Signal Precoding via Spatial and Frequency Domain Vector Segmentation
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Solution Overview
Problem
Current NR systems face high implementation complexity when transmitting with multiple beamformers simultaneously, particularly due to the CSI-RS port to resource element and OFDM symbol mapping structure.
Innovation Solution
The method involves determining spatial and frequency domain precoding vectors based on uplink measurements, applying these vectors to CSI-RS signals to reduce frequency selectivity and implementation complexity. This includes grouping ports with common beams but different delays for transmission in a single OFDM symbol, using a single wideband precoding vector across all ports in each symbol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple beamformers are transmitted simultaneously with frequency-selective precoding, then channel matching performance is improved, but implementation complexity increases significantly
Solution Approach 1:
The precoding function is segmented into two independent parts: a wideband spatial precoder matrix W1 that remains constant across frequency, and a frequency-selective precoder matrix W2 that varies per subband. This segmentation allows the system to achieve frequency-selective channel matching while reducing overall complexity by separating the complex frequency-dependent operations from the spatial beamforming operations.
Solution Approach 2:
The frequency-selective component W2 is extracted from the overall precoding operation and applied separately in the frequency domain before the spatial precoding W1. This extraction allows the frequency-selective adjustments to be made independently, simplifying the implementation by avoiding the need for full frequency-selective precoder matrices while maintaining channel matching performance.
2Adaptability or versatility
If frequency-selective precoder matrices are used for each subband, then channel variations are matched, but processing complexity increases
Solution Approach 1:
Instead of applying full frequency-selective precoding across all frequency bands, the system applies local frequency-selective adjustments only within each subband using the simplified matrix W2. This local quality approach allows the system to adapt to channel variations in each subband independently while avoiding the computational burden of global frequency-selective precoding.
3Device complexity
If wideband precoding is used across the entire bandwidth, then implementation complexity is reduced, but frequency selectivity of the channel is not matched
Solution Approach 1:
The precoding structure uses asymmetry by applying different levels of frequency selectivity to different parts of the signal processing chain. The spatial precoder W1 is wideband and frequency-independent, while the precoder W2 is frequency-selective but spatially simple. This asymmetric approach balances complexity and performance by applying frequency selectivity only where necessary.
Data Source
AI summary
A method (700) for precoding a signal. The method includes determining (s702), based on uplink, UL, measurements, a spatial domain (SD) precoding vector and a frequency domain (FD) precoding vector for a downlink (DL) transmission of the signal. The method also includes applying (s704) the FD precoding vector to the signal over subcarriers for carrying the signal, thus producing a modified signal. The method further includes applying (s706) the SD precoding vector to the modified signal to produce a precoded signal, wherein the SD precoding vector is common for all said subcarriers in one symbol.