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Soft-TDMAC: A Software-Based 802.11 Overlay TDMA MAC with Microsecond Synchronization
March 2012 (vol. 11 no. 3)
pp. 478-491
P. Djukic, Meshlntelligence, Inc., Ottawa, ON, Canada
P. Mohapatra, Dept. of Comput. Sci., Univ. of California at Davis, Davis, CA, USA
We implement a new software-based multihop TDMA MAC protocol (Soft-TDMAC) with microsecond synchronization using a novel system interface for development of 802.11 overlay TDMA MAC protocols (SySI-MAC). SySI-MAC provides a kernel independent message-based interface for scheduling transmissions and sending and receiving 802.11 packets. The key feature of SySI-MAC is that it provides near deterministic timers and transmission times, which allows for implementation of highly synchronized TDMA MAC protocols. Building on SySI-MAC's predictable transmission times, we implement Soft-TDMAC, a software-based 802.11 overlay multihop TDMA MAC protocol. Soft-TDMAC has a synchronization mechanism, which synchronizes all pairs of network clocks to within microseconds of each other. Building on pairwise synchronization, Soft-TDMAC achieves tight network-wide synchronization. With network-wide synchronization independent of data transmissions, Soft-TDMAC can schedule arbitrary TDMA transmission patterns. For example, Soft-TDMAC allows schedules that decrease end-to-end delay and take end-to-end rate demands into account. We summarize hundreds of hours of testing Soft-TDMAC on a multihop testbed, showing the synchronization capabilities of the protocol and the benefits of flexible scheduling.

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Index Terms:
wireless LAN,access protocols,synchronisation,time division multiple access,end-to-end rate demands,soft-TDMAC,software-based 802.11,overlay TDMA MAC,microsecond synchronization,software-based multihop TDMA MAC protocol,802.11 packets,TDMA transmission patterns,end-to-end delay,Synchronization,Time division multiple access,Spread spectrum communciation,IEEE 802.11 Standards,Media Access Protocol,Schedules,Media Access Protocols,network synchronization.,Multihop TDMA MAC,802.11 overlay MAC
P. Djukic, P. Mohapatra, "Soft-TDMAC: A Software-Based 802.11 Overlay TDMA MAC with Microsecond Synchronization," IEEE Transactions on Mobile Computing, vol. 11, no. 3, pp. 478-491, March 2012, doi:10.1109/TMC.2011.56
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