Submission

doc.: IEEE 802.11-13/1409r0November 2013

Adriana Flores, Rice UniversitySlide 1

Dual Wi-Fi: Dual Channel Wi-Fi for Congested WLANs with Asymmetric Traffic Loads

Date: 2013-11-12

Name Affiliations Address Phone email Adriana Flores Rice University 6100 Main, Houston,

Texas 77005-1892 a.flores@rice.edu

Edward W. Knightly

Rice University knightly@rice.edu

Authors:

Submission

doc.: IEEE 802.11-13/1409r0

Motivation

Slide 2 Adriana Flores, Rice University

November 2013

http://netflix.com/movie

•Traffic Asymmetric• Downlink traffic >> Uplink Traffic

Submission

doc.: IEEE 802.11-13/1409r0

Motivation

Slide 3 Adriana 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 802.11-13/1409r0

Motivation

Slide 4 Adriana 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 802.11-13/1409r0

802.11 in Congested WLANs with Traffic Asymmetry

Slide 5 Adriana 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 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 6 Adriana Flores, Rice University

November 2013

Submission

doc.: IEEE 802.11-13/1409r0

802.11 Channel Architecture

Slide 7 Adriana Flores, Rice University

November 2013

UplinkData-ACK

DownlinkData-ACK

Frequency

Tim

e

Total Bandwidth

Submission

doc.: IEEE 802.11-13/1409r0

Dual Wi-Fi Channel Architecture

Slide 8 Adriana Flores, Rice University

November 2013

Frequency

Tim

e

…

FDD

Frequency

Tim

e

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 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 9 Adriana Flores, Rice University

November 2013

Submission

doc.: IEEE 802.11-13/1409r0

Dual Wi-Fi Benefits

Slide 10 Adriana Flores, Rice University

November 2013

Frequency

Tim

e

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

Submission

doc.: IEEE 802.11-13/1409r0

Dual Wi-Fi MAC

Slide 11 Adriana 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

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 12 Adriana Flores, Rice University

November 2013

Submission

doc.: IEEE 802.11-13/1409r0

Dual Wi-Fi Node Architecture

Slide 13 Adriana 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 PHYTX RF RX RF

Data DL MACData TX Data RX

Switch

Transceiver

Data UL PHYTX RF RX RF

Data UL MACData TX Data RX

Control Unit

Submission

doc.: IEEE 802.11-13/1409r0

Node Architecture Design Alternatives

Slide 14 Adriana 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 802.11-13/1409r0

Dual Wi-Fi Performance Gains

Slide 15 Adriana Flores, Rice University

November 2013

626% !

152% 14 to 32%

~-30%

KEY: UL and DL Medium access

isolation

Submission

doc.: IEEE 802.11-13/1409r0

Impact of Contention Asymmetry

Slide 16 Adriana Flores, Rice University

November 2013

0.34

DL -25%

0.11

DL -40%

1.01 1.04DW: 1% Ideal

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 17 Adriana Flores, Rice University

November 2013