  Millimeter-wave (mmWave) bands will be used for the fifth generation
communication systems to support high data rates. For the proper
characterization of the mmWave propagation channel, it is essential to measure
the power angular-delay profile (PADP) of the channel which includes
angle-of-departure (AoD) and angle-of-arrival (AoA) of the multipath components
(MPCs). In this paper, we first describe in detail our 28 GHz channel sounder
where directional horn antennas are placed on rotating gimbals. Then, for this
specific sounder class, we describe and address the following two problems in
extracting the MPCs from the measurements: 1) For the channel measurements at
large distances between the transmitter (TX) and the receiver (RX), it is not
possible to generate the triggering signal for the TX and the RX using a single
clock (SICL). This necessitates the use of separate clocks (SECLs) which
introduces a random timing drift between the clocks. 2) As the positions of the
antennas change during the scanning process, total distance traveled by the
same MPC differs at each measurement. These two errors together cause missing
some of the MPCs and detecting MPCs that do not exist in reality. We propose an
algorithm to correct the clock drift and the errors in the MPC delays due to
the rotation of the antennas. We compare the MPCs from the SICL measurement and
the corrected SECL measurements using a Hungarian algorithm based MPC matching
method. We show that the percentage of the matched MPCs increases from 28.36%
to 74.13% after the correction process.
