Intermodulation Product Cancellation Using Delayed Signal Correlation
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Solution Overview
Problem
In wireless communication systems, particularly cellular networks, passive intermodulation (PIM) interference caused by non-linear components in the signal path is difficult to manage due to unknown locations and varying delays, leading to reduced carrier-to-interference ratios and coverage issues.
Innovation Solution
A method and apparatus that generate simulated intermodulation products using a range of delay values, correlate these with received signals to select the optimal delay for cancellation, and combine the simulated products with the received signal to reduce interference, effectively addressing the challenges of unknown PIM sources and varying delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional field engineer tracking and component replacement methods are used, then PIM interference can be addressed, but the process becomes labor intensive and time consuming
Solution Approach 1:
The system automatically identifies and cancels PIM interference without requiring field engineer intervention. The base station autonomously measures received signals, generates cancellation signals based on stored reference signals, and applies the cancellation without external assistance, transforming a manual process into an automated self-service system.
Solution Approach 2:
The system continuously measures received signals, compares them with stored reference signals to identify PIM products, generates cancellation signals based on the measured interference, and applies feedback control to adjust the cancellation in real-time, creating a closed-loop system that adapts to changing conditions.
2Reliability
If automatic cancellation systems with tone insertion are used, then intermodulation products can be cancelled, but the transmit signal must be modified which is undesirable
Solution Approach 1:
The system performs preliminary measurement of the received signal and identification of PIM products before generating cancellation signals. By analyzing the actual received signal characteristics and storing reference signals in advance, the system can generate appropriate cancellation signals without needing to insert tones or modify transmit signals during operation.
3Reliability
If delay values are adjusted to align cancellation signals with transmitter signals, then intermodulation products can be cancelled, but the delay adjustment range is limited by aliasing constraints
Solution Approach 1:
The system dynamically adjusts delay values based on measured signal characteristics and identified PIM products. Rather than using fixed delay values constrained by aliasing, the system adapts the delay in real-time according to the actual interference conditions, allowing flexible adjustment over a wider range while maintaining proper signal alignment.
Data Source
AI summary
Interference to a received signal is reduced in a wireless network, the interference comprising intermodulation products of at least a first signal and a second signal. Delayed interference signals comprising simulated intermodulation products are generated on the basis of the first signal and the second signal using a range of differing delay values and each of the delayed interference signals is correlated with the received signal to produce data representing a correlation for each delayed interference signal. At least one delay value is selected in dependence on a the data representative of the correlations and an interference signal comprising simulated intermodulation products generated from the first signal and the second signal using the at least one delay value is combined with the received signal.