Patent Description:
According to a first aspect of the present disclosure, there is provided a system comprising a first optical line terminal (OLT) of a first passive optical network (PON), the first OLT configured to receive user data from a BBU and send the user data to a RRU via a first optical network unit (ONU) of the first PON using a first wavelength, and a second OLT of a second PON, the second OLT configured to obtain control and management (C&M) information, share the C&M information with the first OLT, and send the C&M information to a second ONU that is co-located with the first ONU using a second wavelength. In the above embodiment or in a separate embodiment, the second OLT is configured to send the C&M information to the second ONU independently of the first OLT sending the user data to the first ONU; wherein the second PON is deployed substantially parallel to the first PON; wherein the first OLT is co-located with the second OLT; the first OLT and the second OLT are communicatively coupled to each other; wherein the second ONU is configured to share the C&M information with the co-located first ONU; wherein the C&M information is generated by any of the BBU, the first OLT, the second OLT, the first ONU, or the second ONU; wherein the first OLT is configured to communicate with the first ONU via an optical distribution network, ODN, forming the first PON; the second OLT is configured to communicate with the second ONU via the same ODN, forming the second PON; and wherein the first PON and the second PON are part of an efficient common public radio interface, eCPRI. In any of the above embodiments or in a separate embodiment, the second OLT is configured to perform MAC processing before sending the C&M information to the second ONU. In any of the above embodiments or in a separate embodiment, the second ONU is configured to share the C&M information with the co-located first ONU. In any of the above embodiments or in a separate embodiment, the C&M information comprises at least one of ranging information, time of day (ToD) information, registration information, or dynamic bandwidth allocation (DBA) information. In any of the above embodiments or in a separate embodiment, the system further comprises an OLT memory coupled to the first OLT and the second OLT, wherein the C&M information is stored in the OLT memory, and wherein the first OLT and the second OLT both use the C&M information. In any of the above embodiments or in a separate embodiment, the first OLT and the second OLT use a same time quanta (TQ). In any of the above embodiments or in a separate embodiment, the first OLT comprises a first clock having a first TQ, wherein the second OLT comprises a second clock having a second TQ, and wherein the second TQ is a positive integer multiple of the first TQ. In any of the above embodiments or in a separate embodiment, the second OLT is configured to generate a moving average ToD from received ToD measurements, wherein the first OLT is configured to use the moving average ToD to adjust a clock of the first OLT. In any of the above embodiments or in a separate embodiment, the first PON is part of an efficient/Ethernet/evolved common public radio interface (eCPRI).

Common public radio interface (CPRI) is an interface used for radio base stations between the radio equipment controller (REC) (e.g. the BBU) and the radio equipment (RE) (e.g. the RRU) and is used in many mobile fronthaul configurations. But CPRI is not very bandwidth-efficient. To increase the efficiency of CPRI, eCPRI is being defined. One implementation of eCPRI uses a PON in the mobile fronthaul architecture (e.g. the PON operates between the BBU and the RRUs and implements eCPRI). When eCPRI is used with a traditional PON for mobile fronthaul, the overall latency due to both mobile-media access control (MAC) and PON-MAC processing is unacceptably large, especially for time-sensitive applications such as fifth generation (<NUM>) RANs, which require a latency of less than one millisecond. Moving various C&M functions out of the eCPRI would increase the bandwidth efficiency and decrease overall latency of the eCPRI.

Disclosed herein is a C-RAN architecture comprising a first PON that implements eCPRI to exchange user data between the BBU and the RRUs, and a second PON, deployed substantially in parallel with the first PON, that exchanges C&M information for both the first PON and the second PON. The two PONs feature wavelength division multiplexing in some embodiments, such that each PON has its own upstream and downstream wavelengths. The two OLTs share an OLT memory in some embodiments, and the two ONUs share an ONU memory in some embodiments, where the OLT memory and the ONU memory can each store at least some of the C&M information. The C&M information can include some or all of ranging information, ONU registration information, ToD information, or DBA information. The two PONs are clock synchronized with the BBU and the RRU. Because the second PON is not involved in transmission of user data, the second PON can be a lower- data transfer rate, lower-cost PON, such as a GPON or an EPON, which reduces implementation costs.

<FIG> illustrates a C-RAN <NUM> in an embodiment. In the depicted embodiment, the C-RAN <NUM> comprises a BBU <NUM>, a first OLT <NUM> and a second OLT <NUM> (collectively, OLTs <NUM>, <NUM>), an optical distribution network (ODN) <NUM>, a first ONU <NUM> and a second ONU <NUM> (collectively, ONUs <NUM>, <NUM>), and a plurality of RRUs <NUM>. The BBU <NUM> communicates with an upstream network (not shown) via electrical or optical means, for example. The RRUs <NUM> wirelessly communicate with various mobile devices <NUM>, such as mobile telephones, tablets, or mobile computing devices, for example. The RRUs <NUM> can further communicate with other user devices or electronic devices. Such other devices are contemplated and are within the scope of the description and claims, including Internet of Things (IoT) devices and sensors, for example. The BBU <NUM> and the OLTs <NUM>, <NUM> are located at a central location, such as a central office, whereas the ONUs <NUM>, <NUM> and the RRUs <NUM> are located at remote locations, such as cellular towers <NUM>. One or more of each of the ONUs <NUM>, <NUM> may be located at each cellular tower <NUM>, and each first ONU <NUM> may be associated with at least one RRU <NUM>. In an embodiment, the first OLT <NUM> is integrated with the second OLT <NUM> such that they are part of a single device, but still maintain the functionality described herein. Similarly, in an embodiment the first ONU <NUM> is integrated with the second ONU <NUM> such that they are part of a single device, but still maintain the functionality described herein. While three cellular towers <NUM> are shown in <FIG>, there may be more or fewer cellular towers in other embodiments of the C-RAN <NUM>.

The first OLT <NUM> communicates with the first ONUs <NUM> via the ODN <NUM>, thereby forming a first PON. Similarly, the second OLT <NUM> communicates with the second ONUs <NUM> via the same ODN <NUM>, thereby forming a second PON. Each PON has a separate upstream and downstream transmission wavelength, which allows the PONs to be wavelength division multiplexed and share the ODN <NUM>. In addition, each PON is a communication network that does not require any active components to distribute data between the OLTs <NUM>, <NUM> and the ONUs <NUM>, <NUM>. Instead, each PON uses passive optical components in the ODN <NUM> to distribute data between the OLTs <NUM>, <NUM> and the ONUs <NUM>, <NUM>. In an embodiment, the first PON and the second PON are part of a single PON.

In an embodiment, the BBU <NUM> is any device that is configured to implement base station functions, including base station C&M functions. As such, the BBU <NUM> provides many of the same functions as a radio element controller. In some embodiments, the BBU can provide backhaul transport processing, MAC layer processing, channel coding, channel interleaving, channel modulation, multiple input/multiple output (MIMO) processing, transmit power control of each physical channel, frame and slot signal, quadrature amplitude modulation (QAM) equalization, processed signal decoding, and forward error correction (FEC). Although only a single BBU <NUM> is illustrated in <FIG>, a plurality of the BBUs <NUM> may be located at the central office to form a BBU pool. When the central office comprises multiple BBUs <NUM>, the multiple BBUs <NUM> may be linked such that they share information, or they may be separated such that they are unable to communicate with each other.

The first OLT <NUM> is a device that is configured to communicate with the first ONUs <NUM> and the BBU <NUM>. Specifically, the first OLT <NUM> forwards user data received from the BBU <NUM> to a first ONU or ONUs <NUM>, and forwards user data received from the first ONUs <NUM> to the BBU <NUM>. As used herein, user data is data that is exchanged between the BBU <NUM> and the RRU <NUM> using the first PON (e.g. the first OLT <NUM> and the first ONU <NUM>), and that ultimately terminates or originates at the mobile device <NUM>.

User data does not include C&M information. User data is not typically exchanged using the second PON (e.g. the second OLT <NUM> and the second ONU <NUM>). However, the second PON may be used for some overflow user data that can tolerate the latency and/or reduced data transfer rate of the second PON.

The second OLT <NUM> is a device that is configured to communicate with the second ONUs <NUM>, but not with the BBU <NUM> or the RRUs <NUM> in some embodiments. Instead, the second OLT <NUM> exchanges C&M information for the two PONs with the second ONUs <NUM>. As used herein, the C&M information is any information used to control and/or manage the first PON and/or the second PON. C&M information does not include user data. Examples of C&M information include one or more of ranging information (e.g. the ranging delay), ONU registration information (e.g. the ONU's identifier (ID)), ToD information for synchronizing clock frequencies, or DBA information. The C&M information is generated by any of the BBU <NUM>, the first OLT <NUM>, the second OLT <NUM>, the first ONU <NUM>, or the second ONU <NUM>. The C&M information is not exchanged using the first PON (e.g. the first OLT <NUM> and the first ONU <NUM>). The first OLT <NUM> and the second OLT <NUM> are communicatively coupled to each other. Additionally or alternatively, the second OLT <NUM> may be communicatively coupled to the BBU <NUM>. Additionally or alternatively, the second OLT <NUM> may be communicatively coupled to both the BBU <NUM> and the first OLT <NUM>. The first OLT <NUM> is co-located with the second OLT <NUM>.

The ODN <NUM> is a passive optical data distribution system that does not require any power to distribute optical signals between the OLTs <NUM>, <NUM> and the ONUs <NUM>, <NUM>. In the embodiment in <FIG>, the ODN <NUM> comprises an optical trunk line <NUM>, an optical splitter <NUM>, and branching optical fibers <NUM>. While the ODN <NUM> in <FIG> has a single splitter <NUM>, the ODN <NUM> may be alternatively configured with multiple splitters <NUM>. In various embodiments, the ODN <NUM> may also comprise optical couplers, distributors, multiplexers, and/or other optical equipment as needed to distribute the optical signals from the OLTs <NUM>, <NUM> to the ONUs <NUM>, <NUM>.

The first ONUs <NUM> are devices that are configured to communicate with the first OLT <NUM> and the RRU <NUM>. Specifically, each first ONU <NUM> forwards user data received from the respective RRUs <NUM> to the first OLT <NUM>, and forwards user data received from the first OLT <NUM> to at least one RRU <NUM>. In some embodiments, the second ONUs <NUM> are devices that are configured to communicate with the second OLT <NUM>, but not with the BBU <NUM> or the RRUs <NUM>. Instead, the second ONU <NUM> exchanges C&M information for the two PONs with the second OLT <NUM>. As used herein, ONUs <NUM>, <NUM> and optical network terminals (ONTs) are functionally similar, and thus the term "ONU" encompasses both ONUs and ONTs. In some embodiments, the first ONUs <NUM> and the second ONUs <NUM> are communicatively coupled to each other. Additionally or alternatively, the second ONUs <NUM> may be communicatively coupled to the RRUs <NUM>. In an embodiment, the first ONU <NUM> is co-located with the second ONU <NUM>.

The RRUs <NUM> are devices that wirelessly communicate with one or more mobile devices <NUM> via antennas (not shown) on the cellular towers <NUM>. The RRUs <NUM> are located at a cellular tower <NUM> (such as an evolved node B (eNode B or eNB)). The RRUs <NUM> perform radio functions, including frequency conversion, amplification, channel filtering, carrier multiplexing, analog to digital (A/D) conversion, digital to analog (D/A) conversion, cyclic prefix removal/addition, fast Fourier transform (FFT)/inverse FFT (IFFT) processing, and resource block mapping/demapping. To perform these functions, the RRUs <NUM> may comprise power amplifiers, duplexers, and digital signal processors. In an embodiment, the RRUs <NUM> operate at the same one or same set of carrier frequencies.

<FIG> illustrates a C-RAN <NUM> in another embodiment. In the C-RAN <NUM>, the user data passes from the BBU <NUM> to the first OLT <NUM>, to the ODN <NUM>, to the first ONU <NUM>, and to the RRU <NUM> connected to antennas (not shown) on the cellular towers <NUM>. In an embodiment, the C&M information passes from the BBU <NUM> to the second OLT <NUM>, to the ODN <NUM>, to the second ONU <NUM>, and to the RRU <NUM>. Thus, <FIG> illustrates an embodiment where C&M information flows from the BBU <NUM> to the second PON and to the RRU <NUM> without passing through the first PON.

<FIG> illustrates a C-RAN <NUM> in another embodiment. In the C-RAN <NUM>, user data passes from the BBU <NUM> to the first OLT <NUM>, to the ODN <NUM>, to the first ONU <NUM>, and to the RRU <NUM> connected to antennas (not shown) on the cellular towers <NUM>. However, the C&M information in <FIG> passes from the BBU <NUM> to the first OLT <NUM>, to the second OLT <NUM>, to the ODN <NUM>, to the second ONU <NUM>, to the first ONU <NUM>, and to the RRU <NUM>. Thus, <FIG> illustrates an embodiment where C&M information flows from the BBU <NUM> to the first OLT <NUM>, to the second PON, to the first ONU <NUM>, and to the RRU <NUM>.

<FIG> illustrates a C-RAN <NUM> in another embodiment. In the C-RAN <NUM>, user data passes from the BBU <NUM> to the first OLT <NUM>, to the ODN <NUM>, to the first ONU <NUM>, and to the RRU <NUM> connected to antennas (not shown) on the cellular towers <NUM>. However, the C&M information in <FIG> passes from the BBU <NUM> to the second OLT <NUM>, to the ODN <NUM>, to the second ONU <NUM>, to the first ONU <NUM>, and to the RRU <NUM>. Thus, <FIG> illustrates an embodiment where C&M information flows from the BBU <NUM> directly to the second PON (e.g. bypassing the first OLT <NUM>), to the first ONU <NUM>, and to the RRU <NUM>.

<FIG> illustrates a C-RAN <NUM> in another embodiment. In the C-RAN <NUM>, user data passes from the BBU <NUM> to the first OLT <NUM>, to the ODN <NUM>, to the first ONU <NUM>, and to the RRU <NUM> connected to antennas (not shown) on the cellular towers <NUM>. However, the C&M information in <FIG> passes from the BBU <NUM> to the first OLT <NUM>, to the second OLT <NUM>, to the ODN <NUM>, to the second ONU <NUM>, and to the RRU <NUM>. Thus, <FIG> illustrates an embodiment where C&M information flows from the BBU <NUM> to the first OLT <NUM>, to the second PON, and directly to the RRU <NUM> (e.g. bypassing the first ONU <NUM>).

<FIG> illustrates the PON portion <NUM> of the C-RAN in an embodiment. Specifically, the PON portion <NUM> comprises the first PON <NUM>, which comprises the first OLT <NUM>, a first optical multiplexer <NUM>, the ODN <NUM>, a second optical multiplexer <NUM>, and the first ONU <NUM>. The PON portion <NUM> also comprises the second PON <NUM>, which comprises the second OLT <NUM>, the first optical multiplexer <NUM>, the ODN <NUM>, the second optical multiplexer <NUM>, and the second ONU <NUM>. The OLTs <NUM>, <NUM> are each coupled to an OLT memory <NUM> and the first optical multiplexer <NUM>, whereas the first OLT <NUM>, but not the second OLT <NUM>, is coupled to the BBU <NUM>. Similarly, the ONUs <NUM>, <NUM> are each coupled to an ONU memory <NUM> and the second optical multiplexer <NUM>, whereas the first ONU <NUM>, but not the second ONU <NUM>, is coupled to the RRU <NUM>.

As mentioned above, the first PON <NUM> is a high-data transfer rate PON that allows user data to be exchanged between the BBU <NUM> and the RRUs <NUM>. In one embodiment, the first PON <NUM> transmits both upstream and downstream messages at a first rate, such as <NUM> Gigabit per second (Gb/s) using a frame-and-timeslot arrangement similar to GPON, which is defined by International Telecommunication Union Telecommunications Standardization Sector (ITU-T) G. In another embodiment, the receivers in the first PON <NUM> include A/D converters and optical digital signal processors (oDSPs), which allows the upstream and downstream messages to be transmitted at <NUM> Gb/s. In yet another embodiment, the transmitters in the first PON <NUM> implement advanced modulation formats, such as DMT or PAM4, and the receivers in the first PON <NUM> include A/D converters and oDSPs, which allow the upstream and downstream messages to be transmitted at <NUM> Gb/s.

The first PON <NUM> implements eCPRI to exchange data (e.g. user data) between the BBU <NUM> and the RRUs <NUM>. eCPRI provides a transport network interface between the eCPRI radio equipment controller (e.g. the BBU <NUM>) and the eCPRIradio equipment (e.g. the RRUs <NUM>). While eCPRI can be implemented using Ethernet, it can also be implemented using other packet-based protocols, such as Internet Protocol (IP) and multi-protocol label switching (MPLS). As such, the first PON <NUM> implements a packet-based transport protocol, such as Ethernet, IP, or MPLS, to transport the user data from the BBU <NUM> to the RRUs <NUM>. The eCPRI meets the latency requirements of <NUM> systems, and is able to achieve a latency of less than <NUM> microseconds. Specifically, the first PON described herein is configured to transmit upstream and downstream user data in bursts that are cycled at a time interval that is less than or equal to <NUM> microseconds in some embodiments.

In an embodiment, the eCPRI represents the functional split between the RRUs <NUM> and the BBU <NUM>. Some fronthaul configurations limit the functions performed at the RRU <NUM> to radio frequency (RF)-to-baseband conversion and A/D conversion. In such instances, the BBU <NUM> has to perform many functional steps, including cyclic prefix removal, performing FFT, resource block demapping, QAM equalization and processed signal decoding, and forward error correction. In an embodiment, eCPRI moves various functions, such as cyclic prefix removal, performing FFT, and resource block demapping, for example, from the BBU <NUM> to the RRUs <NUM>. Such a configuration improves the operational efficiency of the mobile fronthaul.

The second PON <NUM> supports the first PON <NUM> by handling the C&M information exchange that would normally be handled by the first PON <NUM>. Specifically, the C&M information for the first PON <NUM> is exchanged through the second OLT <NUM> and the second ONU <NUM> at a second rate instead of through the first OLT <NUM> and the first ONU <NUM> at a first rate. In some embodiments, the second PON <NUM> features a lower data transfer rate, wherein the second PON <NUM> transfers data at a second rate that is slower than the first rate, wherein the first rate is used for transferring user data. In some embodiments, the second PON <NUM> is a GPON as defined by ITU-T G. <NUM> or an EPON as defined by Institute of Electrical and Electronics Engineers (IEEE) <NUM>. These networks typically have data transfer rates of <NUM> Gb/s, <NUM> Gb/s, or <NUM> Gb/s. Alternatively, the second PON <NUM> may be a ten Gb/s GPON (XGPON) as defined by ITU-T G. <NUM>, a <NUM>-EPON as defined by the IEEE <NUM>. 3av, or a broadband PON (BPON) or an asynchronous transfer mode PON (APON) as defined by ITU-T G.

The OLT memory <NUM> is a volatile or non-volatile memory structure configured to store the C&M information, and may store other data, such as computer executable instructions, machine code, and other various forms of data. For example, the OLT memory <NUM> stores ToD information received from the BBU <NUM> or any other central office component (e.g. as described in IEEE <NUM>), and is accessible by the OLTs <NUM>, <NUM>. In addition, the OLT memory <NUM> stores ranging information, registration information, and bandwidth allocation information for the ONUs <NUM>, <NUM>, which is accessible by all OLTs <NUM>, <NUM>. In an embodiment, the bandwidth information is periodically adjusted to give each ONU <NUM>, <NUM> more or less bandwidth as needed. The OLT memory <NUM> also stores any other information needed by the OLTs <NUM>, <NUM>.

The first OLT <NUM> comprises a first OLT MAC component <NUM>, a first OLT transmitter <NUM>, and a first OLT receiver <NUM>. The first OLT MAC component <NUM> receives downstream user data from the BBU <NUM>, performs any needed MAC processing, and sends the downstream user data to the RRU <NUM> via the first optical multiplexer <NUM>, the ODN <NUM>, the second optical multiplexer <NUM>, and the first ONU <NUM>. The process is reversed for upstream user data. In an embodiment, the first OLT MAC component <NUM> is a processor configured to implement the functional steps described here. In another embodiment, the first OLT MAC component <NUM> is a processor that executes instructions stored in a memory (e.g. OLT memory <NUM>) to perform the functional steps described herein. The first OLT transmitter <NUM> comprises an electrical to optical (E/O) converter, such as a laser diode, and optionally comprises a digital to analog converter (DAC) upstream of the E/O converter. These components allow the first OLT transmitters <NUM> to receive electrical signals from the first OLT MAC component <NUM>, convert the electrical signals into optical signals, and transmit the optical signals through the ODN <NUM> via the first optical multiplexer <NUM>. The first OLT receiver <NUM> comprises an optical to electrical (O/E) converter, such as a photodiode, and optionally comprises an ADC downstream of the O/E converter. These components allow the first OLT receiver <NUM> to convert the optical signals received from the ODN <NUM> into electrical signals that are then passed to the first OLT MAC component <NUM>.

The second OLT <NUM> comprises a second OLT MAC component <NUM>, a second OLT transmitter <NUM>, and a second OLT receiver <NUM>. In some cases, the second OLT MAC component <NUM> obtains C&M information (e.g. ToD information and DBA information) from the OLT memory <NUM>, performs any needed MAC processing, and sends the C&M information to the second ONU <NUM> via the first optical multiplexer <NUM>, the ODN <NUM>, and the second optical multiplexer <NUM>. In other cases, the second OLT MAC component <NUM> requests C&M information (e.g. registration information for the ONUs <NUM>) from the second ONU <NUM>, receives the C&M information from the second ONU <NUM> via the second optical multiplexer <NUM>, the ODN <NUM>, and the first optical multiplexer <NUM>, performs any MAC processing, and stores the C&M information in the OLT memory <NUM>. In an embodiment, the ONUs <NUM>, <NUM> are physically close to each other, in which case the second OLT MAC component <NUM> can assume that the ranging information for the ONUs <NUM>, <NUM> is the same, and can store a common ranging delay for both the ONUs <NUM>, <NUM> in the OLT memory <NUM>. In an embodiment, the second OLT MAC component <NUM> is a processor configured to implement the functional steps described here. In another embodiment, the second OLT MAC component <NUM> is a processor that executes instructions stored in a memory (e.g., OLT memory <NUM>) to perform the functional steps described herein. The second OLT transmitter <NUM> and the second OLT receiver <NUM> are similar to the first OLT transmitter <NUM> and the first OLT receiver <NUM>, respectively.

The first optical multiplexer <NUM> and the second optical multiplexer <NUM> are any optical components that can separate a combined light stream into its separate wavelengths (or wavelength bands), and vice-versa. Specifically, the first optical multiplexer <NUM> and the second optical multiplexer <NUM> are configured to wavelength division multiplex light signals in one direction and wavelength division demultiplex light signals in the opposite direction. In one embodiment, the first optical multiplexer <NUM> and the second optical multiplexer <NUM> are arrayed waveguide gratings (AWGs). The optical multiplexers <NUM>, <NUM> may also be referred to as wavelength multiplexers.

The ONU memory <NUM> is a volatile or non-volatile memory structure configured to store the C&M information, but also may store other data, such as computer executable instructions, machine code, and other various forms of data. For example, the ONU memory <NUM> stores synchronization information and ToD information received from the second OLT <NUM>. The synchronization information and ToD information is accessible by the ONUs <NUM>, <NUM> and the RRUs <NUM> or any other co-located equipment (e.g. as described in IEEE <NUM>). In addition, the ONU memory <NUM> stores ranging information, registration information, and bandwidth allocation information for the ONUs <NUM>, <NUM>, which is accessible by the ONUs <NUM>, <NUM>. As described above, DBA may be periodically performed to give each ONU <NUM>, <NUM> more or less bandwidth as needed.

The first ONU <NUM> comprises a first ONU MAC component <NUM>, a first ONU transmitter <NUM>, and a first ONU receiver <NUM>. The first ONU MAC component <NUM> receives upstream user data from the RRU <NUM> and sends the upstream user data to the BBU <NUM> via the second optical multiplexer <NUM>, the ODN <NUM>, the first optical multiplexer <NUM>, and the first OLT <NUM>. The process is reversed for downstream data. In an embodiment, the first ONU MAC component <NUM> is a processor configured to implement the functional steps described here. In another embodiment, the first ONU MAC component <NUM> is a processor that executes instructions stored in a memory (e.g. ONU memory <NUM>) to perform the functional steps described herein. The first ONU transmitter <NUM> and the first ONU receiver <NUM> are similar to the first OLT transmitter <NUM> and the first OLT receiver <NUM>, respectively.

The second ONU <NUM> comprises a second ONU MAC component <NUM>, a second ONU transmitter <NUM>, and a second ONU receiver <NUM>. In some cases, the second ONU MAC component <NUM> receives C&M information (e.g. ToD information and DBA information) from the second OLT <NUM> via the first optical multiplexer <NUM>, the ODN <NUM>, and the second optical multiplexer <NUM>, and stores that C&M information in the ONU memory <NUM>. In other cases, C&M information (e.g. ranging information and registration information for the second ONU <NUM>) is generated by the second ONU MAC component <NUM>, and reported to the second OLT <NUM> via the second optical multiplexer <NUM>, the ODN <NUM>, and the first optical multiplexer <NUM>. In yet other cases, the C&M information (e.g. ranging information and registration information for the first ONU <NUM>) is generated by the first ONU MAC component <NUM> and stored in the ONU memory <NUM> for access by the second ONU MAC component <NUM>. In that case, the second OLT MAC <NUM> retrieves the C&M information from the ONU memory <NUM> and reports the C&M information to the second OLT <NUM> via the second optical multiplexer <NUM>, the ODN <NUM>, and the first optical multiplexer <NUM>. In an embodiment, the second ONU MAC component <NUM> is a processor configured to implement the functional steps described here. In another embodiment, the second ONU MAC component <NUM> is a processor that executes instructions stored in a memory (e.g. ONU memory <NUM>) to perform the functional steps described herein. The second ONU transmitter <NUM> and the second ONU receiver <NUM> are similar to the first OLT transmitter <NUM> and the first OLT receiver <NUM>, respectively.

The optical signals transmitted by the first OLT transmitter <NUM> and the second OLT transmitter <NUM> are multiplexed by the first optical multiplexer <NUM>, distributed through the ODN <NUM>, and demultiplexed by the second optical multiplexer <NUM> before arriving at the first ONU receiver <NUM> and the second ONU receiver <NUM>, respectively. Similarly, the optical signals transmitted by the first ONU transmitter <NUM> and the second ONU transmitter <NUM> are multiplexed by the second optical multiplexer <NUM>, are distributed through the ODN <NUM>, and are demultiplexed by the first optical multiplexer <NUM> before arriving at the first OLT receiver <NUM> and the second OLT receiver <NUM>, respectively.

Each optical transmitter is assigned its own wavelength so that the various optical signals do not interfere with each other. These wavelengths correspond to the coarse WDM (CWDM) spacing grid as defined in ITU-T G. However, dense WDM (DWDM) (as defined in ITU-T G. <NUM> or other spacing grid) may also be used. In an embodiment, the first OLT transmitter <NUM> can be configured to transmit at <NUM>±<NUM> nanometers (nm), the second OLT transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, the first ONU transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, and the second ONU transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, for example. By using wavelength multiplexing, the OLTs <NUM>, <NUM> and ONUs <NUM>, <NUM> do not interfere with each other.

<FIG> illustrates the PON portion <NUM> of the C-RAN in an embodiment. The PON portion <NUM> is substantially the same as the PON portion <NUM> described above, but comprises a third PON <NUM>. The third PON <NUM> comprises a third OLT <NUM>, optical multiplexers <NUM>, <NUM>, the ODN <NUM>, and a third ONU <NUM>. The third OLT <NUM> comprises a third OLT MAC component <NUM> coupled to the OLT memory <NUM> and the BBU <NUM>, a third OLT transmitter <NUM> coupled to the third OLT MAC component <NUM> and the first optical multiplexer <NUM>, and a third OLT receiver <NUM> coupled to the third OLT MAC component <NUM> and the first optical multiplexer <NUM>. Alternatively, the third OLT MAC component <NUM> is coupled to and communicates with a different BBU (not shown) than the BBU <NUM>. The third ONU <NUM> comprises a third ONU MAC component <NUM> coupled to the ONU memory <NUM> and the RRU <NUM>, a third ONU transmitter <NUM> coupled to the third ONU MAC component <NUM> and the second optical multiplexer <NUM>, and a third ONU receiver <NUM> coupled to the third ONU MAC component <NUM> and the second optical multiplexer <NUM>. Alternatively, the third ONU MAC component <NUM> is coupled to and communicates with a different RRU (not shown) than the RRU <NUM>. The third OLT MAC component <NUM>, the third OLT transmitter <NUM>, the third OLT receiver <NUM>, the third ONU transmitter <NUM>, the third ONU receiver <NUM>, and third ONU MAC component <NUM> are similar in structure and function to the first OLT MAC component <NUM>, the first OLT transmitter <NUM>, the first OLT receiver <NUM>, the first ONU transmitter <NUM>, the first ONU receiver <NUM>, and first ONU MAC component <NUM>, respectively.

In one embodiment, the third PON <NUM> is wavelength division multiplexed with the first PON <NUM> and the second PON <NUM> such that the third PON <NUM> operates at upstream and downstream wavelengths that are different from the first PON <NUM> and the second PON <NUM>. Use of the third PON <NUM> can expand the available bandwidth for transferring user data, for example. In an embodiment, the first OLT transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, the second OLT transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, the third OLT transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, the first ONU transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, the second ONU transmitter <NUM> can be configured to transmit at <NUM>±<NUM>, and the third ONU transmitter <NUM> can be configured to transmit at <NUM>+<NUM>, for example. In another embodiment, the third PON <NUM> is time division multiplexed with either the first PON <NUM> or the second PON <NUM> such that the third PON <NUM> operates at upstream and downstream wavelengths that are the same as the first PON <NUM> or the second PON <NUM>, but uses time division multiplexing (TDM)/time division multiple access (TDMA) to transmit downstream/upstream messages using the upstream and downstream wavelengths.

<FIG> is a protocol diagram of a method <NUM> for using the PON portion of the C-RAN in an embodiment. When an ONU (e.g. one of ONUs <NUM>, <NUM>) is added to the either the first PON or the second PON, the second OLT <NUM> sends a first C&M information message <NUM> to the second ONU <NUM> at a second rate. In one embodiment, the first C&M information message <NUM> includes a request for C&M information, such as ranging information and/or registration information for the newly added ONU. Upon receipt of the first C&M information message <NUM>, the second ONU <NUM> determines whether it possesses the requested C&M information. If the second ONU <NUM> does not already possess the requested C&M information, the second ONU <NUM> accesses the ONU memory (e.g. ONU memory <NUM>; not shown in <FIG>) to obtain the requested C&M information (such would be the case for registration information for the first ONU <NUM>). If the second ONU <NUM> already possesses the requested information, the second ONU <NUM> does not need to access the ONU memory (such would be the case for registration information for the second ONU <NUM>). The second ONU <NUM> then sends a first C&M information response <NUM> to the second OLT <NUM> with the requested C&M information, at which point the second OLT <NUM> stores the C&M information in the OLT memory (e.g. OLT memory <NUM>, not shown in <FIG>).

In an alternative embodiment, the first C&M information message <NUM> includes C&M information obtained from the OLT memory, such as ToD information and/or bandwidth assignments for the first ONU <NUM> and/or the second ONU <NUM> (e.g. DBA information). Upon receipt of the first C&M information message <NUM>, the second ONU <NUM> stores the C&M information in the ONU memory. The second ONU <NUM> then sends the first C&M information response <NUM> to the second OLT <NUM> acknowledging receipt of the C&M information. In either embodiment, the exchange of the first C&M information message <NUM> and the first C&M information response <NUM> occurs through the ODN (not shown in <FIG>) and may occur as many times as needed to properly configure all the components of the first PON and the second PON.

In either embodiment, the first OLT <NUM> and the second OLT <NUM> use the C&M information stored in the OLT memory, and the first ONU <NUM> and the second ONU <NUM> use the C&M information stored in the ONU memory. Recall that the BBU <NUM> (or another central office component) provides certain C&M information (e.g. ToD information) to the OLT memory. When the first OLT <NUM> and the second OLT <NUM> use the ToD information to set their clocks, the first OLT <NUM> and the second OLT <NUM> will be time synchronized with the BBU <NUM>. In addition, since the second OLT <NUM> shares the ToD information with the second ONU <NUM> and the second ONU <NUM> can use the ToD information to set its clock, the second ONU <NUM> is time synchronized with the BBU <NUM>, the first OLT <NUM>, and the second OLT <NUM>. Finally, recall that the second ONU <NUM> stores the ToD information in the ONU memory where it can be accessed by the first ONU <NUM> and the RRU <NUM>. Since the first ONU <NUM> and the RRU <NUM> can use the ToD information to set their clocks, the first ONU <NUM> and the RRU <NUM> are time synchronized with the BBU <NUM>, the first OLT <NUM>, the second OLT <NUM>, and the second ONU <NUM>. Generally, the first C&M information message <NUM> and the first C&M information response <NUM> can be referred to as an initialization phase.

At some point, the BBU <NUM> receives user data destined for the RRU <NUM>, e.g. from an upstream network (not shown). The BBU <NUM> sends the user data to the first OLT <NUM> in a first user data message <NUM>. The first OLT <NUM> then sends the user data to the first ONU <NUM> in a second user data message <NUM>, which may be an eCPRI message. The second user data message <NUM> is sent at a first rate, which is faster than the second rate. For example, the first rate can be <NUM> Gb/s and the second rate can be <NUM> Gb/s, as described above. The user data is therefore transferred at a higher data rate than the C&M information in this embodiment. In addition, the second user data message <NUM> traverses the same ODN as the first C&M information message <NUM> and the first C&M information response <NUM>. The first ONU <NUM> then sends the user data to the RRU <NUM> in a third user data message <NUM>. The user data carried in the user data messages <NUM>, <NUM>, <NUM> may comprise many types of data, but does not comprise any of the C&M information in some embodiments.

Also at some point, the RRU <NUM> receives user data destined for the BBU <NUM>, e.g. from a mobile device (not shown). The RRU <NUM> sends the user data to the first ONU <NUM> in a fourth user data message <NUM>. The first ONU <NUM> then sends the user data to the first OLT <NUM> in a fifth user data message <NUM>, which may be an eCPRI message. The fifth user data message <NUM> is typically sent at the first rate. The fifth user data message <NUM> traverses the same ODN as the first C&M information message <NUM> and the first C&M information response <NUM>. The first OLT <NUM> then sends the user data to the BBU <NUM> in a sixth user data message <NUM>. The user data carried in the user data messages <NUM>, <NUM>, <NUM> may comprise many types of data, but does not comprise any of the C&M information.

At various points, the second OLT <NUM> and the second ONU <NUM> need to exchange additional C&M information. In such as case, the second OLT <NUM> sends a second C&M information message <NUM> to the second ONU <NUM>, where the second C&M information message <NUM> either comprises at least some of the C&M information, or requests at least some of the C&M information (e.g. similar to the first C&M information message <NUM>). The second ONU <NUM> then sends a second C&M information response <NUM> to the second OLT <NUM>, where the second C&M information response <NUM> either acknowledges receipt of the C&M information, or replies with at least some of the C&M information (e.g. similar to the first C&M information response <NUM>). The exchange of the second C&M information message <NUM> and/or the second C&M information response <NUM> is shown happening subsequent to user data messages <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, but may also happen concurrently with the exchange of user data messages <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. Alternatively, the second C&M information message <NUM> and/or the second C&M information response <NUM> may occur before any of the user data messages <NUM>, <NUM>, and <NUM>.

In embodiments such as PON portion <NUM>, where there is a third OLT and a third ONU, the method <NUM> may be expanded to include, for example, the C&M information carried in the first C&M information message <NUM> and/or the first C&M information response <NUM> can include the C&M information for the third OLT and the third ONU. In addition, the BBU <NUM> and the RRU <NUM> can exchange user data using the third OLT and the third ONU in a manner similar to user data messages <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The data transfer rate of the first PON relative to the second PON is a consideration when designing and operating the first PON and the second PON (and optionally the third PON). Specifically, clock inaccuracy is a function of the TQ of the OLT, and the TQ of the OLT is a factor of the PON data transfer rate. As used herein, TQ is the smallest time unit available in the OLTs and/or the ONUs. TQ is functionally the same as envelope quanta (EQ), and thus the term "TQ" includes both TQ and EQ. Table <NUM> below illustrates the relationship between PON data transfer rate, MAC frequency/time period, and OLT/ONU TQ:.

Selection of a base TQ that can be multiplied by an integer to obtain other TQs allows the clocks in OLTs and ONUs of different rates to be synchronized. For example, if the first PON operates at <NUM> Gb/s, a first clock in the first OLT and a second clock in the first ONU have a TQ of <NUM> ns. A <NUM> ns TQ is beneficial because it can be multiplied by an integer multiple (e.g. <NUM>, <NUM>, <NUM>, <NUM>, etc.) to obtain any of the TQs shown in <FIG>. For example, the second PON can operate at <NUM> Gb/s, and as such a third clock in the second OLT and a fourth clock in the second ONU will have at TQ of <NUM> ns. Moreover, a TQ of <NUM> ns has a multipoint control protocol (MPCP) clock inaccuracy of ±<NUM> ns. The TDMA scheme used in the EPON has ±<NUM> TQ of tolerance (called the guardThresholdOLT), so the resulting TimeStamp drift error is reduced to ±<NUM> ns (<NUM> TQ * <NUM> ns/TQ). Assuming that the fiber propagation induced timing error is ±<NUM> ns, the total timing error will be ±<NUM> ns. However, if ±<NUM> ns accuracy is insufficient, the first PON can take multiple ToD measurements per time period (e.g. hour, day, etc.) and perform averaging to increase the accuracy of the ToD measurements fed to the second PON.

<FIG> shows a protocol diagram of a method <NUM> for using the C-RAN according to another embodiment. <FIG> is an alternative method to <FIG>. In this embodiment, the BBU <NUM> sends the user data to the first OLT <NUM> in a first message <NUM>. However, in this embodiment the BBU <NUM> also sends the user data directly to the second OLT <NUM> (e.g. bypassing the first OLT <NUM>) in a second message <NUM>. In some embodiments, the first message <NUM> and/or the second message <NUM> may comprise the C&M information, with the second OLT <NUM> accepting the C&M information from the BBU <NUM>. Messages <NUM>, <NUM> can correspond to the arrangement of the BBU <NUM> and the OLTs <NUM>, <NUM> shown in <FIG> and <FIG>, for example. In an alternative embodiment, the second message <NUM> may be excluded, and the first OLT <NUM> sends the user data and/or C&M information to the second OLT <NUM> in a fourth message <NUM>. In this alternative embodiment, messages <NUM>, <NUM> can correspond to the arrangement of the BBU <NUM> and the OLTs <NUM>, <NUM> shown in <FIG> and <FIG>, for example. In either embodiment, the first OLT <NUM> receives or accepts the user data, and sends the user data, but not the C&M information, to the first ONU <NUM> in a third message <NUM>. At some point in time, the second OLT <NUM> sends the C&M information and optionally the user data to the second ONU <NUM> in fifth message <NUM>. The fifth message <NUM> may be sent at any point in time after the C&M information has been received by the second OLT <NUM>.

In an embodiment, the second ONU <NUM> sends any user data and/or the C&M information to the first ONU <NUM> in sixth message <NUM>. The first ONU <NUM> sends the user data and/or the C&M information to the RRU <NUM> in seventh message <NUM>. Messages <NUM>, <NUM> can correspond to the arrangement of the ONUs <NUM>, <NUM> and the RRU <NUM> shown in <FIG> and <FIG>, for example. In an alternative embodiment, the second ONU <NUM> sends the user data and/or the C&M information directly to the RRU <NUM> (e.g. bypassing the first ONU <NUM>) in an eighth message <NUM>. In this alternative embodiment, the eighth message <NUM> can correspond to the arrangement of the ONUs <NUM>, <NUM> and the RRU <NUM> shown in <FIG> and <FIG>, for example.

At some point, the RRU <NUM> may send some user data to the first ONU <NUM> in ninth message <NUM>. The first ONU <NUM> sends the user data to the first OLT <NUM> in tenth message <NUM>. Additionally or alternatively, the first ONU <NUM> may send some of the user data and optionally some C&M information to the second ONU <NUM> in eleventh message <NUM>. In this embodiment, messages <NUM>, <NUM> can correspond to the arrangement of the RRU <NUM> and the ONUs <NUM>, <NUM> shown in <FIG> and <FIG>, for example. Alternatively, the RRU <NUM> sends some user data directly to the second ONU <NUM> (e.g. bypassing the first ONU <NUM>) in twelfth message <NUM>. In this alternative embodiment, the twelfth message <NUM> can correspond to the arrangement of the RRU <NUM> and the ONUs <NUM>, <NUM> shown in <FIG> and <FIG>, for example. In either embodiment, the second ONU <NUM> sends the C&M information and the user data to second OLT <NUM> in a thirteenth message <NUM>. The thirteenth message <NUM> may be sent at any point in time after the C&M information has been received by the second ONU <NUM>.

In one embodiment, the second OLT <NUM> sends the user data and at least some of the C&M information to the first OLT <NUM> in fourteenth message <NUM>. The first OLT <NUM> then sends the user data to the BBU <NUM> in fifteenth message <NUM>. In this embodiment, messages <NUM>, <NUM> can correspond to the arrangement of the BBU <NUM> and the OLTs <NUM>, <NUM> shown in <FIG> and <FIG>, for example. In an alternative embodiment, the second OLT <NUM> sends the user data directly to the BBU <NUM> (e.g. bypassing the first OLT <NUM>) in sixteenth message <NUM>. In this alternative embodiment, the sixteenth message <NUM> can correspond to the arrangement of the BBU <NUM> and the OLTs <NUM>, <NUM> shown in <FIG> and <FIG>, for example.

It will be appreciated that the described system has many advantages. For example, using a second PON to carry C&M information for the first PON improves the bandwidth of the first PON. In addition, implementing the second PON using legacy (e.g. GPON or EPON) components allows the second PON to be added to the first PON at a relatively low cost. Moreover, the described architecture allows the various components (BBU, OLTs, ONUs, and RRUs) to be clock synchronized with each other. The clock synchronization remains even if the clocks on the components of the first PON are faster than the clocks on the components of the second PON. This is because the two OLTs use the same TQ (e.g., <NUM> ns). Such also improves the synchronization accuracy. Furthermore, the second PON reads multiple ToD measurements per day from the OLT memory, performs a moving average of the ToD measurements, and stores the moving average of the ToD measurements in the OLT memory, where the first OLT uses the moving average of the ToD measurements to adjust its clock. Doing so reduces the timing error due to uncertainties caused by clock inaccuracies and TimeStamp drift error, and hence further improves synchronization accuracy.

While the above text describes the various PONs in terms of mobile fronthaul, it will be appreciated that the described PONs are not limited to such. In an embodiment, the described PONs are used to pass user data between any two components (e.g. not just a BBU and an RRU). For example, the described PONs can be implemented in metro or access networks to distribute user data to residential or commercial subscribers. In such cases, using a second PON to carry C&M information for the first PON, which carries user data destined for an end user instead of the mobile devices, improves the bandwidth of the first PON.

According to a first aspect of the present disclosure, there is provided a system comprising means for receiving user data from a BBU, means for sending the user data to a RRU via a first ONU of the first PON using a first wavelength, and means for obtaining C&M information, means for sharing the C&M information with the first OLT, and means for sending the C&M information to a second ONU that is co-located with the first ONU using a second wavelength. In the above embodiment or in a separate embodiment, the C&M information is sent independent of sending the user data to the first ONU. In any of the above embodiments or in a separate embodiment, the system includes means for performing MAC processing before sending the C&M information. In any of the above embodiments or in a separate embodiment, the second ONU is configured to share the C&M information with the co-located first ONU. In any of the above embodiments or in a separate embodiment, the C&M information comprises at least one of ranging information, ToD information, registration information, or DBA information. In any of the above embodiments or in a separate embodiment, the system further comprises means for storing the C&M information in the OLT memory, wherein the first OLT and the second OLT both use the C&M information. In any of the above embodiments or in a separate embodiment, the first OLT and the second OLT use a same TQ. In any of the above embodiments or in a separate embodiment, the first OLT comprises a first clock having a first TQ, wherein the second OLT comprises a second clock having a second TQ, and wherein the second TQ is a positive integer multiple of the first TQ. In any of the above embodiments or in a separate embodiment, the system further comprises means for generating a moving average ToD from received ToD measurements, wherein the first OLT is configured to use the moving average ToD to adjust a clock of the first OLT. In any of the above embodiments or in a separate embodiment, the C&M information is sent by the second OLT at a second data transfer rate, wherein the user data is sent at a first data transfer rate that is faster than the second data transfer rate. In any of the above embodiments or in a separate embodiment, the first PON is part of an eCPRI, the second PON is a GPON or an EPON, and the eCPRI is a functional split between the BBU and the RRU.

According to a second aspect of the present disclosure, there is provided a system comprising means for transmitting downstream user data to a first ONU of the first PON at a first data transfer rate using a first wavelength, and means for transmitting downstream information to a second ONU that is collocated with the first ONU, wherein the downstream information is sent at a second data transfer rate that is lower than the first data transfer rate, and wherein the downstream information is sent using a second wavelength. In the above embodiment or in a separate embodiment, the downstream information sent at the second data transfer rate comprises C&M information. In the above embodiment or in a separate embodiment, the first OLT is configured to couple to a BBU. In any of the above embodiments or in a separate embodiment, the system further comprises means for communicating with the BBU, and means for transmitting a second downstream user data to a third ONU at the first data transfer rate using a third wavelength, wherein the system further includes means for obtaining C&M information from to the second OLT. In any of the above embodiments or in a separate embodiment, the system further includes means for reading multiple ToD measurements per day from the OLT memory, means for performing a moving average of the ToD measurements to generate a moving average ToD, and means for providing the moving average ToD to the first OLT, wherein the first OLT is further configured to use the moving average ToD to adjust a first OLT clock. In any of the above embodiments or in a separate embodiment, the system includes means for sending the C&M information to the second ONU independent of the means for sending the user data to the first ONU. In any of the above embodiments or in a separate embodiment, the system includes means for performing MAC processing before sending the C&M information to the second ONU. In any of the above embodiments or in a separate embodiment, one or more of the first ONU, the second OLT, the second ONU, the BBU, or the RRU are clock synchronized with the first OLT as a result of sharing the C&M information. In any of the above embodiments or in a separate embodiment, the second ONU shares the C&M information with the co-located first ONU. In any of the above embodiments or in a separate embodiment, the system further comprises an OLT memory coupled to the first OLT and the second OLT, wherein the C&M information is stored in the OLT memory, and wherein the first OLT and the second OLT both use the C&M information. In any of the above embodiments or in a separate embodiment, the first OLT and the second OLT use a same TQ. In any of the above embodiments or in a separate embodiment, the first OLT comprises a first clock having a first TQ, wherein the second OLT comprises a second clock having a second TQ, and wherein the second TQ is a positive integer multiple of the first TQ. In any of the above embodiments or in a separate embodiment, the system further comprises means for generating a moving average ToD from received ToD measurements, and means for using the moving average ToD to adjust a clock of the first OLT. In any of the above embodiments or in a separate embodiment, the first PON is part of an eCPRI, wherein the second PON is a GPON or an EPON, and wherein the eCPRI is a functional split between the BBU and the RRU.

According to a third aspect of the present disclosure, there is provided a system comprising means for sending upstream user data to a first OLT of the first PON at a first data transfer rate using a first wavelength, and means for sending C&M information to a second OLT of the second PON, the C&M information being for the first ONU and the second ONU, wherein the C&M information is sent at a second data transfer rate using a second wavelength, and wherein the user data is sent at a first data transfer rate that is faster than the second data transfer rate. In any of the above embodiments or in a separate embodiment, the first ONU comprises a first ONU receiver comprising an ADC and a first digital signal processor. In any of the above embodiments or in a separate embodiment, the first ONU comprises a first ONU transmitter, the second ONU comprises a second ONU transmitter, and the system further comprises a wavelength multiplexer coupled to the first ONU transmitter and the second ONU transmitter. In any of the above embodiments or in a separate embodiment, the first ONU comprises a first ONU receiver, the second ONU comprises a second ONU receiver, and the system further comprises a wavelength de-multiplexer coupled to the first ONU receiver and the second ONU receiver. In any of the above embodiments or in a separate embodiment, the upstream user data is transmitted in bursts that are cycled at a time interval that is less than or equal to <NUM> microseconds.

Claim 1:
A system comprising:
a first optical line terminal, OLT (<NUM>), of a first passive optical network, PON (<NUM>), the first OLT configured to:
receive user data from a baseband unit, BBU (<NUM>); and
send the user data to a remote radio unit, RRU (<NUM>), via a first optical network unit, ONU (<NUM>) of the first PON using a first wavelength; and
a second OLT (<NUM>) of a second PON (<NUM>), the second OLT (<NUM>) configured to:
obtain control and management, C&M, information; and
the system being characterized by that:
the second OLT (<NUM>) is further configured to:
share the C&M information with the first OLT (<NUM>);
communicate with a second ONU (<NUM>) and send the C&M information to the second ONU (<NUM>) that is co-located with the first ONU (<NUM>) using a second wavelength;
wherein the second PON (<NUM>) is deployed substantially parallel to the first PON (<NUM>);
wherein the first OLT (<NUM>) is co-located with the second OLT (<NUM>); the first OLT (<NUM>) and the second OLT (<NUM>) are communicatively coupled to each other;
wherein the second ONU (<NUM>) is configured to share the C&M information with the co-located first ONU (<NUM>);
wherein the C&M information is generated by any of the BBU (<NUM>), the first OLT (<NUM>), the second OLT (<NUM>), the first ONU (<NUM>), or the second ONU (<NUM>);
wherein the first OLT (<NUM>) is configured to communicate with the first ONU (<NUM>) via an optical distribution network (<NUM>), ODN, forming the first PON (<NUM>); the second OLT (<NUM>) is configured to communicate with the second ONU (<NUM>) via the same ODN (<NUM>), forming the second PON (<NUM>); and
wherein the first PON and the second PON are part of an effecient common public radio interface, eCPRI.