Importance

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Abstract

In order to collect data messages at a base station which is in radio communications with portable data collection terminals, such as bar code readers, that may move between different locations, all remote from the base station, a set of successive polling messages are broadcast from the base station addressed to different individual remote units during successive polling cycles. Increases in speed of polling cycles are obtained by eliminating from the polling cycle messages addressed to remote units which are turned off, or are inactive for a time since the unit recently sent data to the base station. During the last polling cycle in a set, the base station transmits acknowledgment of the collection of valid data to all of the units which have transmitted data. The time required for data collection depends upon the activity of the units and complex error and collision avoidance codes are not required. The system is also adapted for use with polarization diversity radio transmission whereby the one of a pair of antennas disposed at the base station in polarization diversity relationship (orthogonal to each other) can be selected for transmission for each units next poll depending upon which of the antennas received the strongest poll response signal from that unit on the previous cycle of polling signals.

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First Claim