Dynamic PRACH Scheduling via PDCCH for NR-U Random Access
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Solution Overview
Problem
In 5G and NR-U systems, terminal devices may experience LBT failures when attempting to access unlicensed spectrum, leading to impaired random access performance due to the inability to send PRACH on scheduled resources.
Innovation Solution
A method where a network device sends a PDCCH with PRACH resource indication information, including details of the PRACH resource, synchronization signal block SSB, and PRACH preamble, allowing the terminal device to perform random access using a flexibly scheduled common PRACH resource.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a terminal device uses semi-static PRACH resource configuration for random access on unlicensed spectrum, then the device can follow the listen before talk principle, but the device may suffer from LBT failure and cannot send PRACH on scheduled resources, degrading random access performance
Solution Approach 1:
The patent transforms the static PRACH resource configuration into a dynamic scheduling mechanism. The network device sends DCI messages to indicate PRACH resources dynamically, allowing the system to adapt to changing channel conditions and LBT outcomes. This enables the terminal device to receive updated PRACH resource assignments based on current channel state, resolving the contradiction between reliability and adaptability.
Solution Approach 2:
The patent changes the scheduling parameters from semi-static to dynamic by introducing DCI-based resource indication. The network device can modify PRACH resource parameters (time, frequency, preamble) on-demand through DCI messages, allowing the system to respond to LBT failures and channel variations. This parameter change enables both reliable access and adaptive resource allocation.
2Productivity
If the network device configures semi-static PRACH resources, then the configuration is simple and stable, but the terminal device cannot adapt to LBT failures and channel variations, limiting random access opportunities
Solution Approach 1:
The patent introduces DCI (Downlink Control Information) as an intermediary mechanism between the network device and terminal device. The DCI carries PRACH resource indication information that mediates the resource allocation process. This intermediary enables dynamic resource indication without requiring complex direct negotiation, increasing random access opportunities while managing scheduling complexity through standardized control messaging.
Solution Approach 2:
The patent segments the PRACH resource configuration into multiple independently schedulable components. Instead of configuring all PRACH resources as a single semi-static block, the system divides resources into time-frequency-preamble dimensions that can be individually indicated through DCI. This segmentation allows flexible resource allocation and increases access opportunities without overwhelming complexity.
3Reliability
If the terminal device performs LBT before sending PRACH, then the device follows unlicensed spectrum access rules, but LBT failures prevent the device from using scheduled PRACH resources, reducing access success rate
Solution Approach 1:
The patent applies preliminary action by having the network device perform LBT and obtain channel access before scheduling PRACH resources to the terminal device. The network device's successful LBT creates a Channel Occupancy Time (COT) during which PRACH resources are pre-allocated. This preliminary channel acquisition ensures that when the terminal device receives the DCI scheduling, the channel is already reserved, eliminating the need for the terminal to perform separate LBT and avoiding time loss from LBT failures.
Solution Approach 2:
The patent provides beforehand cushioning by establishing a protected time window (COT) through the network device's LBT success. Within this cushioned time period, the scheduled PRACH resources are guaranteed to be available without terminal device LBT failure risk. This prior cushioning protects against access failures and ensures reliable PRACH transmission within the protected window.
Data Source
AI summary
Provided are a random access network device and a device, which can improve the random access performance of a terminal device in an unlicensed spectrum. The network device includes: receiving, by a terminal device, a PDCCH, where the PDCCH includes PRACH resource indication information, the PRACH resource indication information is used for indicating a common PRACH resource scheduled by a network device, the PRACH resource indication information includes at least one of the following information: information of the PRACH resource, information of a synchronization signal block SSB associated with the PRACH resource, and information of a PRACH preamble transmitted on the PRACH resource; and sending, by the terminal device according to the PRACH resource indication information, a PRACH using the PRACH resource.