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A Glimpse at Three Wireless Networking Problems

Bob Kinicki Computer Science Department rek@cs.wpi.edu Colloquium October 5, 2007. A Glimpse at Three Wireless Networking Problems. Outline. Thoughts and Mini-Motivation Wireless Networking Primer #1 Dynamic Rate Adaptation Performance problems with ARF

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A Glimpse at Three Wireless Networking Problems

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  1. Bob Kinicki Computer Science Department rek@cs.wpi.edu Colloquium October 5, 2007 A Glimpse at Three Wireless Networking Problems

  2. Outline • Thoughts and Mini-Motivation • Wireless Networking Primer • #1Dynamic Rate Adaptation • Performance problems with ARF • Rate Adaptation Algorithms • RBAR, CARA, RFT and CARAF • Wireless Sensor Networks (WSNs) • #2 Dynamic Cluster Formation • #3Power-Aware MAC Protocols • SMAC, TMAC, WiseMAC, SCP-MAC and Crankshaft October 5, 2007 Three Wireless Networking Problems

  3. My Research Space Networking 1983 2003 2006 Wireless Networking Wireless Sensor Networks October 5, 2007 Three Wireless Networking Problems

  4. The Future of Sensor Networks? October 5, 2007 Three Wireless Networking Problems

  5. Wireless Primer

  6. LAN Terminolgy 802.3:: Ethernet CSMA/CD 802.11a/b/g:: WiFi CSMA/CA 802.15.4:: ZigBee 802.11-based lower data rates, lower power Bluetooth:: TDMA - wireless Personal Area Networks (PANs) that provide secure, globally unlicensed short-range radio communication. • Clusters with max of 8: cluster head + 7 nodes WSNs October 5, 2007 Three Wireless Networking Problems

  7. Wireless LANS • Infrastructure with AP (Access Point) • Mobile Ad Hoc Networks (MANETs) • Wireless Sensor Networks (WSNs) • Interacting AP Topologies October 5, 2007 Three Wireless Networking Problems

  8. Infrastructure Internet client Access Point client client client October 5, 2007 Three Wireless Networking Problems

  9. Mobile Ad Hoc Network (MANET) Wireless Sensor Network (WSN) BS October 5, 2007 Three Wireless Networking Problems

  10. Wireless LAN Protocols (a) A sending an RTS to B. (b) B responding with a CTS to A. node D is possible hidden terminal Tanenbaum slide October 5, 2007 Three Wireless Networking Problems

  11. Virtual Channel Sensing in CSMA/CA • C (in range of A) receives the RTS and based on information in RTS creates a virtual channel busy NAV(Network Allocation Vector). • D (in range of B) receives the CTS and creates a shorter NAV. Tanenbaum slide October 5, 2007 Three Wireless Networking Problems

  12. Basic CSMA/CA possible collision !! [N. Kim] October 5, 2007 Three Wireless Networking Problems

  13. One-to-One Configuration {Ad Hoc} Access Point client October 5, 2007 Three Wireless Networking Problems

  14. One-to-One Configuration {Ad Hoc} Access Point client October 5, 2007 Three Wireless Networking Problems

  15. One-to-One Configuration {Ad Hoc} Access Point client Distance Impacts: attenuation fading interference October 5, 2007 Three Wireless Networking Problems

  16. #1 Dynamic Rate Adaptation

  17. 802.11 Physical Layer ‘Adjust transmission rate on the fly’ [N. Kim] October 5, 2007 Three Wireless Networking Problems

  18. BER vs SNR [Pavon] October 5, 2007 Three Wireless Networking Problems

  19. Throughput vs SNR [Pavon] October 5, 2007 Three Wireless Networking Problems

  20. Rate Adaptation versus Distance [J. Kim] October 5, 2007 Three Wireless Networking Problems

  21. Single AP multiple clients (homogeneous) client Node Contention: Produces collisions client client Access Point client October 5, 2007 Three Wireless Networking Problems

  22. Node Contention without RTS/CTS [N. Kim] October 5, 2007 Three Wireless Networking Problems

  23. Single AP multiple clients (heterogeneous) client client Multiple Node Effects Collisions AP queue overflow link capture hidden terminal performance anomaly different NIC cards (Rate Adaptation NOT Standardized!!) Access Point client client October 5, 2007 Three Wireless Networking Problems

  24. Unfairness [Choi] October 5, 2007 Three Wireless Networking Problems

  25. Multiple APsmultiple clients (heterogeneous) client client client client Access Point Access Point client client client client October 5, 2007 Three Wireless Networking Problems

  26. Hidden Terminals Without a hidden terminal, loss ratio ~5.5%. One hidden AP with mild sending rate (0.379 Mbps) yields: [Wong] October 5, 2007 Three Wireless Networking Problems

  27. RTS/CTS Summary • RTS/CTS can reduce collisions. • RTS/CTS can guard against and reduce hidden terminals. • RTS/CTS adds overhead that reduces throughput. • Normally, RTS/CTS is turned off! October 5, 2007 Three Wireless Networking Problems

  28. Rate Adaptation Algorithms AARF ARF AMRR CARA CROAR DOFRA Fast-LA HRC LA LD-ARF MiSer MultiRateRetry MPDU OAR ONOE PER RBARRFT RRAA SampleRate SwissRA October 5, 2007 Three Wireless Networking Problems

  29. Rate Adaptation Algorithms 1997 ARF 1998 1999 2000 2001 RBAR 2002MPDU OAR PER 2003LA MiSer SwissRA 2004AARF AMRR HRC MultiRateRetry 2005Fast-LA LD-ARF RFT SampleRate 2006 CARA CROAR DOFRA RRAA 2007 October 5, 2007 Three Wireless Networking Problems

  30. Rate Adaptation Algorithms Uses recent history and probes:ARF, AARF, SampleRate Long interval smoothing:ONOE,SampleRate Multiple rates: MultiRateRetry, AMRR, RRAA Uses RTS/CTS:RBAR, OAR, CROAR, CARA Uses RSSI to approximate SNR, each node maintains 12 dynamic RSS thresholds:LA Puts checksum on header and use NACK to signal link loss error:LD-ARF Table lookup with thresholds:HRC,MPDU(len,rSNR,count) Fragmentation: DOFRA, RFT Miscellaneous:PER, MiSer, SwissRA, Fast-LA October 5, 2007 Three Wireless Networking Problems

  31. Auto Rate Fallback (ARF) • If two consecutive ACK frames are not received correctly, the second retry and subsequent transmissions are done at a lower rate and a timer is started. • When the number of successfully received ACKs reaches 10 or the timer goes off, a probe frame is sent at the next higher rate. However, if an ACK is NOT received for this frame, the rate is lowered back and the timer is restarted. October 5, 2007 Three Wireless Networking Problems

  32. ARF and AARF October 5, 2007 Three Wireless Networking Problems

  33. Receiver Based Auto Rate (RBAR) • Receivers control sender’s transmission rate. • RTS and CTS are modified to contain info on size and rate {not 802.11 compatible}. • Uses analysis of RTS reception (RSSI) to estimate SNR and send choice back to sender in CTS. • Receiver picks rate based on apriori SNR thresholds in a lookup table. October 5, 2007 Three Wireless Networking Problems

  34. Collision Aware Rate Adaptation (CARA) CARA uses two methods for identifying collisions: • RTS probing • Clear Channel Assessment (CCA) detection RTS Probing {Idea: Assume all RTS/CTS transmission failures after a successful RTS/CTS exchange must be due to channel errors. (Note – this assumes hidden terminals are not possible) } October 5, 2007 Three Wireless Networking Problems

  35. RTS Probing CARA-1 • Data frame transmitted without RTS/CTS. • If the transmission fails, RTS/CTS exchange is activated for the next retransmission. If this retransmission fails {assume channel quality problem}, then the rate is lowered. • If retransmission with RTS/CTS is successful {assume collision occurred}, stay at same rate and send next frame without RTS/CTS. October 5, 2007 Three Wireless Networking Problems

  36. Clear Channel Assessment (CCA) ACK [J. Kim] October 5, 2007 Three Wireless Networking Problems

  37. CCA Option • Case 2: It is a collision. • Transmit without increasing failure count and lowering the transmission rate. No RTS/CTS probe is needed. • Case 1 and Case 3: • Initiate RTS/CTS probe scheme. October 5, 2007 Three Wireless Networking Problems

  38. CARA-1 (with RTS Probing) [J. Kim] October 5, 2007 Three Wireless Networking Problems

  39. CARA-2 (with CCA) [J. Kim] October 5, 2007 Three Wireless Networking Problems

  40. 802.11 MAC Fragmentation [Zhu] October 5, 2007 Three Wireless Networking Problems

  41. Rate-based Fragmentation Thresholding (RFT) • Fragmenting a frame can increase the probability of the fragment being received successfully. • Propose a dynamic fragmentation scheme with different fragmentation thresholds based on different channel conditions. • Namely, fragment sizes vary with the chosen adaptation rate. October 5, 2007 Three Wireless Networking Problems

  42. CARAF (CARA with Fragmentation) Dan Courcey’s MS thesis: Combine CARA with Fragmentation. Top Level Scheme: • Upon CCA determination of collision, use fragmentation. • If CCA shows idle, initiate RTS/CTS probe. • If probe fails lower transmission rate. {Investigate how to vary fragment size to maximize throughput and increase the likelihood of CCA case 2} October 5, 2007 Three Wireless Networking Problems

  43. Wireless Sensor Networks (WSNs)

  44. Wireless Sensor Networks • A distributed connection of nodes that coordinate to perform a common task. • In many applications, the nodes are battery powered and it is often very difficult to recharge or change the batteries. • Prolonging network lifetime is a critical issue. • Sensors often have long period between transmissions (e.g., in seconds). • Thus, a good WSN MAC protocol needs to be energy efficient. October 5, 2007 Three Wireless Networking Problems

  45. Wireless Sensor Networks • Another attribute is scalability to change in network size, node density and topology. • In general, nodes can die, join later or be mobile. • Often high bandwidth is not important. • Nodes can take advantage of short-range, mulit-hop communication to conserve energy. October 5, 2007 Three Wireless Networking Problems

  46. Wireless Sensor Networks • Sources of energy waste: • Idle listening, collisions, overhearing and control overhead. • Idle listening dominates (measurements show idle listening consumes between 50-100% of the energy required for receiving.) Idle listening:: listen to receive possible traffic that is not sent. October 5, 2007 Three Wireless Networking Problems

  47. Power Measurements October 5, 2007 Three Wireless Networking Problems

  48. Wireless Sensor Networks • Duty cycle:: ratio between listen time and the full listen-sleep cycle. • central approach – lower the duty cycle by turning the radio off part of the time. • Three techniques to reduce the duty cycle: • TDMA • Schedule contention periods • LPL (Low Power Listening) October 5, 2007 Three Wireless Networking Problems

  49. Techniques to Reduce Idle Listening • TDMA requires cluster-based or centralized control. • Scheduling – ensures short listen period when transmitters and listeners can rendezvous and other periods where nodes sleep (turn off their radios). • LPL – nodes wake up briefly to check for channel activity without receiving data. • If channel is idle, node goes back to sleep. • If channel is busy, node stays awake to receive data. • A long preamble (longer than poll period) is used to assure than preamble intersects with polls. October 5, 2007 Three Wireless Networking Problems

  50. #2Dynamic Cluster Formation

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