Chapter 1 / 1.5

1.5 REVISION QUESTIONS

1. Draw a block diagram of a simple communications system (as in Figure 1.1) and identify the source, transmitter, channel, receiver, and sink. Briefly describe the role of each block in transferring information from one point to another.

1. What is meant by the term communications channel? Give three examples of physical channels and briefly describe one key characteristic of each.

1. Briefly describe the difference between noise and interference. What are the principal sources of noise and interference in a communications channel?

1. Figure 1.2 expands the simple communications model into a more-detailed system. Why is this additional level of detail necessary for understanding modern digital communications systems?

1. What is the purpose of source encoding (compression)? Why does source encoding typically remove redundancy, while channel encoding deliberately adds redundancy?

1. In what situations is encryption required in a communications system? What functions beyond confidentiality can encryption provide?

1. What problem does channel encoding address, and how does it improve system performance in the presence of noise and interference?

1. Explain the difference between multiplexing and multiple access. Why is this distinction important in systems serving many users?

1. Why are signals often modulated before transmission across a communications channel? What practical constraints make direct baseband transmission undesirable or impossible in many systems?

1. What is meant by signal spreading, and what advantages can it offer in a hostile or interference-limited environment?

1. List the major processing steps performed by a receiver, starting from the received channel signal and ending at the sink. How do these steps relate to the functions performed by the transmitter?

1. Not all communications systems include every block shown in Figure 1.2. Give two examples of systems where certain blocks may be omitted and explain why.