HARQ Feedback for Two-Step RACH Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current wireless communication systems, particularly in 5G NR and LTE, face challenges in improving the random access channel (RACH) procedure efficiency, especially in two-step RACH procedures, which affect the reliability and speed of user equipment (UE) access to the network.
Innovation Solution
A hybrid automatic repeat request (HARQ) procedure is implemented for the RACH response message in a two-step RACH procedure, allowing UE to send a RACH message with a preamble and payload, and the base station (BS) to respond with a success or fallback RAR, enabling ACK, NACK, or no transmission based on successful decoding, thereby improving reliability and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a two-step RACH procedure is implemented to reduce access latency, then the speed of network access is improved, but the reliability of message delivery deteriorates due to lack of HARQ feedback mechanism
Solution Approach 1:
The patent introduces HARQ feedback mechanisms where the UE sends ACK/NACK responses to BS's RACH response messages. When the BS successfully decodes the RACH message, it sends a success RAR; when decoding fails, it sends a fallback RAR or no response, enabling the UE to detect transmission status and request retransmission if needed, thus improving message delivery reliability while maintaining fast access
Solution Approach 2:
The patent implements dynamic behavior where the UE adapts its response based on the RAR window outcome: sending ACK if success RAR is received, sending NACK if fallback RAR or no response is received, and conditionally retransmitting RACH messages based on HARQ process state. This dynamic adaptation allows the system to balance speed and reliability based on real-time transmission conditions
2Reliability
If HARQ feedback mechanisms are added to improve reliability, then the reliability of RACH procedure is improved, but the device complexity increases due to additional monitoring and response protocols
Solution Approach 1:
The patent segments the RACH procedure into distinct phases with specific HARQ behaviors: initial RACH message transmission, RAR window monitoring phase, and response transmission phase. Each phase has clearly defined actions (monitor for success/fallback RAR, send ACK/NACK, conditional retransmission), which simplifies the implementation complexity by breaking down the complex HARQ protocol into manageable, discrete steps that can be independently processed
3Reliability
If the UE monitors for RACH response messages during the RAR window to improve reliability, then the message delivery reliability is improved, but the power consumption increases due to continuous monitoring
Solution Approach 1:
The patent implements periodic monitoring during the RAR window where the UE activates its receiver at specific time intervals to check for success RAR or fallback RAR messages from the BS. This periodic action pattern allows the UE to maintain reliability by detecting RAR messages while consuming power only during monitoring intervals rather than continuously, thus balancing reliability improvement with power consumption reduction
Data Source
AI summary
Certain aspects of the present disclosure provide techniques for a hybrid automatic repeat request (HARQ) procedure for the random access channel (RACH) response message in a two-step RACH procedure. A method that may be performed by a user equipment (UE) includes sending a RACH message to a base station (BS) during a two-step RACH procedure. The RACH message includes a RACH preamble and a RACH payload. The UE monitors a RACH response message from the BS during a random access response (RAR) window. The UE transmits a retransmission of the RACH message, an acknowledgement (ACK) to the RACH response message, a negative acknowledgment (NACK) to the RACH response message, or does not transmit, to the BS based on whether a RACH response message carrying a success RAR or a fallback RAR, or no RACH response message, is received from the BS during the window.