Packet data communication system

• US 5,479,441 A
• Filed: 01/18/1994
• Issued: 12/26/1995
• Est. Priority Date: 06/29/1989
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Kramer, John W. Jr., Tymes, LaRoy
• Primary Examiner(s): Cain, David C.
• Application Number:
  US08/183,069
• Time in Patent Office: 707 Days
• Field of Search: 375/1
• US Class Current: 375/130
• CPC Class Codes: G06K 17/0022 arrangements or provisious for transferring data to distant stations, e.g. from a sensing device "transfer between computer elements G06F13/00 "; data-transmission H04L
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04L 1/1678 where the control information is for timing, e.g. time stamps
• CPC Class Codes: H04L 1/1867 Arrangements specially adapted for the transmitter end
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint
• CPC Class Codes: H04L 5/1484 operating bytewise
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals

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. Direct sequence spread spectrum modulation is used for the RF link. 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.

Claims

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;

b) receiving at said one unit from said base station a reply signal during a second time period occurring only during a selected time window after said first time period, said second time period being the same for at least some of said units.

2. A method according to claim 1 wherein said steps of transmitting and receiving are by spread spectrum RF signals.

3. A method according to claim 1 wherein said remote terminal unit is one of a plurality of remote stations associated with the transmitter of said reply signal.

4. A method according to claim 3 wherein said remote stations are hand-held data-gathering units which include manual control elements, and wherein at least some of said remote stations include bar-code reading devices.

5. A method according to claim 1 wherein said reply signal is transmitted by a second station which is one of a plurality of said second stations physically spaced from one another, and there are a plurality of said remote terminal units for each said second station.

6. A method according to claim 1 including the step of listening at said unit prior to said step of transmitting said data packet to see if other like units are transmitting.

7. A system for transmitting data packets from one of a plurality of first stations to a second station, comprising:

a) a transmitter in said one first station for transmitting a data packet from said one first station to the second station during a first time period selected by said one first station;

b) a receiver in said one first station for receiving a reply signal from the second station during a second time period occurring only in a time window referenced to said first time period by a selected delay, said selected delay being the same for all said plurality of first stations.

8. A system according to claim 7 wherein said transmitter and receiver employ spread spectrum RF signals.

9. A system according to claim 7 wherein said first station is one of a plurality of remote stations associated with a transmitter of said reply signal.

10. A system according to claim 9 wherein said remote stations are hand-held data-gathering units which include manual control elements, and wherein at least some of said remote stations include bar-code reading devices.

11. A system according to claim 7 wherein said reply signal is transmitted by a second station which is one of a plurality of said second stations physically spaced from one another, and there are a plurality of said first stations for each said second station.

12. A method according to claim 7 including means for listening at said first station prior to said transmitting said data packet to see if other like units are transmitting.