142 and after demultiplexing by the corresponding demux 144, RRU 110 detects the analog optical data signal 138, which is subsequently converted by O/E transducer(s) 148 into a second analog data signal. RRU controller 146 causes filter and/or amplifier 152 to filter and amplify the second analog data signal, and causes antenna(s) 154 to transmit a first RF signal, over the air, based on the second analog data signal. In examples, the first RF signal is at its original wavelength up to a millimeter wave (“mmWave”) range (e.g., corresponding to a frequency of 60+ GHz or so), while the optical carrier signal for carrying the first RF signal is one of an original band (“O-band”) channel (at wavelengths between about 1260 and about 1360 nm), a conventional band (“C-band”) channel (at wavelengths between about 1530 and about 1565 nm), a long wavelength band (“L-band”) channel (at wavelengths between about 1565 and about 1625 nm), or any other band where the amplifier can operate (e.g., a 4G spectrum channel (at wavelengths between about 100 and about 400 nm), a 5G spectrum channel (at wavelengths between about 300 and about 1000 nm), or a millimeter wave (“mmWave”) channel (at wavelengths between about 1 and about 10 mm)).

In another aspect, an RRU 115 receives a second RF signal using antenna(s) 158. RRU controller 156 uses filter and/or amplifier 160 to filter and/or amplify the second RF signal, and the filtered second RF signal is used as input into laser(s) 162, in some cases, using E/O transducer(s) 164 to convey electrical signals onto an optical signal(s). The E/O transducer(s) 164 uses one of two modulation methods: (1) direct modulation of a laser(s), in which the current of the laser is modulated by the incoming analog signal; or (2) external modulation of the laser(s), where the output of the laser(s) is coupled to an external optical modulator, which is driven using a drive signal with the analog signal. Optical amplifier(s) 166 amplifies the second optical data signal to produce analog optical data signal 168, which is multiplexed and sent to the BBU 105 via a corresponding mux 170, a corresponding HCF fronthaul link 172, and a corresponding demux 174 that communicatively couple the BBU 105 and the RRU 115. Alternatively, the second optical data signal is multiplexed by a corresponding mux 170, and is amplified by optical amplifier(s) 166′ to produce analog optical data signal 168, and the analog optical data signal 168 is sent to the BBU 105 via a corresponding HCF fronthaul link 172 and a corresponding demux 174 that communicatively couple the BBU 105 and the RRU 115. After transmission through the corresponding HCF fronthaul link 172 and after demultiplexing by the corresponding demux 174, BBU 105 detects and converts the analog optical data signal 168 into a third analog data signal using O/E transducer(s) 176 (in some cases, including photodetector(s) 178), and filters the third analog data signal using filter(s) 180. BBU controller 122 causes signal processing system(s) 130 to convert the third analog data signal into a second data packet that is sent to the network(s) 120 via data network interface 128. In some examples, the signal processing system(s) 130 includes various sub-blocks. For the uplink to BBU, the various sub-blocks filter, down-convert, digitize, down-convert, then demodulate data signals, with bits and packets being subsequently extracted. For the downlink from the BBU to the RRU, only filtering and amplification occurs. In examples, an amplitude of the analog optical data signal 138 that is sent from the BBU 105 to the determined RRU 110 is greater than an amplitude of the analog optical data signal 168 that is sent from the RRU 115 to the BBU 105. This is due to a need to ensure sufficient energy for transmission over the air as an RF signal for the analog optical data signal 138 from the BBU 105 to the RRU 110, in contrast with conversion into a data packet, which has lower energy requirements (particularly if the O/E transducer(s) 176 and/or the photodetector(s) 178 is sufficiently sensitive), for the analog optical data signal 168 from the RRU 115 to the BBU 105.

In an example, BBU controller 122 causes signal processing system(s) 130 to convert a common clock signal from system clock 126 into a first analog clock signal. The BBU controller 122 further causes each E/O transducer 134 to convert the first analog clock signal into another clock control signal that is used by each corresponding laser 132 to generate an optical clock signal, which is amplified by each corresponding optical amplifier 136 (before muxes 140) or 136′ (after muxes 140). Alternative to using the signal processing system(s) 130, BBU controller 122 causes each E/O transducer 134 to convert the common clock signal directly into a clock control signal that is used by each corresponding laser 132 to generate the optical clock signal. In either case, the optical clock signal is sent to each of the RRUs 110a-110x and 115a-115x via corresponding muxes 140, corresponding HCF fronthaul links 142, and corresponding demuxes 144. The optical clock signal is received and converted by O/E transducer(s) 148 into yet another analog clock signal, which is converted by RRU controller 146 into a clock synchronization signal. In some examples, the O/E transducer(s) 148 includes (or is the same as) photodetector(s) 150. RRU controller 146 synchronizes a local clock using the clock synchronization signal.

FIGS. 2A-2C depict various example sets of components 200A and 200B that are used, and an example series of optical signals 200C that is sent as output of one of a plurality of muxes from a BBU to an RRU(s), when implementing improved cellular fronthauling. FIG. 2D depicts an example set of components 200D that is used for sending optical signals from an RRU to a BBU when implementing improved cellular fronthauling. In some embodiments, BBU 205, data network interface 210, synchronization signal/fault detection/monitoring systems 215a-215n and 215a′-215n′, BBU to RRU data transfer systems 220a-220z, feed to RRU systems 230, E/O—amplification systems 240, muxes 246a-246n, HCF fronthaul links 256 and 256a-256n, demuxes 252a-252n, RRUs 260a-260z, 265a-265z, 270a-270z, and 275a-275z, feed to BBU systems 262a-262z, 266a-266z, 272a-272z, and 276a-276z, E/O—amplification systems 264′ or 264a-264z, 268′ or 268a-268z, 274′ or 274a-274z, and 278′ or 278a-278z, muxes 254a-254n, HCF fronthaul links 258 and 258a-258n, demuxes 252a-252n, and O/E—amplification 232a′-232z′, 234a′-234z′, 236a′-236z′, and 240a′-240z′ of FIGS. 2A-2D may be similar, if not identical, to the BBU 105, data network interface 128, BBU controller 122/system clock 126, signal processing system(s) 130, laser(s) 132/E/O transducer(s) 134/optical amplifier(s) 136 or 136′, mux(es) 140, HCF fronthaul links 142, demux(es) 144, RRUs 110a-110x and 115a-115n, RRU controller 156/filter and/or amplifier 160, laser(s) 162/E/O transducer(s) 164/optical amplifier(s) 166 or 166′, muxes 170, HCF fronthaul links 172, demuxes 174, and O/E transducer(s) 176/photodetector(s) 178, respectively, of system 100 of FIG. 1, and the description of these components of system 100 of FIG. 1 are similarly applicable to the corresponding components of FIGS. 2A-2D. Herein, m, n, x, and z are non-negative integer numbers that may be either all the same as each other, all different from each other, or some combination of same and different (e.g., one set of two or more having the same values with the others having different values, a plurality of sets of two or more having the same value with the others having different values).

With reference to FIG. 2A, in an example, the example set of components 200A includes BBU 205, HCF fronthaul links 256a-256n (collectively, “HCF fronthaul links 256”), demuxes 252a-252n, and RRUs 260a-260z, 265a-265z, 270a-270z, and 275a-275z. In examples, in BBU 205, data network interface 210 communicatively couples a network(s) (e.g., network(s) 120 of FIG. 1) with each of feed to RRU systems 230 in BBU to RRU data transfer systems 220a-220z. The feed to RRU systems 230 include feed to RRU systems 222a-222z, 224a-224z, 226a-226z, through 230a-230z, each communicatively coupled to corresponding E/O—amplification systems 232′ or 232a-232z, 234′ or 234a-234z, 236′ or 236a-236z, through 240′ or 240a-240z (collectively, “E/O—amplification systems 240”). In examples, feed to RRU systems 230 each performs functions similar, if not identical, to signal processing system(s) 130 of FIG. 1, as described in detail above. The feed to RRU systems 222a-222z, 224a-224z, 226a-226z, through 230a-230z each communicatively couples with a corresponding one of the E/O—amplification systems 232a-232z, 234a-234z, 236a-236z, through 240a-240z. In some examples, E/O—amplification systems 232a-232z, 234a-234z, 236a-236z, through 240a-240z each performs functions similar, if not identical, to a combination of laser(s) 132, E/O transducer(s) 134, and/or optical amplifier(s) 136 or 136′ of FIG. 1, as described in detail above. The feed to RRU systems 230 and corresponding E/O—amplification systems 240 are grouped into a plurality of BBU to RRU data transfer systems 220a-220z. As shown in FIG. 2A, synchronization signal/fault detection/monitoring systems 215a-215n each communicatively coupled with one of muxes 246a-246n. Each of E/O—amplification systems 232a-232z communicatively couples with mux 246a, and each of E/O—amplification systems 234a-234z communicatively couples with mux 246b, while each of E/O—amplification systems 236a-236z communicatively couples with mux 246c, and each of E/O—amplification systems 240a-240z communicatively couples with mux 246n. Muxes 246a-246n communicatively couples with corresponding demuxes 252a-252n via corresponding HCF fronthaul links 256a-256n (collectively, “HCF fronthaul links 256”). Demux 252a communicatively couples with RRUs 260a-260z, and demux 252b communicatively couples with RRUs 265a-265z, while demux 252c communicatively couples with RRUs 270a-270z, and demux 252n communicatively couples with RRUs 275a-275z. In some cases, each of muxes 246a-246n outputs an analog optical signal into a corresponding one of optical amplifiers 232′, 234′, 236′, or 240′, which amplifies the analog optical signal prior to transmission over the corresponding HCF fronthaul links 256a-256n to a corresponding one of demuxes 252a-252n.

For ease of illustration, in FIG. 2A, different line types are used to depict:

- (a) connection between E/O—amplification systems 232a-232z and RRUs 260a-260z via mux 246a, HCF fronthaul link 256a, and demux 252a (depicted by the solid lines);
- (b) connection between E/O—amplification systems 234a-234z and RRUs 265a-265z via mux 246b, HCF fronthaul link 256b, and demux 252b (depicted by the long-dashed lines);
- (c) connection between E/O—amplification systems 236a-236z and RRUs 270a-270z via mux 246c, HCF fronthaul link 256c, and demux 252c (depicted by the short-dashed lines); and
- (d) connection between E/O—amplification systems 240a-240z and RRUs 275a-275z via mux 246n, HCF fronthaul link 256n, and demux 252n (depicted by the dotted lines).

Referring to FIG. 2B, in an example, the example set of components 200B includes a feed to RRU system 230 (e.g., corresponding to one of the feed to RRU systems 230 of FIG. 2A). Each feed to RRU system 230 includes a plurality of wireless service in-phase and quadrature (“I/Q”) channels 280a-280m each communicatively coupled to a corresponding one of mixing to RF/filtering/electrical amplification systems 285a-285m. Each I/Q channel 280a-280m carries an in-phase data signal and a quadrature data signal, which are amplitude-modulated sinusoidal signals (modulated using an I/Q modulator) that have the same frequency but a phase difference of 90°. When summed, the in-phase data signal and the quadrature data signal (collectively, “I/Q signal”) doubles the data sent. Each mixing to RF/filtering/electrical amplification system 285a-285m, which converts the I/Q signals into analog RF data signals, performs filtering, and performs amplification of filter analog RF data signals, communicatively couples with a power coupling/amplification/filtering system 290. The power coupling/amplification/filtering system 290 couples the amplified and filtered analog RF data signals from each of the mixing to RF/filtering/electrical amplification system 285a-285m of the feed to RRU system 230, then performs additional amplification and filtering. In examples, the output of the power coupling/amplification/filtering system 290 is input into the corresponding E/O—amplification system 240 of FIG. 2A.

Turning to FIG. 2C, an example series of optical signals 200C is sent as output of one of the plurality of muxes 246a-246n from the BBU 205 to an RRU among the RRUs 260a-260z, 265a-265z, 270a-270z, and 275a-275z. As shown in FIG. 2C, a synchronization signal 292 is followed by a plurality of optical carrier signals 294a-294y (collectively, “optical carrier signals 294”). Each optical carrier signal 294 is carried over an optical channel among a plurality of channels λ₁-λ_y. Each optical carrier signal 294 includes double-sideband modulation of optical data signals 1 through Z corresponding to data traffic received from each of E/O—amplification systems 232′ or 232a-232z, data traffic received from each of E/O—amplification systems 234′ or 234a-234z, data traffic received from each of E/O—amplification systems 236′ or 236a-236z, or data traffic received from each of E/O—amplification systems 240′ or 240a-240z. In the example of FIG. 2C, each optical data signal among signals 1 through Z is a double-sideband modulation of the optical data signals or double-sideband modulated optical data signals (as depicted in FIG. 2C by triangular-shaped bands on either side of arrows denoted 1, 2, 3, through Z). A double-sideband modulated signal in general can concurrently carry two separate amplitude modulated signals (e.g., RF signals that are modulated on the optical carrier at an RF frequency). In examples, double-sideband modulation is used for direct detection (e.g., using intensity of light). In some examples, the receiver and transmitter side modulation can be changed to have different flavors of such optical modulation for direct detection. Various such flavors include Optical Carrier+Single-sideband, in which the transmission side optical modulation is optimized to only have the optical carrier and one set of subcarriers 1-Z, with the mirror image removed. Alternatively, Coherent transmission and detection can be used, where intensity/phase and polarization are used (and, in some cases, optical modulation and reception are also changed). Herein, m, n, x, y, and Z or z are non-negative integer numbers that may be either all the same as each other, all different from each other, or some combination of same and different (e.g., one set of two or more having the same values with the others having different values, a plurality of sets of two or more having the same value with the others having different values). As used herein, double-sideband modulation or the double-sideband modulated optical data signals (as depicted in FIG. 2C) is characterized by a mirrored arrangement of a sequence of optical data signal among signals 1 through Z on one side of a center wavelength of each channel λ and a reverse sequence of optical data signal among signals Z through 1 on the other side of the center wavelength of that channel λ. In examples, direct modulation is used that creates a double-sideband signal. In some cases, a different modulation (e.g., a different implementation of external modulation) is used to create only a single-sideband. As shown in FIG. 2C, in some examples, a fault detection signal 296 and a line monitoring signal 298 follow the plurality of optical carrier signals 294a-294y. Where the synchronization signal 292 is used to synchronize the RRUs (as described above), the fault detection signal 296 is used as a trigger for fault detection systems at the RRUs, in a technique referred to as reflectometry. Like optical frequency domain reflectometry (“OFDR”) or optical time domain reflectometry (“OTDR”), a signal is launched at the BBU side. If there are defects in the particular optical link, a reflection at the same transmitted wavelength is received, which assists with determining where the link is/was broken or damaged. In other words, upon detection of a fault, a corresponding error signal is returned to the BBU (e.g., to synchronization/fault detection/line monitoring systems 215a′-215n′ of FIG. 2D) from the RRU where the fault occurs. The line monitoring signal 298 likewise is used as a trigger for line monitoring between the BBU and the corresponding RRU. Upon detection of a line fault, a corresponding error signal is returned to the BBU.

With reference to FIG. 2D, in an example, the example set of components 200D includes RRUs 260a-260z, 265a-265z, 270a-270z, and 275a-275z and BBU 205, each corresponding to RRUs 260a-260z, 265a-265z, 270a-270z, and 275a-275z and BBU 205 of FIG. 2A. The example set of components 200D further includes muxes 254a-254n and HCF fronthaul links 258a-258n (collectively, “HCF fronthaul links 258”). As shown in FIG. 2D, each of RRUs 260a-260z includes a corresponding one of feed to BBU systems 262a-262z and a corresponding one of E/O—amplification systems 264a-264z, each such feed to BBU system 262 being communicatively coupled with the corresponding E/O—amplification system 264. Similarly, each of RRUs 265a-265z includes a corresponding one of feed to BBU systems 266a-266z and a corresponding one of E/O—amplification systems 268a-268z, each such feed to BBU system 266 being communicatively coupled with the corresponding E/O—amplification system 268. Likewise, each of RRUs 270a-270z includes a corresponding one of feed to BBU systems 272a-272z and a corresponding one of E/O—amplification systems 274a-274z, each such feed to BBU system 272 being communicatively coupled with the corresponding E/O—amplification system 274. Similarly, each of RRUs 275a-275z includes a corresponding one of feed to BBU systems 276a-276z and a corresponding one of E/O—amplification systems 278a-278z, each such feed to BBU system 276 being communicatively coupled with the corresponding E/O—amplification system 278.

BBU 205 further includes demuxes 248a-248n, synchronization signal/fault detection/monitoring systems 215a′-215n′, and O/E—amplification 232a′-232z′, 234a′-234z′, 236a′-236z′, and 240a′-240z′. Each of RRUs 260a-260z communicatively couples with mux 254a, and each of RRUs 265a-265z communicatively couples with mux 254b, while each of RRUs 270a-270z communicatively couples with mux 254c, and each of RRUs 275a-275z communicatively couples with mux 254n. Muxes 254a-254n communicatively couples with corresponding demuxes 248a-248n via corresponding HCF fronthaul links 258a-258n. In some cases, optical amplifiers 264′, 268′, 274′, or 278′each amplifies signals from a corresponding one of the muxes 254a-254n prior to transmission over a corresponding one of the HCF fronthaul links 258a-258n to a corresponding one of demuxes 248a-248n. Demux 248a communicatively couples with O/E—amplification 232a′-232z′, and demux 248b communicatively couples with O/E—amplification 234a′-234z′, while demux 248c communicatively couples with O/E—amplification 236a′-236z′, and demux 248n communicatively couples with O/E—amplification 240a′-240z′. Each of demuxes 248a-248n further communicatively couples with a corresponding one of synchronization signal/fault detection/monitoring systems 215a′-215n′.

In examples, with reference to FIGS. 2A-2D, the operations of the BBU 205 (and its components), the RRUs 260a-260z, 265a-265z, 270a-270z, and 275a-275z (and their components), the muxes 246a-246n and 254a-254n, the demuxes 248a-248n and 252a-252n, and the HCF fronthaul links 256a-256n and 258a-258n are otherwise similar to corresponding components of FIG. 1 in terms of structure and function.

With reference to FIG. 3, the operations of example method 300 may be performed by a BBU (e.g., BBUs 105 and 205 of FIGS. 1 and 2A) and an RRU(s) (e.g., RRUs 110, 260a-260z, 265a-265z, 270a-270z, and 275a-275z of FIGS. 1 and 2A). Referring to FIG. 4, the operations of example method 400 may be performed by a BBU (e.g., BBUs 105 and 205 of FIGS. 1 and 2D) and an RRU (e.g., RRUs 115, 260a-260z, 265a-265z, 270a-270z, and 275a-275z of FIGS. 1 and 2D).

FIG. 3 depicts an example method 300 for sending data from a BBU to an RRU among a plurality of RRUs when implementing improved cellular fronthauling. In the example of FIG. 3A, method 300, at operation 305, includes a BBU controller at the BBU receiving a first data packet for transmission to one of the plurality of RRUs for RF transmission, using a data network interface. In some cases, the BBU controller receives multiple streams dedicated to various RRUs, and the BBU controller manages and directs each stream to its corresponding RRU. At operation 310, the BBU controller determines which RRU among the plurality of RRUs to send the first data packet. The BBU controller routes the first data packet to a signal processing system of the BBU, based on the determined RRU to send the first data packet (at operation 315). At operation 320, the signal processing system converts the first data packet from digital data into a first analog data signal. A first electrical to optical transducer of the BBU converts the first analog data signal into a first optical data signal (at operation 325). In some examples, converting the first analog data signal into the first optical data signal (at operation 325) includes the first electrical to optical transducer converting the first analog data signal into a first optical control signal; and a first laser at the BBU generating the first optical data signal based on the first optical control signal. In examples, method 300 either continues onto the process at operation 330 or continues onto the process at operation 335. At operation 330, method 300 further includes a first filter at the BBU filtering the first optical data signal. Method 300 continues onto the process at operation 335. At operation 335, a first optical amplifier at the BBU causes amplification of the first optical data signal to produce a first amplified optical data signal. Method 300, at operation 340, the first amplified optical data signal is sent to the determined RRU via a first multiplexer, over a corresponding HCF fronthaul link among a plurality of HCF-based fronthaul links, and via a first demultiplexer. In some examples, rather than the filtering step at operation 330, the first multiplexer (at operation 340) adds a filter profile that is used to filter the first optical data signal. In examples, the first optical amplifier is disposed after the first multiplexer, and amplification of the first optical data signal occurs after being multiplexed by the first multiplexer.

At operation 345, a first photodetector at the determined RRU receives the first amplified optical data signal, from the first demultiplexer. The first optical to electrical transducer at the RRU converts the first amplified optical data signal into a second analog data signal (at operation 350). In examples, method 300 either continues onto the process at operation 355 or continues onto the process at operation 360. At operation 355, method 300 further includes a second filter at the RRU filtering (and amplifying) the second analog data signal. Method 300 continues onto the process at operation 360. At operation 360, the RRU controller at the RRU sends, over the first antenna, a first RF signal based on the second analog data signal.

FIG. 4 depicts an example method 400 for sending data from an RRU to a BBU when implementing improved cellular fronthauling. In the example of FIG. 4A, method 400, at operation 405, includes an antenna of the RRU receiving a first RF signal. At operation 410, an RRU controller of the RRU converts (and electrically amplifies) the first RF signal into a first analog data signal. An electrical to optical transducer of the RRU converts the first analog data signal into a first optical data signal (operation 415). In some examples, converting the first analog data signal into the first optical data signal (at operation 415) includes the electrical to optical transducer of the RRU converting the first analog data signal into a first optical control signal; and a laser at the RRU generating the first optical data signal based on the first optical control signal. In examples, method 400 either continues onto the process at operation 420 or continues onto the process at operation 425. At operation 420, method 400 further includes a filter at the RRU filtering the first optical data signal. Method 400 continues onto the process at operation 425. At operation 425, an optical amplifier of the RRU causes amplification of the first optical data signal to produce a first amplified optical data signal. Method 400, at operation 430, the first amplified optical data signal is sent to the BBU via a multiplexer among a plurality of multiplexers, over an HCF fronthaul link among a plurality of HCF-based fronthaul links, and via a demultiplexer among a plurality of demultiplexers. In some examples, rather than the filtering step at operation 420, the multiplexer (at operation 430) adds a filter profile that is used to filter the first optical data signal. In examples, the optical amplifier is disposed after the multiplexer, and amplification of the first optical data signal occurs after being multiplexed by the multiplexer. Method 400 continues onto the process at operation 435. Here, the first optical data signal can be amplified to a high level of amplification. As HCF does not have any issues with high-power transmission, amplification can be as high as possible. In an example, high-power lasers can be used that are modulated and then multiplexed, and the multiplexed signal is then amplified to very high powers (e.g., 34+ dBm or greater). In another example, each individual optical signal is amplified before the mux after the modulation stage with a separate amplifier, raising the transmission power (e.g., to 30-34+ dBm), then multiplexing all of the amplified optical signals. In either example, the line system (e.g., amplification and mux) can be performed in HCF or in free space.

At operation 435, a photodetector among a plurality of photodetectors at the BBU receives the first amplified optical data signal from the demultiplexer. Because high-power optical signals are being transmitted, the plurality of photodetectors includes high-power photodetectors that are capable of receiving the high-power optical signals and generating high-power electrical RF signals. An optical to electrical transducer among a plurality of optical to electrical transducers at the BBU converts the first amplified optical data signal into a second analog data signal (at operation 440). In examples, method 400 either continues onto the process at operation 445 or continues onto the process at operation 450. At operation 445, method 400 further includes a second filter at the BBU filtering the second analog data signal. Method 400 continues onto the process at operation 450. At operation 450, a signal processing system among the plurality of signal processing systems at the BBU converts the second analog data signal into a first data packet. A BBU controller at the BBU sends the first data packet through a data network, via a data network interface at the BBU (at operation 455).

While the techniques and procedures in methods 300, 400 are depicted and/or described in a certain order for purposes of illustration, it should be appreciated that certain procedures may be reordered and/or omitted within the scope of various embodiments. Moreover, while the methods 300, 400 may be implemented by or with (and, in some cases, are described below with respect to) the systems, examples, or embodiments 100 and 200A-200D of FIGS. 1 and 2A-2D, respectively (or components thereof), such methods may also be implemented using any suitable hardware (or software) implementation. Similarly, while each of the systems, examples, or embodiments 100 and 200A-200D of FIGS. 1 and 2A-2D, respectively (or components thereof), can operate according to the methods 300, 400 (e.g., by executing instructions embodied on a computer readable medium), the systems, examples, or embodiments 100 and 200A-200D of FIGS. 1 and 2A-2D can each also operate according to other modes of operation and/or perform other suitable procedures.

As should be appreciated from the foregoing, the present technology provides multiple technical benefits and solutions to technical problems. For instance, implementing RAN or C-RAN (or O-RAN) using conventional infrastructure (e.g., using solid core fiber-based systems) generally raises multiple technical problems. For example, one technical problem is that such conventional infrastructure requires analog microwave signals to be digitized for transport over fronthaul links, because normal solid core optical fibers otherwise induce distortions such as fading effects and the generation of spurious signals that are detrimental to quality of the microwave signals. The digitization process involves a significant multiplication in the effective payload data rates, which can sometimes require base stations needing fiber delivery of data rates on the order of 10s to 100s of Terabits per second, and potentially Petabits per second for next generation systems. As a consequence, greater complexity is required for the hardware and software, as well as greater power consumption. Synchronization is also made difficult due to solid core fibers being susceptible to stretching caused by temperature variations and stresses, which in turn causes changes in refractive index over time that results in changes in delay over time being different for different fibers. Further, for C-RAN systems, there is a latency range that needs to be adhered to which will reduce the maximum distance between RRU and RRH, but for solid core fibers, the latency is higher than for HCF.

The present technology provides for a low complexity and low latency implementation for cellular fronthauling. At a BBU, data packets received from a data network are converted into analog data signals, which are in turn converted into analog optical signals that are optically amplified and sent over an HCF-based fronthaul link(s) to an RRU(s). At the RRU(s), the analog optical signals are converted into analog data signals that are sent over the air as RF signals via an antenna(s). In some cases, the analog data signals are filtered and amplified prior to transmission as RF signals. RF signals that are received, via antennas, at an RRU are conversely filtered and converted into analog optical signals, transmitted over the HCF-based fronthaul link(s) to the BBU, where the analog optical signals are converted into data packets for transmission over the data network. In this manner, digitization of the optical data signal and back to analog after transmission over the fronthaul link is obviated. High-power or high intensity optical signals can also be sent over the HCF-based fronthaul link(s) compared with solid core fiber-based fronthaul links, which are susceptible to chromatic dispersion and nonlinearities due to interaction between high intensity propagating optical signals and silica in the solid core fibers. This is due to the structure of HCFs minimizing Kerr effects, thus minimizing chromatic dispersion and nonlinearities. Further, the reduced latency with the use of HCF allows for further distances between the RRU and the RRH. Overall, the present technology results in energy savings, reduced hardware requirements, enhanced reliability, reduced error rates, low complexity, and low latency.