Double Difference Phase Detection for OFDM Signal Presence
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Solution Overview
Problem
Conventional OFDM communications systems face challenges in detecting transmitted signals at remote receivers, especially in noisy environments, due to asynchronous signal arrival and difficulty in distinguishing signal presence from noise.
Innovation Solution
The system employs a preamble field with a known data pattern pre-coded to generate complex modulation values, using FFT and IFFT algorithms to detect signal presence by calculating phase differences and comparing them to expected phases, thus being insensitive to phase offsets and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal power comparison at different frequencies is used to detect sub-carrier presence, then signal detection capability is improved, but additional bandwidth must be allocated and noise discrimination becomes difficult
Solution Approach 1:
The patent applies preliminary action by pre-coding the preamble data pattern before transmission. The receiver uses this pre-coded pattern to generate expected phase values and compares them with detected phases, enabling signal detection before full signal processing occurs. This resolves the contradiction by providing accurate detection without requiring additional bandwidth allocation.
Solution Approach 2:
The patent changes the detection parameter from signal power comparison to phase difference comparison. By computing phase differences between adjacent sub-carriers and comparing against expected phase differences derived from the pre-coded preamble, the system achieves reliable signal detection in noisy environments without requiring additional bandwidth, thus resolving the technical contradiction.
2Ease of operation
If conventional power-based detection is used in noisy environments, then detection simplicity is maintained, but noise discrimination becomes difficult and detection reliability decreases
Solution Approach 1:
The patent changes the detection parameter from signal power to phase difference. By computing phase differences between adjacent sub-carriers and comparing them against expected phase differences from the pre-coded preamble pattern, the system achieves reliable noise discrimination while maintaining operational simplicity. The phase-based approach is inherently more robust to noise than power-based methods.
Solution Approach 2:
The patent introduces the pre-coded preamble data pattern as an intermediary reference. This known pattern serves as a mediator between transmission and detection, providing a reliable reference for phase comparison that enables accurate signal detection even in noisy environments, resolving the contradiction between simplicity and reliability.
3Adaptability or versatility
If remote reception of transmitted signals is implemented, then communication range is improved, but signal arrival becomes asynchronous and detection difficulty increases
Solution Approach 1:
The patent applies preliminary action by pre-coding the preamble data pattern at the transmitter before transmission. The receiver uses this pre-coded pattern to generate expected phase values and compares them with detected phases, enabling reliable detection of asynchronous signals. This resolves the contradiction by providing a reference framework that works regardless of signal arrival timing.
Solution Approach 2:
The patent transitions from time-synchronization-based detection to phase-difference-based detection. By operating in the phase domain rather than relying on precise time alignment, the system can detect asynchronous signals from remote transmitters, resolving the contradiction between extended communication range and detection difficulty.
Data Source
AI summary
A method that allows a digital communications system to detect the presence of transmitted messages in noisy environments. The system includes an OFDM transmitter and an OFDM receiver. The OFDM transmitter converts a digital signal to be transmitted to a plurality of sub-signals, each corresponding to a respective sub-carrier frequency. The signal is a packet including a preamble field having a known data pattern. The transmitter pre-codes the preamble data pattern, maps the data to corresponding phase information, converts the sub-signals to the time domain, and converts the sub-signals to analog form for subsequent transmission. The OFDM receiver receives the transmitted sub-signals, converts the sub-signals to digital form, converts the sub-signals to the frequency domain, and subjects the sub-signals to preamble detection processing to detect the signals' presence. By pre-coding the preamble data pattern and defining the received sub-signals in terms of the phase difference between adjacent sub-carriers, the detection of the transmitted messages can be performed in a manner that is insensitive to phase offset.