Reference Signal Transmission for Small Cell Overhead Reduction
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Solution Overview
Problem
In wireless communication systems, especially in LTE release 12, there is a challenge in optimizing small cell enhancements to reduce signaling to the core network while maintaining efficient reference signal transmission and minimizing overhead, particularly in heterogeneous networks where energy savings and interference reduction are crucial.
Innovation Solution
A method for transmitting a reference signal that involves receiving synchronization signals in contiguous subframes with specific OFDM symbols and resource blocks, allowing for accurate channel estimation and efficient resource allocation, including the use of new carrier types that optimize reference signal structure without backward compatibility, thereby reducing overhead and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cell-specific reference signals (CRS) are transmitted in all subframes, then channel estimation accuracy is maintained, but overhead and energy consumption increase
Solution Approach 1:
The patent segments the reference signal transmission by introducing different reference signal types (CRS and DM-RS) for different purposes and locations. CRS is transmitted only in specific subframes for channel estimation, while DM-RS is used for demodulation in data regions, reducing overall overhead while maintaining estimation accuracy.
Solution Approach 2:
The patent implements periodic transmission of CRS in specific subframes (e.g., every 5th or 10th subframe) rather than continuous transmission. This periodic action maintains channel estimation accuracy at critical intervals while significantly reducing reference signal overhead and energy consumption in non-critical subframes.
2Quantity of substance
If new carrier type (NCT) is introduced for small cell optimization, then overhead and energy consumption are reduced, but backward compatibility with legacy UEs is lost
Solution Approach 1:
The patent applies local quality by allowing different carrier types (legacy and NCT) to coexist in the same network. Each carrier can be independently configured with appropriate reference signal structures, enabling NCT carriers to use optimized DM-RS-based transmission while legacy carriers maintain CRS-based transmission for compatibility with older UEs.
Solution Approach 2:
The patent creates a universal reference signal framework that supports both legacy CRS-based UEs and newer DM-RS-based UEs. The system can dynamically select which reference signal type to use based on UE capability, making the network universally compatible across different UE generations while optimizing for each type.
3Reliability
If reference signals are transmitted in every subframe, then channel estimation reliability is improved, but energy consumption and interference increase
Solution Approach 1:
The patent implements periodic reference signal transmission where CRS is sent only in specific subframes (e.g., every 5th or 10th subframe) rather than every subframe. This periodic transmission maintains channel estimation reliability at critical intervals while significantly reducing base station energy consumption and minimizing interference in non-critical subframes.
Solution Approach 2:
The patent uses preliminary channel estimation based on CRS transmitted in earlier subframes to prepare for data reception in subsequent subframes. This preliminary action allows the system to maintain reliable channel knowledge without transmitting reference signals in every single subframe, reducing energy consumption while preserving estimation reliability.
Data Source
AI summary
The method of transmitting the reference signal includes receiving a synchronization signal in a subframe including contiguous first slot and second slot, and receiving a reference signal in the subframe, in which each of the first slot and the second slot includes a plurality of RBs and a plurality of OFDM symbols, the synchronization signal includes a PSS and a SSS, the PSS is received in the last OFDM symbol of the first slot, the SSS is received in a previous symbol before the last OFDM symbol of the first slot, a cell identifier is acquired based on the PSS and the SSS, the synchronization signal is received in center 6 RBs among the plurality of RBs, and the reference signal is received in at least one 01-DM symbol among the plurality of OFDM symbols in the second slot through the center 6 RBs.