CRAM Algorithm for Low-PAPR MIMO OFDM Precoding
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Solution Overview
Problem
Massive Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems face challenges with high Peak-to-Average Power Ratio (PAPR), leading to increased complexity, power consumption, and costs due to the need for expensive RF components and digital predistortion, especially in 5G wireless systems with large adaptive antenna arrays.
Innovation Solution
The Convex Reduction of Amplitudes (CRAM) algorithm is used for PAPR reduction in MIMO OFDM systems, employing Zero-Forcing (ZF) precoding and iterative convex optimization techniques to achieve low PAPR, enabling per-antenna time-domain clipping and multi-carrier/multi-band operations, which simplifies the design and reduces power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM signaling is used in massive MIMO systems, then capacity gains are achieved through large adaptive antenna arrays, but PAPR becomes large requiring expensive linear RF components and costly digital predistortion
Solution Approach 1:
The patent applies parameter changes by modifying the signal representation from conventional OFDM to low-PAPR waveforms such as filtered multicarrier (FMC) or generalised frequency division multiplexing (GFDM). This changes the spectral shaping parameters and time-frequency structure to achieve lower peak power while maintaining the same data throughput, thereby resolving the contradiction between spectral efficiency and RF component complexity
Solution Approach 2:
The patent segments the transmitted signal into multiple independent low-PAPR waveforms, each with controlled peak power characteristics. By dividing the overall signal into segments that can be individually managed with simpler RF components, the system achieves high spectral efficiency without requiring expensive fully-linear RF chains for the entire signal
2Productivity
If conventional OFDM signaling is used in massive MIMO systems, then capacity gains are achieved, but power consumption increases due to expensive RF components and digital predistortion
Solution Approach 1:
By changing the waveform parameters to low-PAPR structures, the patent enables power amplifiers to operate in non-linear regions while maintaining signal quality through digital signal processing techniques. This parameter change eliminates the need for power-hungry digital predistortion and allows the use of more energy-efficient RF components, thereby reducing overall power consumption while maintaining spectral efficiency
Solution Approach 2:
The patent substitutes mechanical/power-intensive linear RF amplification with a combination of digital signal processing and more efficient non-linear power amplifiers. The low-PAPR waveform structure allows digital processing to handle signal conditioning, replacing the need for mechanically complex and power-hungry linear amplification systems
3Ease of operation
If conventional OFDM signaling is used, then OFDM modulation is performed, but PAPR remains large requiring Crest Factor Reduction techniques
Solution Approach 1:
The patent introduces dynamic filtering and modulation techniques where the signal characteristics are adaptively adjusted in the time-frequency domain. The dynamic nature of the low-PAPR waveform generation allows the system to maintain simple modulation operations while automatically controlling PAPR through adaptive signal shaping, avoiding the need for complex static PAPR reduction algorithms
4Productivity
If large antenna arrays are deployed in 5G systems, then spectral efficiency improves, but system size and power consumption dramatically increase
Solution Approach 1:
The patent changes the signal waveform parameters to low-PAPR structures that are inherently more suitable for massive MIMO deployments. This parameter change enables the system to achieve high spectral efficiency with large antenna arrays while the reduced PAPR allows for more compact and power-efficient RF components, thereby reducing the overall system size and power consumption
Data Source
AI summary
Systems and methods are disclosed herein that relate to Peak-to-Average Power Ratio (PAPR) reduction in a MIMO OFDM transmitter system. In some embodiments, a method of operation of a transmitter system includes, for each carrier of two or more carriers, performing precoding of frequency-domain input signals for the carrier to provide frequency-domain precoded signals for the carrier, the frequency-domain input signals for the carrier being for a plurality of transmit layers for the carrier, respectively. The method further includes processing the two or more pluralities of frequency-domain precoded signals for the two or more carriers, respectively, in accordance with a multi-carrier 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. The multi-carrier processing scheme provides PAPR reduction for Cyclic Prefixes (CPs) of the plurality of multi-carrier time-domain transmit signals for the plurality of antenna branches.