1. Submission doc.: IEEE 802.11-13/1409r0 November 2013 Adriana Flores, Rice UniversitySlide 1 Dual Wi-Fi: Dual Channel Wi-Fi for Congested WLANs with Asymmetric Traffic Loads Date: 2013-11-12 Authors:

2. Submission doc.: IEEE 802.11-13/1409r0 Motivation Slide 2Adriana Flores, Rice University November 2013 http://netflix.com/movie Traffic Asymmetric Downlink traffic >> Uplink Traffic

3. Submission doc.: IEEE 802.11-13/1409r0 Motivation Slide 3Adriana Flores, Rice University November 2013 Traffic Asymmetric Downlink traffic >> Uplink Traffic High Contention High number of backlogged nodes competing for the same resources

4. Submission doc.: IEEE 802.11-13/1409r0 Motivation Slide 4Adriana Flores, Rice University November 2013 Traffic Asymmetric Downlink traffic >> Uplink Traffic High Contention High number of backlogged nodes competing for the same resources Hidden Terminals Cause collisions Spectrum Underutilization Affects downlink

5. Submission doc.: IEEE 802.11-13/1409r0 802.11 in Congested WLANs with Traffic Asymmetry Slide 5Adriana Flores, Rice University November 2013 Shared resources – Defer to one another transmissions – Performance dependency Spectrum Underutilization (Coordination Time, Collisions) E.g. Collisions by Hidden Terminals Disproportionate contention – Uplink Data: many clients vs. Downlink Data: few APs – Same CWmin yields equal medium access probability N backlogged Clients : – Uplink Data: N/(N+1) Downlink Data: 1/(N+1)

6. Submission doc.: IEEE 802.11-13/1409r0 Goal Define a random access MAC that provides configurable spectrum resources for upload vs. download traffic – Enables matching resources to demand – Enables high spectral efficiency Slide 6Adriana Flores, Rice University November 2013

7. Submission doc.: IEEE 802.11-13/1409r0 802.11 Channel Architecture Slide 7Adriana Flores, Rice University November 2013 ↓Data AP  STA ↑ ACK STA  AP ↑ Data STA  AP ↓ ACK AP  STA Uplink Data-ACK Downlink Data-ACK Frequency Time Total Bandwidth

8. Submission doc.: IEEE 802.11-13/1409r0 Dual Wi-Fi Channel Architecture Slide 8Adriana Flores, Rice University November 2013 Frequency Time ↑ Data STA  AP ↓ ACK AP  STA ↓Data AP -> STA ↑ACK STA  AP Downlink Data Channel Uplink Data Channel … FDD Frequency Time ↑ Data STA  AP ↓ ACK AP  STA ↓Data AP  STA ↑ACK STA  AP Downlink Data Channel Uplink Data Channel E.g. Channel 36: 5.1 GHz E.g. Channel 165: 5.8 GHz … Dual Wi-Fi

9. Submission doc.: IEEE 802.11-13/1409r0 Features of Dual Wi-Fi Channel Architecture Logical Division (direction of data) – Decouple medium access Medium access directly weighted on the traffic load of that direction – Independent and asynchronous operation – Independent performance – Independent resource allocation – Flexible bandwidth division Bi-directional traffic within channels – Support the complete MAC-layer Data-ACK handshake – In-channel control feedback paired with transmitted data Unlike FDD, no generic control messages use the channel Slide 9Adriana Flores, Rice University November 2013

10. Submission doc.: IEEE 802.11-13/1409r0 ↑ Data STA  AP ↓ ACK AP  STA ↑ACK STA  AP ↓Data AP  STA Dual Wi-Fi Benefits Slide 10Adriana Flores, Rice University November 2013 Frequency Time ↓Data AP  STA ↑ACK STA  AP Downlink Data Channel Uplink Data Channel E.g. Channel 36: 5.1 GHz E.g. Channel 165: 5.8 GHz … Match spectrum resources to traffic asymmetry Contention asymmetry: remove uplink and downlink competition for the same spectrum resources Reduce medium contention and collisions  Increase spectral efficiency ↑ Data STA  AP ↓ ACK AP  STA

11. Submission doc.: IEEE 802.11-13/1409r0 Dual Wi-Fi MAC Slide 11Adriana Flores, Rice University November 2013 Isolate downlink and uplink medium access – Dual Wi-Fi ensures APs do not contend with STAs 802.11 CSMA basic access Smaller number of contending nodes per channel: ↓ Coordination time, collisions and retransmissions  Increased spectral efficiency Downlink Data Channel Only same-channel APs CW still necessary CW size tune to # of in-channel APs 1 AP: Collision-Free No Contention Downlink Data Channel Only same-channel APs CW still necessary CW size tune to # of in-channel APs 1 AP: Collision-Free No Contention Uplink Data Channel Only STAs Remove contention with heavy downlink traffic Uplink Data Channel Only STAs Remove contention with heavy downlink traffic

12. Submission doc.: IEEE 802.11-13/1409r0 Dual Wi-Fi vs. EDCA variation Identify downlink data traffic as high-priority traffic providing strict or partial priority to APs to access the medium Advantage: Counters traffic asymmetry with minimal protocol modifications Disadvantages: Issues of shared band: – Medium Access aggressiveness Dependency in number STAs and load – Coupled Medium Access Downlink transmissions must defer to uplink transmissions – Coupled Performance Throughput fraction is dependent on the load – Lead to starvation Collisions – No guaranteed resources provided to downlink data traffic Slide 12Adriana Flores, Rice University November 2013

13. Submission doc.: IEEE 802.11-13/1409r0 Dual Wi-Fi Node Architecture Slide 13Adriana Flores, Rice University November 2013 Two radio approach – Clients and APs – Tx and Rx in each channel independently and asynchronously – Full Duplex (Different frequencies) – Co-channel Interference Guard Band – WiFi-NC :100 KHz TCP/IP Data DL PHY TX RFRX RF Data DL MAC Data TXData RX Switch Transceiver Data UL PHY TX RFRX RF Data UL MAC Data TXData RX Control Unit

14. Submission doc.: IEEE 802.11-13/1409r0 Node Architecture Design Alternatives Slide 14Adriana Flores, Rice University November 2013 Half-Duplex Clients – AP smart selection of downlink data transmissions Transmit to clients which it is not currently receiving from 1.Single radio clients Only Tx or Rx in a single channel at a time Filter to select either channel 2.Dual radio clients Only Tx or Rx in a single channel at a time Only operate a single radio at a time – Avoid cross talk

15. Submission doc.: IEEE 802.11-13/1409r0 Dual Wi-Fi Performance Gains Slide 15Adriana Flores, Rice University November 2013 626% ! 152% 14 to 32% ~-30% KEY: UL and DL Medium access isolation

16. Submission doc.: IEEE 802.11-13/1409r0 Impact of Contention Asymmetry Slide 16Adriana Flores, Rice University November 2013 0.34 DL -25% 0.11 DL -40% 1.01 1.04 DW: 1% Ideal

17. Submission doc.: IEEE 802.11-13/1409r0 Conclusion Spectrum independence between uplink and downlink MAC data traffic – Can provide performance that is proportional to imposed demand – Adaptable to any traffic asymmetry or network density Flexible design that adapts to changes in actual usage Applications Efficient use of resources Key solution to address congested scenarios White Spaces – isolation of hidden terminals Faster downlink data delivery – Traffic asymmetry Slide 17Adriana Flores, Rice University November 2013