OVERVIEW

The baseband and bandpass digital communication systems described in Chapter 2, "Baseband Modulation and Demodulation," and Chapter 3, "Bandpass Modulation and Demodulation," used a single source of information, and transmitted the data across a single communication channel. However, multiple sources of information sharing one or more communication channels is a typical occurrence. Multiplexing allows a group of independent sources to share a communication channel without interference, by exploiting the orthogonality of the data transmission in the time or frequency signal space.

The independent data sources can be separated in time by transmitting at different intervals using the same baseband or bandpass range of frequencies. This technique is called time division multiplexing (TDM). The independent data sources can be separated in frequency by transmissions using non-overlapping ranges of bandpass frequencies. This technique is called frequency division multiplexing (FDM). The independent data also can be transmitted at the same time and in the same range of bandpass frequencies by processing the sources with a unique code to make them orthogonal. This technique is called code division multiplexing (CDM) or code division multiple access (CDMA).

Finally, orthogonal frequency division multiplexing (OFDM) separates a single data source into multiple subchannels, each of which carries only a portion of the total information, but at a lower data rate. OFDM provides an effective technique for the mitigation of multipath fading in wireless communication channels.

On the CD The models for these SystemVue simulations in TDM, FDM, CDM, and...