Abstract: A digital communication system and method, in which a convolutional coding of input data sequence Bm (m=1, 2, 3, . . . ) is carried out, and first coded data X1 of first coded data sequence Xm are deleted to output second coded data sequence Xn onto a transmission line. First receive data X1' are uniquely determined on the basis of receive data sequence Xn' transmitted via the transmission line, corresponding to the second coded data sequence Xn, and the last decoded data B0' of a data sequence which is previously received and decoded, to produce data sequence Xm' which are decoded by a maximum likelihood coding to obtain a decoded data sequence. Hence, a fixed amount of information of the data can be always compressed to transmit the compressed data even in a low line quality environment.

Abstract: This invention provides a method for substantially reducing the time drift f a network clock in a frequency hopping communications system, without the need for a master unit to keep network time. The automatic network time tracking mechanism of each receiver is disabled when a network time update is received within a critical period of time from the closest synchronization update time or frequency hop time. The critical period is defined as the time between the closest synchronization update time to the local time when reception occurs less one-half the minimum tracking adjustment of the receiver plus the minimum processing or decoding delay, and that closest synchronization update time plus one half the minimum tracking adjustment of the receiver plus the maximum processing or decoding delay.