FDD Uplink Frequency Shifting for LTE-NR Grid Alignment

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Solution Overview

Problem

Existing wireless communication networks face challenges in efficiently coexisting on the same bandwidth due to misaligned subcarrier grids and interference issues between different communication technologies like LTE and NR, particularly when using Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

Innovation Solution

Implementing a frequency shift in the uplink transmissions for the second wireless communication network, such as NR, to align its subcarrier grid with the first network, like LTE, by adjusting the duplex distance or applying a ½ subcarrier shift in baseband, especially for FDD, while avoiding shifts for TDD to maintain resource efficiency and minimize interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a frequency shift is applied to align subcarrier grids for FDD, then interference between networks is reduced, but device complexity increases due to additional signal processing

Engineering Contradiction:

Improveinterference between networksVSAvoidsignal processing complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies a frequency shift parameter change to the uplink transmissions in the second network, specifically shifting by ½ subcarrier (7.5 kHz) to align the subcarrier grid with the first network. This parameter modification directly reduces interference between coexisting networks while maintaining compatibility with DFTS-OFDM waveform characteristics.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of shifting the downlink or applying complex filtering to remove interference, the patent inverts the approach by shifting the uplink transmissions. This反向 approach simplifies the solution by modifying the transmission side rather than the reception side, reducing overall system complexity.

Inventive Principle:

Principle #13The other way round (Inversion)

2Productivity

If subcarrier grid alignment is implemented for coexisting networks, then resource efficiency improves, but modulation quality may deteriorate due to frequency shifting

Engineering Contradiction:

Improveresource efficiencyVSAvoidmodulation quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent carefully selects a ½ subcarrier shift (7.5 kHz) as the optimal parameter change that achieves grid alignment while minimizing impact on modulation quality. This specific parameter value balances resource efficiency gains against potential degradation in modulation accuracy.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies a partial shift (½ subcarrier rather than full subcarrier shift) to achieve sufficient alignment for resource efficiency while avoiding excessive frequency displacement that would severely impact modulation quality. This partial action optimizes the trade-off between the two competing requirements.

Inventive Principle:

Principle #16Partial or excessive action

3Stability of the object's composition

If frequency shift is applied to uplink transmissions, then subcarrier grid alignment is achieved, but PAPR characteristics of DFTS-OFDM waveform are degraded

Engineering Contradiction:

Improvesubcarrier grid alignmentVSAvoidpower amplifier efficiency

Core Design Contradiction:

Stability of the object's compositionVSUse of energy by moving object

Solution Approach 1:

The patent modifies the frequency parameter of uplink transmissions by ½ subcarrier to achieve grid alignment, accepting a controlled degradation in PAPR characteristics. This parameter change enables coexistence with the first network while maintaining reasonable power amplifier efficiency.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potential harm of PAPR degradation into a benefit by demonstrating that the ½ subcarrier shift, while affecting PAPR, enables successful network coexistence and resource efficiency improvements that outweigh the power amplifier efficiency loss.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS12362973B2Radio network node, wireless device and methods performed therein for handling communication in a wireless communication network

Publication Date: 2025.07.15 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Embodiments herein disclose e.g. a method performed by a wireless device (10) for handling communication for the wireless device in a second wireless communication network. The second wireless communication network coexists with a first wireless communication network on a same bandwidth in frequency, wherein the first wireless communication network applies a first shift in frequency in uplink transmissions. The wireless device receives from a radio network node (12, 13), an indication indicating application of a second shift in frequency to uplink transmissions in case the second wireless communication network uses Frequency Division Duplex (FDD). The wireless device further applies the second shift in frequency to uplink transmissions, wherein the second shift defines a shift in frequency to a subcarrier relative to a subcarrier grid of the second wireless communication network or a shift in frequency to the subcarrier grid of the second wireless communication network.