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





Outdoor – Line of sight


Challenges in indoor range calculations / measurements
Keenan-Motley path loss model
ETSI path loss model between office floors
Measurements by Atheros Communication
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
Outdoors / open space with standard antenna
Office / light industrial setting
Residential setting
Range at 11 Mbps
230-300 m
45-100 m
75-100 m
30-45 m
40-60 m
18-24 m
References: [2]
Challenges in indoor range
calculations and measurements

Obstacles between reciever
and transmitter

Reflections, diffraction and
scattering

Materials like metal, stone,
brick and heavy woods
References: [1], [2] and [3]
Defined receiver sensitivity for 802.11

Minimum input level for data link rate:
– 6 Mbits/s: -82 dBm
 b – 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)
a
References: [8] and [9]
Keenan-Motley partition path loss
model (in dB)
plKeenanMotley  fc , , d   plfs  fc , d     d
where
 c  2 
 
pl fs  f c , d   10 log10 
 f c  4d  
and
Linear path loss coefficient  (typ. indoor 0.44dB/m)
References: [4] and [5]
path loss [dB]
Keenan-Motley model for 802.11a
-60
-62
-64
-66
-68
-70
-72
-74
-76
-78
-80
-82
-84
-86
-88
-90
-92
-94
-96
-98
-100
-102
-104
-106
-108
-110
Keenan-Motley path loss model, =0.44dB/m
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
distance [m]
References: [6]
path loss [dB]
Keenan-Motley model for 802.11b/g
-54
-56
-58
-60
-62
-64
-66
-68
-70
-72
-74
-76
-78
-80
-82
-84
-86
-88
-90
-92
-94
-96
-98
-100
-102
-104
Keenan-Motley path loss model, =0.44dB/m
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
distance [m]
References: [6]
ETSI path loss model
- for Indoor Office [dB]:
L = 37 + 30 Log10(R) + 18.3 n
((n+2)/(n+1)-0.46)
 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]
Path loss indoor with multiple floors
(statistical)
If 1 floor = 3m in height:
ETSI Indoor Office test environment
0
-20
-40
Path loss [dB]

-60
-80
Serie1
-100
-120
-140
-160
1
2
3
4
Serie1 -69,6136 -93,8681 -109,216 -120,423
5
-129,35
Number of floors
6
7
8
-136,862 -143,415 -149,276
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]
Range measurements in a typical
office environment
– by Atheros Communications

Measurement results (1 feet = 0,3m)
References: [13]
Theoretical performance simulation
- range vs throughput (outdoor)


Requirements: Transmitt power = 15 dBm, Total
thermal noise = 10 dB, using omni-directional antenna
802.11a:

802.11g:
References: [14]
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:

802.11a – 5 GHz:
Parameter:

802.11g – 2.4 GHz:
Value:
Unit:
Parameter:
Value:
Unit:
Transmitter output power
17
dBm
Transmitter output power
20
dBm
Feeder loss transmitter
1,5
dB
Feeder loss transmitter
1,5
dB
Transmitter antenna gain
3,5
dBi
Transmitter antenna gain
2,2
dBi
Free space loss
XX
dB
Free space loss
XX
dB
1
dBi
Receiver antenna gain*
1
dBi
Feeder loss receiver
1,5
dB
Feeder loss receiver
1,5
dB
Normal input level
-72
dB
Normal input level
-79
dB
Receiver treshold
-87
dBm
Receiver treshold
-94
dBm
dB
Fading margin
Receiver antenna gain*
Fading margin
15
15
dB
To get Normal Input level = -72, the free space loss have to be:
To get Normal Input level = -79, the free space loss have to be:
L_fs = 17-1,5+3,5+1-1,5+72 = 90,5 dB
Which gives the theoretical range 160 m
L_fs = 20-1,5+2,2+1-1,5+79 = 99,2 dB
Which gives the theoretical range 910 m
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)

-30 to -59 dB
Measurement results:
 802.11a
37m
-60 to -69 dB
– 5 GHz
-70 to -89 dB
25m
20m
Cisco AP1240
– My own measurements at the same floor (indoor)

Measurement results:
 802.11g
45m
– 2.4 GHz
32m
-30 to -59 dB
-60 to -69 dB
-70 to -90 dB
23m
Cisco AP1240
– My own measurements between multiple floors (indoor)

Measurement setup



The height between each floor is approx. 3 meters
For both networks, the same 4 locations were used for
measurements:
Results:

a:

g:

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:
-74 dB
No sig.
Result comparisons
- Between theoretical models and real measurements

Indoor (office environment)
802.11a: 802.11b/g:
Keenan-Motley model
Stated by Wi-Fi Alliance
Stated by Cisco
Measurements by Atheros
Measurements by me

20m
N/A
100m
++68m
37m
50m
40-60m
140m
++68m
45m
Outdoor
802.11a: 802.11b/g:
Theoretical simulation
Stated by Wi-Fi Alliance
Stated by Cisco
My link budget

750m
N/A
200m
160m
1600m
230-300m
290m
910m
Between floors - 802.11g
1st.
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 (199804);
[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