PACKET DATA COMMUNICATION SYSTEM

摘要

A packet data transmission system is used to link a number of remote han d- held data-gathering units such as bar code readers to a central computer whi ch maintains a database management system. Data packets are sent from the remot e 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 t he RF energy level in such channel (i.e. to identify a channel having the lowest R F energy level); (b) producing a value indicative of the transmission error rate in t he 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.