EE 7052: Advanced Communications

Overview of Lecture #1 - Wednesday, October 9, 1996

Handouts: Syllabus, Topical Outline

• Definitions of multiplexing, duplexing, and multiple access.
• Examples: TDM, FDM, TDD, FDD, TDMA, FDMA.
• Random access.
• The orthogonal nature of TDMA, FDMA.
• The correlation receiver.
• Code division Multiple Access (CDMA) using orthogonal signaling.
• Other Multi-Input Multi-Output (MIMO) Channels: transmitter and receiver diversity, bundled cables, dually polarized radio.
• Echo cancellation in V.32.

Conventional multiple access schemes can be highly inefficient, and the capacity and spectral efficiency of cellular networks and other multiuser systems can be improved significantly using advanced multiuser communication techniques. A good illustration of this concept is provided by the 2x2 MIMO system comprised of a pair of full-duplex voiceband data modems. Prior to 1984, frequency-division duplexing was used to avoid interference between the two transmitters. In contrast, the V.32 standard allows both transmitters to use the same frequency band, and mitigates the resulting interference using echo cancellation. The result is a doubling of capacity.

In other words, if the goal is to make the most out of the shared medium, it makes no sense to apply high-tech bandwidth-efficient coding and equalization techniques to each subchannnel of a FDM system if FDM is itself an inefficient multiplexing technique to being with.

In this class we will examine physical-layer signal processing techniques for improving the efficiency of multiuser and MIMO communication systems.