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WLAN-range: - Comparison of theory and measurements

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

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WLAN-range: - Comparison of theory and measurements

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  1. WLAN-range:- Comparison of theory and measurements By Thomas F. Wiig

  2. 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

  3. Maximum Wi-Fi range (2.4 GHz)- according to the Wi-Fi alliance References: [2]

  4. 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]

  5. Defined receiver sensitivity for 802.11 • Minimum input level for data link rate: • a – 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) References: [8] and [9]

  6. Keenan-Motley partition path loss model (in dB) where and Linear path loss coefficient a (typ. indoor 0.44dB/m) References: [4] and [5] References: [4] and [5] References: [4] and [5]

  7. Keenan-Motley model for 802.11a References: [6] References: [6]

  8. Keenan-Motley model for 802.11b/g References: [6]

  9. 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 ((n+2)/(n+1)-0.46) L = 37 + 30 Log10(R) + 18.3 n References: [7]

  10. Path loss indoor with multiple floors (statistical) • If 1 floor = 3m in height:

  11. 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]

  12. Range measurements in a typical office environment– by Atheros Communications • Measurement results (1 feet = 0,3m) References: [13] References: [13] References: [13]

  13. Theoretical performance simulation - range vs throughput (outdoor) • Requirements:Transmitt power = 15 dBm, Total thermal noise = 10 dB, using omni-directional antenna • 802.11a: • 802.11a: • 802.11a: • 802.11g: • 802.11g: • 802.11g: References: [14]

  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]

  15. 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: • 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 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 References: [11] and [12]

  16. 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: = Access Point = Measured Point

  17. Cisco AP1240– My own measurements at the same floor (indoor) -30 to -59 dB • Measurement results: • 802.11a – 5 GHz -60 to -69 dB -70 to -89 dB 20m 25m 37m

  18. Cisco AP1240– My own measurements at the same floor (indoor) -30 to -59 dB • Measurement results: • 802.11g – 2.4 GHz -60 to -69 dB -70 to -90 dB 23m 32m 45m

  19. 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 Measurement setup The height between each floor is approx. 3 meters For both networks, the same 4 locations were used for measurements: Cisco AP1240– My own measurements between multiple floors (indoor) • Results: • a: • g:

  20. Result comparisons- Between theoretical models and real measurements • Indoor (office environment) • Outdoor • Between floors - 802.11g

  21. 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]

  22. 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

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