Thierry Letertre

Survey on the Future Aeronautical Communication System and Its Development for Continental Communications

We present in this survey new technologies proposed for the evolution of the aeronautical communication infrastructure. Motivated by studies that estimate the growth of air traffic flow, it was decided to develop a future communication infrastructure (FCI) adapted to the future aeronautical scenario. The FCI development involves researchers, industrials, and aeronautical authorities from many countries around the world, and started in 2004. The L-band Digital Aeronautical Communication System (L-DACS) is the part of the FCI that will be in charge of continental communication. The L-DACS is being developed in Europe since 2007 and two candidates were preselected: L-DACS1 and L-DACS2. In this paper, we first describe the motivations of the FCI. We then give an overview of its development activities from 2004 to 2009. After that, we provide some insights about both preselected L-DACS candidates, at their physical and medium access layers. Finally, we address the challenges on the development of the FCI/L-DACS.

Electromagnetic environment of RFID systems

In this paper, the influence of the electromagnetic environment on RFID (radio frequency identification) systems is studied. By electromagnetic environment, we consider the electromagnetic waves interference on a RFID system performance produced by applications located nearby. In particular, we analyze the effects of using a GSM mobile phone near an UHF-868 MHz RFID system. For the tested configurations, the results show that the read range (the maximum distance of labels detection) of the RFID is considerably reduced. Also, the GSM mobile communication can be affected by the waves radiated by the RFID system.

Interference analysis for the future aeronautical communication system

General and commercial aviation authorities have been using amplitude modulation communication systems for more than 70 years. Due to the great increase of air traffic during the last years, the VHF band tends towards saturation, whereas the aeronautical community faces new requirements: data rate, spectral efficiency and network capacity (maximum number of aircrafts simultaneously connected). Recently, the development of a new digital aeronautical communication system, named L-DACS, was proposed. This system will operate in the L band part allocated to aeronautics. There were many proposals but only two candidates have been pre-selected by the ITU and ICAO for this future communication system: L-DACS1 and L-DACS2. The deployment of this new system is expected to start after 2020. Among other issues, one important aspect is the impact of L-DACS on legacy systems. Actually, there are many onboard systems operating in L band, and any disfunction can put in danger the flight safety. This paper studies the maximum interference level generated by the two L-DACS candidates on a generic onboard receiver. Taking into account the antenna radiation pattern and the specific transmission mask of both candidates, the study determines the worst interference level and the corresponding spatial positions of the aircrafts around the receiver. The results show that the interference level can be determined by considering the several nearest aircrafts to the victim.

Effect of the Aeronautical L-DACS2 Radio-Frequency Signals on the DME System Performance

In this paper, we consider the Radio-Frequency Compatibility (RFC) of a candidate system for the future aeronautical communication infrastructure. This infrastructure is being developed within the International Civil Aviation Organization since 2004, to accommodate the air traffic load and improve the aerial security. The system presented in this paper is one of the two preselected proposals for the L-band Digital Aeronautical Communication System (L-DACS), which will be responsible for the continental communications. This proposed candidate is named L-DACS2 and is foreseen to use part of the L-band spectrum (960 to 1164 MHz) allocated to the Aeronautical Mobile Service reserved for communications relating to safety and regularity of flight. Despite its potentially large spectrum, the L-band is a challenging environment for aeronautical communications because of the channel propagation characteristics and the dense spectral occupation by a large number of aeronautical systems. On the other hand, the RFC characterizes the electromagnetic compatibility between two radio systems and determines if they can coexist in the same electromagnetic environment. For this reason, the RFC is one of the main issues for L-DACS deployment and if it is not satisfied, the flight safety could be endangered. Hence, we propose to study in this paper the impact of the L-DACS on the Distance Measuring Equipment (DME), which is a very important equipment that has been using this band for decades. According to recent studies performed in the frequency domain , that is assuming continuous transmissions and no time domain variations, the achieved RFC level seems insufficient. The main objective of this work is to analyze the RFC between L-DACS2 and DME taking into account the time domain aspects of both systems. The idea is to verify and quantify the impact of the radio- frequency signals generated by a L-DACS2 interferer on the performance of a DME victim receiver. The study is performed for the co-site case (\emph{i.e.} when both equipments are onboard of the same airplane), which is the most critical interference scenario due to the proximity of both systems. The results are obtained through computer simulations as well as laboratory measurements. They present the DME performance degradation for some values of the Signal to Interference Ratio, assuming a constant DME signal level and different L-DACS2 interference powers.

Total radiated power measurements of WiFi devices using a compact reverberation chamber

A compact reverberation chamber is herein considered for the TRP (Total Radiated Power) measurements of WiFi devices. An immediate difficulty when testing WiFi devices is the lack of a standard emulator which allows robust control of the emitted signal for power measurement purposes. The average power delivered by a WiFi device depends upon the data rate which itself can also vary during time. Multipath environments also influence the data rate and the signal delivered by the device. The procedure proposed herein is developed in order to ensure repeatable measurements. The mechanical stirring of the reverberation chamber is optimized to enable fast measurements.

Radioelectric compatibility of the future aeronautical communication system

The aeronautical community has recently decided to develop a new digital aeronautical communication system, named L-DACS, in order to fulfill the new air traffic requirements. This system, which will operate in the L frequency band (960 to 1164 MHz), would be internationally deployed from 2020. Many technologies were considered for this new aeronautical system but only two among them were preselected by the International Civil Aviation Organization (ICAO): candidate one, named L-DACS1, is based on a FDD-OFDM technology and candidate two, named L-DACS2, is based on a TDD-GMSK technology. One of the most important issues for both candidates is the electromagnetic compatibility (EMC) with the legacy systems operating in the same band or/and in adjacent bands. Different scenarios have to be evaluated due to the fact that these systems will be implanted either in the airplanes (on board) or in ground stations. In this paper, we propose to evaluate the air-air scenario, where we focus on the signals generated by onboard L-DACS transmitters on onboard victim receivers, taking into account the L-DACS antenna radiation pattern and the frequency mask. The study emphasizes that the interference phenomenon can be one of the main limitations for the L-DACS development.

A novel measurement procedure for the Specific Absorption Rate conformity assessment of WiFi devices

The Specific Absorption Rate (SAR) conformity assessment of WiFi devices is herein investigated. In order to derive the time-average of the SAR, a common approach is to evaluate an ensemble average of the measured samples. This approach cannot be applied when measuring non-deterministic signals typically transmitted by WiFi devices. The signal transmitted between WiFi devices during data exchange is complex and unpredictable. An alternative procedure based on the peak detection measurement of the signal is proposed. The feasibility of the peak detection scheme is studied by analyzing the probes time-domain response and the salient features of the WiFi communication protocol.

Accurate Measurement of RF Exposure from Emerging Wireless Communication Systems

Isotropic broadband probes or spectrum analyzers (SAs) may be used for the measurement of rapidly varying electromagnetic fields generated by emerging wireless communication systems. In this paper this problematic is investigated by comparing the responses measured by two different isotropic broadband probes typically used to perform electric field (E-field) evaluations. The broadband probes are submitted to signals with variable duty cycles (DC) and crest factors (CF) either with or without Orthogonal Frequency Division Multiplexing (OFDM) modulation but with the same root-mean-square (RMS) power. The two probes do not provide accurate enough results for deterministic signals such as Worldwide Interoperability for Microwave Access (WIMAX) or Long Term Evolution (LTE) as well as for non-deterministic signals such as Wireless Fidelity (WiFi). The legacy measurement protocols should be adapted to cope for the emerging wireless communication technologies based on the OFDM modulation scheme. This is not easily achieved except when the statistics of the RF emission are well known. In this case the measurement errors are shown to be systematic and a correction factor or calibration can be applied to obtain a good approximation of the total RMS power.

Electromagnetic field measurements of WIMAX systems using isotropic broadband probes

In the context of human exposure to Radio Frequency (RF), measurements of electromagnetic fields are performed, according to standard measurement protocols, using isotropic broadband probes with or without service filters. Two electric field measurement probes are herein examined. Their responses to different typical WIMAX emissions are analysed. Results show that these probes are not accurate enough for the next generation OFDM (Orthogonal Frequency Division Multiplexing) communication systems. A new correction method for these probes is proposed for the evaluation of the RF exposure due to WIMAX systems.

Study of RF emissions of various electronic devices used by the public

For the purpose of EMC immunity and people exposure, we have studied the radiation characteristics of various electronic devices widespread used by the public. During the first phase, we have identified typical electronic devices found at residences and offices (microwave ovens, wifi routers, walk-talkies, mobile phones, cordless phones, Bluetooth devices etc.). During the second phase, we have defined measurement protocols based on specific measuring equipment to study the radiation properties of such devices. One of the great challenges of this work was to provide efficient measurement protocols that could enable the evaluation and comparison of a large range of systems, taking into consideration their particularities. Mostly here, the RF emissions have been analyzed seeing the influence of measurement parameters on the study of various complex radiated signals.