802.11ec: Collision Avoidance without Control Messagesem9/publications/802_11ec-slides.pdf ·...
Transcript of 802.11ec: Collision Avoidance without Control Messagesem9/publications/802_11ec-slides.pdf ·...
802.11ec: Collision Avoidance withoutControl Messages
Eugenio Magistretti, Omer Gurewitz,and Edward Knightly
Rice UniversityBen Gurion University
802.11ec stands for 802.11 with Encoded Control and does not represent an IEEE standard
Ideal Wi-Fi
tota
lth
roug
hput
CLI
QU
E
100%
Low Power & Obstructions
100%
HT
Collisions
tota
lth
roug
hput
CLI
QU
E
100%
HT
Collisions
tota
lth
roug
hput
CLI
QU
ETwo hidden terminals70% throughput loss
Ex.
Low Power & Obstructions
100%
tota
lth
roug
hput
CLI
QU
E
HT
Low Power & Obstructions
RTS/CTS
RTS
/CTSCollisio
ns
100%
Overhead
RTS
/CTS
tota
lth
roug
hput
CLI
QU
E
HT
Collision Penalty Overhead Penalty
Collisio
ns
100%
Overhead
RTS
/CTSCollisio
ns
tota
lth
roug
hput
CLI
QU
E
HT
RTS/CTS/ACK overhead~ max size packet
@ 54 Mbps
Ex.
Collision Penalty Overhead Penalty
Objective
Fundamentally Fundamentally re-think the way controlre-think the way controlinformation is conveyedinformation is conveyed in order to in order toguarantee guarantee low overheadlow overhead and and robustnessrobustness
Control Messages CSS
ACK
DATARTS
CTSLong Duration
Messages
- Preamble- Header- Base Rate Data
Control Messages CSS
• Correlatable Symbol Sequences (CSS) are pre-defined pseudo-noise (PN) bit sequences detected via cross-correlation
ACK
RTS
CTS
Messages
Correlatable SymbolSequences
- Preamble- Header- Base Rate Data
Long Duration
DATA
DATA
Control Messages CSS
ACK
RTS
CTS
Messages
Correlatable SymbolSequences
- Preamble- Header- Base Rate Data
Long Duration
ShorterMore Robust
✔✔
- Preamble- Header
DATA
DATA
• Correlatable Symbol Sequences (CSS)
• Control Information via CSS
• 11ec Protocol Illustration
• Experimental Results
Outline
Why Correlatable Symbol Sequences?
CSS’s key idea: Signal detection is more robust than decoding
Why Correlatable Symbol Sequences?
CSS’s key idea: Signal detection is more robust than decoding
• Sender and receiver agree upon a set of pre-defined CSS
• The receiver can detect a specific CSS u(k) bycorrelating it with the incoming samples y(k)
Why Correlatable Symbol Sequences?
CSS’s key idea: Signal detection is more robust than decoding
• Sender and receiver agree upon a set of pre-defined CSS
• The receiver can detect a specific CSS u(k) bycorrelating it with the incoming samples y(k)
)()()(1
0
* !+=! "#
kykuCL
!
C(") # L 0)( !"C
CSS NON MATCHINGCSS MATCHING
Why Correlatable Symbol Sequences?
CSS’s key idea: Signal detection is more robust than decoding
• Sender and receiver agree upon a set of pre-defined CSS– CSS length L determines the max size of the CSS set
• The receiver can detect a specific CSS u(k) bycorrelating it with the incoming samples y(k)
)()()(1
0
* !+=! "#
kykuCL
!
C(") # L 0)( !"C
CSS NON MATCHINGCSS MATCHING
CSS Intuition
CSS u(k)
CSS+INTERFERENCE as received by R
Information K
• Node S wants to convey control information (“Information K”) to node Rvia a pre-defined CSS u(k)
CSS Intuition
CSS u(k)
CSS+INTERFERENCE as received by R
Noise Signal
• Node S wants to convey control information (“Information K”) to node R via a pre-defined CSS u(k)
CSS Intuition
MATCHING at R
Information KReceived
• The correlator spikes when thepre-defined CSS is received
||
• Node S wants to convey control information (“Information K”) to node R via a pre-defined CSS u(k)
CSS Intuition
MATCHING at R
Information KReceived
NON MATCHING(at any other node)
||
• Node S wants to convey control information (“Information K”) to node R via a pre-defined CSS u(k)
CSS Intuition
MATCHING at R NON MATCHING(at any other node)
||
• Node S wants to convey control information (“Information K”) to node R via a pre-defined CSS u(k)
Information KReceived ???||
CSS Summary
• AdvantagesLow Overhead
– No preamble– No encoding
High Robustness– To low SINR– To collisions
• Correlatable Symbol Sequences (CSS) are pre-definedPN bit sequences detected via cross-correlation
• CSS do not need any preamble/header
Length L limits number of pre-defined CSS
• Correlatable Symbol Sequences (CSS)
• Control Information via CSS
• 11ec Protocol Illustration
• Experimental Results
Outline
Control Messages CSS
ACK
DATARTS
CTS
Messages
Correlatable SymbolSequences
Long Duration
ShorterMore Robust
✔✔
Limited Number
DATA
Control Information via CSS
• 802.11 control message structure
Preamble Fixed ControlField Type DurationAddresses
• 802.11 control message structure
• Define a small dictionary of CSS to representthe message information content
Preamble Fixed ControlField Type DurationAddresses
Control Information via CSS - Dictionary
• 802.11 control message structure
• Define a small dictionary of CSS to representthe message information content
– Type Limited Set
Preamble Fixed ControlField Type DurationAddresses
Map to different CSS(e.g., RTS CTS ACK)
Control Information via CSS - Dictionary
• 802.11 control message structure
• Define a small dictionary of CSS to representthe message information content
– Type Limited Set
– Address
Preamble Fixed ControlField Type DurationAddresses
Map to different CSS(e.g., RTS CTS ACK)
One CSS per nodeLarge Set butLocally Limited
Control Information via CSS - Dictionary
• 802.11 control message structure
• Define a small dictionary of CSS to representthe message information content
– Type Limited Set
– Address
– Duration Large Set
Preamble Fixed ControlField Type DurationAddresses
Map to different CSS(e.g., RTS CTS ACK)
New CSS types + TimingCode (e.g., channel free)
Large Set butLocally Limited
Control Information via CSS - Dictionary
One CSS per node
• 802.11 control message structure
• CSS Information Scope Control
Preamble Fixed ControlField Type DurationAddresses
Control Information via CSS - Scope
• 802.11 control message structure
• CSS Information Scope Control
– Public
Preamble Fixed ControlField
To be received by all nodes(e.g., Channel Reservation/Release)
Type DurationAddresses
All nodes detect the CSS(i.e., possess the correlator)
Control Information via CSS - Scope
• 802.11 control message structure
• CSS Information Scope Control
– Public
– Unique Feature: Private
Preamble Fixed ControlField
To be received by all nodes(e.g., Channel Reservation/Release)
To be received by theother endpoint (e.g., ACK,source/destination address)
Type DurationAddresses
All nodes detect the CSS(i.e., possess the correlator)
Selected nodes detect the CSS
Control Information via CSS - Scope
• Correlatable Symbol Sequences (CSS)
• Control Information via CSS
• 11ec Protocol Illustration
• Experimental Results
Outline
• 11ec follows the fundamental concepts of 802.11
11ec Protocol Illustration
neighbor
sender
receiver
hidden terminal HT
• 11ec follows the fundamental concepts of 802.11
s
r
neighbor
11ec Protocol Illustration
hiddenterminal
• 11ec follows the fundamental concepts of 802.11
Private CSS conveying thereceiver address
Ic(r) InitiationIc(r)
s
r
11ec Protocol Illustration
neighbor
hiddenterminal
• 11ec follows the fundamental concepts of 802.11
Private CSS conveying thereceiver address
Ic(r) InitiationIc(r)
s
r
11ec Protocol Illustration
Every Receiver isassociated with an Ic(r)
neighbor
hiddenterminal
• 11ec follows the fundamental concepts of 802.11
Public CSS
Ic(r) Initiation
Rc Channel Reservation
Ic(r)
s
r
Rc
11ec Protocol Illustration
Rc is a unique CSS
neighbor
hiddenterminal
BUSY CHANNEL
TIMEOUT
• 11ec follows the fundamental concepts of 802.11
Ic(r)
s
r
Rc
DATA
Ic(r) Initiation
Rc Channel Reservation
BUSY CHANNEL
11ec Protocol Illustration
DATA contains 802.11preamble P
Data Reception
TIMEOUT
neighbor
hiddenterminal
P
• 11ec follows the fundamental concepts of 802.11
Ic(r)
s
r
Rc
DATA
Ic(r) Initiation
Rc Channel Reservation
11ec Protocol Illustration
P
Neighbor nodes detect Pand NAVs
Data Reception
BUSYneighbor
hiddenterminal
BUSY CHANNEL
TIMEOUT
• 11ec follows the fundamental concepts of 802.11
Ic(r)
s
r
Rc
DATA
Ic(r) Initiation
Rc Channel Reservation
11ec Protocol Illustration
P
Neighbor nodes detect Pand NAVs
Data Reception
BUSY
802.11ec can co-exist with 802.11
neighbor
hiddenterminal
BUSY CHANNEL
• 11ec follows the fundamental concepts of 802.11
Private CSS conveying thesender address
Ac(s)
Ic(r)
s
r
Rc
DATA
Ic(r) Initiation
Rc Channel Reservation
Ac(s) Acknowledgement
11ec Protocol Illustration
P
Data Reception
BUSYneighbor
hiddenterminal
BUSY CHANNEL
TIMEOUT
• 11ec follows the fundamental concepts of 802.11
Private CSS conveying thesender address
Ac(s)
Ic(r)
s
r
Rc
DATA
Ic(r) Initiation
Rc Channel Reservation
Ac(s) Acknowledgement
11ec Protocol Illustration
Every Sender isassociated with an Ac(s)
P
Data Reception
BUSYneighbor
hiddenterminal
BUSY CHANNEL
TIMEOUT
Ac(s)
11ec Protocol Illustration
Ic(r)
s
r
• 11ec follows the fundamental concepts of 802.11
Ic(r) Initiation
Rc Channel ReservationRc
DATA
Ac(s) Acknowledgement
Fc Channel ReleasePublic CSS
Fc
BUSY CHANNEL
P
BUSY
Data Reception
Fc is a unique CSS
neighbor
hiddenterminal
Experimental Results Roadmap
• WARP
- CSS Robustness
• Channel Measurement Emulation
- Tput/Fairness/Airtime Utilization
- Fundamental and Small Topologies
• Large Network Simulations
- 20-node Random Topology
CSS Implementation
1. Repeatable and controllable experiments
Sender Receiver Interferer
LogicalConnection
PhysicalCabling
CSS Performance Metric
CSS Performance Metric
• Threshold SelectionProbability of false positives ~10-8
PerformanceProbability of false negatives
CSS Robustness
• CSS are correlatable even at low SINR
Robustness
L=63
L=127
L=255
L=511
[dB]
Robustness and Overhead Gains
Duration: Message Control vsCoded Control
11b/g 11a 11ec~1000 µs ~184 µs ~41 µs
10 dB more robust 78% less overhead
Robustness
RTS Decoding
(BPSK 1/2)
Ic(r) Detection
(127-symbol)
[dB]
CSS Implementation
1. Repeatable and controllable experiments
Sender Receiver Interferer
LogicalConnection
PhysicalCabling
2. Emulation based on Realistic Channel Measurements
Hidden Terminals with Heterogeneous Rates
54 Mbps 6 Mbps
Hidden Terminals with Heterogeneous Rates
54 Mbps 6 Mbps
• Strong link RTS captures over weak link’s
• 802.11ec data collisions are rare
THROUGHPUT
802.11ec
RTS/CTS
802.11
THROUGHPUT
802.11ec
RTS/CTS
802.11
Hidden Terminals with Heterogeneous Rates
54 Mbps 6 Mbps
• Strong link RTS captures over weak link’s
• 802.11ec data collisions are rare
Jain Index 0.98 0.52 0.78fairest
FAIRNESS
THROUGHPUT
802.11ec
RTS/CTS
802.11
AIRTIME UTILIZATION
RTS/
CTS
802.
11802.
11ec
Hidden Terminals with Heterogeneous Rates
54 Mbps 6 Mbps
Tota
l Airt
ime
Util
izat
ion
• Differently from 802.11, 802.11ecdoes not penalize weak and lowdata-rate links
802.11ec increases airtime utilization
• 802.11ec increases fairness AND channel utilization
AIRTIME UTILIZATION
802.
11ec
RTS/
CTS
802.
11
Hidden Terminals with Heterogeneous Rates
54 Mbps 6 Mbps
Tota
l Airt
ime
Util
izat
ion
THROUGHPUT
802.11ec
RTS/CTS
802.11
Jain Index 0.98 0.52 0.78
20-Node Random Topologies
• Simulations
Frac
tion
of L
inks
Throughput [Kbps]
802.11ec
RTS/CTS802.11
• CDF of throughput distribution
20-Node Random Topologies
• Simulations
802.11ec vsRTS/CTS
0.2 7x
0.4 4x
0.6 1.9x
GAINS
• By reducing collisions, 802.11ec improves the weak links
Throughput [Kbps]
802.11ec
RTS/CTS802.11
• CDF of throughput distribution
Frac
tion
of L
inks
20-Node Random Topologies
• Simulations
802.11ec vsRTS/CTS
0.2 7x
0.4 4x
0.6 1.9x
GAINS
• By reducing collisions, 802.11ec improves the weak links
Throughput [Mbps]
Frac
tion
of L
inks• CDF of throughput distribution
Throughput [Kbps]
802.11ec
RTS/CTS802.11
Frac
tion
of L
inks
Summary and Conclusions
• Objective: Fundamentally Objective: Fundamentally re-thinkre-think the way controlthe way controlinformation is conveyedinformation is conveyed in order to guarantee in order to guarantee lowlowoverheadoverhead and and robustnessrobustness
•• CSSCSS’’s s have short duration and improve robustnesshave short duration and improve robustness
•• 802.11 802.11ecec uses uses CSSCSS’’s s to convey control informationto convey control information
—— Small CSS Dictionary Small CSS Dictionary
—— Scope Control Scope Control
•• 802.11802.11ecec improves fairness while also increasing channel improves fairness while also increasing channel utilizationutilization
—— Ex. 3x fairness, 1.5x airtime utilization, up to 12x throughputEx. 3x fairness, 1.5x airtime utilization, up to 12x throughput
802.11ec: Collision Avoidance withoutControl Messages
Eugenio Magistretti, Omer Gurewitz,and Edward Knightly
Rice UniversityBen Gurion University