Performance Comparison of Scheduling Techniques to Manage Transactions for Real-Time Mobile Databases in Ad Hoc Networks

A Mobile Ad-hoc Network (MANET) ¡s an autcnomous system of mobile hosts (MHs) with similar transmission power and computation capabilities that communicate over relatively bandwidth constrained wireless links. Applications such as emergency/rescue operations, conferences/meetings/lectures, dísaster refief efforts, bluetooth (Personal Area Network} and military networks can be conceived as applications of MAIMET due to the fact that they cannot rely on centralized and organized connectivity. In these environment transactions are time-crltical and require to be executed not only correclly but also within their deadlines, that is, the user that submit a transaction would like it to be completed before a certain time in the future. This study focuses on the comparison of four scheduling techniques based on the policy of assigning priorities to transactions on the system. The techniques are: First Come First Serve (FCFS) [1,2], Earliest Deadline (ED) [1,2,5], Least Slack (LS) [1,2,8] and Least Slack Mobile (LSM) proposed in [3] where some modifications to the Least Slack Technique with respect to energy constraints, disoonnection and transaction type (firnVsoft) are considered. Applying these modifications to Earliest Deadline, the performance of the system will be evaluated to measure the percentage of transaction missing deadlines and the total energy consumption in the mobile hosts. The performance evaluation of the techniques will be carried out by means of simulation. The simulation model is implemented using Visual Slam/Awesim [7]

AN ENERGY-EFFICIENT CONCURRENCY CONTROL ALGORITHM FOR MOBILE AD-HOC NETWORK DATABASES

With the rapid growth of the wireless networking technology and mobile computing devices, there is an increasing demand for processing mobile database transactions in mission-critical applications such as disaster rescue and military operations that do not require a fixed infrastructure, so that mobile users can access and manipulate the database anytime and anywhere. A Mobile Ad-hoc Network (MANET) is a collection of mobile, wireless and battery-powered nodes without a fixed infrastructure; therefore it fits well in such applications. However, when a node runs out of energy or has insufficient energy to function, communication may fail, disconnections may happen, execution of transactions may be prolonged, and thus time-critical transactions may be aborted if they missed their deadlines. In order to guarantee timely and correct results for multiple concurrent transactions, energy-efficient database concurrency control (CC) techniques become critical. Due to the characteristics of MANET databases, existing CC algorithms cannot work effectively.In this dissertation, an energy-efficient CC algorithm, called Sequential Order with Dynamic Adjustment (SODA), is developed for mission-critical MANET databases in a clustered network architecture where nodes are divided into clusters, each of which has a node, called a cluster head, responsible for the processing of all nodes in the cluster. The cluster structure is constructed using a novel weighted clustering algorithm, called MEW (Mobility, Energy, and Workload), that uses node mobility, remaining energy and workload to group nodes into clusters and select cluster heads. In SODA, in order to conserve energy and balance energy consumption among servers so that the lifetime of the network is prolonged, cluster heads are elected to work as coordinating servers. SODA is based on optimistic CC to offer high transaction concurrency and avoid unbounded blocking time. It utilizes the sequential order of committed transactions to simplify the validation process and dynamically adjusts the sequential order of committed transactions to reduce transaction aborts and improve system throughput.Besides correctness proof and theoretical analysis, comprehensive simulation experiments were conducted to study the performance of MEW and SODA. The simulation results confirm that MEW prolongs the lifetime of MANETs and has a lower cluster head change rate and re-affiliation rate than the existing algorithm MOBIC. The simulation results also show the superiority of SODA over the existing techniques, SESAMO and S2PL, in terms of transaction abort rate, system throughput, total energy consumption by all servers, and degree of balancing energy consumption among servers