Threshold-less collision detection and bit arbitration in a cfsk data

Abstract

In a chirped-frequency-shift-keyed data system, in which a plurality of stations each contain a data transmitter and a data receiver constantly monitoring a common system communications medium even while the companion transmitter is transmitting digital data, the CFSK signal is received during each of a successive plurality of synchronous bit time intervals with a first amplitude. The received signal is: squared and filtered in a first channel; multiplied with a locally generated signal of a second amplitude and associated with a first binary chirp condition, and then filtered, in a second channel; and multiplied with another locally generated signal of the second amplitude and associated with the remaining binary chirp condition, and then filtered, in a third channel. The channel outputs are functions of the signal amplitudes and also of the number of system transmitters simultaneously transmitting one or the other of the binary data states. Comparison of the energy contents of the various channels determines if a collision has occurred; and if a collision is detected, further comparisons arbitrate the collision to the bit state of the larger number of transmitters then active. The collision detection and bit arbitration is carried out without reference to a threshold value.