EDACS

Enhanced Digital Access Communications System (EDACS) is available in VHF, UHF, 800 and 900 frequency bands and wideband (25 kHz) and narrowband (12.5 kHz) configurations. This spectrum resource provided a springboard for the development of trunking systems. Public service radio manufactures working with Associated Public-Safety Communications Officers (APCO) developed a requirements document (APCO 16) for trunked radio systems.

EDACS provides coordinated communication between agencies and integrates all services; Dispatch, Secure Voice, Telephone and Data within a single common communication system. EDACS systems have a single control channel communicating between the system and the field radios. These configurations range from Basic EDACS to EDACS Level 4, consisting of Voted and Simulcast Systems. An EDACS Multisite Network links Systems together via a Multisite Controller (MSC) or Integrated Multisite and Console Controller (IMC).

There are two types of radio channel designations are used in EDACS: One of them is the Control Channel and the other is the Working Channel. The Control Channel is used to send digital data between sites to the radios. This data is continually transmitted to the field units. The Working Channels sends voice and data over the air.

• Control Channel

* Used for continuous data (full duplex) Inbound and Outbound 9600/4800 bits per second.

• Working Channel

* Up to 23 per Site
* Voice and Data
* Data message 9600/4800 bits per second.
* Low Speed Data for updating units: Analog Calls 150 Bits per sec, Individual and scan group calls
* Units will send 75Hz and 150Hz Trunked Unit Transmitting.

• Failsoft Trunking

* Control Channel GETC must be reset to bring site out of Failsoft Manual or Remote accomplished.
* Failsoft sites can work in Multisite configuration less than .5 second Channel Access.
* If NO Working Channel available the Call goes into Queuing an available channel.

• Data Rate

* Wide Band (25/30) kHz: 9600 baud
* Narrow Band (12.5) kHz 4800 baud

• Data Synchronization

* 9600 Baud Rate at 0.1 bit (0.01ms)
* 150 Baud Rate at 0.01 bit (0.06ms)

• Audio Equalization

* Amplitude of 0.25 dB (300-3000Hz)
* Phase of 25 degrees (600-2600 Hz)

• Channel Access

* Channel Access Time: Less than 500 ms
   

• Timing and Distance Limitations

* Max ISI Time: 52 uS (Allowing for 10 uS of Jitter)
* Max Site Separation: 7.8 miles (Without Timing Adjustments)
* Velocity of Propagation: 3.0 X 10E8 m/s
* 9600 Baud Period: 104 uS
   

• Path Requirements

* Bell Standard T1 or DS1 Grade Circuits Via: Digital Microwave - Fiber Optic - 
  Phase Stable Analog Multiplex / Microwave

• Logical ID

* Total Number of Logical Address Schemes: 16,384 (0 to 16,383)
* Logical ID uses 14 bits
* Used for System Validation
* LID 0: Test Unit when making Test Calls
* LID < 64 for Host Computers or Mainframe
* LID > 100 for Consoles

• Group ID

* Total Number of Group Address Scheme: 0 to 2048

• Physical ID

* Each Radio has a Physical ID
* 20 bits Physical ID
* 1,048,576 possibilities
* ESN

• Simulcast

* Simultaneous Broadcast by two or more transmitters located at different sites operating on 
  the same RF Frequency. A Simulcast trunked system requires the same number of channels with 
  a common set of RF Frequencies at each site. For this reason, alignment of simulcast systems
  become very important.
   

• Capture

* The ability of an FM Discriminator to lock on the incoming signal: 
  RF Level 1 > RF Level 2 by 12 dB