System and method of adaptive frequency hopping with look ahead interference prediction
A novel and useful adaptive frequency hopping scheme for wireless devices and networks operating in a congested environment of similar devices, where capacity maximization is desired. The hopping sequence of each wireless link is dynamically adapted such that the impact of the surrounding interference is minimized and the interference induced onto the coexisting systems is also minimized. The scheme detects the repetitive presence of interference on a particular channel and comprises a replacement mechanism for swapping the interfered frequency-channel with one that would be clear for that particular time-slot. The mechanism detects interference during a redundant portion of the transmission (i.e. header or trailer) without having to experience packet failures (i.e. data loss). If the interference impact (e.g. corrupted header bits) exceeds a predefined threshold, that frequency channel is declared temporarily unusable for that time slot and is replaced with another in accordance with a frequency replacement policy. Periodic interference at a particular frequency, originating from a coexisting system of similar operating parameters, may also be detected at instances that are distant from the timeslots for which that particular frequency is to be used, such that frequency replacement in the hopping sequence can be scheduled ahead of time and collisions would be avoided altogether.
1. A method of adapting a periodic frequency hopping sequence in a frequency hopping communication system having fixed slot timing, said method comprising the steps of:
detecting the presence of repeated interference at a particular frequency having specific timing with respect to time slots at which that particular frequency is periodically used by said system; and
replacing the potentially interfered frequency of said time slot with a replacement frequency.
2. The method according to claim 1 , wherein said step of detecting the presence of repeated interference comprises the steps of:
detecting an impact on a received packet causing corruption of one or more bits in a redundant portion of said received packet; and
declaring said particular frequency channel unusable if said impact exceeds a predefined threshold.
3. The method according to claim 2 , wherein said redundant portion of said received packet comprises one or more trailer bits.
4. The method according to claim 2 , wherein said redundant portion of said received packet comprises one or more header bits.
5. A method of adapting a periodic frequency hopping sequence in a frequency hopping communication system having fixed slot timing, said method comprising the steps of:
detecting the presence of repeated interference at a particular frequency having specific timing with respect to time slots at which that particular frequency is periodically used by said system, wherein said step of detecting the presence of repeated interference comprises the steps of:
detecting the presence of periodic transmissions from neighboring coexisting systems occurring at said frequency assigned to a time slot having specific timing with respect to said time slots at which this frequency is used by said system;
determining a drift in the relative timing between said periodic transmissions and the timing at which said system periodically uses said frequency; and
declaring said particular frequency unusable if the detected level of said periodic transmissions exceeds a predefined threshold and
replacing the potentially interfered frequency of said time slot with a replacement frequency.
6. The method according to claim 5 , wherein said repeated interference is detected before it causes any loss of payload data in said system.
7. A method comprising the steps of:
adapting in an apparatus a frequency hopping sequence having a plurality of frequency channels by detecting an impact on a transmitted packet in a particular channel causing corruption of one or more bits in a redundant portion of said transmitted packet;
declaring said particular channel unusable if said impact exceeds a threshold; and
replacing the frequency of an unusable channel with an alternate frequency.
8. The method according to claim 7 , wherein said redundant portion of said transmitted packet comprises one or more header/trailer bits which appear either before or after the payload in a packet.
9. The method according to claim 7 , wherein potential periodic interference is detected without any loss of payload data.
10. A mobile communications device for use in a frequency hopping communication system having a plurality of frequency channels, comprising:
a frequency hopping based radio transceiver;
a processor coupled to said transceiver, said processor operative to:
detect the presence of repeated interference at a particular frequency having specific timing with respect to time slots at which that particular frequency is periodically used by said transceiver; and
replace the potentially interfered frequency of said time slot with a replacement frequency.
11. The mobile communications device according to claim 10 , wherein said frequency hopping based transceiver comprises a Bluetooth transceiver.
12. The mobile communications device according to claim 10 , wherein said processor is further operative to:
replace said potentially interfered frequency by detecting the interference impact in a received packet through its corruption of one or more bits in a redundant portion of said packet; and
declare said particular frequency channel unusable if said interference impact exceeds a predefined threshold.
13. The mobile communications device according to claim 10 , wherein said processor is further operative to:
replace said potentially interfered frequency by detecting the presence of periodic bursty transmissions from other coexisting systems occurring at said frequency at specific timing with respect to said time-slots at which this frequency is used by said system;
determine the drift in the relative timing between said periodic transmissions and the timing at which said system periodically uses said frequency; and
declare said particular frequency channel unusable if the detected level of said periodic transmissions, which can potentially create interference once their timing drifts into that at which said frequency is used by the system, exceeds a predefined threshold.
14. The mobile communications device according to claim 10 , wherein the presence of said repeated interference is detected before it causes any loss of payload data in said device.
15. A method of adapting a periodic frequency hopping sequence in a frequency hopping communication system having fixed slot timing, said method comprising the steps of:
detecting the presence of potential periodic interference from transmissions by neighboring coexisting systems occurring at a frequency assigned to a time slot to occur in the future in the potentially interfered system and having specific timing with respect to time slots at which the frequency is used by said system;
determining a drift in relative timing between said periodic transmissions and the timing at which said system periodically uses said frequency; and
declaring said particular frequency unusable if the detected level of said periodic transmissions repeatedly exceeds a first predefined threshold, and replacing said unusable frequency with a replacement frequency.
16. The method according to claim 15 , wherein said potential periodic interference is detected before it causes any loss of payload data in said system.
17. The method according to claim 15 , further comprising the step of detecting the presence of potential periodic interference from transmissions by neighboring coexisting systems occurring at said replacement frequency, such that the potentially interfered frequency would not be replaced with another potentially interfered frequency.
18. The method according to claim 17 , further comprising the step of selecting a second replacement frequency if the level of periodically detected interference at said second replacement frequency exceeds a second predefined threshold.