OFDM Receiver Autocorrelation for Carrier Frequency Offset
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Solution Overview
Problem
OFDM WLAN systems face performance degradation due to carrier frequency offset, leading to loss of subcarrier orthogonality and impaired signal reception.
Innovation Solution
The implementation of an OFDM receiver system that includes receiving modulated signals through multiple antennas, generating autocorrelated signals, determining signal strength, disabling antennas with low signal strength, combining weighted autocorrelated signals, and demodulating the combined signal to assess the wireless channel state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carrier frequency offset is present in OFDM WLAN systems, then signal reception is impaired and subcarrier orthogonality is lost, but system performance degrades
Solution Approach 1:
The patent applies preliminary action by performing autocorrelation operations on received OFDM signals before demodulation to detect and correct carrier frequency offset. The system calculates autocorrelation values of pilot symbols or data symbols in advance, uses these to estimate frequency offset, and compensates for it before the main signal processing, thereby preventing orthogonality loss and performance degradation
2Reliability
If multiple antennas are used to receive OFDM signals, then signal reception robustness is improved, but system complexity increases
Solution Approach 1:
The patent merges the processing of multiple antenna signals by combining autocorrelation results from all antennas to jointly estimate carrier frequency offset. Instead of processing each antenna independently, the system combines the received signals or their autocorrelation values, performs a unified frequency offset estimation, and applies single compensation to all channels, thereby reducing computational complexity while maintaining diversity gain
Solution Approach 2:
The system uses the signal itself to perform frequency offset detection through autocorrelation operations on the received OFDM symbols. The received signals contain embedded pilot symbols or data symbols that, when autocorrelated with themselves, provide direct information about frequency offset without requiring external reference signals or additional hardware, enabling the system to self-diagnose and self-correct frequency errors
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances channel synchronization and detection, improving the overall performance of OFDM WLAN systems by mitigating the effects of carrier frequency offset and ensuring reliable data transmission.
Implementation Method 1
The signals are sent to autocorrelators 16-1, 16-2, . . . , and 16-n (referred to collectively as autocorrelators 16). The autocorrelators 16 find repeating patterns in a signal, such as determining the presence of a periodic signal which has been buried under noise.
Data Source
AI summary
A method for performing a clear channel assessment to determine whether a wireless channel is clear for transmission of a transmit signal. The method includes receiving, through the wireless channel, a plurality of signals, wherein the plurality of signals are respectively received via a plurality of antennas of the receiver determining a signal strength of each of the plurality of signals, autocorrelating the plurality of signals to respectively generate a plurality of autocorrelated signals, weighting each autocorrelated signal of the plurality of autocorrelated signals based on one or more of the signal strengths determined for each of the plurality of signals, combining each autocorrelated signal, as weighted, to generate a combined signal, demodulating the combined signal, and determining, based at least in part on the demodulation of the combined signal, whether the wireless channel is clear for the transmission of the transmit signal onto the wireless channel.