RedCap RACH Access Using Repeated RAR Transmissions
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Solution Overview
Problem
Reduced capability (Redcap) devices, such as industrial wireless sensors and wearables, face significant coverage reduction due to reduced receive/transmit antennas and bandwidth, impacting the transport block size for downlink transmissions like random access response (RAR) messages, necessitating solutions for coverage recovery.
Innovation Solution
A processor in Redcap devices performs measurements on signal synchronization blocks (SSBs) to select PRACH groups based on predetermined thresholds, providing these measurements to a base station for initial access, and monitors for RAR messages with indicated repetition numbers, using techniques like multiplexing, dynamic indication of repetition numbers through DCI Format 1_0, and multi-beam/multi-TRP repetitions to enhance coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If Redcap devices use reduced number of antennas and bandwidth to save power, then power consumption is reduced, but coverage is significantly reduced
Solution Approach 1:
The base station determines the repetition number for RAR message transmissions in advance based on UE capability information and channel conditions, and indicates this repetition number to the UE through DCI Format 1_0 before the actual RAR transmission. This preliminary determination allows the system to prepare appropriate repetition strategies to compensate for the reduced coverage area of Redcap devices.
Solution Approach 2:
The system dynamically adjusts the repetition number for RAR message transmissions based on varying channel conditions and UE capabilities. The base station can change the repetition number adaptively by indicating different values through DCI Format 1_0, allowing the coverage to be dynamically compensated according to actual transmission conditions.
2Use of energy by moving object
If Redcap devices use reduced bandwidth (20 MHz instead of 100 MHz) to save power, then power consumption is reduced, but transport block size for downlink transmissions is reduced
Solution Approach 1:
The RAR message is transmitted multiple times according to the determined repetition number, creating periodic transmissions. This allows the UE to accumulate multiple copies of the same message, effectively increasing the total data received and compensating for the reduced transport block size caused by narrower bandwidth.
Solution Approach 2:
The system transmits copies of the RAR message multiple times instead of sending a single large transport block. By sending repeated copies through the limited 20 MHz bandwidth, the system ensures reliable delivery of the same information, effectively compensating for the reduced capacity of the narrower bandwidth channel.
3Adaptability or versatility
If the base station indicates repetition number through DCI Format 1.0, then flexibility in adapting to channel conditions is improved, but message size and processing complexity increase
Solution Approach 1:
The repetition number indication is implemented locally within the DCI Format 1_0 structure, which is used specifically for random access response scheduling. This localized implementation allows the repetition information to be embedded in an existing control message format without requiring system-wide changes, thereby limiting the increase in processing complexity to a specific function while maintaining adaptability.
Data Source
AI summary
A base station and a user equipment (UE) may exchange messages to perform a Random Access Channel (RACH) procedure. The UE performs measurements on a plurality of signal synchronization blocks (SSBs), selects M physical random access channel (PRACH) groups based on one or more of the measured SSBs satisfying a predetermined threshold, provides the measurements for the M PRACH groups to a base station in an initial access transmission for a RACH procedure and monitors for a random access response (RAR) message based on a repetition number for the RAR message indicated by the base station.