Radio-Wave Propagation Into Large Building Structures—Part 1: CW Signal Attenuation and Variability William F

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 58, NO. 4, APRIL 2010 1279 Radio-Wave Propagation Into Large Building Structures—Part 1: CW Signal Attenuation and Variability William F. Young, Member, IEEE, Christopher L. Holloway, Fellow, IEEE, Galen Koepke, Member, IEEE, Dennis Camell, Member, IEEE, Yann Becquet, and Kate A. Remley, Senior Member, IEEE Abstract—We report on our investigation into radio commu- problems faced by emergency responders (firefighters, police nications problems faced by emergency responders in disaster and medical personnel) in disaster situations involving large situations. A fundamental challenge to communications into and building structures. The goal is to create a large body of statis- out of large buildings is the strong attenuation of radio signals caused by losses and scattering in the building materials and tical data in the open literature for improved communication structure. Another challenge is the large signal variability that system development and design. For example, these results occurs throughout these large structures. We designed experi- are useful to technology advancement initiatives focused on ments in various large building structures in an effort to quantify improving public safety communications such as [9]–[11]. As continuous wave (CW) radio-signal attenuation and variability part of our effort, we are investigating the propagation and cou- throughout twelve large structures. We carried radio frequency transmitters throughout these structures and placed receiving pling of radio waves into large building structures. This paper systems outside the structures. The transmitters were tuned to is the first part of a two-part series covering radio frequency frequencies near public safety, cell phone bands, as well as ISM propagation into large structures. Part 2 summarizes results and wireless LAN bands. This report summarizes the experi- from [12] where we investigate time domain and modulated ments, performed in twelve large building structures. We describe signal propagation behavior into some of these same structures. the experiments, detail the measurement system, show primary results of the data we collected, and discuss some of the interesting The complete results for this set of measurements are found in propagation effects we observed. [13]. The experiments reported here were performed in twelve Index Terms—Emergency responder communications, large building radio frequency propagation, radio-frequency propaga- different large building structures and are essentially mea- tion measurements. surements of the reduction in radio signal strength caused by penetration into the structures. These structures include four office buildings, two apartment buildings, one hotel, one I. INTRODUCTION grocery store, one shopping mall, one convention center, one sports stadium, and one oil refinery. In order to study the radio HEN emergency responders enter large structures (e.g., characteristics of these structures at the various frequencies of W apartment and office buildings, sports stadiums, stores, interest to emergency responders, we chose frequencies near malls, hotels, convention centers, warehouses) communication public-safety and cell phone bands, as well as ISM and wireless to individuals on the outside is often impaired. Cell phone LAN bands (approximately 50 MHz, 150 MHz, 225 MHz, 450 and mobile-radio signal strength is reduced due to attenuation MHz, 900 MHz, 1.8 GHz, 2.4 GHz, 4.9 GHz). caused by propagation through the building materials and The experiments performed here are referred to as “radio scattering by the structural components [1]–[8]. Also, the large mappings.” This involved carrying transmitters (or radios) amount of signal variability throughout the structures causes tuned to various frequencies throughout the twelve structures degradation in communication systems. while recording the received signal at sites located outside the Here, we report on a National Institute of Standards and building. The reference level for these data was a direct, unob- Technology (NIST) project to investigate the communications structed line-of-sight signal-strength measurement with both transmitters and receiver external to the different structures. The purpose of the radio-mapping measurements was to inves- Manuscript received December 18, 2008; revised August 10, 2009; accepted tigate how the signals at the different frequencies couple into September 25, 2009. Date of publication February 05, 2010; date of current ver- the structures, and to determine the field strength variability sion April 07, 2010. This work was supported in part by the U.S. Department of Justice, Community-Oriented Police Services through the NIST Public-Safety throughout the structures. Communications Research Laboratory. Several previous papers, e.g., [14]–[17], have provided W. F. Young is with Sandia National Laboratories, Albuquerque, NM 87185 results on radio mapping in buildings. Others such as [18]–[27] USA (e-mail: [email protected]). C. L. Holloway, G. Koepke, D. Camell, Y. Becquet, and K. A. Remley are provide results on building penetration for a few of the with the National Institute of Standards and Technology, Boulder, CO 80305- frequency bands discussed here. Reference [28] outlines a 3328 USA (e-mail: [email protected]). measurement campaign at 2.4 GHz and 5.2 GHz carried out in Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. support of a overall system design effort, while [26] and [27] Digital Object Identifier 10.1109/TAP.2010.2041142 focus on measurements for public safety. With respect to the 0018-926X/$26.00 © 2010 IEEE Authorized licensed use limited to: NIST Virtual Library (NVL). Downloaded on July 15,2010 at 17:13:08 UTC from IEEE Xplore. Restrictions apply. 1280 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 58, NO. 4, APRIL 2010 TABLE I TABLE II PUBLIC SAFETY COMMUNITY FREQUENCIES CELLULAR PHONE FREQUENCIES TABLE III FREQUENCY BANDS USED IN THE EXPERIMENTS breadth of our measurement campaign, [29] provides a review of similar radio propagation measurements up to 1990 within our bands of interest, and also proposes a building classification scheme. Our effort is different is several ways: (1) a wider range and number of frequencies are covered per building, (2) multiple large building structures are investigated, and (3) the walk-through path and receive site locations are selected to emulate an emergency response scenario. Hence, this work are typically below 2 GHz. New frequency allocations and builds upon previous work designed to accurately characterize systems including higher frequencies (e.g., around 4.9 GHz) wireless RF propagation in some key environments by adding will become increasingly important in the future. We chose much needed data to building categories 5 and 6 in [29], and to eight frequency bands below 5 GHz, from about 50 MHz to 4.9 the general body of radio propagation measurements into and GHz. These include four VHF bands typically used for analog within buildings. FM voice, one band used for multiple technologies (analog FM This paper is organized as follows. Section II provides more voice, digital trunked FM, and cellular telephone), one band detail on the frequencies, the transmitters, and the automated near the digital cellular telephone band, and wireless LAN measurement system used in the radio-mapping measurements. bands. Section III describes the different structures and details our In designing an experiment to investigate the propagation experimental procedures for each structure. Section IV presents characteristics into large buildings at these different frequency representative data from the complete set of results in [13]. bands, we chose frequencies very close, but not identical, to the Finally, Section V summarizes the results of these experiments above bands. If frequencies were chosen in the public safety or and discuss some of the interesting propagation effects ob- commercial land-mobile bands, interference to the public safety served. and cellular systems could possibly occur. Conversely, these existing systems could interfere with our experimental setup. II. EXPERIMENTAL PARAMETERS AND EQUIPMENT In addition, obtaining frequency authorizations in these bands This section covers the frequency bands, transmitter descrip- for our experiments would have been problematic due to the tions, and the receiver configurations used in the experiments. intense crowding of the spectrum. To circumvent these issues, we were able to receive temporary authorization to use frequen- A. Frequency Bands cies in the U.S. government frequency bands adjacent to these An overview of the frequencies used by the public-safety public safety bands. Table III lists the frequency bands that were community nationwide (federal, state, and local) is given in used in the experiments. The lower four bands correspond to Table I, which shows a broad range of frequencies ranging from the frequencies used by the public-safety community; 902 MHz 30 MHz to 4.9 GHz. The modulation scheme has historically can be associated with several services including both public been analog FM, but this is slowly changing to digital as Project safety and cellular phones; 1830 MHz is near the digital cellular 25 radios come online [9]. The modulation bandwidth in the phone; 2450 MHz covers a wireless LAN band; 4900 MHz rep- VHF and UHF bands has been 25 kHz, but due to the need resents a new public safety band. The

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