S-72.227 Digital Communication Systems
Study Guide 9: Introduction to Spread Spectrum Systems

Topics

• Direct sequence (DS), frequency hopping (FH) and time hopping (TH)

• Interference & SS

• Pseudo-random code generation & properties

• FDMA, TDMA and CDMA system comparison

• BPSK and QPSK direct sequence transmitter and receiver.

• Near/far effect

General

• Consider how DS suppresses narrowband interference

• Compare Direct Sequence (DS), Frequency Hopping (FH), and Time Hopping (TH) systems

• When DS/FH should be used? Consider practical systems that utilize these techniques.

• Discuss pseudo-random code generation and their properties

• How code autocorrelation and cross correlation effects system performance in different channels?

• Consider frequency reuse in CDMA and TDMA cellular systems

• Discuss BPSK and QPSK direct sequence transmitter and receiver. What are their error rates and which one to use? 

• What is near/far effect? How its effect can be minimized?

References

Lecture notes; A.B. Carlson: Communication Systems, John G. Proakis: Digital Communications (selected parts), Use Web for additional info!
 

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.