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Fairness and Efficiency of Co - located WLAN Networks

Fairness and Efficiency of Co - located WLAN Networks. Date: 2013-07- 15. Authors:. The environments that HEW devices will work in “Most environments are characterized by the overlap, in the same area, of multiple Wi-Fi networks that need to cohabit efficiently and fairly.” (657r2)

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Fairness and Efficiency of Co - located WLAN Networks

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  1. Fairness and Efficiency of Co-located WLAN Networks Date: 2013-07-15 Authors:

  2. The environments that HEW devices will work in • “Most environments are characterized by the overlap, in the same area, of multiple Wi-Fi networks that need to cohabit efficiently and fairly.” (657r2) • Typical environments: transportation hub, shopping mall, convention center • In such environment, the Wi-Fi networks may include, not limited to, • Public AP: set up by government or large organizations, usually free to use, no QoS guarantee • Operator AP: set up by operators, for a fee, dedicate for subscribers, QoS requirements, high UL/DL throughput • Kiosk AP: set up by stores or restaurants, mainly for information pushing and internet browsing services, small coverage and less clients • Soft AP: set up by individuals, low power, low coverage, mobile, sometimes for P2P services Scenarios of HEW

  3. A Typical Scenario: Airport • These APs locate close to each other, and their BSSs are severely overlapped. In such an environment, users have high probability to have a bad experience.

  4. Different management entities • Lack of collaborations between APs lead to long access delay and packet collision. • If user has no knowledge of APs’ capability and load at the moment, random selection of an AP may make problem worse. • Different services supported • e.g. If BSS supporting web browsing services primarily and BSS supporting voice/video services are overlapped, user experiences on latter BSS are much worse. Potential Issues

  5. Different AP coverage • APs support various coverage • Interference between long range BSS and short range BSS • Interference between similar range BSSs • Interference depending on how much the overlapping area is • Different network infrastructures • Infrastructure BSS, IBSS, MBSS, Wi-Fi Direct devices, etc. • Solution should consider the characteristic of network infrastructure Potential Issues

  6. Different power requirements • Some mobile devices are very power sensitive • Soft APs also have power saving requirement • They can be affected a lot more than others by long delay and retransmission Potential Issues HW E5s 3G wireless router

  7. SIMULATION

  8. AP1 and AP2 overlaps but cannot hear each other. STA2 is located in the overlap area of AP1 and AP2. Consider downlink traffic from AP1 to STA1 and STA2 and AP2 to STA3. Ideal channel condition RTS/CTS disabled Channel bandwidth=11Mbps Fig.1 shows the throughput of STA1, STA2 and STA3 when the data rates of “AP1 to STA1” and “AP2 to STA3” change from 1 to 10 Mbps. (Data rate of “AP1 to STA2” is 5Mbps) Fig.2 shows that the data rate of “AP1 to STA2” changes from 1 to 15 Mbps while the data rate of “AP1 to STA1” and “AP2 to STA3” is 4 Mbps. Unfairness problem in HEW: Downlink BSS1 BSS2 STA2 STA1 STA3 AP1 AP2 Fig. 1 Fig. 2 • The throughput of the overlapped STA (STA2) decreased dramatically with the increasing of the data rate of the non-overlapped STAs (STA1 and STA3). (Fig.1) • The throughput of the overlapped STA (STA2) may not increase with its data rate. The throughput of STA1 is affected by the transmission of STA2 significantly. (Fig.2) • The unfairness between BSSs (BSS1 and BSS2) and STAs (STA1, STA3 and STA2) is obvious. • RTS/CTS mechanism may not solve the unfairness problem since STA2 would not get the same transmission opportunity as STA3.

  9. AP1 and AP2 overlaps but cannot hear each other. STA2 is located in overlap area of AP1 and AP2. Consider uplink traffic from STA1 and STA2 to AP1 and STA3 to AP2. Ideal channel condition RTS/CTS disabled Channel bandwidth=11Mbps Fig.3 shows the throughput of STA1, STA2 and STA3 when the data rate of STA1 and STA3 change from 1 to 8 Mbps. (Data rate of STA2 is 5Mbps) Fig.4 shows the data rate of STA2 change from 1 to 10 Mbps while the data rate of STA1 and STA3 is 4 Mbps Unfairness problem in HEW: Uplink BSS1 BSS2 STA2 STA1 STA3 AP1 AP2 Fig. 3 Fig. 4 • The throughput of the overlapped STA (STA2) decreased dramatically with the increasing of the data rate of the non-overlapped STAs (STA1 and STA3). (Fig.3) • The throughput of the overlapped STA (STA2) may not increase with its data rate. The throughput of STA1 and STA3 is affected by the transmission of STA2 significantly. (Fig.4) • The unfairness between STAs (STA1, STA3 and STA2) is obvious. • System throughput is much lower than that of the non-overlap system. • RTS/CTS mechanism may not solve the unfairness problem since STA2 would not get the same transmission opportunity as STA1 and STA3.

  10. The unfairness and efficiency problem when various WLAN networks co-locate together is complicated and severe. When considering the co-located WLAN networks scenario, multiple factors should be taken into consideration. Conclusion

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