Packet data communication system

• US 5,142,550 A
• Filed: 12/28/1990
• Issued: 08/25/1992
• 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:
  US07/635,859
• Time in Patent Office: 606 Days
• Field of Search: 375/1
• 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 1/1664 the supervisory signal being transmitted together with payload signals; piggybacking
• CPC Class Codes: H04L 1/1671 the supervisory signal being transmitted together with control information
• CPC Class Codes: H04L 1/1854 Scheduling and prioritising arrangements
• CPC Class Codes: H04L 1/188 Time-out mechanisms
• CPC Class Codes: H04L 1/203 Details of error rate determination, e.g. BER, FER or WER
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint
• CPC Class Codes: H04L 43/0847 Transmission error
• CPC Class Codes: H04L 5/1484 operating bytewise
• CPC Class Codes: H04W 36/06 Reselecting a communication resource in the serving access point
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: Y02D 30/70 in wireless communication networks

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 a communications unit, comprising the steps of:

a) transmitting a data packet from said unit during a first time period selected by the unit, the data packet including a type indicator;

b) receiving at said unit an acknowledge signal during a second time period occurring only at selected time delay after said first time period, said time delay being determined by said type indicator.

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 communications unit is one of a plurality of remote stations associated with the transmitter of said acknowledge signal, and wherein said transmitted data packet and said acknowledge signal each include identification of said communications unit.

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 acknowledge 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 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 a first station to a second station, comprising:

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

b) a receiver in the first station for receiving an acknowledge signal from the second station beginning during a second time period occurring only in a time window referenced to said first time period, said acknowledge signal having a type indicator specifying a length of time during which data is transmitted from the second station to the first station after the beginning of the acknowledge signal.

8. A system according to claim 7 wherein said transmitted data packet and said acknowledge signal are sent by 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 said second station, and wherein said transmitted data packet includes identification of said first station and said acknowledge signal includes identification of said first station.

10. A system according to claim 9 wherein said remote stations are hand-held data-gathering units which include manual control elements, wherein said units each include a processor executing instructions stored in a memory, and wherein at least some of said units include bar-code scanners.

11. A system according to claim 9 wherein all of said plurality of second stations are coupled to a host station by a communication link.

12. A system according to claim 7 wherein the transmitter at said first station listens prior to transmitting said data packet to see if other stations are transmitting.

13. A method of data transmission between a plurality of terminals and a base station, comprising the steps of:

a) transmitting a data packet from one of said terminals to said base station, the data packet including identification of said one of the terminals, and including a first type identifier;

b) receiving said transmitted data packet at said base station and transmitting an acknowledgement from the base station to said one of said terminals in a predetermined time window determined by said first type identifier, said acknowledgement including identification of said terminal and including a second type identifier, wherein said acknowledgement may include data to be transferred from said base station to said one terminal;

c) receiving said acknowledgement at said one terminal during said predetermined time window and continuing to receive for a period determined by said second type identifier.

14. A method according to claim 13 including the step of first listening at said one terminal to determine if another of said plurality of terminals is transmitting, before transmitting said data packet.

15. A method according to claim 14 wherein said transmitting is by wireless RF of the spread spectrum type.

16. A method of data transmission between a plurality of terminals and host computer via a base station, comprising the steps of:

a) initiating a fixed-time broadcast mode of operation by said host computer, and sending to said base station a fixed time value;

a) transmitting a data packet from each one of said terminals to said base station at times before said fixed time value, the data packet including identification of each one of the terminals;

b) receiving said transmitted data packets at said base station and transmitting an acknowledgement from the base station to individually to each one of said terminals in a predetermined time window after each data packet, said acknowledgement including identification of said terminal and including said fixed time value;

c) receiving said acknowledgement at each one of said terminals during said predetermined time window after said data packet for each terminal; and

d) thereafter receiving data at all of said terminals simultaneously beginning at said fixed time value.

17. A method according to claim 16 including the step of sending from each one of said terminals an acknowledgement during a time after receiving said data beginning at said fixed time value.

18. A method according to claim 16 including the step of first listening at said each one of said terminals to determine if another of said plurality of terminals is transmitting, before transmitting said data packet by each one of said terminals.

19. A method according to claim 16 wherein said transmitting is by wireless RF of the spread spectrum type.

20. A method of selecting a frequency channel for RF wireless packet data communication between a base station and plurality of remote terminals;

said base station and each of said remote terminals being able to transmit and receive data packets on any of a plurality of frequency channels, and initially transmitting and receiving on an initial one of said plurality of channels;

comprising the steps of;

a) receiving signals by said base station on other of said channels different from said initial one and producing a value for each of said other channels indicative of the RF energy level in such channel, to thereby identify one of the other channels having the lowest RF energy level;

b) producing a value indicative of the transmission error rate in said initial one of the channels;

c) if said transmission error rate exceeds a selected threshold level, sending a message from the base station to each of the remote terminals directing that transmission and reception of data packets between the base station and the remote terminals will change to said identified one of the other channels.

21. A method according to claim 20 including a plurality of said base stations and a plurality of said remote terminals for each said base station.

22. A method according to claim 20 wherein if one of said remote terminals does not receive data packets from said base station then said one remote terminal sends a data packet to said base station on another of said channels and listens for an acknowledgement data packet from the base station, and if necessary repeats said sending and listening, to thereby find the correct channel.

23. A method according to claim 20 wherein each of the remote terminals sends a data packet to the base station at a time selected by the remote terminal, and receives an data packet from the base station during only a fixed time window after said time.

24. A method according to claim 20 wherein said wireless RF communication is by the spread spectrum technique.

25. A method according to claim 20 wherein a data packet transmitted by at lest one of said remote terminal includes the results of reading a bar code symbol by a bar code scanner in said remote terminal.

26. A method of selecting a frequency channel for packet data transmission between a base station and plurality of remote terminals, said base station and each of said remote terminals being able to transmit and receive data packets in any of a plurality of channels, a selected one of said channels being designated at a given time for transmission and reception of data packets, comprising the steps of:

a) receiving signals by said base station and producing a signal indication for a plurality of said channels, then selecting a preferred one of said frequency channels responsive to said signal indications, when said remote terminals are not transmitting said data packets;

b) receiving data packets from said remote terminals by said base station in said selected channel, and measuring the quality of reception of said data packets;

c) if said measured quality is below a threshold, transmitting to each of said remote terminals separate acknowledge messages responsive to data packets received by said base station designating said preferred one of said channels for transmission and reception of data packets in the future.

27. A method according to claim 26 wherein said acknowledge messages are transmitted from the base station to said remote terminals in a predetermined time window, and said acknowledge messages are received at each remote terminal only during said predetermined time window.

28. A method according to claim 26 including the step of first receiving at each said remote terminal to detect transmission by another of said plurality of remote terminals, before transmitting a data packet.

29. A method according to claim 26 wherein said transmitting is by wireless RF modulated by the spectrum technique.

30. A method according to claim 26 wherein at least some of said data packets include the results of reading a bar code symbol by a bar code scanner in a remote terminal.

31. A method of transmitting data from a remote terminal unit to a base station, comprising the steps of:

a) transmitting a data packet from said remote unit to said base station during a first time period starting at a first time selected by the unit;

b) receiving at said remote unit from said base station an acknowledge signal during a second time period occuring only a fixed time delay after said first time;

said remote unit having a standard operating mode responsive to transmission from said base station only during said second time period and only after transmitting a data packet.

32. A method according to claim 31 wherein there are a plurality of said remote terminal units in a system, and at least some of said remote units also have another operating mode in which a type indicator transmitted with said data packet indicates a selected value for said second time period longer than a standard value for said second time period.

33. A method according to claim 31 wherein there are a plurality of said remote terminal units in a system, at least some of said remote units also have another operating mode in which a type indicator transmitted with said acknowledge signal indicates a selected value for said second time period longer than a standard value for said second time period.

34. A method according to claim 31 wherein there are a plurality of said remote terminal units in a system, and at least some of said remote units also have another operating mode in which a type indicator transmitted with said acknowledge signal indicates a fixed starting time at which extended data is to be transmitted by said base station without another data packet being transmitted by a remote unit.

35. A method according to claim 31 wherein said step of transmitting is by a spread spectrum RF signal, and said step of receiving includes receiving a spread spectrum RF signal.

36. A method according to claim 31 wherein said transmitted data packet and said acknowledge signal each include identification of said remote terminal unit.

37. A method according to claim 31 wherein said remote unit includes a bar-code reading device.

38. A method according to claim 31 wherein said remote unit includes a keyboard input and visual display.

39. A method according to claim 31 wherein there are a plurality of said remote terminal units in a system, and said acknowledge signal is transmitted by a base station which is one of a plurality of like base stations, and each one of said base stations is coupled by a local area network for communication with a central computer.

40. A method according to claim 31 including the step of receiving at said unit prior to said step of transmitting said data packet, to detect transmission by another one of said remote terminal units.

41. A method according to claim 40 wherein said steps of transmitting is and receiving are by spread spectrum RF signals;

wherein said transmitted data packet and said acknowledge signal each include identification of said remote terminal unit;

wherein said remote terminal unit includes a bar-code reading device.