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Radio Frequency Noise Measurements and Models for Indoor Wireless Communications at 918 Mhz, 2.44 Ghz, and ,4.0 Ghz

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Radio Frequency Noise Measurements and Models for Indoor Wireless Communications at 918 Mhz, 2.44 Ghz, and ,4.0 Ghz EMC Test & Design, July/August 1991, pp. 25-33 Industrial Equipment Radio Frequency Noise Measurements and Models for Indoor Wireless Communications at 918 MHz, 2.44 GHz, and ,4.0 GHz A Presentation of the Measurement Techniques and Statistical Analyses of Average and Impulsive Noise in Several Common Work- Place Environments By Kenneth L. Blackard, Theodore S. Rappaport, and Bruce Tuch Development of radio-frequency communi­ rates and coding requirements for indoor department store located in a suburban area cations equipment for wireless indoor net­ communication systems. Further, if spe­ near a busy 4-lane highway (Site B), two works is an active field. A thorough cific devices are known to be noise sources, large open-plan office buildings located in a understanding of the channel characteristics this knowledge can be used to assist in the metropolitan district (Site C and Site D), is needed to develop reliable system design successful deployment of indoor wireless and in a closed-plan office building .(Site E) guidelines and installation techniques for networks. located in a rural area. The measurements future indoor wirel~ss systems. These This article describes the experiment were performed at 918 MHz, 2.44 GHz, systems will be used for reconfigurable design, measurement procedures, and sta­ and 4.0 GHz. Models and statistical charac­ voice, data, and video networks that link tistical results of average and impulsive terizations of the noise data, as a function portable computers, vision systems, cash noise measurements made in a suburban oflocation, frequency, and noise source, are registers, and telephones in stores, offices, grocery store (denoted as Site A), a presented in the form of average noise level and factories [1]. Researchers have given considerable Theodore S. Rappaport received T.S. Rappaport in the Mobile and Portable attention to the investigation and modeling B.S.E.E., M.S.E.E., and Ph.D. de­ Radio Research Group. of indoor radio wave propagation in recent grees from Purdue University. Dr. Rappa­ Bruce Tuch received the B.S.E.E. years [1-4]. However, it appears that little port is an assistant professor and director degree from the State University of New scientific work has been done to determine of the Mobile and Portable Radio Research York and the M.S. degree from The the significance of indoor radio-frequency Group, Virginia Tech, Blacksburg, VA. Technical University of Eindhoven, Hol­ (RF) noise and its impact on system Kenneth L. Blackard received the land. He is Project Leader with in the performance. Noise models for indoor B.S.E.E. from Virginia Tech and is Wireless Indoor Network Division at NCR channels and specific noise sources are currently pursuing a M.S.E.E. degree Systems Engineering, Utrecht, the Nether­ important for determining irreducible error from Virginia Tech working with Professor lands. SUPERHETERODYNE NOISE RECEIVER RECEIVER CALIBRATION CURVES Typical Case -20 ····· ..... -25 E' -30 ro -35 ~ 0 -40 c c -45 2 -50 c <( -55 ..... .... 0 -60 L QJ -65 ~ 0 -70 Q_ -o -75 QJ ,;:: -80 , QJ .... u -85 c.rQJ -90 -95 -100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Cscilloscope Deflection (Volts) Figure 1. Block diagram ni the three-band noise _measurement Figure 2" 1}rpjca} receiver calibration curves. This figure illustrates system. the receiver baseband response to an applied- CWsigncil a1 --.thr--e~.~~ receiver antenna terminal. EMC Test & Design II -25 111901.o~.ll 918 MHz 100 us; Bin Duration -25 Al901b.I2 918 MHz 1.0 us; Bin Duration B-35 Snapshot It 211 llvQ. Pc;~ak Pouc;~r = -72. 57 dEia~ 8-..35 Sn.aps;hot 1116 llvQ. Pc;~ak Pouar = -71.33 dBa~ E ! ! l45 j-45 ~-55 ~-55 ~ ~ ~-65 ~-65 l 0 ~~~~~~~.. ~~,~~-~~~~.~.~~~~ ~-75~~~~~~~~mM~~~~~~- ~-75 i i ·~-85 ·~-85 0::; I U:; I -95~-~~~-L~~~~~~I-LI~I~I~I~I~I~~~~~~~~I ~~~~~~ -95· I I I I I I I I I I I I I I I I I I I I 0 2 4 6 8 10 12 14 16 18 20 0.0 . 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Tim.e (microseconds) Time (milliseconds) Figure 3(a). Snapshots of typical impulsive noise waveforms Figure 3(b). Snapshots of typical impulsive noise waveforms measured during 3-minute measurement runs near an operating measured during 3-minute measurement runs near an operating cash register using 1 s/div. · cash register using 100 sldiv. distributions, amplitude probability distribu­ block diagram of the noise measurement band. tions, pulse duration distributions, and pulse system'is shown in Figure 1. A broadband omni-directional discone spacing (interarrival time) distributions. The noise receiver incorporated a bank antenna measured noise from all azimuth of microstrip band pass filters, wide band directions. Three directional helical anten­ Measurement System low noise amplifiers, and a logarithmic video nas, with gains of approximately 12 dB, The three-band noise measurement sys­ detector which provided over 70 dB of measured RF noise characteristics of indi­ tem consisted of a superheterodyne noise dynamic range. The noise receiver had a vidual sources. Detailed descriptions of receiver, omni-directional and directional 3-dB RF bandwidth of 40 MHz centered discone and. helical antenna designs can be antennas, a spectrum analyzer, a digitizing around the 918 MHz and 4.0 GHz bands, found in [5] and [6]. · oscilloscope, and a personal computer. The and 30 MHz centered about the 2.44 GHz A spectrum analyzer allowed the system -25 1119Dlc.J2 918 11Hz 100 us; Bin Duration IMPULSIVE NOISE APD 8--35 Snaps;hot II 35 llvQ. Pa.ak Pouar = -70. 15 dBa~ Typical Cases- Site A (All Locations) 0 100 VI ! (I) ·u (I) j-45 ~ 10 w ~-55 "0 ~ Q_ ~ \ E I <( r..-65 \ \ \ :0£ 0.1 \ ~ \ 0 Q;,-75 .0 " \. \ \ e 918 MHz \ I i ~ 0.01 2.44 GHz \ c \ <!) 4.0 GHz \ J-85 ~ ' <!) \ ' 0..0.001 ' -95~-L-L~~~~~~~~~~~~~~ 0 5 10 15 20 25 30 35 40 45 50 0 20 40 60 80 100 120 140 160 180 200 Amplitude in dB above Mean Thermal Noise Time (milliseconds) Figure 3(c). Snapshots of typical impulsive noise waveforms Figure 4. Typical amplitude probability distributions (APDs) measured during 3-minute measurement runs near an operating determined from all data recorded at Site A .. Notice how the cash register t:sing 10 ms/div. amplitude level for a probability of 0. 001 percent is higher at 918 MHz than at 2.44 GHz and 4.0 GHz. This is caused by higher path losses at the two higher frequencies. July/August 1991 IMPULSIVE NOISE PDD IMPULSIVE NOISE PSD Typical Cases- Site A (All Locations) All Measurements T b = 40 ns T b = 40 ns 100 100 0 0 (/) ~ VI (/) .... ~ VI .-r 'i) ;-.. 'Li ~ (/) (/) .D 10 ::_\, .D 10 ~ . <( A ' 'V c ~ ' \, 0 g' :,:::; \, '[i ~ 0 :J a. ' V> 0 ' g ' ' ' g 0.1 \ \, :.0 0.1 E- :0 ' 0 0 \ .D \ .D 918 MHz e 0 2.44 GHz Q.. 918 MHz \ n: 4.0 GHz 0.01 2.44 GHz +'c 0.01 ~ \ v Ill 4.0 GHz ~ ~ t> Ill Ill 0.. ~ Q.. 0.001 0.001 ·-'- 4 4 3 4 5 3 4 5 10-7 3 10-6 :} 1 Q-5 10-7 10-6 10-5 2 Pulse Duration (sec) Spacing Between Consecutive Pulses (sec) Figure 5. Typical pulse duration distributions (PDDs) determined Figure 6(a). Pulse spacing distributions (PSDs) of impulsive noise from the impulsive noise data recorded at Site A using a 1 s/div measured at all sites with sweep speeds of 1 s/div. horizontal sweep speed. These PDDs were calculated using a threshold level equal to the average peak power of each measured waveform. operator to visually detect CW and modu­ check-out counter) and involve.d: 1) re­ generator and the spectrum analyzer. The lated signals in the measured frequency ceiver calibration and 2) average and impul­ amplitude and bandpass responses in each bands. The oscilloscope digitized the base­ sive noise measurements. band were consistently flat throughout the band output of the logarithmic detector and Receiver Calibration. Before all meas­ measurement campaign. stored the digitized waveforms on the urement runs, the noise receiver was Average and Impulsive Noise Meas­ computer's hard disk. calibrated to allow antenna output power urements. Before each measurement run, levels to be determjned from oscilloscope a 50 Ohm "dummy" load was placed at the Experimental Procedures vertical deflection. The power level of an receiver antenna terminal. The time­ In most buildings, six three-minute meas­ applied CW signal was varied over a 75 dB average DC signal out of the log-detector urement runs were performed over a penod range above the receiver noise floor, and was then recorded. This DC level corre­ of an hour in each frequency band at each the time-average DC signal level at the sponded to the average thermal noise floor measurement location. This procedure is output of the log detector was measured of the receiver at that location, and was a recommended in [7]. In each building, and stored in the computer. A typical function of the noise figure of the receiver. measurements were made at several loca­ calibration curve is given in Figure 2. The This value was stored for future data tions deemed likely for future indoor com­ system's bandpass response in each band processing and varied by less than 1 dB munication systems (for example, near a was also calibrated using a white-noise throughout the measurement campaign.
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