RIU/GNI Real-Time Platform
The Radio Interface Unit (RIU) and Ground Network Interface (GNI) systems
are components of the FAA’s Next Generation Communications (NEXCOM) system
architecture. The NEXCOM system <http:// www. faa.gov/nexcom/>will
replace the current analog AM air-ground communications with a completely
digital RF communication system and will support voice and data
transmission. Due to voice compression and a time division multiple access (TDMA)
scheme, the new system will support 4 air-ground channels in the 25 kHz
frequency band now used for a single AM channel.
RIU
The RIU is typically located at an FAA remote site and provides protocol and
timing support for the Multimode Digital Radio (MDR). The MDR is a digital
ground radio designed to support both the current analog AM communication
scheme as well as the new NEXCOM digital communication scheme. The RIU
supports separate T1 connections (1.544 Mbs) with up to four MDR units (main
and standby transmitters and receivers). The timing needed to support TDMA
communication is provided on the first two timeslots in the T1 connection.
An HDLC channel is used to transmit voice, data, control and status
information between the RIU and MDR. The RIU provides burst timing
information and other RF media access control (MAC) layer functions. It also
provides link layer and session layer protocol support between the ground
and airborne communication equipment.
GNI
The GNI is typically located at an FAA control site and provides connection
between network data services, air traffic voice switches, and the remote
site. It supports multiple audio and discrete radio control signals that are
compatible with existing FAA voice switches like the VSCS, the ICSS, and the
ETVS. The GNI also interfaces with an ATN router (for data services).
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CIE has partnered with BCI <http://www.bcisse.com/ Services /FAA/air_ground.html> to provide prototype RIU/GNI equipment to the FAA William J. Hughes Technical Center. The prototype equipment is being used to validate the NEXCOM system architecture and to test other NEXCOM system components (e.g. MDR). The prototype RIU/GNI consists of a Real-Time Platform (RTP) provided by CIE and a software control system (SCS) provided by BCI. |
The RTP performs all real
time processing functions under the control of the software control system (SCS).
The RTP and SCS communicate via a high speed serial link. A modular approach
was used to enable the same platform and control system components to
function as either an RIU or a GNI with minor software/hardware
reconfiguration.
The RTP system includes a VME chassis with a custom backplane and two or
more modules. Two basic module types are available: an Octal T1 Module (OTM)
and a Voice Channel Module (VCM). A minimal system includes one OTM and one
VCM. The OTM provides all timing and message routing services. It includes
the T1 connections to the MDR and remote unit T1 interfaces (for GNI-to-RIU
communication). It also includes high speed serial and USB ports for SCS
control. The VCM provides all voice processing services
including ATC-10B voice compression, analog-to-digital voice conversion, and
gain/volume adjustment. All modules use custom designed Analog Devices
ADSP-2188M microprocessor boards.
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CIE Engineering, Inc. • 6001 Woodlake Lane • Alexandria, VA 22315 • Phone: (703) 922-7061