QPSK Base Sequences for IFDMA Uplink DMRS
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Solution Overview
Problem
Current LTE systems face challenges in efficiently transmitting demodulation reference signals (DMRS) over multiple resource blocks with Interleaved Frequency Division Multiple Access (IFDMA) in uplink communications, leading to suboptimal power utilization and inter-cell interference, particularly with existing base sequences not adequately supporting scheduling of odd or even number of resource blocks.
Innovation Solution
The implementation of new sets of quadrature phase shift keying (QPSK) base sequences of lengths 6, 18, and 30, derived from cyclic shifts and orthogonal cover codes, which are specifically designed to reduce peak-to-average power ratio (PAPR) and cubic metric, while maintaining low cross-correlation, enabling efficient transmission and multiplexing of DMRS over one, three, or five resource blocks with IFDMA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing base sequences are used for DMRS transmission in LTE uplink, then the system can maintain compatibility with current standards, but the peak-to-average power ratio is high and inter-cell interference is suboptimal
Solution Approach 1:
The patent applies parameter changes by modifying the base sequence design parameters - specifically using QPSK modulation with optimized phase sequences and cyclic shifts. The new base sequences have lower cubic metrics and controlled cross-correlation properties, which directly reduce the peak-to-average power ratio and improve demodulation performance while lowering power consumption.
2Ease of manufacture
If existing base sequences are used for DMRS transmission, then implementation is straightforward, but cross-correlation between sequences is high leading to inter-cell interference
Solution Approach 1:
The patent applies local quality by designing base sequences with specific local properties - the QPSK sequences are constructed with controlled phase differences and cyclic shift patterns that locally minimize cross-correlation. This allows the system to maintain implementation simplicity while significantly reducing inter-cell interference through optimized sequence characteristics.
3Adaptability or versatility
If DMRS is transmitted over multiple resource blocks, then resource allocation flexibility is improved, but power efficiency deteriorates due to high PAPR
Solution Approach 1:
The patent applies dynamics by enabling flexible resource allocation across different numbers of resource blocks (1, 3, or 5 RBs) while maintaining optimized base sequences for each configuration. The system dynamically selects appropriate base sequences with suitable cyclic shifts and lengths to match the allocated resource blocks, ensuring low PAPR and high power efficiency regardless of the resource allocation size.
4Stability of the object's composition
If existing base sequences are used, then the system maintains current operational characteristics, but cubic metric is high reducing power amplifier efficiency
Solution Approach 1:
The patent applies parameter changes by optimizing the base sequence parameters - using QPSK modulation with specifically designed phase sequences that have lower cubic metrics. The optimized sequences maintain system operational stability through controlled cross-correlation and proper cyclic shift selection, while significantly improving power amplifier efficiency by reducing the cubic metric.
Data Source
AI summary
A method of transmitting demodulation reference signals (DMRS) over one, three or five resource blocks (RBs) with Interleaved Frequency Division Multiple Access (IFDMA) from a wireless device to a wireless network node in a wireless network wherein Single Carrier Frequency Division Multiple Access (SC-OFDMA) is deployed in uplink, is provided. At least one of: a set of base sequences including thirty quadrature phase shifting keying, QPSK, sequences of length 6, 18 or 30 is determined, a demodulation reference signal sequence is derived from the determined set of base sequences, the demodulation reference signal sequence is multiplexed, and the multiplexed demodulation reference signal sequence is transmitted, by the wireless device, to the wireless network node.