CA2355192C - Packet data communication system - Google Patents

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 method of selecting a frequency channel for RF
window packet data communication is described. The method includes: (a) receiving signals by the base station on other channels different from an initially selected channel and producing a value for each of the other channels indicative of the RF
energy level in such channel (i.e. to identify a channel having the lowest RF
energy level); (b) producing a value indicative of the transmission error rate in the initial one of the channels and (c) if the transmission error rate exceeds a threshold, 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 the identified channel.

Claims (11)

Claims:

1. A method of selecting a frequency channel for RF wireless packet data communication between a base station and a 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; and 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.

2. A method according to claim 1 including a plurality of said base stations and a plurality of said remote terminals for each said base station.

3. A method according to claim 1 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.

4. A method according to claim 1 wherein each of the remote terminals sends a data packet to the base station at a time selected by the remote terminal, and receives a data packet from the base station during a fixed time window after said time.

5. A method according to claim 1 wherein said wireless RF
communication is by the spread spectrum technique.

6. A method according to claim 1 wherein a data packet transmitted by at least one of said remote terminal includes the results of reading a bar code symbol by a bar code scanner in said remote terminal.

7. A method of selecting a frequency channel for packet data transmission between a base station and a 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; and 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.

8. A method according to claim 7 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 during said predetermined time window.

9. A method according to claim 7 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.

10. A method according to claim 7 wherein said transmitting is by wireless RF modulated by the spectrum technique.

11. A method according to claim 7 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.