Reconfigurable intelligent surface (RIS) is a promising technology for future communication systems, and the channel propagation environment can be controlled in an RIS-assisted network. In this letter, the problem of the joint channel estimation and device activity detection is investigated in an RIS empowered massive Internet of Things system. To achieve a satisfactory trade off between the system

Benefiting from the extended coverage of simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) in comparison with the conventional reflecting-only RIS, the combination of STAR-RIS and non-orthogonal multiple access (NOMA) is a promising solution to improve spectrum/energy efficiency and enhance coverage quality for future communication networks. In this letter, we concentrate

A sparse superimposed vector transmission (SSVT) scheme is proposed for short-packet ultra-reliable and low-latency communications (URLLC) in high-mobility scenarios. Unlike conventional pilot-less sparse vector coding (SVC) schemes, a small number of pilots are superimposed on top of data vector in SSVT to track time-varying channels, leading to high spectral efficiency. Two joint channel estimation

We study an X-type non-orthogonal multiple access (NOMA) wireless relay network that consists of an uplink multiple access channel and a downlink broadcast channel. We formulate a non-convex optimization problem to obtain an optimal power allocation factor and an optimal rate vector that maximize the end-to-end sum rate. To solve the optimization problem, we prove four theorems that contain closed-form

We propose a user-driven method for adaptive quantization and feedback of channel state information (CSI) in frequency division duplexing systems. The approach can be combined with existing autoencoder neural networks and requires only a single codebook shared between the users and the base station. Users can provide feedback with different numbers of bits depending on their data rates, without system

In this letter, we investigate the discrete phase shift design of the intelligent reflecting surface (IRS) in a time-division duplexing (TDD) multi-user multiple-input-multiple-output (MIMO) system. We modify the design of deep reinforcement learning (DRL) scheme so that we can maximizing the average downlink data transmission rate free from the sub-channel channel state information (CSI). Based on

As a cutting-edge technique of the sixth generation mobile communication, reconfigurable intelligent surface (RIS) is compatible with many existing technologies very well. In the existing literature, the inter-RIS reflecting signals are usually ignored for simplification. In this letter, we consider a double cooperative-RIS-assisted uplink non-orthogonal multiple access (NOMA) system with inter-RIS

In this letter, we develop a matrix reconstruction algorithm-assisted multi-carrier differential chaos shift keying (DCSK) scheme, named MRA-MC-DCSK scheme. Especially, the frequency-selective fading channel is considered in the proposed scheme. We establish a matrix reconstruction algorithm (MRA) to reconstruct the information-bearing signal, which can solve the performance deterioration of the conventional

The reconfigurable intelligent surface (RIS) is an emerging technology that changes how wireless networks are perceived, therefore its potential benefits and applications are currently under intense research and investigation. In this letter, we focus on electromagnetically consistent models for RISs inheriting from a recently proposed model based on mutually coupled loaded wire dipoles. While existing

Communications system with analog or hybrid analog/digital architectures usually relies on a pre-defined codebook to perform beamforming. With the increase in the size of the antenna array, the characteristics of the spherical wavefront in the near-field situation are not negligible. Therefore, it is necessary to design a codebook that is adaptive to near-field scenarios. In this letter, we investigate

A deep learning (DL)-based cluster delay estimation method using prior sparsity is proposed. Firstly, the columns of the covariance matrix of channel frequency response in the time delay domain are formulated as undersampled noisy linear measurements of the delay spectrum. Then, a deep convolutional network (DCN) is used to recover the delay spectrum from the measurement vector. Compared with conventional

The focus of this letter is on the reduction of the large pilot overhead in orthogonal frequency division multiplexing (OFDM) based massive multiple-input multiple-output (MIMO) systems. We propose a novel joint channel estimation and equalization technique that requires only one pilot subcarrier, reducing the pilot overhead by orders of magnitude. We take advantage of the coherence bandwidth spanning

Non-orthogonal multiple access (NOMA) is regarded as one of the primary enabling candidates for fifth-generation cellular systems. In this letter, we compare NOMA with orthogonal multiple access (OMA) for visible light communication (VLC) systems, and show that the relationship between NOMA and OMA in VLC is different from that in radio frequency (RF) systems, since the traditional Shannon formula

This letter proposes spectrally efficient frequency division multiplexing (SEFDM) combined with orthogonal frequency division multiplexing (OFDM) using index modulation (IM). The conventional OFDM-IM provides energy efficiency but results in data rate (DR) loss because of inactive subcarriers. The coexistence of OFDM and SEFDM using IM (OFDM-SEM) improves the DR by avoiding frequency resource deactivation

In this letter, the sequency domain is introduced as a novel resource to propose a new index modulation, which is named sequency index modulation (SeIM). In SeIM, information bits are implicitly conveyed through the indices of the activated sequencies enabling bit error rate (BER), spectral efficiency, and power efficiency enhancement. Also, two strategies are proposed to allocate power among the activated

Timing synchronization (TS) is vital for orthogonal frequency division multiplexing (OFDM) systems, which makes the discrete Fourier transform (DFT) window start at the inter-symbol-interference (ISI)-free region. However, the multi-path uncertainty in wireless communication scenarios degrades the TS correctness. To alleviate this degradation, we propose a learning-based TS method enhanced by improving

This letter proposes an innovative energy-efficient Radio Access Network (RAN) disaggregation and virtualization method for Open RAN (O-RAN) that effectively addresses the challenges posed by dynamic traffic conditions. In this case, the energy consumption is primarily formulated as a multi-objective optimization problem and then solved by integrating Advantage Actor-Critic (A2C) algorithm with a

In this letter, we investigate a sensing assisted communication system employing the Orthogonal Time Frequency Space (OTFS) waveforms. We first develop a channel sensing algorithm to estimate the channel coefficients in the delay-Doppler domain based on the multiple signal classification algorithm. Specifically, by searching over the three-dimensional spectrum, including the angle, delay, and Doppler

This letter proposes a new coupled phase-shift intelligent omni-surface (IOS) aided rate splitting multiple access (RSMA) transmission framework. Specifically, the base station (BS) splits user messages into common and private parts and precodes the common stream carefully to exploit the operation of IOS aided communication for spectral efficiency improvement. A resource allocation problem to maximize

Intelligent edge services should consider not only service provider’s resource constraints but also end user’s quality of experience (QoE) demands. In this regard, we study a digital twin service caching and request routing problem with consideration of both resource and fairness-awareness under the collaboration of multi-access edge computing (MEC) servers. We first formulate the problem as an integer

The Orthogonal Time Sequency Multiplexing (OTSM) waveform demonstrates superior performance compared to the Orthogonal Frequency Division Multiplexing (OFDM) waveform under linear time-varying (LTV) channels and multiple Doppler conditions. However, the direct conversion OTSM transceiver system is constrained by hardware impairments like carrier frequency offset (CFO) and IQ imbalance. In this Letter

Active reconfigurable intelligent surface (ARIS) is a newly emerging RIS technique that leverages radio frequency (RF) reflection amplifiers to empower phase-configurable reflection elements (REs) in amplifying the incident signal. Thereby, ARIS can enhance wireless communications with the strengthened ARIS-aided links. In this letter, we propose exploiting the signal amplification capability of ARIS

Intelligent reflecting surface (IRS) has been considered as a revolutionary technology to enhance the wireless communication performance. To cater for multiple mobile users, adjusting IRS beamforming patterns over time, i.e., dynamic IRS beamforming (DIBF), is generally needed for achieving satisfactory performance, which results in high controlling power consumption and overhead. To avoid such cost

Spectrum sensing of non-orthogonal multiple access (NOMA) signals is a challenging issue, as not only the presence/absence of primary users (PUs) but also the number of PUs needs to be identified. In this letter, we formulate NOMA spectrum sensing as a multiple hypotheses testing problem, where the estimated channel gains from PUs to a secondary user are used as test-statistics. Then, to reduce the

In Cell-free massive multiple-input multiple-output (CF mMIMO) systems, most works aim to improve the overall performance within the coverage range. It may result in the transmission capacity is not fully utilized in low traffic density areas and is insufficient in high traffic density areas. To overcome this issue, we design a traffic demand-oriented network whose transmission capacity can match with

Orthogonal Time Frequency Space (OTFS) is proposed to improve the performance of Orthogonal Frequency Division Multiplexing (OFDM) in time-variant channels. However, when Message Passing (MP) algorithm is utilized, the receiver always makes a tradeoff between BER performance and convergence speed due to the damping factor. In this letter, a Variable Damping factor Message Passing (VD-MP) algorithm

This letter addresses the problem of signal detection in flat-fading channels. In this context, receivers based on the expectation propagation framework appear to be very promising although presenting some critical issues. We develop a new algorithm based on this framework where, unlike previous works, convergence is achieved after a single forward-backward pass, without additional inner detector iterations

In this letter, we propose a novel network architecture for integrating terrestrial and non-terrestrial networks (NTNs) to establish connection between terrestrial ground stations which are unconnected due to blockage. We propose a new network framework where reconfigurable intelligent surface (RIS) is mounted on an aerodynamic high altitude platform station (HAPS), referred to as aerodynamic HAPS-RIS

Cooperative perception has been widely used in autonomous driving to alleviate the inherent limitation of single automated vehicle perception. To enable cooperation, vehicle-to-vehicle (V2V) communication plays an indispensable role. This letter analyzes the performance of cooperative perception accounting for communications channel impairments. Different fusion methods and channel impairments are

Millimeter-wave (mmWave) and sub-6 GHz hybrid heterogeneous network (HetNet) has gained wide attention for future mobile communications. However, the difference in propagation characteristics of mmWave and sub-6 GHz presents several challenges to achieve efficient utilization of network resources in hybrid HetNets. In this letter, we consider a joint optimization framework that combines user association

In this letter, we consider a double-active-intelligent reflecting surface (IRS) aided wireless communication system, where two active IRSs assist the communication from a base station (BS) to multiple users via double-reflection links. Under the assumption of fixed per-element amplification power for each active-IRS element, we formulate a rate maximization problem subject to practical constraints

Recently, the integration of quasi-orthogonal space-time block codes (QOSTBC) and spatial modulation (SM) has been suggested for efficient downlink multiple-input multiple-output (MIMO) transmission. In this letter, we propose a class of low-complexity sphere decoding (SD) detectors for such a system termed quasi-orthogonal space-time block coded spatial modulation (QOSTBC-SM). Compared to the traditional

The presented research proposes the $\alpha $ -modification of the Beaulieu-Xie shadowed fading channel for wireless communications. For the assumed model the closed-form analytical description of the basic statistical characteristics is carried out (i.e., probability density function, cumulative distribution function, and their asymptotics). The derived statistical description is exemplified on the

In this letter, a sub-connected hybrid precoding system was designed to realize energy-efficient millimeter-Wave (mmWave) unmanned aerial vehicle (UAV) communications. Considering the limited capacity of the UAV battery, the system was jointly optimized with a UAV trajectory to increase the energy efficiency of the UAV under quality-of-service (QoS) and power budget constraints. The dynamic motion

This letter proposes a novel cooperative non-orthogonal multiple access (C-NOMA) based on precoded faster-than-Nyquist (FTN) signaling. The additional gain in degrees of freedom obtained from precoded FTN signaling is exploited in the context of relaying-induced diversity inherent to C-NOMA. We derive the achievable ergodic rate of the proposed scheme while also deriving a closed-form expression of

We propose secure max-min fairness (MMF) precoding for a downlink multi-antenna system with multiple users and eavesdroppers. Since the problem is non-convex and non-smooth and partial channel knowledge is assumed, it is highly challenging to solve. To resolve the difficulties, we first reformulate the problem with conditional average rates, allowing to exploit the partial channel knowledge. Then,

This letter explores a joint improvement scheme for physical-layer secret key generation rate and communication performance with the aid of a reconfigurable intelligent surface (RIS) in quasi-static environments. Some RIS elements are exploited to construct random beams for key generation, and others are designed for energy-enhanced directional beamforming to improve the legitimate users’ signal-to-noise

This letter proposes a new L-shape array based technique for massive Multiple Input Multiple Output (MIMO) systems to overcome the cross user correlation (CUC) of tightly coupled users in a near line-of-sight scenario in fifth-generation massive MIMO systems without changing signal processing complexity. The performance of the scheme is validated using standard performance metrics like CUC and achievable

Combination of millimeter wave (mmWave) and massive multiple input multiple output (MIMO) forms a promising technology for future sixth generation networks. As the number of antennas increases, propagation channel starts yielding spherical wavefronts, for which the traditional channel estimation algorithms are no longer applicable. To overcome this technical gap, a novel MIMO channel estimation scheme

In this letter, we study joint channel estimation and turbo equalization for coded orthogonal time frequency space (OTFS) and orthogonal frequency division multiplexing (OFDM). To the best of our knowledge, this is the first study that compares performance of OTFS and OFDM coded systems using the state-of-the-art message passing (MP) and soft minimum mean square error (MMSE) equalizers, under imperfect

Physical layer security is a sought-after concept to complement the established upper layer security techniques in wireless communications. An appealing approach to achieve physical layer security is to use cooperative jamming with interference that is known to and suppressible by the legitimate receiver but unknown to, and hence not suppressible by, the eavesdropper. Suppressing known interference

In this letter, we propose a new regularization approach to low-precision Cholesky decomposition. This decomposition is employed to inverse an ill-conditioned matrix in the linear detector of the Multi-User Massive Multiple Input, Multiple Output (MU-MIMO) receivers. The proposed method was implemented in half-precision format and tested in realistic scenarios generated by the QuaDRiGa 2.0 channel

We study the performance of a selection combining (SC) receiver operating over independent but non-identically distributed log-logistic $(\mathcal {LL})$ fading channels. We first characterize the statistics of the output instantaneous signal-to-noise ratio (SNR) of the SC receiver. Based on the SNR statistics, we derive exact analytical expressions, in terms of multivariate Fox H-functions, for the

The lower and upper bounds on the decoding error probability for the optimal code given a signal-to-noise ratio and a code rate are investigated in this letter for the reconfigurable intelligent surface (RIS) communication system at the short blocklength regime. The sphere packing technique is used to derive our main results. The Wald sequential ${t}$ -test lemma and the Riemann sum are the main tools

Orthogonal chirp division multiplexing (OCDM) has been proposed as a novel modulation scheme to take advantage of its double-spreading feature in both the time and frequency domains. It shows more resilient against different impairments. However, it is mainly investigated under time-invariant channels. In this letter, we propose a channel estimation method based on pilot chirps for OCDM transmissions

Pseudo base station (BS) is an illegal radio device that exploits the security vulnerabilities of fifth generation (5G) communications and then implements corresponding network attacks, such as spoofing attack. These malicious actions cause security and privacy threats and hinder the wide deployment of wireless access networks. To address these problems, efficient BS identification mechanisms are necessary

With the advantage of flexible deployment in all terrains, unmanned aerial vehicles (UAV) equipped with lightweight computing module can bring mobile edge computing (MEC) service closer to both survivors and rescuers in disaster scenarios. However, the mismatch between the sudden computing demands of mobile users (MUs) and limited computation resources of UAVs cannot meet the high delay sensitivity

As future wireless systems trend towards higher carrier frequencies and large antenna arrays, receivers with one-bit analog-to-digital converters (ADCs) are being explored owing to their reduced power consumption. However, the combination of large antenna arrays and one-bit ADCs makes channel estimation challenging. In this letter, we formulate channel estimation from a limited number of one-bit quantized

Target-to-user (T2U) association is a prerequisite to fully exploit the potential of the sensing function in communication-centric integrated sensing and communication (ISAC) systems, e.g., for beam and blockage management. This letter proposes to purposely mount a RIS on the roof of the vehicular user equipment (VUE), which can serve as an intentional back-reflector towards the base station. By controlling

We consider a $4 \times 4$ line-of-sight multiple-input multiple-output (LoS MIMO) system with uniform circular arrays (UCAs) at the transmitter (Tx) and receiver (Rx). First, we show that the optimum design of non-tilted UCAs of four antennas can be generalized to the design of optimum elliptical arrays (EAs). Afterwards, we investigate the effect of tilting the Tx or Rx UCA over different transmit

We propose a blind direction of arrival (DOA) estimation method for multicarrier code-division multiple access (MC-CDMA) systems, which does not require knowledge of the spreading codes of transmitters. Our method involves reconstructing a fourth-order tensor with observations from the antenna array at the receiver. We then apply higher-order singular value decomposition (HOSVD) to separate the signal

Long Term Evolution (LTE) frequency bands are being considered for use in 5G due to their coverage advantage. However, LTE usage is expected to be non-negligible for a while, so the amount of spectrum resources for it should be carefully estimated. In this letter, we propose a criterion for evaluating the adequacy of LTE spectrum resources in terms of edge user Quality of Service (QoS). For resource

Due to the dynamics of wireless channels and limited wireless resources (i.e., spectrum), deploying federated learning (FL) over wireless networks is challenged by frequent FL parameter transmission errors and incomplete FL model aggregation from devices. In order to overcome these challenges, we propose a G l o bal MO del RE use strategy (GoMORE) that reuses global FL models received at previous FL

Orthogonal time frequency space (OTFS) modulation is an emerging technique for next-generation communication due to its robustness to the doubly dispersive channels under high mobility scenarios. We have designed and analyzed a deep learning (DL)-based OTFS system (DL-OTFS) in the presence of hardware impairments (HI) such as in-phase and quadrature-phase (IQ) component mismatch and DC offset. Further

Compared to passive intelligent reflecting surface (IRS), active IRS is viewed as a more efficient promising technique to combat the double-fading impact in IRS-aided wireless network. In this letter, in order to boost the achievable rate of user in such a wireless network, three enhanced-rate iterative beamforming methods are proposed by designing the amplifying factors and the corresponding phases

Millimeter-Wave (mmWave) communication has been considered as one of enabling technologies for the sixth generation (6G) network and beyond to boost the system throughput, which however is hard to provide robust and reliable transmissions since it is easy to be blocked. Coordinated multi-beam transmission has emerged as an effective way to overcome this challenge. In this letter, we first define an

Despite the promising attributes of the 12 GHz band for expanding terrestrial 5G network’s capacity and coverage, interference between coexisting networks remains a major issue. This letter develops a simulation-based evaluation framework and investigates the harmful interference between the 5G radio links and incumbent fixed non-geostationary satellite orbit (NGSO) fixed satellite services (FSS) receivers

In this letter, we study the coordinated multipoint (CoMP) scheme in the uplink cellular-connected UAV network. By considering the LoS and NLoS components in air-to-ground (A2G) transmission, we adopt the strongest average received signal strength (RSS)-based CoMP scheme. We then develop an analytical framework to evaluate the network performance in terms of coverage probability and area spectral efficiency

Reconfigurable intelligent surface (RIS), a key technology for future wireless communications, allows intelligent reflection of signals and information transmission. The RIS-based modulation is considered a prospective information transmission mechanism. In this letter, a RIS-based opposite phase index modulation system is proposed, in which RIS can enhance the received power of user signals while

This letter exploits secure beamforming for achieving security-reliability tradeoff in rate splitting multiple access (RSMA)-based communications against eavesdropper collusion. Considering user fairness, we maximize the minimum secrecy rate (MSR) among all legitimate users subject to the quality of service (QoS) constraints and transmit power constraint. A feasibility check problem is first presented