US-12627376-B2 - Band-converted transmission of RF over fiber

Abstract

A system includes a downconverter, an optical transmitter, an optical receiver, and an upconverter. The downconverter includes an LO1 circuit and a mixer. The LO1 circuit generates an LO1 signal synchronized with an LO synchronization signal. The mixer receives RF signals in first frequency bands and downconverts them to second frequency bands by mixing the RF signals with the LO1 signal. The optical transmitter modulates the downconverted RF signals and the LO synchronization signal onto optical beams and transmits the modulated optical beams over a fiber. The optical receiver demodulates the modulated optical beams to reconstruct the downconverted RF signals and the LO synchronization signal. The upconverter includes an LO2 circuit and a mixer. The LO2 circuit generates an LO2 signal responsively to the reconstructed LO synchronization signal. The mixer mixes the reconstructed RF signals with the LO2 signal to reconstruct the RF signals in the first frequency bands.

Inventors

• David Gabbay

Assignees

• RFOPTIC LTD.

Dates

Publication Date

20260512

Application Date

20240130

Claims (18)

1. 1 . A system for communication, comprising: a downconverter comprising: a first Local Oscillator (LO) circuit configured to generate a first LO signal, which is synchronized with an LO synchronization signal; and a mixer coupled to receive one or more radiofrequency (RF) signals in respective first frequency bands and to downconvert the received RF signals to respective second frequency bands by mixing the RF signals with the first LO signal; an optical transmitter, which is configured to modulate the downconverted RF signals and the LO synchronization signal onto one or more optical beams and to transmit the one or more modulated optical beams over a fiber; an optical receiver, which is configured to receive and demodulate the one or more modulated optical beams from the fiber to reconstruct the downconverted RF signals and the LO synchronization signal; and an upconverter comprising: a second LO circuit, configured to generate a second LO signal responsively to the reconstructed LO synchronization signal; and a mixer configured to mix the reconstructed RF signals with the second LO signal to reconstruct the one or more radiofrequency (RF) signals in the respective first frequency bands.
2. 2 . The system according to claim 1 , wherein the second LO circuit is configured to lock a phase of the second LO signal on a phase of the first LO signal using the LO synchronization signal.
3. 3 . The system according to claim 1 , wherein the first LO signal comprises one or more first LO signals associated respectively with the received RF signals, and wherein the second LO signal comprises one or more second LO signals associated respectively with the reconstructed RF signals.
4. 4 . The system according to claim 3 , wherein, for a given RF signal and corresponding reconstructed RF signal, the second LO circuit is configured to lock on a same LO frequency of the first LO signal, based on the reconstructed LO synchronization signal.
5. 5 . The system according to claim 3 , wherein the first LO circuit comprises a first Direct Digital Synthesizer (DDS), configured to generate the first LO signals, and wherein the second LO circuit comprises a second DDS, configured to generate the second LO signals.
6. 6 . The system according to claim 5 , wherein the first DDS and the second DDS are configured to generate the first LO signals and the second LO signals by cyclically serializing predefined bit patterns associated respectively with the RF signals.
7. 7 . The system according to claim 6 , wherein the first DDS and the second DDS are configured to generate at least one of a frequency hopping first LO signal and a frequency hopping second LO signal, by switching, at specified instances, among different bit patterns.
8. 8 . The system according to claim 5 , wherein the first DDS is configured to apply phase modulation to an RF signal downconverted by a given LO signal, by shifting the bit pattern used for generating the given LO signal to corresponding points in the bit pattern, at specified instances.
9. 9 . The system according to claim 1 , wherein based on the LO synchronization signal, the second LO circuit is configured to keep relative phase differences among the reconstructed RF signals so as to match respective relative phase differences among the received RF signals.
10. 10 . A method for communication, comprising: generating a first LO signal, which is synchronized with an LO synchronization signal; receiving one or more radiofrequency (RF) signals in respective first frequency bands and downconverting the received RF signals to respective second frequency bands by mixing the RF signals with the first LO signal; modulating the downconverted RF signals and the LO synchronization signal onto one or more optical beams and transmitting the one or more modulated optical beams over a fiber; receiving and demodulating the one or more modulated optical beams from the fiber to reconstruct the downconverted RF signals and the LO synchronization signal; generating a second LO signal responsively to the reconstructed LO synchronization signal; and mixing the reconstructed RF signals with the second LO signal to reconstruct the one or more radiofrequency (RF) signals in the respective first frequency bands.
11. 11 . The method according to claim 10 , and comprising locking a phase of the second LO signal on a phase of the first LO signal using the LO synchronization signal.
12. 12 . The method according to claim 10 , wherein the first LO signal comprises one or more first LO signals associated respectively with the received RF signals, and wherein the second LO signal comprises one or more second LO signals associated respectively with the reconstructed RF signals.
13. 13 . The method according to claim 12 , and comprising, for a given RF signal and corresponding reconstructed RF signal, locking on a same LO frequency of the first LO signal, based on the reconstructed LO synchronization signal.
14. 14 . The method according to claim 12 , wherein generating the first LO signals comprises generating the first LO signals using a first Direct Digital Synthesizer (DDS), and wherein generating the second LO signals comprises generating the second LO signals using a second DDS.
15. 15 . The method according to claim 14 , generating the first LO signals and the second LO signals comprises cyclically serializing predefined bit patterns associated respectively with the RF signals by the first DDS and the second DDS, respectively.
16. 16 . The method according to claim 15 , and comprising generating at least one of a frequency hopping first LO signal and a frequency hopping second LO signal, by switching, at specified instances, among different bit patterns.
17. 17 . The method according to claim 14 , and comprising applying phase modulation to an RF signal downconverted by a given LO signal, by shifting the bit pattern used for generating the given LO signal to corresponding points in the bit pattern, at specified instances.
18. 18 . The method according to claim 10 , wherein based on the LO synchronization signal, keeping relative phase differences among the reconstructed RF signals so as to match respective relative phase differences among the received RF signals.

Description

TECHNICAL FIELD Embodiments described herein relate generally to RF transmission, and particularly to methods and systems for band-converted transmission of RF signals over fiber. BACKGROUND Modern communication technologies require the transmission of wideband high frequency Radio Frequency (RF) signals over distance. In various applications RF signals may be transmitted via optical fibers with very low transmission loss. Communication links supporting the transmission of RF signals over optical fibers are collectively referred to as “RF over Fiber” (RFoF) links. SUMMARY An embodiment that is described herein provides a system for communication, including a downconverter, an optical transmitter, an optical receiver, and an upconverter. The downconverter includes a first Local Oscillator (LO) circuit, and a mixer. The first LO circuit is configured to generate a first LO signal, which is synchronized with an LO synchronization signal. The mixer is coupled to receive one or more radiofrequency (RF) signals in respective first frequency bands and to downconvert the received RF signals to respective second frequency bands by mixing the RF signals with the first LO signal. The optical transmitter is configured to modulate the downconverted RF signals and the LO synchronization signal onto one or more optical beams and to transmit the one or more modulated optical beams over a fiber. The optical receiver is configured to receive and demodulate one or more modulated optical beams from the fiber to reconstruct the downconverted RF signals and the LO synchronization signal. The upconverter includes a second LO circuit and a mixer. The second LO circuit is configured to generate a second LO signal responsively to the reconstructed LO synchronization signal. The mixer is configured to mix the reconstructed RF signals with the second LO signal to reconstruct the one or more RF signals in the respective first frequency bands. In some embodiments, the second LO circuit is configured to lock a phase of the second LO signal on a phase of the first LO signal using the LO synchronization signal. In other embodiments, the first LO signal includes one or more first LO signals associated respectively with the received RF signals, and the second LO signal includes one or more second LO signals associated respectively with the reconstructed RF signals. In yet other embodiments, for a given RF signal and corresponding reconstructed RF signal, the second LO circuit is configured to lock on a same LO frequency of the first LO signal, based on the reconstructed LO synchronization signal. In an embodiment, the first LO circuit includes a first Direct Digital Synthesizer (DDS), configured to generate the first LO signals, and the second LO circuit includes a second DDS, configured to generate the second LO signals. In another embodiment, the first DDS and the second DDS are configured to generate the first LO signals and the second LO signals by cyclically serializing predefined bit patterns associated respectively with the RF signals. In yet another embodiment, the first DDS and the second DDS are configured to generate at least one of a frequency hopping first LO signal and a frequency hopping second LO signal, by switching, at specified instances, among different bit patterns. In some embodiments, the first DDS is configured to apply phase modulation to an RF signal downconverted by a given LO signal, by shifting the bit pattern used for generating the given LO signal to corresponding points in the bit pattern, at specified instances. In other embodiments, based on the LO synchronization signal, the second LO circuit is configured to keep relative phase differences among the reconstructed RF signals so as to match respective relative phase differences among the received RF signals. There is additionally provided, in accordance with an embodiment that is described herein, a method for communication, including generating a first LO signal, which is synchronized with an LO synchronization signal. One or more radiofrequency (RF) signals in respective first frequency bands are received, and the received RF signals are downconverted to respective second frequency bands by mixing the RF signals with the first LO signal. The downconverted RF signals and the LO synchronization signal are modulated onto one or more optical beams, and the one or more modulated optical beams are transmitted over a fiber. The one or more modulated optical beams are received from the fiber and demodulated to reconstruct the downconverted RF signals and the LO synchronization signal. A second LO signal is generated responsively to the reconstructed LO synchronization signal. The reconstructed RF signals are mixed with the second LO signal to reconstruct the one or more radiofrequency (RF) signals in the respective first frequency bands. These and other embodiments will be more fully understood from the following detailed description of the embodiments thereof, ta