Hierarchical PDCCH Search Space Design for 5G NR
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Solution Overview
Problem
The existing LTE search space design for downlink control channels is not optimal for 5G NR systems as it increases UE complexity due to the need for channel estimation across all control channel elements, and the blocking probability is higher in the nested search space approach used in NR, which requires a more efficient search space design to reduce UE complexity and blocking probability.
Innovation Solution
The proposed solution involves a hierarchical search space design for NR, where the number of control channel candidates is reduced by overlapping CCEs between aggregation levels, and the use of random hashing functions to determine the starting position and gap between PDCCH candidates, thereby decreasing the channel estimation burden and blocking probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing LTE search space design is used in 5G NR, then the UE can monitor control channels, but the UE complexity increases due to channel estimation across all control channel elements
Solution Approach 1:
The control channel elements are segmented into different aggregation levels (AL1, AL2, AL4, AL8, AL16) with different monitoring requirements. The UE only performs channel estimation on a limited subset of CCEs corresponding to its assigned aggregation levels, rather than all CCEs, thereby reducing complexity while maintaining monitoring capability
Solution Approach 2:
Different search spaces are assigned different monitoring properties based on local requirements. Common search spaces use pseudo-random starting positions for all UEs, while UE-specific search spaces use dedicated starting positions and gaps, optimizing the channel estimation burden for each UE's specific needs
2Productivity
If the nested search space approach is used in NR, then the search space design is more efficient, but the blocking probability increases
Solution Approach 1:
Search spaces are organized in a nested structure where common search spaces (CSS) and UE-specific search spaces (USS) are layered. CSS monitors first with broader coverage, then USS monitors with more targeted efficiency. This nested arrangement maintains search space efficiency while distributing the monitoring load to reduce blocking probability
Solution Approach 2:
The system performs preliminary channel estimation and candidate identification in the common search space before proceeding to UE-specific search spaces. This preliminary action filters out unlikely candidates early, reducing the overall blocking probability while maintaining efficiency in the subsequent UE-specific monitoring phase
Data Source
AI summary
Embodiments may be directed to techniques to determine physical downlink control channel (PDCCH) candidates to assign to a user equipment (UE) based on one or more aggregation levels, each PDCCH candidate in a highest aggregation level of the one or more aggregation levels assigned by a random distribution over a whole control channel element (CCE) domain, and each PDCCH candidate in one or more non-highest aggregation levels of the one or more aggregation levels assigned a random distribution over one or more CCEs utilized by PDCCH candidates of the highest aggregation level. Embodiments also include selecting at least one of the PDCCH candidates to utilize to send downlink control information (DCI) to the UE, and causing transmission of the DCI to the UE via the PDCCH candidates selected.