The present invention relates to the field of telecommunication networks and more specifically to fast transmission enabling a fast transmission of data within a limited area and for a limited cost.
Optical fibers enable fast transmissions with large throughput thanks to the wavelength multiplexing. However, such networks require expensive equipment to ensure signal detection. Such equipments are fast tunable receivers based on coherent detection. Thus, for some applications such as the communication between neighboring base stations of a cellular network, such equipments are too expensive and provide a higher quality than required due to the limited distance between the different base stations.
It is therefore an object of the present invention to overcome the above mentioned drawbacks of the state of the art and to provide a solution that enables fast transmission within a limited area without requiring expensive equipment such as fast tunable receivers.
Thus, the present invention refers to an optical node destined to be implemented in an optical ring network comprising links configured for transmitting a plurality of multiplexed wavelength channels wherein at least one wavelength channel is dedicated to signals targeted to a particular node wherein the optical node comprises:
According to another aspect of the present invention, the wavelength blocker comprises an isolator coupled with at least one Bragg grating.
According to a further aspect of the present invention, the receiving unit comprises at least one non-coherent receiver.
According to an additional aspect of the present invention, the transmission unit comprises at least one fast tunable laser.
According to another aspect of the present invention, the transmission unit and the reception unit are combined in a transceiver.
According to a further aspect of the present invention, the transmission unit and the reception unit are remote from the main branch and the optical node comprises a first optical circulator located next to the main branch and connected to the first and the second optical coupler and a second optical circulator connected to the transmission unit and the reception unit, the first and second optical circulators being linked by an optical link, the first circulator being configured for transmitting the signals received from the first coupler to the second optical circulator and for transmitting the signals received from the second optical circulator to the second optical coupler, the second optical circulator being configured for transmitting the signals received from the first optical circulator to the reception unit and for transmitting the signals received from the transmission unit to the first optical circulator.
According to an additional aspect of the present invention, the optical node comprises a base station remote from the main branch and the reception unit and the transmission unit are implemented within the base station.
The embodiments of the present invention also refer to an optical ring network comprising a plurality of nodes in accordance with one of the previous claims, the said nodes being linked by optical links, the said links being configured for transmitting a plurality of multiplexed wavelength channels wherein at least one wavelength channel is dedicated to signals targeted to a particular node.
According to another aspect of the present invention, the nodes comprise a base station of a cellular network, the base stations of the nodes being neighboring base stations and the optical ring network comprises an additional node linked to a backbone network.
According to a further aspect of the present invention, the additional node comprises:
According to an additional aspect of the present invention, the base stations are remote from the main branch of the nodes and comprise the transceivers.
In these drawings, the elements having the same reference correspond to elements having a similar function.
The embodiments of the present invention refer to an optical ring network 1 comprising a plurality of nodes, four in the present example noted Ni with i=1 . . . 4, as represented in
A second output of the first optical coupler 5 is connected to a main branch 9 comprising a wavelength blocker 11. The wavelength blocker 11 is implemented with an isolator 13 and a Bragg grating 15. The Bragg grating 15 is configured to send back the signals transmitted in the wavelength channel λ1 dedicated to the node N1, the said signals being blocked by the isolator 13. Alternatively, the wavelength blocker 11 could be implemented with a ring resonator configured to route the wavelength channel λ1 toward a receiver 7 of the node N1 and for transmitting the other wavelength channels toward the next node N2. The wavelength channel λ1 dedicated to the node N1 is therefore freed at the output of the Bragg grating 15 so that new signals can be added on this wavelength channel λ1 by the subsequent nodes. The output of the Bragg grating 15 is connected to an input of a second optical coupler 17, for example a 3 dB coupler. An other input of the second optical coupler 17 is connected to a transmission unit herein implemented as a transmitter 19, for example a fast tunable laser, configured to transmit signals on the wavelength channels λ2, λ3 and λ4 dedicated to the other nodes N2, N3 and N4.
In order to transmit these signals, the transmitter 19 has to be aware of the free time intervals, for example time slots in the case of a slotted network, within these wavelength channels λ2, λ3 and λ4 to avoid the superimposition of two signals within a single wavelength channel which would not be detectable by the targeted node. Such determination of the free time intervals can be achieved for example by photodiodes located at the input of the node and configured for detecting signals transmitted on the different wavelength channels λ2, λ3 and λ4. Alternatively, the transmission of the different signals can be scheduled by a centralized control interface so that the authorization for transmitting on a wavelength channel is given directly by the control interface to the transmitter 19. If signals need to be transmitted from node N1 to node N4, the transmitter 19 is tuned on the wavelength λ4 dedicated to signals targeted to node N4 and when a free time interval is detected on this wavelength channel λ4, the transmitter emits a signal, for example a packet or a plurality of packets if depending on the duration of the free time interval, which are transmitted to the second optical coupler 17.
Thus, the signals coming from the transmitter 19 and from the main branch 9 are transmitted by the second optical coupler 17 to the output 18 of the node toward the next node N2 via the optical link L1.
Such configuration enables providing a low cost optical ring network as neither fast tunable receivers nor coherent detection equipment are necessary. Furthermore, such optical ring network can be easily modified to cope with an increase of traffic. Indeed, instead of allocating one wavelength channel to a given node, two wavelength channels can be dedicated to signals targeted to the said node. Such modification only requires an additional Bragg grating 15 configured for blocking the signals transmitted on the additional wavelength channel and one additional receiver 7 tuned to the additional wavelength. An additional transmitter 19 may also be added to transmit more packets toward the other nodes if the other nodes are also upgraded with an additional receiver 7.
Thus, such optical ring network configuration allows an easy adaptation to the variations of traffic. Furthermore, if the size of the optical ring network 1 remains limited, for example a few dozens of kilometers (up to 50 kilometers for example), no amplifier is required which contributes to a low cost optical ring network.
According to another embodiment of the node Ni which will be described in more details in the following of the description based on
According to an aspect of the present invention, the optical ring network 1 is used to connect the neighboring base stations of a cellular network. The neighboring base stations herein refers to base stations located in a common area so that a user terminal can be connected simultaneously to two of these neighboring base stations. The number of base stations connected to the optical ring network 1 is limited, for example to six base stations as represented in
It has to be noted that the optical ring network 1 of
Furthermore, as indicated previously, the capacity of a node can be increased to cope with an increase of traffic. In such case, the structure of node N2 represented in
The node structure disclosed in
Thus, the nodes and the optical ring network of the present invention enable to obtain a low cost ring network providing modularity to adapt to an increase of traffic and are particularly well adapted to connect neighboring base stations of a cellular network and to ensure communication with the backbone network.
Number | Date | Country | Kind |
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13290228 | Sep 2013 | EP | regional |
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PCT/EP2014/068334 | 8/29/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/043871 | 4/2/2015 | WO | A |
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