LTE Small Cell Discovery via CSI-RS and PRS Segmentation
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Solution Overview
Problem
In wireless communications systems, especially in hotzones with deployed small cells like pico, femto, and nano cells, severe inter-cell interference degrades the detectability of Primary Synchronization Signals (PSS)/Secondary Synchronization Signals (SSS)/Cell-Specific Reference Signals (CRS) for user equipment (UE), making it challenging for UE to detect these cells effectively.
Innovation Solution
Introducing a new physical signal for cell detection, such as a modified Channel State Information Reference Signal (CSI-RS), and new procedures for using existing legacy signals like CSI-RS and Position Reference Signals (PRS) to enhance cell detection and measurement, along with Coordinated Multi-Point (CoMP) transmission point detection, to improve UE's capability in detecting small cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional cell search methods using PSS/SSS/CRS are used, then the cell detection process is simple, but detection accuracy deteriorates in hotzones with severe inter-cell interference
Solution Approach 1:
The patent segments the cell detection process into multiple stages: initial synchronization using PSS/SSS, followed by enhanced detection using discovery signals (CSI-RS/PRS) with specific resource configurations. This segmentation allows different signal types to address different aspects of the detection problem, improving overall accuracy in interference-prone environments.
Solution Approach 2:
The patent introduces discovery signals (CSI-RS and PRS) as intermediary elements between the traditional synchronization signals and the final cell detection decision. These intermediary signals provide additional measurement opportunities and interference mitigation capabilities, acting as a bridge that improves detection accuracy without replacing the existing synchronization mechanism.
2Measurement precision
If discovery signals are introduced to improve cell detection, then detection accuracy improves, but system complexity increases
Solution Approach 1:
The patent makes existing reference signal resources (CSI-RS and PRS) multi-functional by configuring them for discovery purposes in addition to their original functions. This universality approach allows the system to improve cell detection without adding entirely new signal types, thereby limiting the increase in system complexity while still achieving enhanced measurement precision.
Solution Approach 2:
The patent improves detection accuracy by changing parameters of existing signals rather than introducing fundamentally new signal structures. Specifically, it modifies resource element mappings, transmission periodicities, and measurement configurations of CSI-RS and PRS to optimize them for discovery operations, thereby achieving improved precision with manageable complexity increases.
3Reliability
If multiple reference signals are transmitted for channel measurement, then measurement reliability improves, but resource overhead increases
Solution Approach 1:
The patent merges the functions of multiple reference signals by configuring discovery CSI-RS and discovery PRS to work together in a coordinated manner. By combining these signals with specific resource element mappings and transmission configurations, the system achieves improved measurement reliability while avoiding the need to transmit all possible reference signal types simultaneously, thereby controlling resource overhead.
Data Source
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AI summary
A system and method for enhanced cell detection by a User Equipment (UE) is provided. The UE includes a transceiver configured to receive a discovery reference signal (DRS) occasion from at least one transmission point. The DRS occasion comprising a set of consecutive DRS sub-frames. The UE also includes processing circuitry configured to: in response to detecting a physical cell identity (PCID) of a Primary Synchronization Signal (PSS)/ Secondary Synchronization Signal (SSS)/ Common Reference Signal (CRS) that is the same as a reference PCID for a configured Channel State Information Reference Signal (CSI-RS) resource, the processing circuitry attempts to detect or measure the CSI-RS using the timing obtained from the PSS/SSS/CRS; and in response to not detecting a PCID of PSS/SSS/CRS that is the same as the reference PCID for a configured CSI-RS resource (TP), the processing circuitry does not attempt to detect or measure the CSI-RS.