Packet data communication system
First Claim
1. A method of transmitting data packets from one of a plurality of remote terminal units to a base station, comprising the steps of:
- a) transmitting a data packet from said one unit to said base station during a first time period selected by the unit, said data packet being transmitted at a selected radio frequency which is one of a set of different radio frequencies in a fixed band, a different one of said set of radio frequencies in said fixed band being selected at repetitive timing intervals according to a given sequence of selected radio frequencies;
b) receiving at said one unit from said base station an acknowledge signal during a second time period occurring only a fixed time delay after said first time period;
said acknowledge signal including an indication of the order of said selected radio frequency in said given sequence and an indication of elapsed time within one of said timing intervals.
2 Assignments
0 Petitions
Accused Products
Abstract
A packet data transmission system is used to link a number of remote hand-held data-gathering units such as bar code readers to a central computer which maintains a database management system. Data packets are sent from the remote units by an RF link to intermediate base stations, then sent by the base stations to the central computer by a serial link. A frequency-hopping transmission method is used for the RF link. The remote units and base stations are all synchronized to a repeating pseudo-random sequence of frequencies in a band (902-928 MHz) which allows this type of transmission. The remote hand-held units initiate an exchange using RF transmission to and from the base stations, receiving only during a rigid time window following a transmission from the remote unit. The base stations cannot initiate communication to the remote units, but instead send data to the remote units only as part of the exchange. The reply messages from the base stations to the remotes contain synchronizing information to maintain coherence with the pseudo-random sequence.
323 Citations
33 Claims
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1. A method of transmitting data packets from one of a plurality of remote terminal units to a base station, comprising the steps of:
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a) transmitting a data packet from said one unit to said base station during a first time period selected by the unit, said data packet being transmitted at a selected radio frequency which is one of a set of different radio frequencies in a fixed band, a different one of said set of radio frequencies in said fixed band being selected at repetitive timing intervals according to a given sequence of selected radio frequencies; b) receiving at said one unit from said base station an acknowledge signal during a second time period occurring only a fixed time delay after said first time period;
said acknowledge signal including an indication of the order of said selected radio frequency in said given sequence and an indication of elapsed time within one of said timing intervals. - View Dependent Claims (2, 3, 4, 5)
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6. A system for transmitting data packets from one of a plurality of first stations to a second station, comprising:
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a) a transmitter in said one first station for sending a data packet from said one first station to the second station during a first time period selected by said one first station;
said transmitter sending said data packet at a selected radio frequency which is one of a set of different radio frequencies in a fixed band;
said transmitter including means for selecting a different one of said set of radio frequencies at repetitive timing intervals according to a given sequence of selected radio frequencies;b) a receiver in said one first station for receiving an acknowledge signal from the second station during a second time period occurring only in a time window referenced to said first time period by a fixed delay;
said acknowledge signal including an indication of the order of said selected radio frequency in said given sequence and an indication of elapsed time within one of said timing intervals. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of transmitting data packets from a first station to a second station, comprising the steps of:
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a.) transmitting a data packet from said first station to said second station at a selected frequency which is one of a predetermined sequence of frequencies in a band, said selected frequency being changed at regular intervals within a repeat period, said data packet including an indication of a position of said selected frequency in said predetermined sequence and an elapsed time in one of said regular intervals; b) receiving said data packet at said second station at said selected frequency and synchronizing said second station in response to said indication. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A data transmission system, comprising:
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a) a first station having means for transmitting information at a selected frequency which is one of a predetermined sequence of frequencies in a band, said selected frequency being changed at regular intervals, said information including an indication of a position of said selected frequency in said predetermined sequence and an elapsed time in one of said regular intervals; b) a second station having means for receiving said information at said selected frequency and means for synchronizing said second station in response to said indication. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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29. A method of transmitting data packets from a remote station to a base station, comprising the steps of:
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a) transmitting a data packet from said remote station to said base station during a first time period, said data packet being transmitted at a selected radio frequency which is one of a set of different radio frequencies in a fixed band, a different one of said set of radio frequencies in said fixed band being selected at repetitive timing intervals according to a given sequence of selected radio frequencies; b) receiving at said remote station from said base station a reply signal during a second time period after said first time period;
said reply signal including an indication of the order of said selected radio frequency in said given sequence and an indication of elapsed time within one of said timing intervals. - View Dependent Claims (30, 31, 32, 33)
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Specification