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ACP-WGW4/IP-09/
International Civil Aviation Organization
INFORMATION PAPER / ACP-WGW4/IP-09
2011/09/12
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
FOURTH MEETING OF THE WORKING GROUP OF THE WHOLE
Montreal, Canada 14 – 16 September 2011
Agenda Item 2: / Future Communication Infrastructure, progress update and recommendationsLDACS1 Physical Layer Laboratory Demonstrator
(Presented by Nikolaos Fistas, Eurocontrol)
(Prepared by Michael Schnell, DLR)
In this information paper, the LDACS1 physical layer laboratory demonstrator developed by the German Aerospace Center (DLR) is introduced and it is shown that this demonstrator is suitable for L-band compatibility testing. In addition, current and planned activities are reported.
ACTION
The ACP WGW is invited to note that DLR has already set-up an LDACS1 physical layer laboratory demonstrator which is suitable for compatibility testing between LDACS1 and existing L-band systems and that first compatibility measurements performed indicate that coexistence in L-band between LDACS1 and DME is possible.
1. INTRODUCTION
1.1 Current work on LDACS, the L-band Digital Aeronautical Communication System, is mainly performed under the framework of the SESAR Joint Undertaking (SJU). The corresponding SJU project P15.2.4 „Future Mobile Data Link System Definition“ has started activities on LDACS within an Early Task mid of February 2010. Main goals of this Early Task with respect to LDACS are the refinement of L-DACS specifications, the development of evaluation criteria and test plans for L-band compatibility testing, and the definition of the test-bed for the LDACS evaluation. Further LDACS development, including LDACS prototyping, L-band compatibility testing, and LDACS selection, will be performed within the P15.2.4 full project. The starting date of the P15.2.4 full project is not yet fixed, but planned to be during November/December 2011.
1.2 During the last 4-5 years, substantial work has been performed by the consortium between DLR, Frequentis AG, and University of Salzburg to develop and evaluate LDACS1 [1]-[16], proposal number one of the two remaining proposals for LDACS. The work from the initial study on B-AMC up to the development of the first LDACS1 specification [17] was mainly funded by Eurocontrol contracts. In February 2010, the LDACS1 specification was handed over to the SJU.
2. LDACS1 Laboratory Demonstrator
2.1 Beside the current SJU activities, the German Aerospace Center (DLR) has already implemented an LDACS1 physical layer laboratory demonstrator in FPGA technology based on the current LDACS1 specification [17]. The demonstrator enables investigations of both the influence of the LDACS1 waveform on the legacy L-band systems and the interference of the legacy L-band systems on the LDACS1 receiver. These investigations are especially of interest for the so-called “inlay” deployment scenario, where LDACS1 and the Distance Measuring Equipment (DME) share the L-band as common spectrum resource by implementing LDACS1 channels of approximately 500 kHz bandwidth between two adjacent DME channels.
2.2 Since the proof of L-band compatibility is the main scope of the DLR demonstrator, the focus is on the physical layer implementation [1][2]. The demonstrator is implemented in FPGA technology and comprises a complete implementation of the physical layer of the L-DACS1 transmitter, including adaptive coding and modulation as well as the complete framing structure for forward and reverse link. The receiver is implemented only partly in hardware. Mainly a data grabber function is realized which comprises sampling and digital down-conversion followed by fast data storage. The subsequent baseband processing, like synchronization, interference mitigation, channel estimation/equalization, decoding, and demodulation is realized in software for offline processing of the data gathered by the receiver hardware. This concept allows rapid demonstrator set-up and provides high flexibility for receiver optimization.
2.3 The LDACS1 transmitter as well as the LDACS1 receiver implementation comprises an analogue signal interface at an intermediate frequency (IF) of 10.7 MHz. The design and realization of a radio frequency (RF) frontend, which converts the IF signal into the L-band and vice versa, has been ordered by DLR from an external supplier. The RF frontend has been recently delivered to DLR and is now available for LDACS1 testing. The output power of the RF frontend is 15 dBm (27 dBm peak) which is sufficient for laboratory testing. In addition, a high power amplifier can be connected to the RF frontend output to achieve realistic LDACS1 transmit power level.
2.4 Having available the complete LDACS1 laboratory demonstrator, DLR has already performed measurements for testing the demonstrator. These test measurements comprise functional tests at IF and RF, which proved the proper working of both the LDACS1 implementation and the RF frontend, as well as the proper working of the software receiver.
2.5 In addition, DLR together with DFS already performed first preliminary compatibility tests at the labs of DFS where a restricted set of scenarios has been investigated. These tests comprise investigations of the impact of both the LDACS1 interference towards DME and the DME interference towards LDACS1. Our first findings indicate that coexistence in L-band between LDACS1 and DME is possible. For more details, please refer to [18].
3. Current and Planned Activities
3.1 Currently, DLR and DFS are performing detailed compatibility measurements which are based on the findings obtained so far within the Early Working Activity EWA04-2 “LDACS Evaluation Criteria” of the SJU Project P15.2.4. The compatibility testing of LDACS1 will continue for some time depending on the availability of laboratory measurement time at DFS labs and equipment availability.
3.2 Although the current compatibility measurements take place outside the SJU activity, the findings of these measurements will be input to the SJU Project P15.2.4 for further consideration.
3.3 In addition, the DLR LDACS1 laboratory demonstrator will be made available for compatibility testing within the SJU Project P15.2.4. Thus, there will be two LDACS1 demonstrators available for compatibility testing within SJU Project P15.2.4 – the LDACS1 demonstrator produced within the project and the DLR demonstrator.
3.4 Further information obtained from the compatibility measurements will also be presented to ICAO ACP as available.
4. ACTION BY THE MEETING
4.1 The ACP WGW is invited to note that DLR has already set-up an LDACS1 physical layer laboratory demonstrator which is suitable for compatibility testing between LDACS1 and existing L-band systems, like DME/TACAN, SSR Mode S, JTIDS/MIDS.
4.2 The ACP WGW is invited to note that first compatibility measurements performed indicate that coexistence in L-band between LDACS1 and DME is possible.
4.3 Further information about LDACS1 compatibility testing will be made available to ACP during the next meetings as available.
5. References
[1] N. Franzen, A. Arkhipov, M. Schnell, “L-DACS1 Physical Layer Laboratory Demonstrator”, Integrated Communications Navigation and Surveillance Conference (ICNS 2010), Herndon, VA, USA, May 2010
[2] M. Schnell, N. Franzen, S. Gligorevic, “L-DACS1 Laboratory Demonstrator Development and Compatibility Measurement Set-up”, 29th Digital Avionics Systems Conference (DASC 2010), Salt Lake City, UT, USA, October 2010
[3] N. Schneckenburger, Chr. Klein, M. Schnell, “OFDM Based Data Link for the DLR Research Aircraft ATRA”, Integrated Communications Navigation and Surveillance Conference (ICNS 2011), Herndon, VA, USA, May 2011
[4] U. Epple, M. Schnell, “Channel Estimation in OFDM Systems with Strong Interference”, 15th International OFDM Workshop (InOWo 2008), Hamburg, Germany, September 2010
[5] S. Brandes, U. Epple, M. Schnell, “Compensation of the Impact of Interference Mitigation by Pulse Blanking in OFDM Systems”, IEEE Global Communications Conference (GlobeCom 2009), Honolulu, HI, USA, December 2009
[6] U. Epple, S. Brandes, S. Gligorevic, M. Schnell, “Receiver Optimization for L-DACS1”, 28th Digital Avionics Systems Conference (DASC 2009), Orlando, FL, USA, October 2009
[7] S. Brandes, U. Epple, S. Gligorevic, M. Schnell, B. Haindl, M. Sajatovic, “Physical Layer Specification of the L-band Digital Aeronautical Communications System (L-DACS1)”, Integrated Communications Navigation and Surveillance Conference (ICNS 2009), Arlington, VA, USA, May 2009
[8] Th. Gräupl, M. Ehammer, C.-H. Rokitansky, “L-DACS1 Data Link Layer Design and Performance”, Integrated Communications Navigation and Surveillance Conference (ICNS 2009), Arlington, VA, USA, May 2009
[9] B. Haindl, Chr. Rihacek, M. Sajatovic, B. Phillips, J. Budinger, M. Schnell, D. Lamiano, W. Wilson, “Improvement of L-DACS1 Design by Combining B-AMC with P34 and WiMAX Technologies”, Integrated Communications Navigation and Surveillance Conference (ICNS 2009), Arlington, VA, USA, May 2009
[10] S. Brandes, M. Schnell, “Interference Mitigation for the Future Aeronautical Communication System in the L-Band”, 7th International Workshop on Multi-Carrier Systems and Solutions (MC-SS 2009), Herrsching, Germany, May 2009
[11] M. Schnell, S. Brandes, S. Gligorevic, M. Walter, Chr. Rihacek, M. Sajatovic, B. Haindl, “Interference Mitigation for Future L-band Digital Aeronautical Communications System”, 27th Digital Avionics Systems Conference (DASC 2008), St. Paul, Minnesota, USA, October 2008
[12] Th. Gräupl, M. Ehammer, C.-H. Rokitansky, “Link-layer Quality of Service in the L-band Digital Aeronautical Communication System B-AMC”, 27th Digital Avionics Systems Conference (DASC 2008), St. Paul, Minnesota, USA, October 2008
[13] S. Brandes, M. Schnell, “Mitigation of Pulsed Interference in OFDM Based Systems”, 13th International OFDM-Workshop 2008 (InOWo 2008), Hamburg, Germany, August 2008
[14] M. Schnell, S. Brandes, S. Gligorevic, Chr. Rihacek, M. Sajatovic, C.-H. Rokitansky, “B-AMC – Broadband Aeronautical Multi-carrier Communications”, Integrated Communications Navigation and Surveillance Conference (ICNS 2008), Bethesda, Maryland, USA, May 2008
[15] C.-H. Rokitansky, M. Ehammer, Th. Gräupl, M. Schnell, S. Brandes, S. Gligorevic, Chr. Rihacek, M. Sajatovic, “B-AMC – A System for Future Broadband Aeronautical Multi-carrier Communications in the L-band”, 26th Digital Avionics Systems Conference (DASC 2007), Dallas, TX, USA, October 2007
[16] C.-H. Rokitansky, M. Ehammer, Th. Gräupl, M. Schnell, S. Brandes, S. Gligorevic, Chr. Rihacek, M. Sajatovic, “B-AMC – Aeronautical Broadband Communication in the L-Band”, First CEAS European Air and Space Conference (CEAS 2007), Berlin, Germany, September 2007
[17] www.eurocontrol.int/communications/public/standard_page/Lib.html
[18] N. Schneckenburger, N. Franzen, S. Gligorevic, M. Schnell, “L-band Compatibility of L-DACS1”, 30th Digital Avionics Systems Conference (DASC 2011), Seattle, WA, USA, October 2011