  Reliable network measurements are a fundamental component of networking
research as they enable network analysis, system debugging, performance
evaluation and optimization. In particular, decoding the LTE control channel
would give access to the full base station traffic at a 1 ms granularity, thus
allowing for traffic profiling and accurate measurements. Although a few
open-source implementations of LTE are available, they do not provide tools to
reliably decoding the LTE control channel and, thus, accessing the scheduling
information. In this paper, we present OWL, an Online Watcher for LTE that is
able to decode all the resource blocks in more than 99% of the system frames,
significantly outperforming existing non-commercial prior decoders. Compared to
previous attempts, OWL grounds the decoding procedure on information obtained
from the LTE random access mechanism. This makes it possible to run our
software on inexpensive hardware coupled with almost any software defined radio
capable of sampling the LTE signal with sufficient accuracy.
