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Specifications
APCO Project 25
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| APCO Project 25 Specifications |
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| spectrum: | VHF (136-178 MHz)
UHF (low: 400-470 MHz, high: 450-520 MHz)
800 MHz trunking (805-825 / 850-870 MHz) |
| modulation: | QPSK-C, 6.25 kHz bandwidth
C4FM, 12.5 kHz bandwidth |
| aggregate bit rate: | 9.6 kbps |
| vocoder: | IMBE (Improved MultiBand Excitation), operating at 4.4 kbps |
| low speed data channel: | 88.9 bps |
| transmit power: | 2 - 8 W continuous (representative) |
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Specifications:
- Telecommunications Industry Association (TIA) documents:
- TSB 102, Project 25 System and Standards Definition
- Interim Standard 102.AAAA, Project 25 DES Encryption Protocol
- Interim Standard 102.BAAA, Project 25 Common Air Interface
- TSB 102.BAAB, Project 25 CAI Conformance Testing
- Interim Standard 102.BABA, Project 25 Vocoder Description
- TSB 102.CAAA, Project 25 Transceiver Measurements and Methods
- TSB 102.CAAB, Project 25 Transceiver Performance Recommendations
- National Security Agency (NSA) document:
- NSA Specification V23-94-1, Project 25 Type 1 Encryption (classified document).
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Project 25 technology makes significant use of Intellectual Property Rights (IPR) of Motorola. Motorola recently published an open letter announcing they would provide licenses for its modulation, channel protocol, and trunking patents required in the Project 25 standards, as well as essential encryption patents, royalty free to signatories of the industry's IPR-Memorandum of Understanding (IPR-MOU).
The CQPSK modulator consists of a table look-up, the two outputs of which (I and Q) are Nyquist filtered and then amplitude modulated, in phase and quadrature phase, before summing. The information bits are processed by the look-up table to yield a 5-level I signal and a 5-level Q signal. The I and Q signals are filtered with a Nyquist Raised Cosine Filter. The I signal is then multiplied by the carrier and the Q signal is multiplied by the carrier after it has been delayed by 90 degrees. The modulated I and Q carriers are then summed together to yield the modulator output.
The C4FM modulator consists of a Nyquist Raised Cosine Filter, cascaded with a shaping filter, cascaded with a frequency modulator.
List of Standards
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