Multi-Antenna Reference Signal Transmission via Orthogonal Covering Codes
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Solution Overview
Problem
Current wireless communication systems, particularly in the 3GPP LTE system, lack a method for effectively transmitting reference signals in MIMO systems, which hampers channel estimation performance due to low reference signal density and interference from thermal noise.
Innovation Solution
A method and apparatus for transmitting reference signals in a multi-antenna system by generating reference signal sequences with different cyclic shift values, mapping them to SC-FDMA symbols, and transmitting these through multiple antennas, with each sequence being multiplied by +1 or −1 based on an OCC index in the downlink control information, ensuring proper allocation and interference minimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reference signals are transmitted with low density to increase data transmission capacity, then productivity is improved, but measurement precision deteriorates due to insufficient channel estimation accuracy
Solution Approach 1:
The patent combines multiple reference signal sequences from different layers into a single composite reference signal for transmission. By merging the reference signals and processing them together at the receiver, the system achieves better channel estimation accuracy without requiring increased reference signal density, thus maintaining high data transmission capacity
Solution Approach 2:
The patent changes the processing parameters by applying orthogonal covering codes (OCC) to reference signal sequences and using specific cyclic shift values. These parameter changes enable the receiver to distinguish between different layer reference signals and improve channel estimation accuracy even when reference signals are sparsely distributed in the time-frequency grid
2Measurement precision
If reference signals are transmitted for all subcarriers to improve channel estimation accuracy, then measurement precision is improved, but loss of energy increases due to reduced data transmission efficiency
Solution Approach 1:
The patent segments the reference signal transmission by assigning different reference signal sequences to different layers and using orthogonal covering codes to separate them. This segmentation allows the system to transmit reference signals only on necessary subcarriers for each layer, improving energy efficiency while maintaining accurate channel estimation through the structured segmentation approach
3Measurement precision
If multiple reference signal sequences are transmitted simultaneously through multiple antennas to improve channel estimation, then measurement precision is improved, but object-generated harmful factors increase due to inter-sequence interference
Solution Approach 1:
The patent applies preliminary actions by assigning orthogonal covering codes and specific cyclic shift values to reference signal sequences before transmission. This preliminary structuring ensures that even when multiple reference signal sequences are transmitted simultaneously through multiple antennas, they remain orthogonal or sufficiently separated, preventing inter-sequence interference while enabling accurate channel estimation
Solution Approach 2:
The patent introduces orthogonal covering codes as an intermediary mechanism that mediates between multiple reference signal sequences. These codes act as separators that allow the receiver to distinguish and process reference signals from different layers independently, eliminating harmful interference while maintaining measurement precision
Data Source
AI summary
A method is provided for transmitting, by a user equipment (UE), a demodulation reference signal (DMRS) in a wireless communication system. A first DMRS sequence, which is associated with a first layer, and a second DMRS sequence, which is associated with a second layer, are transmitted to a base station. A first orthogonal cover code (OCC) is applied to the first and second DMRS sequences. A third DMRS sequence, which is associated with a third layer, and a fourth DMRS sequence, which is associated with a fourth layer, are transmitted to the base station. A second OCC is applied to the third and fourth DMRS sequences.