A wideband substrate integrated waveguide (SIW) power divider with enhanced out-of-band rejection is proposed. Periodic butterfly radial slots are etched on top layer of SIW to realise a pass-band combining with high-pass characteristics of SIW. An experimental circuit has been fabricated by the standard printed circuit board process. Simulated results are compared with measured data and good agreement is reported.

A swap time-aware garbage collection (STGC) policy for the NAND flash-based swap system is proposed, which focuses on reducing the cleaning cost and improving the degree of wear-levelling. STGC calculates the cleaning index value of each block to select a victim block and the normalised value of the elapsed swap time of each valid page within the victim blocks to identify the hot valid page and cold valid page. Trace-driven simulations with a synthetic trace show that the STGC outperforms the existing garbage collection policies.Introduction: NAND flash memory provides an out-of-place update scheme to address its erase-before-write hardware constraint. The out-of-place update scheme is a method of writing the new data to the free space of NAND flash memory and invalidating the pages containing the old data. Therefore, a garbage collection policy should be included in the flash-aware file systems [1] or the flash translation layer (FTL) [2] to reclaim garbage, namely the invalid pages. The cleaning cost and the degree of wear-levelling are the two primary concerns of the garbage collection policy. In this case, a number of garbage collection policies have been studied for the NAND flash-based storage system. Only a little research has been done to design garbage collection policies for NAND flash-based swap systems. Kwon and Koh [3] proposed a garbage collection policy called S-Greedy, which extends the greedy policy by considering the swapped-out time of each valid page within the victim block and the erase count of each block. Kwon and Koh [4] also proposed a swap-aware garbage collection policy called SAGC, which computes the value of each block in terms of the sum of the elapsed invalidation time of each invalid page within the block and evicts the block with the largest value. Ji and Shin [5] proposed a locality and duplication-aware garbage collection policy called LDA-GC for flash-aware virtual memory systems. LDA-GC significantly reduces the cleaning cost of the garbage collection policy for the hybrid mapping FTL by considering the update probability of duplicated data.In this Letter, we propose a swap time-aware garbage collection policy, called STGC, for the NAND flash-based swap system. STGC calculates the cleaning index value of each block and selects the block with the largest cleaning index value as a victim block. To separate the hot valid pages from the cold ones and redistribute them to different free blocks, STGC computes the normalised value of the elapsed swap time of each valid page within the victim blocks to identify the hot and cold valid pages. We conducted trace-driven simulations with a synthetic trace, and the performance results show that STGC outperforms the existing garbage collection policies designed for NAND flash-based swap systems.

Proposed is a swap-aware garbage collection policy, called SCATA, for a flash-aware Linux swap system. SCATA not only introduces an improved victim block selection method to reduce cleaning cost and improve the degree of wear-levelling, but also redefines the concept of hot page and cold page according to the least-recently-used page replacement algorithm and clusters hot pages separately from cold pages, and then redistributes them to different free blocks during the migration step of garbage collection operation to reduce cleaning cost and obtain much more free space. Swap I/O traces from the Linux kernel have been collected and trace-driven simulations performed, which show that the proposed policy greatly outperforms existing garbage collection policies.Introduction: As a result of the limited memory resource of embedded systems, embedded systems exploit an efficient Linux swap system [1 -3] considering flash memory as swap storage as a cost-effective solution to extend limited memory space. All write operations of flash-memorybased swap storage are requested during the page replacement operation. Since a page slot of which the size is 4 K bytes is always allocated to accommodate the page swapped out from main memory during the page replacement operation and out-of-place update scheme is adopted to solve the erase-before-write constraint of flash memory, the flashmemory-based swap area is always used up in a short period of time. In this case, an efficient garbage collection policy for the Linux swap system considering flash memory as swap storage is needed to reclaim garbage and obtain free blocks.The cleaning cost and the degree of wear-levelling are two primary concerns of a garbage collection policy. Namely, an efficient garbage collection policy should minimise the cleaning cost of garbage collection and wear down all blocks as evenly as possible. A number of garbage collection policies have been studied. Wu et al. proposed the greedy algorithm (GR) [4] to select victim blocks with the least utilisation for erasure, hoping to obtain free space as much as possible with the least cleaning cost. The greedy algorithm can be implemented simply, but does not consider the degree of wear-levelling. The cost-benefit algorithm (CB) [5] proposed by Kawaguchi et al. adopts the benefit-cost ratio used in the formal discipline of cost-benefit analysis to choose victim blocks with highest benefit-cost for erasure. Chiang et al. proposed the cost age time (CAT) policy [6], which extends CB by considering the erasure count of each block during the selection of victim blocks in order to improve the degree of wear-levelling. To reduce cleaning cost and reclaim the largest amount of invalid pages to obtain the largest amount of free space, the CAT policy clusters hot pages separately from cold pages and redistributes them to different free blocks during the migration step of the garbage collection operation. Han et al. proposed the cost-agetime with age-sort (CATA) algorithm [7] for which the selection method of victim bloc...