Theory and Applications of Ofdm and Cdma
Wideband Wireless Communications
Chapter One
Basics of Digital Communications
1.1 Orthogonal Signals and Vectors
The concept of orthogonal signals is essential for the understanding of OFDM (orthogonal
frequency division multiplexing) and CDMA (code division multiple access) systems. In
the normal sense, it may look like a miracle that one can separately demodulate overlapping
carriers (for OFDM) or detect a signal among other signals that share the same frequency
band (for CDMA). The concept of orthogonality unveils this miracle. To understand these
concepts, it is very helpful to interpret signals as vectors. Like vectors, signals can be
added, multiplied by a scalar, and they can be expanded into a base. In fact, signals fit into
the mathematical structure of a vector space. This concept may look a little bit abstract.
However, vectors can be visualized by geometrical objects, and many conclusions can
be drawn by simple geometrical arguments without lengthy formal derivations. So it is
worthwhile to become familiar with this poi ... read full excerpt from Theory and Applications of OFDM and CDMA: Wideband Wireless Communications ebook
