Radio Receiver AFC Loop Freezing During Preamble Synchronization
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Solution Overview
Problem
Existing radio receivers face challenges in accurately compensating for frequency differences between the local oscillator and incoming signal, leading to potential errors in data reception, especially during the initial synchronization phase with digital communications systems.
Innovation Solution
A method and apparatus that involves freezing and unfreezing an automatic frequency compensation (AFC) loop in a radio receiver, switching between a first and second clock signal using a multiplexer, and utilizing a preamble circuit to detect the preamble in the radio signal to adjust the AFC loop's operation, allowing for more precise frequency tuning by sampling data near peaks or troughs of the incoming signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the AFC loop operates continuously during preamble detection, then frequency compensation is maintained, but sampling errors occur due to frequency offset between local oscillator and incoming signal
Solution Approach 1:
The patent applies preliminary action by detecting the preamble sequence before normal data reception and freezing the AFC loop at this stage. The preamble detection occurs in advance to establish synchronization, and the AFC loop is frozen during this preliminary phase to prevent frequency offset from causing sampling errors in the actual data reception that follows.
Solution Approach 2:
The patent applies dynamics by switching the AFC loop between two operational states: running state during normal operation and frozen state during preamble detection. This dynamic control allows the system to adapt its frequency compensation behavior based on the reception phase, ensuring accuracy during data reception while enabling proper synchronization during preamble detection.
2Reliability
If the AFC loop is frozen during preamble detection, then sampling errors are reduced, but frequency compensation is not updated during this period
Solution Approach 1:
The patent applies periodic action by implementing a cyclic operation where the AFC loop alternates between running and frozen states. During normal data reception, the AFC loop runs continuously to maintain frequency compensation. When a preamble is detected, the loop freezes temporarily. After the preamble processing is complete, the loop resumes running, creating a periodic pattern that ensures both accurate sampling and continuous frequency updates.
3Device complexity
If a single clock signal is used in the AFC loop, then the system is simpler, but frequency tuning precision is insufficient for accurate synchronization
Solution Approach 1:
The patent applies segmentation by dividing the clock signal source into multiple distinct signals: a first clock signal for general operation and a second clock signal for precise frequency tuning during preamble detection. This segmentation allows each clock signal to be optimized for its specific function, with the second clock signal providing the additional precision needed for accurate synchronization without complicating the overall system architecture.
Data Source
AI summary
A method an apparatus for performing automatic frequency compensation (or control) is disclosed. A method and apparatus for performing automatic frequency compensation (or control) is disclosed. In one embodiment, a method includes a radio receiver receiving a radio signal and detecting a preamble in the radio signal. The method further includes freezing an automatic frequency compensation (AFC) loop responsive to detecting the preamble. A clock source of the AFC loop may be switched from a first clock signal to a second clock signal. The method further includes subsequently unfreezing the AFC loop.