Snjezana Gligorevic

Interleaving for outer convolutional codes in DS-CDMA systems

The paper deals with coding for direct-sequence code-division multiple-access (DS-CDMA) channels. A novel method for interleaver design is introduced which significantly improves the probability of error on Gaussian multiple-access channels. It is theoretically shown for a certain kind of interleaving and finite code length that almost the complete influence of interuser interference can be eliminated. Hence, the performance of a coded DS-CDMA system comes close to transmission without interuser interference. Simulations are used to confirm the analysis.

Physical layer specification of the L-band Digital Aeronautical Communications System (L-DACS1)

L-DACS1 is the broadband candidate technology for the future L-band Digital Aeronautical Communications System (L-DACS). The flexible design of L-DACS1 allows the deployment as an inlay system in the spectral gaps between two adjacent channels used by the Distance Measuring Equipment (DME) as well as the non-inlay deployment in unused parts of the L-band. In this paper, the specification of the L-DACS1 physical layer enabling the deployment as an inlay and as a non-inlay or as a mixed inlay and non-inlay system is presented. Apart from the transmitter design, the design of the L-DACS1 receiver is addressed including methods for mitigating interference from other L-band systems. Special emphasis is put on channel estimation which has to be robust towards interference. The different proposed algorithms for channel estimation are evaluated in simulations of the overall L-DACS1 physical layer performance. The results show that L-DACS1 is capable of operating even under severe interference conditions, hence confirming the feasibility of the inlay concept.

B-AMC a system for future broadband aeronautical multi- carrier communications in the L-BAND

The Broadband Aeronautical Multi-carrier Communications (B-AMC) system is a candidate for a future aeronautical communications system to be operated in the L-Band (960-1164 MHz). It is based on the Broadband-VHF (B-VHF) system recently developed for aeronautical communications in the VHF band. As conditions in the L-Band significantly differ from those in the VHF band, basic physical layer parameters had to be adapted, which in turn required a re-design of the higher layers as well. B-AMC offers air/ground (A/G) as well as direct air/air (A/A) communication capabilities without ground relay. The physical layer has been designed to coexist with other systems located in the aeronautical L-Band. The B-AMC data link layer is optimized for low latency and low duty cycle data communication. The B-AMC study is funded by EUROCONTROL.

B-AMC — broadband aeronautical multi-carrier communications

The broadband aeronautical multi-carrier communications (B-AMC) system is a promising candidate for the future L-band radio system called L-band digital aeronautical communications system (L-DACS). In this paper, the design of the physical (PHY) as well as of the data link layer (DLL) is addressed. As B-AMC is intended to be operated in the L-band between two adjacent distance measuring equipment (DME) channels, the avoidance of mutual interference between existing L-band systems and B-AMC has been in the focus of the PHY layer design. In order to demonstrate the feasibility of the coexistence with DME, a draft frequency planning has been performed for Europe, resulting in successful frequency assignments in wide parts of Europe. The B-AMC DLL supports data link communication with low latency and high throughput. It is designed to be highly configurable and to support different service requirement sets and traffic profiles. In this paper, the current DLL configuration featuring a low RL duty-cycle and graceful degradation is discussed in detail.

Interference mitigation for broadband L-DACS

One deployment option for the future broadband L-band digital aeronautical communications system (L-DACS) is operating as an inlay system between two adjacent channels of the distance measuring equipment (DME) system. Investigations for the broadband aeronautical multi-carrier communications (B-AMC) [1] system, one candidate for the broadband L-DACS, have shown that interference originating from DME systems operating in adjacent channels has a strong impact on the B-AMC system. To enable the utilization of spectral gaps between two adjacent DME channels, two efficient methods for mitigating the impact of interference are proposed and investigated for the B-AMC system, namely pulse blanking and erasure based decoding. Simulations show that the impact of DME interference onto the L-DACS can be reduced considerably by choosing an appropriate coding scheme to make the transmit signal robust against interference. The impact of interference is mitigated by means of the proposed methods, resulting in a performance close to the performance in the interference-free case.

Receiver optimization for L-DACS1

L-DACS1 is the broadband candidate technology for the future L-band Digital Aeronautical Communications System (L-DACS). The flexible design of L-DACS1 allows the deployment as an inlay system in the spectral gaps between two adjacent channels used by the Distance Measuring Equipment (DME) as well as the non-inlay deployment in unused parts of the L-band. In this paper, the synchronization procedure in L-DACS1, when deploying it as inlay system is presented. It will be investigated how the synchronization suffers from interference in the L-band. In addition, interference mitigation techniques are briefly described and their influence onto the synchronization is examined. Finally, the performance of an appropriate combination of interference mitigation and robust synchronization is presented, showing that even under severe interference conditions, a reliable synchronization can be accomplished, hence confirming the feasibility of the inlay concept.

Final Assessment of the B-VHF Overlay Concept

B-VHF is a proposal for a future aeronautical communication system in the very high frequency (VHF) band based on an overlay concept, i.e. during the transition phase the B-VHF system shares the same frequency band with legacy VHF systems without interfering with them. In this paper, the feasibility of the overlay concept is evaluated by simulations of the physical and higher layers as well as by laboratory measurements with a demonstrator. Simulation results show that the B-VHF overlay system works in presence of interference from legacy VHF systems. The protocol is designed to allow using the available resources very efficiently and to provide voice and data services with the required quality of service. In addition, the impact of mutual interference between the B-VHF system and legacy VHF systems is evaluated in laboratory test with a simplified B-VHF demonstrator and commercial VHF radios.

L-band compatibility of LDACS1

In order to cope with the increasing demand of communication capacity in the aeronautical sector, the Future Communications Infrastructure has been developed. For air ground communications currently two candidates are considered for the L-band digital aeronautical communication system. Both L-band systems use frequency bands assigned to both civil and military navigation systems. Hereby of special interest is the distance measurement equipment due to its wide and extensive use in the civil aviation. Prior to the deployment of any of the candidates, the compatibility towards those legacy systems has to be confirmed. This paper presents the result obtained during compatibility measurements of LDACS1 carried out at labs of the German air navigation service provider in March and August, 2011. Both results for interference on the DME caused by LDACS1 and vice versa are dealt with.

L-DACS1 laboratory demonstrator development and compatibility measurement set-up

In this paper, the L-DACS1 physical layer laboratory demonstrator development is described which has been recently carried out by the German Aerospace Center (DLR). The main goal of the lab demonstrator is to perform first compatibility measurements between L-DACS1 and legacy L-band systems where interference from L-DACS1 towards the legacy systems as well as interference from the legacy systems onto the L-DACS1 receiver is considered. In addition to the demonstrator description, results from functional tests of the lab demonstrator as well as the measurement scenarios foreseen for compatibility testing are presented. The compatibility measurements will take place at the labs of the Deutsche Flugsicherung GmbH (DFS) — the German ATC provider — in fall this year.

Scatterer based airport surface channel model

Based on measurements at Munich airport and the observation of the spreading function, this paper analyzes different types of scatterers which occur in the spreading function and their temporal behavior. The scatterer analysis reveals the non-stationary character of the airport surface channel and is useful for stochastic modeling. The proposed geometry-based, stochastic channel modeling approach may be realized by either randomly placing reflecting objects based on the scatterer analysis or utilizing an appointed airport environment. The proposed channel model yields a spreading function characteristic for the apron area.