Adaptive Downlink Preamble Length for LoRa Window Detection
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Solution Overview
Problem
Conventional LoRa networks face issues with downlink data frame loss due to unstable crystal oscillator errors in terminals, particularly in Class B mode, where precise window calibration is required, leading to missed preambles and subsequent data loss.
Innovation Solution
A server acquires crystal oscillator error and operating rate information of terminals and adjusts preamble length accordingly to improve the detection of downlink data frames by extending the preamble duration, ensuring successful data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a default length preamble is adopted with high operating rate, then transmission rate is improved, but window calibration precision requirement increases and preamble detection reliability deteriorates
Solution Approach 1:
The preamble length is made dynamic and adjustable based on operating rate and crystal oscillator error characteristics. The server configures different preamble lengths according to terminal operating rates and measured oscillator errors, allowing the system to adapt between short preambles for high-speed transmission and long preambles for reliable detection under high oscillator error conditions.
Solution Approach 2:
The system changes the preamble length parameter based on operating conditions. When crystal oscillator error is large or operating rate is high, the preamble length is extended to improve detection reliability. When oscillator error is small and transmission speed is prioritized, shorter preambles are used.
2Measurement precision
If crystal oscillator is used for time calibration, then time synchronization is achieved, but time error stability deteriorates due to unstable oscillator characteristics
Solution Approach 1:
The server measures the crystal oscillator error of each terminal and uses this feedback information to configure appropriate preamble lengths. The system continuously monitors oscillator performance and adjusts preamble parameters accordingly, creating a closed-loop control system that compensates for oscillator instability.
Solution Approach 2:
The system prepares for potential time synchronization failures by extending the preamble length in advance when oscillator error is detected to be large. This creates a time buffer that cushions against potential missed detections, allowing terminals more time to accurately detect preambles despite oscillator drift.
3Ease of operation
If receiving window is opened for predictable time, then downlink data reception is enabled, but preamble detection reliability deteriorates when terminal misses preamble due to oscillator error
Solution Approach 1:
The server sends a configuration message before the receiving window to inform the terminal of the upcoming downlink transmission and the configured preamble length. This allows the terminal to prepare its receiver in advance, ensuring it is properly synchronized and ready to detect the extended preamble when the receiving window opens.
Data Source
AI summary
Embodiments of the present disclosure provide a server data sending method and a server data sending apparatus. The method can include: acquiring, by a server, crystal oscillator error information and operating rate information of a terminal; setting, by the server, preamble length information according to the crystal oscillator error information and the operating rate information; and sending, by the server, a downlink data frame to the terminal, the downlink data frame comprising a preamble aligned with the preamble length information.