  Millimeter wave (\texttt{mmWave}) channels in device to device (\texttt{D2D})
communication are susceptible to blockages in spite of using directional beams
from multi-input multi-output (\texttt{MIMO}) antennas to compensate for high
propagation loss. This motivates one to look for the presence of obstacles
while forming \texttt{D2D} links among user equipments (\texttt{UEs}) which are
in motion. In \texttt{D2D} communication, moving \texttt{UEs} also act as
relays to forward data from one \texttt{UE} to another which introduces the
problem of relay selection. The problem becomes more challenging when the
obstacles are also in motion (dynamic obstacles) along with the moving
\texttt{UEs}. First we have developed a probabilistic model for relay selection
which considers both moving \texttt{UEs} and dynamic obstacles. Then we have
analyzed the probability of dynamic obstacles blocking a link in 3D Euclidean
space by exploiting the information from \texttt{MIMO} radar connected to the
base station. Finally, using this information, we have developed unique
strategies based on simple geometry to find the best relay which maximizes the
expected data rate. Through simulations we have shown that our proposed
strategy gives a significant improvement in packet loss due to mobility of
nodes and dynamic obstacles in a \texttt{mmWave} channel over traditional
approaches which do not consider dynamic obstacle's presence.
