System and method of adaptive frequency hopping in a wireless communication system
A novel and useful acknowledgement and adaptive frequency hopping mechanism for use in wireless communication systems such as IO-Link Wireless. One or two additional acknowledgement bits are added to packet transmissions. One is a current acknowledgment bit which indicates whether a packet was successfully received anytime during the current cycle. The second bit is a previous acknowledgment bit which indicates whether packets were received successfully anytime during the previous cycle. An adaptive hopping table is constructed using a greedy algorithm which chooses frequencies with the best PER for transmission of higher priority packets, while equalizing the PER products across cycles. A last resort frequency mechanism further improves transmission success by switching to a better performing channel for the last subcycle when previous attempts to transmit a high priority packet have failed.
1. A method of reliable communications between a master and a plurality of devices in a frequency hopping wireless communications network adapted to communicate both critical and non-critical data, comprising: ordering frequency channels by one or more performance metrics; and for critical data only, allocating unique frequency channels to a plurality of subcycles within a cycle, whereby best performing frequency channels are allocated to higher priority subcycles in each cycle, wherein allocating unique frequency channels comprises utilizing a greedy algorithm operative to assign a best frequency channel from available frequency channels to a subcycle within a currently worst performing cycle such that performance of cycles is substantially equalized across transmissions.
2. The method according to claim 1 , wherein subcycle priority is ordered from highest to lowest, such that a first transmission of process data (PD) packets as defined in the IO-Link Wireless standard has the highest priority.
3. The method according to claim 1 , wherein said one or more performance metrics comprises packet error rate (PER).
4. The method according to claim 1 , wherein ordering frequency channels comprises generating a list of frequency channels ordered by increasing packet error rate (PER).
5. The method according to claim 1 , wherein process data (PD) packets as defined in the IO-Link Wireless standard are transmitted in said high priority subcycles.
6. The method according to claim 1 , further comprising allocating worse performing frequency channels to low priority subcycles in each cycle.
7. The method according to claim 6 , wherein on-demand data (OD) packets as defined in the IO-Link Wireless standard are transmitted in said low priority subcycles.
8. The method according to claim 1 , wherein allocating unique frequency channels comprises utilizing a greedy algorithm to determine, in accordance with said performance metrics, which frequency channel to assign to a subcycle.
9. The method according to claim 1 , further comprising maintaining long term statistics and short term statistics on channel performance.
10. The method according to claim 9 , further comprising triggering a re-allocation of frequency channels to subcycles in the event a probability of said short term statistics occurring compared to said long term statistics is lower than a threshold.
11. The method according to claim 10 , further comprising transmitting said frequency channel re-allocation from the master to said plurality of devices.
12. The method according to claim 9 , further comprising updating said long term statistics to reflect a change in said short term statistics in the event a probability of said short term statistics occurring compared to said long term statistics is lower than a threshold.
13. The method according to claim 1 , further comprising triggering a re-allocation of frequency channels to subcycles once transmission of all allocated frequency channels is exhausted.
14. The method according to claim 1 , wherein a total number of frequency channels allocated is an integer multiple of a number of subcycles per cycle.
15. A method of reliable communications between a master and a plurality of devices in a frequency hopping wireless communications network adapted to communicate both critical and non-critical data, comprising:
ordering frequency channels by corresponding packet error rate (PER);
for critical data only, performing a greedy algorithm to allocate frequency channels to a plurality of subcycles within a cycle, said greedy algorithm operative to allocate best performing frequency channels to higher priority subcycles in each cycle in accordance with said corresponding PERs;
maintaining long term statistics and short term statistics on channel performance; and
triggering a re-allocation of frequency channels to subcycles in the event a probability of said short term statistics occurring given said long term statistics is lower than a threshold and/or transmission of all allocated frequency channels is exhausted.
16. The method according to claim 15 , wherein subcycle priority is ordered from highest to lowest, such that a first transmission of process data (PD) packets has the highest priority.
17. The method according to claim 15 , wherein process data (PD) packets as defined in the IO-Link Wireless standard are transmitted in said high priority subcycles.
18. The method according to claim 15 , further comprising allocating worse performing frequency channels to low priority subcycles in each cycle.
19. The method according to claim 18 , wherein on-demand data (OD) packets as defined in the IO-Link Wireless standard are transmitted in said low priority subcycles.
20. The method according to claim 15 , wherein said greedy algorithm determines for each subcycle in each cycle a locally optimal frequency channel to allocated thereto such that a resulting channel frequency table is approximately globally optimal.
21. The method according to claim 15 , wherein channel frequencies are allocated to subcycles such that performance of cycles is substantially equalized across transmissions.
22. An apparatus for reliable communications between a master and a plurality of devices in a frequency hopping wireless communications network adapted to communicate both critical and critical data, comprising:
a frequency hopping radio transmitter;
a frequency hopping radio receiver;
a processor coupled to and operative to control said frequency hopping radio transmitter and said frequency hopping radio receiver;
said processor programmed to:
order frequency channels by corresponding packet error rate (PER);
for critical data only, perform a greedy algorithm to allocate frequency channels to a plurality of subcycles within a cycle, said greedy algorithm operative to assign best frequency channels from available frequency channels to a subcycle within currently worst performing cycles in accordance with said corresponding PERs such that performance of said cycles is substantially equalized across transmissions;
maintain long term statistics and short term statistics on channel performance; and
trigger a re-allocation of frequency channels to subcycles in the event a probability of said short term statistics occurring given said long term statistics is lower than a threshold and/or transmission all allocated frequency channels is exhausted.
23. The apparatus according to claim 22 , wherein said radio transmitter and said radio receiver are configured to conform to the IO-Link Wireless standard.