Dual Subcarriers for Phase Tracking in OFDM Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current wireless communication systems using OFDM face challenges in accurately tracking phase corrections due to phase noise and thermal noise, leading to increased transmit power requirements and data rate reductions, as they rely on a limited number of pilot subcarriers for phase tracking.
Innovation Solution
The implementation of a system that utilizes a doubled number of subcarriers, designated as dual subcarriers, for phase tracking, which are protected by a short forward error correction code, allowing for more efficient use of subcarriers and reduced estimation jitter without increasing the total number of subcarriers in a subband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pilot subcarriers is increased to improve phase tracking accuracy, then phase error estimation precision is improved, but the total number of subcarriers in a subband increases
Solution Approach 1:
The patent segments the phase tracking function by separating dual subcarriers (dedicated for phase tracking) from payload subcarriers (for data transmission). This segmentation allows phase tracking to be performed using only the dual subcarriers, improving phase error estimation precision without increasing the total number of subcarriers in the subband, as the dual subcarriers replace rather than supplement the pilot subcarriers.
2Measurement precision
If transmit power is increased to reduce phase correction estimation error, then phase tracking accuracy is improved, but energy consumption increases
Solution Approach 1:
The patent substitutes the traditional approach of increasing transmit power to improve signal-to-noise ratio with a signal processing approach using dual subcarriers. By using two subcarriers per payload subcarrier and applying complex multiplication to combine their phase information, the system achieves better phase tracking accuracy through mathematical processing rather than increasing physical transmit power, thereby reducing energy consumption.
3Measurement precision
If data rate is decreased by selecting lower code rate to reduce phase correction estimation error, then phase tracking accuracy is improved, but productivity decreases
Solution Approach 1:
The patent segments the subcarriers into dual subcarriers for phase tracking and payload subcarriers for data transmission. This segmentation allows the system to maintain high data rates on payload subcarriers while using the dual subcarriers specifically for accurate phase tracking, eliminating the need to reduce overall data rate to improve phase tracking accuracy.
Solution Approach 2:
The dual subcarriers serve multiple functions: they carry phase information for PLL tracking and can also be used for data transmission. This multi-functionality allows the system to achieve both accurate phase tracking and maintain high data rates, as the dual subcarriers provide the necessary phase reference without sacrificing payload data capacity.
4Stability of the object's composition
If loop bandwidth is narrowed to reduce phase error variance, then phase tracking stability is improved, but speed of tracking channel changes decreases
Solution Approach 1:
The patent enhances the feedback mechanism by using dual subcarriers to provide more reliable phase error measurements. The complex multiplication of the two subcarriers produces a combined phase error signal with reduced variance, which feeds back to the PLL with higher accuracy. This improved feedback quality allows the PLL to maintain stability even with wider bandwidth, enabling faster tracking of channel changes.
Data Source
AI summary
Examples of wireless OFDM communication systems are described herein which replace pilot subcarriers having known modulation with lower dual subcarriers. At the transmitter, for each resource block, the bits that modulate a few payload subcarriers are selected and then encoded with a short dual code thereby forming dual systematic bits and dual check bits. Such selected payload subcarriers are designated as upper dual subcarriers and the dual check bits modulate the lower dual subcarriers, At the receiver, for each resource block, the dual subcarriers are phase adjusted, demodulated, decoded using the short dual code, and re-modulated thereby forming the original dual subcarrier modulation without phase noise nor channel impairments. The re-modulated dual subcarriers are compared against the received dual subcarriers for channel estimation or carrier phase-locked-loop purposes. For example, prior-art OFDM systems with 4 pilots per resource block could be replaced with 8 dual subcarriers for a rate 1/2 short dual code. An increase in the number of subcarriers used for channel estimation or carrier phase-locked-loop tracking has less error in the channel estimate or phase estimate. Lower error permits lower payload BER, lower transmit power, or wider PLL bandwidth to track higher Doppler frequency shifts.