RIS-Aided Initial Access via SSB Reflection Indexing
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Solution Overview
Problem
Current wireless communication systems face challenges in efficiently performing initial access, particularly in scenarios where the wireless transmit/receive unit (WTRU) is out of coverage due to obstructions, and in maintaining backward compatibility with legacy systems.
Innovation Solution
The implementation of a reconfigurable intelligent surface (RIS) aided initial access system, which includes a network node, a RIS, and one or more WTRUs. The network node configures the RIS to reflect synchronization blocks (SSBs), allowing the WTRU to detect the reflected SSBs and perform initial access even when out of direct coverage. This system maintains compatibility with legacy systems by using legacy SSB transmission patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a RIS is introduced to reflect SSBs for initial access, then coverage and reception quality are improved, but device complexity and system configuration complexity increase
Solution Approach 1:
A RIS is introduced as an intermediary device between the gNB and WTRU to reflect SSBs and enable initial access in blocked coverage scenarios. The RIS receives configuration information from the gNB including SSB index mappings and reflects the appropriate SSBs to WTRUs, thereby improving initial access reliability without requiring complex changes to the core network architecture.
Solution Approach 2:
The gNB performs preliminary configuration of the RIS by providing configuration information that includes mappings between SSB indices and reflected SSB indices. This preliminary action allows the RIS to be pre-configured with the necessary information to reflect the correct SSBs, reducing the complexity of real-time decision-making and simplifying the overall system operation.
2Adaptability or versatility
If multiple configuration informations are transmitted to RIS for different SSB transmissions, then adaptability and coverage are improved, but loss of time and signaling overhead increase
Solution Approach 1:
The system employs periodic SSB transmissions with each SSB burst set associated with specific configuration information for the RIS. The gNB transmits configuration information periodically along with the SSB bursts, allowing the RIS to be updated with new configuration data at regular intervals. This periodic approach balances adaptability with time efficiency, as the RIS can operate with existing configuration during periodic updates rather than requiring continuous reconfiguration.
Solution Approach 2:
Configuration information is transmitted in advance with each SSB burst set, allowing the RIS to be pre-configured before the actual SSB reflection occurs. This preliminary configuration approach reduces the time required during the critical initial access phase, as the RIS already has the necessary configuration information ready when WTRUs need to access the network.
3Measurement precision
If SSB index mapping is used to identify reflected SSBs, then measurement precision and access accuracy are improved, but device complexity increases
Solution Approach 1:
The system uses local quality differentiation by assigning specific SSB index mapping relationships to different spatial paths (direct path vs. RIS-reflected path). WTRUs can identify whether they are receiving SSBs directly from the gNB or reflected by the RIS based on the index mapping, allowing precise identification of the signal source without requiring complex global system changes. Each path has its own quality characteristics encoded in the index mapping.
Solution Approach 2:
The SSB index space is segmented into different ranges or mappings that correspond to different transmission paths. By dividing the index mapping into distinct segments (direct path indices vs. reflected path indices), the system enables WTRUs to identify the signal source through simple index comparison rather than complex analysis, reducing device complexity while maintaining measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The RIS-aided initial access system enhances coverage and reception quality by allowing WTRUs to detect SSBs reflected by the RIS, even when obstructed from direct network coverage. This approach supports backward compatibility, ensuring seamless integration with existing wireless communication systems.
Implementation Method 1
The RIS may reflect the SSB transmitted by the network node. Based on the configuration information, the RIS may reflect the SSB towards a WTRU.
Data Source
AI summary
A WTRU may detect a reflected SSB transmission from a RIS. The reflected SSB is associated with an index. The WTRU may determine a source device of the reflected SSB transmission based on the index. For example, the WTRU may determine that the reflected SSB transmission was reflected by the RIS based on the index associated with the RIS. The WTRU may perform a random access procedure with a network device via the RIS based on the index. The SSB transmission may be associated with an SSB burst transmission comprising a plurality of SSB transmissions, where each of the plurality of SSB transmissions may be associated with the index. The plurality of SSB transmissions may comprise SSB transmissions reflected by the RIS and/or SSB transmissions not reflected by the RIS. The spatial state of the RIS may be maintained constant and/or may change during the SSB burst transmission.