Optical communications system with back-up link
A device and method for operational switching between line-of-sight wireless communications transceivers requires evaluating a useful received signal strength intensity (RSSI) for a first transceiver, and switching to a second transceiver when the consequent bit error rate (BER) is not useful for the first transceiver. Subsequent switching between the first and second transceivers is accomplished in accordance with a timed sequence regimen that involves variable time delays, and considerations of RSSI changes within determined time periods. Preferably, the first transceiver transmits and receives on a laser beam and the second transceiver transmits and receives on a microwave beam.
1. A device for operational switching between line-of-sight optical communications systems which comprises:
a first transceiver for transmitting and receiving a signal on a first carrier wave;
a means for determining a bit error rate (BER) for said signal;
a means for comparing the bit error rate with a reference rate;
a means for switching to a second transceiver for transmitting and receiving said signal on a second carrier wave when said BER is above the reference rate; and
a first delay circuit for continuing a transmission of said signal by said first transceiver for a first time interval (Δt) immediately after said BER goes above said reference rate.
2. A device as recited in claim 1 further comprising a second delay circuit for continuing transmission of said signal by said second transceiver for a second time interval (Δτ) immediately after the BER goes below said reference rate.
3. A device as recited in claim 2 further comprising means for decrementing said first time interval (Δt) and incrementing said second time interval (Δτ) whenever there have been an n number of changes in the BER from below said reference rate to above said reference rate within a total time period (T), wherein T≧n(Δt+Δτ).
4. A device as recited in claim 3 further comprising means for resetting original values for said first time interval (Δt) and said second time interval (Δτ) whenever there have been less than n number of changes in the BER from below said reference rate to above said reference rate within a total time period (T) wherein T≧n(ΔtΔτ).
5. A device as recited in claim 2 wherein Δt is less than approximately one second, and Δτ is approximately five seconds.
6. A device as recited in claim 1 wherein said first carrier wave is a laser light beam and said second carrier wave is a microwave beam.
7. A device as recited in claim 1 wherein said first carrier wave has a received signal strength intensity (RSSI), and the BER is determined by calculations using the RSSI.
8. A device as recited in claim 1 further comprising means for avoiding saturation of said first transceiver by switching from said first transceiver to said second transceiver when a characteristic of said signal has a predetermined value.
9. A device as recited in claim 8 wherein said first carrier wave has a d.c. level and said signal has an a.c. level, and wherein said predetermined value is a ratio of said a.c. level to said d.c. level.
10. A device for operational switching between line-of-sight optical communications systems which comprises:
a first system for evaluating a signal received by a first transceiver to determine when said signal has a useful received signal strength intensity (RSSI) for said first transceiver and wherein the RSSI is used to calculate a bit error rate (BER) for said signal;
a second system, responsive to said first system, for switching between said first transceiver and a second transceiver, in accordance with a variable timed sequence regimen, for operation of said second transceiver when said signal does not have a useful RSSI for said first transceiver;
a means for comparing the bit error rate with a reference rate; and
a first delay circuit for continuing a transmission of said signal by said first transceiver for a first time interval (Δt) immediately after said BER goes above said reference rate.
11. A device as recited in claim 10 wherein said first transceiver transmits and receives on a laser beam and said second transceiver transmits and receives on a microwave beam.
12. A device as recited in claim 10 further comprising a second delay circuit for continuing transmission of said signal by said second transceiver for a second time interval (Δτ) immediately after said BER goes below said reference rate.
13. A device as recited in claim 12 further comprising:
a means for decrementing said first time interval (Δt) and incrementing said second time interval (Δτ) whenever there have been an n number of changes in said BER from below said reference rate to above said reference rate within a total time period (T) wherein T≧n(Δt+Δτ); and
a means for resetting original values for said first time interval (Δt) and said second time interval (Δτ) whenever there have been less than n number of changes in said BER from below said reference rate to above said reference rate within said total time period (T).
14. A device as recited in claim 10 further comprising means for avoiding saturation of said first transceiver by switching from said first transceiver to said second transceiver when a characteristic of said signal has a predetermined value.
15. A device as recited in claim 14 wherein said first carrier wave has a d.c. level and said signal has an a.c. level, and wherein said predetermined value is a ratio of said a.c. level to said d.c. level.
16. A method for operationally switching between line-of-sight optical communications transceivers which comprises the steps of:
determining a bit error rate (BER) for a signal received by a first transceiver;
comparing the BER with a reference rate;
switching to a second transceiver in accordance with a variable timed sequence regimen, for transmitting and receiving said signal when said BER is above the reference rate; and
delaying said switching step for a first time interval (Δt) immediately after said BER goes above said reference rate.
17. A method as recited in claim 16 wherein said variable timed sequence regimen is accomplished by the steps of:
continuing transmission of said signal by said second transceiver for a second time interval (Δτ) immediately after said BER goes below said reference rate;
decrementing said first time interval (Δt) and incrementing said second time interval (Δτ) whenever there have been an n number of changes in said BER from below said reference rate to above said reference rate within a total time period (T) wherein T≧n(Δt+Δτ); and
resetting original values for said first time interval (Δt) and said second time interval (Δτ) whenever there have been less than n+1 number of changes in said BER from below said reference rate to above said reference rate within said total time period (T).
18. A method as recited in claim 17 wherein said signal has a received signal strength intensity (RSSI), and said BER is determined by calculations using the RSSI.
19. A method as recited in claim 16 further comprising the step of avoiding saturation of said first transceiver by switching from said first transceiver to said second transceiver when a d.c. level in said signal has a predetermined value.