Hidden Terminal Problem Between Adjacent Piconets Prepared by
Hidden Terminal Problem Between Adjacent Piconets Prepared by: Michael Sim Panasonic Singapore Lab michael. simhc@sg. panasonic. com Panasonic Singapore Lab
General Problem • Assumption: System consists of beaconing devices and non-beaconing devices • Non-beaconing devices associated to different beaconing device interfere with each other. Beaconing devices are out of range of each other A B C • How do we D interference – detect such situation? – resolve such situation when detected? Panasonic Singapore Lab 2
Detection • Active Detection – RX when idling (power consuming. Not recommended) – Perform random periodic superframe • Listen for TX from beaconing/non beaconing devices • Passive Detection – Missing beacon frame (e. g. for m. Max. Lost. Beacons) – Control/Data packet TX failure (e. g. above certain threshold T) Panasonic Singapore Lab 3
Resolution • At least one non-beaconing device switch role to become beaconing device (recommended) – 15. 3 becoming child/neighbor PNC – Panasonic’s 15. 3 based method (Method A) – Philips’ beacon period based method (Method B) • Both do not wish to be beaconing device despite knowing potential interference – Continue to operate with interference – Request piconet master to switch channel? Panasonic Singapore Lab 4
Resolution – 15. 3 Method • Using 15. 3 Child/Neighbor Piconet – As discussed, 15. 3 does not handle SOP well – In example, C hears both B and D’s beacon. However, B and D think that device A and D respectively controls the medium access time – C can also informs D of B’s superframe and D set aside a CTA for it B C D – How to resolve CTA collision between A B and D? A Panasonic Singapore Lab B C D 5
Resolution – Method A • Case 1: Only B switch role – First, notify A by announcing in A’s CAP – B start beaconing B time C time – C able to detect B through superframe scan – B and C able to communicate using each other’s CAP – B and C to take note of slot offset or synchronize slot boundary B time C time Panasonic Singapore Lab 6
Resolution – Method A • Case 2: B and C switch role – B notifies A, C notifies D – B and C start beaconing B time C time – B and C can detect each other by superframe scan – B and C to take note of slot offset or synchronize slot boundary B time C time Panasonic Singapore Lab 7
Resolution – Method B • Case 1: Only B switch role – First, notify A using announcement slot in BP – Select last free slot for beaconing B time B C time C – C able to detect B’s BP through superframe scan – How can C communicate with D and B if there is no CAP and C does not beacon? Panasonic Singapore Lab 8
Resolution – Method B • Case 2: B and C switch role – B notifies A, C notifies D, using announcement slots – B and C select last free slot for beaconing B time C time – Piconet either: • take note of slot offset, or • Synchronize slot offset and Merge beacon period B time C time Panasonic Singapore Lab 9
Conclusion • If 2 (or more) devices are brought together into interference range (regardless of what kind of beaconing protocol used): – If all these devices are non-beaconing, or have no periodic TX pattern, detection of an alien interference source is only possible through: • A 3 rd party (reliable) • Random periodic scan (not reliable) • TX failure above a certain threshold (depending on threshold set) • Best way to resolve such situation is to switch at least one of the interfered device into beaconing mode. Panasonic Singapore Lab 10
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