Abstract A frequency hopping spread spectrum wireless data communications network is disclosed. Time mark frames are transmitted by each base station at a regular cadence and each time mark frame contains all information necessary to determine the hopping sequence of channels, a sub-set of possible channels in use, and the particular channel upon which the time mark was transmitted. Receipt of the time mark resynchronizes a slot clock that is used by the wireless terminals in implementing a media access protocol with defined synchronous time slots. The base station to roaming terminal radio link is half duplex. Each base station broadcasts an end-of-message frame during a hop period that indicates that it has no more data to send during that hop. If there are no inbound messages a roaming terminal needs to send, it puts its receiver in a low power mode until the next hop time approaches. Look ahead acquisition of the hopping sequence for a nearby base station when the received signal level for the current base station drops is also disclosed.
In a radio frequency data communication system of the type comprising at least one base station and a plurality of terminals, said system employing a media access protocol of the type that defines a plurality of discrete time slots generated locally at each of said plurality of terminals and at said base station, the improvement comprising in combination therewith: a frequency hopping spread spectrum transmitter at said base station for transmitting an information signal for a predetermined hop period on each of a predetermined plurality of career frequencies in a predetermined sequence; a first interval within each hop period and subsequent to transmission of said information signal, wherein during said first interval said base station transmits outgoing messages addressed to specific terminals, said messages being of variable duration; and a second interval within at least one of said hop periods, subsequent to said first interval, wherein during said second interval any of said terminals may transmit messages intended for said base station using a contention-free, discrete time slotted protocol.
Claim 2
Dependent Claim
169 words
In a radio frequency data communication system of the type comprising at least one base station and a plurality of terminals, said system employing a media access protocol of the type that defines a plurality of discrete time slots generated locally at each of said plurality of terminals and at said base station, the improvement comprising in combination therewith: a frequency hopping spread spectrum transmitter at said base station for transmitting an information signal for a predetermined hop period on each of a predetermined plurality of career frequencies in a predetermined sequence; a first interval within each hop period and subsequent to transmission of said information signal, wherein during said first interval said base station transmits outgoing messages addressed to specific terminals, said messages being of variable duration; and a second interval within at least one of said hop periods, subsequent to said first interval, wherein during said second interval any of said terminals may transmit messages intended for said base station using a contention-free, discrete time slotted protocol.
Claim 3
Dependent Claim
72 words
The radio frequency data communication system recited in claim 1 wherein at least some of said information signals provide a time mark frame for at least some of said plurality of carrier frequencies, wherein said time mark frame serves as a slot synchronizing signal for both: (1) the predetermined sequence of said plurality of carrier frequencies between said base station and said plurality of terminals, and (2) the discrete time slotted protocol.