Optimum Information-Acquisition Systems

The conditions for optimum information acquisition by means of communication systems involve two basic costs (1) average communication cost and (2) average risk cost. Communication cost is determined by the values of the basic communication parameters, power, bandwidth, and time. It depends on the operational conditions of message density, method of modulation, and the coding technique. Risk cost is the cost of decision and arises in the detection of signals in noise. It is a function of the method of decoding received signals and decreases with increasing reliability of detection. Increases in power, bandwidth, and time decrease risk cost and increase communication cost, respectively Specification of the constraints existing between power, bandwidth, and time in an actual communication system permit risk cost as well as communication cost to be expressed as a function of the three communication parameters. Since a trade-off exists between risk and communication costs, the optimum operating condition for a communication system can be found by solving for the minimum average total cost. This method is applied to a comparative evaluation of binary communication systems using three fundamental means for acquiring information in the presence of noise unidirectional, bidirectional employing information feedback, and bidirectional employing decision feedback.