Preamble Detection Using Time-Domain Windowing for False Alarm Reduction
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Solution Overview
Problem
In LTE compliant wireless communication systems, the detection of preambles in received signals is hindered by high false alarm rates due to discontinuities and high-power other-channel signals, which existing filtering techniques alone cannot adequately address, especially when the power difference is significant, such as 35 dB.
Innovation Solution
A method and apparatus that preprocess and post-process the received signal using time-domain window functions to smooth discontinuities and suppress spikes, respectively, in conjunction with filtering to isolate the preamble signal from other-channel signals, thereby reducing false alarm rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If filtering techniques are used to extract the PRACH signal from the uplink signal, then the power levels of other-channel signals are reduced, but the false alarm rate remains high when the power level difference is substantial (e.g., 35 dB)
Solution Approach 1:
The patent applies preliminary action by pre-processing the received signal before filtering. Specifically, a time-domain window function is applied to smooth discontinuities at symbol boundaries of other-channel signals before the filtering operation. This preliminary smoothing reduces the impact of high-power other-channel signals on the false alarm rate during subsequent correlation detection, addressing the limitation of conventional filtering alone.
Solution Approach 2:
The patent introduces an intermediary processing step between the received signal and the filtering operation. The time-domain window function acts as an intermediary that modifies the signal characteristics before filtering. This intermediary step smooths out discontinuities and reduces spurious correlations, thereby reducing false alarm rates without requiring complex post-filtering operations.
2Ease of operation
If conventional filtering is applied to isolate the preamble signal, then the preamble detection is simplified, but discontinuities between successive time-domain symbols cause high false alarm rates
Solution Approach 1:
The patent applies preliminary action by pre-processing the received signal before filtering. Specifically, a time-domain window function is applied to smooth discontinuities at symbol boundaries of other-channel signals before the filtering operation. This preliminary smoothing reduces the impact of high-power other-channel signals on the false alarm rate during subsequent correlation detection, addressing the limitation of conventional filtering alone.
Solution Approach 2:
The patent changes the signal parameters by applying a time-domain window function that modifies the temporal characteristics of the received signal. The window function smooths discontinuities and changes the signal's frequency content, making the preamble detection more robust against false alarms from other-channel signals while maintaining detection simplicity.
3Use of energy by moving object
If the power level difference between PRACH and other-channel signals is large (e.g., 35 dB), then the PRACH signal can be detected with minimal power, but filtering techniques alone are insufficient to reduce false alarm rates
Solution Approach 1:
The patent applies preliminary action by pre-processing the received signal before filtering. Specifically, a time-domain window function is applied to smooth discontinuities at symbol boundaries of other-channel signals before the filtering operation. This preliminary smoothing reduces the impact of high-power other-channel signals on the false alarm rate during subsequent correlation detection, addressing the limitation of conventional filtering alone.
Solution Approach 2:
The patent converts the harmful effect of high-power other-channel signals into a beneficial outcome. By applying the time-domain window function, the discontinuities caused by these high-power signals are smoothed, transforming them from sources of false alarms into less problematic signal components. This allows the system to maintain low false alarm rates even with significant power differences between signal types.
Data Source
AI summary
This invention discloses a method and an apparatus for reducing false alarm rate in preamble detection due to discontinuities between successive symbols in a received signal. The invention is usable in, e.g., a LTE compliant system. In one embodiment, the apparatus includes a filter for filtering the received signal to yield a filtered signal, and a correlator for correlating the filtered signal with a predetermined preamble. The apparatus further comprises a first multiplier for modifying the received signal before it is filtered, or a second multiplier for modifying the filtered signal before it is correlated, or both. The first multiplier multiplies the received signal with a first time-domain window function configured to substantially smooth discontinuities at symbol boundaries in the received signal. The second multiplier multiplies the filtered signal with a second time-domain window function configured to substantially suppress spikes present in the filtered signal around the symbol boundaries.