NR Random Access Response Synchronization Sequence Selection
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Solution Overview
Problem
In New Radio (NR) wireless communications, the challenge lies in ensuring accurate detection and decoding of Random Access Response (RAR) signals by user equipment (UE) despite timing uncertainty and potential overlap of RAR signals from different cells or UEs, which can lead to synchronization errors and incorrect decoding.
Innovation Solution
The solution involves defining multiple synchronization sequences that are specific to each UE, determined by the synchronization signal (SS), the PRACH preamble, or additional network-known information, allowing the UE to detect and decode RAR signals independently, even when signals arrive simultaneously. This is achieved by using sequences like Zadoff-Chu sequences and scrambling techniques, ensuring the UE only searches for a single or limited set of sequences, reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple synchronization sequences are used to handle timing uncertainty and signal overlap, then the reliability of RAR detection is improved, but the device complexity increases due to multiple sequences to manage
Solution Approach 1:
The synchronization sequence is segmented into multiple candidate sequences (first synchronization sequence and second synchronization sequence) that are differentiated by their association with different cell identifiers. This segmentation allows the UE to distinguish between RAR signals from different cells by searching for sequences associated with the expected cell ID, thereby improving detection reliability without requiring the UE to blindly search through all possible sequences.
Solution Approach 2:
Different synchronization sequences are assigned different local qualities through their association with specific cell identifiers. The UE uses this local quality differentiation to optimize its search process by focusing on sequences corresponding to the expected cell ID, reducing the search space and computational complexity while maintaining high reliability in distinguishing between multiple RAR signals.
2Reliability
If the UE searches for multiple synchronization sequences to handle signal overlap, then the reliability of RAR detection is improved, but the computational complexity for the UE increases
Solution Approach 1:
The network performs preliminary action by pre-associating specific synchronization sequences with cell identifiers before the random access procedure. The UE uses this pre-established mapping to guide its search process, only needing to check sequences associated with expected cell IDs rather than exhaustively searching all possible sequences. This preliminary organization significantly reduces UE computational complexity while maintaining detection reliability.
Solution Approach 2:
The cell identifier acts as an intermediary that mediates between the multiple synchronization sequences and the UE's detection process. Instead of the UE directly handling the complexity of distinguishing multiple sequences, the cell identifier provides a simplified search criterion, reducing the detection task to matching sequences with expected cell IDs, thereby lowering computational complexity.
3Device complexity
If a single synchronization sequence is used for all RAR transmissions, then the device complexity is minimized, but the reliability of RAR detection deteriorates due to inability to distinguish between different cells or UEs
Solution Approach 1:
The single synchronization sequence is segmented into multiple sequences differentiated by cell identifier associations. This segmentation enables the UE to distinguish between RAR signals from different cells by searching for sequences corresponding to the expected cell ID, thereby improving detection reliability while keeping the UE implementation relatively simple through structured search.
Solution Approach 2:
The solution adds a new dimension of differentiation by associating synchronization sequences with cell identifiers. This dimensional extension allows the UE to use cell ID information as an additional search criterion, improving the ability to distinguish between multiple RAR signals without significantly increasing overall system complexity.
Data Source
AI summary
According to certain embodiments, a method for use in a network node comprises broadcasting a synchronization signal (SS) to one or more wireless devices. The SS comprises basic information about the network node. The method further comprises receiving a preamble from one of the wireless devices via a random access channel and determining a reference signal (RS) sequence based at least in part on the preamble received via the random access channel and/or the SS that was broadcast to the one or more wireless devices. The method further comprises transmitting a random access response comprising the RS sequence.