5G NR RACH Sub-band Allocation for RedCap UEs

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Solution Overview

Problem

5G NR networks face challenges in efficiently managing the random access channel (RACH) process for reduced capability user equipment (RedCap UEs), which have varying wireless capabilities, leading to increased overhead resources and reduced coverage area due to limited bandwidth allocation.

Innovation Solution

The 5G NR network divides the bandwidth into smaller sub-bands and distributes physical RACH resources among these sub-bands, allowing RedCap devices to successfully attach to a cell with reduced overhead resources while ensuring coverage, by selecting appropriate PRACH sub-bands and formats based on device capabilities and location within the cell.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the network allocates dedicated RACH resources for RedCap UEs, then the coverage area is improved, but the overhead resources are increased

Engineering Contradiction:

Improvecoverage areaVSAvoidoverhead resources

Core Design Contradiction:

Area of stationary objectVSQuantity of substance

Solution Approach 1:

The patent segments the RACH resources by dividing the uplink bandwidth into multiple RACH sub-bands, where some sub-bands are designated for RedCap UEs and others for regular UEs. This segmentation allows the network to allocate RACH resources specifically for RedCap devices without dedicating the entire RACH bandwidth, thereby improving coverage for RedCap UEs while controlling overhead resource consumption.

Inventive Principle:

Principle #1Segmentation

2Area of stationary object

If the network uses full bandwidth for RACH transmission, then the coverage area is maximized, but the power consumption of RedCap devices increases

Engineering Contradiction:

Improvecoverage areaVSAvoidpower consumption

Core Design Contradiction:

Area of stationary objectVSUse of energy by moving object

Solution Approach 1:

By segmenting the RACH bandwidth into sub-bands, RedCap UEs can transmit random access preambles using only the allocated sub-band resources rather than the full bandwidth. This reduces the transmission power required from RedCap devices while still achieving adequate coverage through the dedicated sub-band allocation.

Inventive Principle:

Principle #1Segmentation

3Productivity

If the network allocates separate RACH resources for RedCap UEs, then the network access efficiency is improved, but the device complexity increases

Engineering Contradiction:

Improvenetwork access efficiencyVSAvoiddevice complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent implements dynamic RACH sub-band selection where the network can flexibly allocate different sub-bands for RedCap UEs based on current network conditions, traffic load, and device capabilities. This dynamic allocation improves network access efficiency for RedCap devices without requiring complex static configuration, as the system adapts resource allocation in real-time based on operational parameters.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS12256425B2Network access by a reduced capability user equipment

Publication Date: 2025.03.18 APPLE INC

AI summary

A user equipment (UE) may attempt to access a base station of a network. The UE receives, from the base station of a wireless network, a broadcast including a system information block (SIB) identifying a plurality of random access channel (RACH) sub-bands of an uplink (UL) bandwidth and which of the plurality of RACH sub-bands includes physical random access channel (PRACH) resources. The base station selects one of the plurality of RACH sub-bands for a PRACH transmission and selects a preamble from the selected RACH sub-band and transmit the preamble to the base station to initiate a RACH procedure.