Cell Reselection Method for PRACH Collision Reduction
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Solution Overview
Problem
In 5G mobile communication systems, a large number of user equipment (UEs) in an RRC idle or inactive state simultaneously attempting to access a specific service or function can lead to PRACH resource collisions, resulting in failed random access due to limited physical random access channel (PRACH) resources.
Innovation Solution
A cell reselection method that allows UEs to periodically or network-instructively select a target cell or frequency providing the desired service or function, ensuring that only UEs with a compatible service or function perform cell reselection, thereby reducing PRACH resource contention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large number of UEs simultaneously access a specific service or function, then service availability is improved, but PRACH resource collisions increase causing access failures
Solution Approach 1:
The patent segments UEs into different groups based on their desired services or functions, and assigns each group to select target cells from different candidate cell sets. This segmentation prevents all UEs from simultaneously accessing the same cell's PRACH resources, thereby reducing collisions while maintaining overall service access capacity.
Solution Approach 2:
The patent introduces a new dimension for resource allocation by using service type as a classification criterion. Instead of all UEs competing for the same PRACH resources in the time-frequency domain, UEs are differentiated by their service requirements, and each service group is directed to different target cells, effectively adding a spatial dimension to resource distribution.
2Ease of operation
If UEs perform cell reselection to a single target cell, then access to desired service is improved, but PRACH resource contention increases
Solution Approach 1:
The patent divides the candidate target cells into multiple sets, where each set is assigned to a specific service type. UEs desiring a particular service are instructed to select from the corresponding cell set, which segments the PRACH access load across multiple cells rather than concentrating it on a single target cell.
Solution Approach 2:
Different cells are assigned to serve different service types, creating local specialization. Each cell becomes optimized for specific services, and UEs access the cell that locally provides their desired service, reducing contention by matching service requirements with cell capabilities rather than all UEs targeting the same cell.
3Area of stationary object
If multiple UEs access the same cell simultaneously, then service coverage is improved, but PRACH resource exhaustion occurs
Solution Approach 1:
The patent extends the resource allocation from a single-dimension (time-frequency PRACH resources) to multi-dimensional by incorporating spatial distribution across multiple cells. UEs are distributed across different cells based on service type, effectively using the cell dimension to expand resource availability and prevent PRACH exhaustion in any single cell.
Solution Approach 2:
The patent segments the UE population by service type and segments the target cell selection accordingly. This dual segmentation ensures that while service coverage is maintained across the network area, the PRACH resource load is distributed across multiple cells rather than concentrated in one cell, preventing resource exhaustion.
Data Source
AI summary
In a first aspect, a cell reselection method is used in a user equipment in an RRC idle state or an RRC inactive state, the cell reselection method including: specifying a service or a function that the user equipment desires to use; selecting a target in response to an instruction from a network or periodically with, as a candidate, a cell or a frequency having a result of measurement processing, the result satisfying a predetermined condition, the measurement processing being performed on a cell or a frequency different from a current existing cell; and performing cell reselection to the target selected. The selecting of the target includes performing control for selecting, as the target, a cell or a frequency providing the service or the function specified.