Reference Signal Multiplexing in LTE-A Uplink
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Solution Overview
Problem
Current wireless communication systems face inefficiencies in transmitting reference signals and data, particularly in LTE-A Physical Uplink Shared Channel, where the overhead for demodulation reference signals (DMRS) consumes significant resources, impacting channel estimation performance and data throughput.
Innovation Solution
The technique involves multiplexing reference signals and data on different sets of subcarriers using frequency division multiplexing (FDM), allowing for flexible allocation based on a tradeoff between overhead, channel estimation performance, and data throughput, by transmitting the DMRS on a subset of subcarriers and data on remaining subcarriers, and potentially across multiple symbol periods or from multiple antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference signal is transmitted on all subcarriers, then channel estimation performance is improved, but resource overhead increases and data throughput decreases
Solution Approach 1:
The patent divides the subcarriers into different sets, with reference signals transmitted on a first set of subcarriers and data on a second set of subcarriers. This segmentation allows selective placement of reference signals only where needed for channel estimation, rather than on all subcarriers, thereby reducing overhead while maintaining estimation performance.
Solution Approach 2:
The patent applies local quality by transmitting reference signals on specific subsets of subcarriers rather than uniformly across all subcarriers. The reference signal allocation is adapted to local channel conditions and requirements, placing reference signals only in frequency regions where channel estimation is most beneficial, thus optimizing the tradeoff between overhead and performance.
2Productivity
If reference signal overhead is reduced, then data throughput is improved, but channel estimation performance deteriorates
Solution Approach 1:
The patent implements dynamic reference signal allocation where the density and placement of reference signals can be adjusted based on channel conditions, mobility scenarios, and data throughput requirements. In high mobility scenarios, reference signal density is increased to maintain estimation accuracy, while in stable conditions, density is reduced to maximize throughput.
Solution Approach 2:
The patent changes key parameters such as reference signal subcarrier spacing, time density, and frequency distribution to optimize the balance between overhead and performance. By adjusting these parameters dynamically, the system can achieve high data throughput when channel conditions permit while maintaining sufficient reference signals for accurate estimation when needed.
3Reliability
If reference signal is transmitted frequently, then channel estimation accuracy is improved, but resource consumption increases
Solution Approach 1:
The patent employs periodic reference signal transmission with variable periods based on channel conditions and mobility. Instead of continuous reference signal transmission, the system uses periodic bursts adapted to the required estimation accuracy, reducing overall resource consumption while maintaining reliability when needed.
Solution Approach 2:
The system uses self-service by leveraging channel reciprocity and previous channel estimates to reduce the frequency and density of reference signals. The receiver can interpolate channel information between reference signals, allowing the system to maintain accuracy with fewer transmitted reference signals, thus reducing resource consumption.
Data Source
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AI summary
Techniques for efficiently multiplexing a reference signal and data on different sets of subcarriers in the same symbol period are described. In one design, a user equipment (UE) performs a discrete Fourier transform (DFT) on a set of modulation symbols for data to obtain data symbols. The UE also obtains reference symbols generated based on a reference signal sequence corresponding to a cyclic shift of a base sequence. The UE maps the reference symbols to a first set of subcarriers and maps the data symbols to a second set of subcarriers. The UE then generates a transmission symbol based on the mapped reference symbols and the mapped data symbols. The UE may also transmit reference signals and data (i) in multiple symbol periods of a slot or a subframe and/or (ii) from multiple antennas using frequency division multiplexing (FDM) or code division multiplexing (CDM).