H - Electricity – 04 – K
Patent
H - Electricity
04
K
325/16, 325/3
H04K 1/00 (2006.01) H04B 1/713 (2006.01)
Patent
CA 1251262
RAPID ANTI-JAM FREQUENCY-HOPPING TIME SYNCHRONIZATION ABSTRACT OF THE DISCLOSURE A method is disclosed for synchronizing the operation of frequency hopping, spread spectrum communi- cation devices in a network. One device (20) (the "NTU") is deemed to be keeping the network time, to which the other devices (25, 30, 35) must synchronize in order to communicate over the network. In a broad- cast mode of the method an unsynchronized unit (25, 30, 35) (a "RTU") operates in an idle state to receive on a discrete set of receive frequencies. The total communication time period is divided into intervals, and a unique synchronization code is generated for each time interval which defines the idle state frequencies and time information transmit frequencies to be employed in accordance with the method. The time kept by the RTU is assumed to within a predetermined number of time interval of the present network time interval. In a broadcast mode the NTU transmits sequences of sychroni- zation messages, each sequence including a message transmitted at a receive frequency for each of the past, present and future time intervals necessary to cover the time uncertainty time. This sequence is transmitted at a transmit hop rate substantially higher than the RTU receive hop rate, so that all possible receive frequencies and synchronization codes are brac- keted by the transmission sequence. Each message includes information enabling the RTU to predict the time and frequency at which network time information will be transmitted by the NTU. The RTU receives one of the messages and tunes to the appropriate receive frequency to receive information enabling it to synch- ronize to the network time. In a demand entry mode, the sequence of synchronization messages can be trans- mitted by an RTU, and the NTU operating in the idle state receives one message, interprets it to determine the time and frequency at which the RTU expects to receive time information transmissions, and provide such transmission at the expected time and frequency. In a passive mode, one RTU may receive a synchroniza- tion transmission from a third party RTU operating in the demand mode, and thereafter receive the time infor- mation transmission from the NTU. Synchronization is achieved within a time which is significantly shorter than the initial time uncertainty between the network time kept by the NTU and the time kept by a RTU.
519625
Lane Keith A.
O'connor Roger J.
Hughes Aircraft Company
Sim & Mcburney
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