## 2 Background and Related Work  
### Related Work  
A wireless grid is a system that integrates a traditional grid with a wireless system to provide users with various services that can be conveniently accessed through wireless devices. Many researchers have studied this subject. [PERSON] _et al_. [9] proposed a wireless grid service system, RWGSP, which employs a grid, mobile agents and wireless networks to create a wireless-device accessible grid environment. In the RWGSP system, messages can be ultimately delivered to their destinations, even though connectivity of the sender and the receiver is intermittent. However, the transmission quality of network connections in a wireless grid environment changes frequently, which will largely decrease the efficiency of data delivery.  
The Interleaved Resource Status Monitoring algorithm (IRSM for short), proposed by [PERSON] and [PERSON] [10] for a wireless grid, monitors important resources more frequently to achieve higher monitoring accuracy so that it can allocate the most suitable resources of the grid environment to satisfy different users' needs. For example, for a computation task, CPU capability is more important than the amount of available memory in a grid node. Therefore, the IRSM monitors CPU more frequently than the amount of available memory. Higher accuracy of the monitored CPU load will lead the grid system to allocate more appropriate resources to serve user tasks. Consequently, the result is better system performance. In addition, three algorithms were proposed in [10], but the authors did not effectively compare their performance with that of the state-of-the-art algorithms proposed in their related articles.  
[PERSON] _et al_. [11] introduced an agent-based wireless grid in which mobile agents are classified into five categories, including Job Processing Agents, Job Mobile Agents, Resource Monitoring Agents, Actual Organization Resource Agents, and Virtual Organization Resource Manager. After the resource broker determines how to allocate resources to a task, mobile agents are employed to notify the requesting side and the service side. Moreover, the system calculates the service costs for each node so that the total cost of the whole system can be dramatically reduced. The basic criteria being considered for resource allocation include system load, the number of competitive resources, the previous accessing history of the visiting user, and the status of demand for the resources. However, the authors did not consider the network bandwidth, which is a key issue in evaluating the transmission efficiency of a wireless system.  
[PERSON] _et al_. [12] designed a storage system for a wireless grid, which stores data in the nodes with higher computation capability, and uses proxies to manage devices. Nodes in different districts can communicate with each other through their own proxies and keep the data in different districts. However, the system has only one crawler server, which might be a bottleneck.  
[PERSON] _et al_. [13] proposed a scheduling algorithm to schedule jobs and allocate resources in a mobile grid environment. The main ideas are rescheduling and replication, which make use of resources sufficiently when resources are active. But the authors did not consider capacity and capability difference among the resources.  
In a wireless grid, we also consider multi-path routing that can avoid congestion, and improve throughput and security [14; 15; 16].