Technical Field

[0001] The present disclosure relates to a base station in a cellular

communications network, and more particularly to the detection of an error (e.g., an incorrect connection or an altered/damaged connector or cable) with a combination of interconnected Radio Frequency (RF) components (e.g., a connector, a feeder cable, and an antenna) coupled to an RF output of a transmitter of the base station.

Background

[0002] Base stations in modern cellular communications networks may have many transmitters and many antennas. Each transmitter is connected to an antenna via a number of Radio Frequency (RF) components such as a connector and a feeder cable. When installing or servicing a base station, it is often necessary to determine whether a transmitter is connected to the correct antenna. Conventionally, this is done using a manual process where a technician visually inspects the base station to determine whether the transmitter is connected to the correct antenna. This is burdensome and time-consuming and, as such, there is a need for a system and method for verifying that a transmitter of a base station is coupled to the correct antenna without the need of visual inspection.

[0003] United States Patent Application Publication No. 2014/0225790 A1 , entitled "ANTENNAS WITH UNIQUE ELECTRONIC SIGNATURE," proposes a solution that uses reflectometry to determine whether the correct antenna has been connected to an antenna port that relies on manufacturing antennas with a unique electronic signature. More specifically, the solution described in

2014/0225790 A1 relies on intentionally altering the antenna characteristics by connecting a Resistor-Inductor-Capacitor (RLC) circuit that creates a unique frequency response as an electronic signature of the antenna. However, by doing so, the radiation pattern and the working bandwidth of the antenna will be altered. In addition, this solution relies on an additional signal source for sending a wideband, or frequency sweep signal, to the antenna to be identified. This wideband signal may create unwanted emission and interference. Other problems with this solution may include a common standardization process in manufacturing antennas with unique electronic signatures, something nonexistent today in the industry, and replacing all old antennas with newer antennas using the electronic signature RLCs.

[0004] European Patent Application Publication No. 1962374 A1 , entitled "IDENTIFICATION OF ANTENNAS VIA CABLES," proposes a solution for identifying antennas by using an external testing apparatus consisting of an external active or semi-active Radio Frequency Identification (RFID) circuit/tag connected to the antenna. The RFID reader sends a trigger signal to the RFID tag in the antenna, receives a response signal from the RFID tag via the feeder cable, and decodes the received response signal to identify the antenna. The disadvantages of this solution are similar to those for the solution of

2014/0225790 A1 , i.e. additional equipment, special non-standardized antennas, emissions, and interference.

[0005] Another issue that arises with base stations is that the RF components connecting a transmitter to an antenna (e.g., a connector and/or a feeder cable) may be altered or damaged due to, e.g., aging such that the RF components no longer meet the original specification. This results in less than ideal performance of the base station (e.g., increased power consumption). As such, there is also a need for a system and method for determining whether the RF components connecting a transmitter to an antenna have been altered or damaged.

Summary

[0006] Systems and methods are disclosed for determining whether there is an error with a combination of interconnected Radio Frequency (RF) components coupled to an RF output of a transmitter of a base station of a cellular

communications network. The combination of interconnected RF components may include, for example, one or more connectors, one or more feeder cables, and an antenna. The error may be, e.g., that the combination of RF components have been altered or damaged such that they no longer meet original

specifications and/or that the transmitter is coupled to an incorrect antenna.

[0007] In some embodiments, a method of operation of a processing system to determine whether there is an error with a combination of interconnected RF components connected to an RF output of a transmitter of a base station comprises obtaining an actual Return Loss (RL) frequency profile of the combination of interconnected RF components connected to the RF output of the transmitter of the base station, determining a similarity metric that is indicative of a degree of similarity between the actual RL frequency profile of the combination of interconnected RF components and a reference RL frequency profile of the combination of interconnected RF components, and determining whether the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is greater than a predefined threshold. The method further comprises determining that there is an error with the combination of interconnected RF components upon determining that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is not greater than the predefined threshold. In this manner, an error with the combination of interconnected RF components can be detected based on inherent

characteristics of the combination of the interconnected RF components without the need for additional components.

[0008] In some embodiments, the method further comprises determining that there is no error with the combination of interconnected RF components upon determining that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is greater than the predefined threshold.

[0009] In some embodiments, obtaining the actual RL frequency profile of the combination of interconnected RF components comprises obtaining a forward RF signal that propagates through the combination of interconnected RF

components in a forward direction and a reflected RF signal that propagates through the combination of interconnected RF components in a reverse direction during transmission of a signal by the base station, obtaining a power spectrum of the forward RF signal and a power spectrum of the reflected RF signal, and generating the actual RL frequency profile from the power spectrum of the forward RF signal and the power spectrum of the reflected RF signal. In some embodiments, the actual RF frequency profile may be obtained during

transmission of a live signal by the base station.

[0010] Further, in some embodiments, the power spectrum for the forward RF signal comprises a plurality of forward power values for a plurality of frequency bins spanning a frequency range, the power spectrum for the reverse RF signal comprises a plurality of reflected power values for the plurality of frequency bins spanning the frequency range, and generating the actual RL frequency profile comprises computing a ratio of forward-reflected signal cross-correlation over forward signal autocorrelation for each of at least a subset of the plurality of frequency bins spanning the frequency range. Further, in some embodiments, generating the actual RL frequency profile further comprises filtering out one or more of the plurality of frequency bins that contain only noise.

[0011 ] In some embodiments, determining the similarity metric comprises computing a cross-correlation between the actual RL frequency profile of the combination of interconnected RF components and the reference RL frequency profile of the combination of interconnected RF components, wherein the similarity metric is based at least in part of a result of the cross-correlation.

[0012] In some embodiments, the method further comprises obtaining the reference RL frequency profile. Further, in some embodiments, obtaining the reference RL frequency profile of the combination of interconnected RF components comprises obtaining a forward RF signal that propagates through the combination of interconnected RF components in a forward direction and a reflected RF signal that propagates through the combination of interconnected RF components in a reverse direction during transmission of a signal by the base station, obtaining a power spectrum of the forward RF signal and a power spectrum of the reflected RF signal, and generating the reference RL frequency profile from the power spectrum of the forward RF signal and the power spectrum of the reflected RF signal. In some embodiments, the actual RF frequency profile may be obtained during transmission of a live signal by the base station.

[0013] Further, in some embodiments, the power spectrum for the forward RF signal comprises a plurality of forward power values for a plurality of frequency bins spanning a frequency range, the power spectrum for the reverse RF signal comprises a plurality of reflected power values for the plurality of frequency bins spanning the frequency range, and generating the reference RL frequency profile comprises computing a ratio of forward-reflected signal cross-correlation over forward signal autocorrelation for each of at least a subset of the plurality of frequency bins spanning the frequency range. Further, in some embodiments, generating the reference RL frequency profile further comprises filtering out one or more of the plurality of frequency bins that contain only noise.

[0014] In some embodiments, obtaining the reference RL frequency profile comprises obtaining the reference RL frequency profile from memory.

[0015] In some embodiments, the combination of interconnected RF components comprises at least one connector, at least one feeder cable, and an antenna.

[0016] Embodiments of the base station are also disclosed. In some embodiments, a base station comprises a transmitter comprising an input and an RF output, a combination of interconnected RF components coupled to the RF output of the transmitter, and a processing system operable to obtain an actual RL frequency profile of the combination of interconnected RF components connected to the RF output of the transmitter of the base station, determine a similarity metric that is indicative of a degree of similarity between the actual RL frequency profile of the combination of interconnected RF components and a reference RL frequency profile of the combination of interconnected RF components, determine whether the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is greater than a predefined threshold, and determine that there is an error with the combination of interconnected RF components upon determining that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is not greater than the predefined threshold.

[0017] In some embodiments, the processing system is further operable to determine that there is no error with the combination of interconnected RF components upon determining that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is greater than the predefined threshold.

[0018] In some embodiments, the base station further comprises a

bidirectional coupler comprising a first port coupled to the RF output of the transmitter, a second port coupled to the combination of interconnected RF components, a third port operable to provide a forward RF signal, and a fourth port operable to provide a reverse RF signal. In order to obtain the actual RL frequency profile of the combination of interconnected RF components, the processing system is further operable to obtain the forward RF signal that propagates through the combination of interconnected RF components in a forward direction from the third port of the bidirectional coupler and a reflected RF signal that propagates through the combination of interconnected RF components in a reverse direction from the fourth port of the bidirectional coupler during transmission of a signal by the base station, obtain a power spectrum of the forward RF signal and a power spectrum of the reflected RF signal, and generate the actual RL frequency profile from the power spectrum of the forward RF signal and the power spectrum of the reflected RF signal. In some

embodiments, the actual RF frequency profile may be obtained during

transmission of a live signal by the base station.

[0019] Further, in some embodiments, the power spectrum for the forward RF signal comprises a plurality of forward power values for a plurality of frequency bins spanning a frequency range, the power spectrum for the reverse RF signal comprises a plurality of reflected power values for the plurality of frequency bins spanning the frequency range, and, in order to generate the actual RL frequency profile, the processing system is further operable to compute a ratio of forward- reflected signal cross-correlation over forward signal autocorrelation for each of at least a subset of the plurality of frequency bins spanning the frequency range. Further, in some embodiments, in order to generate the actual RL frequency profile, the processing system is further operable to filter out one or more of the plurality of frequency bins that contain only noise.

[0020] In some embodiments, in order to determine the similarity metric, the base station is further operable to compute a cross-correlation between the actual RL frequency profile of the combination of interconnected RF components and the reference RL frequency profile of the combination of interconnected RF components, wherein the similarity metric is at least based on a result of the cross-correlation.

[0021] In some embodiments, the processing system is further operable to obtain the reference RL frequency profile. Further, in some embodiments, in order to obtain the reference RL frequency profile of the combination of interconnected RF components, the processing system is further operable to obtain a forward RF signal that propagates through the combination of interconnected RF components in a forward direction from the third port of the bidirectional coupler and a reflected RF signal that propagates through the combination of interconnected RF components in a reverse direction from the fourth port of the bidirectional coupler during transmission of a signal by the base station, obtain a power spectrum of the forward RF signal and a power spectrum of the reflected RF signal, and generate the reference RL frequency profile from the power spectrum of the forward RF signal and the power spectrum of the reflected RF signal. In some embodiments, the reference RF frequency profile may be obtained during transmission of a live signal by the base station.

[0022] Further, in some embodiments, the power spectrum for the forward RF signal comprises a plurality of forward power values for a plurality of frequency bins spanning a frequency range, the power spectrum for the reverse RF signal comprises a plurality of reflected power values for the plurality of frequency bins spanning the frequency range, and, in order to generate the reference RL frequency profile, the processing system is further operable to compute a ratio of forward-reflected signal cross-correlation over forward signal autocorrelation for each of at least a subset of the plurality of frequency bins spanning the frequency range. Further, in some embodiments, in order to generate the reference RL frequency profile, the processing system is further operable to filter out one or more of the plurality of frequency bins that contain only noise.

[0023] In some embodiments, the reference RL frequency profile is obtained from memory.

[0024] In some embodiments, the combination of interconnected RF components comprises at least one connector, at least one feeder cable, and an antenna.

[0025] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the embodiments in association with the accompanying drawing figures.

Brief Description of the Drawings

[0026] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0027] Figure 1 illustrates one example of a cellular communications network;

[0028] Figure 2 illustrates a base station subsystem, which is a subsystem of a base station of a cellular communications network such as, e.g., the example cellular communications network of Figure 1 , according to some embodiments of the present disclosure;

[0029] Figure 3 illustrates a process for detecting an error in a combination of interconnected Radio Frequency (RF) components connected to an RF output of a transmitter of a base station according to some embodiments of the present disclosure;

[0030] Figure 4 illustrates a process for obtaining a Return Loss (RL) frequency profile of a combination of interconnected RF components coupled to an RF output of a transmitter of a base station according to some embodiments of the present disclosure;

[0031 ] Figures 5 through 8 illustrate plots of RL frequency profiles of different examples of combinations of cables and antennas; and

[0032] Figure 9 is a block diagram of a processing system according to one embodiment of the present disclosure.

Detailed Description

[0033] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0034] Systems and methods are disclosed for determining whether there is an error with a combination of interconnected Radio Frequency (RF) components coupled to an RF output of a transmitter of a base station of a cellular

communications network. The combination of interconnected RF components may include, for example, one or more connectors, one or more feeder cables, and an antenna. The error may be, e.g., that the combination of RF components have been altered or damaged such that they no longer meet original

specifications and/or the transmitter is coupled to an incorrect antenna.

[0035] In particular, embodiments of the system and method are disclosed herein for identifying errors with a combination of interconnected RF components connected to an RF output of a transmitter of a base station, where the errors may include: (a) the wrong feeder cable(s) or antenna being accidentally connected to the antenna port of the transmitter and/or (b) the connected cable(s) or antenna having been altered due to damage or aging and no longer meeting the original specification. Embodiments of the present disclosure are able to identify the above errors with a high degree of accuracy by extracting and comparing the inherent electronic fingerprint of the combination of interconnected RF components (e.g., the cable(s) and the antenna) with a reference electronic fingerprint obtained previously (e.g., extracted at the factory or during original installation of the base station). Furthermore, in some embodiments, the detection may be done with a live narrow band digital RF signal (e.g., such as a normal Long Term Evolution (LTE) transmission) and does not require an external signal source. Note, however, that an external signal source may alternatively be used, in some embodiments, in controlled environments.

[0036] Figure 1 illustrates one example of a cellular communications network 10. In this example, the cellular communications network 10 is a 3 ^rd Generation Partnership Project (3GPP) LTE cellular communications network; however, the present disclosure is not limited thereto. As illustrated, the cellular

communications network 10 includes an Evolved Universal Terrestrial Radio Access Network (EUTRAN) 12, which is more generally referred to herein as a Radio Access Network (RAN) 12. The RAN 12 includes base stations 14 that serve corresponding cells 16 of the cellular communications network 10. User Equipment devices (UEs) 18 are wirelessly connected to the base stations 14. The base stations 14 can communicate with one another via a base station to base station interface, which in LTE is referred to as an X2 interface. The base stations 14 are also connected to an Evolved Packet Core (EPC) 20 via corresponding interfaces, which in LTE are referred to as S1 interfaces. The EPC 20 includes various core network nodes such as, for example, one or more Mobility Management Entities (MMEs) 22, one or more Serving Gateways (S- GWs) 24, and one or more Packet Gateways (P-GWs) 26.

[0037] Each base station 14 may include multiple transmitters coupled to multiple antennas. In this regard, Figure 2 illustrates a subsystem of a base station 14. Notably the subsystem of Figure 2, which is referred to herein as a base station subsystem 28, is only a portion of the overall architecture of the base station 14. In other words, the base station 14 includes additional components that are not illustrated in Figure 2. As illustrated in Figure 2, the base station subsystem 28 includes a transmitter 30, a bidirectional coupler 32, and a combination of interconnected RF components, which in this example include a connector 34, a feeder cable 36, a connector 38, and an antenna 40. Notably, the combination of interconnected RF components may include additional or alternative components to those illustrated in the embodiment of Figure 2.

[0038] The transmitter 30 includes transmit (TX) circuitry 42 and an amplifier 34, in this example. The transmit circuitry 42 may include various components such as, for example, digital-to-analog conversion circuitry, up-conversion circuitry, filtering circuitry, and the like. The transmitter 30 also includes an input port 46 and an output port 48, which is also referred to herein as an RF output of the transmitter 30. The output port 48 of the transmitter 30 is connected to a first port 50 of the bidirectional coupler 32. A second port 52 of the bidirectional coupler 32 is connected to one end of the feeder cable 36 via the connector 34. The other end of the feeder cable 36 is connected to the antenna 40 via the connector 38.

[0039] In operation, the transmitter 30 receives an input signal at the input port 46. The input signal is processed by the transmit circuitry 42 and amplified by the amplifier 44 to provide an RF transmit signal at the output port 48. The RF transmit signal passes from the first port 50 of the bidirectional coupler 32 to the second port 52 of the bidirectional coupler 32 and then passes through the connector 34, the feeder cable 36, and the connector 38 to the antenna 40. Due to imperfect impedance matching (e.g., due to manufacturing tolerances), a portion of the RF transmit signal is reflected by the combination of interconnected RF components back into the second port 52 of the bidirectional coupler 32. This reflected signal passes from the second port 52 of the bidirectional coupler 32 to a fourth port 56 of the bidirectional coupler 32. In addition, the RF transmit signal input to the first port 50 of the bidirectional coupler 32 passes from the first port 50 to a third port 54 of the bidirectional coupler 32.

[0040] Embodiments of the present disclosure rely on the inherent electronic characteristics existing in any cable or antenna system, which differ (to a very small degree) to otherwise identical cables or antenna systems. In practice, when an RF signal is transmitted through a cable to an antenna, a small percentage of the signal is always reflected back even when the output of the transmitter is "perfectly" matched to the impedance of the cable and the antenna. The frequency profile of the reflected signal is unique and it depends on the combination of the connector(s), the cable(s), and the antenna that the RF signal was transmitted to, due to tolerances in the manufacturing process of the connectors, cables, and antennas. This frequency profile is related to the bandwidth and frequency of the transmitted RF signal. In some embodiments, this frequency profile can be measured a priori for the frequency band that the base station is intended to operate on, stored, and used as a reference to compare against during a feeder cable connection checkup.

[0041 ] The frequency profile of the combination of interconnected RF components is generated by separating forward and reflected signals during transmission of a signal with the use of the bidirectional coupler 32. The ratio of forward-reflected signal cross-correlation over forward signal autocorrelation, which represents a Return Loss (RL) per frequency (i.e., what percentage of power is reflected back for each frequency), is obtained. This function of RL over frequency represents the frequency profile of the particular combination of interconnected RF components, and is referred to herein as a "RL profile" or "RL frequency profile." In some embodiments, a cross-correlation of the reference RL frequency profile and the measured, or actual, RL frequency profile is computed. This cross-correlation indicates the degree of similarity between the reference cable/antenna and the one the radio is connected to. Based on the similarity (e.g., expressed as a percentage), a decision is made on the

correctness of the connection. The similarity threshold used for this decision may be predefined according to an RF component variability and a required sensitivity.

[0042] In this regard, a processing system 58 operates to process the forward RF signal and the reflected RF signal during transmission a signal by the base station 14, in particular by the transmitter 30, to generate an actual RL frequency profile of the combination of interconnected RF components. In some embodiments, the signal transmitted by the base station is a "live" signal. As used herein, a "live" signal is a normal transmission with live, or real, traffic. As discussed below in more detail, this actual RL frequency profile of the

combination of interconnected RF components is compared to a reference RL frequency profile of the combination of interconnected RF components to determine whether there is an error with the combination of interconnected RF components (e.g., the transmitter 30 is connected to the wrong antenna 40 or a combination of RF components no longer meets original specifications due to, e.g., being altered or damaged due to, e.g., aging).

[0043] In this example, the processing system 58 includes a dual RF receiver and demodulator 60 and a main processing system 62 including a Fast Fourier Transform (FFT) and RL profile extraction processor 64 and a cross-correlation processor 66. In addition, the processing system 58 includes a reference RL profile storage 68. The components of the processing system 58 may be implemented in hardware or a combination of hardware and software. For example, the FFT and RL profile extraction processor 64 and the cross- correlation processor 66 may be implemented as one or more processors (e.g., one or more Application Specific Integrated Circuits (ASICs) and/or one or more Field Programmable Gate Arrays (FPGAs)).

[0044] A reference RL frequency profile of the combination of RF components is first obtained and stored in the reference RL profile storage 68. The reference RL profile may be determined at the factory and stored in the reference RL profile storage 68. Alternatively, the reference RL frequency profile may be obtained from the forward RF signal and the reflected RF signal during transmission of a signal out of the base station 14, as discussed below. This may be done, for example, during initial installation of the base station 14. The processing system 58 determines an actual RL frequency profile of the combination of

interconnected RF components and compares the actual RL frequency profile to the reference RL frequency profile to determine whether there is an error with the combination of interconnected RF components. [0045] In this example, the processing system 58 determines the actual RL frequency profile of the combination of interconnected RF components based on the forward RF signal and the reflected RF signal during transmission of a signal by the base station 14, and in particular by the transmitter 30 of the base station 14. More specifically, the dual RF receiver and demodulator 60 separately receives and demodulates the forward RF signal and the reflected RF signal and outputs two streams of digital complex data, one stream for the forward signal (referred to herein as a received forward signal) and another stream for the reflected signal (referred to herein as a received reflected signal).

[0046] Then, in order to obtain the actual RL frequency profile, the FFT and RL profile extraction processor 64 performs an FFT of the received forward signal output by the dual RF receiver and demodulator 60 to provide a power spectrum for the forward signal with frequency resolution equal to the FFT size (for example a 1024 point FFT will generate a power spectrum for 1024 frequency bins). Likewise, the FFT and RL profile extraction processor 64 performs an FFT of the received reflected signal output by the dual RF receiver and demodulator 60 to provide a power spectrum for the reflected signal.

[0047] The actual RL frequency profile of the combination of interconnected RF components is then computed for each FFT frequency bin by computing a ratio of forward-reflected signal cross-correlation over forward signal

autocorrelation. In addition, filtering may be performed to remove values for those frequency bands that contain only noise (i.e., the frequency bands that contain only noise are not used for subsequent comparison). With regard to filtering, the Nyquist band is usually wider than the transmitted bandwidth. As such, there will be frequency bands that do not contain power, but only noise.

[0048] The cross-correlation processor 66 then computes the cross- correlation of the actual RL frequency profile of the combination of

interconnected RF components and the reference RL frequency profile of the combination of interconnected RF components. The resulting cross-correlation coefficient, or metric, is a similarity metric that is indicative of a degree of similarity between the actual RL frequency profile and the reference RL frequency profile. In some embodiments, the correlation coefficient obtained by, or resulting from, the cross-correlation is a value between 0 and 1 , and this correlation coefficient is converted into a percentage value between 0 and 100. If the similarity metric is such that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile is greater than a predefined threshold (e.g., 99.5 %), then the processing system 58 determines that there is no error with the combination of interconnected RF components. However, if the similarity metric is such that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile is not greater than the predefined threshold (e.g., 99.5%), then the processing system 58 determines that there is an error with the combination of interconnected RF components. In this example, the processing system 58 outputs a result, which is indicative of whether or not an error with the combination of interconnected RF components has been detected. This result may be provided to, for example, the controller or other processor of the base station 14, another network node (e.g., a core network node), or some other device or system associated with an operator of the cellular communications network 10. For example, a warning may be provided to an operator of the cellular communications network 10, a technician that is installing or servicing the base station 14, or the like.

[0049] Figure 3 is a flowchart that illustrates a process for determining whether there is an error with respect to the combination of interconnected RF components connected to an RF output of the transmitter of a base station 14 according to some embodiments of the present disclosure. For instance, the process of Figure 3 may be implemented by the processing system 58 of Figure 2, but is not limited thereto. As such, references to the processing system 58 of Figure 2 are sometimes made in the discussion below. However, these references should not be construed as limiting the scope of the process of Figure 3 to the particular implementation of the processing system 58 of Figure 2.

[0050] As illustrated, a reference RL frequency profile is obtained for the combination of interconnected RF components connected to the output of the transmitter 30 of the base station 14 (step 100). As discussed above, the reference RL frequency profile of the combination of interconnected RF components may be determined at the factory and stored at the base station 14. As such, in some embodiments, step 100 is optional (as indicated by the dashed box) in the sense that the processing system 58 does not itself obtain, or determine, the reference RL frequency profile. In other words, the reference RL frequency profile may be obtained, or determined, by some external entity and stored in the reference RL profile storage 68 of the processing system 58.

[0051 ] In some embodiments, the reference RL frequency profile of the combination of interconnected RF components is obtained using a transmission by the base station 14. For example, during transmission of a signal by the base station 14, forward and reflected RF signals from the bidirectional coupler 32 are processed by the processing system 58 to determine an RL frequency profile of the combination of interconnected RF components. Here, rather than using the determined RL frequency profile as the actual RL frequency profile of the combination of interconnected RF components, the determined RL frequency profile is stored as a reference RL frequency profile for subsequent comparison to a measured, or actual, RL frequency profile for the purpose of determining an error.

[0052] In order to determine whether there is an error with a combination of interconnected RF components connected to the RF output of the transmitter 30 of the base station 14, an actual RL frequency profile of the combination of interconnected RF components is obtained (step 102). As discussed above, the actual RL frequency profile of the combination of interconnected RF components is obtained using a transmission by the base station 14. More specifically, during transmission of a signal by the base station 14, forward and reflected RF signals from the bidirectional coupler 32 are processed by the processing system 58 to determine the actual RL frequency profile of the combination of interconnected RF components.

[0053] A similarity metric that is indicative of a degree of similarity between the actual RL frequency profile and the reference RL frequency profile is then determined based on a comparison (e.g., cross-correlation) of the actual RL frequency profile and the reference RL frequency profile of the combination of interconnected RF components (step 104). As discussed above, in some embodiments the similarity metric may be a cross-correlation coefficient or may be a percentage value derived from a cross-correlation coefficient.

[0054] A determination is then made as to whether the degree of similarity, as indicated by the similarity metric, between the actual RL frequency profile and the reference RL frequency profile is greater than a predefined threshold (step 106). This predefined threshold is such that if the degree of similarity between the actual RL frequency profile and the reference RL frequency profile is greater than the predefined threshold, then it is acceptable to assume that there is no error with the combination of interconnected RF components. Conversely, the predefined threshold is such that if the degree of similarity between the actual RL frequency profile and the reference RL frequency profile is not greater than the predefined threshold, then it is acceptable to assume that there is an error with the combination of interconnected RF components. As such, the predefined threshold may be defined according to a known variability of the combination of interconnected RF components (e.g., due to acceptable aging, temperature, manufacturing tolerances, etc.) and the required sensitivity for the error determination. If the degree of similarity is greater than the predefined threshold, then the determination is made that there is no error with the combination of interconnected RF components (i.e., RESULT = OK) (step 108). Otherwise, if the degree of similarity is not greater than the predefined threshold, the determination is made that there is an error with a combination of interconnected RF components (i.e., RESULT = ERROR) (step 1 10).

[0055] Figure 4 is a flowchart that illustrates a process for obtaining an RL frequency profile for a combination of interconnected RF components according to some embodiments of the present disclosure. This process may be used to, e.g., obtain the actual RL frequency profile in step 102 of Figure 3 and, in some embodiments, separately used to obtain the reference RL frequency profile in step 100 of Figure 3. For example, the process of Figure 4 may be used at the time of, or shortly after, deployment/installment of the base station 14 to determine the reference RL frequency profile of the combination of interconnected RF components. The process of Figure 4 may thereafter be repeated, e.g., periodically, to obtain the actual RL frequency profile of the combination of interconnected RF components for comparison to the reference RL frequency profile in order to detect errors. In some embodiments, the process of Figure 4 is performed by the processing system 58 of Figure 2. As such, references to the processing system 58 and the components of the processing system 58 are sometimes used in the following discussion. However, these references are not to be construed as limiting the scope of Figure 4 to the processing system 58 of Figure 2.

[0056] As illustrated, the forward and reflected RF signals are obtained during transmission of a signal by the base station 14 (step 200). Power spectrums for the forward and reflected RF signals are obtained (step 202). For example, as discussed above, the power spectrums may be obtained utilizing FFTs. An RL frequency profile of the combination of interconnected RF components is then generated from the power spectrums of the forward and reflected RF signals (step 204). In some scenarios, the generated RL frequency profile is the actual, or measured, RL frequency profile. In other scenarios, the generated RL frequency profile is the reference RL frequency profile, in which case the generated reference RL frequency profile may be stored in the reference RL frequency profile storage 68 of the processing system 58 of Figure 2. As discussed above, in some embodiments, the generation of the RL frequency profile includes computing a ratio of forward-reflected signal cross-correlation over forward signal autocorrelation for each of at least a subset of the frequency bins, and potentially all of the frequency bins, of the power spectrums of the forward and reflected RF signals (step 300). Optionally, in some embodiments, frequency bins containing only noise are filtered out such that they do not contribute to the RL frequency profile, and/or are not considered in the

subsequent comparison of the actual RL frequency profile to a reference RL frequency profile (step 302). [0057] Notably, in some embodiments, different systems may be used for generating the reference RL frequency profile than that used for measuring the actual RL frequency profile. If so, the bidirectional coupler 32 is preferably calibrated before measuring the actual RL frequency profile. Any suitable calibration technique may be used. For example, the so-called ABC calibration technique that characterizes a coupler by three complex coefficients may be used. These coefficients may then be applied to the measured actual RL frequency profile to compensate for the impairment of the bidirectional coupler 32.

[0058] Figures 5 through 8 illustrate plots of the RL frequency profiles of different combinations of cables and antennas. The data was obtained from a lab implementation of one example implementation of the base station subsystem 28 with the transmitter 30 transmitting a 20 megahertz (MHz) LTE signal. The functionality of the FFT and RL profile extraction processor 64 and the cross-correlation processor 66 were simulated in Matlab with the live data streams from the dual RF receiver and demodulator 60. Note that the scales of the plots are not identical because they were automatically resized by Matlab. In particular, with respect to Figures 7 and 8, the plots come from different simulations with different RF signals, so the different magnitudes of noise forced Matlab to use different scaling.

[0059] In particular, Figure 5 illustrates a reference RL frequency profile for a cable/antenna combination. The rectangular window indicates an example of a window that can be used to exclude the frequency bins without power (i.e., noise only). Figure 6 illustrates a measured RL frequency profile of a different cable than in Figure 5, but visually identical, connected to the same antenna. Here, an error will be detected. Figure 7 illustrates an example of another cable/antenna reference RL frequency profile. Figure 8 illustrates a measured RL frequency profile of the same cable/antenna combination as in Figure 7, indicating the similarity percentage. Repeated RL frequency profile measurements of the same cable/antenna can be used to define an optimum threshold to minimize the probability of false alarms and/or miss-detection of wrongly connected cables. Small variability is due to noise and fluctuations in the power of the transmitted signal.

[0060] Figure 9 illustrates the processing system 58 of the base station 14 according to some embodiments of the present disclosure. As illustrated, the processing system 58 includes a number of modules 70-76, each of which may be implemented in software. In particular, the processing system 58 includes an actual RL frequency profile obtaining module 70 configured to obtain an actual RL frequency profile of the combination of interconnected RF components connected to the output port 48 of the transmitter 30 of the base station 14, as described above. The processing system 58 also includes a similarity metric determining module 72 configured to determine a similarity metric that is indicative of a degree of similarity between the actual RL frequency profile of the combination of interconnected RF components and a reference RL frequency profile of the combination of interconnected RF components, as described above. In addition, the processing system 58 includes a degree of similarity determining module 74 configured to determine whether the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is greater than a predefined threshold, as described above. Finally, the processing system 58 includes an error determining module 76 configured to determine that there is an error with the combination of interconnected RF components upon determining that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is not greater than the predefined threshold, as described above. The error determining module 76 is also configured to determine that there is no error with the combination of interconnected RF components upon determining that the degree of similarity between the actual RL frequency profile and the reference RL frequency profile, as indicated by the similarity metric, is greater than the predefined threshold, as described above.

[0061 ] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the main processing system 62 according to any one of the embodiments described herein is provided. In some embodiments, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0062] While not being limited to or by any particular advantages, some example advantages provided by at least some of the embodiments described herein are as follows. The embodiments described herein can be used with any digital transmitter system during a normal operation with live data traffic, e.g. live LTE data traffic, and requires no additional hardware if the radio is already equipped with a bidirectional coupler and a dual RF receiver, which is typically used for Voltage Standing Wave Ratio (VSWR) measurements in many cases. The main processing system 62 of Figure 2 can be either added or incorporated into an existing testing and measurement system in the base station radio system. Embodiments described herein do not transmit signals outside the operational band and therefore are not prone to create unwanted emissions and interference. The majority of VSWR measurement applications require sophisticated calibration procedures; however, if the same system is used both in generating the reference RL frequency profile and during a measurement of an

RL frequency profile, then calibration is not required.

[0063] The following acronyms are used throughout this disclosure.

• 3GPP 3 ^rd Generation Partnership Project

• ASIC Application Specific Integrated Circuit

• EPC Evolved Packet Core

• EUTRAN Evolved Universal Terrestrial Radio Access Network

• FFT Fast Fourier Transform

• FPGA Field Programmable Gate Array

• LTE Long Term Evolution

• m Meter

• MHz Megahertz

• MME Mobility Management Entity P-GW Packet Gateway

RAN Radio Access Network

RF Radio Frequency

RFID Radio Frequency Identification

RL Return Loss

RLC Resistor-Inductor-Capacitor

S-GW Serving Gateway

TX Transmit

UE User Equipment

VSWR Voltage Standing Wave Ratio

[0064] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.