Tower Top PIM Cancellation via Nonlinear Signal Modeling
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Solution Overview
Problem
Existing PIM cancellation technologies in wireless communications systems face challenges such as low modeling precision, resource-intensive implementations, and limited application scenarios, particularly due to the difficulty in accurately canceling passive intermodulation interference signals in multi-carrier scenarios and across different device manufacturers.
Innovation Solution
A tower top device with PIM cancellation functionality is positioned between an antenna and RRU, utilizing a model processing circuit to generate a cancellation signal based on a digital transmit signal and a non-linear model, which is then used to cancel PIM interference signals, ensuring the cancellation signal is similar to the actual interference source, thereby improving cancellation effectiveness without introducing additional distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PIM cancellation is performed in a BBU using baseband signal modeling, then PIM cancellation can be implemented, but modeling precision is low and many resources are consumed
Solution Approach 1:
The patent moves PIM cancellation from baseband domain to RF domain by placing the cancellation device at the tower top near the antenna. This dimensional change in signal processing domain enables direct access to the actual transmit signal that generates PIM, achieving high-precision modeling without requiring complex baseband signal processing resources.
Solution Approach 2:
The patent introduces a coupler as an intermediary component to extract a portion of the transmit signal from the RF path. This intermediary enables the cancellation device to obtain the actual transmit signal for accurate PIM modeling without interfering with the main signal transmission path, resolving the conflict between precision and resource usage.
2Adaptability or versatility
If PIM cancellation is performed in an RRU, then PIM cancellation can be implemented, but PIM cancellation between multiple RRUs cannot be achieved
Solution Approach 1:
The patent merges multiple RRU transmit signals through a combiner at the tower top, allowing a single PIM cancellation device to process and cancel PIM from multiple RRUs simultaneously. This combining approach enables multi-RRU PIM cancellation without requiring separate cancellation devices for each RRU, reducing overall system complexity while achieving the desired adaptability.
3Reliability
If PIM cancellation is performed in transit devices between BBU and RRU, then PIM cancellation can be implemented, but implementation is complex and many resources are consumed due to interface differences
Solution Approach 1:
The patent creates a copy of the actual transmit signal path by placing the cancellation device at the tower top where it can directly access the RF transmit signal through a coupler. This copying approach bypasses the need to interface with multiple RRU and BBU devices with different protocols, achieving reliable PIM cancellation while avoiding interface complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances PIM cancellation efficiency by using a transmit signal similar to the real interference source, reducing interference in received signals, and supports PIM cancellation between multiple RRUs, while simplifying system processing and reducing resource consumption.
Implementation Method 1
non-linear modeling is performed on a transmit signal and a PIM interference signal to obtain a cancellation signal
Implementation Method 2
the cancellation signal is superposed on a receive channel of a BBU in a reverse-phase manner, to cancel PIM generated by the transmit signal
Implementation Method 3
a passive intermodulation (English: Passive Inter Modulation, PIM for short) signal is generated. So-called passive intermodulation means that a plurality of carrier signals of different frequencies are intermodulated due to a frequency mixing effect
Data Source
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AI summary
A tower top device (103) and a passive intermodulation cancellation method are provided. The tower top device (103) is connected between an antenna (104) and an RRU (102) to perform PIM cancellation, so as to reduce interference of PIM to a received signal on an uplink, thereby improving quality of the received signal. The tower top device (103) includes: a model processing circuit (301), configured to generate (601) a cancellation signal based on an input digital transmit signal and a non-linear model, where the non-linear model is used to represent a non-linear relationship between a source signal generating PIM interference and a PIM interference signal; and a cancellation circuit (302), connected to the model processing circuit (301), and configured to: obtain the cancellation signal generated by the model processing circuit (301), and perform (602), based on the cancellation signal, PIM cancellation on a digital received signal including an actual PIM interference signal.