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).
