A Proposal of Green Wireless LAN System Based on Dynamic Power Supply Control Ryo Nakamura Graduate school of Information Science and Electrical Engineering, Kyushu University. Maho Hirasaka Faculty of Literature, Chikushi Jogakuen University. Mari Suenaga Faculty of Literature, Chikushi Jogakuen University. Motoyuki Ohmori Faculty of Literature, Chikushi Jogakuen University. Koji Okamura Research Institute for Information Technology, Kyushu University.

Contents Background Purpose Problem Our Research – Proposed Method for Green Wireless LAN System Design and Implementation Evaluation Experiment Consideration of power-saving Conclusion 2

Background-Wireless LAN Wireless LAN has been used in many companies, factories and universities. It needs an AP (Access Point) that relays the communication between STA(STAtion)s. – The AP needs to keep working because the AP must respond to a STA if the STA requests for connecting to the wireless LAN. Some electric power is wasted when there is no STA AP STA1 STA2 3

Purpose When no user uses an AP, we turn it off. Then, the wireless LAN server turns on or off the AP according to STAs’ presence. Green wireless LAN system AP(on) AP(off) current style our proposal We do not need to turn on an AP which has no user 4

Problem While all APs turned off, how does a STA connect to an AP? We need two functions. – Receiving a STA request instead of an AP. – Turning on the best AP according to the STA. We introduce a sensor BQ(Base Quacker) and C3 (Collection, Calculation and Control server) for archiving these functions. 5

Our Research Proposed Method for Green Wireless LAN System 6

What is BQ ? A BQ can response to a STA instead of an AP. However, the BQ does not connect to the STA. – A BQ never send Association Response. Then, the BQ sends frame and RSSI （ Received Signal Strength Indicator ） value of a STA request to a C3 as STA information. The number of BQs is less than that of APs. (but at least three) 7

What is C3 ? A C3 has three functions (command) – Collection (apowerbpd) A C3 collects STA information from all BQs. – Calculation (apowersd) A C3 estimates the location of a STA by RSSI-based localization. – Control (apowerapd) A C3 turn on or off an AP. In C3 database, the location of APs, BQs or estimated STAs and their MAC addresses are recorded. 8 Timestamp BQ IP address [MAC address ] STA MAC address SNR and noise value collect RSSI = (SNR + noise) value STA request type STA information BQ C3 Where is the STA ?? AP Wake up !!

RSSI-based localization RSSI value => Distance Distance => The coordinates of the STA 9 STA BQ RSSI: Pr(d) [dBm] Distance: d[m] BQ1 BQ2 BQ3 STA d 1 [m] d 2 [m] d 3 [m] Indoor propagation model(ITU-R P.1238) We can estimate the location of a STA by using RSSI value

For connecting to an AP In this system, a STA must purses two phase. Location Phase – A C3 estimates the location of the STA. Association Phase – The C3 turns on an AP for the STA, and makes the STA connect to the AP. 10

Research Overview 1.Start connection 2.A STA requests for connecting 3.BQs measure RSSI value 4.The BQs send it to a C3 as STA information(apowerbqd) 5.The C3 estimates the location of the STA(apowersd) 7.After the AP sends beacon 6.The C3 starts the best AP for the STA (apowerapd) 8.The STA establishes connection 9.When the STA stops connection 10.The C3 turns off the AP (apowerapd) BQ1 BQ2 BQ3 C3 Where is the STA ?? 11 Location Phase Association Phase RSSI ?

Design and Implementation(1/2) We show design and implementation in our research. BQs and APs – Linux Fedora 9 based desktop PCs with a wireless LAN adapter – We use modified Madwifi as firmware. Madwifi is made for Atheros IEEE802.11g chipset. C3 – Linux Fedora 9 based desktop PC 12

Design and Implementation(2/2) Specification for experiments. 13

Evaluation Experiment We made two experiments. – Experiment 1: Calculation STA location accuracy at Location Phase – Experiment 2: Confirmation of connection flow 14

Experiment 1 (1/2) STA location estimation error (Difference between the true location and the estimated location) Place : A Chapel in Chikushi Jogakuen University (There are few obstacles) RSSI measuring time: 30 seconds The number of STA points: 20 Location patterns of BQs: 3 (We wanted to measure RSSI with various pattern of BQ) Total: 60 points 15 Right Triangle Equilateral Triangle Obtuse Triangle

Experiment 1 (2/2) In RSSI-based localization, we select two RSSI values; maximum RSSI value (Max RSSI) and average RSSI value (Ave RSSI) Therefore, we use two radio propagation model for conversion RSSI value to distance. – Max RSSI : P(0)=15.04[dBm], N=28.94 – Ave RSSI : P(0)=-4.20[dBm], N= ・ P(0) and N are calculated beforehand by using least-square method. ・ Lf = 0 because we do not consider affection of floor.

Result of Experiment 1 Total 60 points estimation error (Cumulative probability) 17 We could estimate the location of the STA within 10 meters with 93 percent of confidence z within 15 meters with 100 percent of confidence We could estimate the location of the STA within 10 meters with 82 percent of confidence within 15 meters with 88 percent of confidence Max RSSI Ave RSSI

Experiment 2 We confirm whether a STA can connect to the best AP according to the following connection flow. As a result,a STA could connect to the AP near the STA. 18 beacon Probe Request Probe Response Authentication Request Authentication Response Probe Response Association Request Transmission STA information Starting AP Confirmation of the STA Approval Association Response STABQAPC3 Location Phase Association Phase A C3 receives STA information for five seconds after the first BQ sends STA information to the C3.

Consideration of power-saving(1/3) In this section, we present a simple simulation about the power consumption of wireless interfaces. Assumption: – APs have two mode. An AP with users is in the Active Mode. An AP turned on but not used is in the Standby Mode. A BQ is equal to be in the Standby Mode. – Active Mode consumes more power than Standby Mode. 19

Consideration of power-saving(2/3) e.g.) There are some APs in a certain place. – The number of all APs : N (A in N APs are used) – Power consumption: Active Mode : 500 [mW] Standby Mode : 330[mW] – Current style consumes {500*A+330*(N-A)}=(330N+170A)[mW] – Our proposal consumes {500*A+330*3}={500A+990} [mW] 20 current style Our proposal needs 3 BQs in addition. our proposal : AP turned on but not used : AP turned off : AP with users

Consideration of power-saving(3/3) The interface power consumption rate (N = 10). When the number of APs not used is more than three, our proposal is superior. 21 The number of APs not used Interface power consumption rate [%] (our proposal / current style)

Conclusion We proposed STA localization method and connection flow for green wireless LAN system. We showed the STA location accuracy by experiment. – By using Max RSSI, we could estimate the location of STAs within 10m at the probability of 93%, and within 15m at that of 100%. – By using Ave RSSI, we could estimate the location of STAs within 10m at the probability of 82%, and within 15m at that of 88%. Though STA location is not an intended purpose, better accuracy is requested from an efficient AP selection. Therefore, we need to take care of radio shadowing and multipath fading. – By human shadowing, RSSI values of a BQ just behind of a STA were weaker than those of a BQ that was far away from the STA. – By multipath fading, a BQ got various RSSI values. (-20~-95[dBm]) 22

When weak RSSI values which was effected by multipath fading are ignored (threshold : -75[dBm] (2) or -70[dBm] (3) ) 23 Bad estimation errors are improved!

Conclusion - Future work Reduce the affection of radio multipath fading and shadowing. Make a system using user authentication like EAP (Extensible Authentication Protocol) or encryption like WEP (Wired Equivalent Privacy) or WPA (Wi-Fi Protected Access). Turbo mode implementation – Our system needs a longer connection sequence so that a STA can connect to an AP than existing wireless LAN system. – In addition, when the number of APs not used is less than three, our method interfaces consume more power than usual. – Therefore, we must introduce Turbo mode in our system. (for faster connection and less power consumption) Confirm power saving efficiency by experiment. 24

Apology 25

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Thank you