Signal quality measure in packet data communication

• US 5,103,461 A
• Filed: 12/19/1990
• Issued: 04/07/1992
• 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: Tymes, LaRoy
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): CAIN, DAVID C
• Application Number:
  US07/630,047
• Time in Patent Office: 475 Days
• Field of Search: 375/1, 380/34
• US Class Current: 375/141
• 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: H04L 5/1484 operating bytewise
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements

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 compuer 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 producing an indication of received-signal quality in a packet data communication system, the system including a plurality of stations, comprising the steps of:

a) sending a data packet from a first one of said stations to a second one of said stations, said data packet including an encoded portion having a predetermined number of encoded bits representing a selected code;

b) receiving said packet at said second station and translating said encoded portion to produce decoded bits of said predetermined number;

c) comparing said decoded bits with said selected code to produce a quality measure related to the number of valid bits found in said comparing; and

d) selecting a station of said plurality of stations for sending data packets to said first station based upon said quality measure.

2. A method according to claim 1 wherein said step of sending is by RF transmission.

3. A method according to claim 2 wherein said RF transmission employs spread spectrum modulation.

4. A method according to claim 3 wherein said encoded portion is encoded using a pseudo-random sequence.

5. A method according to claim 4 wherein said encoded portion is a leading part of said packet, and includes at least about forty bits.

6. A method according to claim 5 wherein said packet is discarded unless a selected minimum number of said bits are valid.

7. A method according to claim 1 wherein said first station is a remote terminal and said second station is a base station.

8. A method of producing an indication of received-signal quality in a packet data communication system, comprising the steps of:

a) sending a data packet from a first station to a second station, said data packet including an encoded portion having a predetermined number of encoded bits representing a selected code;

wherein said first station is a remote terminal and said second station is a base station; and

wherein a plurality of said base stations are included in a system, and each said remote terminal receives acknowledge packets from only one selected base station;

b) receiving said packet at said second station and translating said encoded portion to produce decoded bits of said predetermined number;

c) comparing said decoded bits with said selected code to produce a quality measure related to the number of valid bits found in said comparing.

9. A method according to claim 8 including the step of selecting one of said base stations to send acknowledge packets to each of said remote terminals in response to said quality measure.

10. A packet data communication system having a plurality of stations, each station transmitting and receiving data packets, comprising:

a) a first one of said stations including means for transmitting a data packet having an encoded portion with a predetermined number of encoded bits representing a selected code;

b) a second one of said stations receiving said data packet and translating said encoded portion to produce decoded bits of said predetermined number;

c) means in said second one of the stations for comparing said decoded bits with said selected code to determine the number of valid bits in said encoded portion to thereby produce a measure of receive-signal quality for said transmitted data packet;

said second one of said stations processing said received data packet as valid data if said measure is greater than a selected value even though said number of valid bits is less than said predetermined number.

11. A system according to claim 10 wherein said transmitting is by wireless RF.

12. A system according to claim 11 wherein said wireless RF employs spread spectrum modulation.

13. A system according to claim 12 wherein said encoded portion is encoded using a pseudo-random sequence.

14. A system according to claim 13 wherein said encoded portion is a leading part of said data packet, and includes at least about forty bits.

15. A system according to claim 14 wherein said packet is discarded by said second one of the stations unless a selected minimum number of said bits are valid.

16. A system according to claim 10 wherein said first one of the stations is one of a plurality of remote terminals and said second one of the stations is a base station.

17. A packet data communication system having a plurality of stations, each station transmitting and receiving data packets, comprising:

a) a first one of said stations including means for transmitting a data packet having an encoded portion with a predetermined number of encoded bits representing a selected code;

b) a second one of said stations receiving said data packet and translating said encoded portion to produce decoded bits of said predetermined number;

wherein said first one of the stations is one of a plurality of remote terminals and said second one of the stations is a base station;

wherein said remote terminals send data packets to said base stations during a time window selected by said remote terminals, and said base stations send acknowledge packets to a remote terminal only in a fixed window referenced to said time window;

c) means in said second one of the stations for comparing said decoded bits with said selected code to determine the number of valid bits in said encoded portion to thereby produce a measure of received-signal quality for said transmitted data packet.

18. A packet data communication system having a plurality of stations, each station transmitting and receiving data packets, comprising:

a) a first one of said stations including means for transmitting a data packet having an encoded portion with a predetermined number of encoded bits representing a selected code;

b) a second one of said stations receiving said data packet and translating said encoded portion to produce decoded bits of said predetermined number;

wherein said first one of the stations is one of a plurality of remote terminals and said second one of the stations is a base station;

wherein a plurality of said base stations are included in said system, and each said remote terminal receives acknowledge packets from only a selected one of said base stations;

c) means in said second one of the stations for comparing said decoded bits with said selected code to determine the number of valid bits in said encoded portion to thereby produce a measure of received-signal quality for said transmitted data packet.

19. A system according to claim 18 only one of said base stations sends acknowledge packets to each of said remote terminals, and said one of said base stations is selected in response to said measure of received-signal quality.

20. A system according to claim 19 wherein at least some of said remote terminals include bar code readers to generate bar code data for transmitting in said data packets.

29. A method according to claim 20 including the step of selecting one of said base stations to send acknowledge packets to each of said remote terminals in response to said quality measure.

21. A receiver for direct sequence spread spectrum modulated RF data packets, comprising:

a) means for translating an initial encoded portion of a received data packet to produce decoded bits of a predetermined number;

b) means for comparing said decoded bits with a predetermined code to determine the number of valid bits in said encoded portion to thereby produce a measure of received-signal quality for said data packet;

said receiver processing said received data packet as valid data if said measure is greater than a selected value even though said number of valid bits is less than said predetermined number.

22. A receiver according to claim 21 wherein said predetermined number is at least about forty.

23. A receiver according to claim 21 wherein said received packet is discarded if said number of valid bits is less than about thirty-five.

24. A method of operating a packet data communication system, comprising the steps of:

a) sending a data packet from a first station to a second station, said data packet including an encoded portion having a predetermined number of encoded bits representing a selected code;

b) receiving said packet at said second station and translating said encoded portion to produce decoded bits of said predetermined number;

c) comparing said decoded bits with said selected code to produce a quality measure related to the number of valid bits found in said comparing; and

d) continuing to receive said data packet as valid data if said quality measure exceeds a selected value, even though the number of valid bits found in said comparing is less than said predetermined number.

25. A method according to claim 24 wherein said step of sending is by spread spectrum RF transmission, and wherein said encoded portion is encoded using a pseudo-random sequence.

26. A method according to claim 25 wherein said encoded portion is a leading part of said packet, and includes at least about forty bits.

27. A method according to claim 26 wherein said packet is discarded unless a selected minimum number of said bits are valid.

28. A method according to claim 25 wherein said first station is a remote terminal and said second station is a base station;

and wherein a plurality of said base stations are included in a system, and each said remote terminal receives acknowledge packets from only one selected base station.