arXiv subjects

Pawel Kryszkiewicz

Publications and source records attributed to Pawel Kryszkiewicz.

At least 19 recordsLinked to original sources

arXiv2026

Energy-Efficient Resource Allocation for PA Distortion-Aware M-MIMO OFDM System

Maintaining high energy efficiency (EE) in wireless networks is crucial, particularly with the adoption of massive MIMO technology. This work introduces a resource allocation framework that jointly optimizes transmit power assigned to each user and the number of active antennas, while explicitly accounting for a nonlinear Power Amplifier (PA). We consider a downlink MU-MIMO-OFDM transmission with zero forcing (ZF) precoding, Rayleigh fading channels, and soft-limiter PAs, with both ideal and realistic PA architectures. In contrast to existing formulations, our optimization framework avoids imposing an explicit transmit power constraint, since the nonlinear distortion inherently limits the feasible operating region. To solve the resulting non-convex problem, an alternating optimization approach is adopted that, by exploiting properties of the EE function, guarantees convergence to a stationary point. Extensive simulations demonstrate consistent performance gains over distortion-neglecting and power-only optimized baselines. In a scenario of a 5 km radius cell serving 60 randomly distributed users, the median EE gains over the distortion-neglecting allocation reach 40% for ideal PAs and 20% for Class B PAs, confirming high impact of the proposed solution.

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arXiv2025

Energy-Efficient Power Control in Single-User M-MIMO-OFDM System with PA Nonlinearity

Although multiple works have proposed energy-efficient resource allocation schemes for Massive Multiple-Input Multiple-Output (M-MIMO) system, most approaches overlook the potential of optimizing Power Amplifier (PA) transmission power while accounting for non-linear distortion effects. Furthermore, most M-MIMO studies assume narrow-band transmission, neglecting subcarrier intermodulations at the non-linear PA for an Orthogonal Frequency Division Multiplexing (OFDM) system. Therefore, this work investigates the energy-efficient power allocation for a single-user equipment (UE) M-MIMO downlink (DL) system employing OFDM with nonlinear PAs. Unlike prior works, we model wide-band transmission using a soft-limiter PA model and derive a closed-form expression for the signal-to-distortion-and-noise ratio (SNDR) under Rayleigh fading and Maximal Ratio Transmission (MRT) precoding. Next, the Energy Efficiency (EE) function is defined considering two PA architectures and a distorted OFDM signal. We then propose a low complexity root-finding algorithm to maximize EE by transmit power adjustment. Simulation results demonstrate significant EE gains over a fixed PA back-off baseline, with over $100\%$ improvement under both low and high path loss. Our findings reveal how the optimal operating point depends on the antenna count, the PA model, and the propagation conditions.

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arXiv2025

Optimal Distortion-Aware Multi-User Power Allocation for Massive MIMO Networks

Real-world wireless transmitter front-ends exhibit certain nonlinear behavior, e.g., signal clipping by a Power Amplifier (PA). Although many resource allocation solutions do not consider this for simplicity, it leads to inaccurate results or a reduced number of degrees of freedom, not achieving the global performance. In this work, we propose an optimal PA distortion-aware power allocation strategy in a downlink orthogonal frequency division multiplex (OFDM) based massive multiple-input multiple-output (M-MIMO) system. Assuming a soft-limiter PA model, where the transmission occurs under small-scale independent and identically distributed (i.i.d) Rayleigh fading channel, we derive the wideband signal-to-noise-and-distortion ratio (SNDR) and formulate the power allocation problem. Most interestingly, the distortion introduced by the PA leads to an SNDR-efficient operating point without explicit transmit power constraints. While the optimization problem is non-convex, we decouple it into a non-convex total power allocation problem and a convex power distribution problem among the users (UEs). We propose an alternating optimization algorithm to find the optimum solution. Our simulation results show significant sum-rate gains over existing distortion-neglecting solutions, e.g., a median 4 times increase and a median 50\% increase for a 64-antenna and 512-antenna base station serving 60 users, respectively.

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arXiv2025

Nonlinear symbols combining for Power Amplifier-distorted OFDM signal reception

Nonlinear distortion of a multicarrier signal by a transmitter Power Amplifier (PA) can be a serious problem when designing new highly energy-efficient wireless systems. Although the performance of standard reception algorithms is seriously deteriorated by the nonlinear distortion, the more advanced solutions allow the utilization of additional frequency diversity caused by nonlinear PA. However, while most of the advanced receivers are decision-aided, their gains are observed mostly in a relatively low Bit Error Rate (BER) region, not targeted by adaptive Modulation Coding Schemes utilizing Forward Error Correction (FEC). In this paper, a non-decision-aided Higher-Order Combining (HOC) reception scheme is proposed. While the analytical formulas for finding symbols combining coefficients are not known, machine learning is used for deriving them. The simulation results show an improved BER performance with respect to a standard reception and one of the established decision-aided receivers. However, as HOC has computational complexity that increases rapidly with the number of subcarriers utilized, more studies are needed to apply it in a wideband system.

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arXiv2025

Power Amplifier-Aware Transmit Power Optimization for OFDM and SC-FDMA Systems

The Single Carrier-Frequency Division Multiple Access (SC-FDMA) is a transmission technique used in the uplink of Long Term Evolution (LTE) and 5G systems, as it is characterized by reduced transmitted signal envelope fluctuations in comparison to Orthogonal Frequency Division Multiplexing (OFDM) technique used in the downlink. This allows for higher energy efficiency of User Equipments (UEs) while maintaining sufficient signal quality, measured by Error Vector Magnitude (EVM), at the transmitter. This paper proposes to model a nonlinear Power Amplifier (PA) influence while optimizing the transmit power in order to maximize the Signal to Noise and Distortion power Ratio (SNDR) at the receiver, removing the transmitter-based EVM constraint. An analytic model of SNDR for the OFDM system and a semi-analytical model for the SC-FDMA system are provided. Numerical investigations show that the proposed transmit power optimization allows for improved signal quality at the receiver for both OFDM and SC-FDMA systems. However, SC-FDMA still outperforms OFDM in this matter. Such a power amplifier-aware wireless transmitter optimization should be considered to boost the performance and sustainability of next-generation wireless systems, including Internet of Things (IoT) ones.

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arXiv2024

V2V Path Loss Modeling at 26 GHz Based on Real-Traffic Measurements

In this letter, we investigate single-slope path loss models complemented with shadowing effects in the context of vehicular communications. We present several models obtained based on extensive measurement campaigns with inter-vehicle transmission conducted at 26.555 GHz in real-traffic experiments, mainly along high-speed roads. Particular attention has been put on the impact of aerial characteristics (omnidirectional versus directional), surrounding environment (e.g., urban versus rural), and their mounting point on cars (at the rooftop, on the bumper, and below the car chassis). Finally, the effect of signal ducting and of the number of blocking cars has been analyzed and the decorrelation time has been discussed

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arXiv2023

Open RAN xApps Design and Evaluation: Lessons Learnt and Identified Challenges

Open Radio Access Networks (RAN) offer diverse economic opportunities. A transition to a flexible, modular approach within the disaggregated RAN framework is crucial, involving careful planning of RAN architecture and the deployment of specialized software applications. Collaboration across sectors is essential for efficiency and reliability, with the open-source community driving innovation. This paper explores challenges for third-party application developers in Open RAN. It provides a comparative analysis of solutions, focusing on xApp development and implementation. Challenges arise in two areas: the complexities of xApp development, particularly for advanced use cases like beam management, and issues in low-level software implementation within open platforms. In conclusion, key challenges must promote academia-industry collaboration in Open RAN. This paper shares early lessons from xApp development, guiding the field's evolution.

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arXiv2023

Clipping noise cancellation receiver for the downlink of massive MIMO OFDM system

Massive multiple-input multiple-output (mMIMO) technology is considered a key enabler for the 5G and future wireless networks. In most wireless communication systems, mMIMO is employed together with orthogonal frequency-division multiplexing (OFDM) which exhibits a high peak-to-average-power ratio (PAPR). While passing the OFDM signal through one of the common RF front-ends of limited linearity, significant distortion of the transmitted signal can be expected. In mMIMO systems, this problem is still relevant as in some channels the distortion component is beamformed in the same directions as the desired signal. In this work, we propose a multi-antenna clipping noise cancellation (MCNC) algorithm for the downlink of the mMIMO OFDM system. Computer simulations show it can remove nonlinear distortion even under severe nonlinearity. Next, a simplified version of the algorithm is proposed. It was observed that for the direct visibility channels, its performance is only slightly degraded with respect to the MCNC algorithm.

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arXiv2023

Why white noise is not enough? On using radio front-end models while designing 6G PHY

From generation to generation there are increasing requirements for wireless standards both in terms of spectral and energy efficiency. While up to now the layered wireless transceiver architecture worked allowing for, e.g., separation of channel decoding algorithms from front-end design, this may need reconsideration in the 6G era. Especially the hardware-originated distortions have to be taken into account while designing other layer algorithms as the high throughput and energy efficiency requirements will push these devices to their limit revealing their nonlinear characteristics. This position paper will shed some light on new degrees of freedom while cross-layer designing and controlling multicarrier and multiantenna transceivers of 6G systems.

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arXiv2023

Beam Management Driven by Radio Environment Maps in O-RAN Architecture

The Massive Multiple-Input Multiple-Output (M-MIMO) is considered as one of the key technologies in 5G, and future 6G networks. From the perspective of, e.g., channel estimation, especially for high-speed users it is easier to implement an M-MIMO network exploiting a static set of beams, i.e., Grid of Beams (GoB). While considering GoB it is important to properly assign users to the beams, i.e., to perform Beam Management (BM). BM can be enhanced by taking into account historical knowledge about the radio environment, e.g., to avoid radio link failures. The aim of this paper is to propose such a BM algorithm, that utilizes location-dependent data stored in a Radio Environment Map (REM). It utilizes received power maps, and user mobility patterns to optimize the BM process in terms of Reinforcement Learning (RL) by using the Policy Iteration method under different goal functions, e.g., maximization of received power or minimization of beam reselections while avoiding radio link failures. The proposed solution is compliant with the Open Radio Access Network (O-RAN) architecture, enabling its practical implementation. Simulation studies have shown that the proposed BM algorithm can significantly reduce the number of beam reselections or radio link failures compared to the baseline algorithm.

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arXiv2023

Signaling Storm Detection in IIoT Network based on the Open RAN Architecture

The Industrial Internet of Things devices due to their low cost and complexity are exposed to being hacked and utilized to attack the network infrastructure causing a so-called Signaling Storm. In this paper, we propose to utilize the Open Radio Access Network (O-RAN) architecture, to monitor the control plane messages in order to detect the activity of adversaries at its early stage.

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arXiv2023

Memory Enabled Bumblebee-based Dynamic Spectrum Access for Platooning Environments

In this paper, we propose a novel memory-enabled non-uniform sampling-based bumblebee foraging algorithm (MEB) designed for optimal channel selection in a distributed Vehicular Dynamic Spectrum Access (VDSA) framework employed in a platoon operating environment. Given how bumblebee behavioral models are designed to support adaptation in complex and highly time-varying environments, these models can be employed by connected vehicles to enable their operation within a dynamically changing network topology and support their selection of optimal channels possessing low levels of congestion to achieve high throughput. As a result, the proposed VDSA-based optimal channel selection employs fundamental concepts from the bumblebee foraging model. In the proposed approach, the Channel Busy Ratio (CBR) of all channels is computed and stored in memory to be accessed by the MEB algorithm to make the necessary channel switching decisions. Two averaging techniques, Sliding Window Average (SWA) and Exponentially Weighted Moving Average (EWMA), are employed to leverage past samples and are evaluated against the no-memory case. Due to the high variability of the environment (e.g., high velocities, changing density of vehicles on the road), we propose to calculate the CBR by employing non-uniform channel sampling allocations as well as evaluate it using both simplified numerical and realistic Vehicle-to-Vehicle (V2V) computer simulations. The numerical simulation results show that gains in the probability of the best channel selection can be achieved relative to a uniform sampling allocation approach. By utilizing memory, we observe an additional increase in the channel selection performance. Similarly, we see an increase in the probability of successful reception when utilizing the bumblebee algorithm via a system-level simulator.

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arXiv2022

Path Loss and Shadowing Modeling for Vehicle-to-Vehicle Communications in Terrestrial TV Band

Vehicle platooning is considered as one of the key use cases for vehicle-to-vehicle (V2V) communications. However, its benefits can be realized only with highly reliable wireless transmission. As the 5.9GHz frequency band used for V2V suffers from high congestion, in this paper, we consider the use of the terrestrial TV frequencies for intra-platoon communications. In order to be able to evaluate the potential of the new bands fully, propagation models for V2V communications at such frequencies are needed. Therefore, this paper reports new V2V propagation measurements and their modeling results. Particularly, we propose a Double Slope Double Shadowing model as the most accurate one, based on a comparison of various models using the Bayesian Information Criteria. We also investigate the space-time autocorrelation properties of the shadowing, which turned out to be dependent on the speed of vehicles. The proposed path loss and shadowing model differs from the ones proposed for the 5.9GHz band. Mostly, in favor of the TV band, as shown by, e.g., no statistically significant impact of a blocking car.

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arXiv2022

Federated Learning-Based Interference Modeling for Vehicular Dynamic Spectrum Access

A platoon-based driving is a technology allowing vehicles to follow each other at close distances to, e.g., save fuel. However, it requires reliable wireless communications to adjust their speeds. Recent studies have shown that the frequency band dedicated for vehicle-to-vehicle communications can be too busy for intra-platoon communications. Thus it is reasonable to use additional spectrum resources, of low occupancy, i.e., secondary spectrum channels. The challenge is to model the interference in those channels to enable proper channel selection. In this paper, we propose a two-layered Radio Environment Map (REM) that aims at providing platoons with accurate location-dependent interference models by using the Federated Learning approach. Each platoon is equipped with a Local REM that is updated on the basis of raw interference samples and previous interference model stored in the Global REM. The model in global REM is obtained by merging models reported by platoons. The nodes exchange only parameters of interference models, reducing the required control channel capacity. Moreover, in the proposed architecture platoon can utilize Local REM to predict channel occupancy, even when the connection to the Global REM is temporarily unavailable. The proposed system is validated via computer simulations considering non-trivial interference patterns.

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arXiv2021

Frequency Selection for Platoon Communications in Secondary Spectrum Using Radio Environment Maps

Platoon-based driving is an idea that vehicles follow each other at a close distance, in order to increase road throughput and fuel savings. This requires reliable wireless communications to adjust the speeds of vehicles. Although there is a dedicated frequency band for vehicle-to-vehicle (V2V) communications, studies have shown that it is too congested to provide reliable transmission for the platoons. Additional spectrum resources, i.e., secondary spectrum channels, can be utilized when these are not occupied by other users. Characteristics of interference in these channels are usually location-dependent and can be stored in the so-called Radio Environment Maps (REMs). This paper aims to design REM, in order to support the selection of secondary spectrum channel for intra-platoon communications. We propose to assess the channel's quality in terms of outage probability computed, with the use of estimated interference distributions stored in REM. A frequency selection algorithm that minimizes the number of channel switches along the planned platoon route is proposed. Additionally, the REM creation procedure is shown that reduces the number of database entries using (Density-Based Spatial Clustering of Applications with Noise) DBSCAN algorithm. The proposals are tested using real IQ samples captured on a real road. Application of the DBSCAN clustering to the constructed REM provided 7% reduction in its size. Utilization of the proposed channel selection algorithm resulted in a 35 times reduction of channel switches concerning channel assignment performed independently in every location.

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arXiv2021

Out-of-Band Power Reduction in NC-OFDM with Optimized Cancellation Carriers Selection

In this letter, we propose a computationally efficient method for joint selection of cancellation carriers (CCs) and calculation of their values minimizing the out-of-band (OOB) power in non-contiguous (NC-) OFDM transmission. The proposed new CCs selection method achieves higher OOB power attenuation than algorithms known from literature as well as noticable reception performance improvement.

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arXiv2021

Energy Savings by Task Offloading to a Fog Considering Radio Front-End Characteristics

Fog computing can be used to offload computationally intensive tasks from battery powered Internet of Things (IoT) devices. Although it reduces energy required for computations in an IoT device, it uses energy for communications with the fog. This paper analyzes when usage of fog computing is more energy efficient than local computing. Detailed energy consumption models are built in both scenarios with the focus set on the relation between energy consumption and distortion introduced by a Power Amplifier (PA). Numerical results show that task offloading to a fog is the most energy efficient for short, wideband links.

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arXiv2021

In-Band-Interference Robust Synchronization Algorithm for an NC-OFDM System

We consider receiver synchronization in the non-continguous orthogonal frequency division multiplexing (NC-OFDM)-based radio system in the presence of in-band interfering signal, which occupies the frequency-band between blocks of subcarriers (SCs) used by this system, i.e. in-band of NC-OFDM receiver spectrum range. This paper proposes a novel preamble-based synchronization algorithm for estimation of the time and frequency offset based on the received signal cross-correlation with the reference preamble. Contrary to the existing algorithms, it is robust against in-band interference including narrowband interference at the cost of increased complexity. Moreover, in the interference-free system, the probability of frame synchronization error is improved in comparison to all simulated algorithms.

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