Grand Alliance Prototype Transport Stream Encoder Design & Implementation

The Grand Alliance HDTV System has been designed to provide advanced television service to North America. The FCC Advisory Committee on Advanced Television Service & the Grand Alliance have devised a testing program that demonstrates & measures the performance of a prototype system that has been constructed. This paper describes the prototype Transport Stream Encoder subsystem design & implementation. Summary The formation of the Grand Alliance (GA) brought former competitors together to achieve the goal of designing an HDTV system composed of the "best of the best" system components. This paper describes the design of the Grand Alliance Prototype Transport Stream Encoder. A brief discussion concerning the status of the Moving Pictures Expert Group (MPEG2) International Standard on the coding of moving pictures and associated audio during the formative days of the system design & the role of the GA Transport Specialists Group in producing the transport specifications precedes the technical description of the Transport System. The Transport layer of the GA System is directly based upon MPEG2 specifications with the general requirement that the Transport streams be MPEG2 compliant. An overview of the MPEG2 Transport layer, including packet structures, is presented as the foundation for prototype development. The two system architectures that were considered during the system design phase of the project are presented using system block diagrams. A discussion of the rational behind the final choice in architecture follows. The selected prototype system architecture is described in detail. System timing, using Program Clock Reference (PCR), Decode Time Stamps (DTS) & Presentation Time Stamps (PTS), is a primary responsibility of the Transport system. A relatively simple interface that passes Program Clock Reference Base (PCRB) is described. Each program in the Transport Stream has a 27Mhz System Clock Reference that is locked to the pixel sample clock for that program. The relationships involving these parameters are explained in detail. Packetized Elementary Streams (PES) are supplied to the Transport Stream Encoder (TSE) by the individual data encoders. The PES layer carries Decode Time Stamps (DTS) & Presentation Time Stamps (PTS) created using information that is readily available at the individual data encoders. While MPEG2 defines the PES layer as a Transport function, this approach simplifies the interface between the individual PES & TSE encoders. An explanation of this interface and the input data processing circuits is given. 308 0-7803-2140-5195 $3.00 " 1995 IEEE Multiple time related PES streams containing Video, Audio 8z perhaps Data, arrive at Transport bundled as a program. A TSE Program Input Board processes the incoming PES stream prior to the construction of transport packets. These input data processing steps are