In communications signal processing, it is common to use the notion of complex signals. In the implementation sense, a complex signal is nothing more than the combination of two real signals (real and imaginary parts) carried, e.g., by two separate wires or bit-streams. However, the convenience of the complex signal notation in frequency domain analysis has made the complex signal concept and essential ingredient in communication theoretic and communications transceiver signal processing literature.
Another important ingredient in communications signal processing is the bandpass signal concept, and the possibility to model a (real) bandpass system with a complex baseband model (in this context the complex signal concept becomes mandatory). In general, various combinations of real/complex and baseband/bandpass signal and system models are encountered when studying the signal processing algorithms for communications receivers and transmitters.
Most of today's literature is satisfied with a very rudimentary treatment of complex signal and system concepts. However, thorough understanding of the possibilities of complex signal processing, combined with efficient multirate DSP algorithms and digital VLSI technologies offers new tools for efficient communications signal processing implementations.
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