Frequency Offset Detection in VAMOS Multiplexed GSM Terminals
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Solution Overview
Problem
Existing GSM terminals using VAMOS technology face issues with abnormal downlink frequency offset during voice service multiplexing, leading to degraded voice quality or connection loss, as existing methods lack effective detection mechanisms for terminal frequency offset abnormalities.
Innovation Solution
A method and system employing adaptive quadrature phase shift keying modulation to detect frequency offset abnormalities in uplink signals, involving scrambling of downlink signals, frequency offset detection, and determination of abnormal frequency offset changes based on thresholds, with results sent to a base station controller for analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If VAMOS multiplexing is used to improve voice service capacity, then GSM capacity is improved, but frequency offset abnormalities occur leading to degraded voice quality or connection loss
Solution Approach 1:
The patent performs frequency offset detection before voice service abnormalities occur by continuously monitoring frequency offset values during VAMOS multiplexing. The base station detects frequency offset values in uplink signals and compares them against threshold values to identify terminals with abnormal frequency offset trends, enabling proactive intervention before connection loss occurs.
2Productivity
If downlink AQPSK modulation is used for VAMOS multiplexing, then voice service capacity is improved, but downlink automatic frequency correction function becomes abnormal when interfering signal is stronger than valid signal
Solution Approach 1:
The patent uses the uplink signal as an intermediary to detect downlink frequency offset abnormalities. Since the terminal's downlink automatic frequency correction function affects its uplink transmission frequency, monitoring the uplink frequency offset provides indirect but accurate information about downlink frequency offset issues, bypassing the problem of strong interfering signals in direct downlink detection.
3Reliability
If frequency offset detection is performed on uplink signals, then terminal frequency offset abnormalities can be detected, but additional detection complexity is introduced
Solution Approach 1:
The patent leverages the existing uplink signal reception and processing infrastructure already present in the base station for normal voice service operation. The same signal processing chains used for voice transmission are additionally utilized for frequency offset detection, allowing the system to perform dual functions without requiring separate dedicated detection hardware or signal paths.
Data Source
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AI summary
Embodiments of the present invention provide a method, an apparatus, and a system for detecting terminal frequency offset. The method includes: scrambling, by using an adaptive quadrature phase shift keying modulation technology, a downlink signal of a to-be-detected voice service channel corresponding to a to-be-detected terminal; performing frequency offset detection on an uplink signal on the to-be-detected voice service channel after the scrambling, to obtain a frequency offset detection result of the uplink signal of the to-be-detected voice service channel; and sending the frequency offset detection result to a base station controller. In the embodiments of the present invention, a base transceiver station scrambles an uplink signal of a to-be-detected voice service channel, then performs frequency offset detection on an uplink signal on the to-be-detected voice service channel after the scrambling, to obtain a frequency offset detection result of the uplink signal of the to-be-detected voice service channel when the downlink signal of the to-be-detected voice service channel is multiplexed.