Certified two-way sources-initiated transfer

Selen, M. A., Stelzer, T. J. (2008) U.S. Patent CA 2576495 A1. Washington, D.C.: U.S. Patent and Trademark Office

An audience response system comprising a base unit and a plurality of remote units communicating using wireless communication operating on a frequency pair. When a response key on a remote unit is activated, the remote unit transmits a voting signal packet to the base unit. The base unit registers the vote and transmits an acknowledgment signal to the remote unit. When the remote unit receives an acknowledgment signal, the remote unit certifies to the operator that the vote was received. If an acknowledgment signal is not received, the remote unit will attempt at least one retransmission after a random delay before alerting the operator that the vote attempt has failed.

http://www.google.com/patents/CA2576495A1