Media Access Control. Cri$que #3. CSMA/CA Carrier Sense Mul$ple Access, Collision Avoidance. Hidden Terminal Problem. Virtual Carrier Sense: RTS/CTS

Transcription

1 ri$que #3 Due nex Tuesday K. Klues, G. Hackmann, O. hipara and. Lu, omponen ased rchiecure for Power Efficien Media ccess onrol in Wireless Sensor Neworks, M onference on Embedded Neworked Sensor Sysems (SenSys), November Media ccess onrol henyang Lu Deparmen of ompuer Science and Engineering 1 M/ arrier Sense Mul$ple ccess, ollision voidance Hidden Terminal Problem 3 4 Virual arrier Sense: /TS Power Saving M Many applicavons expeced lifevme: monhs or years cual lifevme: bayeries: 2000 mh (if you re lucky) 2420 radio: 19.7 m when idle bu awake (RX mode) 2000 mh / 19.7 m = h 6 days TS This is a problem! SoluVon: keep he radio asleep mos of he Vme Duy cycles on he order of 0.1% 1% NV 5 6 1

2 Types of Power Saving Ms S M: Synchronized ing Scheduled conenvon: nodes periodically wake up in unison, conend for access o channel, hen go back o sleep S M [Ye 2002], T M [van Dam 2003] hannel polling: nodes independenly wake up o sample radio channel M [Polasre 2004], X M [ueyner 2006] Time Division MulVple ccess (TDM): nodes mainain schedule of when o wake and when hey re allowed o ransmi DRND [Rhee 2006] Hybrid proocols: SP [Ye 2006], Z M [Rhee 2005], Funneling M [hn 2006], [IEEE 2003], Nodes say asleep mos of he Vme Periodically wake up for shor inervals o see if anyone s sending Low energy consumpvon when raffic is low Sacrifice laency for longer lifevme 7 8 S M: Sending a Packe S M: Sending a Packe Time awake divided ino wo pars: SYN and Node periodically send SYN packe o keep clocks in sync M/ used o conend for access o wireless channel SYN Wans o SYN secvon used for ransmikng daa M/ again, followed by /TS SYN Wans o SYN Wans o send daa Wans o send daa Wans o SYN & send daa Wans o SYN & send daa 9 10 S M: Sending a Packe Look a S M TS for someone else go o sleep Overhearing avoidance does one /TS hen sends daa for res of frame pplicavon performance >> nodelevel fairness ll daa packes are Ked Packe fragmenavon = higher reliabiliy TS DT K DT K Winner Power savings over sandard M/ M Long lisening inerval is expensive Everyone says awake unless somebody ransmis Time sync overhead even when nework is idle /TS and K overhead when sending daa

3 3 M 13 Look a M Low overhead when nework is idle Simple o implemen eyer power savings, laency, and hroughpu han S M Lower duy cycle longer preambles: Higher average laency Higher cos o send Higher cos o overhear 14 M: Room for Improvemen 15 X M: Overhearing voidance 16 Desinaion X M: Preamble King 17 Desinaion K Look a X M eyer laency, hroughpu, and power consumpvon han M LiYle energy consumed by overhearing SVll simple o implemen On average, cus preamble by half sending packes is svll expensive 18

4 4 SP: Scheduled onen$on + hannel Polling 19 SP: dap$ve hannel Polling dd N sub inervals whenever packe received Reduces laency of bursy daa onvnue adding sub inervals as long as hey re needed, and as long as here s room 20 Look a SP hannel polling: low overhead when idle Scheduled conenvon: low cos o send Low laency for mulv hop raffic omplex o implemen Overhead due o Vme synchronizavon Reduced by piggybacking on daa packes 21 TDM 22 Time Sync Frame Slo Look a TDM Predicable laency, hroughpu, and duy cycle Low packe loss due o less conenvon Schedules mus be changed when nodes leave/ener neighborhood Time synchronizavon overhead Slos wased when scheduled node has nohing o send omplex in mulv hop neworks 23 Z M: TDM + hannel Polling 24 Time Sync

5 Look a Z M Reduces wase from unused slos Higher hroughpu and lower laency Throughpu, laency, and duy cycle no worse han pure TDM Nodes svll say awake if no one ransmis SVll overhead from Vme sync So Why re They Rarely Used? M proocols have radio dependen requiremens beyond normal applicavon code Turn radio on/off, low laency I/O, carrier sense, ec. Typically implemened by forking radio sacks Hard o implemen Mus be mainained as original radio sack changes M layers suppored by TinyOS oday: 2420: ox M 2 (enhancemens o X M) 1100 and 2500: Wake on Radio, X M, M, ox M 1, ox M Unified pproach: ML M Layer rchiecure (ML) [Klues 07] Low level absracvons of radio funcvonaliy High level implemenavons of common M logic Used o creae 5 plaqorm independen M M, X M, SP, TDM, varian of Z M References [S M] W. Ye, J. Heidemann and D. Esrin, Medium ccess onrol wih oordinaed, dapvve ing for Wireless Sensor Neworks, IEEE/M TransacVons on Neworking, June [ M] J. Polasre, J. Hill, and D. uller, VersaVle Low Power Media ccess for Wireless Sensor Neworks, M onference on Embedded Neworked Sensor Sysems (SenSys'04), November [Z M] I. Rhee,. Warrier, M. ia, and J. Min, Z M: a Hybrid M for Wireless Sensor Neworks, M onference on Embedded Neworked Sensor Sysems (SenSys'05), November [X M] M. ueyner, G. Yee, E. nderson, R. Han, X M: Shor Preamble M Proocol for Duy ycled Wireless Sensor Neworks, M onference on Embedded Sensor Sysems (SenSys 06), [SP] W. Ye, F. Silva, and J. Heidemann, Ulra Low Duy ycle M wih Scheduled hannel Polling, M onference on Embedded Neworked Sensor Sysems (SenSys'06), November