ES2 : Managing Link Level Parameters for Elevating Data Rate and Stability in High Throughput WLAN Sandip Chakraborty, Subhrendu Chattopadhyay Department of Computer Science and Engineering Indian Institute of Technology Kharagpur Department of Computer Science and Engineering Indian Institute of Technology Guwahati January 8, 2016 COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 1 / 16
Preface High-throughput extension for wireless local area networks (WLAN): IEEE 802.11n (600 Mbps), IEEE 802.11ax (Gbps wireless) Supports a large set of link control parameters: COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 2 / 16
Preface High-throughput extension for wireless local area networks (WLAN): IEEE 802.11n (600 Mbps), IEEE 802.11ax (Gbps wireless) Supports a large set of link control parameters: Number of MIMO Spatial Streams COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 2 / 16
Preface High-throughput extension for wireless local area networks (WLAN): IEEE 802.11n (600 Mbps), IEEE 802.11ax (Gbps wireless) Supports a large set of link control parameters: Number of MIMO Spatial Streams Channel Bonding: IEEE 802.11n supports 20 and 40 MHz, IEEE 802.11ac supports 20, 40, 80, 120 MHz COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 2 / 16
Preface High-throughput extension for wireless local area networks (WLAN): IEEE 802.11n (600 Mbps), IEEE 802.11ax (Gbps wireless) Supports a large set of link control parameters: Number of MIMO Spatial Streams Channel Bonding: IEEE 802.11n supports 20 and 40 MHz, IEEE 802.11ac supports 20, 40, 80, 120 MHz Advanced Modulation and Coding Schemes – Supports higher physical data rates COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 2 / 16
Preface High-throughput extension for wireless local area networks (WLAN): IEEE 802.11n (600 Mbps), IEEE 802.11ax (Gbps wireless) Supports a large set of link control parameters: Number of MIMO Spatial Streams Channel Bonding: IEEE 802.11n supports 20 and 40 MHz, IEEE 802.11ac supports 20, 40, 80, 120 MHz Advanced Modulation and Coding Schemes – Supports higher physical data rates Frame aggregation and Block Acknowledgement – Reduce channel access overhead COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 2 / 16
Preface High-throughput extension for wireless local area networks (WLAN): IEEE 802.11n (600 Mbps), IEEE 802.11ax (Gbps wireless) Supports a large set of link control parameters: Number of MIMO Spatial Streams Channel Bonding: IEEE 802.11n supports 20 and 40 MHz, IEEE 802.11ac supports 20, 40, 80, 120 MHz Advanced Modulation and Coding Schemes – Supports higher physical data rates Frame aggregation and Block Acknowledgement – Reduce channel access overhead Short Guard Intervals – Saves guard time when interference is less COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 2 / 16
Link Adaptation: What is the Best Link Configuration? Every feature has its own pros and cons: COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 3 / 16
Link Adaptation: What is the Best Link Configuration? Every feature has its own pros and cons: Channel Bonding: Data loss is more for wider channels – channel bonding is not good when channel error rate is high COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 3 / 16
Link Adaptation: What is the Best Link Configuration? Every feature has its own pros and cons: Channel Bonding: Data loss is more for wider channels – channel bonding is not good when channel error rate is high Modulation and Coding: Higher modulation and coding requires higher signal strength to sustain – high modulation and coding rate may not be suitable when SINR is low COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 3 / 16
Link Adaptation: What is the Best Link Configuration? Every feature has its own pros and cons: Channel Bonding: Data loss is more for wider channels – channel bonding is not good when channel error rate is high Modulation and Coding: Higher modulation and coding requires higher signal strength to sustain – high modulation and coding rate may not be suitable when SINR is low Frame Aggregation: Frame aggregation may result in high data loss due to channel interference COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 3 / 16
Some Observations from a Practical Testbed Testbed Configurations: Ralink RT-3352 Wireless Router-on-chip – supports IEEE 802.11n 2 × 2 MIMO Supports 20 MHz and 40 MHz at 5 GHz band – 300 Mbps physical data rate Linux Kernel 2.4.12 – openwrt supported COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 4 / 16
Observation 1: Impact of Modulation and Coding (a) Channel Width = 20 MHz (b) Channel Width = 40 MHz 1 1 0.9 0.9 0.8 0.8 0.7 0.7 PSR PSR 0.6 0.6 0.5 0.5 MCS 4 MCS 4 0.4 0.4 MCS 7 MCS 7 0.3 MCS 11 0.3 MCS 11 MCS 15 MCS 15 0.2 0.2 6 8 10 12 14 16 6 8 10 12 14 16 Average SNR (dB) Average SNR (dB) Observations: Low modulation and coding levels can sustain at low SNR region – provide better PSR compared to high modulation and coding values High modulation and coding levels provide good PSR at high SNR region PSR variation in significantly more in 40 MHz communication compared to 20 MHz communication. COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 5 / 16
Observation 2: Impact of Channel Bonding and Guard Intervals (a) Impact of Channel Bonding (b) Impact of Guard Interval 1 1 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 PSR PSR 0.5 0.5 0.4 0.4 0.3 0.3 0.2 20 MHz 0.2 800 ns 40 MHz 400 ns 0.1 0.1 6 8 10 12 14 16 18 6 8 10 12 14 16 18 Average SNR (dB) Average SNR (dB) Observations: 40 MHz gets more affected due to external noise and interference Short guard interval (400 ns) is effective for low interference scenario COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 6 / 16
Observation 2: Impact of Channel Bonding and Guard Intervals (a) Impact of Channel Bonding (b) Impact of Guard Interval 1 1 0.9 0.9 0.8 0.8 0.7 0.7 0.6 0.6 PSR PSR 0.5 0.5 0.4 0.4 0.3 0.3 0.2 20 MHz 0.2 800 ns 40 MHz 400 ns 0.1 0.1 6 8 10 12 14 16 18 6 8 10 12 14 16 18 Average SNR (dB) Average SNR (dB) Observations: 40 MHz gets more affected due to external noise and interference Short guard interval (400 ns) is effective for low interference scenario We need to develop an adaptive link parameter selection mechanism based on channel condition... COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 6 / 16
Solution Approach: Estimate, Sample and Select (ES2) A three step iterative process: Estimate the SNR at transmitter from the measured received signal strength (RSS) at the receiver Sample the feature sets based on the estimated SNR thresholds Select the final data rate from the filtered samples COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 7 / 16
Estimation of SNR Estimation of SNR is non-trivial, because, The noise level significantly depends on parametric settings (like number of spatial streams, channel width etc) → Simple subtraction of noise level from signal level does not work. The transmitter needs to figure out link parameter settings, whereas SNR is measured at the receiver → SNR prediction is required at transmitter. Piggybacking SNR does not work because the link parameter settings may change! COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 8 / 16
Estimation of SNR: A Kalman Filtering Approach COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 9 / 16
Sample Feature Set SNR is quite fluctuating and may not be a good choice for feature sampling. We use diffESNR – diffESNR t = SNR t ( | SNR 2 t − SNR 2 t − 1 | ) This captures SNR fluctuation as well – if fluctuation is more, some link parameter settings become unstable. COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 10 / 16
Impact of diffESNR (a) Effect of Spatial Streams 60 40 Low DiffESNR High DiffESNR 50 diffESNR Goodput (Mbps) diffESNR (dB) 40 30 30 20 20 10 0 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 MCS (b) Effect of Channel Bonding 7 20 MHz 40 MHz 6 Goodput (Mbps) 5 4 3 2 1 0 5 10 15 20 25 30 diffESNR (dB) COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 11 / 16
Estimate, Sample and Select (ES2) A three step iterative process: Estimate the SNR at transmitter from the measured received signal strength (RSS) at the receiver Sample the feature sets based on the estimated SNR thresholds Select the final data rate from the filtered samples – We are left with only few options! Apply standard rate adaptation... COMSNETS 2016 (Bangalore, India) ES2: Managing Link Level Parameters... January 8, 2016 12 / 16
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