RCTC: Rapid Concurrent Transmission Coordination in Full Duplex Wireless Networks Wenjie Zhou, Kannan Srinivasan, Prasun Sinha Department of Computer Science and Engineering The Ohio State University {zhouwe, kannan, 1

2 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

Full duplex doubles the throughput When both Alice and Bob have packets However, traffic tends to be asymmetric 3 Traffic Pattern and Full Duplex

Traffic Asymmetry and Full Duplex 4 I’m listening “Hi Bob” Busytone packet (fake packet) [MobiCom’11] A waste of channel resources How to use full duplex beyond 2 nodes?

Other opportunities exist… 5 Bob Ellie Alice Charlie Floyd Secondary transmission Introduced in ContraFlow [WiOpt’11] Gauss Enabling exposed and secondary transmission achieves 3X throughput More exposed transmissions enabled, even higher throughput Primary transmission Exposed transmission Hellen

Transmission Modes Bi-directional Transmission Mode Unidirectional Mode Secondary Transmission Mode 6 Bob AliceCharlie Bob Alice Bob Alice Ellie Floyd Ellie Floyd

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 7

RCTC Design 8 1. Rapid Coordination 2. Exposed terminal identification 3. History based receiver selection 4. Exposed terminal suppressing

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] – ec [MobiCom’12] Gold code: – Length: 127 bits – Number of signatures: 129 – Duration: 6.5 μs (BPSK, 20MHz bandwidth) 9 Self correlation results Cross correlation results

Bi-directional Transmission Mode 10 Alice : Bob : SBSB SASA SASA Packet for Bob Packet for Alice Alice’s signatureBob’s signature Bob Alice

Unidirectional Mode 11 Alice: Bob : SBSB SASA SHSH Packet for Bob Busytone for hidden terminal Ellie : Packet Floyd Half duplex signature Bob Alice Ellie Floyd

Secondary Transmission Mode 12 Alice : Bob : SBSB SASA SHSH Packet for Bob Packet for Charlie Bob Alice Charlie Ellie Floyd Ellie : Packet Floyd

RCTC Design Rapid Coordination 2. Exposed terminal identification 3. History based receiver selection 4. Exposed terminal suppressing

14 Bob Ellie Alice Floyd Exposed Terminal Identification Time Signal Strength (dB) Received signal from Alice SIR for data rate d AB Received signal from Ellie Time Signal Strength (dB) Received signal from Ellie SIR for data rate d EF Received signal from Alice Conflict constraints for exposed terminal

SBSB SASA Exposed Terminal Constraint at Bob 15 SBSB SASA Bob Alice Ellie SHSH SHSH

SBSB SASA Signal Strength Reflection 16 SBSB SASA Bob Alice Ellie SHSH SHSH

RCTC Design Rapid Coordination 2. Exposed terminal identification 3. History based receiver selection 4. Exposed terminal suppressing

Ellie History Based Receiver Selection 18 Set p to 1 upon a successful transmission Halve p upon a failed transmission SBSB SASA Bob Alice ExMap: {TX, RX, p} Primary TxExposed Rxp AliceMatt0.25 AliceFloyd1 AliceNeil0.125 AliceLeonard0 BobAlice0.125 ……… 1

RCTC Design Rapid Coordination 2. Exposed terminal identification 3. History based receiver selection 4. Exposed terminal suppressing

Exposed Terminal Suppressing 20 Unidirectional ModeBi-directional Mode How to distinguish? Bob Alice Ellie SASA Bob Alice Ellie SHSH

Exposed Terminal Suppressing 21 Bob Alice Ellie Bi-directional Mode SBSB SASA SFSF {RX, p lost } in certain period {Bob, 0.5} > ∆ Send S F Full duplex signature

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 22

USRP Testbed 23 ~59% ~78%

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

Throughput Breakdown 25 Significant exposed transmission opportunities Limited secondary transmission opportunities 30 APs50 APs

AP Network X compared with FDNative Comparable fairness

Ad hoc network 27 54% gain over FDNative

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 28

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Backup Slides 30

Multiple Datarates 31 Bob Ellie SHSH

Different gain for AP and ad hoc network 32

Different gain for AP and ad hoc network 33

Throughput Breakdown 34 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

AP network (different flows) 35 35% to 111% higher throughput

AP network (different parameter) 36

AP network (download ratio) % to 90.9% higher throughput

Ad hoc network 38 more opportunities for secondary tx Average gain over FDNative changes: (a) from 9% to 54%; (b) from 1% to 29%.

39 Node 1->Node 2 : primary transmission P ij : the received signal strength from node i to node j Δ d : a predefine threshold related with data rate Node 2 Node 4 Node 1 Node 5 P 45 /P 15 > Δ d, AND P 12 /P 42 > Δ d Exposed Node Identification

Signal Strength Reflection 40 TX: RX: S RX S TX SHSH EX:

History Based Receiver Selection 41 Set p to 1 upon a successful transmission. Halve p upon a failed transmission TX: RX: S RX S TX SHSH EX: ExMap: {TX, RX, p} TX RX 1, 0.25 RX 2, 1 RX 3, RX 4, 0

Exposed Terminal Suppressing 42 TX: RX: S RX S TX SHSH EX: TX: RX: S RX S TX Collision at TX!!! TX: RX: S RX S TX Suppressing exposed transmission SFSF

Related Work 43 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

Three Antenna Design (with 2 RF chains and some additional h/w) 44 “Achieving Single Channel, Full Duplex Wireless Communication”, MobiCom’10 ~ 30 dB ~ 25 dB ~ 15 dB

Two Antenna Design (with ~ 3 RF chains) 45 “Full-Duplex Wireless Communications Using Off-The-Shelf Radios: Feasibility and First Results”, ASILOMAR’10 Antenna separation (AS) Analog cancellation (AC) Digital cancellation (DC) c 1 = - (h ab /h z )x 1

Two Antenna Design (with 2 RF chains and some additional h/w) 46 “Practical, real-time, full duplex wireless”, MobiCom’11 ~ 30 dB ~ 43 dB

Two Antenna Design (with 2 RF chains and some additional h/w) 47 “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)

Two Antenna Design for MIMO-FD (with 2 RF chains and phase shifter) 48 “MIDU: Enabling MIMO Full Duplex”, MobiCom’12 Receive Cancellation Transmit Cancellation 20 dB - 30 dB22 dB - 30 dB

Two Antenna Design for MIMO-FD (contd.) (with 2 RF chains and phase shifter) 49 “MIDU: Enabling MIMO Full Duplex”, MobiCom’12

Feasibility of One Antenna Design (with 2 RF chains and addl. h/w) 50 “Picasso: Flexible RF and Spectrum Slicing”, SIGCOMM’12 Not a real full duplex system (TX, RX on different spectrum) 13 dB - 20 dB30 dB

Prior Art: MAC Layer for FD (1 of 3) 51 “Practical, real-time, full duplex wireless”, MobiCom’11 No exposed or secondary transmission

Prior Art: MAC Layer for FD (2 of 3) 52 “Pushing the limits of Full-duplex: Design and Real-time Implementation”, Technical Report’11 (Constraint: A node cannot start new transmission while receiving) AP->M 1, M 1 ->AP AP->M 1, M 2 ->AP No exposed transmissions

Prior Art: MAC Layer for FD (3 of 3) 53 “Efficient and Fair MAC for Wireless Networks with Self-interference Cancellation”, WiOpt’11 No exposed transmissions; Simulations only

RCTC Design Rapid Coordination 2. Exposed terminal identification 3. History based receiver selection 4. Exposed terminal suppressing