Raul de Lacerda

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.

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.

Adaptive modulation and coding scheme for MB-OFDM UWB systems

Energy Efficiency (EE) has become one of the main challenges for the development of wireless communication systems. Thus, many researchers are investigating new solutions to save power. For this reason, in this paper we apply a method based on modulation and coding scheme (MCS) for multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) systems. The MCS scheme is a powerful method known by its ability to improve the spectral efficiency. Our goal in this paper is to investigate the performance of MCS mechanism to diminish the transmitted power under some assumptions. Computer results show the throughput behavior in function of signal to noise ratio (SNR) for different selection of modulation and coding rate. Then, we draw the plot of bit error rate (BER) versus SNR and versus the energy per bit to noise power spectral density ratio (Eb/No).

Channel division multiple access: The access solution for UWB networks

In this paper we study a promising multiple access scheme entitled Channel Division Multiple Access (ChDMA). ChDMA was developed to cope with the particularities of low duty cycle Impulsive Radio Ultra Wideband systems (IR-UWB). The idea is based upon the fact that Channel Impulse Responses (CIR) could be exploited as users signatures. Based on the knowledge of the CIRs at the receiver, transmitted signals can be detected and estimated in a very similar approach as performed by DS-CDMA systems. We present in this contribution initial analysis of the spectral efficiency performance of ChDMA systems. As a matter of fact, ChDMA overcomes the multiple access paradigm of impulsive-radio signaling and provides an efficient and low complex technique to exploit the diversity of UWB communications. For the study, we consider three different receiver structures: optimal receiver, matched filter (MF) and linear minimum mean square error receiver (l-MMSE). As a result, it is shown that under certain conditions ChDMA can even outperform CDMA in terms of Shannons capacity, providing a real option for future communication systems.

Electromagnetic compatibility: New trends for new standards

Interference between radio systems may occur if they share the same environment and use close frequencies at the same time. To ensure their successful coexistence, the Electromagnetic Compatibility (EMC) established rules and regulations within standardisation bodies and aims to protect these systems from harmful interference. Nowadays, with the proliferation of wireless communications and digital technologies, in addition to electronics evolution inside radio terminals, some additional parameters and new techniques are needed to represent more accurately the interference environment and guarantee radio systems coexistence. In this work, we provide an overview of the main standards related to EMC approaches and measurement techniques currently in use, and we show the benefits of considering time-domain parameters in the EMC analysis.

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.

How the L-DACS2 Radio-Frequency signals modulation affects the DME performance

In this paper, we consider the Radio-Frequency Compatibility (RFC) of a candidate system within future aeronautical communication infrastructure, being developed since 2004 to accommodate the evolution of the aeronautical environment. The system presented in this paper is one of the two preselected proposals for the L-band Digital Aeronautical Communication System (L-DACS), in charge of the continental communications. It is named L-DACS2 and will use the 960 to 1164 MHz band, allocated to the Aeronautical Mobile Service reserved for communications relating to safety and regularity of flight. This band is characterized by a very dense spectral occupation by a large number of aeronautical systems. The RFC (branch of electrical science that studies the coexistence of radio systems in the same electromagnetic environment) is very important for L-DACS deployment and if it is not satisfied, the flight safety could be endangered. We propose to study in this paper the impact of the LDACS2 on the Distance Measuring Equipment (DME), which has been using the L-band for decades. According to recent studies performed in the frequency domain (continuous transmissions and no time domain variations), the achieved RFC level seems insufficient. The objective of this work is to analyze the RFC between LDACS2 and DME considering the time domain aspects of both systems. The idea is to quantify the impact of the radio-frequency signals generated by L-DACS2 interferer (transmitter) on the performance of a DME victim (receiver). The study is performed for the co-site case (equipments onboard of the same aircraft). To study the RFC between the two systems, we investigate various modulations for the future communication system. The results are obtained through computer simulations and laboratory measurements with an aeronautical test-bed using a commercial DME unit. The DME performance degradation is evaluated for some values of the Signal to Interference Ratio.

Channel Division Multiple Access analysis in MBOFDM UWB high data rate system

In this contribution we study the challenging issue of WiMedia solution which the ability to support high data rate applications but is limited to three piconets simultaneously communicating in the same area. For this reason we analyze the suitability of Channel Division Multiple Access (ChDMA) approach for Multiband Orthogonal Frequency Division Multiplexing (MBOFDM) Ultra Wide Band (UWB) (MB-UWB) system over IEEE 802.15.3a (UWB) channel model. ChDMA approach exploits the characteristics of MB-UWB system to separate the piconets. Each piconet employs its own Channel Frequency Response (CFR) as a signature code which introduces diversity. We have presented analytical analysis in terms of spectral efficiency (bits/s/Hz) assuming that the receiver knows the channel. Numerical analysis is run over IEEE 802.15.3a high data rate channel justified the importance of ChDMA solution to improve the spectral efficiency of MB-UWB system. Then, performance evaluation is investigated when minimum mean square error (MMSE) and matched filter (MF) receiver is applied. Simulations results show the importance of MMSE receiver to improve the performance of MB-UWB ChDMA system.

ChDMA technique based MB-UWB system over the IEEE 802.15.3a proposal

In this contribution, we study the performance analysis of the Multiband Orthogonal Frequency Division Multiplexing Ultra Wide Band (MBOFDM UWB) high data rate system. The major problem of the MBOFDM UWB high data rate system is the cohabitation of more than three piconets sharing the same group of subbands over the same channel. As an alternative way to enhance the spectral efficiency of MBOFDM UWB system, the Channel Division Multiple Access (ChDMA) could be employed to explore the high diversity of UWB channels. The idea behind the ChDMA is to assimilate the channel impulse response (CIR) related to each user as a CDMA code signature. This approach increases the performance of the system by guarantying simultaneous access. Simulations are run over UWB indoor channel model and it is shown that MBOFDM UWB ChDMA outperforms MBOFDM UWB in respect of the metric of capacity. The simulations are performed through Minimum Mean Square Error receivers (MMSE) and the performance is evaluated based on the tradeoff between spectral efficiency (bit/s/Hz) and the ratio of number of users and “code” length. Numerical results show the advantage of ChDMA approach to enhance spectral efficiency of MBOFDM UWB high data rate system based on the accommodation of simultaneous operating piconets (SOPs).