Multiple-Frequency Beamforming Through Channel Reciprocity

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Solution Overview

Problem

Existing wireless communication systems face challenges in achieving optimal network performance due to coarse channel quantization and latency in codebook-based transmissions, especially in scenarios with stationary or slowly moving wireless devices, leading to throughput loss and uplink control information coverage limitations.

Innovation Solution

Implementing a high-resolution multiple frequency channel reciprocity transform that decouples channel estimation refresh rate from sounding reference signal periodicity, using oversampled DFT and resampling techniques to achieve high spatial resolution and low signaling overhead, enabling reciprocity-based downlink MIMO in FDD and carrier aggregation scenarios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If codebook-based transmissions are used, then implementation simplicity is maintained, but channel quantization precision deteriorates and throughput is reduced

Engineering Contradiction:

Improveimplementation simplicityVSAvoidchannel quantization precision

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent uses channel reciprocity to copy the uplink channel state information to the downlink, eliminating the need for explicit downlink channel estimation and codebook-based quantization. The downlink channel response is obtained by transposing the uplink channel matrix, providing high-resolution channel information without additional signaling overhead.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

Instead of estimating the downlink channel directly using codebook-based methods, the patent inverts the approach by using the uplink channel measurement to infer the downlink channel through reciprocity. This inversion enables precise channel knowledge without the limitations of codebook quantization.

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If codebook-based transmissions are used, then system compatibility is maintained, but feedback latency increases and network performance deteriorates

Engineering Contradiction:

Improvesystem compatibilityVSAvoidfeedback latency

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent performs channel estimation in advance using uplink sounding reference signals before the actual downlink transmission. By pre-obtaining the channel state information through uplink measurements and storing it for later use, the system eliminates feedback latency while maintaining compatibility with existing 3GPP standards.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the uplink channel measurement to serve the downlink channel estimation needs through reciprocity. The uplink transmission automatically provides information about the downlink channel, making the system self-sufficient and eliminating the need for separate downlink feedback mechanisms.

Inventive Principle:

Principle #25Self-service

3Productivity

If Type-II CSI-RS feedback is used, then downlink capacity is improved, but uplink signaling overhead increases

Engineering Contradiction:

Improvedownlink capacityVSAvoiduplink signaling overhead

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The patent copies the channel state information from the uplink to the downlink through reciprocity, eliminating the need for extensive Type-II CSI-RS feedback in the uplink. The downlink channel response is derived by transposing the uplink channel matrix, providing high-capacity downlink transmission without increasing uplink signaling overhead.

Inventive Principle:

Principle #26Copying

4Device complexity

If existing channel reciprocity algorithms are used, then computational complexity is reduced, but spatial resolution deteriorates and performance degrades in rich scattering environments

Engineering Contradiction:

Improvecomputational complexityVSAvoidspatial resolution

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces complex iterative optimization algorithms with a direct matrix transposition approach based on channel reciprocity. This substitution maintains low computational complexity while achieving high spatial resolution through the inherent properties of the channel matrix transpose operation, outperforming existing algorithms in rich scattering environments.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20250300859A1Channel reciprocity transform for multiple frequency beam-forming

Publication Date: 2025.09.25 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method and network node for implementing a channel reciprocity transform for multiple frequency beamforming are disclosed. According to some aspects, a method in a network node includes determining an average angular spectral density (ASD) based at least in part on a Fast Fourier transform (FFT) of an uplink received vector for each of multiple subcarriers from at least one antenna polarization. The method includes resampling the average ASD at a wavelength for a subcarrier of the multiple subcarriers in a downlink sub-band. The method also includes determining a frequency-transposed channel estimate for the downlink sub-band based at least in part on an inverse Fast Fourier transform (IFFT) of the resampled average ASD. The method also includes beamforming a signal to the WD in the downlink sub-band using the determined frequency-transposed channel estimate.