WLAN-range:- Comparison of theory and measurements

By Thomas F. Wiig

WLAN-range: Topics Maximum Wi-Fi range (2.4 GHz) - according to the Wi-Fi

alliance Indoor – Typical office environment

Challenges in indoor range calculations / measurements Keenan-Motley path loss model ETSI path loss model between office floors Measurements by Atheros Communication

Outdoor – Line of sight Theoretical performance simulation – range vs. throughput

Cisco AP 1240 Range stated by Cisco (indoor and outdoor) Link budget (outdoor) My own measurements (indoor)

Result comparisons How to maximize the Range

Maximum Wi-Fi range (2.4 GHz)- according to the Wi-Fi alliance

Maximum Range Range at 11 Mbps

Outdoors / open space with standard antenna 230-300 m 45-100 m

Office / light industrial setting 75-100 m 30-45 m

Residential setting 40-60 m 18-24 m

References: [2]

Challenges in indoor range calculations and measurements

References: [1], [2] and [3]

Obstacles between reciever and transmitter

Reflections, diffraction and scattering

Materials like metal, stone, brick and heavy woods

Defined receiver sensitivity for 802.11

Minimum input level for data link rate:a – 6 Mbits/s: -82 dBmb – 1 Mbits/s: -96 dBm (Cisco AP1240)

g – 1 Mbits/s: -96 dBm (Cisco AP1240)

n – 11 Mbits/s: -88 dBm (Linksys WAP4400N Wireless-router)

References: [8] and [9]

Keenan-Motley partition path loss model (in dB)

ddfpldfpl cfsceyKeenanMotl ,,,

2

10 4log10,

df

cdfpl

ccfs

where

and

Linear path loss coefficient (typ. indoor 0.44dB/m)

References: [4] and [5]References: [4] and [5]References: [4] and [5]

Keenan-Motley model for 802.11a

-110-108-106-104-102-100

-98-96-94-92-90-88-86-84-82-80-78-76-74-72-70-68-66-64-62-60

4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60

pat

h lo

ss [

dB

]

distance [m]

Keenan-Motley path loss model, =0.44dB/m

References: [6]References: [6]

Keenan-Motley model for 802.11b/g

-104-102-100

-98-96-94-92-90-88-86-84-82-80-78-76-74-72-70-68-66-64-62-60-58-56-54

4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60

path

loss

[dB

]

distance [m]

Keenan-Motley path loss model, =0.44dB/m

References: [6]

ETSI path loss model- for Indoor Office [dB]:

R is transmitter-receiver distance in meters n is number of floors in the path path loss L should always be more than free space loss. Log-normal

shadow fading standard deviation of 12 dB

References: [7]

L = 37 + 30 Log10(R) + 18.3 n((n+2)/(n+1)-0.46)

Path loss indoor with multiple floors (statistical)

ETSI Indoor Office test environment

-160

-140

-120

-100

-80

-60

-40

-20

0

Number of floors

Pa

th lo

ss

[d

B]

Serie1

Serie1 -69,6136 -93,8681 -109,216 -120,423 -129,35 -136,862 -143,415 -149,276

1 2 3 4 5 6 7 8

If 1 floor = 3m in height:

Range measurements in a typical office environment– by Atheros Communications

Measurement Setup The entire office floor is 35m x 80m, with conference rooms,

closed offices and semi-open cubicle spaces Data was sent between two Atheros network PC-cards. One

card served as the fixed Access Point (AP) while the other served as a mobile station

Distances up to 68m (225 feet) were measured Output power was 14 dBm for 802.11a, and 15 dBm for 802.11b.

Both used an external antenna with an average gain of 4 dBi For both networks, the same 80 random locations were used for

measurements At each location, 100 broadcast packets were sent at each data

link rate with a fixed packet size at 1500 bytes.

References: [13]References: [13]

Measurement results (1 feet = 0,3m)

Range measurements in a typical office environment– by Atheros Communications

References: [13]References: [13]References: [13]

Requirements: Transmitt power = 15 dBm, Total thermal noise = 10 dB, using omni-directional antenna

Theoretical performance simulation

- range vs throughput (outdoor)

References: [14]

802.11g: 802.11a: 802.11g: 802.11a: 802.11g: 802.11a:

Cisco AP1240

Stated range by Cisco: Indoor (Office environment)

a – 6 Mbits/s: 100m g – 1 Mbits/s: 140m

Outdoor a – 6 Mbits/s: 200m g – 1 Mbits/s: 290m

(Measured with a 3,5 dBi gain omni-directional antenna for a, and 2,2 dBi gain for g)

References: [11]

Cisco AP1240 – Theoretical range, calculated with link budget (LoS/outdoor)

Setting fading margin = 15, allowing some errors on the link, and a feeder loss = 1,5 dB at both Tx/Rx,

We get the distance/range from the free space loss equation:

Parameter: Value: Unit:

Transmitter output power 20 dBm

Feeder loss transmitter 1,5 dB

Transmitter antenna gain 2,2 dBi

Free space loss XX dB

Receiver antenna gain* 1 dBi

Feeder loss receiver 1,5 dB

Normal input level -79 dB

Receiver treshold -94 dBm

Fading margin 15 dB

802.11g – 2.4 GHz:

To get Normal Input level = -72, the free space loss have to be:

L_fs = 17-1,5+3,5+1-1,5+72 = 90,5 dBWhich gives the theoretical range 160 m

Parameter: Value: Unit:

Transmitter output power 17 dBm

Feeder loss transmitter 1,5 dB

Transmitter antenna gain 3,5 dBi

Free space loss XX dB

Receiver antenna gain* 1 dBi

Feeder loss receiver 1,5 dB

Normal input level -72 dB

Receiver treshold -87 dBm

Fading margin 15 dB

To get Normal Input level = -79, the free space loss have to be:

L_fs = 20-1,5+2,2+1-1,5+79 = 99,2 dBWhich gives the theoretical range 910 m

802.11a – 5 GHz:

References: [11] and [12]

Cisco AP1240 – My own measurements at the same floor (indoor)

Measurement setup The entire office floor is 13m x 45m, with conference rooms, closed offices and

semi-open cubicle spaces For both networks, the same 15 locations were used for measurements:

Office

10 sq m

Office

5 sq m

= Access Point = Measured Point

Cisco AP1240 – My own measurements at the same floor (indoor)

Measurement results: 802.11a – 5 GHz

-30 to -59 dB

-60 to -69 dB

-70 to -89 dB

20m25m

37m

Cisco AP1240 – My own measurements at the same floor (indoor)

Measurement results: 802.11g – 2.4 GHz

-30 to -59 dB

-60 to -69 dB

-70 to -90 dB

23m32m

45m

Cisco AP1240 – My own measurements between multiple floors (indoor)

5th. floor: No sig. -75 dB

4th. floor: -77 dB -66 dB

3rd. floor: -56 (AP) -55 (AP)

2nd. floor: -76 dB -65 dB

1st. floor: No sig. -74 dB

g: a:

Results:

Measurement setup The height between each floor is approx. 3 meters For both networks, the same 4 locations were used for

measurements:

Result comparisons- Between theoretical models and real measurements Indoor (office environment)

Outdoor

802.11a: 802.11b/g:Keenan-Motley model 20m 50mStated by Wi-Fi Alliance N/A 40-60mStated by Cisco 100m 140mMeasurements by Atheros ++68m ++68mMeasurements by me 37m 45m

802.11a: 802.11b/g:Theoretical simulation 750m 1600mStated by Wi-Fi Alliance N/A 230-300mStated by Cisco 200m 290mMy link budget 160m 910m

Between floors - 802.11g1st. 2nd. 3rd.

ETSI Indoor Office -70 dB -95 dB -110 dB

Measurements by me -66 dB -77 dB Not meas.

How to maximize the Range

The placement is very important. The base station and its antenna should be high up, off the floor and away from metal, power supplies and electrical outlets and wiring

A unidirectional antenna can narrow the overall beam width of your base station, providing much improved range

Turn off or remove electrical appliances that emit interfering radio waves Cordless phones Microwave ovens Radio-operated toy controls

References: [2]

References[1] John C. Stein, “Indoor Radio WLAN Performance Part II: Range Performance in a Dense Office

Enviroment”, Harris Semiconductor [2] Wi-Fi Alliance: Wi-Fi Range and Environment Issues;[3] Radio Wave Propagation for Telecommunication, Springer, and ETSI TR 101 112 V3.2.0 (1998-

04);[4] J. M. Keenan, A. J. Motley, “Radio coverage in buildings”, British Telecom Technology Journal,

vol. 8, no. 1, Jan. 1990, pp. 19-24;[5] J. Medbo, J.-E. Berg, “Simple and accurate path loss modeling at 5GHz in indoor environments

with corridors”, Proc. VTC 2000, pp. 30-36;[6] Ravi Mahadevappa, Stephan Brink, “Receiver Sensitivity Tables for MIMO-OFDM 802.11n – ppt”,

Realtek Semiconductors, Irvine, CA;[7] ETSI TR 101 112 V3.2.0 (1998-04), Title: Universal Mobile Telecommunications System (UMTS);[8] IEEE Std 802.11a-1999 (R2003)[9] IEEE Std 802.11b-1999 (R2003)[10] Linksys wireless 802.11n router, http://www.xpcgear.com/wap4400n.html [11] Cisco Aironet 1240AG Series 802.11A/B/G Access Point Data Sheet, http://www.cisco.com[12] HP Compaq nc6220 Notebook PCs

http://www.laptrade.ee/files/lapakad/Compaq/nc6220/nc6220.pdf[13] James C. Chen, Ph. D., Jeffrey M. Gilbert, Ph. D. ”Measured Performance of 5-GHz 802.11a

Wireless LAN systems”, Atheros Communications, Inc.[14] Puttipong Mahasukhon, Michael Hempel, Song Ci and Hamid Sharif, “Comparison of Throughput

Performance for the IEEE 802.11a and 802.11g”, University of Nebraska-Lincoln