RCTC: Rapid Concurrent Transmission Coordination in Full Duplex Wireless Networks Wenjie Zhou,...

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RCTC: Rapid Concurrent Transmission

Coordination in Full Duplex Wireless Networks

Wenjie Zhou, Kannan Srinivasan, Prasun SinhaDepartment of Computer Science and Engineering

The Ohio State University{zhouwe, kannan, prasun}@cse.ohio-state.edu

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Full Duplex“Hi Alice”“Hi Bob”

Half Duplex“Hi Alice”“Hi Bob”

Two Transmission slots One Transmission slot

Full duplex doubles the throughput between two nodes

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• Full duplex doubles the throughput• When both Alice and Bob have packets

• However, traffic tends to be asymmetric

Traffic Pattern and Full Duplex

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Traffic Asymmetry and Full Duplex

I’m listening“Hi Bob”

Busytone packet (fake packet) [MobiCom’11] A waste of channel resources

How to use full duplex beyond 2 nodes?

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Other opportunities exist…

Bob

EllieAlice

CharlieFloyd

Secondary transmission

Introduced in ContraFlow [WiOpt’11]

Gauss

Enabling exposed and secondary transmission achieves 3X throughput

More exposed transmissions enabled, even higher throughput

Primary transmissionExposed transmission

Hellen

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Transmission Modes

• Bi-directional Transmission Mode

• Unidirectional Mode

• Secondary Transmission Mode

BobAlice Charlie

BobAlice

BobAliceEllieFloyd

EllieFloyd

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Challenges in MAC Design

1. Rapid coordination among neighbors – Time efficient

2. Identify exposed transmission opportunities– Primary receiver should not be affected

3. Reliable reception at potential receivers– Exposed receivers and secondary receivers should experience little

interference– Avoid exposed transmission collision

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RCTC Design

1. Rapid Coordination

2. Exposed terminal identification3. History based receiver selection

4. Exposed terminal suppressing

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Node Signature• Property of node signature:

– Unique for every node– High self correlation value– Low cross correlation value

• Signature in previous work:– CSMA/CN [MobiCom’10]– E-MILI [MobiCom’11]– 802.11ec [MobiCom’12]

• Gold code:– Length: 127 bits– Number of signatures: 129– Duration: 6.5 μs (BPSK, 20MHz bandwidth)

Self correlation results

Cross correlation results

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Bi-directional Transmission Mode

Alice:

Bob:

SB SA

SA

Packet for Bob

Packet for Alice

Alice’s signatureBob’s signature

Bob

Alice

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Unidirectional Mode

Alice:

Bob:

SB SA

SH

Packet for Bob

Busytone for hidden terminal

Ellie: Packet Floyd

Half duplex signature

Bob

AliceEllie

Floyd

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Secondary Transmission Mode

Alice:

Bob:

SB SA

SH

Packet for Bob

Packet for Charlie

Bob

Alice

Charlie

Ellie

Floyd

Ellie: Packet Floyd

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RCTC Design




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Bob

EllieAlice

Floyd

Exposed Terminal Identification

Time

Sign

al S

tren

gth

(dB)

Received signal from Alice

SIR for data rate dAB

Received signal from Ellie

Time

Sign

al S

tren

gth

(dB)

Received signal from Ellie

SIR for data rate dEF

Received signal from Alice

Conflict constraints for exposed terminal

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TX power:

SB SA

Exposed Terminal Constraint at Bob

SB SA

Bob

Alice

Ellie

SH

Rx Power:

Rx Power:

TX power: SH

Can we obtain on the fly?

Constraint at Bob:

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TX power:

SB SA

Signal Strength Reflection

SB SA

Bob

Alice

Ellie

SH

Rx Power:

SHTX power:

Rx Power:

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RCTC Design




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Ellie

History Based Receiver Selection

• Set p to 1 upon a successful transmission• Halve p upon a failed transmission

SB SA

Bob

AliceExMap: {TX, RX, p}

Primary Tx Exposed Rx pAlice Matt 0.25Alice Floyd 1Alice Neil 0.125Alice Leonard 0Bob Alice 0.125

… … …

1

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RCTC Design




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Exposed Terminal Suppressing

Transmit!

Unidirectional Mode Bi-directional Mode

𝑃 ′𝐵𝐸≤0?

𝑃 𝐵𝐸≤0?

How to distinguish?

BobAlice

Ellie

SA

BobAlice

Ellie

SH

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Bob

Alice

Ellie

Bi-directional Mode

SB SASF

{RX, plost} in certain period

{Bob, 0.5} > ∆

Send SF

Full duplex signature

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Experiments

• USRP testbed– 5 USRPs

• Other schemes:– FDNative[MobiCom’11]: full duplex without exposed and

secondary transmission– CF [WiOpt’11]: full duplex with secondary transmission

enabled

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USRP Testbed

~59%

~78%

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Simulations

• Simulation Setup: – Randomly picked links in AP and Ad hoc network– Varied number of flows, APs, and clients– 200 runs each setup

• Other schemes:– FDNative: full duplex without exposed and secondary

transmission– CF: full duplex secondary transmission enabled– CMAP[NSDI’08]: exposed transmission enabled half duplex– Half-duplex: IEEE 802.11

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Throughput Breakdown

• Significant exposed transmission opportunities• Limited secondary transmission opportunities

30 APs 50 APs

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AP Network2.31X compared with FDNative Comparable fairness

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Ad hoc network54% gain over FDNative

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Summary and future work

Summary:• Fast and low overhead signaling mechanism using node

signatures• Signal strength reflection to identify exposed terminals • Throughput gain as high as 2.31X without losing fairness

Future work:• Multiple datarates• Transmission priority

THANK YOU

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THE ENDTHANK YOU

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Backup Slides

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Multiple Datarates

BobEllieSH

TX power:

Rx Power: TX power:

Rx Power:

, Let

𝑃❑′𝐵𝐸❑ =

𝑃 𝐵𝐸

𝑃 𝐴𝐵

𝐶𝑑

𝑃 𝐴𝑙𝑖𝑐𝑒

<𝐶 ,C is a known constant

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Different gain for AP and ad hoc network

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Different gain for AP and ad hoc network

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Throughput Breakdown

Average exposed throughput of 200 runs: - 30 APs : 31% - 40 APs : 39% - 50 APs : 46% (Compared with FDNative)Secondary transmission is not promising in AP network

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AP network (different flows)

35% to 111% higher throughput

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AP network (different parameter)

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AP network (download ratio)

71.2% to 90.9% higher throughput

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Ad hoc network

more opportunities for secondary txAverage gain over FDNative changes:

• (a) from 9% to 54%;• (b) from 1% to 29%.

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Node 1->Node 2 : primary transmissionPij : the received signal strength from node i to node jΔd : a predefine threshold related with data rate

Node 2

Node 4Node 1

Node 5P45/P15 > Δd, AND P12/P42> Δd

Exposed Node Identification

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Signal Strength Reflection

TX:

RX:

SRX STX

SH

EX:

𝑃𝑇𝑅=𝑃0∨h𝑇𝑅¿2

𝑃 𝑅𝑋=𝐶𝑑

𝑃𝑇𝑅

=𝐶𝑑

𝑃0∨h𝑇𝑅¿2

𝑃 𝑅𝐸=𝑃𝑅𝑋∨h𝑅𝐸 ¿2=𝐶𝑑∨h𝑅𝐸 ¿2

𝑃0∨h𝑇𝑅¿2

𝑃𝑇𝑅

𝑃𝐸𝑅

=𝑃0∨h𝑇𝑅 ¿2

𝑃0∨h𝐸𝑅¿2=

¿h𝑇𝑅 ¿2

¿ h𝐸𝑅¿2>∆𝑑

𝑃 𝑅𝐸=𝐶𝑑∨h𝑅𝐸¿2

𝑃0∨h𝑇𝑅¿2 <

𝐶𝑑

𝑃0

∆𝑑=𝐶 ,𝑖𝑓 { 𝐶𝑑=𝐶𝑃0∆𝑑

¿ h𝐸𝑅¿2=¿h𝑅𝐸¿2

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History Based Receiver Selection

• Set p to 1 upon a successful transmission.• Halve p upon a failed transmission

TX:

RX:

SRX STX

SH

EX:

ExMap: {TX, RX, p}

TX

RX1, 0.25

RX2, 1

RX3, 0.125

RX4, 0

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TX:

RX:

SRX STX

SH

EX:

𝑃 𝑅𝐸=𝐶𝑑∨h𝑅𝐸¿2

𝑃0∨h𝑇𝑅¿2 <

𝐶𝑑

𝑃0

∆𝑑=𝐶

𝑃 𝑅𝐸=0? Transmit!

TX:

RX:

SRX STX

STX

Collision at TX!!!

TX:

RX:

SRX STX

STX

Suppressing exposed transmission

SF

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Related Work

• Full duplex system:– Choi et al. [MobiCom’10], three antennas– Duarte et al. [ASILOMAR’10], two antennas– Jain et al. [MobiCom’11], two antennas– Aryafar et al. [MobiCom’12], full duplex MIMO– Bharadia et al. [SIGCOMM’13], one antenna

• Full duplex MAC:– Singh et al. [WiOpt’11], fairness, secondary transmission– Jain et al. [MobiCom’11], busytone padding– Sahai et al. [Technical Report’11], full duplex triggering

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Three Antenna Design(with 2 RF chains and some additional h/w)

“Achieving Single Channel, Full Duplex Wireless Communication”, MobiCom’10

~ 30 dB

~ 25 dB

~ 15 dB

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Two Antenna Design(with ~ 3 RF chains)

“Full-Duplex Wireless Communications Using Off-The-Shelf Radios: Feasibility and First Results”, ASILOMAR’10

Antenna separation (AS)

Analog cancellation (AC)Digital cancellation (DC)

c1 = - (hab/hz)x1

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Two Antenna Design(with 2 RF chains and some additional h/w)

“Practical, real-time, full duplex wireless”, MobiCom’11

~ 30 dB

~ 43 dB

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Two Antenna Design(with 2 RF chains and some additional h/w)

“Rethinking Indoor Wireless: Low Power, Low Frequency, Full-duplex”, Microsoft Research’09

- Self-interference at the receive antenna was 55 dB - Analog Interference Cancellation (30 dB) - Nulling Antenna (25 dB)

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Two Antenna Design for MIMO-FD(with 2 RF chains and phase shifter)

“MIDU: Enabling MIMO Full Duplex”, MobiCom’12

Receive Cancellation

Transmit Cancellation

20 dB - 30 dB 22 dB - 30 dB

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Two Antenna Design for MIMO-FD (contd.)(with 2 RF chains and phase shifter)

“MIDU: Enabling MIMO Full Duplex”, MobiCom’12

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Feasibility of One Antenna Design(with 2 RF chains and addl. h/w)

“Picasso: Flexible RF and Spectrum Slicing”, SIGCOMM’12

Not a real full duplex system (TX, RX on different spectrum)

13 dB - 20 dB 30 dB

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Prior Art: MAC Layer for FD (1 of 3)“Practical, real-time, full duplex wireless”, MobiCom’11

No exposed or secondary transmission

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Prior Art: MAC Layer for FD (2 of 3)“Pushing the limits of Full-duplex: Design and Real-timeImplementation”, Technical Report’11(Constraint: A node cannot start new transmission while receiving)

AP->M1, M1->AP

AP->M1, M2->AP

No exposed transmissions

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Prior Art: MAC Layer for FD (3 of 3)“Efficient and Fair MAC for Wireless Networks with Self-interference Cancellation”, WiOpt’11

No exposed transmissions; Simulations only

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RCTC Design




RCTC: Rapid Concurrent Transmission Coordination in Full Duplex Wireless Networks Wenjie Zhou,...

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