Digital Baseband Coding
Ifiok E. Otung · 2021
This chapter focuses on the remaining steps involving quantisation and encoding. In discussing pulse code modulation (PCM), it concentrates first on uniform quantisation, which is also called linear analogue-to-digital conversion, in order to discuss in quantitative terms the problem of quantisation noise and various design considerations, including the noise-bandwidth trade-off in PCM. The demerits of uniform quantisation that make them unsuitable for bandwidth-limited applications are highlighted. Attention then shifts to the more practical nonuniform quantisation techniques. The chapter explains encoding and decoding procedures in detail for the standard A-law and μ-law PCM. It discusses various modifications to PCM, mainly aimed at improved spectrum efficiency. These include differential PCM, with delta modulation and adaptive differential pulse code modulation introduced as special cases. The chapter then introduces low bit rate coding techniques for speech. Line codes are introduced as a means of electrically representing a bit stream in a digital baseband communication system.