900-Mhz Multipath Propagation Measurements for US Digital Cellular Radiotelephone

I 132 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 39, NO. 2, MAY 1990 900-MHz Multipath Propagation Measurements for U. S. Digital Cellular Radiotelephone Abstract-The results of multipath power delay profile measurements delay profiles that describe the temporal extent of the of 900-MHz mobile radio channels in Washington, DC, Greenbelt, MD, multipath and the amplitude of multipath components from Oakland, CA, and San Francisco, CA, are presented. The measurements reflecting objects for various radio channels. have focused on acquiring worst case profiles for typical operating locations. The data reveal that at over 98% of the measured locations, Wide-band multipath channels can be grossly quantified by rms delay spreads are less than 12 ps. Urban areas typically have rms their mean excess delay (7) and root mean square (rms) delay delay spreads on the order of 2-3 ps and continuous multipath power out spread (a) [2]-[5], [9]-[14]. The mean excess delay is the first to excess delays of 5 ps. In hilly residential areas and in open areas within moment of the power delay profile and is defined to be a city, root mean square (rms) delay spreads are slightly larger, typically having values of 5-7 ps. In very rare instances, reflections from city ayzk7k skylines and mountains can cause rms delay spreads in excess of 20 ps. f=k. (1) The worst case profiles show resolvable diffuse multipath components at excess delays of 100 ws and amplitudes 18 dB below that of the first c 4 arriving signal. k The rms delay spread is the square root of the second central I. INTRODUCTION moment of the power delay profile and is defined to be ELLULAR RADIOTELEPHONES are becoming in- Ccreasingly popular. First available to the U.S. public in - 1983, over 3 million car phones are in use in the United States a=- where 72=k (2) today. It is predicted that by 1995, there will be over 20 c 4 k million cellular telephones in operation [l]. To date, U.S. cellular radiotelephones have used strictly analog voice and CY: and 7k are derived directly from the digitized transmissions with 30-kHz RF channel spacings in the 800/ oscilloscope values at the receiver. In (1) and (2), the delays of 900-MHz band. However, to accommodate the projected each profile are measured relative to a first detectable signal tenfold increase in users and the need for data as well as voice, arriving at 70 = 0. Excess delay spread (x dB) is defined as the it has been realized that a new U.S. cellular telephone standard maximum excess delay at which a multipath component is must be developed that uses spectrally efficient digital received with an amplitude within x dB of the maximum modulation and speech coding techniques. received signal level within a single power delay profile. This paper presents the results of propagation measurements Multipath profiles measured between a base and mobile in in four typical cellular radio markets throughout the United many types of terrain are given in [3]. In hilly terrain, [3] States [2]. The measurements reveal multipath characteristics indicates that signal components typically arrive 10-25 ps for a variety of topographical surroundings and geographical after the direct (line-of-sight (LOS)) signal and have ampli- regions, and provide large-scale statistics of the temporal tudes 10-20 dB weaker than the direct signal. Building facades extent of impulse responses in UHF cellular radiotelephone induce multipath signals that have excess delays of less than 10 channels. These characterizations are required for determining ps and amplitudes 10 dB below the direct signal. In mountain- suitable equalization requirements for next-generation time- ous regions, significant multipath can arrive with amplitudes division multiple-access (TDMA) U. S. cellular radiotelephone within 10 dB of the direct signal at excess delays of 20 ps or systems, which will gracefully begin to replace existing analog more [3]. systems in 1991 [l]. In [5], it was reported that urban radio channels provide Many researchers have already characterized UHF urban more predictable path loss because of diffraction waves and radio multipath channels worldwide [3]-[9]. These works waveguiding effects along city streets. In residential areas, have been valuable in assessing typical and worst case power shadowing losses are greater and cause wider variations in mean path loss. Data in [3], [5] indicate that measurements in Manuscript received March 9, 1989. Parts of this paper were presented at residential also display larger delay spreads. the 1989 IEEE GLOBECOM, Dallas, TX, Nov. 27, 1989. T. S. Rappaport and S. Y. Seidel are with the Mobile and Portable Radio In [9i9 a simp1e radar cross-section is proposed, and Research Group, Bradley Department of Electrical Engineering, Virginia some measurements indicate a worst case rms delay spread of Polytechnic Institute and State University, Blacksburg, VA 24061. about 2 ps in suburban areas and 1 ps in rural and residential R. Singh is with Lunayach Communications Consultants, Washington, DC 2W5. areas. Maximum excess delay spreads (23 dB) in suburban IEEE Log Number 9035683. areas on the order of 8 ps are reported in [9]. 0018-9545/90/0500-0132$01.00 0 1990 IEEE I I RAPPAPORT et al.: 900-MHz MULTIPATH PROPAGATION MEASUREMENTS 133 U Y U a) Fluke 6062 Signal Generator j) HP 0-1 10 dB Attenuator b) HP 8082 Pulse Generator k) ZHL 42 Amplifier cj ZHL 10421 Amplifier 1) 892 MHz Cavity Filter d) Linear Amplifier (60 W or 7 Wout) m)Tektronix 2710 Spectrum Analyzer e) Bud Wattmeter n) TriangJe PT-22 Detector f) 3 dB 318). whip 0)Tehronix I1401 Digital OsciUoscop g) 9 dB omni p) Compaq Porlable Computer h) 892 MHz Cavitv Filter Fig. 1. Measurement SJ(stem block diagram and equipment list Measurements in [6] have shown that individual multipath indoor radio channels [lo], [13]. To operate close to the components fade according to a Rayleigh distribution, al- cellular radiotelephone band while preventing interference to though significant variations from the Rayleigh distribution do and from adjacent cellular radio channels, a 4-MHz RF occur. This is also reported in [7]. Root mean square delay spectrum centered at 892 MHz was used to transmit a 500-ns spreads in New York City of about 2 ps were reported in [6]. half-power duration RF pulse, which was repeated at 100-ps Except for [5], the above-mentioned works have been intervals. This provided a multipath resolution of about 500 ft. confined to one particular city or geographical setting. In this The transmitter used a linear amplifier with 60-W output, paper, we provide results of a measurement campaign con- which was fed to a 3-dB gain, 318 X vertical whip antenna. ducted for the Cellular Telecommunications Industry Associa- Inverters were used to provide ac power to equipment in the tion during the latter part of December 1988. The work mobile. Measurements in Washington, DC, and Greenbelt, involved the measurement of UHF mobile radio channels in MD, used a 7-W (output) class-C amplifier. By carefully four cities currently served by cellular radio: Washington, limiting the drive power, it is possible to provide linear pulse DC, Greenbelt, MD, Oakland, CA, and San Francisco, CA. amplification with the class-C amplifier. These measurements were performed in a ten-day period to The base receiver front-end used specially designed eight- provide a reasonable sample of local worst case multipath stage cavity filters, which provided less than 4-dB passband profiles from many typical operating cellular markets. These loss with 25-dB attenuation at +2 MHz from center fre- cities were selected because they provided a wide range of quency. These filters were needed to avoid receiver overload usual topographies and were locations where local cellular during operation near cellular base station transmitters. A operators had committed to providing us unrestricted access to spectrum analyzer was used at the receiver to identify the cell sites. First, we describe the measurement apparatus, and strengths and frequency of adjacent signals. A 70-dB low- then give descriptions of the four measurement locations. noise amplifier chain with a decade attenuator was required to Statistics of important channel parameters are then presented, adjust the received signal power to within the dynamic range and the resulting propagation characteristics of each of these of the square-law pulse detector. A digital oscilloscope and four cities are analyzed from the data. The relative frequency IEEE-488 interface recorded the measured impulse responses approach to probability is used to present statistical models for and stored them in a personal computer. The average noise typical next-generation U. S. digital cellular radio channels. floor after the front-end cavity filter (with the antenna connected) was consistently measured to be between - 94 and 11. THEMEASUREMENT APPARATUS - 106 dBm over a 4-MHz 3-dB RF bandwidth at all receiver Fig. 1 shows a block diagram of the apparatus used for the locations (with the decade attenuator set to 0 dB). The system measurements, including an equipment list. The mobile measurement range was 129-148 dB, depending on the base transmitter is capable of generating both pulsed and CW station receiver location and transmitter power. transmissions, and is similar to time-domain multipath mea- Receive antennas at all four measurement locations were 9- surement systems used to measure the power delay profiles in dB omnidirectional vertically polarized antennas typically I I 134 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 39, NO. 2, MAY 1990 used at cellular radio sites. The antenna patterns maximize of the residential south side of San Francisco, near Candelstick power on the horizon, which is desirable for mobile radio Park.

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