Mobile Systems

1. Mobile Systems The IEEE 802.11 WLAN Part III ver. 1.0 Mobile Systems ITU

2. Design Considerations for a WLAN (I) • Carry out a site survey: • Determine the maximum operating range, between • Access Point’s (AP), which are in fixed positions, and • a mobile station for a specified Radio Frequency (RF) power level. AP Mobile Mobile Systems ITU

3. Design Considerations for a WLAN (II) • How to do this in practice: • F.inst. mount an Access Point (AP), and • move the mobile station to a selection of points in the • building considered. • Use the communication link analyzer in the mobile sta- • tion to measure how efficient the transmission path • between the AP and the mobile is. • Identify if there are holes in the WLAN coverage of the • site, which might lead to installing further Access Points • (AP’s). Mobile Systems ITU

4. Design Considerations for a WLAN (III) • Notice that there can be big differences between transmis-sion environments. The number of Access Point’s required • is dependent of • the number of holes in the coverage area, because of • multipath propagation, • signal attenuation through walls, ceilings and floors. Mobile Systems ITU

5. Design Considerations for a WLAN (IV)Multipath Generation Wall Small movement of receiver, can create large loss of signal power. The transmitter wavelength is app. 12.5 cm. Reflected path Direct path 802.11 WLAN transmitter (AP) 802.11 WLAN receiver (AP) The amount of dealy spread in an office environment is approx. 100 nsec. Difference in path length is 100 nsec. / 30 cm/nsec ~ 3 m Mobile Systems ITU

6. Design Considerations for a WLAN (V) • Average specification for indoor operations of a WLAN IEEE 802.11: • The maximum operating distance between an Access Point (AP) and • a mobile station using • the 2.4 GHz frequency band, and • transmitting a Radio Frequency (RF) power of 100 mW, and • data rates of 2 Mbit/sec. and of 11 Mbit/sec. • is approximately • 130 meters at 1 Mbit/sec. and • 33 meters at 11 Mbit/sec. • NOTICE THAT THIS IS AN APROXIMATION, AND SITES MIGHT BE VERY DIF- • FERENT. Mobile Systems ITU

7. Design Consideration for a WLAN (VI)Antenna Diversity Space multiple antennas apart from each other such that • the effect of multipath propagation is minimized. Single antenna Antenna diversity at AP. Mobile Mobile Access Point Mobile Systems ITU

8. Data Rate vs. Aggregate Throughput (I) The 802.11 standard defines data rate in terms of • available bit rate, • transmitted over the Radio Frequency or Infrared medium. This rate is often confused with the aggregated data throughput, which takes into account the overhead associated with the transmission. Mobile Systems ITU

9. Data Rate vs. Aggregate Throughput (II) The aggregated throughput is among others dependent of • the overhead in RTS (Request to Send), CTS (Clear to Send), ACK (Acknowledge) the • the interframe space timing, the • Beacon periods, and • random back-off periods. Rough estimate for throughput in • DCF (Distributed Coordination Function) 75% of data rate, • PCF (Point Coordination Function) 85% of data rate. Mobile Systems ITU

10. References (I) • Bob O’Hara, Al Petrick, ”The IEEE 802.11 Handbook” • IEEE Press, 1999. • Reading material: • p. 1 - 69, • p. 88 (from Power management) - 98 (not including Combining • Management Tools). • 2 Jennifer Bray, Charles F. Sturman, ”Bluetooth”, Prentice-Hall 2001. Mobile Systems ITU

11. References (II) • IEEE Std. 802.11/1997 • ”Part 11: Wireless LAN Medium Access Control (MAC) and Physical • Layer (PHY) specifications”. • IEEE Standards Board, June 26, 1997. • Download: www.dtv.dk -> Search literature -> Search of other • literature at DTV -> IEEE/IEE Electronic Library -> Standards -> • 802.11 GO Mobile Systems ITU

12. References (III) • 4 Brian P. Crow, Indra Widjaja, Jeong Geun Kim, Prescott T. Sakai • ”IEEE 802.11 Wireless Local Area Networks” • IEEE Communications Magazine, September 1997, pp. 116-126. • Reading material: p. 116, p. 117, p. 118 excluding the Physical • Layer. • P. 119, p. 120, p. 121. Mobile Systems ITU