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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, [email protected] 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

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

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