Patent Publication Number: US-2021168638-A1

Title: Methods, apparatus and computer-readable mediums relating to detection of sleeping cells in a cellular network

Description:
TECHNICAL FIELD 
     Embodiments of the present disclosure relate to cellular networks, and particularly to methods, apparatus and computer-readable mediums relating to detection of sleeping cells in a cellular network. 
     BACKGROUND 
     Cellular networks are a ubiquitous part of our modern world, and are becoming increasingly complex and diverse. Each network may comprise many hundreds or thousands of cells, with the deployment of small cells providing additional coverage for macro cells and resulting in increased complexity. Each network may provide multiple different radio access technologies (RATs), with new releases regularly being issued for each RAT. Further, this complexity is only expected to grow further in the future, with the advent of 5G standards providing radio access services for a wide range of terminal devices and corresponding use cases, including enhanced mobile broadband (eMBB), massive machine type communications (mMTC) and ultra-reliable low-latency communications (URLLC). 
     In order to ensure correct (or even optimal) functioning of the network, operators will typically attempt to monitor the performance of network components and cells in their respective networks. However, given the complexity of the networks, this is not a straightforward task. A wide range of different metrics and key performance indicators (KPIs) may be measured to monitor the performance of network components and cells, and this will increase the complexity of the task. Even with all available data, it may not be straightforward to identify a malfunctioning cell or network component given the wide range of use cases which are provided by the network. For example, the performance of a cell providing predominantly mMTC services to its connected devices will appear very different to that of a cell providing predominantly eMBB services to its connected devices. Therefore malfunctioning in those cells can also be expected to appear different. 
     One problem which has been identified in cellular networks is the existence of so-called “sleeping cells”. Sleeping cells are cells which have developed a fault which causes partial or complete degradation of network performance in that cell. The degradation in performance may take place gradually, over a period of time, such that traditional fault detection mechanisms (which may rely on threshold comparison or other methods) fail to detect the problem. 
     The root cause of the sleeping cell can vary. For example, a hardware component in the base station may have failed or developed a fault, leading to reduced performance. Alternatively, software running in the base station may lead to misconfiguration of the radio signals transmitted or detected by the base station. These hardware and/or software problems can lead to negative impacts on the service provided by the cell, from marginally worse performance to complete absence of service. For example, a paper by Chernogorov et al (“Sequence-based Detection of Sleeping Cell Failures in Mobile Networks”, Wireless Networks, October 2015) discusses the problem of random access channel (RACH) failure in a cell, leading to a sleeping cell. In this failure mechanism, the RACH becomes misconfigured such that random access attempts by new devices seeking to connect to the cell will always fail. Thus devices which connected to the cell prior to the RACH misconfiguration will continue to receive coverage, but new devices are unable to connect. Over time, the number of connected devices will fall to zero. However, traditional KPIs will be unable to distinguish this situation from a healthy cell which merely has a light load. 
     The Chernogorov paper addresses this problem through the use of N-gram analysis of minimization of drive tests (MDT) event sequences. MDT was standardized by the 3 rd  Generation Partnership Program (3GPP), and is designed for automatic collection and reporting of user measurements, where possible complemented with location information. The collected data is then reported to the serving cell, which in turn sends it to an MDT server for analysis. The Chernogorov paper proposes the use of N-gram analysis of this data to identify anomalies and subsequently sleeping cells. 
     One problem with this approach is its sheer complexity. The N-gram analysis relies on large quantities of data collected for each monitored cell, requiring use of a large number of sensors which are capable of highly accurate measurement, as well as a long period of time in which to collect the data. Such a large quantity of data implies significant signaling overhead in providing the data from the user devices to the MDT server, as well as high data storage costs at the MDT server itself. Finally, the N-gram analysis of that data is likely to consume significant processing resources and time. 
     SUMMARY 
     Embodiments of the disclosure seek to address one or more of these and other problems. 
     In one aspect, there is provided a method of detecting a sleeping cell in a cellular communication network. The method comprises: monitoring power consumption of a radio transmission point of the cellular communication network; providing the power consumption of the radio transmission point as an input to a classification model, developed using a machine-learning algorithm; and obtaining an output from the classification model, the output classifying the radio transmission point as serving one of a sleeping cell and a non-sleeping cell. 
     Apparatus for performing the method set out above, such as a network node, is also provided. 
     For example, one aspect provides a network node for detecting a sleeping cell in a cellular communication network. The network node comprises processing circuitry and a non-transitory computer-readable medium storing instructions which, when executed by the processing circuitry, cause the network node to: monitor power consumption of a radio transmission point of the cellular communication network; provide the power consumption of the radio transmission point as an input to a classification model, developed using a machine-learning algorithm; and obtain an output from the classification model. The output classifies the radio transmission point as serving one of a sleeping cell and a non-sleeping cell. 
     In another example, a further aspect provides a network node for detecting a sleeping cell in a cellular communication network. The network node comprises a monitoring module and a classification module. The monitoring module is configured to monitor power consumption of a radio transmission point of the cellular communication network. The power consumption of the radio transmission point is provided as an input to the classification module  804 , which implements a classification model, developed using a machine-learning algorithm, and obtains an output from the classification model. The output classifies the radio transmission point as serving one of a sleeping cell and a non-sleeping cell. 
     A further aspect of the disclosure provides a non-transitory computer-readable medium storing instructions which, when executed by processing circuitry of a network node of a cellular communication network, cause the network node to: monitor power consumption of a radio transmission point of the cellular communication network; provide the power consumption of the radio transmission point as an input to a classification model, developed using a machine-learning algorithm; and obtain an output from the classification model. The output classifies the radio transmission point as serving one of a sleeping cell and a non-sleeping cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present disclosure, and to show how it may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: 
         FIG. 1  illustrates a communication network according to embodiments of the disclosure; 
         FIG. 2  is a schematic diagram of a radio transmission point arrangement according to embodiments of the disclosure; 
         FIGS. 3 a  and 3 b    show power consumption patterns of a base station; 
         FIG. 4  is a flow chart of a method for detecting sleeping cells according to embodiments of the disclosure; 
         FIG. 5  is a flow chart of a method of training a classification model to detect sleeping cells according to embodiments of the disclosure; 
         FIG. 6  is a schematic diagram of power consumption data according to embodiments of the disclosure; 
         FIG. 7  is a schematic diagram of a network node according to embodiments of the disclosure; and 
         FIG. 8  is a schematic diagram of a network node according to further embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not to obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers that are specially adapted to carry out the processing disclosed herein, based on the execution of such programs. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. 
     Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. 
     In terms of computer implementation, a computer is generally understood to comprise one or more processors, one or more processing modules or one or more controllers, and the terms computer, processor, processing module and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term “processor” or “controller” also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above. 
       FIG. 1  shows a communication network  100  according to embodiments of the disclosure. Those skilled in the art will appreciate that numerous components have been omitted from the illustration in order to focus on those components essential to a description of the concepts set out herein. 
     The network  100  comprises a cellular network, having a plurality of cells  104   a,    104   b,    104   c  (collectively,  104 ) served by respective base stations  102   a,    102   b,    102   c  (collectively  102 ). In the illustrated embodiment, the cellular network comprises three cells and a corresponding number of base stations. However, it will be understood that the cellular network may comprise any number of cells, and will typically comprise more than three cells. Further, it will be understood that each base station may serve more than one cell. 
     Each base station  102  (which may also be called a NodeB, eNodeB, gNodeB, etc) comprises one or more radio transmission points for transmitting radio signals to wireless terminal devices (e.g., UEs) which are connected to its respective cell  104 , and for receiving radio signals transmitted by those wireless terminal devices. The radio transmission points may be located at the site of the base station, or remote from it (such as, for example, in a distributed configuration where the base station comprises a central unit and one or more distributed units for transmitting and receiving radio signals). 
     Each of the base stations  102  is coupled, via a packet-switched network (such as a backhaul network and/or a core network of the network  100 )  106 , to a server  108 . The server  108  may comprise or form part of an operations support system (OSS) for the network  100 . Alternatively or additionally, the server  108  may be located in a server facility which is remote from the network operator (e.g., in the cloud). 
     In the illustrated embodiment, the cells  104  are neighbouring cells, in the sense that the first cell  104   a  shares a border with the second cell  104   b,  which also shares a border with the third cell  104   c.  Further, as will be apparent from the illustration and the further explanation below, each of the cells  104  comprises the components and operative connections (e.g., to the server  108 ) to benefit from embodiments of the disclosure and to be monitored for detection as a sleeping cell. However, in other embodiments, only some of the cells in a cellular network may comprise the components and operative connections to benefit from embodiments of the disclosure, and these cells may be neighbouring or non-neighbouring cells; that is, the embodiments may apply to only a subset of cells of a cellular network such that only that subset of cells is monitored. 
     According to embodiments of the disclosure, the power consumption (and particularly the power consumption pattern) of a radio transmission point is monitored to detect whether a cell served by that radio transmission point is a sleeping cell or not. Thus power consumption data is input to a classification model developed, using a machine-learning algorithm, which generates an output classifying the radio transmission as serving one of a sleeping cell and a non-sleeping cell. 
     In particular, it can be expected that the power consumption pattern of a radio transmission point serving a sleeping cell will be different from the power consumption pattern of radio transmission point serving a non-sleeping cell. The changes in the pattern may vary widely. For example, a radio transmission point may consume more power due to a deadlock state, or less power as some of the processes are killed and no longer run. A classification model which has been suitably trained (e.g., as described below with respect to  FIG. 5 ) is able to identify power consumption patterns which are indicative of sleeping cells (and conversely, non-sleeping cells) and classify radio transmission points accordingly on the basis of their power consumption. 
     In one embodiment, the power consumption data is the only input to the classification model. In such embodiments, therefore, no additional sensors are required beyond those for measuring the power consumption of the radio transmission point. No data needs to be reported from terminal devices served by the radio transmission point, saving on complexity and network resources, while making the detection process more robust to errors. 
       FIG. 2  is a schematic diagram of a radio transmission point arrangement  200  according to embodiments of the disclosure. Again, those skilled in the art will appreciate that numerous components of the radio transmission point are omitted from the illustration for the sake of clarity. As embodiments of the disclosure relate to measurement of the power consumption of the radio transmission point, the illustration similarly concentrates on the power supply arrangements of the radio transmission point. 
     The arrangement comprises a radio transmission point  202  (e.g., a base station, or a radio transmission point forming part of a base station) having one or more antennas  204  for the transmission and reception of radio signals. Signals to be transmitted are provided to the antennas  204  via a power amplifier  206 , which serves to amplify the signals prior to their transmission. The origin of these signals (i.e., the content of the signals, whether data or control signaling) is not illustrated in  FIG. 2 . 
     Power is supplied to the power amplifier  206  by a power supply  208 . The power supply  208  will typically comprise a connection to a power grid, but may also or alternatively comprise one or more back-up supplies, such as generators (e.g. fossil fuel generators, solar cells, wind turbines, water turbines, etc) and high-capacity batteries. The power supply  208  may also comprise one or more power converters, such as a DC-DC converter to modulate the power output to suitable levels for the power amplifier  206 . 
     The radio transmission point  202  further comprises bias circuitry  210 , which is operable to provide a bias voltage to the signal to be amplified (e.g., so as to ensure that the signal remains in the linear region of the power amplifier  206 ). Although not illustrated, the biasing circuitry  210  may also be supplied with power from the power supply  208 . 
     The arrangement  200  further comprises a classification model  212 . The classification model  212  may be provided at the same site as the radio transmission point  202  or at the same site as a base station to which the radio transmission point belongs, or at a different site which is remote from the radio transmission point  202  or the base station. 
     The classification model  212  is operable to classify the radio transmission point  202  as serving one of a sleeping cell and a non-sleeping cell, based on the power consumption of the radio transmission point  202 . The power consumption may be measured in various places, including the bias circuitry  210  and the power supply to the power amplifier  206 . Thus the arrangement  200  comprises operative connections between the output of the power supply  208  to the power amplifier  206  (e.g., at a power supply rail of the power amplifier  206 , or V DD ) and the classification model  212 , and between the output of the bias circuitry  210  to the power amplifier  206  and the classification model  212 . In alternative embodiments of the disclosure, the classification model  212  may comprise inputs from only one of these measurement points. It is expected that measurement of the bias voltage will provide better granularity than measurement at the power supply rail. 
     The power consumption of a radio transmission point will depend on a large number of factors (e.g., the number of connected devices, the size and shape of the cell, etc), and in general will incorporate power consumed as a result of transmitting reference signaling, data symbols. 
       FIGS. 3 a  and 3 b    show power consumption patterns of a radio transmission point in New Radio (NR) and Long Term Evolution (LTE) radio access technologies. Only power consumption as a result of reference signaling transmission (e.g. synchronization signals, system information broadcast, etc) is shown, for clarity. However, it can be seen that the regular transmission of reference signals results in regular peaks of power consumption in either radio access technology. Even with the addition of data transmissions to terminal devices served by the radio transmission point, the regular peaks corresponding to reference signal transmission can be identified (e.g. using one or more machine-learning techniques). Accordingly, the absence of regular transmission of reference signals can be an indicator of a sleeping cell. 
       FIG. 4  is a flowchart of a method according to embodiments of the disclosure, in which a classification model is used to classify a radio transmission point as serving one of a sleeping cell and a non-sleeping cell. The method may be performed in the radio transmission point arrangement  200  described above with respect to  FIG. 2 , for example. 
     The method begins in step  400 , in which the power consumption of the radio transmission point is monitored. As noted above, the power consumption may be measured at a power supply rail of a power amplifier in the radio transmission point, and/or a bias rail of the power amplifier, for example. The resulting data may be arranged as time-series data, comprising a sequence of values of the power consumption of the radio transmission point at successive points in time. 
     In step  402 , the power consumption is provided as an input to a classification model (such as the classification model  212 ). The classification model is developed using a machine-learning algorithm (see  FIG. 5 ). The classification model may be generic. However, in other embodiments, the classification model may be specific to the radio transmission point in one or more ways. For example, the classification model may be specific to a particular radio access technology employed by the radio transmission point (e.g., GSM, WCDMA, LTE, NR, etc). For example, the classification model may be specific to particular hardware employed in the radio transmission point, such as a particular power amplifier, or a particular antenna arrangement. 
     In a further alternative embodiment, the classification model may be specific to the radio transmission point itself. In such embodiments, the classification model may be received initially from a remote server (such as the server  108 ) before being trained locally at the radio transmission point, based on power consumption data of the radio transmission point itself (see also  FIG. 5 ). In this way, the classification model is adapted based on the particular configuration of the radio transmission point itself. 
     In an extension of this embodiment, once trained locally, the classification model may be transmitted back to the remote server. With multiple radio transmission points transmitting respective classification models to the remote server, the remote server is able to amalgamate (or “stack”) classification models from multiple radio transmission points to generate a final classification model. One method of stacking classification models is to average them. Respective final classification models may be generated for different radio access technologies, power amplifier hardware or software, etc. The final classification models may then be sent back to the relevant radio transmission points for implementation. 
       FIG. 6  is a schematic diagram showing power consumption data according to embodiments of the disclosure. It will be noted that the power consumption data is arranged in a plurality of non-overlapping windows (marked W n ). Thus the power consumption data window W 1  ends at a time t 1 , the power consumption data window W n  ends at time t n , and so on. 
     Returning to  FIG. 4 , in step  404 , the classification model generates an output which maps the power consumption data to one of a sleeping cell and a non-sleeping cell. Thus in one embodiment the classification model is a binary classification model. 
     The classification model in one embodiment is thus configured to detect the presence of a sleeping cell or a non-sleeping cell based on the power consumption data. In one embodiment, the classification model receives as input the power consumption data for one window W n , and generates a corresponding output p n  for that window. Thus the decision as to whether the radio transmission point serves a sleeping cell or a non-sleeping cell may be based on a single window of data. The length of each window may be chosen so as achieve a high-level of confidence that the decision or output for a particular window is correct. For example, each window may be one second or more long. Outputs may be generated periodically (e.g., after each window), or non-periodically (e.g., event driven). 
     The classification model may operate within each window by predicting a next power consumption data value based on one, or typically several, preceding power consumption data values, assuming that the radio transmission point is serving (say) a non-sleeping cell. If the predicted value matches the actual value, then this is an indication that the radio transmission point is indeed serving a non-sleeping cell. If the predicted value does not match the actual value, then this is an indication that the radio transmission point is serving a sleeping cell. Note that this process may take place iteratively, with multiple data samples within each data window being predicted based on preceding data values, and then compared to the actual data values. A determination as to whether the data for the window as a whole is classified as a sleeping cell or a non-sleeping cell may then be based on a combination of these individual predictions. Thus the classification model may take as its inputs the actual data values within a particular window, and also the predicted values within the particular window, and classify the cell as sleeping or not based on those inputs. 
     In further embodiments, the classification model may additionally or alternatively be configured to predict that the radio transmission point will serve a sleeping cell or a non-sleeping cell, i.e., in future. Thus, in this embodiment the classification model generates an output which predicts, based on the power consumption data for a particular (e.g., current) data window, whether the radio transmission point will (e.g., is about to or within a period of time of the particular data window) serve a sleeping cell. Further detail regarding this embodiment is provided below. 
     In step  406 , it is determined whether the output indicates that the radio transmission point is serving or will serve a sleeping cell. If the output of the classification model indicates that the radio transmission point is not serving a sleeping cell (or is not predicted to serve a sleeping cell), the method ends, or returns to step  400  in which the power consumption of the radio transmission point continues to be monitored. 
     If the output of the classification model indicates that the radio transmission point is serving a sleeping cell (or is predicted to serve a sleeping cell), the method moves to step  408 , in which one or more actions are taken to remediate the sleeping state of the cell. 
     For example, one or more of the following actions may be taken: 
     1. Particularly where a future sleeping cell state is predicted, an indication of the sleeping cell state may be transmitted to a scheduler of the network, to activate reference signal output (e.g., synchronization Signal Block) and thereby prevent the sleeping cell state from occurring. 
     2. Power reset of the specific radio transmission point (e.g., power reset of the power amplifier  206 ). 
     3. Resetting a base station to which the radio transmission point belongs. 
     If a sleeping cell state is detected, a power reset of the specific radio transmission point may be actioned first, as this can be expected to take 10 ms to 100 ms and therefore service from the radio transmission point is only momentarily suspended. If this fails to remediate the problem, the base station may be reset. However, this can be expected to take 2-3 minutes, and therefore leads to significant loss of service. 
     Thus the disclosure provides a method whereby a classification model detects the presence of a sleeping cell in a cellular network based on power consumption data, and/or predicts the presence of a sleeping cell in a cellular network. 
       FIG. 5  is a flowchart of a method of training a classification model to detect the presence of a sleeping cell in a cellular network, based on power consumption data. 
     The method begins in step  500 , in which training data is acquired. The training data comprises power consumption data for radio transmission points, as described above. Thus, the power consumption data may be arranged into windows as shown in  FIG. 6 . 
     In step  502 , a prediction model is trained, using a machine-learning algorithm, to predict values of the power consumption data based on one or more preceding values of that data. For example, the prediction model may be trained to predict a value d n  based on a plurality of preceding values d n−1 , d n−2 , d n−3 , etc. Various machine-learning models are suitable for this task, including recurrent neural networks, such as long short-term memory (LSTM), and deep convolutional neural networks. 
     In step  504 , once trained, the prediction model is used to predict values of power consumption data for one or more radio transmission points, based on further training data (which again comprises power consumption data for one or more radio transmission points). The further training data is labeled as corresponding to one of a sleeping cell and a non-sleeping cell. 
     In step  506 , a classification model is trained, using a machine-learning algorithm and based on the further training data and also the predicted power consumption data generated in step  504 , to classify the data as belonging to one of a sleeping cell and a non-sleeping cell. The classification model may therefore be a binary classification model. Thus the classification model may take as its inputs the power consumption data for one or more radio transmission points, and the predicted power consumption data generated based on that power consumption data. 
     As noted above, the training data is labeled (e.g., based on historical data or expert input) as representing a sleeping cell or a non-sleeping cell. Accordingly the classification model may be iteratively trained to produce an output y (i.e. sleeping cell or non-sleeping cell) based on inputs x (power consumption data and predicted power consumption data). Suitable machine-learning algorithms include state vector machines, recurrent neural networks, deep convolutional neural networks, etc. 
     The classification model development in step  506  typically has four phases: the training, development testing, real testing, and the real deployment to the product. The four phases may be in continuous iteration such that if the performance of the model degrades over time, it needs to be retrained. The model training may be done by fitting the input (power consumption) to the output (sleeping or non-sleeping cell), where some part (preferably equal amount of samples for each class) of the dataset is from a sleeping cell and the other part is from a non-sleeping cell. The model training may be performed on a first portion of the training dataset (e.g., 50%). Once the model fits with this first portion, the model is then applied to a second portion (e.g., the next 25%) of dataset, which contains a similar distribution. The classification outputs based on the second portion are compared to the ground truth values (the real labels telling the actual state of the cell; either sleeping or not sleeping). Hyper parameters of the classification model are adjusted, or different machine learning models are experimented with, based on the comparison. Eventually the classification model that yields the best accuracy is selected. Then, the selected model is applied to the real test set, which is a third portion of the full training data set (e.g., the last 25%). Ideally, the accuracy values obtained from the development test and the real test phases are similar. If not, the development phase may be iterated. The aim is to make the accuracies from the phases close to each other and at the same time as high as possible. Once the classification model is developed, it is deployed into the real product such that the model is ready to listen to real-time data to yield probabilities on whether the cell is in a sleeping state or not (e.g.,in steps  402  and  404  described above). 
     The performance of the model may be evaluated by any well-known evaluation metrics. For binary classification models, f1-score, AuC ROC score, precision and recall metrics are often used. The choice of evaluation metrics may depend on the problem formulation. 
     The steps for training the classification model set out above with respect to  FIG. 5  are optional. More generally, machine-learning algorithms such as simultaneous decomposition and classification networks may be able to decompose and classify power consumption data as belonging to one of a sleeping cell and a non-sleeping cell without separately predicting power consumption and then classifying based on the comparison between the predicted and actual power consumption data. 
     As noted above, the classification model in further embodiments may be trained to predict, based on a current power consumption for a radio transmission point, that the radio transmission point will serve a sleeping cell or a non-sleeping cell at some defined point in future. Such a classification model may be trained according to the method described above with respect to  FIG. 5 , but with the labels for the power consumption training dataset changed to reflect the ground truth (i.e. whether the radio transmission point serves a sleeping cell or a non-sleeping cell) at some defined point in the future. Thus, the ground truth for a data window w(t=n) in such embodiments is whether the radio transmission point serves a sleeping cell or a non-sleeping cell at some later time t=n+δ. Note that the prediction interval δ in this embodiment (e.g., the time offset between the power consumption data and the time at which the radio transmission point is predicted to serve one of a sleeping cell and a non-sleeping cell) may be determined through routine testing procedures. 
     Thus the present disclosure also provides methods, apparatus and computer-readable mediums for training a classification model to classify the power consumption data of a radio transmission point into one of a sleeping cell and a non-sleeping cell. 
       FIG. 7  is a schematic diagram of a node  700  according to embodiments of the disclosure. The network node  700  may be configured to carry out the method described above with respect to  FIG. 4 , for example. In one embodiment, the network node  700  comprises a base station or a radio transmission point for a cellular network, such as the base stations  102 , or the radio transmission point  202 . Alternatively, the network node  700  may be implemented in a remote server, such as the server  108  described above with respect to  FIG. 1 . 
     The network node  700  comprises processing circuitry  702  and a machine-readable medium (such as memory)  704 . The machine-readable medium stores instructions which, when executed by the processing circuitry  702 , cause the network node  700  to: monitor power consumption of a radio transmission point of the cellular communication network; provide the power consumption of the radio transmission point as an input to a classification model, developed using a machine-learning algorithm; and obtain an output from the classification model, the output classifying the radio transmission point as serving one of a sleeping cell and a non-sleeping cell. 
     In the illustrated embodiment, the network node  700  also comprises one or more interfaces  706 , for receiving signals from other nodes of the network and/or transmitting signals to other nodes of the network. The interfaces  706  may use any appropriate communication technology, such as electronic signaling, optical signaling or wireless (radio) signaling. 
     In the illustrated embodiment, the processing circuitry  702 , the machine-readable medium  704  and the interfaces  706  are operatively coupled to each other in series. In other embodiments, these components may be coupled to each other in a different fashion, either directly or indirectly. For example, the components may be coupled to each other via a system bus or other communication line. 
       FIG. 8  is a schematic diagram of a network node  800  according to embodiments of the disclosure. The network node  800  may be configured to carry out the method described above with respect to  FIG. 4 , for example. In one embodiment, the network node  800  comprises a base station or a radio transmission point for a cellular network, such as the base stations  102 , or the radio transmission point  202 . Alternatively, the network node  800  may be implemented in a remote server, such as the server  108  described above with respect to  FIG. 1 . 
     The network node  800  comprises a monitoring module  802  and a classification module  804 . The monitoring module  802  is configured to monitor power consumption of a radio transmission point of the cellular communication network. The power consumption of the radio transmission point is provided as an input to the classification module  804 , which implements a classification model, developed using a machine-learning algorithm, and obtains an output from the classification model, the output classifying the radio transmission point as serving one of a sleeping cell and a non-sleeping cell. 
     The network node  800  may also comprise one or more interface modules (not illustrated), for receiving signals from other nodes of the network and/or transmitting signals to other nodes of the network. The interfaces may use any appropriate communication technology, such as electronic signaling, optical signaling or wireless (radio) signaling. 
     The modules described above with respect to  FIG. 8  may comprise any combination of hardware and/or software. For example, in one embodiment, the modules are implemented entirely in hardware. As noted above, hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. In another embodiment, the modules may be implemented entirely in software. In yet further embodiments, the modules may be implemented in combinations of hardware and software. 
     The present disclosure therefore provides methods, apparatus and machine-readable mediums for the detection of sleeping cells in a cellular network. The disclosure also provides methods, apparatus and machine-readable mediums for training a classification model to detect sleeping cells in a cellular network. 
     It should be noted that the above-mentioned embodiments illustrate rather than limit the concepts disclosed herein, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended following claims. The word “comprising” does not exclude the presence of elements or steps other than those listed in a statement, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfill the functions of several units recited in the statements. Any reference signs in the claims shall not be construed so as to limit their scope.