FRAME RATE REDUCTION IN VIDEO TELEMETRY SYSTEMS

Abstract

In video telemetry systems the transmitted picture rate, or temporal resolution, is a critical parameter in determining system performance as well as the transmitted bit rate. In many applications it is important to transmit every TV frame because the maximum temporal resolution must be maintained to analyze critical events such as an encounter between a missile and a target. Typical transmission bit rates for operation at these picture rates are 5.0 to 10.0 mbps. In other cases the frame rate can be reduced slightly to 15 or 7.5 frames/sec. without significantly reducing the value of the output video. At these frame rates it is still possible to sense the continuity of motion although some jerkiness may appear on rapidly moving objects. At these reduced frame rates the transmitted bit rate can go as low as 1.0 mbps. There is a third class of video telemetry applications where the scene is changing very slowly, and it is permissible to transmit a series of still pictures at very reduced rates. For example one picture can be transmitted every second at a transmission bit rate of 100 Kbps. The purpose of this paper is to examine operation of the standard video coding system (Range Commander Council Standard RCC 209) at conventional frame rates as well as a wide range of reduced frame rates. The following section describes the basic digital TV system which employs the standard codec. Two particular modes of operation are discussed: (1) those which reduce the frame rate by a fixed amount and vary the spatial resolution according to the complexity of the TV image; (2) those which maintain the spatial resolution at a fixed level and automatically vary the temporal resolution according to the complexity of the image. A tradeoff analysis is presented illustrating the interaction of spatial resolution, temporal resolution, and transmission bit rate. A video tape is described and presented illustrating system operation at a wide range of frame rates. Finally, conclusions are drawn.