Passive intermodulation signal detection system and method

Abstract

The invention relates to the technical field of signal detection, and discloses a passive intermodulation signal detection system and method.The system comprises a digital-to-analog converter, a connecting position, an analog-to-digital converter, a cross-correlation operation module and a duplexer, the digital-to-analog converter is arranged at the signal upstream of the connecting position, and the analog-to-digital converter is arranged at the signal downstream of the connecting position; the duplexer is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the analog-to-digital converter, the joint is electrically connected with the duplexer, and the cross-correlation operation module is electrically connected with the signal upstream of the digital-to-analog converter and the signal downstream of the analog-to-digital converter respectively. The problems of low detection accuracy and the like in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of signal detection, and in particular to a passive intermodulation signal detection system and method. Background Art

[0002] With the continuous increase in the number of users and the amount of communication data, the single-carrier communication system can no longer meet the communication needs. The introduction of carrier aggregation technology (CA) and multi-band blending technology (Multiband Blending) to improve spectrum utilization can simultaneously support more users to carry out wireless transmission of larger amounts of data, greatly improving the efficiency of the communication system. The above two technologies also bring more challenges. For example, the widening of the frequency band requires higher linearity of the power amplifier, and the multi-carrier technology requires higher performance of the channel filter. In addition, in the FDD (Frequency Division Duplex) system, the introduction of multi-band blending technology and carrier aggregation technology will result in the presence of nonlinear devices in the wireless transceiver system. Passive intermodulation (PIM) will be generated when the transmitted signal passes through these nonlinear devices, and coupled back to the receiver. Under certain carrier configurations, the coupled back PIM signal will fall on the uplink carrier, which will affect the demodulation of the uplink signal by the receiver, reduce the receiver sensitivity, and thus affect the performance of the communication system.

[0003] In order to improve the receiver sensitivity, PIM needs to be corrected in the digital front end of the receiver. However, the complexity of the PIM correction algorithm is very high, and the occupancy rate of the logic and software resources of the remote radio unit (RRU) is very high. From long-term practice, it can be learned that PIM in FDD systems is often introduced by RF connection problems or a small passive device in the system (such as RF connector, etc.). If the PIM correction algorithm is introduced due to such problems, the system complexity will be increased, thereby increasing the product cost. At the same time, whether the passive device of the RRU will introduce PIM is often related to the RF connection between the devices (such as the cable connector between the RRU RF antenna port and the antenna, etc.), that is, when the connection of the passive device is good, PIM will not be introduced. In addition, the strength of PIM may also be related to the processing technology of the passive device. When the RF connection and processing technology are good, if a PIM correction module is added to the RRU, the system resource occupancy and the power consumption of the whole machine will be large.

[0004] In the prior art, when PIM is detected during a service, the power of the transmitted signal will change at any time with the network scheduling, which will affect the power of PIM in the received signal, resulting in a decrease in the accuracy of the PIMD algorithm. In addition, when PIM is detected during a service, the collected received signal contains not only the PIM signal but also the uplink service signal. The power of the uplink service signal is usually much higher than the PIM signal. When performing a cross-correlation operation, the uplink service signal will be considered as noise. At this time, the noise power is greater than the PIM signal power, affecting the accuracy of the cross-correlation operation. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a passive intermodulation signal detection system and method to solve the problems of low detection accuracy in the prior art.

[0006] The technical solution adopted by the present invention to solve the above problems is:

[0007] A passive intermodulation signal detection system comprises a digital-to-analog converter, a connection, an analog-to-digital converter, a cross-correlation operation module and a duplexer, wherein the digital-to-analog converter is arranged at a signal upstream of the connection, the analog-to-digital converter is arranged at a signal downstream of the connection, the duplexer is arranged at a signal downstream of the digital-to-analog converter and a signal upstream of the analog-to-digital converter, the connection is electrically connected to the duplexer, and the cross-correlation operation module is electrically connected to a signal upstream of the digital-to-analog converter and a signal downstream of the analog-to-digital converter, respectively.

[0008] As a preferred technical solution, it includes a power amplifier and a driver. The power amplifier is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the connection. The driver is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the power amplifier.

[0009] As a preferred technical solution, it includes a digital pre-distortion module, which is arranged at the signal upstream of the digital-to-analog converter, and the cross-correlation operation module is electrically connected to the signal upstream of the digital pre-distortion module.

[0010] As a preferred technical solution, it includes a peak factor reduction module, which is arranged at the signal upstream of the digital predistortion module, and the cross-correlation operation module is electrically connected to the signal downstream of the peak factor reduction module.

[0011] As a preferred technical solution, it includes a low noise amplifier, which is arranged at the signal upstream of the analog-to-digital converter and the signal downstream of the connection.

[0012] As a preferred technical solution, it includes an antenna and a radio frequency line, and the connection includes: the connection between the antenna and the radio frequency line.

[0013] As a preferred technical solution, it includes a combiner arranged downstream of the signal of the radio frequency line, the number of digital-to-analog converters, analog-to-digital converters, cross-correlation operation modules, and duplexers are all N and are all arranged downstream of the signal of the combiner, and each digital-to-analog converter, analog-to-digital converter, cross-correlation operation module, and duplexer constitutes a signal branch; the connection includes: the connection between the radio frequency line and the combiner; wherein N≥1 and N is an integer.

[0014] A passive intermodulation signal detection method uses the passive intermodulation signal detection system to perform passive intermodulation signal detection.

[0015] As a preferred technical solution, if the maximum value of the cross-correlation function obtained by the cross-correlation operation module is higher than a set threshold, the radio frequency interface on the communication link is checked.

[0016] As a preferred technical solution, if it is confirmed that the RF interface on the communication link is not faulty, or the RF interface on the communication link is adjusted, and the maximum value of the cross-correlation function obtained by the cross-correlation operation module is higher than the set threshold, the distortion source that introduces the passive intermodulation signal is located according to the position of the maximum value of the cross-correlation function, and the position of the passive device that introduces the passive intermodulation signal is confirmed.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The present invention avoids interference caused by factors such as downlink signal power fluctuation and uplink signal, ensures that the downlink signal power is stable and the uplink signal only contains PIM signals when performing cross-correlation operations, greatly improves the accuracy of the PIM detection algorithm, and makes the judgment of PIM intensity more accurate;

[0019] (2) The present invention detects PIM in the product at the initial stage of product production, which can timely avoid the impact caused by connection problems and nonlinear problems of some passive components, greatly reducing the subsequent equipment inspection and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a structural block diagram of a passive intermodulation signal detection system. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0022] The English abbreviations involved in the present invention are explained as follows:

[0023] ADC: Analog-to-Digital Converter;

[0024] CFR: Crest Factor Reduction, peak factor reduction;

[0025] DAC: Digital-to-Analog Converter;

[0026] DPD: Digital Predistortion, digital predistortion;

[0027] FDD: Frequency Division Duplex, frequency division duplex;

[0028] IM3: Third-order Intermodulation, third-order intermodulation;

[0029] PA: Power Amplifier, power amplifier;

[0030] PIM: Passive Intermodulation, passive intermodulation;

[0031] PPIMD: Pre-Passive Intermodulation Detection, passive intermodulation pre-detection;

[0032] RRU: Remote Radio Unit, radio frequency remote unit;

[0033] Driver: driver;

[0034] LNA: Low Noise Amplifier, low noise amplifier;

[0035] Duplexer: duplexer;

[0036] Combiner: combiner.

[0037] Example 1

[0038] like Figure 1 As shown, a passive intermodulation signal detection system includes a digital-to-analog converter, a connection, an analog-to-digital converter, a cross-correlation operation module, and a duplexer. The digital-to-analog converter is arranged at the signal upstream of the connection, the analog-to-digital converter is arranged at the signal downstream of the connection, the duplexer is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the analog-to-digital converter, the connection is electrically connected to the duplexer, and the cross-correlation operation module is electrically connected to the signal upstream of the digital-to-analog converter and the signal downstream of the analog-to-digital converter, respectively.

[0039] The present invention pre-detects PIM in the RRU (the communication system includes a baseband unit and a radio remote unit) in a communication system. When PIM is detected, the connection between the radio port and the cable can be adjusted, and a passive component in the RRU can be repaired or replaced according to the size of the cross-correlation function and the location of the peak. In this way, the impact of PIM on the communication system can be reduced in the early stage of product design, and the PIM correction module can be discarded in the RRU without PIM, which greatly reduces the cost.

[0040] As a preferred technical solution, it includes a power amplifier and a driver, wherein the power amplifier is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the connection, and the driver is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the power amplifier.

[0041] The main function of the power amplifier is to amplify the transmission signal power to ensure that the signal can be effectively transmitted and improve the transmission efficiency; the main function of the driver is to amplify the input signal to a sufficient amplitude so that the power amplifier can effectively amplify the signal and transmit it to the antenna, ensuring that the power amplifier can work efficiently and stably, while also protecting the power amplifier.

[0042] As a preferred technical solution, it includes a digital pre-distortion module, which is arranged at the signal upstream of the digital-to-analog converter, and the cross-correlation operation module is electrically connected to the signal upstream of the digital pre-distortion module.

[0043] The main function of the digital pre-distortion module is to compensate for the nonlinear distortion of the power amplifier and improve the system efficiency and performance. The main operation is to compensate the signal to be input to the nonlinear power amplifier in a manner opposite to the characteristics of the power amplifier.

[0044] As a preferred technical solution, it includes a peak factor reduction module, which is arranged at the signal upstream of the digital predistortion module, and the cross-correlation operation module is electrically connected to the signal downstream of the peak factor reduction module.

[0045] The main function of the peak factor reduction module is to reduce the peak-to-average ratio of the transmitted signal and narrow the dynamic range of the transmitted signal so that the power amplifier used to transmit the signal can operate in the linear region as much as possible.

[0046] As a preferred technical solution, it includes a low noise amplifier, which is arranged at the signal upstream of the analog-to-digital converter and the signal downstream of the connection.

[0047] The function of the low-noise amplifier is to amplify the low-power signal received from the antenna to ensure that the signal is not overwhelmed by noise during transmission, thereby improving the receiving sensitivity; moreover, the low-noise amplifier has a low-noise characteristic, which can reduce the noise in the received signal and improve the signal-to-noise ratio.

[0048] As a preferred technical solution, it includes an antenna and a radio frequency line, and the connection point is the connection point between the antenna and the radio frequency line.

[0049] Since the connection between the antenna and the RF line is the main source of PIM generated at the connection, this is more conducive to reducing resource consumption.

[0050] As a preferred technical solution, it includes a combiner arranged downstream of the signal of the radio frequency line, the number of digital-to-analog converters, analog-to-digital converters, cross-correlation operation modules, and duplexers are all N and are all arranged downstream of the signal of the combiner, and each digital-to-analog converter, analog-to-digital converter, cross-correlation operation module, and duplexer constitutes a signal branch; the connection includes: the connection between the radio frequency line and the combiner; wherein N≥1 and N is an integer.

[0051] This facilitates detection of PIM generated at the connection between the RF line and the combiner.

[0052] A passive intermodulation signal detection method uses the passive intermodulation signal detection system to perform passive intermodulation signal detection.

[0053] The present invention performs pre-detection of PIM in RRU. When PIM is detected, the connection between the radio frequency port and the cable can be adjusted, and a passive component in the RRU can be repaired or replaced according to the size of the cross-correlation function and the location of the peak. In this way, the impact of PIM on the communication system can be reduced in the early stage of product design, and the PIM correction module can be discarded in the RRU without PIM, which greatly reduces the cost.

[0054] As a preferred technical solution, if the maximum value of the cross-correlation function obtained by the cross-correlation operation module is higher than a set threshold, the radio frequency interface on the communication link is checked.

[0055] This is convenient for avoiding the effects of improper RF connection.

[0056] As a preferred technical solution, if it is confirmed that the RF interface on the communication link is not faulty, or the RF interface on the communication link is adjusted, and the maximum value of the cross-correlation function obtained by the cross-correlation operation module is higher than the set threshold, the distortion source that introduces the passive intermodulation signal is located according to the position of the maximum value of the cross-correlation function, and the position of the passive device that introduces the passive intermodulation signal is confirmed.

[0057] This facilitates repair or replacement of the passive device that introduces PIM according to the location of the passive device.

[0058] Example 2

[0059] like Figure 1 As shown, based on Example 1, this example provides a more detailed implementation method.

[0060] The present invention proposes a passive intermodulation signal detection method to pre-detect PIM in RRU. When PIM is detected, the connection between the radio frequency port and the cable can be adjusted, and a passive component in the RRU can be repaired or replaced according to the size of the cross-correlation function and the location of the peak. In this way, the impact of PIM on the communication system can be reduced in the early stage of product design, and the PIM correction module can be discarded in the RRU without PIM, which greatly reduces the cost.

[0061] Aiming at the actual problem of the source of PIM introduction, the invention designs a PIM pre-detection algorithm (Pre-PIM Detection, PPIMD) based on the FDD system, that is, to detect PIM before the product is actually deployed on the network. Figure 1 shown.

[0062] Figure 1 Taking dual-band PPIMD as an example, the PPIMD algorithm proposed in the present invention can also be extended to single-band and multi-band FDD systems.

[0063] Figure 1 In the example, the connector between the RF cable and the antenna is used as the source of PIM. That is, the transmitted signal passes through the transmitting end to the connection between the antenna and the RF cable and couples back to the receiving end. The path of the transmitted signal is Figure 1 As shown by the curve with an arrow in the middle, the delay experienced in this path is the loop delay of the transmitted signal, which is transmitted from the transmitting end to the connection between the RF line and the antenna and coupled back to the ADC output position in the uplink. At the same time, data is collected at the output end of the crest factor reduction (CFR) module and the output end of the analog-to-digital converter (ADC), and the collected data is used as the input of the cross-correlation operation module for cross-correlation operation. By analyzing the results of the cross-correlation operation, the PIM source related information can be obtained. In this embodiment, the uplink refers to the communication link from the antenna to the ADC, and correspondingly, the communication link from the DAC to the antenna is the downlink.

[0064] The actual approach is to detect PIM in advance, that is, when there is no business transmission, the downlink spontaneously generates two downlink carrier data and sends them (two carriers are used as an example, it can also be one or more carriers). The PIM generated at this time will be coupled back to the receiving end. The frequencies of the uplink and downlink frequency bands must be analyzed to ensure that the selected carrier frequency configuration will generate PIM when passing through nonlinear passive devices and hit the uplink frequency band.

[0065] The method for selecting the downlink carrier frequency (which can be realized by using the existing technology, so the more specific working principle and working process will not be described here) is as follows:

[0066] Taking dual-band products as an example (it can also be single-band or multi-band products), the center frequencies of the two downlink carriers are f1 and f2 respectively. It is necessary to calculate that 2f1-f2 will fall within the uplink frequency band, that is, the 2f1-f2 frequency component in the third-order intermodulation IM3 may hit the uplink carrier. After selecting the downlink carrier, the sending reference signal can be calculated accordingly for cross-correlation operation with the received signal. When 2f1-f2 falls within the uplink frequency band, the sending reference signal can be calculated as:

[0067]

[0068] Where x1 and x2 are the transmitted signals on the two frequency bands collected at the CFR output end. Similarly, when 2f2-f1 falls in the uplink frequency band, the transmitted reference signal is expressed as:

[0069]

[0070] In addition, for single-band or multi-band products, the above process can also be used to calculate a transmission reference signal for cross-correlation calculation.

[0071] After the number of concurrent carrier configurations is determined, the signals at the CFR output and ADC output are collected at the same time. The transmit reference signal x is calculated using the transmit reference signal calculation formula obtained by the above analysis method through the transmit signals on the two frequency bands. ref Then, the cross-correlation function between the received signal and the transmitted reference signal is calculated (this can be achieved by using the existing technology, so the more specific working principle and working process will not be described here), and the calculation formula is as follows:

[0072]

[0073] x ref (n) represents x ref The nth element in Represents x ref (n), r(n) represents the conjugate signal of the received signal, r(nm) is the signal obtained by shifting r(n) right by m positions, n represents the cross-correlation number (that is, the time number), and N represents the cross-correlation length (that is, the total number of time moments).

[0074] The current PIM power level can be obtained by calculating the maximum value of the cross-correlation function. The position of the maximum value of the cross-correlation function in the function represents the loop delay of the entire path of the transmitted signal passing through the PIM distortion source and coupling back to the receiving end. When the PIM power level is detected to be high, the RF interface on the link can be checked and adjusted to avoid the impact caused by improper RF connection. When the RF connection is confirmed to be adjusted, if the maximum value of the cross-correlation function is still higher than the target threshold, the distortion source that introduces PIM can be located according to the position of the maximum value of the cross-correlation function, and the location of the passive device that introduces PIM can be confirmed (that is, the m value in R(m), the m value can be used to confirm the delay between the transmitted signal and the received signal, and then the location of the distortion source can be located according to the signal transmission speed and delay) and repaired or replaced. The above strategy can be used to optimize the system in the early stage of product production, which can largely avoid the impact of PIM introduced by the nonlinearity of the connection or a single device, avoid the introduction of PIM correction algorithm, and thus reduce the cost and power consumption of the product.

[0075] The present invention performs pre-detection (i.e., performs detection when there is no business data) to improve detection accuracy; and performs pre-detection in the production stage to quickly locate the position of the submodule where the PIM is located in the system when a PIM source is detected, so that the submodule can be repaired or replaced in a targeted manner, thereby reducing the cost of later repair and maintenance.

[0076] The present invention proposes a PIM pre-detection algorithm to avoid interference caused by factors such as fluctuations in downlink signal power and uplink signals, and ensures that when performing cross-correlation operations, the downlink signal power is stable and the uplink signal only contains PIM signals, which greatly improves the accuracy of the PIM detection algorithm and makes the judgment of PIM intensity more accurate. In addition, the present invention proposes a PIM pre-detection algorithm, that is, to detect PIM in the product at the initial stage of product production, which can timely avoid the impact caused by connection problems and nonlinear problems of some passive components, and greatly reduce the cost of later equipment inspection and maintenance.

[0077] As described above, the present invention can be preferably implemented.

[0078] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

[0079] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A passive intermodulation signal detection system, characterized in that: It includes a digital-to-analog converter, a connection, an analog-to-digital converter, a cross-correlation operation module, and a duplexer. The digital-to-analog converter is arranged at the signal upstream of the connection, the analog-to-digital converter is arranged at the signal downstream of the connection, the duplexer is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the analog-to-digital converter, the connection is electrically connected to the duplexer, and the cross-correlation operation module is electrically connected to the signal upstream of the digital-to-analog converter and the signal downstream of the analog-to-digital converter, respectively.

2. A passive intermodulation signal detection system according to claim 1, characterized in that: It includes a power amplifier and a driver. The power amplifier is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the connection. The driver is arranged at the signal downstream of the digital-to-analog converter and the signal upstream of the power amplifier.

3. A passive intermodulation signal detection system according to claim 1, characterized in that: It comprises a digital pre-distortion module, which is arranged at the signal upstream of the digital-to-analog converter, and the cross-correlation operation module is electrically connected to the signal upstream of the digital pre-distortion module.

4. A passive intermodulation signal detection system according to claim 3, characterized in that: It comprises a peak factor reduction module, which is arranged at the signal upstream of the digital predistortion module, and the cross-correlation operation module is electrically connected to the signal downstream of the peak factor reduction module.

5. A passive intermodulation signal detection system according to claim 1, characterized in that: The invention comprises a low noise amplifier, which is arranged at the signal upstream of the analog-to-digital converter and the signal downstream of the connection.

6. A passive intermodulation signal detection system according to any one of claims 1 to 5, characterized in that: It includes an antenna and a radio frequency line, and the connection includes: the connection between the antenna and the radio frequency line.

7. A passive intermodulation signal detection system according to claim 6, characterized in that: It includes a combiner arranged at the signal downstream of the radio frequency line, the number of digital-to-analog converters, analog-to-digital converters, cross-correlation operation modules, and duplexers are all N and they are all arranged at the signal downstream of the combiner, and each digital-to-analog converter, analog-to-digital converter, cross-correlation operation module, and duplexer constitutes a signal branch; the connection includes: the connection between the radio frequency line and the combiner; wherein N≥1 and N is an integer.

8. A passive intermodulation signal detection method, characterized in that: A passive intermodulation signal detection system according to any one of claims 1 to 7 is used to perform passive intermodulation signal detection.

9. A passive intermodulation signal detection method according to claim 8, characterized in that: If the maximum value of the cross-correlation function obtained by the cross-correlation operation module is higher than the set threshold, the radio frequency interface on the communication link is checked.

10. A passive intermodulation signal detection method according to claim 8 or 9, characterized in that: If it is confirmed that the RF interface on the communication link is not faulty, or the RF interface on the communication link is adjusted, and the maximum value of the cross-correlation function obtained by the cross-correlation operation module is higher than the set threshold, the distortion source that introduces the passive intermodulation signal is located according to the position of the maximum value of the cross-correlation function, and the position of the passive device that introduces the passive intermodulation signal is confirmed.

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