Baseband Interference Cancellation for Mixed-Modulation Signals
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing interference suppression techniques, such as Single Antenna Interference Cancellation (SAIC), are ineffective in suppressing co-channel interference when the desired and interfering signals have different modulation schemes, particularly when the interfering signal is GMSK-modulated and the desired signal is 8PSK or higher-capacity modulation.
Innovation Solution
A method that involves rotating the composite baseband signal based on the modulation scheme of the interfering signal, filtering to separate the desired and interfering components, and using equalization with branch metrics to recover the desired signal, accounting for the phase rotation difference between the two modulation schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAIC technique is used for suppressing co-channel interference, then interference suppression is achieved when both signals are GMSK-modulated, but interference suppression becomes ineffective when desired and interfering signals have different modulations
Solution Approach 1:
The patent applies dynamics by making the interference cancellation filter coefficients adaptive rather than fixed. The receiver dynamically estimates the modulation type of the interfering signal and adjusts the filter coefficients accordingly. This allows the system to switch between different interference suppression strategies based on the detected modulation scheme, resolving the contradiction between reliable interference suppression and modulation compatibility.
Solution Approach 2:
The patent changes the parameters of the interference cancellation filter based on the detected modulation scheme. When GMSK interference is detected, the filter uses specific coefficients; when 8PSK interference is detected, different coefficients are applied. This parameter adaptation enables the system to maintain high interference suppression effectiveness across different modulation combinations.
2Device complexity
If conventional interference suppression techniques are used, then simple processing is maintained, but complex equalizers and pre-filter coefficient calculations are required when modulation differences exist
Solution Approach 1:
The patent segments the interference suppression process into distinct stages: interference estimation, filter coefficient calculation, and signal filtering. By separating these functions, the system avoids the need for a single complex equalizer while maintaining effective interference cancellation. The segmented approach reduces computational complexity compared to conventional methods that require joint estimation and complex matrix operations.
3Productivity
If 8PSK modulation is used for higher data density, then data transmission capacity increases, but susceptibility to error increases in high noise and interference environments
Solution Approach 1:
The patent introduces an interference cancellation filter as an intermediary component between the received signal and the equalizer. This filter acts as a mediator that specifically targets and removes interfering signals before they can corrupt the 8PSK data. By eliminating the interference component in advance, the system enables reliable 8PSK transmission in high-noise environments that would otherwise be too error-prone.
Data Source
AI summary
A composite baseband signal includes a desired signal component modulated according to a first modulation scheme and an interfering signal component modulated according to a second modulation scheme. Information is recovered from the composite signal by applying a phase rotation associated with the second modulation scheme to the composite signal to generate a rotated signal. Based on the rotated signal, a channel model associated with the desired signal component and interference cancelling filter coefficients associated with the interfering signal component are generated. The rotated signal is filtered according to the interference cancelling filter coefficients to suppress the interfering signal component from the rotated signal. The filtered signal is equalized based on branch metrics derived from the channel model and symbol hypotheses rotated in accordance with a difference in phase rotations associated with the first and second modulations to recover information from the desired signal component.