A Software Based Implementation of an APCO Project 25 Compliant Packet Data Transmitter

This paper describes the effort within the Project54 program at the University of New Hampshire to develop a software based implementation of an APCO Project 25 (P25) compliant packet data base station, utilizing a standard PC interfaced to a commercial analog VHF FM transceiver. The goal is to develop an affordable system (under $10,000) to provide P25 compliant packet data for smaller public safety agencies requiring only a single data capable channel. The base station system is comprised of a standard PC interfaced to a commercial VHF FM transceiver. Software running on the PC implements the standard IP network interface, the P25 Common Air Interface packet assembly, forward error correction encoding, and finally the packet baseband modulation. The resulting analog baseband modulated signal is then input to the commercial VHF FM transceiver which performs the RF modulation. The process is reversed for data packet reception. This paper will focus on the overall design of the software based P25 packet data transmitter, the testing of the various stages for P25 compliance, and the testing of the final result for interoperability with commercial P25 compliant mobile radios.