Adaptive RF Filter for Base Station Transmit Leakage Cancellation
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Solution Overview
Problem
Modern wireless base stations face challenges in effectively isolating transmit signal components from receive chains due to high dynamic range requirements, leading to costly and bulky filtering solutions in duplexers, which impose high linearity demands on receiver front-ends.
Innovation Solution
An RF receive-band filter with an adaptive filter component is implemented at the receive chain input, processing digital baseband signals to generate a subtractive cancellation signal that cancels transmitter leakage signals, reducing the need for expensive filtering devices by isolating desirable received signals from undesirable transmitter leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high-order filters are used in the duplexer to meet stringent rejection requirements, then transmit signal isolation is improved, but device cost and size increase
Solution Approach 1:
The invention divides the signal processing function into two separate stages: (1) the duplexer provides basic frequency separation, and (2) a dedicated transmit signal cancelation circuit actively subtracts leaked transmit signals from the receive path. This segmentation allows each component to be optimized independently, reducing the burden on the duplexer filter while maintaining overall isolation performance.
Solution Approach 2:
The invention introduces an intermediary cancelation signal path that processes a copy of the transmit signal and subtracts it from the receive signal. This intermediary processing stage acts as a mediator between the duplexer and the LNA, actively removing transmit leakage without requiring the duplexer to provide extreme filtering performance.
2Device complexity
If duplexer rejection requirement is relaxed, then device cost and size are reduced, but linearity requirements on the receiver front-end increase
Solution Approach 1:
The cancelation circuit performs preliminary processing of the transmit signal by creating an accurate copy and subtracting it from the receive path before the signal reaches the LNA. This preliminary action removes the harmful transmit leakage component, allowing the LNA to operate in a more linear regime and reducing the stringent linearity requirements that would otherwise be needed.
Solution Approach 2:
The invention takes the harmful transmit signal leakage and converts it into a useful cancelation reference. By deliberately capturing and processing the leaked transmit signal, the system creates an active cancelation mechanism that transforms the harmful interference into a beneficial signal that actively reduces the leakage, thereby relaxing requirements on subsequent components.
3Object-affected harmful factors
If expensive high-order filters are used in the duplexer, then transmit signal isolation is improved, but device cost increases
Solution Approach 1:
The invention replaces expensive, complex high-order filters with a more economical active cancelation circuit that uses readily available components such as power amplifiers, phase shifters, and signal combiners. This approach uses simpler, cheaper components to achieve the same isolation effect that would otherwise require expensive passive filtering hardware.
Solution Approach 2:
The invention substitutes mechanical/passive filtering (high-order LC filters in the duplexer) with an active electronic cancelation system. Instead of relying on complex passive filter structures, the system uses active signal processing with amplifiers and phase control to achieve transmit leakage rejection, thereby reducing hardware cost and complexity.
Data Source
AI summary
Apparatus and methods disclosed herein implement an RF receive-band filter at a receive chain input of a wireless base station with a co-located transmitter and receiver. The RF receive-band filter includes an adaptive filter component to perform filtering operations on samples of a digital baseband or intermediate frequency signal x(n) from a transmit chain associated with the wireless base station. An adaptive filter transfer function is determined in real time such that samples of the baseband transmit signal x(n) are transformed into a cancellation baseband signal z(n). The digital cancelation baseband signal z(n) is then digital-to-analog converted and the resulting analog baseband signal z(t) is up-converted to obtain a subtractive RF cancelation signal c(t). C(t) is summed with a desirable received signal RF component r(t) and an undesirable transmitter leakage RF signal component l(t) appearing at the input to the base station receiver. C(t) cancels l(t), leaving r(t) to be processed by the receiver section of the base station.