NPRACH Receiver Equalizer for Inter-Carrier Interference Removal
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Solution Overview
Problem
The challenge is to reconstruct Narrow-band Internet of Things (NB-IoT) physical random-access channel (NPRACH) signals without a compatible NB-IoT-compatible lower physical layer (LPHY), which is typically designed for LTE or 5G-NR signals, due to the need for additional processing like aliasing filters and decimators.
Innovation Solution
An additional processing module, functioning as an equalizer, is introduced between the existing LTE-LPHY or 5G-NR-LPHY and the NB-IoT PRACH receiver to remove intercarrier interference and enable the NB-IoT PRACH detector to function with LPHYs that only support LTE or 5G-NR operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an additional processing module (equalizer) is introduced to enable NB-IoT PRACH detection with LTE-LPHY, then NB-IoT signal reconstruction capability is achieved, but device complexity increases
Solution Approach 1:
An equalizer is introduced as an intermediary processing module between the LTE-LPHY and NB-IoT PRACH detector. This equalizer compensates for the mismatch between LTE and NB-IoT signal processing by removing inter-carrier interference and adapting the signal characteristics, enabling the detector to process NB-IoT PRACH signals without requiring a dedicated NB-IoT-LPHY implementation.
2Ease of manufacture
If LTE-LPHY is used to process NB-IoT signals, then existing infrastructure can be utilized, but signal processing accuracy deteriorates due to intercarrier interference
Solution Approach 1:
The equalizer is designed to specifically target and remove the inter-carrier interference that arises when LTE-LPHY processes NB-IoT signals. By identifying the characteristic interference patterns caused by the FFT length mismatch and subcarrier subset transmission, the equalizer converts this harmful interference into a correctable distortion, thereby restoring signal detection accuracy while maintaining infrastructure compatibility.
3Productivity
If a different IFFT length is used at transmitter compared to FFT length at receiver, then spectral efficiency is improved, but signal reconstruction difficulty increases
Solution Approach 1:
The system deliberately uses different IFFT lengths at the transmitter (e.g., 8192) compared to the FFT length at the receiver (e.g., 2048 for LTE-LPHY). This parameter mismatch enables spectral efficiency improvements by allowing the transmitter to utilize more subcarriers while the receiver processes only a subset. The equalizer compensates for the resulting signal distortion, making the parameter change viable for practical deployment.
Data Source
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AI summary
A method of Narrow-band Internet of Things physical random-access channel (NPRACH) communication includes: transmitting, from a user equipment (UE), a Narrow-band Internet of Things (NB-IoT) Orthogonal Frequency-Division Multiple Access (OFDMA) symbol using a transmit inverse fast Fourier transform (Tx-IFFT) having a first length; processing, at lower physical layer (LPHY) of a baseband unit (BBU), the NB-IoT OFDMA symbol using a receive fast Fourier transform (Rx-FFT) having a second length different from the first length to generate an Rx-FFT output; sending, from the LPHY of the BBU to upper physical layer (UPHY) of the BBU, a selected number of values of the Rx-FFT output corresponding to desired resources block in the NB-IoT OFDMA symbol; filtering, at the UPHY, intercarrier interference (ICI) from the selected number of values of the Rx-FFT output; and reconstructing, at the UPHY, the NB-IoT OFDMA symbol.