Channel Characteristics for Elevator Shafts at 5 GHz David W. Matolak, Ruoyu Sun Department of Electrical Engineering University of South Carolina Columbia, USA {matolak@, sun55@email}.sc.edu Abstract—We provide some measured channel characterization results for two elevator shaft channels in the 5- GHz band, for two distinct elevator shaft types in two buildings. The elevator shaft channel is of interest for several applications, including public safety. Even though other authors have reported elevator shaft channel characteristics for lower-frequency bands (255-MHz, 900-MHz, 1.9-GHz), to our knowledge ours is the first work for the 5-GHz band. Prior work has also not thoroughly addressed channel characteristics when the elevator car is in motion, whereas here we provide some initial measurement results for this dynamic condition. We measured power delay profiles and from these estimated propagation path loss and root- mean square delay spread (RMS-DS). Path loss exponents were approximately 2 in one building and 6 in the other. Mean RMS- DS values range from 14-60 ns when the elevator car is motionless, with RMS-DS generally increasing with link distance. Maximum RMS-DS values increase to 58 ns and 70 ns in the two buildings when the elevator car is moving and the receiver is inside the car. Keywords- Path loss, delay spread I. INTRODUCTION Research on indoor propagation has been a topic of study since the early 1980s. Environments include office buildings, corridors, and open halls, but there have been only a few studies for propagation through and near elevator shafts. The elevator shaft provides an artificial waveguide, and the shaft and elevator car generally provide a highly reflective propagation environment. Propagation characteristics within elevator shafts are of interest for several possible applications, including public safety. Public safety spectrum in the US has recently been allocated in the 4.95-5 GHz band, and our measurements here are appropriate for this application. The authors in [1] analyzed the propagation of a GSM signal in an elevator shaft, and developed models for attenuation (path loss) for both 900 MHz and 1800 MHz. The path loss exponent of 1.6—less than the free-space value of 2—indicates waveguiding. In [2], the authors also studied 900 MHz propagation within elevator shafts, and produced experimental results on antenna orientation: with a base station antenna in the elevator shaft and a mobile phone in the elevator car, they found that dipole antenna locations and orientations did not significantly affect attenuation. This is likely due to the rich scattering environment that causes depolarization of some multipath components (MPCs). Reference [3] studies cellular system handoff performance when one cell is the elevator car; no propagation results were provided in this work. References [4]-[6] represent the most closely related work, where authors analyzed elevator shaft propagation at UHF (255 MHz), with a very wideband signal of bandwidth 300 MHz. Power delay profiles (PDPs) were taken with the elevator car in different locations, and as expected, the main propagation mechanism was found to be waveguiding along the shaft. Measured root-mean square delay spreads (RMS-DS) from 16.7-176.0 ns were computed for transmitter-receiver (Tx-Rx) distances from 3.5-17.5 m. References [4] and [5] address only the time-invariant case, whereas [6] considers very slow time variation, but does not explicitly describe the conditions. The effect of opening and closing the elevator door and elevator car movement were included in [6]. The authors of [6] employed the Weibull distribution for statistically modeling the MPC amplitude variation. In [7], similar wideband channel sounding results at 255.6 MHz along an elevator shaft on board a ship were presented. In the ship environment RMS-DS ranged from 60.4-237.2 ns for Tx-Rx distances from 2.5-15 m. A path loss exponent of 2.25 was also found. In this paper we report our results for elevator shaft channel measurements in the 5 GHz band for several elevator shafts. Our signal is a 50-MHz spread spectrum signal received with a stepped correlator receiver. We provide results for path loss and RMS-DS for the case of stationary elevator cars, and initial results for the elevator car in motion; to the best of our knowledge, variation of RMS-DS for the moving elevator car has not been reported. Near-term future work will expand upon these moving-car results. The 5 GHz band results, and in particular moving car channel characteristics are the main contribution of this paper. The rest of this paper is organized as follows: Section II describes the environments in which we measured, and reviews the channel measurement equipment features. In Section III we provide the measurement results and analysis, and conclusions appear in Section IV. II. CHANNEL MEASUREMENTS A. Measurement Locations Measurements were performed in fall 2011 and winter 2012 along elevator shafts in two buildings on the campus of Ohio University: Stocker Center (SC) and Porter Hall (PH). Stocker Center is a 5-story office building with classrooms and faculty offices on the first through fourth floors. It also has some laboratories on the ground (basement) floor. Porter Hall is a 6-story building consisting primarily of faculty offices. Table I provides some physical dimensions for the two buildings, along with Tx-Rx distances. Figure 1 shows photographs of the two building exteriors; note that several floors of each building are not discernible from these photographs. The Stocker elevator is within the building core,