One of the most challenging issues in wireless sensor networks is extension of the overall network lifetime. Data aggregation is one promising solution because it reduces the amount of network traffic by eliminating redundant data. In order to aggregate data, each sensor node must temporarily store received data, which requires a specific amount of memory. Most sensor nodes use static random access memory (SRAM) or flash memory for storage. SRAM can be implemented in a one-chip sensor node at low cost; however, SRAM requires standby energy, which consumes a lot of power, especially because the sensor node spends most of its time sleeping, i.e. its radio circuits are quiescent. This study proposes two types of divided SRAM: equal-size divided SRAM and equal-ratio divided SRAM. Simulations show that both proposed SRAM types offer reduced power consumption in various situations.

Space reservation is important in allocating and releasing storage space in DBMSs to support recoverable actions. Since most existing space reservation methods are designed to perform well when few data pages have spaces reserved by more than one transaction, they are not suitable for some of the newly emerging applications, such as workflow and inventory control systems. In these applications, many concurrent transactions frequently insert and delete records into/from a relatively small table. This paper proposes a new space reservation method that performs well for these types of applications by extending the lock control structures to keep detailed and up-to-date information in a reserved state. This paper also shows, by simulation, that the new method performs better than existing ones for applications in which many concurrent transactions frequently insert and delete records into/from a table, and even for applications where data pages rarely have space reserved by more than one transaction.

RAID5 disk arrays provide high performance and high reliability for reasonable cost. However RAID5 suffers a performance penalty during block updates. In this paper, we propose a method to improve the small write performance of RAID5 disk arrays, named Virtual Striping. Instead of updating each block independently, this method buffers a number of updates, generates a new stripe composed of the newly updated blocks, then writes the full stripe back to disk. In order to make free space for write operations, new garbage collection strategy is employed, where the linkage of blocks in a parity stripe is changed in Virtual Striping. The LFS (log-structured file system) based storage management scheme also writes new block onto large free area, which uses copying garbage collection. In this paper, we compare the performance of both methods through simulation. Although the write cost of Virtual Striping is more than that of the LFS based method, Virtual Striping has better performance than the LFS based method. This is due to the high efficiency of garbage collection in Virtual Striping.