HARQ ACK/NACK Signal Modulation in NB-IoT
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Solution Overview
Problem
Conventional Hybrid Automatic Repeat reQuest (HARQ) operations are inefficient for Narrowband Internet of Things (NB-IoT) communication, leading to considerable time delays in data transmission and reception.
Innovation Solution
A method for transmitting HARQ ACK/NACK signals using Quadrature Phase Shift Keying (QPSK) modulation, where the first HARQ ACK/NACK signal changes only one of the I or Q signal's sign, and the second HARQ ACK/NACK signal changes both signs, with specific offset configurations to avoid overlapping subframes and additional phase rotation for Binary Phase Shift Keying (BPSK) modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional HARQ operation is used in NB-IoT communication, then the system maintains compatibility with existing LTE protocols, but time delays in data transmission and reception increase significantly
Solution Approach 1:
The patent changes the modulation parameter from conventional BPSK to QPSK for HARQ ACK/NACK signals. This parameter change allows two bits of information to be transmitted per symbol, effectively halving the time required for HARQ feedback transmission while maintaining protocol compatibility through the standardized QPSK modulation scheme.
Solution Approach 2:
The patent segments the HARQ feedback information into two separate HARQ processes, each with its own ACK/NACK signal. By mapping these to different quadrants of the QPSK constellation, the system can transmit multiple HARQ acknowledgments simultaneously, reducing overall transmission time while maintaining compatibility with existing HARQ process structures.
2Loss of time
If QPSK modulation is used for HARQ ACK/NACK signals, then transmission time is reduced, but signal complexity increases
Solution Approach 1:
The patent applies preliminary phase rotation to the QPSK constellation based on the HARQ process ID and redundancy version. This preliminary action pre-organizes the signal mapping rules, allowing the UE and base station to independently determine the correct constellation interpretation without additional signaling, thus reducing implementation complexity while maintaining fast transmission.
Solution Approach 2:
The patent introduces phase rotation as an intermediary mechanism that maps HARQ process information to specific QPSK quadrants. This intermediary layer simplifies the relationship between multiple HARQ processes and the QPSK constellation, making the system manageable despite the increased modulation complexity by providing a systematic mapping rule.
3Productivity
If multiple HARQ processes are multiplexed using QPSK constellation, then throughput is enhanced, but signal differentiation difficulty increases
Solution Approach 1:
The patent applies asymmetric phase rotation patterns where different HARQ processes are mapped to different quadrants of the QPSK constellation through specific phase rotations (e.g., 0°, 90°, 180°, 270°). This asymmetric mapping creates distinct signal characteristics for each HARQ process, making differentiation easier despite the increased throughput demand.
Solution Approach 2:
The patent incorporates feedback mechanisms where the base station and UE exchange information about the phase rotation applied to each HARQ process. This feedback loop ensures that both ends can correctly interpret the QPSK signals for multiple HARQ processes, reducing detection difficulty while maintaining high throughput through efficient multiplexing.
Data Source
AI summary
A disclosure of the present specification provides a method for transmitting a hybrid automatic repeat request (HARQ) ACK/NACK signal in a narrowband Internet of things (NB-IoT) communication. The method may comprise a step of modulating at least one of a first and a second HARQ ACK/NACK signal by two HARQ processes. The step of modulating may comprise a step of mapping at least one of the first and the second HARQ ACK/NACK signal onto a constellation having a quadrature phase shift keying (QPSK) form. The first HARQ ACK/NACK signal may be a signal generated by a first HARQ process for a first downlink data through a first narrowband physical downlink shared channel (NPDSCH). The second HARQ ACK/NACK signal may be a signal generated by a second HARQ process for a second downlink data through a second NPDSCH.