DC Offset Correction for Local Oscillator Leakage in Wireless Transceivers

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

In single carrier frequency domain equalization (SC-FDE) systems, local oscillator (LO) leakage at the transmitter causes direct current (DC) offset in received signals, leading to reduced signal-to-noise ratio and interference from carrier frequency and phase noise, which are difficult to correct due to block processing and discrete carrier phase jumps.

Innovation Solution

The receiving device measures and communicates DC offset corrections to the transmitting device, allowing it to apply corrective biases to the outbound signals, thereby canceling LO leakage and reducing its impact on the received signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If direct conversion transceiver architecture is used, then computational efficiency is improved, but local oscillator leakage generates DC offset that reduces signal-to-noise ratio

Engineering Contradiction:

Improvecomputational efficiencyVSAvoidDC offset signal

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where the receiving device measures the DC offset in received signals and communicates correction information back to the transmitting device. The transmitting device then adjusts its local oscillator or signal generation based on this feedback to reduce the DC offset at the receiver, thereby resolving the contradiction between computational efficiency and DC offset reduction.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes parameters of the transmitting device's signal generation based on measured DC offset characteristics. By adjusting parameters such as local oscillator frequency or phase, or applying digital correction to the transmitted signal, the system reduces the DC offset component while maintaining the computational efficiency of direct conversion architecture.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If block processing is used in SC-FDE systems, then channel equalization efficiency is improved, but carrier phase jumps between blocks make DC offset correction difficult

Engineering Contradiction:

Improvechannel equalization efficiencyVSAvoidDC offset correction complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent applies DC offset correction to the transmitted signal before modulation and transmission. By pre-compensating the signal at the transmitting device based on feedback information, the system avoids the complexity of correcting DC offset after block processing and carrier phase recovery at the receiver, thus maintaining both equalization efficiency and simplifying correction complexity.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If carrier recovery PLL is positioned after frequency-domain processing, then carrier frequency offset correction is achieved, but DC offset signal becomes jittery low-frequency signal that cannot be removed

Engineering Contradiction:

Improvecarrier frequency offset correctionVSAvoidjittery DC offset signal

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

Instead of attempting to remove DC offset at the receiver after carrier recovery (where it becomes a jittery low-frequency signal), the patent inverts the approach by removing DC offset at the transmitter through pre-compensation. This is achieved by applying correction based on feedback information to the transmitted signal before it causes DC offset issues at the receiver, thereby eliminating the harmful effect before it manifests.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS9166839B2Systems and methods for reducing effects of local oscillator leakage

Publication Date: 2015.10.20 AVIAT U S

AI summary

According to some embodiments, a receiving device: receives a radio frequency (RF) signal from a transmitting device over a wireless channel; performs a channel estimation of the wireless channel based on the RF signal; obtains a direct current (DC) bin measurement based on the channel estimation; determines a direct current (DC) offset correction based on the DC bin measurement; and sending the DC offset correction to the transmitting device via a local transmitter. The transmitting device: receives the DC offset correction information from the receiving device over a first wireless channel; receives data to be transmitted to the receiving device, where the DC offset correction information describing the DC offset correction; applies the DC offset correction to a transient signal that is based on the data; converts the transient signal to an RF signal; and transmits the RF signal to the receiving device over a second wireless channel.