PIM Cancellation Using Backhauled Phase Data
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Solution Overview
Problem
Existing PIM elimination methods in wireless communications systems are ineffective in completely eliminating interference due to the inability to precisely recover the transmitted signal's initial phase and amplitude information, leading to incomplete cancellation of passive intermodulation signals.
Innovation Solution
A method that involves obtaining and utilizing backhauled information, including initial phase and amplitude data from multiple RRUs, to generate a cancellation signal for PIM elimination, which improves the accuracy of PIM cancellation by considering the specific processing information of each RRU, such as frequency-shift, multicarrier combining, crest factor reduction, and digital pre-distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If PIM elimination is performed using modeling based on baseband signal only, then the processing complexity is reduced, but the PIM cancellation precision deteriorates due to inability to recover transmitted signal's initial phase and amplitude information
Solution Approach 1:
The patent applies preliminary action by backhauling initial phase information from NCO and processing information (frequency-shift, multicarrier combining, crest factor reduction, digital pre-distortion) from RRU to BBU before PIM elimination processing. This allows the BBU to accurately reconstruct the transmitted signal characteristics and generate precise cancellation signals, resolving the contradiction between simplified processing and high precision cancellation.
2Loss of information
If carrier initial phase information is not backhauled, then the information transmission overhead is reduced, but the PIM elimination accuracy deteriorates due to inability to learn carrier initial phase before frequency-shift processing
Solution Approach 1:
The patent implements preliminary action by extracting and backhauling carrier initial phase information from the NCO before frequency-shift processing occurs. This timing is critical because the initial phase information is lost after frequency-shift operations. By obtaining this information in advance and transmitting it to the BBU, the system achieves accurate PIM elimination without excessive information overhead.
3Device complexity
If processing information of multiple RRUs is not shared, then the system complexity is reduced, but the PIM elimination performance deteriorates due to inability to learn other RRU's carrier initial phase processing information
Solution Approach 1:
The patent applies merging by combining processing information from multiple RRUs (frequency-shift, multicarrier combining, crest factor reduction, digital pre-distortion) and backhauling it to a central BBU. This allows the BBU to reconstruct the composite transmitted signal across all RRU channels and generate accurate cancellation signals for multi-RRU PIM elimination, achieving high reliability while maintaining manageable system complexity through centralized processing.
Data Source
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AI summary
A passive intermodulation elimination method, an apparatus, and a base station are disclosed. The method includes: receiving, by a network device, N pieces of backhauled information, where one piece of the backhauled information includes initial phase information of each carrier on one transmit channel, and N is an integer greater than or equal to 1; and eliminating, by the network device, a PIM of a received signal on a receive channel on the network device based on the N pieces of backhauled information.