submission doc.: ieee 802.11-13/1409r0 november 2013 adriana flores, rice universityslide 1 dual...
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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
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