DFT-Spread OFDM Waveform Design for Low PAPR and Spectral Efficiency
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Solution Overview
Problem
Current OFDM techniques have high peak-to-average-power ratio (PAPR) and out-of-band emissions, which are limitations for 5G wireless standards requiring low PAPR and efficient spectrum utilization for diverse IoT applications.
Innovation Solution
The method involves applying constellation-specific phase rotation and introducing inter-symbol interference (ISI) using a frequency domain pulse shaping filter, followed by suppression of ISI in the receiver to design a waveform with low PAPR and bit error rate, employing vector/matrix-valued filters for efficient multi-user equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM technique is used for wide area cellular applications, then data rate is improved, but peak-to-average-power ratio (PAPR) becomes very high
Solution Approach 1:
The patent applies parameter changes by transforming the modulation scheme from conventional OFDM to a modified DFT-spread OFDM with pulse shaping. Specifically, it changes the frequency domain signal processing parameters by applying a pulse shaping filter in the frequency domain that introduces controlled inter-symbol interference, which when combined with DFT spreading and phase rotation, significantly reduces the PAPR while maintaining data rate throughput.
Solution Approach 2:
The patent creates a composite modulation technique by combining multiple processing steps: DFT spreading, frequency domain pulse shaping, time domain windowing, and phase rotation. This composite approach integrates different signal processing functions into a unified waveform generation method that achieves both high data rate and low PAPR characteristics.
2Area of stationary object
If OFDM technique is used, then wide area coverage is achieved, but out-of-band emissions are high
Solution Approach 1:
The patent changes the spectral characteristics by applying a pulse shaping filter in the frequency domain with specific excess bandwidth parameters. The filter design controls the roll-off factor and spectral containment, reducing out-of-band emissions while preserving the wide area coverage capability through maintained signal power and coverage area.
Solution Approach 2:
The patent converts the typically harmful inter-symbol interference into a beneficial effect by deliberately introducing controlled ISI through the frequency domain pulse shaping filter. This controlled ISI, when combined with DFT spreading and appropriate filtering at the receiver, reduces out-of-band emissions and improves spectral efficiency.
3Object-generated harmful factors
If DFT-pre-coded-OFDM with SQRC frequency domain pulse shaping filter is used to reduce PAPR, then peak-to-average-power ratio is reduced, but excess bandwidth increases
Solution Approach 1:
The patent applies partial action by using DFT spreading that replicates the signal across multiple subcarriers, combined with frequency domain pulse shaping that applies partial filtering. This partial processing approach reduces PAPR through signal averaging while controlling the excess bandwidth by not applying full bandwidth expansion, achieving a balance between PAPR reduction and spectral efficiency.
4Productivity
If inter symbol interference is introduced by frequency domain pulse shaping filter, then waveform is developed for transmission, but detection complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-compensating for the inter-symbol interference at the transmitter through the frequency domain pulse shaping filter design. The filter is specifically designed to introduce controlled ISI that can be easily equalized at the receiver using simple filtering operations, rather than requiring complex detection algorithms. The cyclic prefix and time domain windowing further prepare the signal for simplified reception.
Data Source
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AI summary
Embodiments herein disclose a method and system for designing a waveform for data communication. The method includes applying, by a phase rotation applying unit, a constellation specific phase rotation between consecutive data symbols in a data stream to obtain a constellation rotated data stream. Further, the method includes introducing, by a frequency domain pulse shaping filter, an inter symbol interference (ISI) between modulated data symbols of the constellation rotated data stream, such that the ISI develops the waveform of the constellated rotated data stream to be transmitted.