SSB Raster Shift for 5G NR Initial Cell Search
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Solution Overview
Problem
In 5G NR mobile communications, the initial cell search time is prolonged due to the need to scan multiple SSB rasters, and existing methods to mitigate frequency offset ambiguity result in signaling overhead and do not support 30 kHz SCS.
Innovation Solution
The SSB raster spacing and offset are defined to maximize frequency separation between adjacent primary SSB entries, supporting both SCS-spaced and 100 kHz channel rasters, with a minimum channel bandwidth of 5 MHz or higher, and SSB raster offset frequency being a multiple of 30 kHz plus or minus 10 kHz, to minimize the number of SSB rasters and reduce cell search time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the SSB raster is aligned with channel raster at 100 kHz grid with 6 PRBs size, then compatibility with LTE is maintained, but the number of SSB rasters increases leading to prolonged initial cell search time
Solution Approach 1:
The patent changes the SSB size parameter from 6 PRBs (LTE alignment) to 20 PRBs (5G NR), and adjusts the raster spacing accordingly. This parameter change reduces the number of rasters needed while maintaining backward compatibility through separate raster definitions for different scenarios.
Solution Approach 2:
The patent segments the SSB raster into different configurations: one for LTE compatibility (6 PRBs, 100 kHz grid) and another for 5G NR optimization (20 PRBs, reduced raster count). This allows the system to switch between configurations based on operational requirements.
2Measurement precision
If existing methods are used to mitigate frequency offset ambiguity, then frequency accuracy is improved, but signaling overhead increases
Solution Approach 1:
The patent makes the UE self-resolve frequency offset ambiguity by using the known SSB raster structure and frequency relationships. Instead of relying on network signaling to disambiguate, the UE autonomously determines the correct frequency offset by checking against the predefined raster positions, eliminating the need for additional signaling messages.
3Area of stationary object
If SSB raster spacing is reduced to increase coverage, then area coverage is improved, but the number of SSB rasters increases leading to longer cell search time
Solution Approach 1:
The patent optimizes the SSB raster spacing parameter to achieve an optimal balance. Rather than simply reducing spacing to maximize coverage, it selects a spacing that provides sufficient coverage while minimizing the total number of rasters the UE must scan, thus reducing cell search time.
4Measurement precision
If SSB raster offset frequency is increased to resolve ambiguity, then frequency accuracy is improved, but hardware implementation complexity increases
Solution Approach 1:
The patent selects specific SSB raster offset frequency values that are multiples of 30 kHz plus or minus 10 kHz. These parameter choices are optimized to provide sufficient frequency offset resolution while keeping the offset values within ranges that can be efficiently implemented in hardware, avoiding excessively large or complex frequency adjustments.
Data Source
AI summary
Various examples with respect to synchronization signal block (SSB) raster shift in mobile communications are described. A processor of a user equipment (UE) performs an initial cell search to identify a cell among one or more cells of a wireless communication system. The processor then camps on the identified cell. In performing the initial cell search, the processor scans through a plurality of SSB entries for frequency bands below 3 GHz with a SSB raster spacing and a SSB raster offset frequency that support sub-carrier spacing (SCS) spaced channel raster and 100 kHz channel raster for both 15 kHz SCS and 30 kHz SCS. A minimum channel bandwidth at 5 MHz or higher for 15 kHz SCS or at 10 MHz or higher for 30 kHz SCS is supported. The SSB raster spacing is a common multiple of 15 kHz and 100 kHz. The SSB raster offset frequency for 100 kHz channel raster is a multiple of 30 kHz plus/minus 10 kHz.