38 GHz and 60 GHz Angle-dependent Propagation for Cellular ...

Published in 2012 IEEE International Conference on Communications, Ottawa, Canada, June 2012to-peer channel may be attributed to larger T-R distances(causing greater delays and attenuation of late arrivingmultipath) and propagation due to the urban canyon effect.Figure 14– Increased excess path loss is associated with higher average RMSdelay spreads for the 38 GHz cellular channel.Figure 13 shows a scatter plot of the measured RMS delayspreads of the cellular channel vs. transmitter and receiverazimuth scanning angle combinations. While large buildingscan cause high delay spreads with near-boresight antennapointing, the probability of a high RMS delay spread link isgenerally lower for smaller azimuth pointing angles than forgreater angles, as illustrated by the linear fit line. Figure 14shows a scatter plot of the RMS delay spread versus the excesspath loss over the reference free space path loss. The figureshows how, like the peer-to-peer channel, RMS delay spreadincreases with excess path loss. Indeed systems that canidentify the strongest NLOS link will more often avoid highRMS delay spread links.V. CONCLUSIONMillimeter wave (38 and 60 GHz) peer-to-peer outdoorurban channels, and a 38 GHz outdoor cellular channel, weremeasured using a broadband sliding correlator channelsounder with rotatable 7 degree beamwidth antennas. The keytrends include near free-space path loss and virtually no RMSdelay spread for all LOS links, while NLOS links have higherRMS delay spread, as much as 122 ns (for the 38 GHz peer-topeerchannel) and 107 ns for the 38 GHz cellular channel. Ingeneral, NLOS links offer increasing RMS delay spread as theazimuth pointing angles are increased away from boresight ateither or both the transmitter and receiver. An interestingresult is that many unique paths can be formed in NLOS andLOS channels using narrow beam antennas. By picking thebest combination of transmitter and receiver antenna pointingangles at any location, path loss and RMS delay spread can bereduced substantially. A key observation is the increase inRMS delay spread for increasing excess path loss (above freespace) for both the peer-to-peer and cellular channels.The data presented here suggest that while NLOS pathsmay be formed for millimeter-wave channels, they will requireequalization and will have greater propagation latency, higherpower consumption, and lower data rates than LOS channels.However, a system capable of determining the bestcombination of antenna pointing angles for NLOS conditionswill benefit from higher SNR and lower expected RMS delayspread. The angles over which links could be formed for the 38GHz cellular channel suggest that outdoor urban canyons,where tall buildings surround the receiver on two sides, willrequire beam steering over a small range of angles at thetransmitter, while the receiver may require more exhaustivebeam steering to find a link. We also found that the position ofthe transmitter relative to the center-line of the urban canyon(i.e. the line mid-way between the two columns of buildingsthat form the urban canyon) will result in minimum path losswhen the transmitter antenna is steered most often to pointtoward this center line. Rain and hail, however, will attenuatelink margin and reduce cell sizes while lowering data rates.Future work is investigating cellular shadowing and link outageover larger propagation distances at mm-wave frequencies.ACKNOWLEDGMENTSThis project is sponsored by Samsung TelecommunicationsAmerica, LLC. 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