Exjobbspresentation: Distortion-Aware Power Allocation for 6G

Exjobbet genomfördes på Ericsson  Mohamid Hamid och Bo Göranson som handledare, Ashkan Sheikhi och Juan Vidal Alegria var akademiska handledare och Ove Edfors examinator.

Future sixth-generation (6G) wireless systems are expected to support extremely high data rates, massive connectivity, and improved energy efficiency.  To meet these requirements, large-scale Multiple-Input Multiple-Output (MIMO) systems combined with Orthogonal Frequency Division Multiplexing (OFDM) are expected to play a central role. However, OFDM signals exhibit a high Peak-to-Average Power Ratio (PAPR), forcing power amplifiers to operate with power back-off in order to satisfy Error Vector Magnitude (EVM) and spectral emission requirements. This reduces the efficiency of the transmitter and increases the energy consumption.

This thesis investigates distortion-aware power allocation for OFDM-based MIMO transmitters that target future 6G deployments. The study focuses on the spatial and spectral characteristics of the distortion introduced by Crest Factor Reduction (CFR) and nonlinear transmitter operation. A simulation framework based on wideband CP-OFDM transmission, DFT beamforming, and multi-user MIMO was developed to analyze distortion behavior under spatial multiplexing, frequency multiplexing, and joint spatial-frequency multiplexing scenarios.

The results show that the distortion observed at individual antenna branches does not directly translate into the distortion experienced by users. As the number of simultaneously scheduled users increases, distortion becomes increasingly decorrelated from the desired user beams, resulting in significantly lower user EVM than branch EVM. Similar effects are observed when users are separated in the frequency domain through sub-band allocation. Larger antenna arrays further improve distortion averaging, reducing user EVM while branch EVM remains approximately unchanged.

The study demonstrates that distortion-aware resource allocation can create additional transmit power headroom without violating EVM constraints. The observed gap between branch-level and user-level distortion suggests that future transmitter optimization strategies can exploit power overbooking opportunities to improve energy efficiency and coverage. These findings provide insight into how hardware aware and distortion-aware resource management can contribute to practical and energy-efficient 6G MIMO transmitter designs.