PUSCH Repetition Selection for RedCap UE Coverage
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Solution Overview
Problem
The 5G NR system faces challenges in maintaining adequate coverage for RedCap UEs due to higher path-loss at higher frequencies, particularly for IoT use cases requiring lower reliability and longer latency, which affects the quality of service compared to legacy radio access technologies like LTE.
Innovation Solution
The method involves transmitting a physical random access channel (PRACH) preamble and receiving a random access response (RAR) message that schedules a message 3 (Msg3) PUSCH with a determined transport block size (TBS) based on a modulation and coding scheme (MCS) field, using a selected number of PUSCH repetitions from a set of candidate numbers indicated by the MCS field to enhance coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If 5G NR operates at higher frequencies (28 GHz or 39 GHz), then data rate and network capacity are improved, but path-loss increases causing worse coverage
Solution Approach 1:
The transmission is segmented into multiple PUSCH repetitions (multiple copies of the same data) transmitted across different time slots. The UE transmits the same transport block multiple times with different redundancy versions, allowing the network to combine these repetitions to achieve the required coverage and reliability while operating at higher frequencies.
Solution Approach 2:
The network pre-configures the UE with a set of candidate PUSCH repetition numbers and redundancy version sequences before actual data transmission. Based on the MCS index indicated in the uplink grant, the UE selects the appropriate number of repetitions and RV sequence from the pre-configured options, enabling rapid adaptation to varying channel conditions without additional signaling overhead.
2Reliability
If PUSCH repetition number is increased to improve coverage, then coverage is improved, but transmission time and latency increase
Solution Approach 1:
The system dynamically adapts the number of PUSCH repetitions based on the MCS index and channel conditions. The UE selects from pre-configured candidate repetition numbers according to the MCS field in the uplink grant, allowing the network to optimize between coverage and latency by choosing appropriate repetition counts for different service requirements and channel states.
Solution Approach 2:
The system changes the parameter of repetition number based on the MCS index value. Different MCS ranges map to different candidate repetition numbers, allowing the network to adjust the trade-off between coverage (more repetitions) and latency (fewer repetitions) by selecting appropriate MCS values and corresponding repetition configurations.
3Device complexity
If RedCap UEs use reduced capabilities (fewer RX antennas or smaller antenna size), then device complexity and cost are reduced, but coverage performance deteriorates
Solution Approach 1:
The transmission is divided into multiple PUSCH repetitions with different redundancy versions. RedCap UEs with reduced antenna capabilities can transmit the same data multiple times across different time slots, allowing the network to combine these repetitions to compensate for the reduced diversity gain from fewer antennas, thereby maintaining coverage performance.
Solution Approach 2:
The system configures different candidate PUSCH repetition numbers and RV sequences specifically for RedCap UEs based on their capability indicators. The network can select more aggressive repetition strategies for RedCap UEs to compensate for their reduced antenna capabilities, ensuring adequate coverage while allowing these UEs to use simpler, lower-cost hardware.
Data Source
AI summary
Methods related to physical uplink shared channel (PUSCH) repetitions, a user equipment (UE), and a network device are provided. In the method, a physical random access channel (PRACH) preamble is transmitted. A random access response (RAR) message responding to the PRACH preamble is received. The RAR message includes an uplink grant that schedules a message 3 (Msg3) PUSCH. A transport block size (TBS) for a transport block (TB) is determined based on a modulation and coding scheme (MCS) field in the uplink grant. The Msg3 PUSCH for the TB is transmitted with the number of PUSCH repetitions. The number of PUSCH repetitions is selected from a set of candidate numbers of PUSCH repetitions based on the MCS field in the uplink grant.