Wakeup Receiver Frequency Tracking for Low-Power Wireless Links
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Solution Overview
Problem
Wakeup receivers in wireless communication systems face challenges with high power consumption due to limited filtering capabilities and vulnerability to interference, as they rely on free-running oscillators with inaccurate frequencies, leading to reduced signal-to-noise ratios and increased interference sensitivity.
Innovation Solution
A wireless communication device with a second transceiver featuring a free-running digitally controlled oscillator for the wakeup receiver, accompanied by an ultra-low power transmitter that periodically transmits signals to a base station, allowing the base station to determine and adjust the oscillator frequency, thereby reducing interference and enhancing signal precision without the need for power-hungry Phase Locked Loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a free-running oscillator is used in the wakeup receiver to reduce power consumption, then power consumption is reduced, but frequency accuracy deteriorates leading to limited filtering capability
Solution Approach 1:
The base station performs preliminary frequency estimation and tracking of the device's oscillator before the device activates its main receiver. The base station sends frequency information in wakeup messages, allowing the device to pre-adjust its local oscillator frequency, eliminating the need for high-precision oscillators in the low-power wakeup receiver
Solution Approach 2:
The base station acts as an intermediary that compensates for frequency inaccuracies. It estimates the device's oscillator frequency, adjusts the wakeup signal frequency accordingly, and provides frequency correction information to the device, thereby mediating the frequency mismatch caused by using low-precision free-running oscillators
2Use of energy by moving object
If modest filtering is applied prior to amplitude detection to maintain low power consumption, then power consumption is reduced, but interference immunity deteriorates
Solution Approach 1:
The base station continuously estimates the device's oscillator frequency based on received signals and provides feedback through wakeup messages. This feedback loop allows the system to adapt to frequency drift over time, maintaining effective filtering and interference rejection without requiring high-power PLLs in the wakeup receiver
Solution Approach 2:
The base station performs preliminary frequency tracking and estimation before the device needs to receive data. By preparing frequency compensation information in advance and including it in wakeup messages, the system enables effective interference filtering to be applied once the main receiver is activated
3Measurement precision
If the amplitude detector operates with weak input signals to detect low-power wakeup signals, then detection sensitivity is improved, but signal-to-noise ratio deteriorates due to the non-linear characteristic
Solution Approach 1:
The base station acts as an intermediary that amplifies and condition the wakeup signal before transmission. By sending stronger wakeup signals with known frequency characteristics, the base station enables the device's amplitude detector to operate in a more favorable signal-to-noise regime while maintaining detection sensitivity
Data Source
Figure 1
Figure 2(a)~2(c)
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AI summary
A wireless communication device (100) comprises a first transceiver (110) comprising a first frequency synthesizer (112) which comprises a first digitally controlled oscillator (DCO1) and a crystal oscillator (XO). The wireless communication device (100) further comprises a second transceiver (120) comprising a wakeup receiver (Rx2), a second transmitter (Tx2) and a second digitally controlled oscillator (DCO2) connected to the wakeup receiver (Rx2) and second transmitter (Tx2). The wireless communication 10 device (100) further comprises a control unit (170) configured to control operation of the wireless communication device. The second transmitter (Tx2) is configured to transmit periodically a signal to a base station. The signal is modulated by a code identifying the wireless communication device (100) and transmitted at a frequency set by the second digitally controlled oscillator (DCO2).