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[Contiki-developers] Transmission Phase-Lock of ContikiMAC
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From: Dominic A. <ast...@gm...> - 2014-04-23 10:15:09
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<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>Dear all</div> <div> </div> <div>I really do not understand the advantage of the transmission phase-lock machanism of the contiki mac. As I see in the document of Adam Dunkels: http://soda.swedish-ict.se/5128/1/contikimac-report.pdf and here: https://github.com/contiki-os/contiki/wiki/Radio-duty-cycling the minimal transmission time for a frame t_s must be bigger then the interval between each CCA t_c + 2 * the time for a valid CCA indication t_r:</div> <div> </div> <div>t_s > t_c + 2 * t_r</div> <div> </div> <div>This means that the duration of a frame must - by definition - be bigger then the time between the periodic channel check of the receiver. And if this is the case the receiver will anyway notice the incoming frame after one try and the sender must anyway send the package dureing the entire poll periode and even once again. So which advantiage gives phase locking in this situation?</div> <div> </div> <div>For example:</div> <div> </div> <div>If I chose t_c as 20ms and t_r as 192us, my minimal package duration is 20.284ms. If I send this package at any, the receiver will recognice it after one try. Then I have to send the package again for the receiver to receive the entire package. The same statement holds if I send the first package just before the receiver wakes up. I can't the the gain in this situation.</div> <div> </div> <div>I see the advantage of phase-locking for example in WiseMAC where they send a Preamble which is maximal t_c long (instead of minimal t_c + 2 * t_r!! ) and which can be cutted if the phase if the receiver's phase is known but I don't see the advantage in contikiMAC.</div> <div> </div> <div>Thank you for any advice, I really want to understand how contikiMac works.</div> <div> </div> <div>Best regards, Dominic</div> <div> </div> <div> </div></div></body></html> |
