YongJoo Song

F/sub max/ enhancement in InP-based DHBTs using a new lateral reverse-etching technique

A new lateral reverse-etching technique, developed for the InP DHBTs with emitters aligned to the [011~] direction which is well known to be more reliable than the other directions, is proposed and demonstrated. Two highly doped InGaAs and InP layers are utilized to alleviate the difficulty of lateral etching due to very little lateral etch rate along this direction. The DHBT with a 1.5/spl times/10 /spl mu/m/sup 2/ emitter size fabricated using this new method shows greatly improved peak f/sub max/ of 172 GHz and peak f/sub T/ of 120 GHz. From comparisons of microwave performance of the two devices which are fabricated with and without the new method, a 41% increase of f/sub max/ and a 45% reduction of base-collector junction capacitance have been achieved. Therefore, it has been verified that the proposed new method is very effective to considerably improve f/sub max/ by reducing the base-collector junction capacitance.

F-TCP: light-weight TCP for file transfer in high bandwidth-delay product networks

We describe F-TCP, a new TCP for file transfer in high bandwidth-delay product networks. TCP is not suitable for file transfer application in high bandwidth-delay product networks. There needs a protocol that should not take away too much bandwidth from standard TCP flows while utilizing the full bandwidth of high-speed networks. This paper presents another important constraint, namely small buffer problems. Small socket buffers at the end-hosts limit the effective window of the transfer, and the maximum throughput. Existing schemes have severe small buffer problems because high bandwidth-delay product networks need a large socket buffer. The proposed mechanism, called F-TCP, is based on direct kernel-to-kernel file transfer architecture. The key idea is that no need of in-order delivery in file transfer process. F-TCP needs only small buffer by allowing out-of-order file transfer with asynchronous loss recovery. Experimental results in several high bandwidth-delay product paths show that F-TCP provides consistently a significant throughput increase (18% to 80%) compared to previous TCP approach. We expect that F-TCP is mostly useful for application such as FTP and P2P in high-speed wide-area networks.

Infrastructure support for ad hoc networks: when and where?

Currently, there are several attempts to connect ad hoc wireless networks with legacy infrastructured wireless networks. This paper is the initial work about how we can efficiently use an ad hoc wireless network with infrastructure from the view of ad hoc TCP. We propose new mathematical models of TCP over an ad hoc network, which mainly depends on hopcount, not congestion window size. Based on the new TCP models, we propose a cost-efficient position plan for base stations (BSs) and a route selection algorithm. The proposed position plan of BSs promises cost reduction with small performance trade-off. Our route selection algorithm makes the decision whether we should use infrastructure support or not. Roughly, a n-hop route using infrastructure support would be better than n/2-hop route only using a pure ad hoc wireless network. We evaluated the TCP models and the proposed infrastructure design principles using the Network Simulator 2.

Reduction of extrinsic base-collector capacitance in InP/InGaAs SHBTs using a new base pad design

A method to isolate the base pad from the intrinsic device structure for reducing the extrinsic base-collector capacitance of InP/InGaAs single heterojunction bipolar transistors(SHBTs) is reported, which uses a new base pad layout. The new layout is designed based on the lateral etching characteristics of an InGaAs collector layer with different crystal orientations. The new layout allows more effective and easier base pad isolation for InP-based HBTs, which have the emitter aligned to [011] or [011~] directions, without excessive lateral or additional etching. The maximum f/sub T/ and f/sub max/ of the fabricated device with a 2 /spl times/ 10 /spl mu/m/sup 2/ emitter size using the new layout were found to be 72 and 242 GHz, respectively.

Providing context-awareness to virtual file system

In ubiquitous environment, adaptive applications require the context-aware data access. This paper proposes a backward-compatible, context-aware virtual file system (CaVFS). Users can find a file by the context without remembering full path. Since CaVFS supports the full backward compatibility, users can even browse hierarchically with the legacy path name, and the legacy applications can access the flies in a context-aware way. We implement CaVFS in Linux kernel 2.6.7-21. The experiments show that the overhead to maintain the context is reasonably small.

S-VFS: Searchable Virtual File System for an Intelligent Ubiquitous Storage

With advances in ubiquitous environments, user demand for easy data-lookup is growing rapidly. Not only users but intelligent ubiquitous applications also require data-lookup services for a ubiquitous computing framework. This paper proposes a backward-compatible, searchable virtual file system (S-VFS) for easy data-lookup. We add search functionality to the VFS, the de facto standard abstraction layer over the file system. Users can find a file by its attributes without remembering the full path. S-VFS maintains the attributes and the indexing structures in a normal file per partition. It processes queries and returns the results in a form of a virtual directory. S-VFS is the modified VFS, but uses legacy file systems without any modification. Since S-VFS supports full backward compatibility, users can even browse hierarchically with the legacy path name. We implement S-VFS in Linux kernel 2.6.7-21. Experiments with randomly generated queries demonstrate outstanding lookup performance with a small overhead for indexing.

Infrastructure support for ad hoc network:when and where?

Currently, there are several attempts to connect ad hoc network with legacy infrastructure network like 802.11 WLAN. This paper is initial work about how we can efficiently use ad hoc network with infrastructure at the view of ad hoc TCP. To design efficient infrastructure support for ad hoc network, we propose mathematical models of TCP over ad hoc network and over hybrid network. Unlikely to previous TCP models for wired network, our models for ad hoc network mainly depends on hop-count, not congestion window size. Based on the new TCP models, we propose a cost-efficient position plan for base stations (BSs) and a route selection algorithm. The proposed position plan of BSs promises cost reduction with small performance trade-off. The route selection algorithm makes the decision on whether we should use infrastructure support or not. Roughly, a n-hop route using infrastructure would be better than n 2 -hop route only using pure ad hoc network. We have evaluated the TCP models and the proposed infrastructure design principals using the Network Simulator2(ns-2).

Mobility Aware Transmission Power Control in Mobile Ad-hoc Network

The energy efficient algorithm which saves network energy consumption by reducing transmission range in static networks cannot maintain the energy efficiency in dynamic networks because of link failure by node mobility and asymmetric links. So we present MATPC which keeps 20% better energy efficiency compare to other approaches in dynamic networks

Monolithically integrated InP-based 1.55 /spl mu/m photoreceivers using V-grooved RFPD/HBT integration technology

InP-based photoreceivers were successfully integrated with the InP V-groove and the refracting facet photodiode (RFPD), for the first time, based on the shared layer integration technology. The InP-V groove optical bench and the RFPD were simultaneously fabricated using the base-collector layers of the InP/InGaAs HBT. The alignment process of the optical fibre was greatly simplified using the fabricated InP V-grooves. The developed integration technology allowing simple and efficient optical coupling using the on-chip InP V-groove was high speed photoreceivers arrays for dense WDM application.