초록 ▼

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. 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 ser

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. 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 an exchange with the remote units, but instead send data to the remote units only as part of the exchange. To alert a remote unit when a message is waiting at a base station to be sent to a particular unit, some of the acknowledge (base-to-remote) packets sent by the base station may contain an identification such as a list of all remote units (identified by ID number) which have messages waiting. Alternatively, a bit map can be used to identify these remotes. These base-to-remote packets with the identification of remotes with messages waiting are called “announcements.”Each remote unit (if not engaged in regular exchanges for a time interval) periodically listens (activates its receiver) to receive an announcement packet containing such a list or bit map and decodes this announcement to see if it has a message waiting. If so, this remote unit then sends a transmit packet so the base can send the waiting message in an acknowledge packet.

대표청구항 ▼

A method of operating a communication system which has a base station and a plurality of remote units, comprising the steps of: a) sending from said base station an announcement message having an identification of particular ones of said remote units which have data messages waiting at said base sta

A method of operating a communication system which has a base station and a plurality of remote units, comprising the steps of: a) sending from said base station an announcement message having an identification of particular ones of said remote units which have data messages waiting at said base station for transmission to said particular ones; b) intermittently turning on a receiver at each one of said remote units to receive said announcement message; c) sending from each one of said particular ones to said base station an inquiry message at a time selected by each respective one of said particular ones; and d) sending a data message from said base station to each one of said particular ones of said remote units.