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A Path Loss Comparison Between the 5 GHz UNII Band(802.11a) and the 2.4 GHz ISM Band (802.11b)

David CheungCliff Prettie

Intel LabsIntel Corporation

January, 2002

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A Path Loss Comparison Between the 5 GHz UNII Band (802.11a) and the 2.4

GHz ISM Band (802.11b)

Abstract

The dominance of 802.11b in the 2.4 GHz wireless LAN market may come to an end with theemergence of 802.11a and its promise of 54 Mbps throughput. However, operation in the 5 GHzUNII band poses challenges to 802.11a radio design that include multipath and additional pathloss. The focus of this report is a comparison of the path loss in the two bands.

Residential propagation measurements taken over the 2-8 GHz frequency range were processedto isolate ISM (802.11b) and UNII (802.11a) band effects. The measurement geometriespermitted us to obtain results regarding the free space path loss and excess path losses due towalls, flooring, and water.

The findings indicate that an 802.11a radio must contend with more propagation loss than an802.11b radio for all of the obstacles measured. Over a 1-10 m range the best fit path lossexponents for the two bands are both 1.9 for line-of-sight geometries. For the non-line-of-sightgeometries, the best fit path loss exponents determined from all measurements over a 3-14 mrange are 3.7 and 4.6 for ISM and UNII bands, respectively. Propagation losses caused by onewall are 4.2 dB greater for the UNII band than for the ISM band. Loss through flooring is 1.5 dBgreater. The most significant differential loss was through water, for which UNII band signalsexperienced a 10.4 dB greater loss. This result suggests that blockage losses due to peoplewalking through the LOS path will be much more significant in the UNII band.

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1. Introduction

The IEEE 802.11b standard has become the prevailing wireless LAN solution, supporting amaximum data rate of 11 Mbps. However, its operation in the unlicensed Industrial, Scientific,and Medical (ISM) band of 2.4-2.5 GHz is adversely affected by interference from a myriad of

other home/office electronics, including cordless telephones, Bluetooth devices, wireless videocameras, and even microwave ovens.

The 802.11a standard, targeted for use in the currently less occupied Unlicensed NationalInformation Infrastructure (UNII) band (5.15-5.35 GHz and 5.725-5.825 GHz), provides for evenhigher data rates up to 54 Mbps and beyond. The use of the UNII band provides 802.11asystems the advantage of spectrum that is used less at the cost of other system design issues.

In this report we focus primarily on the difference in path loss of signals in the ISM band versuspath loss in the UNII band. We base our comparison on channel characterizations that weperformed over the 2-8 GHz band. An advantage of our approach is that we can compare path

loss data in the two frequency bands for the exact same locations and times. In the next section,Section 2, we give an overview of our measurement approach. In Section 3, we describe ourmethod of generating channel statistics and discuss our findings. We present our conclusions inSection 4. Appendix A contains a list of the equipment used. Appendix B describes analysismethodology limitations. Appendix C is a comparison between our ISM band path loss resultsand those determined by another Intel study performed by Greg Peek and Ryan Etzel [1] andsummarized by Rob Cavin [2].

2. Measurement Equipment and Approach

We performed over 2100 measurements over a period of three months in the summer of 2001.Roughly half of these measurements were made in a residential environment a townhouse inOregon. The rest were taken in an office environment and in an anechoic chamber.

The results presented here are based primarily on the residential measurements. The floor planof the townhouse is shown below:

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Townhouse layout.

We consider this townhouse to be a reasonable representation of the residential environment.The townhouse has two floors and measures roughly 13.5 m in length and 5 m in width. An Intelstudy on 802.11b path loss had been made previously in this same townhouse [1]. A discussionof the general agreement between our measurements and the 802.11b path loss survey can befound in Appendix C.

We used an Agilent 8720ES S-Parameter Network Analyzer (NWA) for channel transferfunction (frequency domain) measurements and a Tektronix TDS8000 Digital SamplingOscilloscope for channel impulse response (time domain) measurements and characterizedpropagation effects over a frequency range of 2-8 GHz.

Figure 1 shows a typical configuration for an impulse response measurement. A 2 MHz clocktriggers a Hyperlabs HL9200 ultra-wideband (UWB) pulser, generating an impulse that isfiltered, amplified, and finally transmitted.

The received signal is amplified through at most two gain stages and measured with theoscilloscope. To maintain synchronization, the oscilloscope is triggered with the same 2 MHzclock sent to the Hyperlabs pulser.

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The transmitting antenna was most often an MEC biconic antenna. The receiving antenna waseither another MEC biconic antenna or a Pulsicom Technologies, Ltd., UWB discone antenna.Both antennas are vertically polarized and characterized by an azimuthally symmetric pattern,with a broadband response. The response has a nominal 30 degree beamwidth.

Pulser HPF

5th order

Bessel

Channel

Tx Ant.

Biconic

Pulsicom or

Biconic-- 12.5 GHz low-noise head

-- 200 kHz sampling

-- 25 ps /sample

-- 4000 samples

PA

ZVE-8G

34 dB

Rx Ant.TDS8000

DSO

2 MHz clock

UWB LNA

ZRON 8G

23 dB

UWB LNA

ZRON 8G

23 dB

Figure 1. Time domain measurement equipment configuration.

Figure 2 shows a typical configuration for a channel transfer function measurement. In anattempt to reduce the number of variables in our measurements, this setup is similar to the timedomain measurement configuration.

Channel excitation is induced by the network analyzer sweeping through the frequency band ofinterest (2-8 GHz) with a continuous wave signal of constant power.

HPF

5th order

Bessel

Channel

Tx Ant.

Biconic

Pulsicom or

Biconic-- 2-8 GHz range typical

-- 1600 pts.

-- 16 averages

-- 10 seconds/record

PA

ZVE-8G

34 dB

Rx Ant. UWB LNA

ZRON 8G

23 dB

UWB LNA

ZRON 8G

23 dB

Network Analyzer

Tx (Port 1)

Network Analyzer

Rx (Port 2)

Agilent 8720ES

20 GHz capability

Figure 2. Frequency domain measurement equipment configuration.

Measurements taken using both of these methods have been shown to be equivalent. Therefore,we used the network analyzer and the oscilloscope interchangeably in taking measurements in avariety of locations throughout the townhouse.

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Appendix A is a list of the equipment used in our measurements.

3. Analysis

System Component CompensationCompensation for the non-idealities in the system components was performed to isolate thechannel-associated effects. A comparison between 802.11a and 802.11b would hardly bemeaningful if the analysis rested upon data corrupted by artifacts of the components used tomake the measurements. Consider 60 feet of RG142 low dispersion coaxial cable, a commonlength used in our measurements. Figure 3 is a plot of the loss due to 60 feet of this cable as afunction of frequency. At 2.4 GHz the loss is 12.6 dB. At 5.25 GHz the loss is 20.9 dB. Thedifference between these two is more than 8 dB and is due solely to one simple component of ourmeasurement setup.

Figure 3. 60 cable loss as a function of frequency.

In an attempt to isolate channel effects, compensation for the frequency response of thecomponents of the measurement system (including pulse source, cabling, and gain) has beenperformed for each of the many measurements.

LOS (Free Space) Path LossMost significant among the channel effects is the path loss, which has been modeled in theliterature by the equation:

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path loss (d) =

010

4log20

d+

0

10log10d

dn

where path loss is in dB, is wavelength in meters, dis distance in meters, d0 is thereference distance in meters, and the path loss exponent n is 2 for free space.

Figure 4 is a plot of free space path gain (the negative of the path loss) as a function of frequencyover a distance of 3 m. Based on the above path loss equation, the difference in free space pathloss between the ISM band (with an average of 49.8 dB loss) and the UNII band (with anaverage of 56.7 dB loss) is about 7 dB. In Figure 4, the magenta curve is the free space path gainbased on the above equation. The blue curve is derived from actual measured data (381 line-of-sight measurements at about 3 m distance). The red curve is the line of best fit (on a log-logscale) to the measured path gain. The spectral behavior of the LOS path loss closely matchesthat of free space at this distance.

Figure 4. Free space (3 m) path loss as a function of frequency.

Figures 5a-d show the path gain versus distance of 378 line-of-sight (LOS) townhousemeasurements in each of the different bands of interest (where UNII-I, UNII-II, and UNII-III areabbreviations of the U-NII low band, the U-NII middle band, and the U-NII high band,respectively). These figures show that the path loss exponent n is approximately 2 for line-of-sight measurements. We attribute the fact that n is generally slightly less than 2 to experimentalvariability.

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Figure 5a. Measured LOS path gain as a function of distance for the ISM band.

Figure 5b. Measured LOS path gain as a function of distance for the UNII-I band.

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Figure 5c. Measured LOS path gain as a function of distance for the UNII-II band.

Figure 5d. Measured LOS path gain as a function of distance for the UNII-III band.

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The essentially equivalent free space path loss exponents for the ISM and UNII bands indicatethat the difference in loss will theoretically be about 7 dB in favor of the ISM band for alldistances. Our measurements reveal that for a LOS link this difference is closer to 4 dB. The 3dB gain over theoretical may be due experimental variability. The difference could also be dueto energy recovered by the receiver from multipath scattering that is more prevalent at the higher

UNII band frequencies. We show below that the energy in the UNII band is less able topenetrate obstacles than energy in the ISM band. We surmise that this blocked energy is at leastpartly reflected, contributing to multipath gain for LOS geometries.

NLOS Path LossFor the sake of the analysis, non-line-of-sight (NLOS) paths are defined as any paths in whichthe transmitting antenna cannot be seen by the receiving antenna because of path obstructions.These obstructions may include walls, floors, or other items such as bottles of water.

The equivalence observed in path loss exponents in LOS geometries does not hold for NLOSpaths. Figures 6a-d show the path gain versus distance of 458 NLOS townhouse measurements

in each of the different bands of interest. These figures show that the path loss exponent for aNLOS path is approximately 3.7 for the ISM band and 4.6 for the UNII band. The larger pathloss exponent for the UNII band signifies a greater change in loss over distance as compared toan ISM band signal. This difference is shown in Figures 7a-b. As an example, Figure 7b showsthe difference between ISM and UNII path loss at 3 m to be 4.9 dB. By 10 m this difference hasnearly doubled to 9.4 dB.

Figure 6a. Measured NLOS path gain as a function of distance for the ISM band.

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Figure 6b. Measured NLOS path gain as a function of distance for the UNII-I band.

Figure 6c. Measured NLOS path gain as a function of distance for the UNII-II band.

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Figure 6d. Measured NLOS path gain as a function of distance for the UNII-III band.

Figure 7a. Best fit NLOS path gain for ISM and UNII (average) as a function of distance.

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Figure 7b. Difference in best fit NLOS path gain between ISM and UNII (average) as a function ofdistance.

Table 1 shows the path loss exponent n and standard deviation for each of the various bandsusing only line-of-sight (LOS), only non-line-of-sight (NLOS), and combined LOS/NLOSmeasurements.

n = 4.76

= 5.90 dB

n = 1.83

= 3.17 dB

n = 4.70

= 4.55 dB

UUNNIIII((II))

n = 4.75

= 5.97 dB

n = 1.72

= 2.93 dB

n = 4.48

= 4.34 dB

UUNNIIII((IIII))

n = 4.97

= 6.11 dB

n = 2.15

= 3.00 dB

n = 4.59

= 5.01 dB

UUNNIIII((IIIIII))

n = 3.81

= 4.79 dB

n = 1.91

= 3.15 dB

n = 3.73

= 4.35 dB

IISSMM

n = 4.21

= 4.71 dB

n = 1.72

= 1.48 dB

n = 4.09

= 3.63 dB

UUWWBB((22--88GGHHzz))

AAll ll 883366 ffii lleessLLOOSS 337788 ffii lleessNNLLOOSS 445588 ffii lleess

Table 1. Path loss ex onents and standard deviations for different bands.

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The free space path loss behavior is apparent in the LOS results. The difference in NLOS pathloss exponents between ISM and UNII bands suggests that UNII band signals are attenuatedmore by obstacles such as walls than ISM band signals. The results for the composite set of dataseem to favor the higher NLOS path loss exponent but exhibit the highest RMS value because ofthe inadequacy of a fit of a single power law component to a 2-component distribution.

The NLOS path loss is important for defining system performance requirements for ISM andUNII operation. To better quantify these differences, we examine measurements that passthrough walls, flooring, and water.

For each obstacle, we first present the overall calculated path loss through that obstacle. Webase this value on all signal energy captured by our measurement equipment. For oscilloscopedata, the time record is typically 100 ns. For network analyzer data, the effective time record is267 ns. For all measurements in the townhouse, the delay spread was well within 100 ns(calculated using a frequency domain zero crossing method [Witrisal, 3], the average RMS delayspread for LOS measurements was 9.7 ns and no more than 13.5 ns; for NLOS, the average was

14.1 ns and no more than 19 ns. Using a passband time domain analysis, the delay spreadaveraged 12.8 ns for NLOS data).

While straightforward, the above method includes multipath energy in the determination of pathloss. This multipath energy has not necessarily passed through the obstacle of interest or haspassed through a different number of these obstacles. A prime example of this phenomenon isour water occultation measurement, shown in Figures 8a and 8b. In this measurement, severaljugs of water have been placed directly between the transmitting and receiving antennas. Figure8b shows energy in the direct line-of-sight path between the transmitter and receiver, labeledMain Path, clearly attenuated by the water. However, multipath energy reflected off a nearbywall, labeled Significant Multipath, does not pass through the water and is essentiallyunattenuated. The total signal energy consequently does not accurately characterize theattenuation due to the water.

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Figure 8a. No occlusion of the line-of-sight path between transmitter and receiver.

Figure 8b. Water blocks the line-of-sight path between transmit and receive antennas.

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An alternative and conceivably better approach for determining the path loss is to include in thecalculation only energy that falls within a certain window of time after the first received path.This method isolates the main path and excludes multipath energy. As the first received path isgenerally the direct path between the transmitting and receiving antennas, which always passesthrough the obstacle of interest, we expect that this alternative evaluation of obstacle attenuation

will be more accurate.

Variability due to the dispersive nature of different obstacles makes selection of a time windowdifficult, however. Consequently, we present path loss values for time windows of 2 ns, 4 ns,and 8 ns from the first detected path.

Each path loss calculation is the difference in the time windowed energy in the frequency bandof interest between measurements with the obstacle and measurements without the obstacle. Allsystem components, including free space path loss effects, are removed from the measurement sothat we only compare loss due to the obstacle of interest.

Table 2 shows loss due to one wall, one floor, and one body of water. As the time window isexpanded, more multipath energy is received and the apparent path loss decreases. A change inthe difference between ISM and UNII path losses as the time window increases may indicatediffering amounts of dispersion or the inclusion of energy not passing through the same paths.

ISM UNII Avg ISM - UNII Avg

Wall Path Los s: 528 files

2ns 13.9 17.3 -3.4

4ns 10.7 14.9 -4.2

8ns 8.5 12.6 -4.1

All 3.8 7.5 -3.7

Floor Path Loss: 107 files

2ns 7.3 8.8 -1.5

4ns 5.5 7.0 -1.5

8ns 4.0 7.2 -3.2

All 5.5 8.6 -3.2

Water Path Loss: 2 files

2ns 3.8 14.2 -10.4

4ns 4.9 13.1 -8.2

8ns 4.9 11.4 -6.5

All 2.5 5.3 -2.8Table 2. Summary of path losses due to one wall, one floor, and a body of water. (all values in dB)

Highlighted rows are optimum window sizes.

Wall Path Loss

The 528 NLOS measurements passing through at least 1 and as many as 4 walls were used toestimate the path loss of a single wall. The path loss in excess of free space path loss for each of

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the measurements was determined and then divided by the number of walls blocking the LOSpath to determine a loss per wall. The loss per wall has a significant dependence on the size ofthe time window attributed to the LOS path. However, the UNII band losses consistently exceedISM band losses by about 4 dB. We selected a window size of 4 ns as representative based onvisual inspection of a sampling of measurements.

The walls involved in our measurements were for the most part indoor, consisting of two layersof drywall with wooden studs. A NIST report on drywall [Stone, 4, p.139] indicates that, for asingle 16 mm thick layer of drywall, 0.3 dB gain should be expected for 3 GHz energy and 0.2dB attenuation for 5.5 GHz energy. Stone [4] suggests that the path gain at 3 GHz is due toresonance in the drywall. The results of other residential 5 GHz measurements taken byChung and Bertoni, 2001, [5] suggest a loss per wall of 3-9 dB with an average loss of 5.1 dB.Measurements of wallboard loss at 2.45 GHz by Kara and Bertoni [6], were determined to be 4.9dB. The Kara and Bertoni results were through walls supported by metal studs. The losses wesee with a 4 ns window results are generally larger than those seen in other literature.

Floor Path Loss

Due to the small number of measurements passing through only the floor and no other obstacles,we used 107 measurements passing through one wall and one floor to calculate floor path loss.The floor path loss is isolated from wall path loss by simply subtracting out the expected wallpath loss from the measurement. A window size of 4 ns appears to be optimal as the 8 nswindow and the non-windowed results have the same path loss difference, suggesting that bothinclude multipath energy traveling through an obstacle that attenuates the UNII band morestrongly.

The floor involved in our measurements consisted of one layer each of carpet, plywood, anddrywall. The loss is 1.5 dB worse for the UNII band than for the ISM band. This result isconsistent with the wall results if the wallboard is the predominant attenuator in the system.Since walls have two layers of wallboard and the flooring has only a single layer, one mightexpect floors to exhibit roughly half the loss of a wall. Results of floor loss measurements takenin the Chung and Bertoni, 2001, study [5] at 5 GHz suggest a loss of 5-10 dB for floors withoutmetal ducting. The floor composition is not provided.

Water Path Loss

Two one-gallon jugs and one 1.44 L bottle of water, arranged in a triangle 11 wide and 8 deep,were used to block the line-of-sight path. The water structure was moved across the LOS path in3 inch steps to study the attenuation and diffractive effects.

Visual inspection shows that a window of 2 ns captures all energy from the main path in thewater occultation measurements. Both 4 ns and 8 ns time windows include multipath energy thatdoes not pass through the water, as evidenced by the reduced path loss values.

Figure 9a shows plots of the frequency dependence of the path gain with no water (blue trace)and with water directly in the line-of-sight path between antennas (red trace). The differencebetween these spectra, shown in Figure 9b, is closely related to the path gain due to the water. Adeep fade is evident in the results of Figure 9a at a frequency that varies between 2.7 and 2.9

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GHz for the non-obstructed and obstructed LOS paths. The behavior of this notch is the sourceof the positive excess path gain near 2.7 GHz in the differential spectral plot shown in Figure 9b.The behavior of the differential spectral levels exhibits a gradually increasing signal attenuationfor frequencies above 3 GHz.

Figure 9a. Path gain in first 2 ns of signal with and without water occultation (blue and red, respectively).Curve shows a frequency dependence influenced by the analysis methodology; see Appendix B for more.

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Figure 9b. Water path gain as a function of frequency (as seen by energy in first 2 ns of signal,smoothed by 60 samples). Gain peak at 2.74GHz may be due to a water-induced phase delay in

multipath fading.

Figure 10 shows the spatial dependence of the direct and multipath contributions to the totalreceived signal energy. The components are defined in terms of arrival time using thedesignations of main path (LOS) and multipath as seen in Figure 8b. As the water occludes theLOS path, the main path energy is reduced significantly while the multipath energy remainsrelatively constant.

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Figure 10. Normalized energy received by antenna 1 versus water position (water directly betweenantennas at position 10.5).

Path Loss Effect on 802.11a Data RatesFigure 11 shows a plot of data rates achievable by a hypothetical 802.11a system in our NLOSenvironment. It shows a drop in data rate from 54 Mbps to 36 Mbps in about 5 m of distance.

Note, however, that this plot is generated with many assumptions. The SNR requirements usedfor the plot are based on a 12 MHz symbol rate, a 1.25e-5 BER (about 10% PER for a 1000 bytepacket with uniform errors), and approximations of the coding gain (5 dB for rate , 3.5 dB forrate 2/3, and 2.5 dB for rate ). A noise figure of 8.5 dB is also assumed, as is a total antennagain of 3 dBi, a maximum instantaneous transmitted power of 17 dBm (the FCC limit for UNII-II) with a data rate dependent backoff ranging from 4 to 9 dB for the average transmitted power,and an implementation loss of 4 dB.

We have chosen path loss at a level that is two sigma below the average path loss. Ideally thenthe plot depicts data rates achievable 95% of the time based on our path loss results.

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2 4 6 8 10 12 14 165

10

15

20

25

30

35

40

45

50

55802.11a (UNII II) Data Rates Achievable (NLOS)

Distance (m)

DataRate(Mbps)

Figure 11. Data rates achievable in the UNII-II band by a hypothetical 802.11a system in our NLOS

environment. Many assumptions are made to generate this plot.

4. Conclusions

Table 3 summarizes path loss due to various obstacles for the ISM and UNII bands. For allobstacles, path loss is more severe in the UNII band than in the ISM band. For free space theadditional path loss is about 3 dB less than expected. For water (or people, since humans are 50-75% water) the difference between ISM and UNII bands is especially large (10 dB).

While main path attenuation is severe due to obstacles (11 dB and 15 dB for one wall alone inthe ISM and UNII bands, respectively), overall signal degradation can be reduced if all multipathenergy is successfully recombined at the receiver (a path loss of 4 dB and 7.5 dB for one wall inthe ISM and UNII bands, respectively). The degree to which the obstacles appear to attenuatethe main path is greater than expected and may indicate some bias due to the analysismethodology.

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ISM UNII Mean ISM - UNII

Free space (3m, ideal) 49.8 56.7 -6.9

LOS (3m, measured) 55.1 59.0 -3.9

NLOS (3m, measured) 55.7 60.6 -4.9

Free space (10m, ideal) 60.2 67.1 -6.9LOS (10m, measured) 65.1 68.9 -3.8

NLOS (10m, measured) 75.2 84.6 -9.4

Wall 10.7 14.9 -4.2

Floor 5.5 7.0 -1.5

Water 3.8 14.2 -10.4

LOS Path Loss Exponent 1.9 1.9

NLOS Path Loss Exponent 3.7 4.6

Table 3. Summary of path loss and path loss exponents. Path loss in dB.

It is clear that a UNII band radio must contend with a significantly harsher channel in terms ofpath loss than an ISM band radio. In the comparison of 802.11b and 802.11a systemimplementations, it must be noted that the potential gains for a UNII 802.11a system due toreduced interference and higher data rates are offset by increased path loss caused by obstaclessuch as walls, floors, and water/people.

References

[1] Peek, Greg and Ryan Etzel, 802.11b coexistence results (5 PDF files discussing interference

with Bluetooth, cordless phone, and 802.11b), Intel, May through July 2001.http://people1.patch.intel.com/gpeek/coexistence/home.htm, link to Coexistence test results(ZIP file)

[2] Cavin, Robert, Summary of Wireless Quality-of-Service Tests in Predicted End-UserInterference Environments, Intel Corporation, August 20, 2001.

[3] Witrisal, Klaus, On Estimating the RMS Delay Spread from the Frequency-Domain LevelCrossing Rate,IEEE Communications Letters, vol. 5, no. 7, pp. 287-289, July 2001.

[4] Stone, William C., NIST Construction Automation Program Report No. 3: Electromagnetic

Signal Attenuation in Construction Materials (NISTIR 6055), Washington: NationalTechnical Information Service, October 1997.

[5] Chung, Hyun Kyu and Henry L. Bertoni, Indoor Propagation Characteristics at 5.2 GHz inHome and Office Environments, authors from Polytechnic University, study funded bySharp Laboratory, private communication, 2001.

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[6] Kara, A. and H. L. Bertoni, Blockage/shadowing and polarization measurements at 2.45GHzfor interference evaluation between bluetooth and IEEE 802.11 WLAN, Antennas andPropagation Society, 2001 IEEE International Symposium, Volume: 3, 2001, Pages: 376379.

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Appendix A: Equipment List

Characterization data is available for all components listed below.

Tektronix TDS8000 Digital Sampling Oscilloscope

DC to 50GHz bandwidth (12.5GHz dual-channel, low-noise electrical sampling module[80E02]; 50GHz single-channel electrical sampling module [80E01])

14-bit vertical resolution $30K

Agilent 8720ES S-Parameter Network Analyzer

50MHz-20GHz +5dBm max output power +10dBm max input power, 100dB max dynamic range 2dB output accuracy $60K

Minicircuits ZVE-8G

Medium-high power amplifier, +30dB min gain (generally measured at +34dB) 1dB variation due to temperature 2-8GHz 4.0dB noise figure 1dB compression point at +30dBm output power +20dBm max input power (no damage) +12V, 2A $1,095

Minicircuits ZRON-8G

Medium power amplifier, +20dB min gain (generally measured at +23dB) 2-8GHz 6.0dB noise figure 1dB compression point at +20dBm output power +10dBm max input power (no damage) +15V, 0.310A $495

Picosecond Pulse Labs Amplifier Model X5865

Variable, +25dB min gain (generally measured at +27.5dB) 20kHz to 12.5GHz 5.75dB noise figure (typical at 1GHz) 1.5Vp-p max input (damage threshold) 7Vp-p output (with 0.5Vp-p input) +8V @ 230mA, -5V @ 20mA, +1.5V (negligible draw) $1500

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Hyperlabs HL9200 UWB Pulser Bessel 2GHz high-pass filter (5th order) Chebyshev 2GHz high-pass filter (6th order) Minicircuits attenuators Pasternack Enterprises 50ohm inline terminator (PE-6026) EMCO ETS Double-Ridged Waveguide Horn antenna, Model 3115 (45 beamwidth) Microwave Electronics Corporation (MEC) biconic antenna Pulsicom Technologies, Ltd., UWB discone antenna Pasternack Enterprises RG142 B/U low dispersion coaxial cables (PE-3385) Heliax cables (in OSEL anechoic chamber) DC power supply, +15VDC, 1A DC power supply, +12VDC, 2.5A

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Appendix B: Limitations of Analysis Methodology

The analysis for obstacle path loss involves isolation of the main path from the multipath. Thetruncation in time necessary for this isolation results in a frequency dependence that has not beencompensated out of the figures in this report (Figure 9a, for instance). The figures below show

the effect of performing our path loss analysis on an ideal impulse with 0 dB energy from 2-8GHz. This ideal impulse is shown in Figure B1. As the time window increases, the overallresultant signal magnitude increases as well, shown in Figure B2.

Figure B1. Ideal impulse (0 dB power from 2-8 GHz) with a time window of 4 ns.

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Figure B2. Path gain curves of the ideal impulse for different time windows.

Thus the signal power as seen by our analysis tools (shown in Figure 9a) should only be used ina relative sense. We did not attempt to normalize the signal power since we are only interestedin the relative difference in path loss between ISM and UNII bands.

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Appendix C

A Brief Comparison Between Ryan Etzels 802.11b Measurements and UWB

Measurements

David CheungCliff PrettieNovember 29, 2001

In 2001, Ryan Etzel, an intern working with Greg Peek, took measurements at 39 differentlocations in a townhouse in Oregon using a Berkeley Varitronics Systems Grasshopper IEEE802.11b receiver [1]. About two months later, in the course of performing our ultra-wideband(UWB) channel sounding, we took measurements at those same positions. This paper brieflyexamines the correlation between our measurements and those of Etzel.

The floor plan of the townhouse, marked with the Etzel measurement positions, is shown inFigure C1. Two numbers are associated with each purple dot: a negative number, indicating thesignal power in dBm as measured by the Grasshopper, and a number from 1 to 39, identifyingthe position. This data is recorded in the first two columns of the table in Figure C2. The thirdcolumn of this table is the Etzel data compensated for the 3dBi antenna gain of the Grasshopper(3 dB has been subtracted from each Etzel data point).

The UWB measurements that we made span a frequency range of 2-8 GHz with a frequencyresolution of 3.75 MHz (1601 spectral points total). We have processed this data bycompensating for all system component effects (cable loss, amplifier gain, antenna response,etc.), averaging the power over just the 2.4-2.5 GHz ISM (802.11b) band, and finally adding 5dB to convert the values to dBm (the output port power of the network analyzer used to take themeasurements was +5 dBm). The resulting values are given in the column labeled UWBDerived Measurement in the table in Figure C2.

As Figure C2 shows, the difference between the Etzel measurements and the UWB derivedvalues can be as much as 14 dB. We attribute this difference to multipath fading and differencesbetween Etzel and UWB measurement methodologies (antenna positioning, orientation, etc.).Further, in making the UWB measurements for this study, we only approximated the Etzelpositions in the townhouse based on the townhouse layout that Etzel provided us (Figure C1).

Statistically, however, the data shows excellent agreement. The mean of the differences is only-0.07 dB with a standard deviation of 5.37 dB. Figure C3 shows UWB derived measurementsversus Etzel measurements, showing this agreement in the data.

Figures C4 and C5 show difference versus measurement in an attempt to assess the correlationbetween distance (or more path loss) and error (the difference between our measurements andEtzels). There does not appear to be an obvious correlation between the two, however.

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27

38

36

33

34

32

31

30

22

20

19

17

16

12

10

5 98

7

6

2

1

3

11

1314

15

18

21

23

2526

27

28

29

35 37

39

Figure C1. Townhouse layout with Etzel positions marked.

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RyanPosition

RyanMeasurement

CompensatedRyan

MeasurementUWB DerivedMeasurement Difference

1 -50 -53 -39.25 -13.75

2 -54 -57 -44.74 -12.26

3 -54 -57 -56.70 -0.304 -67 -70 -69.66 -0.34

5 -63 -66 -71.57 5.57

6 -67 -70 -76.32 6.32

7 -70 -73 -69.58 -3.42

8 -64 -67 -73.19 6.19

9 -65 -68 -71.67 3.67

10 -65 -68 -72.14 4.14

11 -73 -76 -71.00 -5.00

12 -71 -74 -71.02 -2.98

13 -68 -71 -75.60 4.60

14 -67 -70 -73.67 3.67

15 -67 -70 -71.60 1.6016 -64 -67 -71.22 4.22

17 -57 -60 -67.97 7.97

18 -50 -53 -48.42 -4.58

19 -65 -68 -69.61 1.61

20 -47 -50 -52.11 2.11

21 -45 -48 -43.66 -4.34

22 -40 -43 -46.64 3.64

23 -33 -36 -42.93 6.93

24 -65 -68 -69.00 1.00

25 -62 -65 -71.73 6.73

26 -62 -65 -73.47 8.47

27 -81 -84 -83.75 -0.25

28 -80 -83 -85.37 2.37

29 -74 -77 -75.54 -1.46

30 -78 -81 -72.74 -8.26

31 -72 -75 -73.66 -1.34

32 -62 -65 -64.64 -0.36

33 -69 -72 -64.66 -7.34

34 -67 -70 -73.19 3.19

35 -62 -65 -59.47 -5.53

36 -59 -62 -57.86 -4.14

37 -57 -60 -60.09 0.09

38 -69 -72 -66.66 -5.34

39 -71 -74 -68.03 -5.97Figure C2. Measurement data for 39 townhouse locations. The last column is the difference betweenEtzel measurements compensated for antenna gain and the UWB-derived measurements..

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Data Agreement

-90

-80

-70

-60

-50

-40

-30

-90 -80 -70 -60 -50 -40 -30

Etzel's Measurement

UWBDerivedMeasuremen

t

Figure C3. UWB-derived measurements versus Etzel measurements for 39 townhouse locations.Magenta line is ideal (based on mean of 0.07 dB).

Difference

-15

-10

-5

0

5

10

-90 -80 -70 -60 -50 -40 -30

Etzel Measurement

Difference

Figure C4. Difference versus Etzel measurements for 39 townhouse locations.

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Difference

-15

-10

-5

0

5

10

-90 -80 -70 -60 -50 -40 -30

UWB Derived Measurement

Difference

Figure C5. Difference versus UWB-derived measurements for 39 townhouse locations.

Reference for Appendix C

[1] http://www.bvsystems.com/Products/WLAN/Grasshopper/grasshopper.htm. Datasheet,manual, and other information about the Berkeley Varitronics Systems Grasshopper IEEE802.11b receiver.