FD-MMAC: Combating Multi-channel Hidden and Exposed Terminals Using a Single Transceiver Yan Zhang, Loukas Lazos, Kai Chen, Bocan Hu, and Swetha Shivaramaiah Electrical and Computer Engineering University of Arizona INFOCOM 2014

Channel Access in Multi-channel Wireless Networks 05/02/2014 INFOCOM 2014, University of Arizona 2 A - D B - E C - F A B D E F C F - D A - B E - C C - A B - F D - E F - C B - A E - D f1f1 f2f2 f3f3 A set of nodes within the same collision domain share access to fixed number of channels -Schedule-based -Contention-based

The Multi-channel Hidden Terminal Problem 05/02/2014 INFOCOM 2014, University of Arizona 3 RTS A CTS B PAPA PAPA A B C hidden terminal to A A B C f1f1 C switches to f 1 t0t0 t1t1 t2t2 t3t3 collision backoff RTS C

The Multi-channel Exposed Terminal Problem 05/02/2014 INFOCOM 2014, University of Arizona 4 RTS B CTS A PBPB PBPB A B C exposed terminal to B A B C f1f1 C switches to f 1 t0t0 t1t1 t2t2 D C defers transmission

Prior-Art on Multi-channel MAC (MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 5 Split-phase designs (SP-MMAC) Frequency hopping rendezvous designs (FH-MMAC) REQ ACK RES Data control phase data phase Data f1f1 f2f2 f3f3 Dedicated control channel designs (DCC-MMAC) REQ ACK RES Data f1f1 f2f2 f3f3

Full-Duplex Multi-Channel MAC (FD-MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 6 Design a distributed MMAC protocol that: Eliminates the use of a control channel Combats the multi-channel hidden terminal problem Reduces control signaling Improves spectral efficiency by enabling the operation of exposed terminals Achieves load balancing and fairness autonomously

MAC for Multi-channel Networks ( MMAC) PAPA BCN B 05/02/2014 INFOCOM 2014, University of Arizona 7 ACK B A B A B PHY MAC PAPA PAPA t ACK tete BCN B PHY CRC ID B t ACK BCN B : BCN B Communication in Full-Duplex (FD) Mode

MAC for Multi-channel Networks ( MMAC) A B PAPA BCN B CO TO RO CO: Collision region - No packet decodable due to collision of P A with BCN B C is only allowed to transmit in TO region TO: Transmitter-only region - P A decodable - Exposed terminal 05/02/2014 INFOCOM 2014, University of Arizona 8 RO: Receiver-only region - BCN B decodable - Hidden terminal C C C FD Carrier Sensing

MAC for Multi-channel Networks ( MMAC) BCN=Yes A B PAPA BCN B CO TO RO C1C1 C2C2 C3C3 C4C4 Use EVM measurement to differentiate TO from CO capture effect Capture effect: C may have a low EVM at C 2 Use RSS to differentiate C 1 from C 2 If RSS is beyond threshold, C assumes it is in the CO Use BCN decodability to differentiate RO from TO/CO 05/02/2014 INFOCOM 2014, University of Arizona 9 BCN=No EVM < γ EVM EVM > γ EVM RSS < γ RSS BCN=No EVM < γ EVM RSS > γ RSS Region Classification Rules

MAC for Multi-channel Networks ( MMAC) C hidden terminal to A A B PAPA BCN B 05/02/2014 INFOCOM 2014, University of Arizona 10 A B C C switches to f 1 t0t0 t1t1 t2t2 defer PHY MAC PAPA PAPA sense ACK B BCN B t (f1)(f1) Combating Multi-channel Hidden Terminals

MAC for Multi-channel Networks ( MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 11 A B PAPA BCN B CO TO RO C D PCPC BCN D A B C PHY MAC PAPA PAPA ACK B BCN B D PHY MAC PCPC PCPC sense backoff C switches to f 1 t2t2 TO region ACK D BCN D (f1)(f1) (f1)(f1) Enabling Exposed Terminal Transmissions

RF Signal Correlation 05/02/2014 INFOCOM 2014, University of Arizona 12 Detect known bit patterns in the presence of collisions C A PCPC B ACK B BCN D ACK B PCPC

MAC for Multi-channel Networks ( MMAC) Switch channel based on Channel State Table (CST) 05/02/2014 INFOCOM 2014, University of Arizona 13 A contention-based, time-slotted protocol based on CSMA/CA No control message overhead related to virtual carrier sensing Destination’s State Diagram

MAC for Multi-channel Networks ( MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 14 f1f1 A B E Channel State Table at destination E (f1)(f1) Channel #Idle time f1f1 t curr f2f2 f3f3 f4f4 E is in RO region of A-B (BCN B decodable) Destination Operation Example

MAC for Multi-channel Networks ( MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 15 f1f1 A B E Channel State Table at destination E (f1)(f1) Channel #Idle time f1f1 t ACK f2f2 t curr f3f3 f4f4 E is in RO region of A-B (BCN B decodable) Destination Operation Example E updates f 1 ’s idle time using t ACK in BCN B (f2)(f2) f2f2 C D E is in TO region of C-D (cannot decode BCN D ) E switches to f 2 because f 2 has earliest idle time

MAC for Multi-channel Networks ( MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 16 f1f1 A B E Channel State Table at destination E Channel #Idle time f1f1 t ACK f2f2 t curr +t MTU f3f3 t curr f4f4 E is in RO region of A-B (BCN B decodable) Destination Operation Example E updates f 1 ’s idle time using t ACK in BCN B (f2)(f2) f2f2 C D E is in TO region of C-D (cannot decode BCN D ) E switches to f 2 because f 2 has earliest idle time E updates f 2 ’s idle time using worst-case estimate E switches to f 3 which is currently idle

MAC for Multi-channel Networks ( MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 17 Sender’s State Diagram

MAC for Multi-channel Networks ( MMAC) 05/02/2014 INFOCOM 2014, University of Arizona 18 Protocol Operation Example A B P A (f 1 ) BCN B (f 1 ) CO TO RO D C P C (f 1 ) A B C PHY MAC PAPA PAPA D sense backoff ACK B BCN B PHY MAC early termination switch sense BCN B PHY MAC PCPC PCPC D resides in f 2 BCN D

Performance Evaluation 05/02/2014 INFOCOM 2014, University of Arizona 19 Simulation setup (OPNET) - 3 orthogonal channels of 2Mbps - Poisson distributed traffic with parameter λ - Protocols to compare: FD-MMAC SP-MMAC, and DCC-MMAC - Simulated topology

Aggregate Throughput – Single Collision Domain 05/02/2014 INFOCOM 2014, University of Arizona 20 3, 6 flows 9, 12 flows

Aggregate Throughput – Exposed/Hidden Terminals 05/02/2014 INFOCOM 2014, University of Arizona 21 One exposed terminal One exposed plus one hidden terminal

Final Remarks 05/02/2014 INFOCOM 2014, University of Arizona 22 Proposed a distributed MMAC protocol that exploits full-duplex communications Eliminates the need for a control channel Coordinates channel access at low control overhead Combats multi-channel hidden terminal problem Achieves destination discovery and load balancing autonomously Improves spatial channel reuse by enabling the operation of multi-channel exposed terminals

Thank you! 05/02/2014 INFOCOM 2014, University of Arizona 23

MAC for Multi-channel Networks ( MMAC) Traditional carrier sensing - Estimate carrier state : free vs. busy - Defer from transmission if carrier is busy FD carrier sensing - Classifies a node’s location relative to an ongoing transmission into three regions - Determines the node’s operation state based on region - Integrates PHY-layer techniques: Error Vector Magnitude (EVM) and Received Signal Strength (RSS) measurements Advantages of FD carrier sensing - Eliminates multi-channel hidden terminal problem - Creates transmission opportunities for exposed terminals 05/02/2014 INFOCOM 2014, University of Arizona 24 FD Carrier Sensing

MAC for Multi-channel Networks ( MMAC) - C needs to wait until P A ’s transmission is completed to verify if P A can be correctly decoded - C cannot decode P A if it switches to a busy channel in the middle of P A ’s transmission Solution: C measures EVM values on received symbols in order to evaluate decodability of P A before packet reception Transmitted symbol Received symbol Problems with traditional decoding method 05/02/2014 INFOCOM 2014, University of Arizona 25 - EVM is computed over window size n - Transmitted symbol is unknown to C for arbitrary data packet - The symbol closest to the received one is selected as ideal symbol when computing EVM Evaluating Decodability of Data Packet

MAC for Multi-channel Networks ( MMAC) Normalized correlation for 10 BCN packets - P A : 500-bit payload - BCN D : 50-bit payload - C applies signal correlation to detect BCN D packets D C BCN D A PAPA - Distance C-A = Distance C-D = 7 ft Correlation peaks correspond to BCN D transmissions - Detection threshold = /02/2014 INFOCOM 2014, University of Arizona 26 RF Correlation Measurements

MAC for Multi-channel Networks ( MMAC) Experiment setup - USRP devices over the 2.4GHz band - QPSK modulation at a transmission rate of 2Mbps - Applied phase/frequency offset correction and time sync using 88-bit preamble sequence A B PAPA BCN B CO TO RO C1C1 C2C2 C3C3 C4C4 - Distance A-B = 7 ft - A and B transmit concurrently - P A : 500-bit payload - BCN B : 50-bit payload P A and 500 BCN B transmitted - EVM, RSS, and decodability of BCN B are measured 05/02/2014 INFOCOM 2014, University of Arizona 27 Experimental Evaluation of Region Classification

MAC for Multi-channel Networks ( MMAC) EVM CDF at RO, CO, and TO regions Average RSS at different positions 05/02/2014 INFOCOM 2014, University of Arizona 28 EVM and RSS Mesurements

Transmission Delay 05/02/2014 INFOCOM 2014, University of Arizona 29 Average delay for transmitting a batch of 100 data packets