PACKET DATA COMMUNICATION SYSTEM

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. Direct sequence spread spectrum modulation is used for the RF link. The remote hand-held units initiate an exchange usi ng RF transmission to and from the base stations, receiving only during a rigid ti me window following a transmission from the remote unit. The base stations cann ot initiate communication to the remote units, but instead send data to the remote units only as part of the exchange.