Alexandra Filip

Variable guard band construction to support key reconciliation

Key reconciliation procedures are needed to correct key differences that can arise as a consequence of independent noise at the two ends of a reciprocal link. We assume a line-of-sight channel and use reconfigurable antenna elements to randomize it, such that it allows for key generation. The Linde-Buzo-Gray algorithm is employed to quantize the complex channel transfer characteristic, and adaptive guard bands, symmetric to the quantization thresholds, are further constructed. To limit the number of key errors, we ensure that only the points that fall outside the guard band interval are accepted for key generation. The steps for constructing the guard bands are presented.

LDPC Code Design Aspects for Physical-Layer Key Reconciliation

In this work, we investigate a physical-layer key reconciliation protocol for a reciprocal, flat fading channel between two legitimate users. We consider the scenario when the n bits of the secret key are measured independently by Alice and Bob without a transmission over the channel. Due to reciprocity, the generated keys are identical except for noise at both ends. We assume Gaussian noise and ignore non-ideal behavior of circuitry and alike. Redundancy information required to reconciliate the key is transmitted from one legitimate user to the other. LDPC codes are employed for the reconciliation procedure. The main focus of this work lies in designing the code structure through density evolution for a multi-edge-type description.

Ambiguity function analysis for LDACS1-based passive radar

The focus of this work is to assess the suitability and limitations of the L-band digital aeronautical communication system type 1 (LDACS1) signals for passive radar purposes. To this end, the self-ambiguity and bistatic ambiguity function of the LDACS1 signal are evaluated. While the former delivers the limits on achievable resolutions and depicts the signal specific ambiguities, the latter allows us to investigate how a change in the system geometry affects the resolution capabilities of the system.

LDACS1 ranging results with Doppler smoothing from new flight experiments

In recent years the German Aerospace Center (DLR) has been actively working on a proposal that extends an L-band Digital Aeronautical Communication System type 1 (LDACS1) to future Alternative Positioning, Navigation, and Timing (APNT) services. In 2012 a flight measurement campaign has been performed to validate LDACS1-based navigational functionality. The results indicated a strong influence of multipath propagation on ranging performance. To better characterize multipath environment for future ground-based APNT services a second measurement has been performed in November 2013. This paper outlines the November 2013 measurement campaign and provides corresponding range estimation results that make use of Bayesian filtering methods and Doppler smoothing to mitigate multipath and improve range estimation.

Physical-Layer Key Generation and Reconciliation

Physical layer security is a technique that makes use of the physical communication channel or medium to provide additional robustness to eavesdroppers and attackers. Key establishment exploiting a multiple-input multiple-output (MIMO) reciprocal wireless channel is proposed and its performance investigated, indicating that secure keys can be rapidly generated between two nodes, even in the presence of close eavesdroppers. The use of reconfigurable antennas is investigated and experimentally proven as a key establishment solution for static channels with limited multipath. Additionally, different options are discussed to handle key-differences due to non-correlated noise together with quantization, either by simply introducing guard intervals or by joint source coding with LDPC codes.