PRACH Repetition Mapping for SSB Grouping and Frequency Offset Feedback
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Solution Overview
Problem
In new radio (NR) systems, PRACH repetition is necessary due to uplink transmitting antenna and power limitations, but existing solutions fail to address issues such as mapping synchronization signal blocks (SSBs) to PRACH occasions, dispersion of PRACH repetitions in time, and coexistence with legacy technology.
Innovation Solution
A mapping mechanism between SSBs and PRACH occasions is introduced, dividing SSBs into groups and configuring PRACH repetitions, with adaptive mapping logic and parameters to ensure consistent understanding between network and user equipment, and incorporating a PRACH repetition starting position cycling mechanism for coexistence with legacy systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PRACH repetitions are transmitted using frequency hopping to improve coverage, then coverage is improved, but uplink frequency synchronization is lost between different hops
Solution Approach 1:
The network device feeds back frequency offset information to the terminal through downlink control information (DCI). The terminal uses this feedback to adjust its frequency positioning for subsequent PRACH repetitions, ensuring frequency synchronization is maintained across frequency-hopped repetitions while preserving coverage benefits
Solution Approach 2:
The terminal dynamically adjusts frequency offset parameters based on network feedback. By changing the frequency positioning parameter according to the fed-back offset information, the system maintains frequency synchronization across multiple PRACH repetitions transmitted on different frequency resources
2Reliability
If multiple PRACH repetitions are transmitted on different physical resources to improve reliability, then reliability is improved, but frequency offset between repetitions causes reception failure
Solution Approach 1:
The network device measures frequency offset on received PRACH repetitions and feeds back correction information to the terminal. This feedback mechanism enables the terminal to compensate for frequency offsets in subsequent transmissions, ensuring reliable reception despite using multiple physical resources for repetitions
Solution Approach 2:
The system performs frequency offset measurement and feedback before the terminal transmits subsequent PRACH repetitions. This preliminary correction action ensures that frequency synchronization is established in advance, preventing reception failure before it occurs
3Productivity
If SSB and PRACH are frequency-division multiplexed to improve resource utilization, then resource utilization is improved, but frequency offset between SSB and PRACH affects reception
Solution Approach 1:
The network device measures frequency offset between SSB and PRACH signals and feeds back this information to the terminal. The terminal uses this feedback to adjust its frequency positioning, maintaining accurate frequency alignment between SSB and PRACH even when they are frequency-division multiplexed on different resources
Data Source
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AI summary
Embodiments of the present application are related to a method and apparatus for physical random access channel (PRACH) repetitions. A method according to an embodiment of the present application includes: receiving signaling information for indicating a synchronization signal block (SSB) group size; mapping indices of a plurality of SSBs to a plurality of physical random access channel (PRACH) occasions for a number of PRACH repetitions, wherein the plurality of SSBs are divided into one or more SSB groups based on the indicated SSB group size; and determining a set of PRACH occasions corresponding to one of the indices of the plurality of SSBs from the plurality of PRACH occasions based on the mapping.