Digital speech transmission for highly encrypted and paramilitary operated land mobile radio communications over a narrowband UHF channel

The functional, technical and operational requirements which determine the design of the speech order are specified. Compression methods including both waveform coding and source coding are reviewed, and their performance together with implementation practicability are discussed. The importance of the type of modulation and encryption methods to be used in conjunction with the encoder is emphasised. It is concluded that robust linear predictive coding algorithms would provide some pragmatic solutions in the future for digital secure voice transmission over narrowband radio channels in the light of rapid development of digital signal processing techniques and very large scale integrated (VLSI) circuits technology. Specifically, code excited linear predicted (CELP) with line spectral pair (LSP) coefficients has shown considerable promise for good quality coding of speech at low bit rates with reduced complexity which is suitable for land mobile communications