Frequency Error Estimation in Half-Duplex Uplink Transmissions
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Solution Overview
Problem
In cellular networks, especially for NB-loT devices operating in half-duplex mode, there is a challenge in efficiently estimating and compensating for frequency errors in low-cost oscillators due to temperature variations and extended transmission durations, which can lead to inter-carrier interference and degrade transmission performance.
Innovation Solution
The method involves splitting repetitive uplink transmissions into multiple transmit periods with configured measurement gaps, allowing the radio device to switch to receive downlink signals, estimate and compensate frequency errors, and then resume transmission, using broadcast channels and synchronization signals for frequency error estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-cost oscillators are used in NB-loT devices, then cost and complexity are reduced, but frequency stability deteriorates due to temperature variations
Solution Approach 1:
The patent implements frequency error estimation using downlink reference signals and feedback mechanisms. The UE estimates frequency errors based on received downlink signals and applies compensation, creating a closed-loop feedback system that maintains frequency stability despite using low-cost oscillators
Solution Approach 2:
The patent changes the timing parameters of transmission by introducing measurement gaps within repetitive transmission sequences. This allows the oscillator characteristics to be measured and compensated at specific intervals, effectively managing frequency drift without changing the oscillator hardware
2Duration of action of moving object
If extended transmission duration is used to support low data rates in extreme coverage, then coverage range is improved, but frequency error increases due to oscillator drift over time
Solution Approach 1:
The patent segments the extended transmission into multiple repetitive transmission sequences with measurement gaps inserted between them. This segmentation allows periodic frequency error estimation and compensation, preventing cumulative frequency errors over the extended transmission duration
Solution Approach 2:
The patent implements periodic frequency error estimation by inserting measurement gaps at regular intervals within the repetitive transmission sequence. This periodic measurement and compensation approach maintains frequency accuracy throughout the extended transmission period
3Device complexity
If half-duplex operation is used in NB-loT devices, then device complexity is reduced, but frequency error estimation capability deteriorates due to inability to receive downlink signals during transmission
Solution Approach 1:
The patent segments the transmission timeline into transmit periods and measurement gaps, allowing the half-duplex device to switch to receive mode during measurement gaps for frequency error estimation, then resume transmission in subsequent periods
Solution Approach 2:
The patent performs frequency error estimation during measurement gaps before continuing the repetitive transmission sequence. This preliminary estimation allows the device to compensate for frequency errors that will occur during the upcoming transmission period
4Reliability
If repetitive transmission is used to achieve low data rates, then data rate reliability is improved, but inter-carrier interference increases due to accumulated frequency errors
Solution Approach 1:
The patent segments the repetitive transmission into sequences separated by measurement gaps, enabling periodic frequency error compensation that prevents the accumulation of frequency errors and the resulting inter-carrier interference
Solution Approach 2:
The patent implements feedback-based frequency error compensation where the UE estimates frequency errors from downlink reference signals and applies corrections to subsequent transmissions, preventing inter-carrier interference while maintaining repetitive transmission for reliability
Data Source
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AI summary
A half-duplex radio device (100) generates a repetitive transmission of an uplink message to a base station (150) of the cellular network. The radio device (100) splits the repetitive transmission of the uplink message into a sequence of multiple transmit periods and configures at least one measurement gap between the transmit periods. In the transmit periods, the radio device (100) sends the repetitive transmission to the base station. In the at least one measurement gap configured between the transmit periods, the radio device (100) temporarily switches to receiving at least one downlink signal from the base station (150). Based on the received at least one downlink signal, the radio device (100) estimates a frequency error of a reference frequency source of the radio device (100).