Radio Receiver Clock Drift Compensation via Packet Timing
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Solution Overview
Problem
Radio communication systems with unsynchronized clocks face inefficiencies in power consumption due to the need for wide listening windows to account for both short-term and long-term clock errors, leading to prolonged wake times and reduced battery life in devices like wireless sensors and speedometers.
Innovation Solution
A radio communication system where the receiver uses the arrival times of connection-event data packets to adjust its ready state entry, compensating for long-term clock drift by varying the time of entry, thereby reducing the necessary listening window duration and increasing sleep state time, thus enhancing power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the receiver opens a wide listening window to account for both short-term and long-term clock errors, then the receiver can reliably detect connection-event data packets despite clock drift, but the receiver must remain in a higher-power ready state for longer periods, increasing energy consumption
Solution Approach 1:
The patent segments clock error compensation into two distinct components: short-term compensation using a phase-locked loop (PLL) that tracks rapid clock variations, and long-term compensation using a digital correction mechanism that adjusts for cumulative drift. By separating these compensation functions, the receiver can use a much narrower listening window while still accounting for both short-term and long-term clock errors, thereby reducing the time the receiver must remain in the high-power ready state and lowering overall energy consumption.
2Use of energy by moving object
If the receiver uses a narrow listening window to reduce energy consumption, then the receiver can spend more time in low-power sleep state, but the receiver may miss connection-event data packets due to clock drift between transmitter and receiver
Solution Approach 1:
The patent implements a feedback mechanism where the receiver measures the actual arrival time of connection-event data packets and uses this information to dynamically adjust the timing of future listening windows. A digital correction value is calculated based on the difference between expected and actual packet arrivals, and this correction is applied to compensate for long-term clock drift. This feedback loop enables the receiver to maintain high detection reliability with a narrow listening window, as the window timing is continuously adapted to match the actual clock drift characteristics.
Solution Approach 2:
The patent applies preliminary correction to the listening window timing based on previously measured clock drift characteristics. Before the next connection event, the receiver pre-calculates the appropriate window start time using accumulated correction values from previous packet arrivals. This preliminary adjustment ensures that the narrow listening window is positioned correctly to capture the incoming packet, compensating for long-term drift in advance rather than reacting to missed packets after the fact.
Data Source
AI summary
A radio communication system comprises a radio transmitter (2), and a radio receiver (12) configured to receive radio transmissions from the transmitter. The transmitter (2) uses a transmitter clock signal to transmit a succession of connection-event data packets (22a′, 22b′, 22c′) according to a predetermined schedule. The receiver (12) enters a sleep state between receiving successive connection-event data packets from the transmitter (2), in which it does not receive and process radio transmissions from the transmitter. It uses a receiver clock signal to determine when a predetermined number of receiver clock cycles has elapsed after receiving one of the connection-event data packets (22b′), and then enters a ready state. The predetermined number of receiver clock cycles is the number of receiver clock cycles (34a) that elapsed between the respective receipts of two of the connection-event data packets (22a′, 22b′) received by the receiver (12) minus a correction factor (38).