VHF Data Link Mode 2 Ground System Supporting The ATS

VHF Data Link Mode 2 Ground System Supporting The ATS
The 23rd International Technical Conference on Circuits/Systems,
Computers and Communications (ITC-CSCC 2008)
VHF Data Link Mode 2 Ground System Supporting The ATS Services Based On
Hyoun-Kyoung Kim1, Tae-Sik Kim2, and Joong-Won Bae3
CNS/ATM System Team, Korea Aerospace Research Institute
45, Eoeun-dong, Yuseong-gu, Deajeon, Korea
E-mail: 1kimhk@kari.re.kr, 2kts@kari.re.kr, 3jwbae@kari.re.kr
Abstract: KARI is developing the VDL M2 system with a
simple ATS application system for test and future use. Now,
the design and implementation of the system is finishing
and the unit tests for the each sub systems are finished.
KARI is preparing the ground test and flight test. This
paper mainly describes the status of the development of the
ground VDL M2 system.
Each DLE has its own timers and INFO queue and XID
queue. All retransmission decision making is processed in
DLE using T1 and T3 timers. Each LME has a DLE in a
normal condition, and 2 DLEs during hand-off.
1. Introduction
VHF Data Link Mode 2 (VDL M2) system provides the
digital communication link between ground station and
aircraft and can be used instead of the current VHF data
link such as VDL MA and VDL M1. The ground VDL M2
system consists of data link service providers(DSP) and
many ground stations. A ground station consists of a
communication management unit(CMU) and a VHF data
radio(VDR). The VDL M2 system shall satisfy the
requirements specified in the SARPS1 and Technical
Manual2 made public by ICAO. VDL M2 protocol is based
on the open system interconnection(OSI) reference model.
VDL M2 deals with from physical layer to subnetwork
layer, VDR covers up to MAC sublayer and CMU covers
the upper layers. The link layer is the key layer for VDL
M2 operation and it supports transmission of data frames,
link managment and handoffs.
KARI is developing the VDL M2 system to support
future data link services in Korea. The development is
mainly focused on the ground system because the aircraft
system can depend on the aircraft manufactures. For the
system, three ground stations, a simple DSP, and three
airborne systems are used.
Currently, KARI finished the software implementation
and now is on the test phase. The unit tests of the GS and
DSP are done. In this paper, the software design for GS,
DSP and AOA module with interface supporting CPDLC
and ADS-B will be mainly described.
Figure 1. Ground System Structure
2. Ground System Structure
Figure 1 shows the ground system structure with one
DSP and three ground stations. The interface between the
DSP and the ground station, and between the DSP and the
application terminal is TCP/IP.
Each ground station has one DLS and several DLEs. DLS
communication. Connection oriented communication is
supported by DLE and connectionless communication is
supported by LLC_1 which is included in DLS. The
software structure and primitives between the VME in the
DSP and the DLS in a ground station is shown in Figure 2.
(a) Ground CMU
Figure 2. Software Architecture
3. Design
For the software detailed design, the functional flow
diagram is shown in Figure 3. There are 4 entities in the
diagram. They are EN_PHY, EN_MAC, EN_DLS,
EN_VME. EN_PHY software is mainly for hardware
calculation. EN_VME software is event-driven software.
EN_MAC and EN_DLS has sequential and event-driven
functions so, their processes are divided into 3 categories,
respectively. Each function blocks has its own flow charts.
Mainly the flow chart is based on the primitives between
the entities.
(b) Ground DSP
Figure 3. Software Architecture
2. 1 TX_Queue Management
Each DLE has its own INFO queue and XID queue. It
has transmitting and receiving counter, V(R) and V(S).
They are used to make AVLC frame in control field and to
check the received frame is in sequence. In DLS, there is
one TXI_Queue for INFO and UI frames and one
TXS_Queue for XID frames and the other supervisory
frames. The TXI_Queue and TXS_Queue has pointers to
INFO queue, XID queue or DLS information. It is because
the state, V(R), V(S), address can be changed during the
AVLC frames in the TXI_Queue or TXS_Queue.
TX_Queue management function is a process that supports
the queue management and the interface to MAC in VDR.
The interface to the VDR is RS-422 and is based on the
ASIP in ARINC 750.
2. 2 Hand-off
Hand-off process shall be started whenever the
following conditions are satisfied. (1)frame retransmission
counter reaches the maximum retransmission value, (2)
LME didn’t receive any frame during maximum idle
activity time, (3) channel congestion. Besides the
conditions, aircraft or ground shall initiate or request the
hand-off when the signal quality of the current link is poor.
In the system, the hand-off means only the link hand-off in
the same ground system. There are 5 link hand-offs, two are
the initiated hand-off(ground or aircraft), two are requested
hand-off(ground or aircraft), and the last one is broadcast
hand-off. The broadcast hand-off and aircraft requested
handoff is not currently supported. So, the last three handoffs are implemented.
2. 3 Application Interface
Basically, the VDL M2 system shall be applied with the
ATN network. But the ATN network is not currently
constructed and the network for the VDL M2 can be
changed to other types, such as TCP/IP. Now, ATS services
such as AFN, CPDLC and ADS-B are supported by
ACARS network, so to support these services, the VDL M2
system shall have interface to ACARS network. KARI
selected AOA to service ATS service with the developed
VDL M2 system. AOA is an interface module to support
the interface between VDL M2 and ACARS network.
Figure 3. Functional Flow Diagram
3.1 Data Link Service Processor (DSP)
A small data link service processor is used to manage all
data links. The DSP includes VME functions to control data
links and ground stations. VME makes a LME for each link,
and a LME has its own state, link id, DLE list, and timers.
LME is implemented by double linked list to be added and
removed dynamically. Each LME has four states – ADM,
ABM_single, ABM_mult, HO_init_pend. ADM means that
there is no link for the LME, ABM means only one link,
ABM_mult means two links. HO_init_pend means that the
LME requested hand-off and waiting for the response form
the aircraft. LMEs are activated by events from GS or
timers. A part of state transition table of HO_init_pend state
is shown in Figure 4. All timers in VME should be handled
in a timer list. The timer is a structure type which has LME
id, link id, timer type such as TG1, TG2, time-out value.
Each timer is inserted to and deleted from the timer list by
the priority of time-out value. The most urgent timer which
has the smallest time-out value has higher priority.
3.3 AOA / ATS Interface
To access ACARS network, KARI VDL M2 system
uses AOA. AOA library is an commercial library, so KARI
developed an interface module between AOA and
application system. KARI wrapper is the interface module.
When the DSP receives an AVLC frame, it extracts the
AOA packet and sends the packet to AOA processing
module. Then the AOA module extracts the ACARS
message and sends the wrapper message block to KARI
wrapper module. The frame format change is shown in
Figure 7. The KARI wrapper communicates with the
application system using TCP/IP. The application system is
bit-oriented system, so the final data frame uses ARINC
622 data format.
Figure 4. LME state transition table - HO_INIT_PEND
3.2 Ground Station (DLS)
There is a DLS and several DLEs in a ground station.
The ground stations are controlled by the DSP. If a LME
requests to create a DLE in the ground station, the ground
station create a new DLE with the following data : link id,
DLE id, source and destination address, DLE state, send
and receive frame number, timers, counters, and queues.
There are three queues, INFO queue, SREJ queue, XID
queue. INFO queue stores user data to send and SREJ
queue stores received out-of-order user data. XID queue
stores XID frames to send. The flow chart for the
processing of the received INFO frame is shown in Figure 5.
Figure 7. AVLC to KARI wrapper frame format
4. Implementation and Test
4.1 Implementation
The software is implemented by C language at Linux
operating system. The software modules are ASIP, DLS,
VME, AOA, and CPDLC interface.
Figure 7. DL_DATA processing in DLS
Figure 5. DLE flow chart – Receive INFO
4.2 Test
The test consists of unit test, interface test, lab test,
ground test, and flight test. The unit test is a test for each
subsystem, and the interface test is a test between
subsystems, and the lab test and ground test is a integration
test. The lab test is done with wire connection between
VDR. The ground test and flight test will be held at
Goheung, the southern part of Korea.
To test the system protocol meets the ICAO standards, a
robust test system is used. The test system is MVDL system
made by ADS pty in Australia. After the protocol test,
KARI will perform the ground/air integration test and full
ground test as the ground test. The integration test
configuration is shown in Figure 8. For the integration test,
a DSP, GS and aircraft system are used. All data are
monitored by MVDL system. The test mainly focus on the
data transfer between aircraft and ground. The full ground
test uses three aircraft systems and a DSP and three GSs. It
mainly test the link establishment and link handoff.
communications including compatibility with digital
voice techniques", DO-224A, 2000.
[5] ISO, "Information technology - telecommunications and
information exchange between systems - High level data
link control(HDLC) procedures, ISO/IEC13239, 2002.
[6] RTCA, "Minimum operational performance standards
for aircraft VDL mode 2 physical, link, and network
layer", DO-281, 2002.
(Airborne Application
Airborne CMU
Airborne VDR
CMU : Communication Management Unit
VDR : VHF Data Radio
DSP : Datalink Service Processor
VDL M2 Test &
Monitoring System
(Ground Station)
(Ground Application
(Ground Station)
VHF 㙼䊀⇌
Figure 8. Ground/Air integration test configuration
5. Concluding Remarks
This paper is mainy focused on the ground system of
KARI VDL M2 system. The detailed design and the
implementation are finished and and the unit test is finished.
Now, KARI is performing the interface test and preparing
the ground test and the flight test. The ground test and the
flight test will be held at Go-heung, the southest area in
Korea on early 2009.
This work was partially supported by the "Development
of VHF Data Link Mode 2 Transceiver" project of the
MLTM(Ministry of Land, Transport and Maritime Affairs).
International Standards and Recommended Practices,
Annex 10, Volum III, Part I, 2000.
[2] ICAO, "Manual on VHF digital link(VDL) mode 2",
Doc 9776, 2002.
[3] ARINC, "VHF data radio", ARINC 750-4, 2004.
[4] RTCA, "Signal-in-space minimum aviation system
performance standards for advanced VHF digital data
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