UE Timing Resolution for Long DRX Sleep Cycles
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Solution Overview
Problem
Wireless communication devices with long sleep cycles face timing uncertainty due to variations in crystal oscillator quality, leading to potential synchronization issues with base stations, especially during deep sleep modes where power conservation is prioritized over timing accuracy.
Innovation Solution
The implementation of pre-wake up procedures, such as one-step and two-step wake-up methods, allows devices to wake up in advance of scheduled communications to acquire system timing and adjust their clocks, ensuring synchronization with base stations, even with large timing uncertainties. These procedures involve obtaining system timing through synchronization signals like PSS/SSS or PBCH, depending on the extent of timing drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a UE enters a long sleep cycle to conserve power, then power consumption is reduced, but timing synchronization with the base station deteriorates due to crystal oscillator drift
Solution Approach 1:
The UE performs cell detection and timing acquisition in advance before the scheduled communication time. By detecting the base station's synchronization signals (PSS/SSS) and acquiring timing information beforehand, the UE compensates for the timing drift that occurs during long sleep cycles, ensuring it wakes up at the correct time for communication while maintaining power savings during the sleep period.
2Reliability
If a UE performs frequent cell detection to maintain timing accuracy, then timing synchronization is improved, but power consumption increases due to frequent wake-ups
Solution Approach 1:
The UE adjusts its cell detection strategy based on the length of the sleep cycle. For longer sleep cycles where timing drift is more significant, the UE performs cell detection and timing acquisition. For shorter sleep cycles where timing drift is minimal, the UE skips cell detection and relies on its existing timing information, thereby reducing power consumption while maintaining adequate timing synchronization.
3Reliability
If a UE uses high-quality crystal oscillators to maintain timing accuracy during sleep, then timing synchronization is improved, but device cost and complexity increase
Solution Approach 1:
The UE uses its existing coarse timing information from the crystal oscillator during sleep and only performs full cell detection and timing acquisition when necessary (based on sleep cycle length and timing drift thresholds). This self-service approach allows the UE to maintain timing synchronization using simple hardware while intelligently activating more complex procedures only when needed, avoiding the need for always-on high-quality oscillators.
Data Source
AI summary
Timing resolution for user equipments (UEs) that operate using a discontinuous reception (DRX) mode that includes various sleep cycles may be addressed through selection of various alternative wake up procedures. A UE selects a wake-up procedure based on the length of the sleep cycle. The UE may use details of the sleep cycle, including a time offset or timing uncertainty associated with the sleep cycle, when selecting the wake-up procedure. The UE may select to obtain system timing information either directly from a serving cell or non-serving cell in sync with the serving cell or may select to perform either a one-step or two-step pre-wake up procedure in order to obtain the system timing. Once the UE obtains the system timing or determines a wake-up procedure, it performs timing correction before the scheduled wake-up times between the sleep cycles.