Bluetooth Transmitter Frequency Dithering for Spectral Line Reduction
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Solution Overview
Problem
Bluetooth Low Energy Long Range (BLR) transmitters face challenges in reducing the amplitude of spectral lines in power spectral density (PSD) to meet communication requirements without decreasing transmit power, which leads to increased transmission errors or reduced range.
Innovation Solution
Applying frequency dithering to the waveform by pseudorandomly adjusting nominal frequency deviations based on bit transitions and sequences, ensuring the transmitted signal stays within Bluetooth transmission limits while allowing higher power transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the transmitter operates at higher power, then transmission range and reliability are improved, but spectral line amplitudes exceed PSD limits
Solution Approach 1:
The patent applies frequency dithering which pseudorandomly adjusts the frequency deviation parameter of the FSK modulated signal. By adding a pseudorandom sequence to the frequency deviation, the spectral lines are spread and their amplitudes are reduced, allowing the transmitter to operate at higher power levels while meeting PSD requirements
Solution Approach 2:
The frequency dithering uses a pseudorandom sequence that can be considered a periodic modulation applied to the frequency deviation. This periodic variation in frequency deviation spreads the spectral energy and reduces peak spectral line amplitudes, enabling higher transmit power operation
2Object-generated harmful factors
If the transmitter reduces power to meet PSD limits, then spectral line amplitudes are reduced, but transmission errors increase and range decreases
Solution Approach 1:
By changing the frequency deviation parameter through pseudorandom dithering, the patent reduces spectral line amplitudes without reducing overall transmit power. This maintains the signal energy needed for reliable transmission while meeting spectral mask requirements
Solution Approach 2:
The pseudorandom dithering sequence acts as an intermediary modulation that modifies the frequency deviation. This intermediary signal spreads the spectral content and reduces peak amplitudes while the underlying data signal maintains its integrity for reliable detection at the receiver
Data Source
AI summary
A method, system, and apparatus for applying dithering to waveforms in a transmitter such as a Bluetooth transmitter. A current waveform corresponding to a current bit of a bitstream is received where the current waveform has a nominal frequency deviation defined by a value of the current bit. Based on the determination that the current waveform and an immediately previous bit of the bitstream are associated with different bit values, a first dithered signal is output which is defined by a first frequency offset pseudorandomly selected from a first set of frequency offsets. A subsequent waveform to the current waveform is received corresponding to a subsequent bit of the bitstream. Based on the subsequent bit and the current bit being associated with bits of the same value, a second dithered signal is output which is defined by a second frequency offset pseudorandomly selected from a second set of frequency offsets.