Uplink Transmission Control for Frequency Error Estimation
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Solution Overview
Problem
In wireless communication systems, user equipment (UE) with reduced capabilities, such as those used in low-cost and low-power applications, face challenges in estimating and correcting frequency errors, especially in half-duplex operation and narrowband channels, which can degrade uplink transmission quality due to instability in local oscillators and limited access to synchronization signals.
Innovation Solution
The proposed solution involves a method for a UE to receive information about downlink reference signal scheduling from the wireless network, allowing it to synchronize and adjust its uplink transmission patterns. This includes dropping or postponing uplink transmissions when they collide with reference signal timing and optionally requesting an aperiodic reference signal for proper synchronization, especially in scenarios where periodic signals are too far apart or resources are limited.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If low-cost oscillators (DCXO or XO) are used in UE to reduce cost and complexity, then device cost and complexity are reduced, but frequency stability deteriorates causing increased frequency errors in uplink transmission
Solution Approach 1:
The base station transmits downlink reference signals before the UE performs uplink transmission. This preliminary action allows the UE to estimate frequency errors in advance and apply corrections before transmitting, compensating for the instability of low-cost oscillators without requiring more expensive frequency reference sources.
Solution Approach 2:
Downlink reference signals act as an intermediary between the base station and UE for frequency synchronization. These reference signals carry frequency information that the UE can use to estimate and correct its local oscillator errors, enabling accurate frequency alignment without direct UE-to-UE frequency referencing.
2Device complexity
If UE operates in half-duplex mode to reduce cost and complexity, then device complexity is reduced, but access to synchronization signals deteriorates because UE cannot simultaneously receive and transmit
Solution Approach 1:
The base station transmits downlink reference signals periodically at specific time intervals. In half-duplex operation, the UE can switch to receive mode during these periodic reference signal transmissions to obtain synchronization information, then switch back to transmit mode for uplink data, maintaining reliable synchronization despite half-duplex constraints.
Solution Approach 2:
The UE dynamically switches between transmit and receive modes based on the timing of downlink reference signals. This dynamic time-division approach allows the UE to access synchronization signals when needed while maintaining half-duplex operation, adapting its operation to the periodic reference signal structure.
3Use of energy by moving object
If UE uses narrowband operation to reduce cost and power consumption, then device cost and power consumption are reduced, but frequency error impact worsens because frequency errors cause larger deviations in narrowband channels
Solution Approach 1:
The UE performs frequency error estimation using downlink reference signals received before narrowband uplink transmission. This preliminary estimation allows the UE to calculate and apply frequency corrections specifically tailored to narrowband operation, compensating for the heightened sensitivity of narrowband channels to frequency errors while maintaining low power consumption.
Data Source
AI summary
A method for controlling uplink, UL, transmission, carried out in a user equipment, UE, comprising a radio unit configured for communication with a wireless network, comprising receiving information from the wireless network, which information identifies scheduling of one or more downlink, DL, reference signals, usable for estimating a time and/or frequency error of the radio unit; receiving, from the wireless network, scheduling of an UL transmission pattern; wherein the information indicates timing of a first reference signal prior to or during the scheduled transmission pattern.