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1 }}}}}} }}}}}} Wireless LAN 1 1 LAN 1997 LAN Mb/s b 11 Mb/s g 54 Mb/s LAN LAN LAN LAN LAN AP (Access Point) 150m 50m AP AP AP STA (Station, ) STA STA1 1 AP STA20 LAN 100 LAN 1 AP AP LAN STA AP LAN STA AP LAN AP AP STA [3][4] LAN AP STA [5] LAN STA AP 1, fukuda@isc.kyutech.ac.jp 50

11g 54 Mb/s LAN LAN LAN LAN LAN AP (Access Point) 150m 50m AP AP AP STA

2 LAN IEEE LAN IEEE LAN 1997 IEEE Mb/s 11 Mb/s IEEE802.11b 54Mb/s IEEE802.11a IEEE802.11b IEEE802.11g IEEE STA 2.1 IEEE LAN LAN 1 1: LAN LAN IEEE b 2.4GHz 1 11Mb/s 14( ) IEEE a 5GHz 6 54Mb/s 4 IEEE g 2.4GHz 1 54Mb/s 14( ) IEEE b/g 2.4GHz GHz GHz 5MHz GHz GHz ISM(ISM band, Industrial Science and Medical band) IEEE a 5GHz GHz 100MHz 10mW IEEE b 1Mb/s DBPSK(Dierential Binary Phase Shift Keying) Mb/s DSSS(Direct Sequence Spectrum Spread) 51

11b/g 2.4GHz 2.400 2.497GHz 2.400 2.4835GHz 5MHz 13 2.484GHz 14 4 1 13 3 14 4 2.4GHz ISM(ISM band, Industrial Science and Medical band) IEEE 802.

3 802.11b Mb/s CCK(Complementary Code Keying) IEEE a OFDM(Orthogonal FrequencyDivision Multiplex ) MHz 5.2GHz 20MHz ( MHz) ( ) 0.25MHz IEEE g IEEE b 20Mbps b 5GHz a IEEE g a OFDM OFDM 6 54Mbps OFDM IEEE b LAN AP b g LAN AP IEEE a OFDM 6Mbps a LAN IEEE : LAN TGa 5GHz LAN (OFDM ) TGb 2.4GHz LAN (CCK ) TGc MAC TGd TGe QoS MAC TGf AP TGg b TGh a TGi MAC TGj 4.9 5GHz ( TGk TGm a/g TGn LAN WNG SC LAN HT SG 52

11a OFDM OFDM 6 54Mbps OFDM IEEE 802.11b LAN AP 802.11b 802.11g LAN AP IEEE 802.11a OFDM 6Mbps 802.

4 2.2 IEEE IEEE LAN STA BSS(Basic Service Set) BSS 2 1 STA 2 STA STA LAN AP AP LAN 1: AP 2: 1 AP BSS LAN BSS LAN ESS (Extended Service Set) ESS 3 ESS STA 1 BSS BSS ESS BSS BSS DS (Distribution System) DS 1 AP AP STA LAN DS BSS DS 53

5 Extended Service Sets (ESS) Basic Service Sets (BSA) 1 BSA 2 AP1 AP2 Distribution System (DS) AP3 AP4 BSA3 BSA4 3: Extended Service Set 2.3 LAN Medium Access Control LAN STA AP MAC (Medium Access Control) IEEE LAN MAC PCF(Point Coordination Function) DCF(Distributed Coordination Function) 2 PCF AP STA STA DCF STA CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) CSMA/CD (Carrier Sense Multiple Access with Collision Detection) LAN STA CSMA/CD CSMA/CA MAC ACK(Acknowledgement) IEEE LAN DCF PCF [1] DCF LAN MAC ACK 3 IFS(Inter Frame Space) 4 SIFS(Short IFS), PIFS (PCF IFS), DIFS (DCF IFS) SIFS MAC ACK PIFS PCF AP STA DCF CSMA/CA 5 CSMA/CA STA STA DIFS DIFS STA CW (Contention Windows) CW

11 LAN MAC PCF(Point Coordination Function) DCF(Distributed Coordination Function) 2 PCF AP STA STA DCF STA CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) CSMA/CD

6 DIFS PIFS Frame SIFS t 4: Some IFS relationships 0 STA 0 STA 2 STA MAC ACK STA Backoff time = b2 4+i 2 rand() 0 1c2Slot Time rand [0; 1] Slot Time STA i 1 i 1 CSMA/CA STA DIFS CW Source Data SIFS Destination ACK DIFS Other Backoff started CW 5: Transmission of DATA Packet 2.4 CSMA/CA LAN STA STA [10] 6 6 STA1 STA2 2 STA 1 AP STA1 STA2 ( ) AP STA1 AP STA2 STA1 STA2 STA1 AP STA1 55

Data SIFS Destination ACK DIFS Other Backoff started CW 5: Transmission of DATA Packet 2.

7 STA2 AP CSMA/CA AP STA 1 STA 2 6: RTS/CTS (Request to Send/Clear To Send) STA 0 RTS STA RTS CTS CTS STA STA STA AP AP RTS CTS RTS CTS STA NAV (Network Allocation Vector) STA 7 RTS/CTS SIFS DIFS Source RTS Data Destination SIFS CTS SIFS ACK DIFS Other NAV (RTS) CW NAV (CTS) Backoff started NAV (DATA) Defer Access 7: Transmission of DATA Packet using RTS/CTS 2.5 LAN IEEE a b 11a g b 80% 11a 18% 11a/g 56

Destination SIFS CTS SIFS ACK DIFS Other NAV (RTS) CW NAV (CTS) Backoff started NAV (DATA) Defer Access 7:

8 1% b 15% 11a 5% 11g 34% 11a/g 46% 11b 11g 11a 11g PC LAN LAN PC LAN VoIP(Voice over IP) PBX VoIP LAN VoIP LAN LAN LAN LAN LAN DCF STA IEEE TGe( 2) IEEE e [9] LAN e PCF LAN AP LAN STA AP 2.6 AP IEEE802.11b CSMA/CA MAC 45Mb/s STA STA STA 1AP STA 1020 STA AP IEEE802.11b AP 4 AP LAN AP LAN STA AP 8 AP 8 AP 2 STA 7 AP-1 5 STA STA AP-1 AP-2 STA AP-2 AP-1 5 STA AP-2 2 STA STA AP AP-1 STA AP-1 1=5 AP-2 STA AP-2 1=2 STA STA AP AP AP STA 57

11b CSMA/CA MAC 45Mb/s STA STA STA 1AP STA 1020 STA AP IEEE802.

9 AP-1 AP-2 STA STA STA STA STA STA STA 8: AP Sender RTS SIFS Frame Receiver SIFS CTS SIFS ACK NAV NAV(RTS) NAV(CTS) DIFS Access to medium deferred Contention window 9: IEEE802.11b AP ESSID(Extended Service Set-IDentier) STA STA AP AP AP LAN LAN STA AP LAN 2.7 AP LAN STA AP 8 8 IEEE802.11b IEEE802.11b 9 [6] Data[bits] t T (1) t T = RT S +CTS + Data(bits) Rate(b=s) + ACK +DIFS + 3SIFS + overhead (1) STA AP PER(Packet Error Rate) P T w (2) T w = t T + 1X i=1 P i 1 (1 0 P ) 1 i 1 t T 58

11b AP ESSID(Extended Service Set-IDentier) STA STA AP AP AP LAN LAN STA AP LAN 2.7 AP LAN STA AP 8 8 IEEE802.11b IEEE802.

10 = t T 1 0 P (2) 8 (3) 8= Data Data 1 (1 0 P ) = (3) T w t T AP N STA (4) 8= Data 1 (1 0 P ) t T 1 N (4) 3 AP AP LAN STA AP 1) STA AP throughputoriented 2) STA AP fairness-oriented 2 STA LAN AP 3.1 throughput-oriented throughput-oriented STA AP AP (4) AP STA N AP PER P 8 STA AP t T Data (5) AP STA W th = 1 0 P N IEEE802.11b 1bit BER(Bit Error Rate) Pe P =10 (1 0 Pe) PacketSize BER AP Probe Response Beacon STA STA PER STA (5) 3.2 fairness-oriented fairness-oriented STA STA AP LAN STA( STA) STA STA AP (6) (7) P max AP STA P 59

1 throughput-oriented throughput-oriented STA AP AP (4) AP STA N AP PER P 8 STA AP t T Data (5) AP STA W th = 1 0 P N IEEE802.

11 0 1 0 P max 0:5 0:5 < 1 0 P max 1 W fair = ( 1 2 q 2(1 0 P max )+0:5) 2 W th (6) W fair = W th (7) (6) P max 1 W fair STA AP (7) STA STA AP P max 0.5 fairness-oriented PER STA P max ( STA PER) AP Probe Response Beacon 4 AP 4.1 NS-2.1b9a[8] shadowing 10 3 AP 4 AP STA 10 STA AP AP STA 3 10 STA STA TCP STA 3 11 Area-1 50m250m STA Area-2 Area-3 STA 40m240m 30m230m Area-1 AP STA Area-2 AP-3 4 STA Area-3 Area-1 STA 1 Area-2 2 Area-3 3 AP STA AP 1)throughput-oriented 2)fairness-oriented AP 3)radio-condition-oriented(radio-oriented) 60

1b9a[8] shadowing 10 3 AP 4 AP 11 40 STA 10 STA AP AP STA 3 10 STA STA TCP STA 3 11 Area-1 50m250m STA Area-2 Area-3 STA 40m240m

12 3: TCP/Sack 1500Byte AP STA 11Mb/s xed Flow : from Source to Station Traffic type : TCP/Sack Packet size : 1,500 Byte Access Point Station Source Switch 10Mb/s 10us Wired 100Mb/s 1us Wireless 10: AP-4 Area1:50m*50m Area2:40m*40m Area3:30m*30m AP-2 AP-3 10m AP-1 11: AP 4.2 LAN STA STA STA balance index[7] balance index (8) 1 1=N B i STA i N STA =( X B i ) 2 =(N 2 X B 2 i ) (8) 61

Wireless 10: AP-4 Area1:50m*50m Area2:40m*40m Area3:30m*30m AP-2 AP-3 10m AP-1 11: AP 4.

13 5 STA STA 40 STA 3 STA radiooriented AP AP STA radio-oriented Mb/s throughput-oriented fairness-oriented AP STA 3 fairness-oriented STA STA radio-oriented Mb/s STA STA AP STA STA STA STA AP STA 5.2 LAN 3 radio-oriented AP STA 2 3 fairness-oriented throughput-oriented fairness-oriented throughput-oriented fairness-oriented AP STA fairness-oriented STA 40 STA 3 STA 12 1 radio-oriented 62

75Mb/s STA STA AP STA STA STA STA AP STA 5.

14 4: 1 AP (Kb/s) (Kb/s) (Mb/s) radio throughput fairness : 2 AP (Kb/s) (Kb/s) (Mb/s) radio throughput fairness : 3 AP (Kb/s) (Kb/s) (Mb/s) radio throughput fairness AP STA radio-oriented radio-oriented radio-oriented STA STA STA AP 14 fairness-oriented Kb/s throughput-oriented 40% fairness-oriented 50% 10% 1 throughput-oriented fairness-oriented fairness-oriented throughputoriented STA 5.3 STA 1618 balance index STA STA 63

15 probability distribution radio-oriented throughput-oriented fairness-oriented average throughput [Kb/s] 12: 1 STA probability distribution radio-oriented throughput-oriented fairness-oriented average throughput [Kb/s] 13: 2 STA probability distribution radio-oriented throughput-oriented fairness-oriented average throughput [Kb/s] 14: 3 STA survival function radio-oriented throughput-oriented fairness-oriented average throughput [Kb/s] 15: 3 64

fairness-oriented 0 0 100 200 300 400 500 600 700 800 900 1000 average throughput [Kb/s] 13: 2 STA 02 radio-oriented throughput-oriented fairness-oriented 0 0 100 200 300 400 500 600

16 radio-oriented balance index 10 STA throughput-oriented fairness-oriented balance index radio-oriented throughput-oriented fairness-oriented time [sec] 16: 1 STA balance index balance index radio-oriented throughput-oriented fairness-oriented time [sec] 17: 2 STA balance index balance index radio-oriented throughput-oriented fairness-oriented time [sec] 18: 3 STA balance index 65

17 6 IEEE LAN 2 Mb/s LAN 54Mb/s LAN LAN LAN LAN CSMA/CA 2 LAN LAN AP 2 LAN WEP LAN IEEE 802.1X RADIUS LAN LAN 1 LAN LAN WEP SSID SSID LAN 3 AP LAN STA AP 1) STA AP throuthput-oriented 2) STA AP fairness-oriented STA LAN AP TCP STA fairness-oriented throughput-oriented LAN AP 66

18 [1] IEEE, \Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks-specic requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specications," IEEE Standard , September [2] B. O'Hara and A. Petrick, \ Handbook -A Designer's Companion," IEEE Press, [3] I. Papanikos and M. Logothetis, \A Study on Dynamic Load Balance for IEEE b Wireless LAN," Proc. 8th International Conference onadvances in Communication & Control, COMCON 8, Rethymna, Crete/Greece, June, [4] A. Balachandran, G. M. Voelker, and P. Bahl, \Hot-Spot Congestion Relief in Public-area Wireless Networks," Proceedings of WMCSA'02, Callicoon, NY, pp. 70{82, June [5] Cisco Systems Web Site,\Cisco Aironet Series," smbiz/aironet/solutions/solution1.html [6] Gast and Matthew \ Wireless Networks:The Denitive Guide," O'REILLY, [7] Dah-Ming Chiu and Raj Jain, \Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks," Computer Networks and ISDN Systems, vol. 17, pp. 1{14, [8] The VINT Project, Network Simulator NS, [9] IEEE, \Draft Supplement to STANDARD for information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specic requirements-part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specications: Medium Access Control (MAC) Enhancement for Quality of Service (QoS)," IEEE Standard e/D3.3, October [10] A. S. Tanenbaum Ed., \Computer Networks - Third Edition," Prentice-Hall International

$Papanikos and M. Logothetis, \A Study on Dynamic Load Balance for IEEE 802.11b Wireless LAN," Proc.$

18 LAN AP (AP, Access Point) LAN (STA, Station) (RSSI, Received Signal Strength Indicator) AP AP STA AP LAN AP STA LAN AP LAN LAN STA AP LAN (Local Ar

LAN AP 19 2 16 18 LAN AP (AP, Access Point) LAN (STA, Station) (RSSI, Received Signal Strength Indicator) AP AP STA AP LAN AP STA LAN AP LAN LAN STA AP LAN (Local Area Network) AP (Access Point) 1 1 2