LTE Reference Signal Time Slot Swapping for Interference Reduction

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Solution Overview

Problem

In LTE communications networks, reference signals from different user equipments interfere with each other, leading to degraded channel estimation accuracy and reduced scheduling flexibility, especially in scenarios with user equipments from different releases and deployments like HetNet, where traditional interference randomization techniques like Sequence Hopping (SGH) are ineffective.

Innovation Solution

The solution involves time-swapping and conjugate operation of reference signals across slots for user equipments, allowing perfect orthogonality and enabling co-scheduling of user equipments from different releases without disabling SGH, thereby reducing interference and enhancing scheduling flexibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If traditional interference randomization techniques like Sequence Hopping (SGH) are used, then interference between reference signals is reduced, but orthogonality is not perfect and scheduling flexibility is limited

Engineering Contradiction:

Improveinterference between reference signalsVSAvoidchannel estimation accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent applies inversion by swapping the time slots of reference signals between two user equipments. Instead of using the same time slot allocation, the first UE's reference signal in slot n is swapped with the second UE's reference signal in slot n+1, creating perfect orthogonality and eliminating interference while maintaining scheduling flexibility

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the time slot parameter assignment for reference signals dynamically. By configuring different time slot allocations for different UE releases and applying the swapping mechanism, the system achieves perfect orthogonality across multiple parameters (time slot, cyclic shift, orthogonal cover code) without disabling SGH

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If user equipments from different releases are co-scheduled, then scheduling flexibility is improved, but reference signal orthogonality is degraded

Engineering Contradiction:

Improvescheduling flexibilityVSAvoidreference signal orthogonality

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent applies local quality by treating different UE releases with different reference signal configurations. Rel-8/9/10 UEs use one configuration while Rel-11 UEs use another, with the swapping mechanism applied selectively to maintain orthogonality between different release types while allowing co-scheduling

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The time slot swapping mechanism inverts the traditional approach by assigning reference signals from different releases to complementary time slots, ensuring that when one UE transmits in slot n, the other transmits in slot n+1, achieving perfect orthogonality across release boundaries

Inventive Principle:

Principle #13The other way round (Inversion)

3Object-affected harmful factors

If Sequence Hopping (SGH) is disabled to achieve orthogonality, then reference signal interference is reduced, but implementation complexity increases and scheduling flexibility is lost

Engineering Contradiction:

Improvereference signal interferenceVSAvoidimplementation complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent maintains SGH enabled by applying the swapping mechanism instead of disabling it. The time slot assignment is inverted/swapped between UEs, which achieves orthogonality while preserving the SGH functionality and avoiding the complexity of disabling it

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The swapping mechanism serves multiple functions simultaneously: it maintains SGH enabled status, achieves perfect orthogonality, supports co-scheduling of different releases, and reduces interference. This multi-functionality avoids the need to disable SGH and reduces overall system complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS9100961B2Methods and devices for handling reference signals in a communications network

Publication Date: 2015.08.04 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Methods in a first user equipment are provided for handling reference signals in a communications network. The user equipment is configured to receive a signal from a base station. The signal comprises a first slot and a second slot. The first slot comprises a first reference signal and the second slot comprises a second reference signal. The user equipment receives, from the base station, information that the first reference signal should be assigned to the second slot and that the second reference signal should be assigned to the first slot. The user equipment assigns the first reference signal to the second slot and the second reference signal to the first slot. The first user equipment processes the first reference signal assigned to the second slot and the second reference signal assigned to the first slot.