Modified CSI-RS Cell Discovery via Frequency Multiplexing
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Solution Overview
Problem
In heterogeneous cellular networks, the legacy method for cell discovery using primary and secondary synchronization signals (PSS/SSS) is inadequate due to high mutual interference among cells, especially in dense deployments, and switching off these signals to save power results in UE inability to detect small cells when they are not needed.
Innovation Solution
A modified channel state information reference signal (CSI-RS) transmission technique is employed, utilizing frequency multiplexing to allow different cells to transmit discovery signals on different physical resource blocks, optimizing resource allocation to maximize cell discovery while minimizing interference and maintaining legacy mechanism performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If PSS/SSS signals are transmitted every 5 ms for cell discovery, then UE can discover cells, but mutual interference between different cells becomes very high in dense deployments
Solution Approach 1:
The patent segments the system bandwidth into multiple resource blocks and assigns different discovery signals to different resource blocks. Each cell transmits its discovery signal on a dedicated resource block rather than all cells transmitting on the same frequency resources, thereby reducing mutual interference while maintaining cell discovery capability.
Solution Approach 2:
The patent introduces a modified reference signal as an intermediary carrier for cell discovery. Instead of using traditional PSS/SSS signals that cause high interference, the invention uses reference signals transmitted on resource blocks as a mediator to convey cell identification information, reducing interference while enabling UE to detect and measure cells effectively.
2Use of energy by moving object
If PSS/SSS transmission is switched off to save power and reduce interference, then energy consumption is reduced, but UE cannot discover the presence of the cell
Solution Approach 1:
The patent makes the reference signal serve multiple functions: it acts as both a channel state information reference signal for legacy UEs and as a cell discovery signal for HetNet cells. This multi-functionality allows the signal to be transmitted continuously without requiring separate discovery signals, enabling power savings while maintaining cell detectability.
Solution Approach 2:
The reference signal serves as an intermediary that carries dual purposes: providing channel state information for existing connections and simultaneously enabling cell discovery for HetNet. This allows continuous transmission with reduced power consumption compared to dedicated discovery signals, while maintaining the ability for UE to detect cell presence.
3Object-generated harmful factors
If frequency multiplexing is used to allow different cells to transmit discovery signals on different PRBs, then interference is reduced and more cells can be discovered, but resource allocation complexity increases
Solution Approach 1:
The patent segments the frequency spectrum into resource blocks and assigns specific resource blocks to specific cells for discovery signal transmission. This segmentation approach systematically allocates resources to minimize interference while providing a clear framework for resource management, balancing interference reduction with implementation complexity.
Data Source
AI summary
The proposed approach contemplates systems and methods configured to utilize a modified reference signal to facilitate efficient discovery of as many cells as possible within one channel state information reference signal (CSI-RS) sub-frame while maintaining certain detection and measurement performance. The proposed approach is configured to unambiguously discover at least the number of anticipated small cells within one cluster and to further identify all small cells within the coverage area of a base station/macro cell. In some embodiments, frequency multiplexing is utilized to allow different cells to transmit their discovery signals on different physical resource blocks (PRBs) rather than one cell using every PRB over the entire system bandwidth.