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CANE, the Pioneer of Scale-Free Autonomous Wireless Mesh Networks

High Efficiency WLAN (HEW)

  • “High-efficiency WLAN” targets the key issues that should be addressed to support continued growth and competitiveness of 802.11 across a broad range of market segments.

HEW can be achieved by realizing a recognizable improvement in Quality of Experience in the real-world data throughput in broad market segments: residential, enterprise, retail, operators, service providers, device vendors, TV/video, medical (it will become high density scenarios).

More specifically, today, a (reliable) 1-5 Mbps connection is adequate for a reasonable user experience with most mobile web applications, including video. This minimum satisfactory throughput will grow 50% per year in the coming years (due to increased cloud services, higher resolution video, …).

  • Aiming the improvement of IEEE 802.11 PHY and MAC in the following scenarios:

    • dense networks with large number of STAs

    • dense heterogeneous networks with large number of APs

    • outdoor deployments

In each scenario, what are the main problems?

  • High number of STAs per AP

    • 802.11 channel access has been designed for and is effective with a limited number of users. However, with a high density of STAs:

      • limitations of CSMA-CA: inefficient after a certain density of STAs due to increased collisions

      • MAC efficiency/airtime use limitations

        • much less efficient for a high number of users, each with limited throughput applications

        • airtime use can be very inefficient with a traffic mix (small and big packets) - a significant proportion of packets are very small, e.g. web browsing: <100B packets represent 90% UL packets and 25% DL packets

    • airtime use can be also very inefficient with a mix of legacy devices

 

  • In very high density deployment scenarios (large no. of APs)

    • saturation with high number of STAs per AP

    • channel reuse is almost impossible

      • co-channel interference strongly limits spatial capacity

      • problem is harder in environments without walls where propagation is very good

    • other interferences (adjacent-channel interference, non Wi-Fi interference)

    • inefficient cohabitation with tethering devices (soft APs) and  Wi-Fi Direct devices

    • difficult to achieve consistent admission control, load balancing and fairness behavior to optimize networks even when APs deployed together

 

  • In outdoor deployment scenarios

    • delay spread issue in typical outdoor ITU UMI channels

    • links can hardly be maintained

      • in non-LOS, even with good received SNR (with Rx power below -70/75 dBm)

    • uplink is the limiting factor - especially with smartphones (10-12dBm Tx power)

    • high levels of interference

    • home gateways leaking outdoors

      • minimum of 15-20 uncoordinated APs per channel (2.4GHz) under coverage(with rather small Rx power – but sufficient to cause interference, especially at BSS-edge)

    • saturation with a high number of STAs per AP

The following issues have to be resolved to improve Quality of Experience.

  • Contention Resolution.

  • Admission Control including ANDSF. (Below figure shows a concept of smarter network selection functions base on S-ANDSF).