Duplex Channel Delay Measurement Using Marked Test Signals
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Solution Overview
Problem
Existing methods for measuring audio signal delay in duplex transmission channels, especially in noisy conditions, are not very accurate, which can lead to echo issues in VHF ground-to-air communication systems.
Innovation Solution
A method and system that generate a test signal with a marking portion, which propagates through the channel, is detected at both ends, and the time difference between the occurrence of the marking portion at the starting point and its return is calculated to determine the propagation time, allowing for accurate delay measurement and echo cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test signal is generated and inserted into the transmission line to make a round trip, then the propagation delay can be measured, but the measurement accuracy deteriorates when applied to noisy transmission channels
Solution Approach 1:
The test signal is segmented into a marking portion and a signal portion. The marking portion consists of a first set of pulses with a first amplitude, while the signal portion consists of a second set of pulses with a second amplitude. This segmentation allows the marking portion to be easily distinguished from the signal portion even in noisy conditions, enabling accurate detection of the marking portion's occurrence times at both ends of the transmission channel.
Solution Approach 2:
The marking portion is made distinct from the signal portion through amplitude differentiation, similar to using color changes for identification. By assigning a different amplitude level to the marking portion, it creates a visually and detectably distinct feature that can be reliably identified despite the presence of noise in the transmission channel.
2Area of stationary object
If the same radio signal is transmitted at offset carrier frequencies from distant stations, then coverage is increased, but echo effect occurs requiring audio delay devices
Solution Approach 1:
Before the actual communication takes place, the propagation delay of the transmission channel is measured using the test signal with the marking portion. This preliminary measurement allows the audio delay devices to be pre-configured with the correct delay values, ensuring that when the same radio signal is transmitted from multiple distant stations, the echo effect is properly cancelled without requiring real-time adjustment.
3Object-generated harmful factors
If audio delay devices are inserted in the transmission links, then echo effect is cancelled, but the complexity of the transmission system increases
Solution Approach 1:
The system uses the transmission channel itself to measure its own propagation delay by sending a test signal through it and detecting the returned signal. This self-measurement capability eliminates the need for external measurement equipment or complex calibration procedures, simplifying the overall system configuration while still enabling accurate echo cancellation through proper setup of audio delay devices.
Data Source
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AI summary
A method and system for measuring the delay time (τ2) of a transmission channel (6) comprises the steps of generating (30) a test signal with a marking portion, applying the test signal to a first end (8) of the transmission channel (6) and returning (38) the test signal received at a second end (10) of the transmission channel (6) back into the transmission channel (6). After detecting (34) the marking portion of the test signal as applied to the first end (8) of the transmission channel (6) and detecting (36) the marking portion of the test signal as received at the first end (8) of the transmission channel (6) after it has been returned (38) at the second end (10) of the transmission channel (6), the time difference between the occurrence of the marking portion of the test signal as applied to the first end (8) of the transmission channel (6) and the occurrence of the marking portion of the test signal as received at the first end (8) of the transmission channel (6) is determined (39).