| 摘要 |
In a synchronous fixed frame boundary system with variable data rates, a transmitter inserts into a current frame an indication of the data rate of the next frame. After the first frame is received and processed at a receiver, the data rates of subsequent frames are known before processing, thereby reducing processing load. Furthermore, because the rate indication is inserted into the frame to be error protected along with the rest of the frame information, reliability is high, while additional data overhead and complexity are very low. As an example, North American code division multiple access digital cellular telephone systems utilize variable data rate transmissions. As a station modem (SM) assembles a current frame for convolutional encoding and further processing, the SM inserts a rate indication for the subsequent frame in accordance with information from a vocoder and CPU of the appropriate data rate for the subsequent frame. On the receiving end, rather than needing to decode multiple times to determine the appropriate data rate for every frame, the receiving SM discovers the rate of each frame subsequent to the first frame by analyzing the information contained in the immediately preceding frame. The rate determination process also includes a verification method based upon a frame quality indicator analysis and a symbol error rate analysis to ensure accurate data rate determination.
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