OFDMA Baseband Clock Synchronization for Wireless Microphones
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Solution Overview
Problem
Existing OFDMA audio systems require additional resources and introduce latency due to the need for a sample rate conversion block to compensate for frequency offsets, which is undesirable in high-quality audio applications.
Innovation Solution
The method involves generating baseband clocks from a common reference oscillator, with subscriber devices tuning their reference oscillators based on phase differences to synchronize with the access point, eliminating the need for a sample rate conversion block by controlling both the audio sample clock and antenna data clock using a modified reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sample rate conversion block is used to compensate for frequency offset, then frequency synchronization is improved, but device complexity and latency increase
Solution Approach 1:
The patent extracts and eliminates the sample rate conversion block from the signal processing chain by implementing frequency synchronization at the baseband clock level. This removes the need for additional conversion blocks while maintaining frequency offset compensation, thereby reducing device complexity and latency without sacrificing synchronization reliability.
Solution Approach 2:
The patent introduces a baseband clock synchronization mechanism as an intermediary that coordinates the timing between the access point and subscriber devices. By synchronizing baseband clocks rather than converting sample rates, the system achieves frequency offset compensation with reduced complexity and lower latency in the audio path.
2Reliability
If a sample rate conversion block is used to compensate for frequency offset, then frequency synchronization is improved, but latency in the audio path increases
Solution Approach 1:
The patent removes the sample rate conversion block from the audio processing path, eliminating the latency it introduces. Frequency synchronization is maintained through baseband clock synchronization, which achieves the same synchronization goal without the time delay associated with sample rate conversion operations.
Solution Approach 2:
The patent performs frequency synchronization in advance by synchronizing baseband clocks before signal processing occurs. This preliminary synchronization eliminates the need for post-processing sample rate conversion, thereby preventing latency from being introduced in the audio path while maintaining frequency offset compensation.
3Reliability
If a sample rate conversion block is used to compensate for frequency offset, then frequency synchronization is improved, but additional resources are required
Solution Approach 1:
The patent extracts and eliminates the sample rate conversion block, removing the additional hardware resources it consumes. Frequency synchronization is achieved through baseband clock synchronization, which requires fewer resources than sample rate conversion while maintaining the same synchronization reliability.
Solution Approach 2:
The patent makes the baseband clock serve multiple functions: it provides timing for both the access point and subscriber devices, enables frequency offset compensation, and coordinates synchronization across the entire system. This multi-functionality eliminates the need for separate sample rate conversion blocks, reducing overall resource requirements.
Data Source
AI summary
A method for synchronizing baseband clocks in an OFDMA wireless microphone system is disclosed. An example method includes receiving a plurality of pilot subcarriers from an audio transmitter. The method also includes determining a timing offset estimate based on the pilot subcarriers. The method further includes determining a tuning value by passing the timing offset estimate through a proportional-integral controller. The method still further includes determining a modified reference signal by modifying a reference oscillator based on the tuning value. And the method yet further includes controlling (i) an audio sample clock and (ii) an antenna data clock based on the modified reference signal.