Hohyun Shim [Alum]


Verification Group

Office: Synopsys Inc. 700 E. Middlefield road , Mountain View, CA 94043

Synopsys Inc. 700 E. Middlefield road , Mountain View, CA 94043

shimho [at] ee.ucla.edu

Tel [work]:

Tel [mobile]:


  • BS in Electrical Engineering, Seoul National University, 2000.
  • MS in Embedded Computing System, University of California, Los Angeles, 2005.
    Thesis: Joint design of ultra low power MAC and routing Protocol
    (done at NESL)

Experience: Synopsys Apr‘05 - present

with Verification Group
working on EDA verification tools.

NCSoft Nov ‘01 - Apr ‘03

- Game Server Programmer
NCSoft is one of the world-famous online game developers in Korea and has many branches in US, Europe, China and so on as well as in Korea. My primary responsibilities were to develop online game servers to maintain tens of thousands of TCP client connections and real-time game information and to process millions of packets per second reliably. In addition, the server also needs to provide easy and extensible interfaces to develop various game client programs. The server was implemented in C++ as a window service application and MS-SQL database was used.

InfoBank Aug ’99 - Nov ‘01

InfoBank is a software company to develop various mobile internet services and applications in Korea.

- SMS Gateway Server (April ’01 - Nov ’01)
The objective of this service is to receive mobile Short Message Server(SMS) packets from clients and forwards them, selectively, to appropriate Mobile Service Providers. This service should be tolerant of various failures such as network disconnection and server outage. The gateway server was implemented in C++ as a UNIX service program with a MySQL Database.

- Mobile Website Builder (Aug ’00 - April ’01)
This is a GUI window application to easily create mobile websites such as WAP. There was a large need to provide mobile interfaces corresponding to commercial internet website such as internet shopping malls. The objective of this program is to provide an easy way to create WAP sites, just as Dreamweaver does for HTML sites.
This program was implemented using Visual C++ and MFC, and provides various Database interfaces such as MS-SQL, Oracle, MySQL, IBM DB, Infomix and so on.

- Knowledge Management System for Korean Fair Trade Committee(Aug ’99 - Aug ’00)
This was a System Integration project to combine Korean Fair Trade Committee intranet with Knowledge Management System. My responsibilities included analyzing clients’ needs, designing the systems, and implementing them.

Research Interests: - Ultra Low-power MAC protocol for Sensor Networks (July ’04 - current)
Radio communication dominates sensor networks power consumption. The objective of this research project is to provide an extremely energy efficient and reliable MAC protocol using time synchronization technique.
Low power MAC protocols periodically turn on and off the radio. However, senders must transmit very long preambles in order to meet receivers’ wakeup time, because they don’t know when receiver nodes are listening. My work eliminates unnecessarily long MAC preambles by synchronizing Radio on-time. A statistical method is employed to ensure that timing-sync doesn’t waste energy to meet application demands. Models include Surge multi-hop routing protocol, Chipcon Radio(CC1000) and B-MAC protocol.
This project is a part of “The Power Aware Sensing Tracking and Analysis (PASTA) project”, which is a DARPA-funded project and is investigating power-efficient systems for unattended ground sensor (UGS) applications.


- Delay Tolerant Network for Sensor Networks (April ’04 - July ’04)
This research aims to provide an end-to-end reliable routing protocol for unstable and intermittent Ad-hoc networks such as a sensor network. A base station, as a data sink, may move around through distributed sensor nodes and some nodes may become suddenly off for some reasons such as out of power, trouble in radio communication or hostile environment. To guarantee the end-to-end reliability in these unstable networks, the DTN protocol provides adaptive routing and store-and-forward packet delivery between sensor networks and the base station.
I implemented the DTN protocol in TinyOS (http://www.tinyos.net) and verified it on the Mica2 sensor node platform (ref to Mica2 hardware).

Reference website : http://www.dtnrg.org/

Recent Publications:

  • Estimating Clock Uncertainty for Efficient Duty-Cycling in Sensor Networks
    Saurabh Ganeriwal, Ilias Tsigkogiannis, Hohyun Shim, Vlasios Tsiatsis, Mani B. Srivastava, and Deepak Ganesan.
    IEEE/ACM Transactions on Networking (Accepted), July 2008. [ Details ]
  • Estimating clock uncertainty for efficient duty-cycling in sensor networks
    Saurabh Ganeriwal, Deepak Ganesan, Hohyun Shim, Vlasios Tsiatsis, and Mani B. Srivastava.
    To appear in the Third ACM Conference on Sensor Networking Systems (SenSys), November 2005. [ Details ]

Other Publications: KeunJoo Kwon, Hohyun Shim, Sang Kyun Cha, "Implementation of Road Navigation System on WWW" , Korea Information Science Society Conference, pp.102-104, Oct. 1999