocols can also be applied to regular networks, but these protocols do not consider the characteristics of regular networks and thus are more complicated and less efficient than the protocols designed for regular networks. Therefore, we propose a novel power management protocol for regular WSNs. Gathering information to the base station is an important operation for WSN. Hence, even some nodes switch to PS mode, the network still needs to be connected so that the sensed information can be sent to the base station through the active nodes. The goal of our protocols is to choose several different connected dominating sets, so that these connected dominating sets can switch to active mode in turn to serve other nodes in PS mode. Simulation results show that our power management protocol can conserve lots of power and greatly extend the lifetime of the WSN with a reasonable extra transmission delay.