Interpolation Module for OFDM Timing Recovery

Solution Overview

Problem

In Orthogonal Frequency Division Multiplexing (OFDM) receivers, existing timing recovery apparatuses face performance degradation due to high Error Vector Magnitude (EVM) when the fractional interval μk equals 1/2N, leading to a wide spread in constellation diagrams and decreased performance, especially in N times sampling timing recovery.

Innovation Solution

An interpolation module comprising a first symbol inverse unit for 180-degree phase shifting of the digital input signal, a piecewise-parabolic interpolator for interpolating sampling values based on a fractional interval, and a second symbol inverse unit for further phase shifting of the interpolated signal, which modifies the interpolation process to improve timing recovery.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional interpolator is used in timing recovery apparatus, then the device complexity is low, but the Error Vector Magnitude (EVM) becomes high when the fractional interval μk equals 1/2N, resulting in wide constellation diagram spread and decreased performance

Engineering Contradiction:

ImproveError Vector Magnitude (EVM)VSAvoidinterpolator structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The interpolator is divided into multiple functional units: a first symbol inverse unit for 180-degree phase shifting of the digital input signal, a piecewise-parabolic interpolator for interpolating sampling values based on fractional interval, and a second symbol inverse unit for further phase shifting of the interpolated signal. This segmentation allows each unit to perform a specific function optimally, reducing overall EVM while maintaining manageable complexity through modular design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first symbol inverse unit performs 180-degree phase shifting of the digital input signal before the interpolation process. This preliminary action prepares the signal in a form that, when combined with the piecewise-parabolic interpolation and subsequent phase shifting, effectively reduces the Error Vector Magnitude (EVM) when the fractional interval μk equals 1/2N, thereby improving timing recovery performance.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If the fractional interval μk equals 1/2N in N times sampling timing recovery, then the sampling rate is maintained, but the Error Vector Magnitude (EVM) increases causing wide constellation diagram spread

Engineering Contradiction:

Improvesampling rateVSAvoidError Vector Magnitude (EVM)

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention changes the signal parameters through 180-degree phase shifting operations performed by the first and second symbol inverse units. This parameter transformation, combined with the piecewise-parabolic interpolation method, effectively reduces the Error Vector Magnitude (EVM) when the fractional interval μk equals 1/2N, thereby improving constellation diagram convergence while maintaining the N times sampling rate.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional interpolation is used, then the hardware design is simple, but the constellation diagram shows wide spread indicating poor timing recovery performance

Engineering Contradiction:

Improvehardware designVSAvoidtiming recovery precision

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The interpolator is divided into multiple functional units: a first symbol inverse unit for 180-degree phase shifting of the digital input signal, a piecewise-parabolic interpolator for interpolating sampling values based on fractional interval, and a second symbol inverse unit for further phase shifting of the interpolated signal. This segmentation allows each unit to perform a specific function optimally, reducing overall EVM while maintaining manageable complexity through modular design.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first symbol inverse unit performs 180-degree phase shifting of the digital input signal before the interpolation process. This preliminary action prepares the signal in a form that, when combined with the piecewise-parabolic interpolation and subsequent phase shifting, effectively reduces the Error Vector Magnitude (EVM) when the fractional interval μk equals 1/2N, thereby improving timing recovery performance.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS7609795B2Interpolation module, interpolator and methods capable of recovering timing in a timing recovery apparatus

Publication Date: 2009.10.27 VIA TECH INC

AI summary

The invention relates to an interpolation module, an interpolator, and methods capable of recovering timing, and in particular, to an interpolation module, an interpolator, and methods capable of recovering timing in a timing recovery apparatus. An interpolation module capable of recovering timing in a timing recovery apparatus comprises a first symbol inverse unit for shifting phase of a digital input signal by 180 degrees to generate a first inverted signal comprising a plurality of sampling values; an interpolator coupled to the first symbol inverse unit for interpolating the plurality of sampling values according to a fractional interval to generate an interpolated signal, which comprises a plurality of interpolants; and a second symbol inverse unit coupled to the interpolator for shifting phase of the interpolated signal by 180 degrees to output a second inverted signal.