CRAM Algorithm for OFDM MIMO PAPR Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current Multiple Input Multiple Output (MIMO) systems face challenges with high Peak-to-Average Power Ratio (PAPR) in OFDM signaling, leading to expensive RF components and signal distortions, particularly in large-scale MIMO systems with hundreds of antenna elements, necessitating effective PAPR reduction techniques.
Innovation Solution
The Convex Reduction of Amplitudes (CRAM) algorithm is employed to reduce PAPR by optimizing frequency-domain vectors for OFDM tones, using iterative solutions that enforce spatial constraints and peak power constraints, and incorporating per-antenna time-domain clipping to manage power levels effectively across antenna branches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM signaling is used in large-scale MIMO systems, then capacity gains are achieved through large adaptive antenna arrays, but Peak-to-Average Power Ratio (PAPR) becomes excessively high requiring expensive linear RF components and costly digital predistortion
Solution Approach 1:
The patent applies digital predistortion in the baseband domain before the signal reaches the RF components. By pre-processing the OFDM symbols through convex optimization to reduce peak amplitudes, the system avoids the need for expensive linear RF components and costly digital predistortion at the RF stage, thus resolving the contradiction between achieving capacity gains and reducing device complexity
Solution Approach 2:
The patent changes the amplitude parameters of the OFDM signal in the baseband domain by applying convex optimization techniques. This transforms the signal characteristics to reduce peak-to-average power ratio while maintaining the capacity benefits of large-scale MIMO, thereby reducing the need for expensive RF components
2Device complexity
If time-domain clipping is applied to reduce PAPR, then PAPR is reduced from large values to 5.0-9.0 dB, but signal distortion is introduced both in-band and out-of-band characterized by EVM between 3% and 20%
Solution Approach 1:
The patent applies convex optimization in the baseband domain before time-domain clipping. By pre-reducing the peak amplitudes through iterative optimization that enforces spatial constraints, the system minimizes the subsequent distortion introduced by time-domain clipping, thereby resolving the contradiction between PAPR reduction and signal distortion
Solution Approach 2:
The patent introduces an intermediary optimization step between the OFDM modulation and time-domain clipping. This intermediate convex optimization process acts as a mediator that prepares the signal to be more compatible with clipping, reducing the harmful distortion effects while still achieving PAPR reduction
3Device complexity
If convex optimization algorithms like FITRA or PROXINF-ADMM are used to reduce PAPR, then PAPR is reduced to 2-4 dB, but the algorithms require multiple iterations (200-2000 iterations for FITRA, 20-200 iterations for PROXINF-ADMM) increasing processing time
Solution Approach 1:
The patent segments the optimization process into two stages: a coarse optimization phase using a simplified algorithm that provides initial PAPR reduction quickly, followed by a fine optimization phase that refines the solution. This segmentation reduces the total number of iterations needed compared to using a single complex iterative algorithm, thereby resolving the contradiction between achieving low PAPR and reducing processing time
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Systems and methods are disclosed herein that related to Peak-to-Average Power Ratio (PAPR) reduction in a (e.g., massive) Multiple-Input Multiple-Output (MIMO) Orthogonal Division Multiplexing (OFDM) transmitter system. In some embodiments, a method of operation of a MIMO OFDM transmitter system comprises, for each carrier of two or more carriers, performing precoding of a plurality of frequency-domain input signals for the carrier to provide a plurality of frequency-domain precoded signals for the carrier, the plurality of frequency-domain input signals for the carrier being for a plurality of transmit layers for the carrier, respectively. The method further comprises processing the frequency-domain precoded signals for the two or more carriers in accordance with a multi-carrier Convex Reduction of Amplitudes (CRAM) processing scheme to provide a plurality of multi-carrier time-domain transmit signals for a plurality of antenna branches, respectively, of the MIMO OFDM transmitter system.