Channel Q function and capacity

Channel Q function is, for a time-invariant channel, the sum of auto-correlation functions of the channel impulse response functions over multiple receivers. It can be used to characterize the performance (output SNR) of acoustic communications using either passive-phase conjugation or decision feedback equalizer. Channel Q function also determines the channel capacity for a single source and multiple receivers (SIMO). We analyze in this paper that the properties of the channel Q function and show that it possesses a universal and stable properties for underwater acoustic waveguides, irrespective of the channel sound speed profiles, source and receiver range/depths. This property is examined with real data collected in various oceans with significant temporal variations in the propagation conditions and/or source-receiver range. The channel Q function determines the single-source multiple-receivers (SIMO) channel capacity. An example is given for a realistic ocean environment.