LTE Reference Signal Transmission with Power Offset
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Solution Overview
Problem
Current LTE and LTE-advanced systems face challenges with inter-cell interference and limited sounding capacity due to the time multiplexing of sounding reference signals (SRS) with demodulation reference signals (DMRS), which degrades channel sounding accuracy and limits the use of advanced features like SU-MIMO and COMP.
Innovation Solution
The method involves transmitting DMRS and SRS in the same time domain resource using a single reference signal sequence, with a power offset for channel sounding, to minimize inter-cell interference and increase sounding capacity, allowing for orthogonal resource allocation and reduced overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If sounding reference signal (SRS) and demodulation reference signal (DMRS) are time multiplexed in separate resources, then inter-cell interference is reduced, but sounding capacity and channel estimation accuracy deteriorate
Solution Approach 1:
The patent combines SRS and DMRS into the same time domain resource, allowing both signals to be transmitted simultaneously in the same SC-FDMA symbol. This merging enables the system to achieve both reduced overhead and improved sounding capacity while maintaining acceptable interference levels through power offset mechanisms.
Solution Approach 2:
The patent applies different power levels (power offset) to different parts of the reference signal sequence within the same resource. The DMRS portion uses higher power for reliable demodulation, while the SRS portion uses lower power for channel sounding, creating local quality differentiation that resolves the interference-accuracy contradiction.
2Object-affected harmful factors
If SRS is transmitted in separate time resources from DMRS, then signal interference is minimized, but resource overhead increases and sounding capacity is limited
Solution Approach 1:
The patent merges SRS and DMRS transmissions into the same time domain resource (same SC-FDMA symbol), eliminating the need for separate time resources. This increases sounding capacity and reduces resource overhead while managing interference through power control and orthogonal resource allocation across different cells.
Solution Approach 2:
The patent moves the differentiation between SRS and DMRS from the time domain to the power domain and frequency domain. By using power offset and orthogonal frequency resource allocation, the system can multiplex both signals in the same time resource without excessive interference, thereby increasing sounding capacity.
3Loss of substance
If a single reference signal sequence is used for both demodulation and channel sounding, then resource overhead is reduced, but signal power distribution becomes challenging
Solution Approach 1:
The patent applies power offset to different portions of the reference signal sequence. The DMRS portion is transmitted with higher power to ensure reliable demodulation, while the SRS portion uses lower power for channel sounding. This local quality differentiation resolves the power distribution challenge while using a single sequence.
Solution Approach 2:
The patent changes the power parameter (amplitude) of different parts of the reference signal sequence to differentiate between DMRS and SRS functions. By adjusting the power offset parameter, the system can optimize the balance between demodulation reliability and channel sounding accuracy while reducing overall resource overhead.
Data Source
AI summary
A method for reference signal transmission is disclosed, wherein a demodulation reference signal DMRS and a sounding reference signal SRS is transmitted in a same time domain resource from a user terminal to an LTE base station. A single reference signal sequence is used both for demodulation and detection of a data channel, and for channel sounding, such that a reference signal sequence part used for the demodulation and detection of the data channel is in a power offset compared to a reference signal sequence part used for the channel sounding. Code division multiplexing is applied on a reference signal sequence by using a cyclic shift of a whole length of the sequence. The cyclic shift is selected such that reference signal sequences allocated to the different user terminals are orthogonal over a minimum allocation granularity of the data channel.