PDCCH Design for 5G NR Analog Beamforming and Latency
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Solution Overview
Problem
Next generation 5G new radio (NR) systems face challenges in Physical Downlink Control Channel (PDCCH) design, particularly in supporting analog beamforming and multiplexing of enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low Latency Communications (URLLC), due to excessive control signaling and increased blind decoding processes.
Innovation Solution
A new PDCCH design is proposed, where each PDCCH is associated with a set of control channel elements (CCEs) using various REG-to-CCE mapping rules to improve frequency diversity and reduce latency, and is transmitted in synchronization signal blocks associated with analog beam directions, allowing UEs to derive PRACH resources for channel access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distributed and localized PDCCH transmission are supported in both common and UE-specific search spaces, then coverage and reliability are improved, but control signaling overhead and blind decoding complexity increase excessively
Solution Approach 1:
The PDCCH search space is segmented into two distinct types: common search space (CSS) for common control information and UE-specific search space (USS) for user-specific control information. This segmentation allows the UE to focus blind decoding efforts in USS while CSS uses simplified monitoring, reducing overall blind decoding complexity while maintaining reliability through distributed transmission in both spaces.
Solution Approach 2:
Different transmission schemes are applied to different search spaces: CSS uses localized transmission for broad coverage while USS supports both localized and distributed transmission based on UE-specific requirements. This local quality approach optimizes reliability for each search space type without requiring the UE to handle all possible transmission modes simultaneously, reducing complexity.
2Reliability
If multiple REG-to-CCE mapping rules are implemented to improve frequency diversity and frequency selectivity, then PDCCH robustness is enhanced, but processing complexity and latency increase
Solution Approach 1:
The system dynamically selects between different REG-to-CCE mapping rules (interleaved and non-interleaved) based on channel conditions and service requirements. For frequency-selective channels, interleaved mapping provides frequency diversity; for latency-sensitive services, non-interleaved mapping reduces processing time. This dynamic adaptation resolves the contradiction between robustness and latency.
Solution Approach 2:
The mapping rule parameter (interleaved vs. non-interleaved) is changed based on traffic type and channel conditions. Downlink control information can use interleaved mapping for reliability while uplink grants may use non-interleaved mapping for low latency. This parameter change approach allows optimization of the diversity-latency tradeoff for different scenarios.
3Productivity
If PDCCH bandwidth is increased to support higher data rates in 5G NR, then peak data rate capability is improved, but control signaling overhead and resource consumption increase
Solution Approach 1:
The PDCCH design supports multiple functions within the same control resource structure: it can carry both common control information (broadcast to all UEs) and UE-specific control information (dedicated grants and acknowledgments). This multi-functionality allows efficient utilization of control resources without requiring separate PDCCH structures for different purposes, reducing overall control signaling overhead while supporting high data rates.
Solution Approach 2:
The patent introduces control resource sets (CORESETs) as a new dimensional organization of PDCCH resources, allowing control channels to be arranged in both frequency and time dimensions. This dimensional change enables more flexible resource allocation and multiplexing, improving spectral efficiency for control signaling while supporting high peak data rates through better resource utilization.
Data Source
AI summary
A new design for physical downlink control channel (PDCCH) is proposed for the next generation 5G new radio systems. A UE receives the configuration of a default control resource set (CORESET) in MIB/SIB from its serving base station. The default CORESET contains both common search space and UE-specific search space for candidate PDCCH transmission. A PDCCH in a default CORESET is mapped to physical resource in a distributed or localized manner. Specifically, various REG-to-CCE mapping rules are proposed to improve frequency diversity gain, or frequency selectivity gain, or to reduce latency of PDCCH processing. Further, to facilitate analog beamforming in mmWave systems, the default CORESET is transmitted in a synchronization signal (SS) block associated with a corresponding analog beam direction.