Phase Coherence Maintenance for Frequency Offset Estimation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In LTE wireless systems, existing methods for estimating frequency offsets in SC-FDMA uplink transmissions are inadequate, especially in small-cell scenarios where reduced DMRS patterns are used, leading to uncertainty in phase coherence between subframes and affecting channel estimation and spectral efficiency.

Innovation Solution

The technique involves maintaining phase coherence between reference symbol transmissions in different subframes by selectively refraining from discontinuous transmission and using multi-shot SRS or TTI bundling to enable accurate frequency offset estimation across multiple subframes, ensuring reliable channel estimation and compensation for frequency offsets.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If reduced DMRS patterns are used in small-cell scenarios, then spectral efficiency is improved and overhead is reduced, but phase coherence between subframes becomes uncertain and frequency offset estimation becomes inadequate

Engineering Contradiction:

Improvespectral efficiencyVSAvoidfrequency offset estimation accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by transmitting Sounding Reference Signals (SRS) in advance before actual data transmission. These SRS are used to pre-estimate the frequency offset, which then compensates for the insufficient phase coherence information that would otherwise be available when using reduced DMRS patterns. This preliminary measurement enables accurate frequency offset estimation even when DMRS overhead is minimized.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces SRS as an intermediary mechanism to bridge the gap caused by reduced DMRS patterns. The SRS serve as a separate reference signal specifically designed for frequency offset estimation, mediating the trade-off between spectral efficiency and measurement precision. By using SRS as an intermediate step, the system can achieve accurate frequency offset estimation without requiring full DMRS overhead during data transmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If discontinuous transmission is used to reduce overhead, then resource utilization is improved, but phase coherence between reference symbol transmissions is lost

Engineering Contradiction:

Improvetransmission overheadVSAvoidphase coherence

Core Design Contradiction:

Loss of energyVSStability of the object's composition

Solution Approach 1:

The system performs preliminary frequency offset estimation using SRS transmitted before the actual data transmission. This preliminary action captures the frequency offset information while phase coherence is still maintainable, allowing the system to then use discontinuous transmission for the actual data without losing the previously estimated frequency offset information.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements periodic SRS transmission at specific intervals (e.g., every 2, 4, or 8 subframes) to maintain frequency offset estimation capability. This periodic action ensures that frequency offset information is refreshed regularly, compensating for the phase coherence loss that occurs during discontinuous transmission periods.

Inventive Principle:

Principle #19Periodic action

3Productivity

If DMRS symbols are dropped to reduce overhead, then spectral efficiency increases, but channel estimation performance deteriorates

Engineering Contradiction:

Improvespectral efficiencyVSAvoidchannel estimation performance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent uses SRS as an intermediary to provide the reference signal information needed for reliable channel estimation when DMRS symbols are dropped. The SRS, transmitted with full overhead, serve as a substitute reference that enables accurate channel estimation without requiring the presence of DMRS symbols in every subframe.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system performs preliminary channel characterization using SRS transmissions before actual data transmission. This preliminary channel estimation, obtained when full reference signals are available, is then used to guide the reduced DMRS operation, ensuring that channel estimation performance is maintained even when DMRS overhead is reduced.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9942017B2Maintaining phase coherence for frequency offset estimation

Publication Date: 2018.04.10 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Techniques for facilitating and performing frequency-offset estimation are disclosed. The disclosed techniques include methods and apparatus for maintaining phase coherence among reference symbols on different transmission-time intervals (TTI) for an accurate estimation of frequency offset. Corresponding techniques utilize channel estimation or measurements of channel-related parameters based on multiple reference symbols belonging to different TTIs. An example method in a radio transceiver for facilitating frequency offset estimation at a remote receiver begins with determining that phase coherence between reference symbol transmissions in a first TTI and a second TTI is required. The radio transceiver selectively maintains phase coherence between reference symbol transmissions in the first and second TTIs, in response to said determining. The radio transceiver then transmits during at least part of a third TTI, following the second TTI, without maintaining phase coherence to the reference symbol transmissions in the first and second TTIs.