A Technical Overview of the Satellite based Indian Meteorological Data Casting System (IMETCAST)

Transcription

1 A Technical Overview of the Satellite based Indian Meteorological Data Casting System (IMETCAST) N. G. Vasantha Kumar 1, Mohanchur Sarkar 1, Vishal Agarwal 1, P. K. Srinivasan 2, M. M. Shaikh, A. S. Buch 2, I. C. Matieda 3 {vasant, msarkar, vagarwal, sac7479, sac5988, asbuch, matieda}@sac.isro.gov.in 1 ACTD ADCTG SNAA, 2 AES - SGSTG - SNAA, 3 DWD - UPDG - EPSA Space Applications Centre AHMEDABAD INDIA 1.0 Introduction ISRO has established a facility known as Meteorological and Oceanographic Satellite Data Archival Center (MOSDAC) to facilitate and promote the exchange of satellite data (various products, metadata and other information) to the research and academic users. It also has an objective to disseminate quality data products from ISRO Satellite missions for meteorology and Oceanography on near real time basis. Currently the MOSDAC access is through a web-based portal and provides KALPANA 1 images, 3ACCD images and MOSDAC metadata information. There is a need to provide the latest KALPANA 1 images and 3ACCD images to the researchers and to the common man. The researchers should be able to use the computer for viewing and further analysis on the data. The common man should be able to view the latest images on his TV. The solution provided here will meet the needs of both the researchers and the common man. This solution is realized using Digital Video Broadcast via Satellite (DVB-S) based IP transmission and is titled as Satellite based Indian Meteorological Data Casting system (IMETCAST). Using this System the researchers in general and weather forecasters in particular will be able to get the access to the real time image files at their PCs which will immensely help their ongoing research and drastically increase the utilization of the Satellite images which at present is restricted to a group of organizations. Moreover considering the widespread deployment of DVB-S based TV service and the percentage of population to which it is accessible it has been decided to provide a hybrid platform in which the Met Data can be simultaneously be available to the TV users also. 2.0 System Overview of IMETCAST Network The system as depicted in Fig 1.0 may be broadly classified into two segments: The Space segment The Ground segment

2 2.1 The Space Segment The Space Segment consists of a powerful Communication satellite that broadcasts the uplinked MET Data from the IMETCAST HUB. The satellite should be powerful enough to enable reception by.75m antenna as is required in DTH type of scenario 2.2 The Ground Segment The Ground segment consist of the IMETCAST HUB Receive Only Terminals (ROT) INSAT LAN ROT IMET CLIENT RF Interface box IMETCAST SERVER IMETCAST LINK GEN. ROT IMET CLIENT IMETCAST SYSTEM OVERVIEW Fig1. IMETCAST System Overview The IMETCAST HUB consists of the IMETCAST Server and the IMETCAST Link Generator. The IMETCAST Server is connected to the MOSDAC Server. The received MET Data is transferred automatically to the IMETCAST Link Generator PC on LAN. IMETCAST Link GEN does the IP packet capturing, IP Encapsulation as per MPE [2][7], Service Information Table Generation [1][6], Multiplexing and generation of MPEG2 TS [4]. 2.0 Proof of Concept Test and Experiments Conducted There are two approaches to broadcast the images. The first approach for this solution is to allocate a separate carrier for the TV based reception and a

3 separate carrier for the PC based reception. In this case using the same satellite two class of broadcast network exist each using separate carrier frequency one supporting PC based Data dissemination and the other a TV based dissemination. This will require separate Modulators and encoders for both the system and users also has to be aware of the frequency in which the two separate transmissions are done. The second approach is to have a combined link (i.e., hybrid transmission system) using a Single frequency which takes advantage of the multiplexing facility of DVB-S MPEG2 [4] and data for PC and TV users are carried inside a single MPEG2TS multiplex. This will lead to a better utilization of resources and flexibility to the user. A proof of concept testing of the IMETCAST system has been performed using the second approach. The purpose of the test was to realize the hybrid transmission system through which images can be received both on a PC and on TV. Fig 2 Proof of Concept Testing of IMETCAST using Satellite Link

4 Fig2 shows the setup of the proof of concept. This setup consists of two chains one for the TV users and the other for the PC based transmission. The real time image data from MOSDAC is converted as S-Video using a VGA to PAL converter and given as input to the COTS MPEG2 Encoder, which in turn delivers the data to the Multiplexer. The same real time image data form MOSDAC is also given as input to the IMETCAST server that provides the input to the Multiplexer as per IP-MPE format. The Multiplexer output is modulated using a DVB-S Modulator and uplinked to satellite. The DVB-S data is received using a commercial IRD in a TV and using a USB based Satellite received to a PC as shown in Fig Proposed Solution for Transmission End In the proposed solution, there will be a standard DVB MPEG-2 encoder transmitting the normal video and audio channels, an Object Carousel server with ASI card interface, multiplexer, modulator and the transmission system. The satellite images are updated in the object carousel server in to the predefined directory whenever the new satellite images are available with the MOSDAC. A Multimedia Home Platform (MHP) application for browsing these images at the set top box is also stored in the object carousel directory. The object carousel is multiplexed with the normal video, audio channels at the multiplexer. The multiplexer output is given to the DVB-S modulator and transmitted via satellite. 4.0 Proposed Solution for Receiving End In receiving the MET Images and the Meteorological data on the Computer, a DVB-S Receiver that can support Object Carousel and IP-MPE support is required. The computer should have the necessary software to run the MHP application in showing the particular image based on the user selection. The computer should also have the necessary software to analyze the meteorological data. At the receiving end a Set Top Box (STB) supporting MHP is required to store the image data and run the MHP application to display the images on TV. Whenever the user selects the meteorological application, the application should store the object carousel content and display the page-containing list of available images. The user will be given a choice to select and view a particular image on TV. This proposed system does not require video bandwidth for transmission. It can be transmitted using low data rates. The images can be displayed on TV / PC based on the type of receiver system at the receiving end.

5 References [1] ETSI EN : "Digital Video Broadcasting (DVB); Interaction channel for satellite distribution systems". [2] ETSI TR : "Digital Video Broadcasting (DVB); Implementation guidelines for Data Broadcasting". [3] Novra S Receiver Instructions in [4] ISO/IEC (1996): "Information technology - Generic coding of moving pictures and associated audio information; Part 1: Systems". [5] ETSI EN : "Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for 11/12 GHz satellite services" [6] ETSI EN : "Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems". [7] ETSI EN : "Digital Video Broadcasting (DVB); DVB specification for data broadcasting" [8] Morris S.: Interactive TV Web, 7/2007,