Adaptive Frequency Hopping for Unlicensed IoT
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Solution Overview
Problem
Current 3GPP LTE systems operating in unlicensed spectrum face challenges in achieving target maximum coupling loss (MCL) in enhanced Machine Type Communication (eMTC) designs, particularly with legacy Cell-Specific Reference Signal (CRS) designs failing to reach the required signal-to-noise ratio (SNR) for reliable frequency hopping in unlicensed frequency bands.
Innovation Solution
The implementation of an adaptive frequency hopping mechanism with an initial detection signal, comprising a plurality of cell-specific reference signals (CRS) or a Zadoff-Chu sequence, that extends over a minimum of 8 orthogonal frequency division multiplexing (OFDM) symbols to ensure reliable presence detection and meet the target MCL of 130 dB per 20 dBm effective isotropic radiated power (EIRP), along with clear channel assessment (CCA) and extended CCA sensing to determine available hopping frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If legacy Cell-Specific Reference Signal (CRS) designs are used for frequency hopping in unlicensed spectrum, then device complexity is reduced, but the signal-to-noise ratio (SNR) is insufficient to achieve target maximum coupling loss (MCL)
Solution Approach 1:
The patent applies preliminary action by extending the detection signal duration to at least 8 OFDM symbols before frequency hopping begins. This extended initial signal allows User Equipment (UE) to perform clear channel assessment (CCA) and detect the presence of the base station signal in advance, ensuring reliable channel detection and meeting the target MCL of 130 dB per 20 dBm EIRP before actual data transmission starts.
2Reliability
If the detection signal extends over at least 8 OFDM symbols to meet target MCL, then coverage and detection reliability are improved, but transmission time duration increases
Solution Approach 1:
The patent applies segmentation by dividing the transmission structure into distinct segments: an extended initial detection signal segment (at least 8 OFDM symbols) followed by data transmission segments. This segmentation allows the detection function to be separated from the data transmission function, enabling reliable channel assessment without unnecessarily extending the overall communication session duration.
Solution Approach 2:
The patent implements periodic action through frequency hopping, where the system periodically switches between different frequency channels according to a predefined hopping pattern. The extended initial signal establishes the hopping parameters, and subsequent transmissions follow periodic hops across multiple frequencies, improving robustness against interference and fading while managing time distribution across frequency domains.
3Reliability
If clear channel assessment (CCA) and extended CCA sensing are performed to determine available hopping frequencies, then interference avoidance is improved, but channel access delay increases
Solution Approach 1:
The patent applies preliminary action by performing CCA and extended CCA sensing during the extended initial detection signal period (at least 8 OFDM symbols) before actual data transmission begins. This allows the base station to identify available frequency channels and establish the hopping pattern in advance, ensuring interference-free operation while minimizing impact on subsequent data transmission timing.
Data Source
AI summary
Technology for a next generation node B (gNB) operable for frequency hopping in MulteFire communications is disclosed. The gNB can perform a clear channel assessment (CCA) for a selected hopping frequency. The gNB can identify a next hopping frequency in a set of hopping frequencies when an energy detection of the CCA is greater than a selected threshold. The gNB can encode data for a downlink transmission at a selected dwell time of a determined hopping frequency in the set of hopping frequencies when an energy detection of the CCA is less than a selected threshold.