Carrier Tracking Subcarrier Allocation in OFDM Systems
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Solution Overview
Problem
In orthogonal frequency division multiplexing (OFDM) communications systems, small carrier frequency offsets can severely degrade demodulation due to amplitude reduction and loss of orthogonality between subcarriers, leading to inter-carrier interference, which existing methods struggle to compensate effectively.
Innovation Solution
A method where a carrier tracking subcarrier is selected based on performance estimates, with a higher target performance margin than other subcarriers, and additional carrier tracking subcarriers are allocated bits accordingly to generate a frequency offset indicator, allowing for adjustments in the OFDM receiver to compensate for frequency offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pilot tones are used for carrier tracking, then carrier frequency offset can be compensated, but spectral efficiency decreases due to dedicated power allocation for carrier tracking instead of data transmission
Solution Approach 1:
The patent makes data subcarriers serve dual purposes: transmitting data and enabling carrier tracking. By selecting certain data subcarriers with higher signal-to-noise ratio estimates to carry both data and tracking information, the system eliminates the need for dedicated pilot tones while maintaining carrier tracking capability, thus improving spectral efficiency without sacrificing reliability
Solution Approach 2:
The system uses its own data subcarriers to perform carrier tracking instead of relying on external pilot signals. The receiver selects data subcarriers with sufficient quality estimates to serve as tracking references, allowing the system to self-service its carrier synchronization needs using existing resources
2Productivity
If carrier frequency offset is not compensated, then spectral efficiency is maintained, but system performance degrades due to inter-carrier interference from loss of orthogonality
Solution Approach 1:
The patent implements a feedback mechanism where the receiver estimates frequency offset using selected data subcarriers, determines the necessary correction, and feeds this information back to adjust the local oscillator frequency. This closed-loop feedback ensures continuous compensation of frequency offset while maintaining spectral efficiency through efficient resource utilization
Data Source
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AI summary
A carrier tracking technique includes allocating a first number of bits per symbol to a carrier tracking subcarrier of a plurality of subcarriers of an orthogonal frequency division multiplexing (OFDM) signal based on a first target performance margin. The technique includes allocating numbers of bits per symbol to other subcarriers of the plurality of subcarriers based on a second target performance margin.