Uplink Transmission Timing Advance in Two-Step Random Access
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Solution Overview
Problem
In communication systems, the lack of a timing advance (TA) value from the network device during the random access process poses a challenge for terminal devices to perform uplink transmission, as they rely on either a preset or maintained TA value for synchronization, especially in two-step random access scenarios where the network device does not send a TA command.
Innovation Solution
The terminal device can perform uplink transmission using a preset or maintained TA value, allowing it to determine the transmission boundary, and the network device can send a TA command on the downlink transmission resource to ensure synchronization, enabling uplink synchronization even without explicit TA value reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the network device does not send a TA command in the two-step random access process, then the random access latency is reduced, but the terminal device cannot obtain a TA value for uplink transmission
Solution Approach 1:
The terminal device performs uplink transmission using a preset TA value or a maintained TA value before receiving any TA command from the network device. This preliminary action allows the terminal to establish uplink transmission timing without waiting for the network device to provide a TA command, thereby reducing random access latency while ensuring proper timing alignment through pre-configured or previously used TA values.
2Reliability
If the terminal device uses a preset TA value for uplink transmission, then uplink synchronization can be achieved without receiving a TA command, but the TA value may not be optimized for the current transmission scenario
Solution Approach 1:
The terminal device dynamically switches between using a preset TA value and a maintained TA value based on the transmission scenario. The maintained TA value is updated based on previous transmission experiences and network feedback, allowing the system to adapt to changing channel conditions and optimize timing alignment over time while maintaining reliability in the current transmission.
Data Source
AI summary
This application provides an uplink transmission method and a communication apparatus. When a terminal device does not obtain a TA value in a two-step random access process, the terminal device can transmit, based on a preset TA value or a maintained TA value, uplink data on an uplink transmission resource assigned in the second step of random access, or perform, based on a preset TA value or a maintained TA value, a feedback for downlink data transmitted on a downlink transmission resource assigned in the second step of random access. In this way, uplink synchronization can be implemented when no TA value is assigned in a random access process.