Communications systems can include wired systems where the physical transfer medium is a cable or power line. They can be wireless systems including HF equipment through to microwave broadband systems. They may also be photonic transceivers using infrared LED interfaces or fiber optics. They are usually broken down into two main categories—digital and analog. Digital communication transmits and receives data that is modulated as an encoded binary sequence where symbols are directly represented by a combination of amplitude and phase. Analog systems transceive data as a continuous modulated signal that is up or down converted between the high-frequency band and the original unmodulated base-band signal.
Communication devices are elements of the information interface, channel processing and transceiver subsystems. Communication devices may transduce physical effects containing information into electronic signals. They may engage in processing electronic signals between the local transducer and the transceiver subsystem, including encapsulating information in a format to facilitate transfer. They may also be part of the conversion and transception of data over the electromagnetic spectrum.