Project 25

APCO P25 (short for Project 25 of APCO International) is a transmission standard, which was developed in order for the government security agencies in North America and met similar requirements as the ETSI TETRA in Europe.

History

Due to the limitations of the analog radio, a trend towards the introduction of digital radio in North America showed. The Association of Public Safety Communications Officials " APCO (Association of liaison officers for security tasks ) it created the" Project 16 ", which accompanies since the late 1970s, the introduction of digital radio with standardization proposals.

With the increasing use of digital radio in the BOS services, there were clear limitations of interoperability. During emergencies the following years it showed a lot of problems, so that in 1988 the U.S. Congress launched a public inquiry for further development. Then was based on the results in 1989, the " Project 25 " initiated.

In addition to the APCO, the development has now been supported by other partners: the National Association of State Telecommunications Directors ( NASTD ), the National Telecommunications and Information Administration ( NTIA ), the National Communications System (NCS ), the National Security Agency (NSA ) and the United States Department of Defense ( DoD). The steering committee was accompanied by the development of FPIC, DHS Coast Guard and the Department of Commerce 's the National Institute of Standards and Technology (NIST ) Office of Law Enforcement Standards.

The introduction of APCO P25 runs in the U.S. due to the cost slowly, but is penetrated after the establishment of the Ministry of Internal Security for a speedy conversion. For new infrastructure projects in the public safety radio communications, the introduction of APCO P25 is mandatory. In addition to North America P25 is also used in Australia, India, Russia and Singapore. Some regional organizations in South and Central America also put a P25, P25 total is used in 54 countries at 660 service networks (as of mid 2004).

At the same time in 2005 ETSI TETRA, however, was already in use in 60 countries, and outside North America is P25 hard to find. The main reason is that the P25 terminals are more expensive many times have found as TETRA equipment ( $ 6,000 compared to $ 900 ), and thus outside the BOS services in mobile radio hardly used. P25 is, however, preferred in North America, because it has the same range and frequency band width as the already existing analog systems. Moreover, since it is backward compatible with analog radio, progressive BOS individual channels from analogue can be converted to digital operation. In addition, P25 is able to cover a larger area with a station, which is advantageous in sparsely populated regions. It is therefore more akin to the francophone Tetrapol, which follows a similar technical approach, as with Tetra.

APCO P25 in amateur radio

Even in amateur radio APCO P25 is used. For commercial APCO P25 devices by radio amateurs be modified and reprogrammed.

Communication procedures

The P25 - talkies allow use in a wide variety of radio channels, including the conventional analog broadcasting. The digital voice transmission allows a number of language codes ( vocoder voice encoder / decoder ), and data encryption (eg, DES, AES, RC4). Due to the variability of the interoperability is not given mandatory - it is achieved by a balance of the acquisition criteria for each of BOS services.

In the current " phase 1" in the United States P25 is used with 12.5 kHz wide channels. Phase 1 Digital devices use Continuous 4 level FM ( C4FM ) with a symbol rate of 4800 baud and 2 bits per symbol, and thus Bruttobits 9600. The receivers are also compatible with CQPSK that requires only 6.25 kHz bandwidth.

For the " Phase 2" a TDMA method is currently being tested with two slots. It is as a vocoder AMBE Advanced Multi - Band Excitation be used, which makes do with the 4800 baud. In the phase 2, the repeater stations can be improved, which can then be re-configured from the central unit in accordance with the deployment scenario.

In P25 the various regional services through a digital network code NAC (Network Access Code ) are addressed (ie not by choice of the radio channel ). The 12-bit long keys allows to create different services according to 4096, the NACs are usually written as three hexadecimal digits. Default value is 293 NAC receiver equipment, NAC F7F is used by devices in an open repeater mode.

Standard Parts

  • Common Air Interface (CAI ), describes the radio interface for terminals.
  • Subscriber Data Peripheral Interface for connecting laptops and handdown to data networks.
  • Fixed Station Interface describes the base station in the P25 network
  • Console Subsystem Interface describes the control protocols in P25.
  • Network Management describes the control station in the P25
  • Data Network Interface describes how to connect to data services.
  • Telephone Interconnect Interface describes the connection to analogue and ISDN networks.
  • Inter RF Subsystem Interface describes how to connect public data networks.
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