ENABLING DETERMINISM IN A BEST EFFORT HOPPING SEQUENCE TIME SLOTTED CHANNEL HOPPING MESH

Techniques are described for sharing a network between flows that follow a deterministic hopping sequence (same sequence for all) and flows that follows a best effort hopping sequence (which depends on the receiver Media Access Control (MAC) address for unicast). This is accomplished by moving the best effort channel in case of a collision in a manner that can be predicted by the sender and that maintains the pseudo-randomness of the selection. DETAILED DESCRIPTION Currently, despite Internet Protocol version 6 (IPv6) over the Time Slotted Channel Hopping (TSCH) mode of IEEE 802.15.4e (6TiSCH), the deterministic wireless world is still fragmented between the deterministic (e.g., Wireless Highway Addressable Remote Transducer Protocol (WirelessHART) and the best effort schools. Both converge on the need to provide TSCH, one way or another. The difference resides in the way the hopping sequence is computed. Channel hopping requires that the next transmission be on a different channel. Time slotting enables this at the scale of a network in a slotted “ALOHA” fashion by synchronizing when a device jumps to a different channel. The hopping sequence is the logic that decides which channel is used subsequently. Channel hopping mitigates the unpredictable effects of co-channel interference and multipath fading. Therefore, it is critical that as many channels as possible are used. Blacklisting or whitelisting channels is not a good option. When determinism is required (e.g., WirelessHART, ISA100.11a, 6TiSCH, etc.), the hopping sequence must be the same for all nodes. If A->B does not interfere with C>D at the beginning of the relevant time, they jump in parallel and never collide. Thus, a 2 Thubert et al.: ENABLING DETERMINISM IN A BEST EFFORT HOPPING SEQUENCE TIME SLOTT Published by Technical Disclosure Commons, 2018 2 5578X time slot can be guaranteed for an undisturbed communication forever (at least by a device that participates in this network). IEEE 802.15.4 TSCH (as used in 6TiSCH) forces all nodes to follow the same hop sequence regardless of the Media Access Control (MAC) address. For 16 channels, the sequence may be as follows: 5 6 12 7 15 4 14 11 8 0 1 2 13 3 9 10 This sequence constitutes a mapping table. The computation of frequency may be freq = map ([ASN + channel offset] mod nbChannels), where the absolute slot number (ASN) is the number of timeslots since the epoch when the network started. In the 2.4GHz band with channels from 11 to 26, this yields: hopsq=[5,6,12,7,15,4,14,11,8,0,1,2,13,3,9,10] freq=hopsq[(asn+choff)%16]+11 This means that if at timeslot N a node transmits on channel 14, then at time N+1 the node transmits on channel 11, at N+2 on channel 8, etc. Figure 1 below illustrates a deterministic schedule from the perspective of a controller that is aware of the entire network and schedules all the transmissions. Time is divided into slotframes that are played repeatedly, and the schedule represents the initial allocations for the duration of a slotframe (represented at time t=0, also referred to as “epoch”). 3 Defensive Publications Series, Art. 1205 [2018] https://www.tdcommons.org/dpubs_series/1205