Project 25 Overview

1
Project 25 Overview

• By Chad Homme
• Communications Coordinator
• Salida Fire Protection District

2
Why Project 25 (P25)?

• January 1982 Air Flight 90 crash in Washington
  D.C. Federal, State, and Local officials could
  not communicate.
• April 1995 Oklahoma City Bombing. Search and
  Rescue could not communicate. Hard-wired and
  cellular systems overloaded. Utilized runners.
• September 2001 Terrorist Attacks. Federal, State,
  and Local officials could not communicate.

3
What is Project 25 (P25)

• Established in 1989 by the Association of Public
  Safety Communications Officials International
  (APCO).
• Involved representatives from Federal, State, and
  Local government.
• Purpose to develop a set of common technical
  standards for land mobile radio systems.

4
Benefits of Project 25 (P25)

• Common standard would allow any number of
  manufacturers to produce compatible equipment.
• Common standard would increase competition and
  lower prices.
• Avoid locking customers into a proprietary system
  from a single manufacturer.
• P25 is not a single standard but a number of
  individual protocols that can be mixed and
  matched (Project 25 Compliant).

5
Common Air Interface

• Uses a Common Air Interface (CAI).
• Any CAI radio can communicate with any other CAI
  radio, regardless of manufacturer.
• Currently, public safety channels are 25 kHz
  wide. P25 radios are designed to use 12.5 kHz
  wide channels. Two conversations can take place
  where only one used to fit.

6
Common Air Interface (cont.)

• Eventually, P25 will support 6.25 kHz channels,
  allowing four times as many conversations
  compared to analog.
• P25 radios will be capable of working in analog
  mode on 25 kHz channels (backwards
  compatibility).
• P25 transmissions may be protected by encryption
  (U.S. Data Encryption Standards DES at a minimum).

7
Common Air Interface (cont.)

• P25 channels (aka traffic channels) operate at
  9600 bits per second.
• Substantial amount of error correction to
  compensate for poor radio frequency conditions.
  Improves useable range.
• P25 also supports data transmission.

8
Digitized Voice

• Voice transmission are now digital rather than
  analog.
• P25 uses a method of digitized voice called
  Improved Multi-Band Excitation (IMBE).
• Voice encoder-decoder listens to a sample of
  audio input and only transmits certain
  characteristics that represent the sound.

9
Digitized Voice (cont.)

• The receiver uses these basic characteristics to
  produce a synthetic equivalent of the input
  sound.
• IMBE is optimized for human speech and does not
  do well with reproducing other types of sounds
  (i.e. DTMF tones).

10
Digitized Voice (cont.)

• The IMBE vocoder (encoder-decoder) samples
  microphone input every 20 milliseconds.
• Produces 88 bits of encoded speech.
• Vocoder is producing speech characteristics at
  4400 bits per second.
• Error correction adds another 2800 bps.
• Signaling overhead brings the total rate to 9600
  bps.
• P25 standards specify exactly how that
  information is structured and transmitted.

11
Recommendation

• Purchase P25 compatible equipment.
• Handhelds Bendix King DPH and DPH-CMD (1450).
  Motorola XTS 1500, XTS 2500, and XTS 5000
  (1250).
• Mobiles Motorola XTL 1500, XTL 2500, and XTL
  5000 (1350). Kenwood TK 5710 (1750).

12
Conclusion

• P25 is a coming standard in communications.
• P25 equipment is backwards compatible with
  existing systems.
• P25 will increase the number of available
  frequencies for radio communications.
• P25 will offer increased interoperability between
  Federal, State, and Local government.