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

Submission doc.: IEEE /1409r0 Motivation Slide 2Adriana Flores, Rice University November Traffic Asymmetric Downlink traffic >> Uplink Traffic

Submission doc.: IEEE /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

Submission doc.: IEEE /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

Submission doc.: IEEE /1409r 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)

Submission doc.: IEEE /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

Submission doc.: IEEE /1409r 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

Submission doc.: IEEE /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

Submission doc.: IEEE /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

Submission doc.: IEEE /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

Submission doc.: IEEE /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 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

Submission doc.: IEEE /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

Submission doc.: IEEE /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

Submission doc.: IEEE /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

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

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

Submission doc.: IEEE /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