Base Station Intermodulation Distortion Cancellation
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Solution Overview
Problem
Multi-carrier base stations experience significant intermodulation distortion due to non-linear transmitter components and physical components near the antenna, which cannot be filtered out by existing band pass filters, leading to signal distortion, especially in weak received signals.
Innovation Solution
A method and apparatus in a base station that generates a modeled signal of intermodulation components from the transmitter source signal, correlates it with the received uplink signal to detect IM products, and produces a cancellation signal to subtract from the received signal, effectively reducing distortion caused by IM products originating from components close to the antenna.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transmitter uses high output power and multiple carriers to provide coverage and capacity, then network performance improves, but intermodulation distortion increases causing signal degradation
Solution Approach 1:
The invention applies preliminary anti-action by generating a cancellation signal that anticipates and counteracts the intermodulation distortion before it degrades the received signal. The system models the expected IM products based on transmitted signal characteristics and subtracts them from the received signal, preventing distortion accumulation.
Solution Approach 2:
The invention converts the harmful intermodulation products into a beneficial cancellation signal. By modeling the IM products generated by known transmitter characteristics and correlating them with the received signal, the system creates a cancellation signal that, when subtracted, eliminates the distortion. The harmful IM products become the basis for their own cancellation.
2Object-affected harmful factors
If a band pass filter is used to block intermodulation products, then some distortion is reduced, but IM products from components after the filter cannot be eliminated
Solution Approach 1:
The invention introduces an intermediary digital signal processing approach between the physical filter and the received signal. Instead of relying solely on physical filtering, the system uses digital correlation and subtraction to eliminate IM products. This intermediary digital cancellation mechanism complements the physical band pass filter, removing its limitations regarding components positioned after the filter.
Solution Approach 2:
The invention replaces the mechanical/physical filtering approach with a digital signal processing substitution. Instead of relying on the physical properties of band pass filters to block IM products, the system uses digital correlation and subtraction operations to eliminate distortion. This substitution allows for more comprehensive cancellation including IM products from components that cannot be physically filtered.
3Ease of operation
If physical components like antennas and cables are used in the transmitter path, then signal transmission is enabled, but they generate additional intermodulation products that cannot be filtered out
Solution Approach 1:
The invention applies feedback by using knowledge of the transmitted signal characteristics to generate an expected IM product model, correlating it with the received signal to detect actual IM products, and then using this information to create a cancellation signal. This feedback loop continuously adapts to cancel distortion generated by physical components in the transmission path.
Data Source
AI summary
A method in a base station is provided for reducing distortion of an uplink signal received in a receiver part (20) of the base station, said distortion being caused by intermodulation, IM, products. The method comprises: generating (106), from a transmitter source signal, a modeled signal of IM components, as nth order IM components of the transmitter source signal, n being an integer value of 2, 3, 4 and/or 5 etc., and detecting (110) IM products of the received uplink signal, the received uplink signal comprising UL traffic components and the IM products, by correlating the received uplink signal with the IM components of the modeled signal. The method further comprises producing (112) a cancellation signal based on the detected IM products of the received uplink signal, and subtracting (114) the cancellation signal from the received uplink signal. Also, a similar apparatus in a base station is provided.