A new modulation technique, named as Orthogonal Frequency Division Multiplexing (OFDM) with Subcarrier Number Modulation (SNM), is proposed for efficient data transmission. In this scheme, the information bits are conveyed by changing the number of active subcarriers in each OFDM subblock. The idea of this scheme is inspired from the integration of OFDM with Pulse Width Modulation (PWM), where the width of the pulse represents the number of active subcarriers corresponding to specific information bits. This is different from OFDM with Index Modulation (OFDM-IM), where the information bits are sent by the indices of the subcarriers instead of their number. The scheme is shown to provide better spectral efficiency than that of OFDM-IM at comparable Bit Error Rate (BER) performances. Another key merit of the proposed scheme over OFDM-IM is that the active subcarriers can be located in any position within the subblock, and thus enabling channel-dependent optimal subcarrier selection that can further enhance the system performance.

This paper provides a comparative study on the performance of different modulation options for orthogonal frequency division multiplexing (OFDM) in terms of their spectral efficiency, reliability, peak-to-average power ratio, power efficiency, out-of-band emission, and computational complexity. The modulation candidates are classified into two main categories based on the signal plane dimension they exploit. These categories are: 1) 2-D signal plane category including conventional OFDM with classical fixed or adaptive QAM modulation and OFDM with differential modulation, where information is conveyed in changes between two successive symbols in the same subcarrier or between two consecutive subcarriers in the same OFDM symbol and 2) 3-D signal plane category encompassing: a) index-based OFDM modulation schemes which include: i) spatial modulation OFDM, where information is sent by the indices of antennas along with conventional modulated symbols and ii) OFDM with index modulation, where the subcarriers' indices are used to send additional information; b) number-based OFDM modulation schemes which include OFDM with subcarrier number modulation, in which number of subcarriers is exploited to convey additional information; and c) shape-based OFDM modulation schemes which include OFDM with pulse superposition modulation, where the shape of pulses is introduced as a third new dimension to convey additional information. Based on the provided comparative study, the relationship and interaction between these different modulation options and the requirements of future 5G networks are discussed and explained. This paper is then concluded with some recommendations and future research directions.

A novel transmission scheme is introduced for efficient data transmission by conveying additional information bits through jointly changing the index and number of active subcarriers within each orthogonal frequency division multiplexing (OFDM) subblock. The proposed scheme is different from the conventional OFDM-subcarrier number modulation (OFDM-SNM) and OFDM-index modulation (OFDM-IM), in which data bits are transmitted using either number or index of active subcarriers. The proposed modulation technique offers superior spectral and energy efficiency compared to its counterparts OFDM-SNM and OFDM-IM, especially at low modulation orders such as binary phase shift keying (BPSK) that can provide high reliability and low complexity, thus making it very suitable for meeting the requirements of Internet of things (IoT) applications. Bit error rate (BER) performance analysis is provided for the proposed scheme, and Monte Carlo simulations are presented to prove the consistency of the simulated BER with the analyzed one. More importantly, it is demonstrated that the proposed scheme can offer much superior BER performance compared to that of OFDM-IM and classical OFDM under equivalent power and spectral efficiency values.

The evolution of wireless communication is rapidly advancing beyond Fifth Generation (5G) systems toward Sixth Generation (6G) and future network paradigms. These networks aim to deliver unprecedented data rates, ultra-reliable low-latency communication (URLLC), massive connectivity, and seamless integration of terrestrial and non-terrestrial infrastructures. Efficient radio resource scheduling (RRS) is essential to meeting these demands while ensuring optimal performance in increasingly complex and heterogeneous environments. This survey presents a comprehensive and structured overview of RRS strategies for 5G, 6G, and beyond. Anchored in a unified taxonomy framework, it systematically classifies scheduling approaches across key dimensions, including scheduling methodology, network architecture, and service types. The paper explores a wide spectrum of techniques—from traditional heuristic algorithms to advanced solutions based on multiple-input multiple-output (MIMO), millimeter-wave (mmWave), network slicing, and cross-layer optimization. Special emphasis is placed on the transformative role of machine learning (ML) and artificial intelligence (AI), including supervised learning (SL), reinforcement learning (RL), and deep learning (DL)-based models for intelligent, adaptive scheduling. The survey also discusses emerging challenges such as joint sensing and communication scheduling, edge computing and localized resource allocation (RA), digital twin-assisted scheduling, multi-carrier scheduling, and quantum-assisted scheduling. By highlighting state-of-the-art techniques, open research gaps, and future directions, this survey serves as a valuable reference for researchers and practitioners aiming to develop scalable, secure, and intelligent RRS solutions for next-generation wireless systems.

Radar and communication coexistence is an upcoming technology with numerous research opportunities in the medium access control (MAC) layer, particularly in scheduling and radio resource management (RRM). More efficient scheduling algorithms are needed with the wide range of applications that the wireless environment is experiencing. We investigate an echo-based scenario in the radar-aided vehicular communication system in which an echo is reflected from a target. Unlike the conventional scheduling mechanisms where signal-to-interference-plus-noise ratio (SINR) is exploited, this paper proposes a new radar-aided communication scheduling algorithm by utilizing parameters such as range and velocity with the classical SINR measurements. The proposed algorithm schedules the available resources by extracting information from the radar echo. The proposed radar-aided communication scheduling scheme provides a more flexible design by adding new parameters, resulting in a more efficient algorithm in a broad variety of scenarios. The proposed scheme is beneficial for B5G communication systems that allow localization and sensing as key features of next-generation wireless networks.

In this paper, we investigate a flexible resource allocation (RA) in the delay and Doppler domains to accommodate services with varying requirements. We demonstrate that our problem is NP-hard and propose an optimization method based on linear programming (LP) and Lagrangian dual (LD). The adoption of flexibility in the delay and Doppler domains for capacity enhancement and addressing the needs of mission-critical services has considerable advantages, according to the obtained numerical results. They show that the new scheduling method outperforms conventional time-frequency (TF) domains in terms of bit rate and latency per user, making it valuable for fifth generation (5G) applications and beyond.