Parking Garage Channel Characteristics at 5 GHz for ... - IEEE Xplore

Parking Garage Channel Characteristics at 5 GHz for V2V Applications Ruoyu Sun, David W. Matolak

Pengyu Liu

Department of Electrical Engineering University of South Carolina Columbia, USA

State Key Laboratory of Rail Traffic Control and Safety Beijing Jiaotong University Beijing, P.R. China

Abstract—We provide results for propagation path loss and rootmean-square delay spread within a parking garage, in the 5 GHz band, aimed at V2V applications. Results for both same-floor, and floor-to-floor propagation are shown for a typical urban parking garage structure. For line-of-sight (LOS) conditions, same-floor propagation path loss is well approximated by a 2-ray model. Same-floor non-LOS path loss shows path loss exponent n~3. Path loss for the floor-to-floor case can be well-modeled by accounting for floor attenuation factors and an additional loss that represents distance of the mobile toward the garage interior, away from the garage’s open sides, i.e., a model that accounts for both vertical and horizontal distance. Mean delay spreads reach nearly 150 ns for the same-floor case, and reduce to ~50 ns for the longest (3-floor) distance floor-to-floor case. Since there have been few results for such environments previously published, our results should prove useful for V2V systems deployed in parking garages. Keywords—Path loss; delay spread; V2V;

I.

INTRODUCTION

Vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) communication systems have seen tremendous attention in recent years, e.g., [1], [2]. As part of intelligent transportation systems (ITS) [3], planning for such vehicular networks is being conducted by governments, industries, and academia. It has long been recognized that the V2V channel is distinct from the typical cellular channel, in that antenna heights of both transmitter (Tx) and receiver (Rx) are low, and both Tx and Rx are mobile [4]. Numerous authors have characterized V2V channel dispersion, e.g., [5]-[7], and more extensive reference lists appear in [8], [9]. In addition, propagation path loss has also been studied [10], [11], and generalizations to MIMO [12] and deterministic ray tracing [13] modeling have been conducted. The classification of V2V channel environments themselves has evolved. The earliest work used channel classifications similar to those used for cellular, i.e., urban, suburban, and rural. Yet as V2V applications were studied further, additional environments such as street intersections [14] and tunnels [15] were deemed sufficiently important to warrant their own channel characterization. This paper extends this idea to another environment most

common in urban areas: the parking garage. These garages will likely support both V2V and V2I communication. Parking garages are usually multi-floored structures built from concrete and steel, and they may be fully enclosed, underground or above-ground, or may have sides that are open to the outside. To our knowledge, only a few investigations of parking garage channel characteristics have been reported. Reference [16] considered ultrawideband (UWB) propagation in underground parking garages with a signal spanning from 3.28-5.03 GHz, and short distances up to only 20 m, for line-of-sight (LOS) conditions. For this completely enclosed structure, a log-distance path loss model was developed that had a path loss exponent n=1.5; standard deviations about the fit were not provided. The authors also characterized root-mean square delay spread (RMSDS), and found values less than 30 ns. A cluster model similar to that of [17] was also developed for the multipath impulse response. In [18] the author reported on path loss only for two parking garages at a frequency of 1.8 GHz, for distances up to approximately 70 m. Antenna heights were 1 m and 1.2 m (lower than that for typical V2V mountings on car roofs). The popular 2-ray model [19] was used to fit measured results. Reference [20] measured indoor-to-outdoor propagation losses for multiple building types, including several parking garages, over a wide frequency range: 800 MHz-8 GHz. In this paper we provide our results for parking garage measurements in the 5 GHz band for a parking garage in an urban area. Our signal is a 50-MHz spread spectrum signal received with a stepped correlator receiver. Results for propagation path loss and RMS-DS for Tx and Rx on the same floor, and on different floors, are shown. The same-floor measurements sample both LOS and non-LOS (NLOS) conditions; the floor-to-floor results are all NLOS. Section II describes the parking garage environments in which we conducted our measurements, and summarizes the channel measurement equipment features. In Section III we provide the measurement results and analysis, and conclusions appear in Section IV.

978-1-4673-6187-3/13/$31.00 ©2013 IEEE

II. CHANNEL MEASUREMENTS A. Measurement Environment Measurements were performed in December 2012 and January 2013 in a parking garage on the University of South Carolina campus: the Horizon garage, located in the block between Main St. and Assembly St., and Blossom St. and Wheat St. in downtown Columbia, SC. Fig. 1 shows a photo of the exterior of the garage taken from Assembly St. Horizon garage has seven floors, and the 7th floor (roof) has no ceiling; the exit is located on the (ground) 2nd floor. Each floor has approximately 160 parking spots. The height of each floor is approximately 3 m. Concrete walls and pillars exist in the garage interior. At the east end of the garage, there are some nearby buildings (within 100 meters). At the building’s west end, the nearest buildings are at least several hundred meters away. As can be seen from Fig. 1, each floor is open to the outside. Measurements in the garage were for several conditions (see Fig. 2-3, not to scale, marked locations just examples): (1) Tx & Rx located on 3rd floor, LOS condition, garage empty of cars, Tx location fixed, 21 Rx locations (motionless) with TxRx distance 5-105 m (5 m increment); measurements w/Rx moving from 5-105 m also conducted for comparison; in Fig. 2, blue hexagon represents Tx, blue stars show Rx locations. (2) The same as case (1) but the garage was full of cars. (3) Tx & Rx located on 3rd floor without LOS, garage full of cars, 15 Rx locations (motionless) were measured for fixed Tx locations 1 to 3; in Fig. 2, three hexagons show Tx locations, yellow stars show example Rx locations for Tx location #3. (4) Tx on 6th floor, Rx on 5th to 3rd floors, garage empty of cars. Red triangles in Fig. 2 show Tx & Rx locations in hori-zontal plane. Fig. 3 illustrates locations in vertical plane. Note that Tx & Rx are always at the same distance from the edge. B. Measurement System The measurement system is the same as that used in [6]: it is a customized version of the Berkeley Varitronics Systems, Inc. [21] “Raptor” spread spectrum (SS) stepped correlator. The SS chip rate is 50 Mcps, yielding an approximate 20 ns delay resolution. Both Tx and Rx antennas were quarter-wave monopoles, connected to Tx or Rx via a short coaxial cable (loss ~2 dB). Antenna heights were approximately 1.5 m. Signal center frequency was 5.12 GHz, and transmit power at transmitter antenna cable input was 33 dBm. Both monopoles are very nearly omni-directional, and were oriented vertically. The Rx outputs power-delay profiles (PDPs) [19], taken at rate ~20 PDPs/sec. During measurements, one person stood behind the Rx for recording (always away from the Tx so that human shadowing did not block the LOS). For measurements when the garage was full of cars, some persons and cars moved in the area at very low speeds (