DMRS Sequence Generation for 5G PAPR Reduction
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Solution Overview
Problem
5G wireless systems face challenges in reducing peak to average power ratios (PAPR) due to high PAPR in OFDM systems, which can lead to out-of-band emissions and inefficient power amplification, particularly in demodulation reference signals (DMRS) when symbols are repeated for ports 2 and 3.
Innovation Solution
Modifying the DMRS sequence generation to depend on the transmission layer/rank/port, generating different random sequences for each port to avoid repetition, thereby reducing PAPR and aligning it with data PAPR levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DMRS symbols are repeated for ports 2 and 3, then channel estimation reliability is improved, but peak to average power ratio increases causing power amplifier saturation
Solution Approach 1:
The patent applies local quality by making the DMRS sequence generation port-dependent. Specifically, ports 0 and 1 use one initialization seed while ports 2 and 3 use a different initialization seed, creating locally differentiated sequence properties. This allows each port to have optimized sequence characteristics that reduce PAPR while maintaining the needed channel estimation reliability for that specific port.
Solution Approach 2:
The patent changes the initialization parameter (seed) of the pseudo-random sequence generator based on the port number. By modifying the seed parameter from a universal value to port-specific values, the patent transforms the DMRS sequences to have different statistical properties, thereby reducing peak power occurrences while preserving the correlation properties needed for reliable channel estimation.
2Area of stationary object
If DMRS symbols are repeated for ports 2 and 3, then coverage is improved, but power amplifier efficiency deteriorates due to saturation
Solution Approach 1:
The patent differentiates the DMRS sequence generation for different port groups (ports 0-1 versus ports 2-3) by using port-dependent initialization seeds. This local differentiation maintains the signal structure needed for coverage while reducing the peak power that causes amplifier saturation, thereby preserving power amplifier efficiency across the coverage area.
Solution Approach 2:
The patent converts the potentially harmful effect of signal repetition (which causes high PAPR) into a beneficial outcome by using port-dependent sequence generation. The repetition structure is maintained for coverage, but the sequence variation across ports reduces peak power, transforming what would be a harmful high-PAPR situation into an efficient power amplification scenario.
3Reliability
If power backoff is applied to reduce PAPR, then amplifier saturation is prevented, but system throughput decreases
Solution Approach 1:
The patent applies preliminary action by modifying the DMRS sequence generation at the source (using port-dependent initialization seeds) to prevent high peak power from occurring in the first place. This proactive approach eliminates the need for reactive power backoff, allowing the power amplifier to operate at full efficiency while maintaining reliable operation.
Solution Approach 2:
The patent converts the need for power backoff (a harmful reduction in throughput) into a benefit by redesigning the sequence generation. Instead of reducing power to avoid saturation, the port-dependent sequences inherently produce lower peak power, allowing full power operation that improves both amplifier reliability and system throughput simultaneously.
Data Source
AI summary
Because the number of transmitted layers can vary dynamically, the number of transmitted demodulation reference signals (DM-RS) can also vary. However, because the network node can know the number of ports, transmitted layers, or the rank, the network node can utilize the number as part of the scheduling information via a downlink or an uplink control channel. Therefore, the DMRS sequence generation can modified such that it depends on the number of ports, transmitted layers, or the rank, thereby generating a different random sequence for different ports.