# 2 Data transmission fundamentals

#### Chapter 2 is all about identifying the factors which are going to dominate in the early stages of a digital communications system design. Without a good understanding of the 'big issues' of bandwidth and noise in dictating data throughput and modem complexity, the more detailed issues of modulation type, hardware implementation and performance optimization, covered in the later chapters, will not fit into place. #### Most of the discussion centres on the engineering aspects and how they influence system design however the first section covers issues which fall outside the control of the engineer, such as regulatory or commercial pressures, yet which often have a significant part to play in dictating the final engineering solution. |

#### Section 2.2 begins to unravel how channel bandwidth and system noise dominate the performance of all digital communication systems, demonstrating that the designer is always faced with a trade-off between the two. Section 2.3 takes us quickly away from binary signals of 1s and 0s to multi-level modulation, where the signal on the channel can represent a single bit or thousands of bits at any one time, as the designer chooses. Finally, Section 2.4 ties up the loose ends of the by-now-familiar noise and bandwidth debate, introducing the theoretical optimum performance for a digital communications link as defined in the Shannon bound.