Abstract: An encoder encodes digital signals representative of data by classifying the digital signals into first and second classes indicative of their influence on data quality and subjects them to error detection encoding capable of generating at least two error detection codes which respectively correspond to the first and second classes. A decoder receives the encoded digital signals classified into first and second digital signal classes, decodes the error detection codes, and generates error signals, corresponding to the respective digital signal classes, from which the quality of the received digital signals is estimated and the utility of the received digital signals is determined.

Abstract: A radio modulator/demodulator particularly suitable for TDMA mobile telephone use employs digital techniques for GMSK phase modulation. Phase numbers representative respectively of an intermediate frequency carrier and modulation symbols are combined digitally to combination phase numbers which are subjected to a single folded cosine table to produce a digital trignometric sequence of numbers for modulating the transmitter. Economy of components and memory is achieved and some of the modulator components are used in demodulation which is effected by the single look-up table used in sine and cosine mode alternately.