Constellation Phase Rotation for PAPR Reduction in SCBT
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Solution Overview
Problem
Existing modulation techniques, particularly for single carrier and single carrier block transmission (SCBT) with circularly non-symmetric constellations like BPSK, face challenges in reducing Peak to Average Power Ratio (PAPR), leading to non-linear distortion and increased out-of-band emissions due to limited linear dynamic range of power amplifiers.
Innovation Solution
The method involves rotating the constellation used for modulation by a phase, with the phase rotation being either constant, pseudo-random, or determined from a stored table, specifically for each symbol, to minimize PAPR, and can be combined with Trellis Coded Modulation or Multi-Level Coded Modulation, with the phase rotation being correctable at the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional modulation techniques are used for single carrier and SCBT with non-symmetric constellations, then the implementation is simple, but the PAPR is high causing non-linear distortion and increased out-of-band emissions
Solution Approach 1:
The patent applies preliminary action by rotating the constellation phase before transmission. Specifically, the constellation is rotated by an angle of π/4 radians for every other symbol in a predetermined manner, which prevents large peak values from occurring in the time-domain signal before it is transmitted through the power amplifier, thereby avoiding non-linear distortion.
Solution Approach 2:
The patent changes the phase parameter of the constellation rotation to reduce PAPR. By rotating the constellation by π/4 radians for alternating symbols, the signal's phase distribution is modified, which reduces the peak instantaneous power while maintaining the same data transmission rate and constellation structure.
2Object-generated harmful factors
If constellation phase rotation is applied to reduce PAPR, then PAPR is reduced and signal stays within linear range, but receiver complexity increases due to need for phase correction
Solution Approach 1:
The patent applies periodic action by using a regular, repeating pattern for constellation rotation - specifically rotating every other symbol by π/4 radians in a predetermined manner. This periodic structure allows the receiver to easily track and compensate for the phase changes using simple periodic phase correction, rather than requiring complex adaptive algorithms.
3Object-generated harmful factors
If π/4-QPSK method is used to reduce PAPR, then PAPR is reduced for QPSK, but the method does not generalize to other constellations like BPSK
Solution Approach 1:
The patent achieves universality by formulating a general constellation rotation method that can be applied to any modulation scheme regardless of constellation shape or symmetry. The method rotates the constellation by π/4 radians for every other symbol, which works effectively for QPSK, BPSK, and other constellations, making it a universal PAPR reduction technique rather than being limited to QPSK only.
Data Source
Figure 1A~1C
Figure 2A
Figure 2B
AI summary
The system (800), transmitter (600), receiver (700), and method of the present invention provide a technique to reduce the Peak to Average Power Ratio (PAPR) for the single carrier and single carrier block transmission (SCBT) modulations, especially when non-symmetric constellations (e.g. BPSK) are used. The constellation used for the modulation of each symbol, is rotated by a phase. Only the constellation is rotated, and the mapping of the bits into each constellation may or may not be similar. Further, in alternative embodiments the modulated bits are either encoded or not encoded. In a further alternative embodiment, a Trellis Coded Modulation (TCM) is used. Because the phase rotation is known a priori, or can be determined from a priori known information, it can easily be corrected at the receiver.