Simulated Performance Results of the OMV Video Compression Telemetry System

Abstract

The Orbital Maneuverable Vehicle (OMV) will use a man-in-the-loop round trip space-to-earth communication link for remote control and docking with an orbiting spacecraft. The control system uses range/range rate radar, a forward command link, and a compressed video return link. Figure 1 illustrates the overall compressed video coding techniques. Analog RS-170 compatible video is available from any one of eight or, at a lower resolution, simultaneously from any two television cameras. The video data is digitized and then compressed by sampling every sixth frame of data. A rate of five frames per second is adequate for the OMV docking speeds. Further compression, at the expense of spatial resolution, is obtained by averaging adjacent pixels. The remaining compression is achieved using differential pulse code modulation (DPCM) and Huffman run length encoding. To protect this compressed video data stream from Space to TDRSS channel errors, a concatenated error correction coding system will be used. This concatenated coding is achieved by encoding with a helical interleaved (depth 8) Reed-Solomon (255,239) block code and then encoding with a rate 112 convolution code (constraint length 7) followed by a periodic convolution interleaver (30,116). Thus, we see that four stages of compression, two types of error correction encoding and two levels of interleaving are utilized in this fairly sophisticated data transmission system. A detailed system description and simulated system performance results are presented in this paper.