Distortion-Aware Power Allocation for 6G MIMO Transmitters

Abstract

Future sixth-generation (6G) wireless systems are expected to support extreme
data rates, massive connectivity, and high energy efficiency. Largescale
Multiple-Input Multiple-Output (MIMO) combined with Orthogonal
Frequency Division Multiplexing (OFDM) is a key enabling technology
to meet these demands. However, OFDM signals exhibit a high Peakto-
Average Power Ratio (PAPR), which forces power amplifiers (PAs) to
operate with significant back-off in order to satisfy Error Vector Magnitude
(EVM) and spectral emission constraints, thereby reducing transmitter efficiency.
This thesis investigates distortion-aware power allocation in OFDMbased
MIMO transmitters with a focus on 6G-oriented system design. The
work analyzes the spatial and spectral behavior of distortion introduced by
Crest Factor Reduction (CFR) and nonlinear PA characteristics. A comprehensive
simulation framework is developed based on wideband CP-OFDM
transmission, DFT beamforming, and multi-user MIMO to evaluate distortion
under spatial, frequency, and joint spatial–frequency multiplexing.
The results reveal that branch-level distortion does not directly translate
to user-experienced distortion. With increasing number of simultaneously
served users, nonlinear distortion becomes progressively decorrelated
from the desired signal components, resulting in significantly lower user
EVM compared to branch EVM. A similar decorrelation effect is observed
when users are separated in the frequency domain through sub-band allocation.
Furthermore, increasing the number of antennas enhances distortion
averaging, leading to improved user-side signal quality while branch-level
distortion remains largely unchanged.
Building on these observations, the study introduces the concept of
power overbooking, whereby additional transmit power can be allocated
without violating user-level EVM constraints. The results demonstrate that
joint exploitation of spatial and frequency resources provides measurable
power headroom gains, enabling reduced PA back-off and improved energy efficiency.
Overall, this work highlights that distortion-aware and hardware-aware
resource allocation can significantly improve transmitter performance. The
findings provide practical design insights for future large-scale MIMO systems,
where exploiting distortion decorrelation across space and frequency
becomes a key enabler for energy-efficient 6G transmitter architectures.

Popular Abstract

Every time we watch a video, make a phone call, or use mobile internet,
wireless signals are transmitted between our devices and nearby base stations.
As society becomes increasingly connected, future mobile networks,
often referred to as 6G, will need to deliver much higher data rates while
consuming less energy.
One of the major challenges is that radio transmitters are not perfectly
efficient. To send information over the air, transmitters use power amplifiers
that boost the signal before it reaches the antenna. However, when
these amplifiers are pushed too hard, they introduce distortion, which can
reduce communication quality and cause interference. To avoid this problem,
transmitters are often operated below their maximum power, which
improves signal quality but wastes energy.
Modern wireless systems use many antennas simultaneously, a technology
known as Multiple-Input Multiple-Output (MIMO). These antennas
work together to direct signals toward specific users. Interestingly, distortion
generated by different antennas does not always combine in the same
way as the desired signal; in many situations, distortion spreads out in different
directions, while the useful signal remains focused on the intended
user.
This thesis investigates how this behavior can be exploited in future 6G
systems. Through computer simulations, different ways of serving multiple
users were studied, including separating users in space, frequency, or a
combination of both. The results show that the communication quality experienced
by users can often be significantly better than what is suggested
by measurements taken directly at the transmitter antennas, meaning that
current design rules can be overly conservative.
These findings indicate that future wireless systems may be able to
operate at higher power levels than currently assumed without reducing
user experience. Such distortion-aware operation could improve energy efficiency,
extend coverage, and increase network capacity, contributing to greener and more efficient wireless communication technologies for future
generations of mobile networks.

• author: Sakalani, Frank Daniel and Gunasekaran, Deepa
• supervisor: Juan Vidal Alegria
• organization: Department of Electrical and Information Technology
• course: EITM02 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: MIMO, OFDM, CFR, Distortion, Transmitter, EVM, Power Overbooking, PAPR
• report number: LU/LTH-EIT 2026-1172
• language: English
• additional info: This thesis was conducted at Ericsson AB in supervision of Mohamed Hamid and Bo Göransson, Also this work was co-supervised by Ashkan Sheikhi from LTH. Frank Sakalani's studies was financed by Swedish Institute.
• id: 9240762
• date added to LUP: 2026-06-23 12:09:01
• date last changed: 2026-06-23 12:09:01