  Vehicular Ad-Hoc Networks (VANETs) aim at enhancing road safety and providing
a comfortable driving environment by delivering early warning and infotainment
messages to the drivers. Jamming attacks, however, pose a significant threat to
their performance. In this paper, we propose a novel Relative Speed Estimation
Algorithm (RSEA) of a moving interfering vehicle that approaches a Transmitter
($Tx$) - Receiver ($Rx$) pair, that interferes with their Radio Frequency (RF)
communication by conducting a Denial of Service (DoS) attack. Our scheme is
completely sensorless and passive and uses a pilot-based received signal
without hardware or computational cost in order to, firstly, estimate the
combined channel between the transmitter - receiver and jammer - receiver and
secondly, to estimate the jamming signal and the relative speed between the
jammer - receiver using the RF Doppler shift. Moreover, the relative speed
metric exploits the Angle of Projection (AOP) of the speed vector of the jammer
in the axis of its motion in order to form a two-dimensional representation of
the geographical area. This approach can effectively be applied both for a
jamming signal completely unknown to the receiver and for a jamming signal
partly known to the receiver. Our speed estimator method is proven to have
quite accurate performance, with a Mean Absolute Error (MAE) value of
approximately $10\%$ compared to the optimal zero MAE value under different
jamming attack scenarios.
