Optical communications system with back-up link

• US 20020181036A1
• Filed: 05/30/2001
• Published: 12/05/2002
• Est. Priority Date: 05/30/2001
• Status: Active Grant

• Current Assignee: MRV Communications Americas, Inc. (MRV Communications Incorporated)
• Original Assignee: Optical Access, Inc. (MRV Communications Incorporated)
• Inventors: Achour, Maha, Korevaar, Eric
• Granted Patent: US 6,928,248 B2
• Time in Patent Office: Days
• US Class Current: 398/27
• CPC Class Codes: H04B 10/032 using working and protection systems H04J14/0287 takes precedence
• CPC Class Codes: H04B 10/1123 Bidirectional transmission

Abstract

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.

Claims

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; and

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.

2. A device as recited in claim 1 further comprising a first delay circuit for continuing a transmission of said signal by said first transceiver for a first time interval (Δ

t) immediately after said BER goes above said reference rate.

3. A device as recited in claim 2 further comprising a second delay circuit for continuing transmission of said signal by said second transceiver for a second time interval (Δ

τ

) immediately after the BER goes below said reference rate.

4. A device as recited in claim 3 further comprising means for decrementing said first time interval (Δ

t) and incrementing said second time interval (Δ

τ

) 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(Δ

t+Δ

τ

).

5. A device as recited in claim 4 further comprising means for resetting original values for said first time interval (Δ

t) and said second time interval (Δ

τ

) 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(Δ

t+Δ

τ

).

6. A device as recited in claim 3 wherein Δ

t is less than approximately one second, and Δ

τ

is approximately five seconds.

7. 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.

8. 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.

9. 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.

10. A device as recited in claim 9 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.

11. 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

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.

12. A device as recited in claim 11 wherein said first transceiver transmits and receives on a laser beam and said second transceiver transmits and receives on a microwave beam.

13. A device as recited in claim 11 wherein the RSSI is used to calculate a bit error rate (BER) for said signal and said device further comprises:

a means for comparing the bit error rate with a reference rate;

a first delay circuit for continuing a transmission of said signal by said first transceiver for a first time interval (Δ

t) immediately after said BER goes above said reference rate; and

a second delay circuit for continuing transmission of said signal by said second transceiver for a second time interval (Δ

τ

) immediately after said BER goes below said reference rate.

14. A device as recited in claim 13 further comprising:

a means for decrementing said first time interval (Δ

t) and incrementing said second time interval (Δ

τ

) 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(Δ

t +Δ

τ

); and

a means for resetting original values for said first time interval (Δ

t) and said second time interval (Δ

τ

) 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).

15. A device as recited in claim 11 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.

16. A device as recited in claim 15 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.

18. A method as recited in claim 17 wherein said variable timed sequence regimen is accomplished by the steps of:

delaying said switching step for a first time interval (Δ

t) immediately after said BER goes above said reference rate;

continuing transmission of said signal by said second transceiver for a second time interval (Δ

τ

) immediately after said BER goes below said reference rate;

decrementing said first time interval (Δ

t) and incrementing said second time interval (Δ

τ

) 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(Δ

t+Δ

τ

); and

resetting original values for said first time interval (Δ

t) and said second time interval (Δ

τ

) 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).

19. A method as recited in claim 18 wherein said signal has a received signal strength intensity (RSSI), and said BER is determined by calculations using the RSSI.

20. A method as recited in claim 17 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.

17. 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; and

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.