Hierarchical Uplink Synchronization in mmWave Systems
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Solution Overview
Problem
In mmWave-based wireless communication systems, existing synchronization methods are inefficient and fail to adapt quickly to changes in communication paths between Line of Sight (LoS) and Non-Line of Sight (NLoS) due to the high propagation characteristics of mmWave signals.
Innovation Solution
A method where user equipment (UE) performs uplink synchronization by repeatedly transmitting a first type random access preamble through coarse beams for primary timing advance (TA) adjustment, followed by a second type preamble with a shorter sequence through fine beams for secondary TA adjustment, ensuring efficient synchronization and adaptation to changing communication paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single type of random access preamble is transmitted, then the synchronization process is simple, but the adaptability to timing variations and LoS/NLoS path changes is insufficient
Solution Approach 1:
The random access preamble is divided into two distinct types: first type preambles for initial access and coarse timing alignment, and second type preambles for fine timing alignment. This segmentation allows the system to handle different synchronization requirements separately, improving adaptability to timing variations while maintaining manageable complexity through specialized handling of each preamble type
Solution Approach 2:
The system dynamically switches between first type and second type preambles based on timing alignment requirements. The UE transitions from using first type preambles during initial access to second type preambles for fine timing alignment, allowing the synchronization process to adapt dynamically to changing timing conditions and LoS/NLoS path changes
2Area of stationary object
If coarse beams with larger beam width are used for initial access, then the coverage area is larger, but the timing alignment precision is reduced
Solution Approach 1:
The beamforming process is segmented into two stages: coarse beam formation for initial access with large coverage area, and fine beam formation for precise timing alignment. This segmentation allows the system to first establish connection coverage with coarse beams, then refine timing alignment precision with fine beams without requiring the fine beams to provide initial coverage
Solution Approach 2:
The system performs preliminary timing alignment using first type preambles transmitted through coarse beams before transitioning to fine beam-based second type preambles. This preliminary action establishes a baseline timing alignment that enables subsequent fine timing refinement, allowing the system to achieve precise timing alignment without requiring fine beams to handle both coverage and precision simultaneously
3Loss of substance
If the random access preamble sequence duration is shortened, then the overhead is reduced, but the ability to cover maximum channel delay spread is compromised
Solution Approach 1:
Different preamble sequence durations are assigned to different preamble types based on their specific requirements. Second type preambles use shorter sequences optimized for fine timing alignment with reduced overhead, while first type preambles use longer sequences to cover maximum channel delay spread during initial access. This local quality differentiation allows each preamble type to be optimized for its specific function without compromising overall reliability
Solution Approach 2:
The system performs preliminary timing alignment using first type preambles with longer sequences that cover maximum channel delay spread. Once coarse timing alignment is achieved, the system transitions to second type preambles with shorter sequences for fine timing alignment. This preliminary action ensures that the shorter second type preambles can operate effectively without needing to cover the full channel delay spread range
Data Source
AI summary
A method for performing uplink synchronization by a terminal in a millimeter wave (mmWave)-based wireless communication system according to an embodiment of the present invention comprises the steps of: repeatedly transmitting a first type random access preamble through a plurality of coarse beams that are sequentially formed for different directions; performing a first timing advance (TA) adjustment on the basis of a response of a base station with respect to a repeated transmission of the first type random access preamble; and transmitting a second type random access preamble through at least one fine beam having a smaller beam width than the coarse beams, wherein the sequence of the second type random access preamble transmitted after the first TA adjustment is configured to be shorter than the sequence of the first type random access preamble on the time axis.