Digital Compensation for Switchable Analog Filter Echo Cancellation
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Solution Overview
Problem
In full duplex DOCSIS cable networks, the narrow gap between sub-bands makes it impractical for analog filters to separate upstream and downstream signals effectively, leading to significant self-interference issues like adjacent channel interference (ACI) and adjacent leakage interference (ALI), which affect the modulation error ratio and require echo cancellation techniques, but existing solutions struggle with seamless switching of resource block assignments without disrupting system operation.
Innovation Solution
A digital compensation system is integrated with a switchable analog filter to compensate for frequency response changes during resource block assignment changes, ensuring seamless operation by using digital filters that match or inverse the frequency responses of the analog filters, allowing concurrent and uninterrupted signal processing across sub-bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If analog filters are used to separate upstream and downstream signals, then signal separation is achieved, but the narrow gap between sub-bands makes it impractical to separate signals effectively, leading to self-interference
Solution Approach 1:
A digital compensation filter is introduced as an intermediary component between the switchable analog filter and the signal processing chain. This digital filter compensates for the frequency response changes and self-interference introduced by the analog filter, enabling effective signal separation despite the narrow sub-band gap. The digital filter acts as a mediator that corrects the limitations of the analog filter in the FDX context.
Solution Approach 2:
The system dynamically changes the parameters of the digital compensation filter to match the switching states of the analog filter. When the analog filter switches between different passband frequencies, the digital compensation filter adjusts its parameters (filter coefficients) accordingly to maintain proper frequency response and minimize self-interference. This parameter adaptation enables the system to handle different resource block assignments effectively.
2Adaptability or versatility
If switchable analog filters are used for resource block assignment changes, then frequency response adaptation is achieved, but seamless switching without disruption is difficult
Solution Approach 1:
The digital compensation filter is pre-configured with multiple sets of filter coefficients corresponding to different analog filter switching states. Before the analog filter switches, the digital compensation filter is already prepared with the appropriate coefficients for the upcoming state. This preliminary preparation ensures that when switching occurs, the transition is seamless and does not disrupt signal processing or cause data loss.
Solution Approach 2:
The system employs feedback mechanisms to monitor the switching state of the analog filter and automatically adjust the digital compensation filter parameters accordingly. This closed-loop control ensures that the digital filter always has the correct parameters to compensate for the current analog filter state, maintaining reliable and seamless operation during resource block assignment changes.
3Object-affected harmful factors
If echo cancellation techniques are implemented, then self-interference mitigation is achieved, but system complexity increases
Solution Approach 1:
The system replaces complex analog echo cancellation mechanisms with a digital compensation approach. Instead of using complicated analog circuitry to cancel echoes and self-interference, the invention uses digital signal processing to compensate for the frequency response changes and interference. This substitution of mechanical/analog systems with digital processing reduces overall system complexity while maintaining effective self-interference mitigation.
Data Source
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AI summary
A cable modem supporting full duplex (FDX) operations. The cable modem includes a transmit circuitry configured to process a transmit signal and a receive circuitry configured to process a receive signal. The receive circuitry includes a switchable analog filter configured to filter the receive signal. The switchable analog filter is configurable for different passband frequencies. The receive circuitry also includes a digital compensation filter configured to compensate a difference in frequency response in a specific frequency band due to switching of the switchable analog filter for a different passband frequency. The cable modem also includes an adjacent channel interference (ACI) cancellation filter and an adjacent leakage interference (ALI) cancellation filter. A digital compensation filter is also used in processing the ACI cancellation signal and the ALI cancellation signal to impose or compensate the difference in frequency response due to the switchable analog filter switching.