MIMO LO sharing in microwave point-to-point systems

1. A microwave MIMO (multiple-input, multiple-output) communications system comprising:

a first microwave antenna for transmitting/receiving first communication signals;

a first outdoor unit coupled to the first microwave antenna;

an indoor unit with a first connection to the first outdoor unit;

a second microwave antenna for transmitting/receiving second communication signals;

a second outdoor unit coupled to the second microwave antenna and further connected to the indoor unit over a second connection; and

wherein the first connection and second connection carry synchronization signals between the first and second outdoor units to synchronize local oscillators located within the first and second outdoor units.

2. The system according to claim 1 , wherein the first outdoor unit and the second outdoor unit further comprising one or more phase locked loops coupled to the local oscillators to provide adjustments to the local oscillators.

3. The system according to claim 2 , wherein the one or more phase locked loops comprise a fixed high frequency fixed phase locked loop and a tunable low frequency phase locked loop.

4. The system according to claim 3 , wherein the tunable low frequency phase locked loop processes the synchronization signals as feedback for the tunable low frequency phase locked loop.

5. The system according to claim 1 , wherein the first and second connections are on intermediate frequency (IF) cables and the first and second microwave antennas use millimeter wave (MMW) signaling.

6. The system according to claim 1 , wherein the microwave MIMO (multiple-input, multiple-output) communications system is part of a microwave MIMO point-to-point communications network.

7. The system according to of claim 6 , wherein the microwave MIMO point-to-point communications network is operable for frequency-division duplexing (FDD).

8. A microwave MIMO (multiple-input, multiple-output) communications system comprising:

a first microwave antenna for transmitting/receiving first communication signals;

a first outdoor unit connected to the first microwave antenna, the first outdoor unit including at least a first local oscillator;

a second microwave antenna for transmitting/receiving second communication signals;

a second outdoor unit connected to the second microwave antenna, the second outdoor unit including at least a second local oscillator;

intermediate frequency (IF) connection cabling interconnecting the first and second outdoor units to at least one indoor unit; and

the first and second outdoor units, further include a phase locked loop comprising:

one of the first or second local oscillators for generating a reference signal;

a mixer for converting the generated reference signal;

a high frequency fixed phase locked loop for generating a high frequency signal having a fixed phase;

a low frequency tunable phase locked loop for generating an output signal; and

a first power amplifier for communicating the output signal across the intermediate frequency (IF) connection cabling; and

a second power amplifier for amplification of a feedback signal received over the intermediate frequency connection cabling to adjust phase of the one of the first or second local oscillators; and

wherein the first and second local oscillators located within the first and second outdoor units are synchronized by transmission of synchronization signals for the first and second local oscillators between the first and second outdoor units over the IF connection cabling.

9. The microwave MIMO communications system according to claim 8 , wherein the intermediate frequency (IF) connection cabling comprises allocated bandwidth to the synchronization signals.

10. The microwave MIMO communications system according to claim 8 , wherein the first and second outdoor units are part of a microwave point-to-point communication system.

11. The microwave MIMO communications system according to claim 8 , wherein the first and second outdoor units are part of a MIMO microwave point-to-point communication system.

12. A method of synchronizing local oscillators of a MIMO microwave communications network, comprising:

generating a low frequency tuned reference signal within at least a first and second outdoor unit separated by a distance d;

transmitting the generated low frequency tuned reference signal across shared intermediate frequency cable connections between the first and second outdoor units, the shared intermediate frequency cable connections including at least a first intermediate frequency connection between the first outdoor unit and its corresponding indoor unit and at least a second intermediate frequency connection between the second outdoor unit and its corresponding indoor unit;

receiving at the first and second outdoor units the transmitted low frequency tuned reference signal; and

feeding the received low frequency tuned reference signal into a tunable phase locked loop for synchronizing the local oscillators.

13. The method according to claim 12 , further comprising the first and second outdoor units communicating high frequency communication signals to microwave antennas.

14. The method according to claim 13 , wherein the high frequency communication signals are communicated over high frequency cables to the microwave antennas.

15. The method according to claim 12 , wherein the shared intermediate frequency cable connections are shared with one or more indoor unit communication signals.

16. The method according to claim 12 , wherein the MIMO microwave communications network is part of a microwave point-to-point communication system comprising millimeter wave (MMW) signaling.

17. The method according to claim 12 , wherein the MIMO microwave communications network is part of a MIMO microwave point-to-point communication system.

18. The method according to claim 12 , wherein the MIMO microwave communications network is operable for frequency-division duplexing (FDD).

19. The microwave MIMO communications system according to claim 8 , wherein the intermediate frequency cable connections are shared with one or more indoor unit communication signals.

20. A microwave MIMO (multiple-input, multiple-output) communications system according to claim 1 further comprising one or more phase locked loops comprising a fixed high frequency fixed phase locked loop and a tunable low frequency phase locked loop and the tunable low frequency phase locked loop processing the synchronization signals as feedback for the tunable low frequency phase locked loop.