Apparatus, method, device and medium for wavelength shift measurement

Abstract

Example embodiments of the present disclosure relate to a communication device, a communication method, a communication apparatus and a computer readable storage medium for wavelength shift measurement. In some example embodiments, in the method, it is determined whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold. The signals are wavelength division multiplexed using the wavelengths. If it is determined that a quality of one of the plurality of signals is below the threshold, a wavelength shift measurement is performed for at least a first wavelength of the plurality of wavelengths, wherein the signal is received using the first wavelength. A shifted wavelength of the plurality of wavelengths is determined based on the wavelength shift measurement, and a wavelength adjustment indication is sent to a communication device that transmits a signal using the shifted wavelength. Such a wavelength shift measurement approach is able to quickly detect a wavelength shift situation, thereby reducing the error correction time and improving the efficiency of the system and network.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to communication technology, and more particularly, to a communication device, a communication method, a communication apparatus and a computer readable storage medium for wavelength shift measurement. BACKGROUND

[0002] Due to the characteristics of high capacity and low latency, wavelength division multiplexing (WDM) technology has been widely applied to next-generation optical access networks, such as Next-Generation Passive Optical Network 2 (NG-PON2) and 5G X-haul systems. In 5G, the WDM-based fiber system connecting base stations and central stations is usually referred to as backhaul, while the fiber system connecting baseband units (BBUs) and remote radio heads (RRHs) is referred to as front-haul.

[0003] Due to factors such as aging of lasers and array waveguide gratings (AWGs) and other devices, changes in the ambient temperature of the equipment, and burst mode operation, there are often problems of wavelength shift in WDM systems. If a certain wavelength drifts out of the corresponding wavelength channel, on the one hand, it will cause power loss of the current channel; on the other hand, such wavelength shift will cause serious interference to the signals of adjacent channels. Therefore, the problem of wavelength shift in WDM systems has attracted great attention in industry development and research work. SUMMARY

[0004] Generally, example embodiments of the present disclosure propose a communication device, a communication method, a communication apparatus and a computer readable storage medium for wavelength shift measurement.

[0005] In a first aspect, example embodiments of the present disclosure provide a communication device. The communication device includes at least one processor and at least one memory storing computer program code. The at least one memory and the computer program code are configured to, with the at least one processor, cause the communication device to determine whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold. The signals are wavelength division multiplexed using the wavelengths. If it is determined that a quality of one of the plurality of signals is below the threshold, the communication device performs a wavelength shift measurement for at least a first wavelength of the plurality of wavelengths. The signal is received using the first wavelength. Based on the wavelength shift measurement, the communication device determines a shifted wavelength of the plurality of wavelengths and sends a wavelength adjustment indication to a communication device that transmits the signal using the shifted wavelength.

[0006] In a second aspect, example embodiments of the present disclosure provide a communication method. In the method, it is determined whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold. The signals are wavelength division multiplexed using the wavelengths. If it is determined that a quality of one of the plurality of signals is below the threshold, a wavelength shift measurement is performed at least for a first wavelength of the plurality of wavelengths, wherein the signal is received using the first wavelength. Based on the wavelength shift measurement, a shifted wavelength of the plurality of wavelengths is determined, and a wavelength adjustment indication is transmitted to a communication device that transmits a signal using the shifted wavelength.

[0007] In a third aspect, example embodiments of the present disclosure provide a communication apparatus. The apparatus comprises means for performing the method according to the second aspect.

[0008] In a fourth aspect, example embodiments of the present disclosure provide a computer readable storage medium having stored thereon a computer program. The computer program comprises instructions which, when executed on a processor of an apparatus, cause the apparatus to perform operations performed by the communication device according to the first aspect.

[0009] It is to be understood that the description in the summary section is not intended to define key or essential features of example embodiments of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0010] The above and other features, advantages and aspects of the present embodiments will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings, in which like references refer to like elements, and in which:

[0011] Figure 1 An example Mobile Fronthaul (MFH) procedure based on a WDM-Passive Optical Network (PON) architecture is shown;

[0012] Figure 2 An example wavelength shift scenario is shown;

[0013] Figure 3(a) shows an example architecture for measuring wavelength shift based on the amplitude difference of signals detected by two photodetectors (PDs);

[0014] Figure 3(b) shows the transmission spectrum of a filter used in the architecture shown in Figure 3(a);

[0015] Figure 4(a) shows an example procedure for measuring wavelength shift based on an Auxiliary Management and Control Channel (AMCC);

[0016] Figure 4(b) shows the relationship between wavelength and received power on which the AMCC-based wavelength offset measurement process shown in Figure 4(a) is based;

[0017] Figure 5 An example communication system in which example embodiments of this disclosure may be implemented is shown;

[0018] Figure 6 A flowchart of a wavelength offset measurement method according to certain example embodiments of the present disclosure is shown;

[0019] Figure 7 An example procedure for wavelength offset measurement according to certain embodiments of this disclosure is shown;

[0020] Figure 8(a) , 8(b) Figures 8(c) and 8(d) illustrate example procedures for performing training on a single communication device according to certain embodiments of the present disclosure;

[0021] Figure 9 An example architecture of a WDM fronthaul system using the WSM scheme of this disclosure is shown;

[0022] Figure 10 It shows in Figure 9 The processing procedures performed by the OLT and ONU in the system shown;

[0023] Figure 11 An example architecture of a WDM fronthaul system according to certain embodiments of this disclosure is shown;

[0024] Figure 12(a) , 12(b) Figures 12(c) and 12(d) show the mean square error (MSE) of the wavelength offset measurement for the ONU after training; and

[0025] Figure 13 A block diagram of an apparatus suitable for implementing certain other example embodiments of this disclosure is shown. Detailed Implementation

[0026] Example embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While some example embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the accompanying drawings and example embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of protection of the present disclosure.

[0027] The term "communication device" as used herein refers to any suitable device having communication functionality. The communication device can also have receiving functionality and can also have transmitting functionality. In certain embodiments, the communication device can be implemented through an optical network unit (ONU) or an optical line terminal (OLT).

[0028] The term "circuitry" as used herein refers to one or more of the following:

[0029] (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and

[0030] (b) combinations of hardware circuits and software, such as (as applicable): (i) combinations of analog and / or digital hardware circuits with software / firmware and (ii) to combinations of any of the hardware processors with software (including digital signal processors, software, and memory that work together to

[0031] (c) hardware circuit(s) and / or processor(s), such as a microprocessor(s) or a portion of microprocessor(s), that requires software (e.g., firmware) for operation, but need not necessarily have software programs (i.e., software instructions) loaded during

[0032] This definition of circuitry applies to all uses of this term in this application including in any claims. As a further example, as used in this application, the term "circuitry" also covers an implementation that has a hardware circuit or processor (or multiple processors) and software (or firmware) that works together to make up that implementation. For example, if a particular element is implemented in hardware and software working together, there is a hardware circuit and a software implementation, and there is a circuitry implementation that includes hardware and software working together to make up that implementation.

[0033] The term "includes" and its variations are meant to cover non-exclusive inclusions, i.e., that the listed items are among those that are included but that other items are also included. The term "based on" means "based, at least in part, on." The term "one example embodiment" means "at least one example embodiment"; the term "another example embodiment" means "at least one additional example embodiment." Related terms shall be construed accordingly.

[0034] The terms "first," "second," and the like, as used herein, can be used to describe various elements, and these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the example embodiments. As used herein, the term "and / or" includes any and all combinations of one or more of the associated terms.

[0035] Currently, WDM technology is the main technology to support 5G X-haul systems and optical access networks. WDM technology can be used to multiplex and transmit signals between multiple optical network units (ONUs) and an optical line terminal (OLT).

[0036] Figure 1 An example mobile fronthaul (MFH) process 100 based on a WDM-Passive Optical Network (PON) architecture is shown.

[0037] In Figure 1 In the architecture shown, multiple ONUs 105-1, 105-2, …, 105-m are connected to a respective set of RRHs 110-1, 110-2, …, 110-m, where m is any appropriate positive integer greater than 2. These ONUs 105-1, 105-2, …, 105-m are also connected to the same OLT 115. It should be understood that m (m > 2) ONUs are merely examples and not limiting. In some cases, one ONU can use multiple wavelengths.

[0038] In the MFH process 100, WDM technology is utilized to multiplex and transmit fronthaul signals between different ONUs 105-1, 105-2, …, 105-m and the OLT 115. As Figure 1 shown, multiple signals from the ONUs 105-1, 105-2, …, 105-m are wavelength division multiplexed by an Array Waveguide Grating (AWG) 120. An AWG 125 is included in the OLT 115 to perform wavelength division demultiplexing on the received signals. In addition, to support data rates of 50 Gb / s or higher per wavelength, an array of Analog-to-Digital Converters (ADCs) 130 and an array of Digital Signal Processors (DSPs) 135 are also included in the OLT 115 to perform corresponding processing.

[0039] Wavelength drift is a widely concerned issue in WDM PON / X-haul systems, which can cause significant degradation in system performance. For example, if a wavelength drift occurs, it can cause power loss in the corresponding wavelength channel, and also interfere with signals of adjacent channels, such as causing a significant increase in Bit Error Rate (BER).

[0040] Figure 2 Two example wavelength drift cases are shown, where the filter result 200 is the result in an ideal case.

[0041] As Figure 2 shown, in case 205, the wavelength 210 of the second laser drifts. In case 215, the entire wavelengths 220, 210, 230, and 240 of the AWG drift.

[0042] It should be noted that if the baud rate per wavelength increases, the wavelength shift problem will become more serious. However, the increase of the baud rate per wavelength is an inevitable trend in the development of current WDM systems.

[0043] Conventionally, an Optical Spectra Analyzer (OSA) is required to measure the wavelength shift. However, this requires the current service to be cut off and manual intervention is required.

[0044] Conventionally, two wavelength shift measurement methods without the aid of an OSA have been proposed. One way is to measure the wavelength shift by comparing the amplitudes of the electrical signals detected based on the two light signals processed by a beam splitter. The key to this method is to insert an optical filter with a transmission spectrum before one of the two photodetectors (PDs) that photoelectrically detect the two light signals. The following refers to Figure 3(a) and 3(b) discusses an example process of this method.

[0045] Figure 3(a) shows an example architecture 305 for measuring the wavelength shift based on the amplitude difference of the signals detected by the two PDs, and Figure 3(b) shows the transmission spectrum 310 of the filter inserted before one of the PDs.

[0046] As shown in Figure 3(a), in the architecture 305, a directly modulated laser (DML) 315 generates an optical signal based on the input from a burst driver 320. The optical signal is split into two light signals 330 and 335 via a beam splitter 325, where the one light signal 330 is converted into an electrical signal via a PD 340 and then to an oscilloscope 345, and the other light signal 335 is also converted into an electrical signal via a PD 350 and then to the oscilloscope 345. In this way, the oscilloscope 345 can display the amplitude difference of the two detected electrical signals.

[0047] In the architecture 305, a filter 355 is inserted before the PD 350, which has a transmission spectrum as shown in Figure 3(b). As can be seen from Figure 3(b), the insertion loss of the filter 355 is different for different wavelengths. When the wavelength of the laser drifts, the received power after the filtering process by the filter 355 will change. In this way, based on the amplitude difference between the two PDs 340 and 350, the wavelength shift can be determined.

[0048] However, this method has high performance requirements for the hardware such as optical filters and PDs, and also requires the current service to be stopped and the received optical signal to be sent to a dedicated measurement device.

[0049] Another way of measuring the wavelength shift without the help of OSA is to use the Auxiliary Management and Control Channel (AMCC) mechanism with power monitoring to measure the wavelength drift. An example process is discussed below with reference to Figure 4(a) and 4(b) An example process is discussed below with reference to

[0050] Figure 4(a) shows an example process 400 of measuring the wavelength shift based on AMCC, and Figure 4(b) shows a plot 405 of the relationship between wavelength and received power.

[0051] In the process 400, if the change ΔP rec in the received power P rec is less than a threshold change ΔP th , i.e. ΔP rec < ΔP th , then the normal mode 415 is executed. If ΔP rec > ΔP th , then the wavelength shift detection mode 420 is entered. In the wavelength shift detection mode 420, if no drop in the output power P out is monitored at block 425, then the wavelength adjustment mode 430 is entered. In the wavelength adjustment mode 430, the wavelength adjustment is made based on the relationship between wavelength and received power as shown in Figure 4(b).

[0052] For example, in the wavelength adjustment mode 430, the wavelength of the laser is first reduced by a predetermined step size at block 435. If the output power P out continues to drop, it means that the wavelength should be increased instead of being reduced, and thus the wavelength is increased accordingly at block 445. After a number of iterations and message exchanges, if ΔP rec becomes greater than ΔP th , then the wavelength adjustment is completed.

[0053] However, this approach requires a large number of iterations and message exchanges, and thus increases the system overhead and latency, reducing the system efficiency.

[0054] Embodiments of this disclosure present a wavelength offset measurement (WSM) scheme for measuring wavelength drift in a WDM system. This scheme monitors the quality of signals received from one or more communication devices (e.g., ONUs) using multiple wavelengths. Signal quality can be measured in any suitable manner. As an example, the bit error rate (BER) of the received signal can be used as a measure of received signal quality. If the quality of the signal received using a certain wavelength shows a significant degradation, for example, falling below a threshold, a wavelength offset measurement is performed at least for that wavelength. For example, wavelength offset measurements can be performed for that wavelength and adjacent wavelengths. Based on the results of the wavelength offset measurement, the communication device exhibiting wavelength drift is identified, and a wavelength adjustment instruction is sent to that device.

[0055] The WSM solution according to embodiments of this disclosure does not require service interruption or manual operation, thus making it more intelligent. Furthermore, the WSM solution according to embodiments of this disclosure can quickly detect wavelength drift, thereby reducing error correction time and improving system and network efficiency.

[0056] Figure 5 An example communication system 500, in which an example embodiment of this disclosure may be implemented, is shown. For example... Figure 5 As shown, the communication system 500 includes multiple communication devices 505-1, ..., 505-K, where K is any suitable positive integer. These communication devices 505-1, ..., 505-K transmit signals to communication device 515 via multiple wavelength division multiplexing (WDM) channels 510-1, ..., 510-M, where M is any suitable positive integer greater than 1, and M >= K. Each communication device 505-1, ..., 505-K can transmit signals to communication device 515 using one or more wavelengths through one or more corresponding channels 510-1, ..., 510-M. The multiple WDM channels 510-1, ..., 510-M can be physically carried by optical fibers. For ease of discussion, the multiple communication devices 505-1, ..., 505-K are referred to individually or collectively as communication device 505, and the multiple WDM channels 510-1, ..., 510-M are referred to individually or collectively as channel 510.

[0057] It should be understood that in some embodiments, only one communication device 505 may transmit to communication device 515 using multiple wavelengths in a wavelength division multiplexing (WDM) manner through multiple WDM channels 510-1, ..., 510-M. It should also be understood that communication device 505 and communication device 515 may include any suitable device. As an example, in some embodiments, communication device 505 may be implemented by an ONU, and communication device 515 may be implemented by an OLT. Communication devices 505 and 515 may also be implemented by other devices that support WDM communication.

[0058] likeFigure 5 As shown, the communications device 515 includes a monitoring module 520 that determines whether the quality of the received signals over the plurality of wavelength division multiplexed channels 510-1,..., 510-M is below a threshold. The communications device 515 also includes a WSM module 525 that detects whether a wavelength shift has occurred on each of the channels 510-1,..., 510-M.

[0059] In embodiments of the disclosure, if the monitoring module 520 detects that the quality of a signal from a certain communications device 505 is below a threshold, the WSM module 525 performs a wavelength shift measurement for at least the wavelength at which the signal was received (referred to as the "first wavelength"). If desired, a wavelength shift measurement can also be performed for a wavelength adjacent to the first wavelength (referred to as the "second wavelength") in addition to the first wavelength. After a wavelength shift is determined to exist at a certain communications device 505 based on the wavelength shift measurement, the communications device 515 sends a wavelength adjustment indication to the communications device 505 to cause the communications device 505 to make a corresponding wavelength shift compensation.

[0060] Figure 6 A flowchart of a method 600 of wavelength shift measurement in accordance with certain example embodiments of the disclosure is shown. The method 600 can be implemented at a communications device 515 of a network 500, such as the communications device 515 of the network 500 of FIG. 1. Figure 5 For ease of discussion, the method 600 will be described below in conjunction with the network 500 of FIG. 1. Figure 5

[0061] At block 605, it is determined whether the quality of a signal received from one or more communications devices 505 using a plurality of wavelengths is below a threshold. For example, the monitoring of the quality of the signal can be performed by the monitoring module 520 in the communications device 515.

[0062] The quality of the received signal can be measured using any suitable criteria, such as bit error rate, eye diagram, power, error vector magnitude (EVM), etc. In certain embodiments, the bit error rate (BER) of the received signal can be monitored as the quality of the received signal. The BER of the received signal can be measured using any suitable manner. As an example, the communications device 505 can periodically transmit a known reference signal, such as a pseudo random code (PRBS) signal, for the communications device 515 to make a bit error rate measurement.

[0063] At block 610, if it is determined that the quality of one of the plurality of signals is below a threshold, which indicates that the quality of the received signal is significantly degraded, a wavelength shift measurement is performed for at least the first wavelength at which the signal was received. In certain embodiments, a wavelength shift measurement can also be performed for a second wavelength adjacent to the first wavelength in addition to the first wavelength.

[0064] ​For example, wavelength offset measurement can be first performed for a first wavelength. If no offset of the first wavelength is detected, measurement of a second wavelength adjacent to the first wavelength is continued. If no offset of the second wavelength is detected either, measurement of other adjacent wavelengths of the first wavelength or adjacent wavelengths of the second wavelength can be continued. Wavelength offset measurement can be stopped after determining that a drift has occurred in a certain wavelength.

[0065] In some embodiments, wavelength offset measurement may not be performed one by one for individual wavelengths, but can be performed simultaneously for multiple wavelengths. For example, the offsets of a first wavelength and one or more adjacent wavelengths can be measured simultaneously.

[0066] Wavelength offset measurement can be performed by the WSM module 525 in the communication device 515 in any suitable manner. The following refers to Figure 7 Discuss an example process of wavelength offset measurement performed by the WSM module 525.

[0067] Figure 7 An example process 700 of wavelength offset measurement according to some embodiments of the present disclosure is shown.

[0068] As Figure 7 shown, in order to measure the offsets of M wavelengths, N signals 705-1, 705-2,..., 705-N received from one or more communication devices 505 using N wavelengths are input into the WSM module 525, where N can be any suitable positive integer greater than 1. Based on these signals 705-1, 705-2,..., 705-N, the WSM module 525 can monitor whether wavelength offsets have occurred in each wavelength at the communication device 505. In some embodiments, N >= M to further improve the accuracy of wavelength offset measurement. It should be understood that this is only an example and not a limitation, and N < M is also feasible.

[0069] In this example, the WSM module 525 includes time-frequency transformation units 710-1, 710-2,..., 710-N for transforming the input time-domain signals 705-1, 705-2,..., 705-N into the frequency domain. For example, by performing a fast Fourier transform (FFT) and logarithmic operations, the power spectral density (PSD) of each signal can be generated. Since the PSD of each signal is symmetric, in order to reduce the computational complexity and further improve the processing efficiency, the WSM module 525 also includes truncation units 715-1, 715-2,..., 715-N for truncating the obtained frequency-domain PSD data. As an example, only the first half of the PSD data can be retained. Subsequently, the WSM unit 720 in the WSM module 525 determines whether a drift has occurred in each wavelength using the truncated PSD data.

[0070] Wavelength shift measurements for a certain wavelength can be performed based on the association between wavelengths. For example, a shift of a first wavelength can be detected based on signals received using the first wavelength and one or more associated other wavelengths. The associated wavelengths can be completely adjacent, can be partially adjacent, or can be non-adjacent. In certain embodiments, all used wavelengths can also be considered to be associated, and thus a shift of a certain wavelength can be measured based on signals received using all wavelengths. In this case, performing a wavelength shift measurement once can determine whether a shift has occurred for all wavelengths.

[0071] In certain embodiments, the association between wavelengths can be pre-constructed. The association can be constructed through a learning, training, or updating process. As an example, Figure 7 The illustrated WSM unit 720 can be implemented by a Deep Neural Network (DNN) module. In such an example, a training process can be first performed on the WSM unit 720. For example, a training process of the wavelength shift measurement performed by the WSM unit 720 can be trained using N signals received from the communication device 505 using N wavelengths as input and corresponding wavelength shifts of the N wavelengths as output.

[0072] In certain embodiments, depending on the association between wavelengths, a training process of the wavelength shift measurement can be performed individually for a certain wavelength based on signals received using associated wavelengths. For example, a training process can be performed for a certain wavelength using signals received using associated wavelengths as input and a shift of the wavelength as output. In this case, multiple WSM units can be included in the WSM module 525, each of which is trained and performs wavelength shift measurement individually. Specific examples are discussed below in connection with Figure 8(a) 、 8(b) , 8(c), and 8(d).

[0073] Figure 8(a) 、 8(b) , 8(c), and 8(d) illustrate example processes 802, 804, 806, and 808 for performing training for a single wavelength according to certain embodiments of the present disclosure.

[0074] In these examples, training is performed separately for the four wavelengths 812, 814, 816, and 818. Wavelength 812 is associated with wavelengths 814 and 816, wavelength 814 is associated with wavelengths 812 and 816, wavelength 816 is associated with wavelengths 814 and 818, and wavelength 818 is associated with wavelengths 814 and 816. The four DNN modules 822, 824, 826, and 828, as an example implementation of a WSM unit, perform wavelength shift measurement for wavelengths 812, 814, 816, and 818, respectively. Accordingly, the four DNN modules 822, 824, 826, and 828 are trained separately.

[0075] For example, in training process 802, DNN module 822 is trained with signals 832, 834, and 836 received using wavelengths 812, 814, and 816 as input, and with shift 842 for wavelength 812 as output. In training process 804, DNN module 824 is trained with signals 832, 834, and 836 received using wavelengths 812, 814, and 816 as input, and with shift 844 for wavelength 814 as output. In training process 806, DNN module 826 is trained with signals 834, 836, and 838 received using wavelengths 814, 816, and 818 as input, and with shift 846 for wavelength 816 as output. In training process 808, DNN module 828 is trained with signals 834, 836, and 838 received using wavelengths 814, 816, and 818 as input, and with shift 848 for wavelength 818 as output.

[0076] Next, continuing to refer to Figure 6 At block 615, based on the wavelength shift measurements performed at block 610, a shifted wavelength among the plurality of wavelengths is determined. The wavelength that shifted can be the wavelength for which the signal quality decreased, or can be an adjacent wavelength to the wavelength for which the signal quality decreased. For example, if a shift in the first wavelength is detected, the first wavelength can be determined to be the shifted wavelength. If a shift in the first wavelength is not detected, but a shift in an adjacent second wavelength is detected, the second wavelength is determined to be the shifted wavelength.

[0077] At block 620, a wavelength adjustment indication is sent to the communication device 505 that transmits the signal using the drifted wavelength, to cause the communication device 505 to make a corresponding wavelength offset compensation. In some embodiments, the wavelength adjustment indication can contain a specific wavelength offset value, which can be the offset value of the drifted wavelength, or can be a wavelength offset value that needs to be adjusted, to indicate to the receiver the amount and direction of the wavelength offset that needs to be adjusted, to further improve the efficiency of the wavelength adjustment and reduce the error correction time. The wavelength adjustment indication can be carried in any suitable message. For example, a dedicated message can be used or an existing message can be multiplexed to send the indication.

[0078] Reference is made below to Figure 9 and Figure 10 to discuss example implementations of embodiments of the present disclosure in a WDM front-haul system.

[0079] Reference is first made to Figure 9 which shows an example architecture of a WDM front-haul system 900 using the WSM scheme of the present disclosure.

[0080] In the system 900, signals transmitted by a plurality of ONUs 905-1, 905-2, …, 905-n (individually or collectively referred to as ONUs 905), where n is any suitable positive integer greater than 2, are wavelength division multiplexed before being transmitted to an OLT 910. Each of the ONUs 905-1, 905-2, …, 905-n can use one or more wavelengths. It should be understood that the ONUs 905-1, 905-2, …, 905-n are example implementations of the communication devices 505 in Figure 5 , while the OLT 910 is an example implementation of the communication device 515 in Figure 5 . It should also be understood that the n ONUs (n > 2) are merely examples and not limiting. In some embodiments, there can be only one ONU 905 that uses multiple wavelengths to transmit to the OLT 910 in a wavelength division multiplexed manner.

[0081] As shown in Figure 9 , each of the ONUs 905-1, 905-2, …, 905-m is connected to a set of RRHs 915-1, 915-2, …, 915-m. Signals transmitted by the m ONUs 905-1, 905-2, …, 905-m are wavelength division multiplexed via an AWG 920 before being transmitted to the OLT 910 through an optical fiber 925. The OLT 910 performs a series of operations to recover the data, which is then transmitted to a Base Band Unit (BBU) pool 930.

[0082] In the system 900, the OLT 910 includes an AWG 935 to wavelength division demultiplex the received signals. It should be understood that Figure 9The implementation of wavelength division multiplexing and demultiplexing by AWG 925 and AWG 935 is merely an example and not a limitation. Wavelength division multiplexing and demultiplexing can be implemented in any suitable manner and using any suitable devices.

[0083] The PD array 940 in OLT 910 is also included for performing photo-detection on the four signals obtained by wavelength demultiplexing, respectively, to convert the received optical signals into electrical signals. The obtained electrical signals are converted into digital signals via an array of analog-to-digital converters (ADCs) 945 and processed via an array of digital signal processors (DSPs) 950.

[0084] In this example, OLT 910 includes a BER monitor 955, which is an example implementation of the monitoring module 520 shown in Figure 5 The BER monitor 955 is configured to monitor whether the BER of the data processed by the array of DSPs 950 exceeds a threshold BER th If the BER of the signal from a certain ONU exceeds the threshold BER th then a wavelength shift measurement is triggered to be performed by a WSM module 960. The WSM module 960 is an example implementation of the WSM module 525 shown in Figure 5 If a shift in the wavelength at which the signal is received is detected, a wavelength adjustment indication is sent to the corresponding ONU 905.

[0085] Figure 10 The process 1000 is shown in the system 900 shown in Figure 9 Figures 9A and 9B. The process 1000 is performed at the OLT 910 and at the ONUs 905-1 and 905-2 in the system 900 shown in

[0086] As shown in Figure 10 Figure 10A, at block 1005, the OLT 910 performs BER monitoring (e.g., by the BER monitor 955). At block 1010, the monitored BER is compared to a threshold BER th to determine whether BER > BER th If it is determined that the BER from the ONU 905-1 is below the threshold BER thIf the wavelength shift of the ONU 905-1 is detected at block 1020, a wavelength adjustment indication containing the wavelength offset value is sent to the ONU 905-1 at block 1025. The ONU 905-1 adjusts the wavelength of the laser according to the received indication at block 1030, and feeds back a "done" signal to the OLT 910.

[0087] If no wavelength shift is detected at block 1020, a WSM is performed for the adjacent ONU 905-2 that transmits using an adjacent wavelength at block 1035. If the signal of the adjacent ONU 905-2 is detected to drift out of its channel and interfere with the signal of the ONU 905-1 at block 1040, a wavelength adjustment indication is sent to the ONU 905-2 at block 1045. The ONU 905-2 adjusts the wavelength of the laser according to the received indication at block 1050, and feeds back a "done" signal. If no wavelength shift is detected at block 1040, it is informed that no wavelength shift is observed at block 1055.

[0088] If no change in BER is found after the wavelength adjustment of the relevant ONUs, the OLT 910 can inform the network operator or administrator that the target ONU 905-1 and the adjacent ONU 905-2 do not have wavelength shift, and thus other possible factors that can cause the BER of the ONU 905-1 to decrease can be considered.

[0089] Reference is made below to Figure 11 and Figure 12(a) , 12(b) , 12(c) and 12(d) discuss another example implementation of the WSM scheme according to embodiments of the present disclosure in a WDM front-haul system with four ONUs 905-1, 905-2, 905-3 and 905-4. In this example, the four ONUs 905-1, 905-2, 905-3 and 905-4 transmit using four adjacent wavelengths.

[0090] Figure 11 An example architecture 1100 of a WDM front-haul system according to certain embodiments of the present disclosure is shown.

[0091] In the architecture 1100, the four ONUs 905-1, 905-2, 905-3 and 905-4 communicate with the OLT 910 through a 20 km long fiber 1105. The ONUs 905-1, 905-2, 905-3 and 905-4 have a working bandwidth of 35 GHz, and use Electro-Absorption Modulation Lasers (EMLs). The signals sent by the ONUs are wavelength division multiplexed with a frequency gap of 100 GHz.

[0092] In this example, the WSM module 960 in the OLT 910 performs wavelength offset measurements based on machine learning algorithms (e.g., DNN algorithms). To improve the accuracy of wavelength offset measurements, the WSM module 960 can be pre-trained.

[0093] To achieve effective training, data collection is performed first. On the ONU 905-1, 905-2, 905-3, and 905-4 sides, the laser wavelength offset ranges from -10 GHz to 10 GHz with a fixed step size of 1 GHz. Within this wavelength offset range, the wavelength of each laser fluctuates randomly. Furthermore, a large amount of pseudo-random binary sequence (PRBS) data is generated using different seed numbers. This data, after undergoing different wavelength offsets, is sent to the OLT 910. On the OLT 910 side, the received signals are sampled using an ADC. The resulting dataset is stored for subsequent processing.

[0094] After collecting sufficient data, training can be performed based on the collected data. As an example, the WSM Module 960 can employ a DNN model. A portion of the collected dataset can be used to train the DNN model, with the remaining data used for testing. During training, the data can be transformed from the time domain to the frequency domain using FFT and logarithmic operations, for example, generating power spectral density (PSD) data. Due to the symmetry of PSD data, only half of the data can be retained to represent the signal spectrum, simplifying computational complexity and saving computational resources.

[0095] Data from multiple associated wavelengths can be combined to predict the shift of a specific wavelength. As an example, this can be based on... Figure 8(a) , 8(b) The wavelength offset prediction described above is performed using the channel correlations shown in 8(c) and 8(d). For example, the wavelength offset of ONU 905-1 can be predicted based on signals from ONU 905-1, 905-2, and 905-3; the wavelength offset of ONU 905-2 can be predicted based on signals from ONU 905-1, 905-2, and 905-3; the wavelength offset of ONU 905-3 can be predicted based on signals from ONU 905-2, 905-3, and 905-4; and the wavelength offset of ONU 905-4 can be predicted based on signals from ONU 905-2, 905-3, and 905-4. Since the actual wavelength offsets of each ONU 905-1, 905-2, 905-3, and 905-4 are known, the WSM module 960 can be trained using the corresponding actual wavelength offsets as output.

[0096] After the WSM module 960 is trained, it can be used to perform WSM processing. For example, when the received signal BER from a certain ONU 905-2 drops, the OLT 910 can send an alarm to the network operator and start the WSM module 960. The WSM module 960 detects the wavelength shift of the ONU 905-2. If the wavelength shift is detected, a wavelength adjustment message is passed to the corresponding ONU 905-2. Otherwise, it is possible that the wavelength drift occurs in the adjacent ONUs 905-1 and 905-3 using adjacent wavelengths, and pollutes the ONU 905-2. At this time, the wavelength shift measurement can be performed on the two ONUs 905-1 and 905-3 to determine whether their wavelengths drift. If the received signal BER from all ONUs 905-1, 905-2, 905-3 and 905-4 drops, the wavelength shift measurement can be performed on each ONU. If the wavelengths all shift, an alarm can be sent to the network operator to inform that the AWG can be damaged.

[0097] The simulation results show that the WSM scheme according to the embodiments of the present disclosure can achieve higher wavelength shift measurement accuracy. In the simulation, a simulation model is constructed using the VPI platform, and the DSP part is implemented using the python language, including BER calculation and wavelength shift measurement. Each ONU 905-1, 905-2, 905-3 and 905-4 uses different random seeds to generate 2048 PRBS data. 4e5 simulations are performed and relevant data are obtained.

[0098] The WSM module 960 uses four DNN models with five hidden layers, which contain 3072, 768, 192, 48 and 16 neurons. Each DNN model is used to measure the wavelength shift of one ONU 905-1, 905-2, 905-3 or 905-4. For the training of the DNN model, the total data quantity, training data and training times are 4e5, 1e5 and 2e3, respectively. One fourth of the collected data set (about 1e5) is used to train the DNN model, and the other data is used to test the DNN model.

[0099] After training, the mean square error (MSE) of the wavelength shift measurement for the four ONUs 905-1, 905-2, 905-3 and 905-4 is Figure 12(a) , 12(b)As shown in 12(c) and 12(d), it can be seen that all four DNN models can achieve an MSE of 1e-6 or less, with the two middle ONUs, 905-2 and 905-3, performing better. During testing, the wavelength shift prediction errors of the four ONUs 905-1, 905-2, 905-3, and 905-4 were all very small, approximately 9.3, 4.6, 4.2, and 12 MHz respectively, achieving a prediction error of less than 15 MHz. This indicates that the wavelength shift measurement accuracy of the WSM scheme according to the embodiments of this disclosure is high.

[0100] Figure 13 A block diagram of a device 1300 suitable for implementing certain example embodiments of the present disclosure is shown. Device 1300 can be... Figure 5 The communication device 515 shown is implemented or is at least a part of the communication device 515.

[0101] As shown in the figure, device 1300 includes a processor 1310. The processor 1310 controls the operation and functions of device 1300. For example, in some example embodiments, the processor 1310 may perform various operations by means of instructions 1330 stored in a memory 1320 coupled thereto. The memory 1320 may be any suitable type suitable for the local technical environment and may be implemented using any suitable data storage technology, including but not limited to semiconductor-based memory devices, magnetic storage devices and systems, and optical storage devices and systems. Although Figure 13 Only one memory cell is shown in the diagram, but there may be multiple physically different memory cells in device 1300.

[0102] Processor 1310 can be any suitable type applicable to the local technical environment and can include, but is not limited to, one or more of a general-purpose computer, a special-purpose computer, a microcontroller, a digital signal controller (DSP), and a controller-based multi-core controller architecture. Device 1300 may also include multiple processors 1310. Processor 1310 is coupled to transceiver 1340. Transceiver 1340 can achieve the reception and transmission of information by means of optical fiber, cable, and / or other components. Processor 1310 can be configured to implement various embodiments of this disclosure.

[0103] Processor 1310 and memory 1320 can cooperate to enable device 1300 to implement as referenced herein. Figure 6 Method 600 is discussed. (See above for reference.) Figure 5 to Figure 1 All the features described in section 2 apply to device 1300 and will not be repeated here.

[0104] In general, the various example embodiments of the present disclosure can be implemented in hardware or special-purpose circuits, software, logic, or any combination thereof. Some aspects can be implemented in hardware, while other aspects can be implemented in firmware or software which can be executed by a controller, microprocessor or other computing device. While various example embodiments of the present disclosure are illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it will be understood that the blocks, devices, systems, techniques or methods described herein can be implemented in, as non-limiting examples, hardware, software, firmware, special-purpose circuits or logic, general purpose hardware or controler or other computing devices, or some combination thereof.

[0105] By way of example, example embodiments of the present disclosure can be described in the context of machine-executable instructions, such as program modules being executed by devices in a target's real or virtual processor. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. In various example embodiments, the functionality of program modules can be combined or split between the described program modules. Machine-executable instructions for program modules can be executed within a local or distributed device. In a distributed device, program modules can be located in both local and remote storage media.

[0106] Computer program code for carrying out operations of the present disclosure can be written in one or more programming languages. The computer program code can be provided to a processor of a general or special purpose computer, or other programmable data processing apparatus, to produce a machine, such that the program code, when executed by the computer or other programmable data processing apparatus, causes the machine to perform the functions / operations specified in the flowcharts and / or block diagrams. The program code can be entirely on the computer, partially on the computer, as a stand-alone software package, partially on the computer and partially on a remote computer, or entirely on a remote computer or server.

[0107] In the context of the present disclosure, a machine-readable medium can be any tangible medium that contains or stores the program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine-readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), or any suitable combination of the foregoing.

[0108] Additionally, although operations are depicted in a particular order, this should not be understood as requiring such an order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing can be advantageous. Likewise, although the above discussion includes certain specifics, this should not be construed as limiting the scope of the application or any claim, but rather as merely providing an example embodiment of the application. Certain features that are described in the context of separate example embodiments can also be implemented in combination in a single example embodiment. Conversely, various features that are described in the context of a single example embodiment can also be implemented separately or in any suitable subcombination. It will be appreciated that various features described herein can be implemented in hardware, software or a combination thereof. Preferably, such software is implemented in a high level procedural or object oriented programming language to

[0109] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

[0110] Various example embodiments of the present disclosure have been described. In addition to or in lieu of the foregoing, the following examples are described. The functionality described in any of the following examples can be used with any of the other examples described herein.

[0111] In some aspects, a communication device includes at least one processor; and at least one memory storing computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the communication device to determine whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold, the plurality of signals being wavelength division multiplexed using the plurality of wavelengths; if it is determined that a quality of one of the plurality of signals is below the threshold, perform a wavelength shift measurement for at least a first wavelength of the plurality of wavelengths, the signal being received using the first wavelength; based on the wavelength shift measurement, determine a shifted wavelength of the plurality of wavelengths; and transmit a wavelength adjustment indication to a communication device of the one or more communication devices that transmits signals using the shifted wavelength.

[0112] In certain embodiments, the communication device is caused to determine the shifted wavelength by determining the first wavelength as the shifted wavelength if a shift of the first wavelength is detected.

[0113] In certain embodiments, the communication device is caused to perform the wavelength shift measurement for the first wavelength by: performing the wavelength shift measurement for the first wavelength if a quality of one of the plurality of signals is determined to be below a threshold; performing the wavelength shift measurement for a second wavelength adjacent to the first wavelength if a shift of the first wavelength is not detected; and determining the second wavelength as the shifted wavelength if a shift of the second wavelength is detected.

[0114] In certain embodiments, the communication device is caused to perform the wavelength shift measurement for the first wavelength by: detecting whether a shift of the first wavelength has occurred based on signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths.

[0115] In certain embodiments, the communication device is further caused to: determine an amount of shift of the first wavelength; and train a process of the wavelength shift measurement with signals received using the first wavelength and the associated one or more other wavelengths as input and with the amount of shift of the first wavelength as output.

[0116] In certain embodiments, the one or more other wavelengths are adjacent to the first wavelength.

[0117] In certain embodiments, the quality of the signal comprises a bit error rate of the signal.

[0118] In certain embodiments, the wavelength adjustment indication comprises an amount of shift and a direction of shift to adjust.

[0119] In some aspects, a method of communication comprises: determining whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold, the plurality of signals being wavelength division multiplexed using the plurality of wavelengths; performing a wavelength shift measurement for at least a first wavelength of the plurality of wavelengths if a quality of one of the plurality of signals is determined to be below a threshold, the signal being received using the first wavelength; determining a shifted wavelength of the plurality of wavelengths based on the wavelength shift measurement; and transmitting a wavelength adjustment indication to a communication device of the one or more communication devices that transmits signals using the shifted wavelength.

[0120] In certain embodiments, determining the shifted wavelength comprises: determining the first wavelength as the shifted wavelength if a shift of the first wavelength is detected.

[0121] In certain embodiments, performing the wavelength shift measurement for at least the first wavelength comprises: performing the wavelength shift measurement for the first wavelength if a quality of one of the plurality of signals is determined to be below a threshold; performing the wavelength shift measurement for a second wavelength adjacent to the first wavelength if a shift of the first wavelength is not detected; and determining the second wavelength as the shifted wavelength if a shift of the second wavelength is detected.

[0122] In certain embodiments, performing the wavelength shift measurement for the first wavelength includes detecting whether the first wavelength has shifted based on the signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths.

[0123] In certain embodiments, the method further includes determining an amount of shift of the first wavelength, and training the process of the wavelength shift measurement using the signals received using the first wavelength and the associated one or more other wavelengths as input and the amount of wavelength shift of the first wavelength as output.

[0124] In certain embodiments, the one or more other wavelengths are adjacent to the first wavelength.

[0125] In certain embodiments, the quality of the signals includes a bit error rate of the signals.

[0126] In certain embodiments, the wavelength adjustment indication includes an amount of wavelength shift and a direction of shift to adjust.

[0127] In some aspects, an apparatus includes means for determining whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold, the plurality of signals being wavelength division multiplexed using the plurality of wavelengths; means for performing a wavelength shift measurement for at least a first wavelength of the plurality of wavelengths in a case that the quality of one of the plurality of signals is below the threshold, the signal being received using the first wavelength; means for determining a shifted wavelength of the plurality of wavelengths based on the wavelength shift measurement; and means for transmitting a wavelength adjustment indication to a communication device of the one or more communication devices that transmits signals using the shifted wavelength.

[0128] In certain embodiments, the means for determining the shifted wavelength includes means for determining the first wavelength as the shifted wavelength in a case that the first wavelength is detected to have shifted.

[0129] In certain embodiments, the means for performing the wavelength shift measurement for the first wavelength includes means for performing the wavelength shift measurement for the first wavelength in a case that the quality of one of the plurality of signals is below the threshold; means for performing the wavelength shift measurement for a second wavelength adjacent to the first wavelength in a case that the first wavelength is not detected to have shifted; and means for determining the second wavelength as the shifted wavelength in a case that the second wavelength is detected to have shifted.

[0130] In certain embodiments, the means for performing the wavelength shift measurement for the first wavelength includes means for detecting whether the first wavelength has shifted based on the signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths.

[0131] In certain embodiments, the apparatus further comprises means for determining an offset amount for the first wavelength; and means for training a process for wavelength offset measurement using as input signals received using the first wavelength and the associated one or more other wavelengths and using as output the wavelength offset amount for the first wavelength.

[0132] In certain embodiments, the one or more other wavelengths are adjacent to the first wavelength.

[0133] In certain embodiments, the quality of the signal comprises a bit error rate of the signal.

[0134] In certain embodiments, the wavelength adjustment indication comprises a wavelength offset amount to adjust and a direction of the offset.

[0135] In some aspects, a computer-readable storage medium has stored thereon program instructions that, when executed by a processor of a device, cause the device to perform embodiments of the present disclosure.

Claims

1. A communication device, comprising: at least one processor; and at least one memory storing computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the communication device to: determine whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold, the plurality of signals being wavelength division multiplexed using the plurality of wavelengths; if it is determined that a quality of one of the plurality of signals is below the threshold, perform a wavelength offset measurement for at least a first wavelength of the plurality of wavelengths, the signal being received using the first wavelength; based on the wavelength offset measurement, determine a drifted wavelength of the plurality of wavelengths; and send a wavelength adjustment indication to a communication device of the one or more communication devices that transmits signals using the drifted wavelength, wherein the communication device is caused to perform the wavelength offset measurement for the first wavelength by: detecting whether the first wavelength has drifted based on signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths.

2. The communication device of claim 1, wherein the communication device is caused to determine the drifted wavelength by: if it is detected that the first wavelength has drifted, determining the first wavelength as the drifted wavelength.

3. The communication device of claim 1, wherein the communication device is caused to perform the wavelength offset measurement for at least the first wavelength by: if it is determined that the quality of the one of the plurality of signals is below the threshold, performing the wavelength offset measurement for the first wavelength; if it is not detected that the first wavelength has drifted, performing a wavelength offset measurement for a second wavelength adjacent to the first wavelength; and if it is detected that the second wavelength has drifted, determining the second wavelength as the drifted wavelength.

4. The communication device of claim 1, wherein the communication device is further caused to: determine an offset amount of the first wavelength; and train a process of the wavelength offset measurement with signals received using the first wavelength and the associated one or more other wavelengths as input and with the wavelength offset amount of the first wavelength as output.

5. The communication device of claim 1 or 4, wherein the one or more other wavelengths are adjacent to the first wavelength.

6. The communication device of claim 1, wherein a quality of a signal comprises a bit error rate of a signal.

7. The communication device of claim 1, wherein the wavelength adjustment indication comprises a wavelength offset amount and a direction of offset to adjust.

8. A communication method, comprising: determining whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold, the plurality of signals being wavelength division multiplexed using the plurality of wavelengths; ​ performing a wavelength shift measurement for at least a first wavelength of the plurality of wavelengths if it is determined that a quality of one of the plurality of signals, received using the first wavelength, is below the threshold; determining a shifted wavelength of the plurality of wavelengths based on the wavelength shift measurement; and sending a wavelength adjustment indication to a communication device of the one or more communication devices that transmits signals using the shifted wavelength, wherein performing the wavelength shift measurement for the first wavelength comprises: detecting whether the first wavelength has shifted based on signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths.

9. The communication method of claim 8, wherein determining the shifted wavelength comprises: determining the first wavelength as the shifted wavelength if it is detected that the first wavelength has shifted.

10. The communication method of claim 8, wherein performing the wavelength shift measurement for at least the first wavelength comprises: performing the wavelength shift measurement for the first wavelength if it is determined that the quality of the one of the plurality of signals is below the threshold; performing a wavelength shift measurement for a second wavelength adjacent to the first wavelength if it is not detected that the first wavelength has shifted; and determining the second wavelength as the shifted wavelength if it is detected that the second wavelength has shifted.

11. The communication method of claim 8, further comprising: determining an amount of shift of the first wavelength; and training a process of the wavelength shift measurement with signals received using the first wavelength and the associated one or more other wavelengths as input and with the amount of shift of the first wavelength as output.

12. The communication method of claim 8 or 11, wherein the one or more other wavelengths are adjacent to the first wavelength.

13. The communication method of claim 8, wherein a quality of a signal comprises a bit error rate of the signal.

14. The communication method of claim 8, wherein the wavelength adjustment indication comprises an amount of wavelength shift and a direction of shift to adjust.

15. A communication apparatus comprising: means for determining whether a quality of a plurality of signals received from one or more communication devices using a plurality of wavelengths is below a threshold, the plurality of signals being wavelength division multiplexed using the plurality of wavelengths; means for performing a wavelength shift measurement for at least a first wavelength of the plurality of wavelengths if it is determined that a quality of one of the plurality of signals, received using the first wavelength, is below the threshold; means for determining a wavelength of the plurality of wavelengths that has shifted based on the wavelength shift measurement; and means for sending a wavelength adjustment indication to a communication device of the one or more communication devices that transmits signals using the wavelength that has shifted, wherein the means for performing the wavelength shift measurement for the first wavelength comprises: means for detecting whether the first wavelength has shifted based on signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths. ​ means for detecting whether a shift has occurred in the first wavelength based on signals received using the first wavelength and one or more other wavelengths of the plurality of wavelengths.

16. A computer readable storage medium having stored thereon program instructions that, when executed on a processor on a device, cause the device to perform the method of any one of claims 8-14.

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