  This paper presents a millimeter-wave (mmWave) wideband sliding correlator
channel sounder with flexibility to operate at various transmission rates. The
channel sounder can transmit and receive up to 1 GHz of RF null-to-null
bandwidth while measuring a 2 nanosecond multipath time resolution. The system
architecture takes advantage of field-programmable gate arrays (FPGAs),
high-speed digital-to-analog converters (DACs), and low phase noise Rubidium
(Rb) references for synchronization. Using steerable narrowbeam antennas, the
system can measure up to 185 dB of path loss. The channel sounder is used to
measure the directional and omnidirectional received power as a receiver
transitions from line-of-sight to non-line-of-sight conditions down an urban
canyon. A 25 dB drop in omnidirectional received power was observed as the
receiver transitioned from line-of-sight (LOS) conditions to deeply shadowed
non-LOS (NLOS) conditions. The channel sounder was also used to study signal
variation and spatial consistency for a local set of receiver locations
arranged in a cluster spanning a 5 m x 10 m local area, where the
omnidirectional received power in LOS and NLOS environments is found to be
relatively stable with standard deviations of received power of 2.2 dB and 4.3
dB, respectively. This work shows that when implementing beamforming at the
transmitter at mmWave, the omnidirectional received power over a local area has
little fluctuation among receiver locations separated by a few to several
meters.
