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One of the critical missions for next-generation wireless communication systems is to fulfill the high demand for massive Machine-Type Communications (mMTC). In mMTC systems, a sporadic transmission is performed between machine users and base station (BS). Lack of coordination between the users and BS in time destroys orthogonality between the subcarriers, and causes inter-carrier interference (ICI). Therefore, providing services to asynchronous massive machine users is a major challenge for Orthogonal Frequency Division Multiplexing (OFDM). In this study, OFDM with index modulation (OFDM-IM) is proposed as an eligible solution to alleviate ICI caused by asynchronous transmission in uncoordinated mMTC networks. In OFDM-IM, data transmission is performed not only by modulated subcarriers but also by the indices of active subcarriers. Unlike classical OFDM, fractional subcarrier activation leads to less ICI in OFDM-IM technology. A novel subcarrier mapping scheme (SMS) named as Inner Subcarrier Activation is proposed to further alleviate adjacent user interference in asynchronous OFDM-IM-based systems. ISA reduces inter-user interference since it gives more activation priority to inner subcarriers compared with the existing SMS-s. The superiority of the proposed SMS is shown through both theoretical analysis and computer-based simulations in comparison to existing mapping schemes for asynchronous systems.

Service time-varying traffic flexible optical networks require a dynamic bandwidth allocation in order to follow the source transmission rate. The problem of service time-varying traffic, assuming that the set of connection requests is not known in advance, is considered in this work. Connection requests arrive randomly and have random durations. The considered dynamic RSA problem involves minimizing the probability of future connections blocking while maintaining spectrum continuity constraints and non-overlapping spectrum assignment constraints between spectrum-adjacent connections on the network links. The proposed algorithm determines the path with the required number of slots around the reference frequency for a connection request. An analysis of the network with time-varying traffic on the network connections was carried out on the basis of spectrum expansion/contraction schemes which allow to determine average blocking probability of the additional slot requests on these connections. The obtained results have been compared with those obtained by a well known algorithm that solves the dynamic RSA problem.

Based on empirical data of an orthogonal frequency division multiplexing system in realistic environments of next‐generation cellular networks, a new analytical model of phase noise and numerical characteristics of the common phase error and intercarrier interference are derived. Applying an asymptotic theory of probability, analytical expressions are present to approximate the mean vector and the covariance matrix of the intercarrier interference. The approximation expression of the covariance matrix is accurate enough and only has three parameters. When applied to estimate original symbols based on additive white Gaussian noise channel, a Gibbs sampler performs better than the current estimation algorithm following Weiner process phase noise. Based on empirical data of an orthogonal frequency division multiplexing system, a new analytical model of phase noise and numerical characteristics of the common phase error and intercarrier interference are derived. When applied to estimate original symbols based on AWGN channel, the proposed algorithm based on the model performs better than the current algorithm for phase noise.

In recent years, Orthogonal Time Frequency Space Modulation (OTFS) has gained popularity in integrated sensing and communications (ISAC) system due to its robustness against Doppler offset and delay changes. Traditional pilot‐based methods for accurate channel parameter estimation are complex and struggle with rapidly changing channel conditions. In this letter, a deep encode‐decode network (DED‐Net) is proposed. It uses DL to automatically learn and eliminate channel interference from OTFS signals. The framework employs a deep encoding and decoding network, similar to a filter, learning complex signal features to effectively remove interference. Our experiments demonstrate DED‐Net's ability to eliminate interference in OTFS modulation signals, offering an alternative to pilot‐based methods and showcasing DL's potential for ISAC systems. In this letter, we propose a deep encode‐decode network (DED‐Net). It uses DL to automatically learn and eliminate channel interference from OTFS signals. The framework employs a deep encoding and decoding network, similar to a filter, learning complex signal features to effectively remove interference. The experiments demonstrate DED‐Net's ability to eliminate interference in OTFS modulation signals, offering an alternative to pilot‐based methods and showcasing DL's potential for ISAC systems.

Coherent multi‐band splicing is an optimal solution for extending existing band‐limited communication systems to support high‐precision sensing applications. Conceptually, the communication system performs narrow‐band measurements at different centre frequencies, which are then concatenated to increase the effective bandwidth without altering the sampling rate. This can be done in parallel for multiple non‐contiguous subbands or by hopping across the different bands. However, multi‐band splicing poses significant challenges, particularly in compensating for phase offsets and hardware distortions before stitching the acquired samples, which can be distributed in contiguous or non‐contiguous manners. This survey paper studies the state of the art in coherent multi‐band splicing and identify open research questions. For beginners in the field, this review serves as a guide to the most relevant literature, enabling them to quickly catch up with the current achievements. For experts, open research questions that require further investigation are highlighted. Coherent multi‐band splicing offers an effective approach, extending existing band‐limited communication systems to support high‐precision sensing applications by combining multiple narrow‐band measurements. However, this method presents considerable challenges, particularly in compensating for phase offsets and hardware distortions before merging the acquired samples, whether they are distributed contiguously or non‐contiguously. This survey paper reviews the current state of the art in coherent multi‐band splicing and identify key challenges that require further exploration by the research community.

This paper is dedicated to the study of the multiple‐input multiple‐output generalized frequency division multiplexing with index modulation (MIMO‐GFDM‐IM) wireless communication system. This system garners significant interest for future communications technologies due to its notable features, such as high spectral efficiency, energy efficiency, and robustness against multipath propagation channels. Preceding the study of the system, the model of signals and systems for MIMO‐GFDM is developed based on the MIMO orthogonal frequency division multiplexing model and detection strategies for the system are presented. A new proposal for MIMO‐GFDM detection, based on two filtering phases, is presented, resulting in an attractive tradeoff between detection performance and computational complexity. The presented system model is then extended to include index modulation as an information carrier, resulting in the MIMO‐GFDM‐IM system. Different proposals for detectors based on processing the complete channel matrix and also for detectors of reduced complexity are evaluated, from the perspective of detection performance and computational complexity. Dedicated to studying the multiple‐input multiple‐output generalized frequency division multiplexing with index modulation wireless communication system, this paper highlights its high spectral and energy efficiency, robustness against multipath channels. It introduces novel detection strategies, including two‐phase filtering, and evaluates detector proposals for performance and complexity.

Multiuser multiple input multiple output (MU‐MIMO) systems can provide high spectral efficiency (SE) that is achieved with transmit/receive combining schemes at the base station (BS) for downlink (DL) and uplink (UL). So far, various combining schemes for DL were proposed, with the regularized zero forcing (RZF) and Tomlinson–Harashima precoding (THP) being usually considered. In a case of massive MU‐MIMO systems, with a large number of antennas, the matrix inversion operation used in the RZF and THP schemes causes high computational complexity that significantly aggravates implementation and raises its costs. The authors propose a low‐complexity transmit combining scheme for the massive MU‐MIMO systems with time division duplex (TDD), devised in a similar manner as the THP scheme, based on the gram‐Schmidt orthogonalization, and show that it achieves slightly better SE than the THP scheme for the estimated channel state information (CSI), but with a much lower complexity than the THP and RZF schemes. In this paper, a low‐complexity transmit combining scheme for the massive MU‐MIMO systems with time division duplex si proposed, devised in a similar manner as the well‐known Tomlinson‐Harashima precoding (THP) scheme. In order to suppress multiuser interference with a lower computational complexity we here employ the Gram‐Schmidt orthogonalization method. The proposed solution is shown to achieve slightly better performance than THP scheme in the case of the estimated channel state information.

Visible light communication (VLC) is a promising solution for future wireless communication systems due to its high data rate, wide bandwidth, and enhanced security features. However, challenges such as high peak‐to‐average power ratio (PAPR) and out‐of‐band (OOB) spectral leakage limit its performance. In this study, we propose the integration of discrete prolate spheroidal sequences (DPSS) with direct current optical generalised frequency division multiplexing (DCO‐GFDM) to enhance the performance of indoor VLC systems. A comparative analysis between traditional DCO‐OFDM and the proposed DCO‐GFDM scheme is conducted under both line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) channel conditions. Simulation results show that the proposed method achieves approximately 2.5 dB reduction in PAPR and 45% reduction in OOB leakage compared to conventional DCO‐OFDM, while maintaining a similar bit error rate (BER) performance. Moreover, the DCO‐GFDM scheme demonstrates higher spectral efficiency without significant degradation in BER, achieving a BER below 10−3 at a signal‐to‐noise ratio (SNR) of 20 dB in both LOS and NLOS scenarios. These improvements underline the effectiveness of the DPSS‐based approach in enhancing the reliability and spectral efficiency of indoor VLC systems. VLC is a promising solution for future wireless communication systems due to its high data rate, wide bandwidth, and enhanced security features. However, challenges such as high PAPR and OOB spectral leakage limit its performance. In this study, we propose the integration of DPSS with DCO‐GFDM to enhance the performance of indoor VLC systems. A comparative analysis between traditional DCO‐OFDM and the proposed DCO‐GFDM scheme is conducted under both LOS and NLOS channel conditions. Simulation results show that the proposed method achieves approximately 2.5 dB reduction in PAPR and 45% reduction in OOB leakage compared to conventional DCO‐OFDM, while maintaining a similar BER performance. Moreover, the DCO‐GFDM scheme demonstrates higher spectral efficiency without significant degradation in BER, achieving a BER below 10−3 at a (SNR of 20 dB in both LOS and NLOS scenarios. These improvements underline the effectiveness of the DPSS‐based approach in enhancing the reliability and spectral efficiency of indoor VLC systems.

Generalized frequency division multiplexing (GFDM) is a flexible block‐structured multi‐carrier scheme recently proposed for next‐generation wireless communication systems. There are various approaches suggested for its analysis and implementation via simulations but testing in real‐time environments is not heavily investigated. This paper carries out the real‐time implementation of the GFDM system utilizing software‐defined radio (SDR) by emphasizing mainly channel estimation and synchronization. Symbol timing, frequency offset, and channel estimate algorithms are applied using a windowed preamble with two identical halves to satisfy low egress noise requirements. Time and frequency estimation is evaluated in terms of residual offsets along with symbol error rate over frequency selective channels. This algorithm is extended to a preamble composed of multiple identical parts. This facilitates a large frequency estimation range at the cost of complexity. For practical validation of the above concepts, the National Instruments (NI) universal software radio peripheral (USRP) 2953R is employed as hardware and it is interfaced with LabVIEW. The block diagram for implementing GFDM pertaining to CFO estimation and depicting the trade off between length of the training symbol and bit error rate.

Here, fast time‐varying channels of high‐mobility vehicle‐to‐vehicle communications for massive multiple‐input multiple‐output orthogonal frequency division multiplexing systems are considered. Large‐scale uniform linear arrays are configured at the transmitter and receiver to separate multiple angle domain Doppler frequency offsets based on transmit and receive beamforming with high spatial resolution. Then, each beamforming branch comprises only one dominant Doppler frequency offset. Next, the conventional channel estimation method is performed for each beamforming branch, and carry out maximum‐ratio‐combining for data detection. Power spectrum density and Doppler spread of the equivalent link between the transmitter and receiver are derived and regarded as the criterion for assessing the residual channel time variation caused by limited antennas in practice. Interestingly, a scaling law between the asymptotic Doppler spread and the number of transceiver antennas shows that asymptotic Doppler spread is proportional to the maximum Doppler frequency offset and decreases at the rate of 1NT2+1NR2 $\\sqrt {\\frac{1}{{{N_T}^2}} + \\frac{1}{{{N_R}^2}}}$ , where NT ${N_T}$and NR ${N_R}$are the number of transmit and receive antennas, respectively. Simulation results confirm the validity of the proposed Doppler suppression framework in high‐mobility vehicle‐to‐vehicle communications. We propose a novel Doppler suppression framework with Doppler frequency offset compensation at the transceiver in angle domain to suppress channel time variation for vehicle‐to‐vehicle communications. We regard Doppler spread as the criterion for assessing the residual channel time variation and derive the scaling law between Doppler spread and the number of transceiver antennas. Simulation results confirm the validity of the proposed Doppler suppression framework for high‐mobility V2V communications.