The ContikiMAC Radio Duty Cycling Protocol

Transcription

1 The ConikiMAC uy Cycling Proocol Adam unkels SICS Technical Repor T211:13 ISSN ecember 211 Absrac Low-power wireless devices mus keep heir radio ransceivers off as much as possible o reach a low power consumpion, bu mus wake up ofen enough o be able o receive communicaion from heir neighbors. This repor describes he ConikiMAC radio duy cycling mechanism, he defaul radio duy cycling mechanism in Coniki 2., which uses a power efficien wake-up mechanism wih a se of iming consrains o allow device o keep heir ransceivers off. Wih ConikiMAC, nodes can paricipae in nework communicaion ye keep heir radios urned off for roughly 99% of he ime. This repor describes he ConikiMAC mechanism, measures he energy consumpion of individual ConikiMAC operaions, and evaluaes he efficiency of he fas sleep and phase-lock opimizaions. 1 Inroducion Low-power wireless devices mus mainain sric power budges o aain years of lifeime. Of all componens on a low-power wireless device, he wireless ransceiver ofen has he highes power consumpion. The wireless ransceiver consumes as much power when passively lisening for ransmissions from oher devices as i does when acively ransmiing, so he ransceiver mus be compleely urned off o save power. Since he device is no able o receive any daa when he ransceiver is urned off, a duy cycling mechanism mus be used o urn he ransceiver on every now and hen. Over he years, numerous duy cycling mechanisms have been proposed (see e.g. ua and unkels for a more horough review of duy cycling mechanisms [9]). This documen describes he ConikiMAC duy cycling mechanism, he defaul duy cycling mechanism in Coniki 2. ConikiMAC is designed o be simple o undersand and implemen. ConikiMAC uses only asynchronous mechanisms, no signaling messages, and no addiional packe headers. ConikiMAC packes are ordinary link layer messages. ConikiMAC has a significanly more power-efficien wake-up mechanism ha previous duy cycling mechanisms. This is achieved by precise iming hrough a se of iming consrains. In addiion, Coniki- MAC uses a fas sleep opimizaion, o allow receivers o quickly deec false-posiive wake-ups, and a ransmission phase-lock opimizaion, o allow run-ime opimizaion of he energy-efficiency of ransmissions. The mechanisms in ConikiMAC are inspired by exising duy cycling proocols. The idea of periodic wake-ups has been used by many proocols, such as B-MAC [21], X-MAC [1], and BoX-MAC [18]. The phase-lock opimizaion has been previously suggesed by WiseMAC [11] and has since been used by oher proocols as well [14]. The use of muliple copies of he daa packe as a wake-up srobe has previously been used by he TinyOS BoX-MAC proocol [18]. The res of his repor is srucured as follows. Secion 2 presens he ConikiMAC mechanism and is underlying principles. Secion 3 describes he implemenaion of ConikiMAC in Coniki 2.. Secion 4 evaluaes he energy efficiency of ConikiMAC, boh wih micro benchmarks and in a daa collecion nework. Relaed work is reviewed in Secion and Secion 6 concludes he repor. 1

2 Send daa packes unil ack received i a A Recepion window aa packe aa packe A A aa packe Acknowledgemen packe Ack Transmission deeced CCA r c r CCA d Figure 1: ConikiMAC: nodes sleep mos of he ime and periodically wake up o check for radio aciviy. If a packe ransmission is deeced, he receiver says awake o receive he nex packe and sends a link layer acknowledgmen. To send a packe, he sender repeaedly sends he same packe unil a link layer acknowledgmen is received. Send daa packes during enire period Transmission deeced Recepion window aa packe Figure 2: Broadcas ransmissions are sen wih repeaed daa packes for he full wake-up inerval. 2 ConikiMAC ConikiMAC is a radio duy cycling proocol ha uses periodical wake-ups o lisen for packe ransmissions from neighbors. If a packe ransmission is deeced during a wake-up, he receiver is kep on o be able o receive he packe. When he packe is successfully received, he receiver sends a link layer acknowledgmen. To ransmi a packe, a sender repeaedly sends is packe unil i receives a link layer acknowledgmen from he receiver. Packes ha are sen a broadcass do no resul in linklayer acknowledgmens. Insead, he sender repeaedly sends he packe during he full wake-up inerval o ensure ha all neighbors have received i. The principle of ConikiMAC is shown in Figure 1 and Figure 2. Figure 3: The ConikiMAC ransmission and CCA iming. 2.1 ConikiMAC Timing ConikiMAC has a power-efficien wake-up mechanism ha relies on precise iming beween ransmissions. ConikiMAC wake-ups use an inexpensive Clear Channel Assessmen (CCA) mechanism ha uses he Received Signal Srengh Indicaor (RSSI) of he radio ransceiver o give an indicaion of radio aciviy on he channel. If he RSSI is below a given hreshold, he CCA reurns posiive, indicaing ha he channel is clear. If he RSSI is above he hreshold, he CCA reurns negaive, indicaing ha he channel is in use. The ConikiMAC iming is shown in Figure 3. The iming requiremens from he figure are: i : he inerval beween each packe ransmission. r : he ime required for a sable RSSI, needed for a sable CCA indicaion. c : he inerval beween each CCA. a : he ime beween receiving a packe and sending he acknowledgmen packe. d : he ime required for successfully deecing an acknowledgmen from he receiver. The iming mus saisfy a number of consrains. Firs, i, he inerval beween each packe ransmission, mus be smaller han c, he inerval beween each CCA. This is o ensure ha eiher he firs or he second CCA is able o see he packe ransmission. If c would be smaller han i, wo CCAs would no be able o reliably deec a ransmission. The requiremen on i and c also place a requiremen on he shores packe size ha ConikiMAC can suppor, 2

3 CCA r s aa packe c Figure 4: A packe ransmission mus be long enough so ha i does no fall beween o subsequen CCAs. as shown in Figure 4. For ConikiMACs wo CCAs o be able o deec he packe, a packe ransmission canno be so shor ha i falls beween he CCAs. Specifically, s, he ransmission ime of he shores packe, mus be larger han r + c + r. When a CCA has deeced a packe ransmission, ConikiMAC keeps he radio on o be able o receive he full packe. When a full packe has been received, a linklayer acknowledgmen is ransmied. The ime i akes for an acknowledgmen packe o be ransmied, a, and he ime i akes for an acknowledgmen packe o be deeced, d, esablishes he lower bound for he check inerval c. We can now consruc he full ConikiMAC iming consrains as r CCA a + d < i < c < c + 2 r < s. (1) Wih an IEEE link layer and a specific radio ransceiver, some of he variables in Equaion 1 are given as consans. Firs, a, he ime beween a packe recepion and he acknowledgmen ransmission, is defined by he IEEE specificaion as 12 symbols. In , one symbol is 4/2 milliseconds long, giving a = 48/2 =.192 milliseconds. Second, an IEEE receiver can reliably deec he recepion of he acknowledgmen afer he 4-bye long preamble and he 1-bye sar of frame delimier is ransmied, which akes 4/2 miliseconds. Thus, d = 4/2. Finally, r is given by he daa shee of he CC242 radio ransceiver as.192 milliseconds. Wih he consans for subsiued, Equaion 1 becomes.32 < i < c < c < s. (2) The remaining variables, i, c, and s can now be chosen. Equaion 2 gives a lower bound on s >.736 milliseconds, which ses a limi on he smalles packe size we can handle. Wih a birae of 2 kilobis per second, his means ha packes mus be a leas 23 byes long, including preamble, sar of frame delimier, and lengh field, which leaves 16 byes of packe daa. To ensure ha all packes are larger han he smalles packe size, packes may be padded wih addiional framing o ensure a minimum packe size. Alernaively, if he nework layer is able o ensure ha packes never go below a given size, no framing is needed. For example, in he case of an IPv6 nework layer, packes wih full IPv6 headers will always be longer han he smalles Coniki- MAC packe size on a IEEE link layer. Wih 6lowpan IPv6 header compression, packes may become smaller, bu ensuring a smalles packe size is simple: do no compress he header of IPv6 packes ha are smaller han a given hreshold. The ConikiMAC implemenaion in Coniki 2. uses he following configuraion: i =.4 milliseconds, c =. milliseconds, and s =.884 milliseconds. 2.2 Packe eecion and Fas Sleep The ConikiMAC CCAs do no reliably deec packe ransmissions: hey only deec ha he radio signal srengh is above a cerain hreshold. The deecion of a radio signal may eiher mean ha a neighbor is ransmiing a packe o he receiver, ha a neighbor is ransmiing o anoher receiver, or ha some oher device is radiaing radio energy ha is being deeced by he CCA mechanism. ConikiMAC mus be able o discern beween hese evens and reac properly. If a neighbor is ransmiing a packe o he receiver, he receiver should say awake o receive he full packe and ransmi a link layer acknowledgmen. Oher nodes, which deec he packe, could quickly go o sleep again. Poenial receivers canno go o sleep o quickly, however, as hey mus be able o receive he full packe. The naive way o deermine how long o be awake when a CCA has deeced radio aciviy is o say awake for l + i + l, 3

4 i Send daa packes unil ack received noise noise A Recepion window aa packe Aciviy deeced Sar of packe no deeced: fas sleep A A Acknowledgemen packe Silence no deeced: fas sleep Transmission deeced Send firs daa packe when receiver is known o lisen Figure : The ConikiMAC fas sleep opimizaion: if a silence period is no deeced before l, he receiver goes back o sleep. If he silence period is longer han i, he receiver goes back o sleep. If no packe is received afer he silence period, even if radio aciviy is deeced, he receiver goes back o sleep. A A Transmission deeced A Recepion window aa packe Acknowledgemen packe where l is he ransmission ime of he longes possible packe. This ensures, if he CCA woke up during he sar of he packe, ha he full packe will be received by he receiver. The fas sleep opimizaion les poenial receivers go o sleep earlier if he CCA woke up due o spurious radio noise. The fas sleep opimizaion leverages knowledge of he specific paern of ConikiMAC ransmissions as follows. Firs, if he CCA deecs radio aciviy, bu he radio aciviy has a duraion ha is longer han he maximum packe lengh l, he CCA has deeced noise and can go back o sleep. I.e., if he aciviy period is no followed by a silence period. Second, if he radio aciviy is followed by a silence period ha is longer han he inerval beween wo successive ransmissions, i, he receiver can go back o sleep. Third, if he aciviy period is followed by a silence period of he correc lengh, followed by aciviy, bu no sar of packe could be deeced, he receiver can go back o sleep. The process is illusraed in Figure. 2.3 Transmission Phase-Lock If we assume ha each receiver has a periodic and sable wake-up inerval, he sender can use knowledge of he wake-up phase of he receiver o opimize is ransmission. A sender can learn of a receiver s wake-up phase by making noe of he ime a which i saw a link layer acknowledgmen from he receiver. Since he receiver mus have been awake o be able o receive he packe, Figure 6: Transmission phase-lock: afer a successful ransmission, he sender has learned he wake-up phase of he receiver and subsequenly needs o send fewer ransmissions. he sender can assume ha he recepion of a link layer acknowledgmen means ha he sender has successfully ransmied a packe wihin he receiver s wake-up window and hus ha he sender has found he receiver s wake-up phase. Afer a sender has learned he phase of a receiver, he sender can commence is successive ransmissions o his receiver jus before he receiver is expeced o be awake. The process is illusraed in Figure 6. 3 Implemenaion The ConikiMAC implemenaion in Coniki 2. uses he Coniki real-ime imers (rimer) o schedule is periodic wake-ups o ensure a sable behavior even if many underlying processes are running. The real-ime imers preemp any Coniki process a he exac ime a which hey are scheduled. The ConikiMAC wake-up mechanism runs as a proohread [6] ha is scheduled by a periodic real-ime imer. This proohread performs he periodic wake-ups and implemens he fas sleep opimizaion. Transmissions are driven by an ordinary Coniki process. If a wake-up is scheduled o occur when he radio is busy during a ransmission, he wake-up imer schedules a 4

5 new wake-up afer anoher wake-up inerval wihou performing he wake-up. The phase-lock mechanism is implemened as a separae module from ConikiMAC, o allow i o be used by oher duy cycle mechanisms, such as he Coniki X- MAC [1] implemenaion. The phase-lock mechanism mainains a lis of neighbors and heir wake-up phases. The ConikiMAC ransmission logic records he ime of each packe ransmission. When a link layer acknowledgmen is received, i noifies he phase-lock module wih he ransmission ime of he las packe. This ime is used as an approximaion of he wake-up phase of he receiver. Before commencing a ransmission, he ConikiMAC ransmission logic calls he phase-lock module o check if i has a recorded wake-up phase of he inended receiver. If so, he phase-lock code queues he packe o be ransmied and ses a callback imer (cimer) a he ime of he expeced wake-up of he receiver. ConikiMAC will hen resume he ransmission when he callback occurs. The ransmission will hen be significanly shorer han a normal ransmission, because i occurs jus before he neighbor is expeced o be awake. Reducing he lengh of he ransmission hus reduces radio congesion. If a neighbor whose phase is known has rebooed, or if is clock has drifed far enough away from is previous wake-up phase, ransmissions o he neighbor will fail. To proec from his, ConikiMAC mainains a coun of failed ransmissions for each known neighbor. Afer a fixed number of failed ransmission (16 in Coniki 2.), he neighbor is eviced from he lis of known neighbors. Likewise, if no link layer acknowledgmen is received wihin a fixed ime (3 seconds in Coniki 2.), regardless of he number of ransmissions, he neighbor is eviced. 4 Evaluaion This repor evaluaes wo aspecs of ConikiMAC: he energy consumpion of he individual ConikiMAC operaions and he power efficiency of ConikiMAC in a daa collecion sensor nework. In addiion o he resuls presened here, we have used ConikiMAC in much recen work. For more ConikiMAC performance resuls, he reader is referred o unkels e al. [3]; uquennoy, Öserlind, unkels [7]; uquennoy e al. [8]; Kovach, uquennoy, unkels [16]; Lundén and unkels [17]; and Curren (ma) Figure 7: A ConikiMAC wake-up wih no signal deeced. The wo CCAs are seen in he lower graph. Curren (ma) Figure 8: A ConikiMAC wake-up wih radio aciviy deeced and where he fas sleep opimizaion quickly urns he radio off. Tsifes and unkels [24]. 4.1 Micro Benchmarks We measure he energy consumpion of he individual ConikiMAC operaions by measuring he curren draw of a Tmoe Sky moe [22] running ConikiMAC. We measure he curren draw wih an oscilloscope by measuring he volage over an 1 Ω resisor conneced in series wih he Tmoe Sky power source. We also insrumen Coniki- MAC o regiser he sae of he radio on one of he Tmoe Sky I/O pins, wih a high curren indicaing ha he radio is on and a low curren indicaing ha he radio is off, and measure he sae of he pin wih he same oscilloscope. All measuremens use ConikiMAC wih a wake-up fre-

6 2 2 Curren (ma) 1 1 Curren (ma) Figure 9: Broadcas recepion: wake-up, packe deeced, broadcas packe received. Figure 11: Broadcas ransmission. 2 Curren (ma) Curren (ma) Figure 1: Unicas recepion: wake-up, packe deeced, unicas packe received quency of 8 Hz, which resuls in a wake-up inerval of 12 ms. Figure 7 shows he curren draw of a ConikiMAC wake-up ha did no resul in any packe recepion. In he lower graph, we see ha he radio is urned on wice, o perform he wo CCAs of he ConikiMAC wake-up. Figure 8 shows a ConikiMAC wake-up where he second CCA deeced spurious radio aciviy. The radio is hen kep on for a while longer, unil he fas sleep opimizaion urns off he radio. Figure 9 and Figure 1 shows a broadcas recepion and a unicas recepion, respecively. In boh cases, he radio was urned on as par of he ConikiMAC wake-up mechanism and he firs CCA deeced radio aciviy. The radio was hen kep on unil he packe was received. We see ha he radio is urned on longer in he unicas recepion Figure 12: Non-synchronized unicas ransmission (wih subsequen wake-up a 11 ms case. This is because of he acknowledgmen ransmission ha is done as par of he unicas packe recepion. The curren draw of ransmissions are shown in Figure 11 hrough Figure 13. Figure 11 shows he curren draw of a broadcas ransmission. A broadcas ransmission mus wake up and deliver is packe o all neighbors. I herefore runs for a full wake-up inerval. Since a broadcas ransmission does no expec any link layer acknowledgmen, he ransmier can urn off is radio beween each packe ransmission o save power, which can be seen in he figure. Figure 12 show he curren draw of a unicas ransmission o a previously unknown neighbor. In his case, he neighbor s wake-up occurred afer roughly 6 ms, which caused he ransmier o repeaedly send is packe some 7 ms. A he sar of he ransmission, he iniial clear channel assessmen can also be seen. Subsequen ransmissions o he same receiver can 6

7 Curren (ma) Table 1: Comparison of he energy consumpion of he wake-up operaion. Proocol Energy (uj) X-MAC [1] 132 Hui and Culler [14] 4 ConikiMAC 12 Figure 13: Synchronized unicas ransmission (wih subsequen wake-up a 11 ms) 2 2 X-MAC ConikiMAC 2 1 Broadcas ransmission duy cycle (%) 1 1 Energyv (uj) 1 Wake-up Fas sleep Unicas Broadcas recepion recepion Firs unicas Subsequen unicas Figure 14: The energy consumpion of he individual ConikiMAC operaions. now be opimized o sar a he expeced wake-up ime of he neighbor, as seen in Figure 13, which shows how he number of ransmissions are reduced because of he phase-lock opimizaion. By compuing he areas under he graphs in Figure 7 hrough Figure 13, we can compue he energy consumpion of each operaion. The resul is shown in Figure 14. We see ha he cos of a broadcas ransmission is many orders of magniude higher han he cos of he wake-up. This is good: he wake-up is he mos common operaion in ConikiMAC execued many imes per second and herefore should be significanly less expensive han he oher operaions. Armed wih he informaion in Figure 14, we can now Channel check rae (Hz) Figure 1: The radio duy cycle in a daa collecion nework wih pah loss, wih X-MAC and ConikiMAC, as a funcion of he wake-up frequency (in he graph called channel check rae). compare he cos of he ConikiMAC wake-up operaion wih he wake-up operaion of oher duy cycling mechanisms. Table 1 shows he cos of a wake-up in Coniki- MAC, in he Coniki X-MAC implemenaion [1], and he duy cycling mechanism by Hui and Culler [14]. 4.2 Nework Power Consumpion To evaluae he nework power consumpion of Coniki- MAC and he efficiency of is opimizaions, we run a se of simulaions in he Coniki simulaion environmen. The Coniki simulaion environmen consiss of he Cooja nework simulaor and he MSPsim device emulaor. MSPsim provides a cycle-accurae Tmoe Sky emulaion, wih a symbol-accurae emulaion of he CC242 7

8 duy cycle (%) No phase lock, no fas sleep No phase lock, wih fas sleep Wih phase lock, no fas sleep Wih phase lock, wih fas sleep duy cycle (%) No phase lock, no fas sleep No phase lock, wih fas sleep Wih phase lock, no fas sleep Wih phase lock, wih fas sleep Channel check rae (Hz) Channel check rae (Hz) Figure 16: The nework radio duy cycle wih Coniki- MAC, averaged for all nodes a he nework wihou pah loss. radio ransceiver. I enables he sudy of he behavior of ConikiMAC in a iming-accurae and conrolled environmen. We run a se of simulaions wih a 2-node simulaion opology. All nodes run Coniki and he Coniki Collec proocol. The Coniki Collec proocol, which is par of he Coniki Rime sack [4], is an address-free daa collecion proocol ha builds a ree rooed in one or more sinks, owards which packes are roued. The performance of Coniki Collec has been experimenally shown [1] o be similar o oher daa collecion proocols, such as he TinyOS Collecion Tree Proocol [12]. The nodes send a daa packe owards he sink once every 12 seconds. Every ransmission is sen wih 31 hop-by-hop reransmissions. Each node sends 1 packes owards he sink. The simulaion is run unil all daa packes have been received by he sink. In all simulaions, Coniki Collec was able o successfully deliver all packes o he sink. The purpose of he simulaions is boh o measure he ypical radio duy cycle ha can be achieved wih ConikiMAC and o measure he effec of he fas sleep and phase-lock opimizaions. We vary he wake-up frequency and he simulaed loss levels. We run one se of simulaions wih no pah loss: packes are no los due o radio fading, bu only due o collisions wih oher pack- Figure 17: The nework radio duy cycle wih Coniki- MAC, averaged for all nodes in a nework wih pah loss. es. The second se of simulaions use a pah loss model where he probabiliy of a packe loss is proporional o he square of he disance beween he sender and he receiver. We measure he radio duy cycle wih Coniki s Powerrace ool [2]. We use he radio duy cycle as a proxy for he power consumpion of he nework, as he radio ransceiver has a linear power draw ha depends on is on-ime [, 22]. We firs compare he performance of ConikiMAC wih ha of X-MAC [1] in a nework wih pah loss. We expec he power consumpion of X-MAC o be significanly higher han ha of ConikiMAC due o he more cosly wake-up mechanism in X-MAC. Figure 1 shows he resul: he power consumpion of ConikiMAC is significanly lower for all wake-up frequencies in he experimen. Nex, we measure he efficiency of he individual ConikiMAC opimizaions. We run he simulaions wih he ConikiMAC opimizaions swiched on and off. The resuls are shown in Figure 16 and Figure 17. Figure 16 shows he radio duy cycle when here is no pah loss. We see ha he radio duy cycle increases wih he wakeup frequency: wih more wake-ups, he oal power consumpion of he nework increases. We also see ha he fas sleep and phase-lock opimizaions significanly re- 8

9 duce power consumpion. Figure 17 shows he resuls in he nework wih pah loss. We see ha he phase-lock and fas sleep opimizaions are more efficien in he face of loss. This is because of a phase-locked ransmission being shorer han nonphase-locked ransmissions, leading boh o less energy being spen on ransmissions and o less radio congesion. Relaed Work The high power consumpion of he radio ransceiver is a well-known issue ha has spurred much work on radio duy cycling. duy cycling mechanisms can be divided ino wo main caegories: synchronous and asynchronous. Synchronous mechanisms depend on neighboring nodes being synchronized wih each oher whereas asynchronous mechanisms do no depend on any a priori synchronizaion. Asynchronous mechanisms can furher be subdivided ino sender-iniiaed and receiveriniiaed mechanisms. In sender-iniiaed mechanisms, he sender iniiaes communicaion beween a sender and a receiver, whereas in receiver-iniiaed mechanisms, he receiver iniiaes communicaion. ConikiMAC is a sender-iniiaed asynchronous mechanism. The lieraure provides many examples of mechanisms from hese caegories as well as hybrid mechanisms ha combine feaures from more han one of he caegories. Examples of synchronous proocols as he early work on S-MAC [26] and T-MAC [2] as well as he more recen TSMP [2]. In S-MAC and T-MAC, nodes periodically wake up in a scheduled manner such ha communicaion can ake place when adjacen nodes are awake. The wake-up schedules are arranged o avoid overlapping and medium conenion. In TSMP, ime is divided ino 1 ms long slos. Nodes are given a schedule of when o be awake. Nodes wake up briefly a he sar of each slo o lisen for any aciviy on he radio medium. If aciviy is deeced, he radio is kep on longer o be able o receive incoming packes. Asynchronous proocols have he advanage of no requiring synchronizaion and he research communiy has explored many differen varians of asynchronous proocols. Early work on sensor nework archiecures found a simple asynchronous mechanism called low-power lisening [13] in which nodes periodically wake up o sample he medium for a wake-up one. If a wake-up one is found, he radio is kep on o receive a ransmission. To send a packe, he sender firs ransmis a wake-up one o wake is neighborhood up. Laer varians of his scheme used scheduled ransmissions o avoid sending a oo long wake-up one [11]. The low-power lisening scheme was moved o a packeizing radio wih X-MAC [1]. In X- MAC, he wake-up one is composed of a series of srobe packes. When he receiver wakes up, i sends a link-layer acknowledgmen o he sender o indicae ha i is awake and ready o receive he daa packe. Ohers have subsequenly improved upon hese proocols [21, 14]. ConikiMAC is highly similar o exising low-power lisening proocols bu has a significanly more effecive wake-up mechanism due o he precise iming beween each daa packe ransmission. -iniiaed proocols have a shorer hisory han sender-iniiaed proocols. Low-Power Probing (LPP) is perhaps he firs example of a receiver-iniiaed proocol for low-power wireless [19]. In LPP, when a node inends o send a packe, i urns on is radio o lisen for probes from poenial receivers. When he sender hears a probe from he inended receiver of he packe, i ransmis is packe. RI-MAC [23] is a similar bu more effecive mechanism of he same ype. A-MAC [1] makes he wake-up signal more efficien, making boh idle power consumpion lower and ransmissions more effecive 6 Conclusions This repor presens he ConikiMAC radio duy cycling mechanism for low-power wireless neworks, he defaul radio duy cycling mechanism in Coniki 2.. Coniki- MAC is designed o be simple o undersand and implemen, uses only asynchronous and implici synchronizaion, and requires no signaling messages or addiional headers. ConikiMAC uses a simple bu elaborae iming scheme o allow is wake-up mechanism o be highly power efficien, a phase-lock mechanism o make ransmissions efficien, and a fas sleep opimizaion o allow receivers o quickly go o sleep when faced wih spurious radio inerference. Measuremens show ha he wake-up mechanism is significanly lower han for exising duy cycling mechanisms and ha he phase-lock and fas sleep mechanisms reduce he nework power con- 9

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