Parity checking in a real-time digital communications system

Abstract

In a digital communication system for voice signals, a system and method for improving the quality of a received signal. The invention comprises a system for arranging the data and parity bits in a data frame and a corresponding method for analyzing and using the received frames. In the present invention, the data are conveyed in short independent segments, such as one or a few ADPCM nibbles. The length of each segment is chosen to be short enough that the loss of one segment of data from the received signal does not significantly degrade the quality of the output analog signal. The transmitter generates a parity bit for each of these segments and composes transmit frames by alternating data segments with their corresponding parity bits. The receiver then receives each data segment along with its corresponding parity bit. This arrangement allows the receiver to identify specific received segments that contain errors, and minimizes the receiver's delay between receiving the segment and determining if contains an error. The invention also comprises a system and method for detecting such an erroneous segment and blanking it. If a received frame contains more than a threshold number of erroneous segments, then the remaining segments of the frame can be muted. Subsequent frames can then also be muted until one of the subsequent frames contains fewer than a second threshold number of errors.