1. Development and application of CDMA and OFC communication technology in ground based GPS sensor network in Northeast China
Zhang Jingjiang Zhang Chaolin
Institute of Urban Meteorology (IUM), CMA, Beijing, China
Abstract
Up to the 1st quarter of this year, there are 48 ground-based GPS observation stations in Northeast China, they belong to Beijing Meteorological Bureau(BMB), Beijing Municipal Government and China Meteorological Administration (CMA), respectively. The Bernese GPS software is used to do the post-processing work. By the cooperation with NCAR/UCAR, BMB can calculate GPS-derived precipitable water vapor of Northeast China almost in real time (less than 2 hours delay). The operational GPS-Met products include the PWV variation charts in Northeast China (every 30 minutes), meteorological elements (air pressure, temperature and relative humid ) variation at each stations and (every 30 minutes) and GPS water-vapor topography at Fangshan area in Beijing (2 days delay). Data assimilation of GPS PWV has been put into the MM5 NWP and LAPS system successfully.
By support of Beijing Municipal Science and Technology Commission, BMB has set up 14 stations at the end of These 14 stations are divided into two group , one group is located in Fangshan county which includes 8 stations , the other group is in Huairou county which includes 6 stations. BMB has developed a GPS data communication system based on the CDMA wireless telecommunication technology. Therefore, the observation data can be transmitted to BMB in every 30 minutes with no more than 10 minutes delay. The bandwidth is about 100kbps. The Beijing Municipal Government has invested to build 16 GPS stations in each county of Beijing area for civilian use, most of them are built in local weather station. Optical fiber cables (OFC, 2M ) connect to the stations so observation data can be get in real time.
Both of CDMA and OFC can be used to reliably transfer data in real-time. CDMA does meet the requirement of operational demand, though its bandwidth is narrower than OFC. Since it takes less money and time to set up data transferring links by CDMA than by OFC, it is more suitable for those stations in remote area, where stations are not man-operated.
The operational GPS-Met products
GPRS/CDMA Data Transfer Topology Network
LAN of BMB
GPRS/CDMA online Watch
Permanent IP
GPRS/CDMA
Internet
GPS Receiver
Catalyst 3900
Data Processing
GPRS/CDMA Wireless Unit
Data Transfer System based on PSTN
PSTN
Modem
Location of GPS site in North China
Tianjin
BMB
Beijing Government
CMA
Optical fiber cables instrument
CDMA Instrument