Motorola Corporation

Shmuel Katar

Shlomo Scop

Haim Kashi

A communications system is described having a central station and a number of remote units arranged for communication over a common communications channel. Each remote unit has a predetermined priority parameter and each remote unit has a processor element (30), a receiver (28), a channel monitoring circuit (26) for sensing when the channel is free and a transmitter (29). The processor element is arranged to identify from received data a priority parameter of a unit currently transmitting. A comparison is performed between the priority parameter of that unit and the predetermined priority parameter, to initiate a timer function (108) in response to the channel monitoring circuit when the channel monitoring circuit indicates that the channel has become free, and to reset the timer function if the channel monitor circuit indicates that the channel has become occupied. The timer function times a selectable period which is dependent on the comparison and the timer function causes activation of the transmitter when the timer function times the selectable period. The invention is applicable to, but not limited to use in supervisory control and acquisition-of-data (SCADA) systems.

Communications system with priority scheme for reduced access delay

In a radio frequency communication system, a primary unit interrogates a plurality of secondary units over a radio communication channel. The primary unit receives a command to initiate an interrogation cycle over the communication channel. The primary unit then selects a time delay from a set of time delays, and transmits an interrogation request to each secondary unit of at least a subset of the plurality of secondary units in series after the selected time delay if the channel is free at the end of the selected time delay. The primary unit then selects the longest time delay for the next interrogation cycle if a channel grant command is received, and selects a shorter time delay for the next interrogation cycle if no channel grant command is received.

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Tnuvot, Israel

Shmuel Katar