Transmitter-Side Pre-Filtering for Echo Cancellation
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Solution Overview
Problem
Wireless communication receivers face interference from undesired replicas of transmitted signals, particularly in satellite communication systems where the same frequency band is reused for both directions, leading to echo interference that degrades reception quality.
Innovation Solution
A transceiver generates a local copy of the transmitted signal and estimates a filter response to compensate for spectral differences between the local copy and the undesired replica, applying this filter to the transmitted signal before transmission to match and cancel the interference when the replica is received, using transmitter-side pre-filtering to reduce echo noise effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If receiver-side compensation methods are used to cancel echo interference, then echo cancellation can be achieved, but noise enhancement occurs and performance is limited
Solution Approach 1:
The patent applies preliminary action by implementing transmitter-side pre-filtering before the signal is transmitted. The filter coefficients are calculated at the transmitter based on estimated spectral differences, and the transmitted signal is pre-filtered using these coefficients. This proactive approach compensates for spectral mismatches before they cause interference, avoiding the noise enhancement problem associated with receiver-side compensation methods that try to correct errors after they occur.
2Reliability
If transmitter-side pre-filtering is applied to match spectral response, then echo cancellation depth increases, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the filter coefficients based on estimated spectral differences between the transmitted and received signals. The filter response is calculated using the formula h(n) = IDFT(X(k)) where X(k) represents the spectral differences, and these coefficients are updated adaptively. This allows the system to achieve deep echo cancellation by optimizing filter parameters in real-time without requiring overly complex fixed-structure systems.
Data Source
AI summary
A method includes, in a transceiver (24), receiving from a repeater (32) a received signal, which includes a desired signal for reception and an undesired replica of a transmitted signal that was transmitted from the transceiver and retransmitted by the repeater. A local copy of the transmitted signal is generated in the transceiver. A filter response that, when applied to the transmitted signal before transmission, compensates for a difference in spectral response between the local copy and the undesired replica, is estimated in the transceiver. The undesired replica of the transmitted signal, which is received in the received signal, is matched with the local copy of the transmitted signal, by at least pre-filtering the transmitted signal before transmission with the estimated filter response. Interference caused by the undesired replica to the desired signal is canceled, by combining the local copy and the received signal.