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EDACS


Contents

Overview

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 Trunked Radio Systems. Public service radio manufacturers working with Associated Public-Safety Communications Officers (APCO) developed a requirements document (APCO-16) for trunked radio systems.

EDACS was created by General Electric and then further engineered by Ericsson. The EDACS technology has had numerous owners and is currently owned by Harris Corporation.

EDACS is very similar to Motorola trunking. EDACS provides for the same features yet has different names for them. Simulcast networks work the same yet EDACS networks, which are similar to AMSS networks, are all independent of each other but still interconnected. A radio is programmed with each system independently and selects each system based on control channel quality. Rather than have a site number a system is basically assigned a simple number to differentiate it.

Motorola uses a specific bandplan or a complicated frequency defined system to assign frequencies. EDACS uses what are called Logical Channel Numbers LCN. Rather than assign a frequency with a specific identifier, each frequency at a site is assigned a number between 1 through 25. When a channel announcement occurs it contains only the LCN. With this in mind each radio must be programmed with which frequency corresponds to which LCN.

Digital communications is also available for EDACS systems and exists in two different formats, AEGIS and ProVoice. Previously, VoiceGuard was also available. AEGIS was the first format introduced and ProVoice was the last and current format. Neither one is APCO-25 Common Air Interface compliant unlike Motorola's ASTRO, which is. Also, neither AEGIS nor ProVoice can communicate with each other.

There are three different types of EDACS control channels. The most common is the wideband EDACS control channel, which operates at 9600 baud. Listen to it here. There is also a narrowband EDACS control channel which operates at 4800 baud and primarly is used for EDACS systems in the 900 MHz band. Listen to the narrowband control channel here. Finally, there is the wideband EDACS "encrypted" control channel which is basically a variation on the standard 9600 baud wideband control channel. M/A-COM's trademark name for this feature is ESK (EDACS Security Key).

Types

Digital Voice Types

  • AEGIS - M/A-COM's older Digital Voice Solution
  • ProVoice - M/A-COM's current Digital Voice Solution using the IMBE vocoder

Miscellaneous Information

Links

  • EDACS Development History
  • Harris Corporation - The homepage for the Harris Corp, which currently owns and supports EDACS systems and technologies.
  • Racom Inc - Distributors of Ericsson EDACS equipment. See the Products tab to link to their products and services page which has detailed information on Ericsson EDACS mobile and portable radios.
  • Hall Electronics GETECH Page - Lots of detailed information on progamming Com-Net Ericsson Radio equipment here. Cable pin-outs, connections, software versions etc can be found at this page for most of M/A-COM's radio equipment.
  • General Electric Radios

Technical Information

Etrunker Information

All EDACS systems have 25 real LCN channel frequencies, and then an additional six 'status' channels that show up under Etrunk. They are not actual frequencies, but they indicate a certain status message to the calling radio. It is recommended that you add the following to all EDACS system files:

s  DOWNLINK,1a,ffff,0
s  RESERVED,1b,ffff,0
s  CONVERTc,1c,ffff,0
s  QUEUEDid,1d,ffff,0
s  SYS-BUSY,1e,ffff,0
s  DENIEDid,1f,ffff,0

The DOWNLINK LCN is reserved for the downlink GETC/SitePro/SIM in a multi-site EDACS system. It is used to send call activity and status information from the site to the CEC/IMC. RESERVED is usually used for the redundant downlink GETC/SitePro. Both DOWNLINK and RESERVED are unlikely to show up over the air. CONVERTc stands for "Convert to Callee" and occurs when a radio that presses the PTT in the short time frame between another caller on the same talk group pressing the PTT and receiving a channel grant. The system generates a "convert to callee" message, which will sends the caller to listen to the talkgroup and give them a short error tone. QUEUEDid stands for "queued call" because an RF channel is unavailable on the system. The caller is placed in the busy queue and is released on a system managed priority level (in enhanced an d premium EDACS systems) or in a first in, first out basis for basic EDACS systems. SYS-BUSY means that a resource (other than an RF channel) is unavailable on the system. This can take place when there are no telephone interconnect lines available, the maximum number of simultaneous individual calls has been exceeded, or a number of other conditions. DENIEDid is if that radio ID and/or talk group is administratively denied on the system or site.

Information from the Manufacturer

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 an 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.
    • Basic EDACS systems are always in failsoft trunking due to the lack of a site controller or SIM.
  • 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 (Non-Extended Addressing) : 16,384 (0 to 16,383)
    • Logical ID uses 14 bits
    • Used for System Validation
      • LID 0: Test Unit when making Test Calls
      • LID 16383: Validation LID for all LIDs that are not in the database with a defined set of permissions.
      • 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

See also


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