S-72.227 Digital Communication Systems
Study Guide 6: Digital Transmission over Fading Channels

Topics

• Narrowband system (introduction, basic concepts)
• Wideband TDMA system (introduction, basic concepts: need for adaptive equalization)
• Wideband DS-CDMA system (introduction, basic concepts: need for Rake receiver structure)
• Rake receiver & Maximum Ratio Combining (concepts, structure, and analysis of functions)

• What is meant by digital transmission over a narrowband (i.e. flat fading) channel?
• How can transmission performance over a flat fading channel be improved? (Answer: use a diversity scheme => future lecture)
• What means TDMA transmission over a wideband (i.e. selectively fading) channel?
• How can TDMA transmission performance over a selectively fading channel be improved? (Answer: use adaptive equalization => future lecture)
• What means DS-CDMA transmission over a wideband (i.e. selectively fading) channel?
• How can DS-CDMA transmission performance over a selectively fading channel be improved? (Answer: use a Rake receiver)
• What is the basic purpose and general structure of a Rake receiver? This topic was selected, since it provides insight into (at a basic level) how a DS-CDMA system functions.
• The concept of equivalent low-pass signal domain is important (please consult Proakis' book if this concept is not familiar).
• What is the meaning of channel estimation, Rake fingers, phase synchronization/alignment, and Maximum Ratio Combining (MRC)?
• What are the implications of autocorrelation and cross-correlation on transmission performance?

Lecture notes; John G. Proakis: Digital communications (selected parts)
 

DAG Instructions

This guide is intended for Discussion Agent Group (DAG) members, but it can be used also by other students. DAG members should get themselves familiar with the lecture material and Study Guide well before the lecture and make clear for themselves the themes they would like to generate discussion. If it appears that there remain unsolved questions after the session they will be discussed in next sessions. It is important to note that the time reserved for discussion is maximum of 45 min. only.

Group's tasks

• Group should select session Chair. The role of the session chair is to give the floor for audience and to guide discussion generally.
• Group should select a secretary whose task is to write down all the questions and answers popping out at the session. The minutes should be submitted to the course instructor within two days and it will appear at the course homepage.
• Lecture themes (from lecture transparencies and study guides) must be divided to group members such that each member shall carry about the same workload. Also chair and secretary must participate on drafting the questions.

Each group member should

• Make a list of interesting questions/issues she/he knows the answer. Purpose of these questions is to clarify/underline important topics of the lecture (from one's personal view)
• Make a list of topics/themes/details that are not understood
• Propose answers to the suggested questions (as listed above)
• Ask the suggested questions from the audience during the session.