1. Wireless Networking & Mobile Computing CS 752/852 - Spring 2012 Tamer Nadeem Dept. of Computer Science Lec #5: Advanced MAC Schemes Dual Busy Tone & Collision Notification

2. Page 2 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Dual Busy Tone Multiple Access (DBTMA) : A Multiple Access Control Scheme for Ad Hoc Networks * Dual Busy Tone Multiple Access (DBTMA) : A Multiple Access Control Scheme for Ad Hoc Networks * (Z. Haas and J. Deng) * Slides adapted from Z. Haas This paper completely solves hidden and exposed terminal problems

3. Page 3 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Key Idea & Goals & Main Results Key idea:  Continuously protect data packet transmission  Use out-band channels to distribute information Goals  Solve hidden & exposed terminal problems Main Results  DBTMA: two out-of-band busy tones & RTS  Completely solve hidden & exposed terminal problems

4. Page 4 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Related Works  BTMA (Busy Tone Multiple Access, F. A. Tobagi & L. Kleinrock 1975):  Using two channels: data channel & control channel  A control center - basestation  When base station senses the transmission of a terminal, it broadcasts a busy tone signal to all terminals, keeping them (except the current transmitter) from accessing the channel  RI-BTMA (Receiver-Initiated Busy Tone Multiple Access, C. Wu & V. O. K. Li 1987)  Time is slotted (similar to slotted ALOHA & need time clock synchronization)  A packet preamble is sent to intended receiver by the transmitter  Receiver sets up an out-of-band busy tone and waits for the data  When sensing busy tone, transmitter sends the data packet  FAMA (Floor Acquisition Multiple Access, C. L. Fuller & J.J Garecia-Luna-Aceves 1995)  FAMA-NPC (NPC = on-persistent packet sensing) oMACA  FAMA-NCS (NCS non-persistent carrier sensing) oSensing carrier before sending RTS If clear, sends RTS Otherwise, waiting a random time, sensing carrier again oCTS is more larger than RTS

5. Page 5 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing DBTMA Two narrow-bandwidth tones BTt (Transmitter Busy Tone) Set up by the node which has data to send Stop when completing transmitting RTS BTr (Receiver Busy Tone) Set up by the node which receives RTS Stop when completely receives the data packet All nodes sensing any busy tone are not allowed to send RTS Any node sensing no busy tone is allowed to transmit RTS CA DATA RTS DATA RTS B

6. Page 6 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Functionalities of Busy Tones BTr (set up by receiver)  Notifying the RTS sender that RTS has been received and channel has been acquired  Announcing to its neighbor nodes that it is receiving data packet and they should refrain from accessing the channel BTt (set up by sender)  Providing protection for the RTS packet

7. Page 7 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Seven DBTMA Operation States IDLE  Node with on packets to send stays in IDLE state CONTEND  Node has data to send but it is not allowed to send RTS, it stays in CONTEND state S_RTS  Node sending RTS is in S_RTS state S_DATA  Node sending data is in S_DATA state WF_BTR  RTS packet sender waiting for the ACK from its intended receiver is in WF_BTR state WF_DATA  Receiver waiting for DATA is in WF_DATA state WAIT  Node send out RTS and senses BTr and waits a mandatory time, it is WAIT state

8. Page 8 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Finite State Machine of DBTMA

9. Page 9 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing More Details for DBTMA When A has data to send Senses BTt and BTr If both are clear Turns on BTt Sends out RTS and enters S_RTS state Turns off BTt at the end of RTS transmission and gets out S_RTS state Sets a timer for expected BTr and enters WF_BTR state If BTr is sensed, enters WAIT state and waits for tmw, then enters S_DATA state and sends data packet Otherwise, timer goes to zero, A goes to IDLE state Enters IDLE state Otherwise Sets a random timer and goes to CONTENT state If BTt or BTr is still sensed when timer goes to zero, A goes to IDLE state Otherwise, A turns on BTt and enters S_RTS state and sends out RTS if no any busy tone signal is sensed

10. Page 10 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing More Details for DBTMA When B receives RTS, B turns on BTr and sets a timer for expected data packet and enters WF_DATA state If B has not received data packet before timer goes to zero  B turns off BTr and goes to IDLE state Otherwise, B receives data packet and turns off its BTr when completely getting the data packet  When BTr sensed by any Other Node which is in S_RTS state, the node aborts it RTS and goes to IDLE state

11. Page 11 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Time Diagram of DBTMA RTS DATA A B BTr of B BTt of A tmw RTS C

12. Page 12 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Channel Throughputs of DBTMA (Single Broadcast Region) Capacity = 1 Mbps Data packet = 4096 b RTS = 200 b 20 nodes in 50 by 50 m^2 Radio transmission range = 35m Maximum propagation delay = 0.12

13. Page 13 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Impact of Busy Tone Detection Delay RTS DATA A B BTr of B BTt of A tmw C Busy Tone Detection Delay

14. Page 14 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Performance Analysis (single broadcast domain case) Assumptions: A lot of nodes and all nodes are in the same broadcast domain No channel fading, capture effect Packet collisions are the only reason for packet errors Data processing time and transmit/receive turn around time are negligible Bandwidth consumption of busy tones is negligible compared with data channel

15. Page 15 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Channel Throughput (ad-hoc network) Capacity = 1 Mbps Data packet = 4096 b RTS = 200 b Radio transmission range = 2 km Propagation delay = 6.7

16. Page 16 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Comparisons of Channel Throughput Capacity = 256 kbps Data packet = 4096 b RTS = 200 b Each node are 6 km from each other Propagation delay = 20

17. Page 17 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Comparison of Different Length of Control Packet Full connected network Every node randomly choose its destination for each generated data packet Capacity = 1 Mbps Data packet size =4096 b 20 nodes in 50 by 50 m^2 Radio transmission range = 35 m Propagation delay = 0.12

18. Page 18 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Network Utilization of DBTMA in Multi-Hop Networks 50 nodes in 400 by 400 m^2 Radio transmission range = 100 m RTS size = 200 b Packet size = 4096 b Capacity = 1 Mbps Propagation delay = 0.33 Packet arrival at each node is Poisson distributed Each node randomly selects a neighbor as the destination of each packet Modified DBTMA 4.2 FAMA-NCS 2.4 DBTMA 5.7 RI-BTMA 4.8 MACA 2.2

19. Page 19 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 19 Summary DBTMA does solve hidden & exposed terminal problems DBTMA is based on the idea presented in RI-BTMA Some idea  Using some kind of out-of-band control channel to propagate some info to achieve some performance targets

20. Page 20 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Towards Collision Detection in Wireless Networks* Towards Collision Detection in Wireless Networks* (Souvik Sen, Naveen Santhapuri, Romit Roy Choudhury, Srihari Nelakuditi) * Slides adapted from Souvik Sen

21. Page 21 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 21 Collision in Wireless Networks T1RT2 t0t0 t1t1 ACK Timeout Retransmit time Collision

22. Page 22 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 22 Collision in Wireless Networks T1RT2 Collision t0t0 t1t1 Retransmit time Not Efficient! T1 should have stopped right after collision ACK Timeout

23. Page 23 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 23 Collision in Wired Networks ✦ Transmitter aborts transmission on collision ✦ Transmitter senses the signal while transmitting ✦ If (sensed != transmitted), abort T1RT2 Collision Ethernet BUS Collision Detection (CSMA/CD)

24. Page 24 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 24 Is CSMA/CD Beneficial in Wireless? R2 Collision Detected Collision T2 T1 R1 T3 R3 Dont Transmit!

25. Page 25 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 25 Is CSMA/CD Beneficial in Wireless? R2 Collision Detected T2 T1 R1 T3 R3 Dont Transmit! Abort Tx! Collision

26. Page 26 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 26 Is CSMA/CD in Wireless Beneficial? R2 Collision Detected T2 T1 R1 T3 R3 Channel free now

27. Page 27 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 27 Is CSMA/CD in Wireless Beneficial? R2 Collision Detected T2 T1 R1 T3 R3 CSMA/CD frees the channel for other transmissions CSMA/CD frees the channel for other transmissions Lets Transmit!

28. Page 28 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Can we imitate CSMA/CD on Wireless?

29. Page 29 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 29 Practical Requirements? 1. Transmitter cannot detect collision Receiver needs to detect it Tx Rx Collision!

30. Page 30 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 30 Practical Requirements? 1. Transmitter cannot detect collision Receiver needs to detect it 2. Receiver needs to convey collision notification to the transmitter Tx Rx Collision!

31. Page 31 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 31 1. Transmitter cannot detect collision Receiver needs to detect it 2. Receiver needs to convey collision notification to the transmitter 3. Transmitter needs an additional antenna To receive notification Tx Rx Collision! Practical Requirements?

32. Page 32 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 32 Overview MAC PHY CrossLayer MAC PHY CrossLayer Data Transmission (S1) S=S1 TxRx If Collision, Notify Tx If Notification, Abort Tx Notify Collision (S2)

33. Page 33 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 33 Overview S=S1+S2 MAC PHY CrossLayer MAC PHY CrossLayer Notify Collision (S2) Data Transmission (S1) S=S1 TxRx If Notification, Abort Tx If Collision, Notify Tx

34. Page 34 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 34 Two Key Challenges S=S1+S2 2. Detect Collision in real time 2. Detect Collision in real time 1. Find Notification on Listening Antenna 1. Find Notification on Listening Antenna MAC PHY CrossLayer MAC PHY CrossLayer Notify Collision (S2) Data Transmission (S1) TxRx If Notification, Abort Tx If Collision, Notify Tx

35. Page 35 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing CSMA/CN key idea: Correlation 2. Detect Collision in real time 2. Detect Collision in real time 1. Find Notification on Listening Antenna 1. Find Notification on Listening Antenna

36. Page 36 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 36 Challenge 1: Detecting Notification Hard to decode notification on same channel Self-signal too strong Let Tx and Rx share a unique signature Tx correlates with shared signature Detects collision notification, aborts Observe: No decoding, just correlate MAC PHY

37. Page 37 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 37 Notification Signature Correlation Self Signal Challenge 1: Detecting Notification

38. Page 38 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 38 Whenever there is a notification, there is a jump in correlation Whenever there is a notification, there is a jump in correlation Correlation Sample Number Challenge 1: Detecting Notification

39. Page 39 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 39 Data R Correlate (Sign(R1)) Sign(R1)Sign(R2) Collision T1 T2 R2 R1 Collision Correlation, Notification, and Abort

40. Page 40 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 40 Data R Sign(R1) Corr (Sign(R1)) Notification ! Stop Tx Collision T1 T2 R2 R1 Correlate (Sign(R1)) Sign(R1)Sign(R2) Collision Correlation, Notification, and Abort

41. Page 41 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 41 Performance Evaluation 7 node USRP testbed Zigbee CC2420 PHY Max data rate: 250Kbps Signature size: 5 bytes Compare with 802.11-like and PPR PPR detects interfered portion of received packet Transmitter sends only the interfered portion

42. Page 42 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 42 Notification Detection at Tx Notification Signal << Self Signal How weak can the notification signal be? MAC PHY

43. Page 43 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 43 How weak the notification signal be? Signal power Self Signal Notification Signal } 18 dB ✔

44. Page 44 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 44 How weak the notification signal be? Signal power ✘ } 18 dB Self Signal Notification Signal

45. Page 45 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 45 Interference Detection at Rx Interference detection accuracy of 93% Receiver should detect interference quickly Quicker detection Faster Tx abortion MAC PHY

46. Page 46 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 46 Interference Detection: Speed CSMA/CN predicts collision within 7 bytes Bytes after interferer started

47. Page 47 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 47 Testbed Experimentation One link doing CSMA/CN CSMA/CN link has an exposed and hidden terminal Whenever CSMA/CN link fails due to interference CSMA/CN link stops Exposed terminal transmits reducing channel wastage

48. Page 48 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 48 Testbed Throughput PPR continues to transmit under collision, worse than CSMA/CN

49. Page 49 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 49 Traced Based Evaluation Upto 50% gain in per link throughput 50% Throughput in Kbps

50. Page 50 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing 50 Summary CSMA/CN imitates CSMA/CD in wireless Rx uses correlation to detect interference Tx uses correlation to detect notification Others can utilize freed-up channel

51. Page 51 Spring 2012 CS 752/852 - Wireless Networking and Mobile Computing Questions