Daniele Coppola

Vukasin Bozic, Danilo Dordevic, Daniele Coppola et al. · eth-zurich

This work presents an analysis of the effectiveness of using standard shallow feed-forward networks to mimic the behavior of the attention mechanism in the original Transformer model, a state-of-the-art architecture for sequence-to-sequence tasks. We substitute key elements of the attention mechanism in the Transformer with simple feed-forward networks, trained using the original components via knowledge distillation. Our experiments, conducted on the IWSLT2017 dataset, reveal the capacity of these "attentionless Transformers" to rival the performance of the original architecture. Through rigorous ablation studies, and experimenting with various replacement network types and sizes, we offer insights that support the viability of our approach. This not only sheds light on the adaptability of shallow feed-forward networks in emulating attention mechanisms but also underscores their potential to streamline complex architectures for sequence-to-sequence tasks.

Claudio Anliker, Daniele Coppola, Giovanni Camurati et al.

Time-of-arrival (ToA) estimation via cross-correlation is an essential building block of time-of-flight ranging. However, in narrowband systems, it is notoriously difficult to protect against distance-decreasing attacks such as Early-Detect/Late-Commit (ED/LC). We present and analyze two new attacks that reshape ranging signals to compromise correlation-based ToA estimation. The first attack multiplies the signal by a symbol-periodic waveform in the time domain, while the second passes it through a negative group delay (NGD) filter. In contrast to ED/LC, our attacks do not require real-time symbol detection or adaptive compensation; they are completely symbol-agnostic. We describe implementation strategies for both attacks and discuss NGD filtering in the context of Bluetooth Channel Sounding (CS), a recent narrowband ranging system. To this end, we simulate an NGD circuit in LTspice and a ToA estimator in MATLAB, demonstrating that the attack can result in distance reductions of up to 18 m against Bluetooth CS RTT ranging. Finally, we verify the feasibility of the NGD approach by building a prototype using commercial off-the-shelf components.