ldacs1 – overview and current · pdf file© frequentis 2013 # dglr symposium #...

© FREQUENTIS 2013 # DGLR Symposium # LDACS1 Overview and Current Status # Bernhard Haindl # 13-03-21 # Page: 1

LDACS1 – Overview and Current Status

Datenlink-Technologien für bemannte und unbemannte Missionen

DGLR SymposiumMünchen, 21.03.2013


Outline

� Motivation

� Requirements and Preconditions

� Concepts and Capabilities

� System Overview

� Challenges

� Current Status and Next Steps


Motivation

� Key principles for the future ATM system:

– The 4D Trajectory

– The System Wide Information Management

– Automation

� Efficient communication services are required to enable these key principles!

� A future Air/Ground data link, supporting ATS and ATC services for all airspace users is such an enabler.

� Future ATM concept introduces new ATM services that are demanding in data exchanges (latency, capacity, availability, …)

– 4D Trajectories Management, ASAS, …

– CDM, Meteo info, SWIM


European ATM Master Plan


Future Communication Infrastructure (FCI)

� Planned FCI� Airport data link: AeroMACS

� ATM over satellite: ESA Iris, Antaris

� Terrestrial A/G communications: LDACS

� Two LDACS candidates:

– LDACS1 - Broadband system based on OFDM; combining B-AMC and P34

– LDACS2 - Narrowband system based on single-carrier technology (GMSK); combining LDL and AMACS

� Alternatives to LDACS:

– VDL Mode 2: Capacity: 31.5 kbps gross data rate (~25 kbps L2 net data rate) MAC scheme: CSMA; inefficient, limited throughput; Planned channel assignment: 4 VHF channels

– Satellite Communications: ESA/Iris, Iridium, Inmarsat; Satellite beams cover large geographic areas; multi-beam antennas; Large delays due to multiple-access and distance


LDACS1 - System Environment

Part of Future Radio System (FRS)

AR

AIR-ES

G-Sub Networks

ATSG-Sub Network

AOC-ES

ATS-ES

AOCG-Sub Network

Aircraft LAN

G/G-R

A/A-R

A/G-R 1

GS

LDACS1-Sub NetworkGround Segment

Future Communication Infrastructure (FCI)

A/G-R n

Application

Presentation

Session

Transport

Network

Data link

Physical

LDACS1 LLCLDACS1 MAC

LDACS1 PHY

TCP/UDP

IPv6

ATN Application

Adaptation SL LDACS1 A/G Link


LDACS1 Concept

� OFDM-based cellular radio system using FDD with 0.5 MHz channel grid

� LDACS1 GS provides „cell coverage“ with seamless handover between LDACS1 cells

� Centralized communication via ground station

– AS must log-on at the GS

– GS controls its ASs

– GS manages all resource requests

� Multiple-access schemes

– Forward link (FL): Broadcast OFDM

– Reverse link (RL): OFDMA-TDMA

LDACS1 Cell

L-DACS1 GS

AS#1

AS#2AS#n


LDACS1 Capabilities

� LDACS1 supports data and voice (optional) A/G communications

� Supporting ATS/AOC A/G data links for safety-critical services

� LDACS1 is designed to meet the COCRv2 requirements for future radio systems

� LDACS1 is designed for the aeronautical environment –aeronautical channels (en-route, take-off/landing, parking)

� Capacity: FL net data rates from 291 kbps to 1.3 Mbit/sRL net data rates from 220 kbps to 1.04 Mbit/s

� Cell size: designed for 200 nm range (guard time of 1.2ms); Performs better with ~ 120 nm cells


LDACS1 Key Features:

� Cellular radio system with up to 512 users per cell.

� Acknowledged and unacknowledged point-to-point communication between ground-station and aircraft station.

� Unacknowledged multicast communication between ground-station and aircraft stations (ground-to-air direction only).

� Hierarchical sub-network architecture with transparent handovers between radio cells

� User- and cell-specific adaptive coding and modulation modes

� Local quality of service management using separate queues for different service classes.

� Guaranteed maximum duty cycle on the reverse link (Reverse Link Allocation Algorithm)


LDACS1 System Overview – Framing Structure

Multiframe 1(58,32 ms)




RA

Superframe (240 ms)





BC

BC FL

RL

6,72 ms

RA 1 RA 2 DataDC

Data DataCC

Random Access channel (net entry)

Broadcast Channel (cell information)

Dedicated Control Channel (ressource request, ACK)

Common Control Channel (mapping of FL and RL user data, ACK)


Challenges: Co -site Operation

JTIDS

Strong FEC coding for LDACS1

signal

…

Limited airborne LDACS1

duty-cycle


Challenges: Deployment in L -band

� L-band is heavy occupied by the DME system

– It is difficult to find „empty“ DME allocations to be used for LDACS1

� DME is the preferred back-up system for GNSS navigation

– The number of deployed DME GSs may even increase in the near future

� Communications demands will probably continue to increase

� It would be desirable including the navigation capability within the LDACS1 communication system

– LDACS1 GSs could provide signals-in-space that could be used by an aircraft for ranging (requires further improvement of OFDM synchronization)

– Together with DME signals, it could be used for navigation

� This would reduce the need for additional DMEs and create place for further expansion of the LDACS1 communication coverage


978 (UAT) 1030 (SSR/ACAS)

960

1213

969 1008 1053 1065 1113

DME-X

DME-Y

DME-Y

JTIDS/ MIDS

L-DACS1

1150

FIXED 1090 (SSR/ADS-B)

GSM/ UMTS

RSBN Type 1/2/3

1000.5 1164

960

1087

1206

GPS/Galileo

1166 1563

1025

Aeronautical L -band: LDACS1 Deployment

Heavy pulsed interference (~ µs)

High transmitting powers (~ kW)

1009 1048985 1072

FL RL

RL FL

1156964 970 1150

RLFL

Initial proposal

DFS proposal

1090 + 63 = 1153 ± 3 MHz1030 - 63 = 967 ± 3 MHz

FLRL MNWG proposal

A

C

B 4 LDACS1 sub-ranges:

963.5 – 970.5 MHz

985.5 – 1008.5 MHz

1048.5 – 1071.5 MHz

1149.5 – 1156.5 MHz


Challenges: Inlay Deployment

� Concept allows for placing LDACS1 channels on existing DME allocations or between current DME allocations

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-160

-150

-140

-130

-120

-110

-100

-90

-80

-70

-60

frequency [MHz]

norm

aliz

ed p

ower

spe

ctra

l den

sity

[dB

m/H

z]

Careful frequency planning required!


Challenges: Implementation

� Transmitter- PAPR reduction required (e.g. PAPR of 11dB reduction by 6dB -> peak TX

power of +53 dBm;

- Very stringent TX spectral mask -> linear transmitter

- Phase noise requirements -> LO frequency accuracy of ± 0.1 ppm

- Broadband noise power density of -145 dBc/Hz (∆f ≥ 4.0 MHz )

- AS TX Noise Density in Inactive State below -153 dBm/Hz

� Receiver:- Dynamic Range: signal power range from -104 dBm to -21 dBm plus a

PAPR of 11dB -> peak RX power of -10 dBm;

- Immunity to strong pulsed interference; DME pulses with +25 dBm peak power should not damage any part of the receiver

- DME pulses are de-sensitising the receiver; LNA recovery time less than 2us

- Frequency Switchover Time of less than 0,5ms

- Interference Detection and Mitigation (Pulse Blanking + Compensation)


LDACS1 Achievements

- First LDACS1 system specification was completed 2008 and based on B-AMC, P34 and WiMAX

- Current LDACS1 specification (03.2011) is a stable and mature baseline for further LDACS1 activities. Based on:

- Detailed simulations of PHY and data link layer

- Feedback from simulated data traffic patterns and performance evaluations (latency, continuity) derived from air traffic models.

- Results from reference implementations and first compatibility tests

- Reference implementation of the specification in System C

- LDACS1 lab demonstrator from DLR

- First L-band compatibility measurements (DLR/DFS)

- LDACS1 Transmitter implementation for FL and RL (PHY and parts of DL Layer) with a transmission power: 42 dBm


Conclusion and Next Steps

� LDACS1 is well-suited to serve modern ATM application and future needs.

� No significant degradation in operation/performance of the present L-band systems due to the operation of the LDACS1 system

� Design of extension for long-term evolution - LDACS1 is highly flexible and scalable

� L-band compatibility testing of LDACS1 within SJU P15.2.4

� Include the navigation capability into the LDACS1 communications system


Questions?

ldacs1 – overview and current · pdf file© frequentis 2013 # dglr symposium #...

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