WiFi. A Fast Beacon Scanning Method for WiFi Positioning System. Yusuke Konishi 1 and Toshiyasu Nakao 1 LAN PDA LAN STA STA. 2.1 IEEE 802.

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1 WiFi 1 1 LAN LAN LAN IEEE LAN IEEE 82.11b/g DSSS A Fast Beacon Scanning Method for WiFi Positioning System Yusuke Konishi 1 and Toshiyasu Nakao 1 Recently, WLAN infrastructure and mobile terminals with WLAN interface have been widely spreaded, and many users began to use network services based on WLAN system. On the other hand, to enjoy the seamless and persistent network services with WLAN system, it is needed to shorten scanning delay. In this paper, we proposed and evaluated methods which can shorten the scanning delay based on characteristics of DSSS transmission method adopted by IEEE 82.11b/g standard. 1 NEC Service Platforms Research Laboratories, NEC Corporation 1. IEEE ) LAN PDA LAN LAN LAN LAN 2) 5) LAN IEEE82.11 STA: STAtion AP: Access Point AP ) STA LAN AP STA STA IEEE 82.11b/g IEEE GHz DSSS: Direct Sequence Spread Spectrum 1 c 211 Information Processing Society of Japan

2 22MHz CH1 5MHz 2.412GHz 25MHz CH 2.437GHz CH GHz 12MHz 1 IEEE 82.11b/g Fig. 1 Channel assignment for IEEE 82.11b/g IEEE 82.11b IEEE 82.11g CH GHz IEEE 82.11b/g 2.412GHz CH GHz CH13 5MHz 13 IEEE 82.11b 2.484GHz CH DSSS 5MHz 22MHz IEEE MAC STA AP IEEE MAC MAC 2 2 AP STA 1ms 1 2-a STA STA AP MAC BSSID AP DS Param Set RSSI AP 1ms 1 1 ms 2 F ram e Co n t ro l 2 D u rat i o n (a) (b ) (c ) D A S A MAC Header 2-34 S S I D S S I D B S S I D S S I D S eq u en c e Co n t ro l 3 D S P aram S et 3 D S P aram S et F ram e B o dy 2 Fig. 2 Format of management frames related with scanning 1.5 s STA 2-b AP 2-c STA STA AP AP BSSID RSSI STA MinChannelTime MinChannelTime AP MaxChannelTime MinChannelTime 1 7ms MaxChannelTime 11ms 7) 35 5ms AP STA LAN VoIP 15ms 4 F CS 2 c 211 Information Processing Society of Japan

3 8) 2.2 IEEE AP STA STA 9) 12) AP STA MAC STA LAN AP AP STA Kwon 13) AP MaxChannelTime Ramani 7) AP STA Mustafa 14) Chen 15) IEEE 82.11b/g MAC IEEE 82.11b/g AP STA 3. IEEE 82.11b/g 2.1 IEEE 82.11b/g DSSS LAN IEEE 82.11b/g AP STA AmbiCom IEEE 82.11b LAN WL11C-CF Intrinsyc Linux CerfBoard255 LAN raw IEEE MAC STA STA CH1 CH13 1 AP AP BSSID RSSI STA AP BSSID RSSI 3 3 AP STA AP STA RSSI 3 AP-2 AP-5 AP 3 RSSI 3 AP- AP 2 RSSI [db] STA Receiver(STA)'s channel AP : -9 Fig. 3 3 Result of preliminary experiment about beacon scanning AP-1 AP-2 AP-3 AP-4 AP-5 AP- 3 c 211 Information Processing Society of Japan

4 STA AP AP STA RSSI AP RSSI AP IEEE 82.11b/g DSSS IEEE 82.11b/g 2 ( 1 ) AP 2 STA AP MAC ( 2 ) AP STA STA AP RSSI 2 RSSI ,5,9,12 2,4,,8,1, STA A A 2.1 AP AP AP BSSID RSSI STA AP A B A A B B 4 1 Fig. 4 Flow chart of our first proposed method stepwise scanning AP BSSID RSSI AP AP AP AP BSSID RSSI 1 AP 2 STA B B A STA AP 2 AP 4 c 211 Information Processing Society of Japan

5 2 AP AP AP AP RSSI RSSI STA AP STA C C 3.1 A B STA AP AP AP RSSI AP BSSID RSSI RSSI RSSI Fig. 5 C C C R S S I 5 2 Flow chart of our second proposed method partial scanning f ( 1) f ( ch) f ( + 2) ch RSSI Fig. Correction model used by RSSI estimation for partial scanning STA AP ch STA RSSI STA AP RSSI ˆR f ( ch) f ( ch) STA LAN STA STA ch s STA AP ch a STA RSSI R ˆR (1) ˆR = R + f (ch s ch a) (1) AP AP (1) RSSI ˆR AP AP RSSI AP 4. RSSI IEEE82.11b/g CH1 5 c 211 Information Processing Society of Japan

6 CH LAN 7) 1 1 SetupTime STA 2 A D 4 A B STA AP 2 C D STA AP 1 CH1 CH13 AP 1 Table 1 Parameters of scanning used by the simulation SetupTime 19ms ChannelTime 15ms MinChannelTime 4ms MaxChannelTime 11ms 2 Table 2 Scan list used by the simulation A 2, 7, 12 B 2, 5, 9, 12 C 2, 5, 7, 9, 12 D 2, 4,, 8, 1, 12 [ms] AP A 7 8 AP 1ms MinChannelTime MaxChannelTime 3 4ms 1 AP ms 3 1ms AP 7 Fig. 7 Simulation result of passive scanning [ms] AP 8 Fig. 8 Simulation result of active scanning c 211 Information Processing Society of Japan

7 [ms] AP 9 Fig. 9 Simulation result of active stepwise scanning [ms] AP 1 Fig. 1 Simulation result of active partial scanning R SSI [ d B ] f ( ch) STA AP ch Fig. 11 An example of correction model 3 RSSI Table 3 Evaluation results of RSSI estimation [db] RSSI 2 1 AP AP STA RSSI RSSI AP 3.2 RSSI 3 STA 4 AP CH7 AP STA 7 1m 3m STA AP 2 CH5 CH9 RSSI 7 4 AP 28 STA CH5 CH9 RSSI f ( ch) = R 7 R ch+7 (2) R ch STA ch RSSI 28 (2) 11 STA RSSI (1) STA AP RSSI 4 AP 3 AP 1 AP (1) RSSI 7 c 211 Information Processing Society of Japan

8 RSSI 3 3 RSSI RSSI 2 C D 5. IEEE82.11b/g LAN IEEE82.11b/g DSSS LAN LAN 1) IEEE Standards Association: IEEE 82.11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications (27). 2) Bahl, P. and Padmanabhan, V.: RADAR: an in-building RF-based user location and tracking system, Proceedings of the 19th Annual Joint Conference of the IEEE Computer and Communications Societies, Vol.2, pp (2). 3) LaMarca, A., Chawathe, Y., Consolvo, S., Hightower, J., Smith, I., Scott, J., Sohn, T., Howard, J., Hughes, J., Potter, F., Tabert, J., Powledge, P., Borriello, G. and Schilit, B.: Place Lab: Device Positioning Using Radio Beacons in the Wild, Proceedings of the 3rd International Conference on Pervasive Computing, pp (25). 4) PlaceEngine WiFi - pp (2). 5) locky.jp: LAN Vol.25, No.9, pp (25). ) Mishra, A., Shin, M. and Arbaugh, W.: An Empirical Analysis of the IEEE MAC Layer Handoff Process, ACM SIGCOMM Computer Communication Review, Vol.33, pp (23). 7) Ramani, I. and Savage, S.: SyncScan: Practical Fast Handoff for Infrastructure Networks, Proceedings of the 24th Annual Joint Conference of the IEEE Computer and Communications Societies, Vol.1, pp (25). 8) ITU-T: International telephone connections and circuits - General Recommendations on the transmission quality for an entire international telephone connection, g.114 edition (23). 9) Singh, G., Singh, A., Singh, R. and Sohi, B.: IAPP Modifications for a Location based Fast hand off Technique in wireles networks, Proceedings of the first International Conference on Communication System Software and Middleware, pp.1 7 (2). 1) Huang, P.-J., Tseng, Y.-C. and Tsai, K.-C.: A Fast Handoff Mechanism for IEEE and IAPP Networks, Proceedings of the IEEE 3rd Vehicular Technology Conference, Vol.2, pp.9 97 (2). 11) Ok, J., Morales, P., Darmawan, A. and Morikawa, H.: Using Shared Beacon Channel for Fast Handoff in IEEE Wireless Networks, Proceedings of the IEEE 5th Vehicular Technology Conference, pp (27). 12) Powar, Y. and Apte, V.: Improving the IEEE MAC Layer Handoff Latency to Support Multimedia Traffic, Proceedings of the IEEE Wireless Communications and Networking Conference 29, pp.1 (29). 13) Kwon, K. and Lee, C.: A Fast Handoff Algorithm using Intelligent Channel Scan for IEEE WLANs, Proceedings of the th International Conference on Advanced Communication Technology, Vol.1, pp.4 5 (24). 14) Mustafa, N., Mahmood, W., Chaudhry, A. and Ibrahim, C.: Pre-Scanning and Dynamic Caching for Fast Handoff at MAC Layer in IEEE Wireless LANs, Proceedings of the IEEE International Conference on Mobile Adhoc and Sensor Systems Conference, p.122 (25). 15) Chen, Y.-S., Chen, C.-K. and Chuang, M.-C.: DeuceScan: Deuce-Based Fast Handoff Scheme in IEEE Wireless Networks, Proceedings of the IEEE 4th Vehicular Technology Conference, pp.1 5 (2). 8 c 211 Information Processing Society of Japan