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Multiple Input Multiple Output (MIMO) is a technology that combines multiple antennas and Orthogonal Frequency Division Multiplexing (OFDM) modulation to increase the data rate and spectral efficiency of wireless communication systems. Equalization problems are one of the key issues with MIMO-OFDM systems, which are caused by multiple antennas and subcarriers. Optimal Power Allocation (OPA) in MIMO-OFDM is a critical component for achieving high spectral efficiency and improving the overall performance of the system. OPA refers to the process of allocating power to the different subcarriers and antennas in MIMO-OFDM systems in an optimal way. This study proposes the Dynamic OPA (DOPA) algorithm for MIMO-OFDM systems to dynamically adjust power allocation based on the changing channel conditions and reduce pilot contamination issues. This approach allocates more power to subcarriers and antennas with better channel conditions and less power to subcarriers and antennas with worse channel conditions. DOPA in MIMO-OFDM systems is necessary to maximize data rates, minimize interference, improve system capacity, and reduce power consumption. Simulation results showed that the proposed MIMO-OFDM-DOPA had reduced bit error rates, mean square error, and transmitter power and increased energy efficiency and capacity compared to existing state-of-the-art methods. [ABSTRACT FROM AUTHOR]

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Offloading computation-intensive tasks to mobile edge computing (MEC) servers, such as road-side units (RSUs) and a base station (BS), can enhance the computation capacities of the vehicle-to-everything (V2X) communication system. In this work, we study an MEC-assisted multi-vehicle V2X communication system in which multi-antenna RSUs with liner receivers and a multi-antenna BS with a zero-forcing (ZF) receiver work as MEC servers jointly to offload the tasks of the vehicles. To control the energy consumption and ensure the delay requirement of the V2X communication system, an energy consumption minimization problem under a delay constraint is formulated. The multi-agent deep reinforcement learning (MADRL) algorithm is proposed to solve the non-convex energy optimization problem, which can train vehicles to select the beneficial server association, transmit power and offloading ratio intelligently according to the reward function related to the delay and energy consumption. The improved K-nearest neighbors (KNN) algorithm is proposed to assign vehicles to the specific RSU, which can reduce the action space dimensions and the complexity of the MADRL algorithm. Numerical simulation results show that the proposed scheme can decrease energy consumption while satisfying the delay constraint. When the RSUs adopt the indirect transmission mode and are equipped with matched-filter (MF) receivers, the proposed joint optimization scheme can decrease the energy consumption by 56.90% and 65.52% compared to the maximum transmit power and full offloading schemes, respectively. When the RSUs are equipped with ZF receivers, the proposed scheme can decrease the energy consumption by 36.8% compared to the MF receivers. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs) have been generally applied in the field of communication due to their small size, flexible mobility, and convenient deployment. As a mobile base station, the UAV node can quickly establish a line-of-sight link with the ground node, thereby improving communication performance. In this paper, we study a multi-UAV assisted data collecting system. Specifically, in the case of limited system energy consumption, UAV flight energy consumption and ground node data transmission energy consumption are considered as an general limitation, and considering the channel interference between nodes, a multi-UAV assisted data collection model is studied. An non-convex problem that maximizes the minimum amount of data collected from ground nodes is further formulated. Since the original optimization problem is non-convex that difficult to solve directly, the problem is first decomposed into four sub-problems, and then the solution of each sub-problem is obtained by using successive convex approximation and block coordinate descent method. Finally, based on the solution of the four subproblems, an iterative algorithm for joint optimization of data transmission planning, transmission power, UAV trajectory and mission time is proposed. Simulation experiments show that the proposed algorithm can obtain more transmission data than the baseline algorithms.

This article presents the implementation and the evaluation of a transmission–reception system for Physical Downlink Control Channel (PDCCH) within the context of fifth-generation cellular networks (5G/NR). The research focuses on characterizing the behavior of the PDCCH channel concerning different User Equipment (UE) positions through simulations conducted in MATLAB. Two scenarios are considered: a lossless system and a system with losses, where the outcomes are presented in terms of Bit Error Rate (BER) vs. Signal to Noise Ratio (SNR) and BER vs. Transmit Power, respectively. One contribution of the paper is the explanation transmission–reception system for PDCCH in MATLAB, while the second contribution is the presentation of simulation results. From results, it was deduced that higher UE height corresponds to improved channel performance, greater UE elevation angle leads to enhanced channel performance, and increased carrier frequency results in reduced performance of the physical control PDCCH channel. [ABSTRACT FROM AUTHOR]

In this research work, the authors propose an error constrained data transmission approach using non-orthogonal multiple access (NOMA) protocol with hybrid automatic repeat request (HARQ) and different packet combining schemes. In this proposed work, the transmitter simultaneously transmits two data packets to the users (UEs) by considering the superposition coding technique in the power domain. The decoding scheme of the receiver changes according to the message decoding status in the previous rounds. This combined protocol has the capability of realizing ultra-reliability, error correction power in high error prone wireless links. The receiver adopts successive interference cancelation (SIC) to decode its own packet. Retransmission process is performed when the data is erroneously received by the destination and the receiver corrects the error by applying HARQ with Packet Combining (HARQ-PC) and HARQ with Aggressive Packet Combining (HARQ-APC) schemes. This paper analyzes the data rates, outage probabilities and bit error rates of UEs for downlink NOMA systems with respect to the transmit power using some basic parameters. The proposed schemes can greatly outperform the conventional NOMA with HARQ (NOMA-HARQ) in terms of data rates, outage probability and bit error rate in dynamic wireless channels. [ABSTRACT FROM AUTHOR]

The GENESIS mission prepared for launch in 2027 integrates the four space-geodetic techniques on a single spaceborne platform in medium Earth orbit. With its unique observations and alternative tie concepts, the mission aims to contribute to an improved accuracy and homogeneity of future terrestrial reference system realizations. To assess the expected contribution of Global Navigation Satellite System (GNSS) tracking, a comprehensive GNSS coverage analysis is performed based on detailed link-budget simulations, taking into account the best available gain patterns and signal-specific transmit power estimates derived for this work from measurements of a high-gain dish antenna. The benefit of different receiver antenna concepts for the GENESIS spacecraft is assessed, and it is demonstrated that a single-antenna system with either a nadir-looking or side-looking boresight is a viable alternative to the dual-antenna configuration considered in initial mission studies. Compared to terrestrial users and missions in low Earth orbit, GENESIS will collect GNSS signals transmitted at up to two times larger off-boresight angles. Only limited information on the actual transmit antenna phase patterns is presently available in this region, which hampers a quantitative assessment of the expected measurement and orbit determination accuracy. As such, a comprehensive release of manufacturer calibrations is encouraged for all blocks of GPS and Galileo satellites. In parallel, a need for in-flight characterization and calibration of the GNSS transmit antennas for off-boresight angles of up to 30 ∘ using observations of the GENESIS mission itself is expected. The impact of such calibrations on the overall quality of terrestrial reference frame parameters will need to be assessed in comprehensive simulations of global GNSS network solutions with joint processing of terrestrial and GENESIS GNSS observations. [ABSTRACT FROM AUTHOR]

The utilization of the global navigation satellite system (GNSS) is becoming an attractive approach for autonomous navigation of the geostationary orbit (GEO) satellites. As one of the global navigation systems, the feasibility of using GLONASS in high-orbit spacecraft has attracted attention. A receiver compatible with GLONASS has been mounted in the GEO satellites of TJS-2 and TJS-5 to demonstrate the ability to track signals and real-time orbit determination. In accordance with flight data, the GLONASS signal characteristics are analyzed, including the observation availability and distribution. When the side lobe signals are considered, the mean number of GLONASS satellites tracked increases from 1.8 to 5.8. The transmit power of each GLONASS satellite was estimated by using the C/N0 measurements. Based on the influence analysis results, we found that the side lobe signal transmit power plays an important role in increasing the number of observations. In particular, we investigate the characteristics, such as quantity, C/N0, and doppler, of the GLONASS antipodal satellite signals tracked simultaneously in the GEO case. We give the navigation performance assessment based on GLONASS-only flight data through comparisons with the precision reference orbits. For single-epoch least square solutions, the root mean squares (RMS) of position differences in radial, along-track, and cross-track is 157.0, 29.5, and 21.5 m, respectively. The navigation accuracy is significantly improved when using the real-time orbit determination method, and the RMS of position differences in radial, along-track, and cross-track is 5.19, 8.98, and 3.15 m, respectively. [ABSTRACT FROM AUTHOR]

With increasing penetration of wireless charging technologies comes an ever-rising demand for wireless power transfer (WPT) structures that demonstrate high power transfer and power transfer efficiency (PTE), especially over wide transfer distance. The concern with reliability in adopting wireless charging technologies in consumer and industrial applications (including mobile chargers and dynamic wireless charging of electric vehicles, EVs) stems from fluctuating output power and low power transfer efficiency (PTE). Moreover, the inherently high resonant frequency of existing metamaterial (MM)-based WPT designs imposes a high switching stress on power semiconductors and passive components, resulting in high power dissipation, especially in high power applications. This manuscript presents a critical survey of recent studies and developments in MM-based WPT systems. First, the fundamental concepts and classification of WPT technologies based on magnetic resonant coupling (MRC), inductive coupling etc. are discussed. Going forward, key MM design considerations, including resonance operating frequencies, effective permittivity ( $\epsilon _{r}$ ), effective permeability ( $\mu _{r}$ ), numerical modeling, equivalent circuit representations, and 3D fabrication technologies are widely analyzed and critiqued. Additionally, the performance enhancing effect of integrating different MM designs with existing WPT systems are explicitly discussed. Finally, the technical challenges associated with the resonant operating frequencies of MM, miniaturization of MM design footprint, and 3D prototyping are investigated while also presenting potential solutions.

Non-orthogonal multiple access (NOMA) is a better multiple access technique than orthogonal multiple access (OMA), precisely orthogonal frequency division multiple access (OFDMA) scheme, at the conceptual level for fifth-generation (5G) networks and beyond 5G (B5G) networks. We investigate the potentials of the schemes by comparing the proposed NOMA scheme with the traditional cooperative communication NOMA (CCNOMA) scheme, rather than the comparison between NOMA and OMA only. To probe the effectiveness of NOMA as a multiple access technique, we propose a novel NOMA scheme considering two adjacent BSs with a special design of the transceiver architecture. The proposed scheme provides a reasonable data rate to both near user (NU) and far user (FU) without compromising the quality of service (QoS) to anyone of them. The conclusive analyses on the optimization framework of multi-user sum rate, capacity, transmit power, spectral efficiency (SE), and energy efficiency (EE) trade-off for NOMA and OFDMA schemes have been established to a succession of derivations. Under the analytical optimization framework, we also prove quite a few properties for them. Simulation results confirm the theoretical findings and show that the two schemes can efficiently approach the optimal power allocation, minimization of power consumption, and optimal SE-EE trade-off, and the proposed NOMA scheme provides comparatively better data sum rates than the baseline OMA scheme.

Covert device-to-device (D2D) communication is recently proposed to help D2D pairs hide the existence of transmission from being detected by a warden. However, most of the existing works only focus on guaranteeing the communication covertness, while they ignore the information freshness and energy consumption which are important for the delay-sensitive applications and energy-constrained devices. In this work, we propose an energy-efficient transmit probability-power control scheme for covert D2D communication with the information freshness requirement. Specifically, we first construct a novel status update model in covert D2D communication, and further derive the closed-form average age of information (AoI) to characterize the freshness of status information. Then, from the perspective of warden, we analyze its detection performance and derive the minimum detection error probability to measure the communication covertness. Subsequently, from the perspective of D2D pair, we propose the notion of covert energy efficiency (EE) to characterize the tradeoff between covert rate and power consumption. Guided by this, we jointly optimize the transmit probability and transmit power of status information to maximize the covert EE of the D2D pair subject to the constraints of communication covertness and information freshness. Due to its intractability, we design an iterative algorithm based on the successive convex approximation (SCA) approach. Simulation results verify the correctness of derived expressions and show the effectiveness of our proposed scheme. [ABSTRACT FROM AUTHOR]

This study focuses on the downlink (DL) transmission of massive multiple-input-multiple-output (MIMO) with the support of simultaneous wireless information and power transfer (SWIPT) system based on a power-splitting (PS) scheme. To reach the green design target in the concept of wireless communication networks, this paper maximizes the system’s energy efficiency (EE) using joint system-level optimization. First, the closed-form expressions of the harvested energy and achievable data rate are first derived. Then, we formulated the EE maximization problem by jointly optimizing user equipment (UE) pilot transmission time allocation, the received PS ratios, a base station (BS) transmit power allocation, and a number of BS antennas while considering the minimum data rate as user’s quality-of-service (QoS) requirement and the maximum BS power transmission constraint. However, the formulated EE maximization problem is non-convex and non-linear which is difficult to solve. Hence, we propose an efficient low-complex alternative optimization (LCAO) algorithm to solve the non-convex problem iteratively with an acceptable computational complexity level. Simulation results are provided to evaluate the derived closed-form expressions and validate the proposed LCAO algorithm’s efficiency. The optimality, convergence, and complexity of the LCAO algorithm are analytically investigated. Results indicate that the proposed LCAO algorithm outperforms the equal power allocation (EPA) scheme by 15% better EE gain and 4% better than the max-min fairness scheme when the BS power transmission capacity is higher than 3 (Watt). [ABSTRACT FROM AUTHOR]

This work tackles the joint optimization of the modulation order $L$ and transmit power $P$ of pulse-position modulation (PPM) in covert communications. Specifically, we consider two scenarios where $L$ used by the PPM at a transmitter Alice for communicating with a receiver Bob is known and unknown to the warden Willie, respectively. In the former scenario, our numerical examination obtained based on our analysis indicates that the optimal $L$ is generally 2, which is mainly due to the fact that Willie’s detection performance increases with $L$ when he knows it. Interestingly, in the latter scenario, we show that the optimal $L$ is 2 when the covertness constraint is strict, while it is 4 when the covertness constraint is relaxed. The main reason is that Willie’s detection performance does not depend on $L$ when he does not know it, and the bit error rate for $L=2$ is close to that for $L=4$ when the signal-to-noise ratio is extremely low caused by the strict covertness constraint, while $L=2$ requires less bandwidth and may achieve a higher bandwidth efficiency. Furthermore, we theoretically prove that the covert communication performance is better when Willie does not know $L$ relative to when he knows $L$. [ABSTRACT FROM AUTHOR]

In this paper we study an intelligent reflecting surface (IRS) assisted non-orthogonal multiple access (NOMA) network where the direct link between the base station (BS) and one of the users is blocked and the IRS is deployed to serve the blocked user. The IRS designs under both the ideal IRS with continuous phase shifting and the non-ideal IRS with discrete phase shifting are considered. For both cases, by leveraging the isotropic random vector and the Laguerre series, we derive insightful results and closed-form expressions on performance measures including the average required transmit power, the outage probability, and the diversity order. Our analytical results show that the transmit power scales down linearly with the BS antenna number and quadratically with the IRS element number. The diversity order equals the smaller of the BS antenna number and the IRS element number with a scaling coefficient. Our results also reveal the effect of the phase quantization resolution to the system performance when non-ideal IRS is used. Numerical results are provided to validate the accuracy of our analysis and the non-ideal IRS with four or more bits for quantization is shown to achieve nearly the same performance as the ideal IRS. [ABSTRACT FROM AUTHOR]

Paving the path toward the fifth generation (5G) of wireless networks with a huge increase in the number of user equipment has strengthened public concerns on human exposure to radio-frequency electromagnetic fields (RF EMFs). This requires an assessment and monitoring of RF EMF exposure, in an almost continuous way. Particular interest goes to the uplink (UL) exposure, assessed through the transmission power of the mobile phone, due to its close proximity to the human body. However, the UL transmit (TX) power is not provided by the off-the-shelf modem and RF devices. In this context, we first conduct measurement campaigns in a multi-floor indoor environment using a drive test solution to record both downlink (DL) and UL connection parameters for Long Term Evolution (LTE) networks. Several usage services (including WhatsApp voice calls, WhatsApp video calls, and file uploading) are investigated in the measurement campaigns. Then, we propose an artificial neural network (ANN) model to estimate the UL TX power, by exploiting easily available parameters such as the DL connection indicators and the information related to an indoor environment. With those easy-accessed input features, the proposed ANN model is able to obtain an accurate estimation of UL TX power with a mean absolute error (MAE) of 1.487 dB.

In this paper, we analyze the average transmit power of non-orthogonal multiple access (NOMA) systems with requirements on the user signal-to-interference-plus-noise-ratios (SINRs), and propose new transmission schemes and user clustering algorithms to reduce the average transmit power. First, for systems with a multi-antenna base station (BS) and a single cluster of two single-antenna users, the average transmit power with SINR constraints is analyzed for channel-alignment-based NOMA and multi-user beamforming with matched filter (MF) beamformers. Properties of the average transmit power are obtained with respect to the alignment threshold and the BS antenna number. It is shown that using either scheme alone without the alignment consideration leads to unbounded average transmit power. With the observation that the two schemes have distinct preferred regions of channel alignment, hybrid transmissions of NOMA and multi-user beamforming are proposed for power saving and outage avoidance. Further, for systems with more than two users, clustering algorithms are developed to group users into multiple two-user clusters with respect to the minimization of the total transmit power for NOMA and hybrid schemes. Simulation results are provided to validate our theoretical results. In addition, the proposed transmission schemes and clustering algorithms are shown to achieve significant saving in the average transmit power. [ABSTRACT FROM AUTHOR]

Wireless body area networks (WBANs) present unique challenges due to their specific characteristics of mobility and over-the-body radio propagation. A huge amount of factors—both internal and external to the network—affect WBAN channel conditions, so a reliable and comprehensive theoretical model of these communications is unfeasible and impractical in real scenarios. Thus, an empirical performance analysis of several WBAN channels is presented in this work, based on the receiver signal strength indicator (RSSI) and packet reception rate (PRR) metrics. Four different static and dynamic activities have been characterized: standing, sitting, cycling and walking. This analysis confirms the theoretical notions of path attenuation due to body parts obstructing the signal path, while serving as a benchmark for the design of future algorithms. The experiments have been carried out with real hardware nodes with wireless interfaces in three ISM bands: 433 MHz, 868 MHz and 2.4 GHz, evaluating the effect of the transmit power and node placement for different subjects. In all scenarios, the PRR metric reaches its maximum of 100% for both sub-GHz bands. Finally, our study concludes that the RSSI metric is sufficient to exploit the periodicity of dynamic activities, without the need for any extra hardware resources. [ABSTRACT FROM AUTHOR]

Securing wireless communication, being inherently vulnerable to eavesdropping and jamming attacks, becomes more challenging in resource‐constrained networks such as internet‐of‐things. Towards this, physical layer security (PLS) has gained significant attention due to its low complexity. The authors address the issue of random inter‐node distances in secrecy analysis and develop a comprehensive quality‐of‐service (QoS) aware PLS framework for the analysis of both eavesdropping and jamming capabilities of the attacker. The proposed solution covers the spatially stochastic deployment of nodes. The secrecy performance is characterised against both attacks using inter‐node distance‐based probabilistic distribution functions. The model takes into account the practical limits arising out of underlying QoS requirements, which include the maximum distance between legitimate users driven by transmit power and receiver sensitivity. A novel concept of eavesdropping zone is introduced, and the relative impact of jamming power is investigated. Closed‐form expressions for asymptotic secrecy outage probability are derived offering insights into the design of optimal system parameters for desired security level against the attacker's capability of both attacks. The analytical framework, validated by numerical results, establishes that the proposed solution offers a potentially accurate characterisation of the PLS performance and key design perspective from point‐of‐view of both legitimate user and attacker. [ABSTRACT FROM AUTHOR]

Unlike most studies assuming exact knowledge of the transmit power and path-loss exponent, we address the localization problem under a more practical assumption that the exact values of the transmit power and/or path-loss exponent are unavailable. We propose an algorithm based on the differential evolution, opposition based learning, and adaptive redirection that jointly estimates the position of the target node and the parameters. Results from simulation and indoor experiments show that the proposed algorithm provides higher localization accuracy and requires less computational time than conventional algorithms especially when the exact values of the transmit power and path-loss exponent are unavailable simultaneously. [ABSTRACT FROM AUTHOR]

Future devices are likely to have the capability to harvest energy from radio-frequency (RF) signals. In this paper, we consider such energy harvesting (EH) devices operating in a two-tier orthogonal frequency-division multiple access-based heterogeneous network. Critically, we investigate how such EH devices can be supported alongside non-RF harvesting or legacy devices. Our aim is to minimize the downlink sum transmit power of both femto and macro base stations and ensure that legacy and EH devices receive a given data rate and amount of energy, respectively. Critically, we study sub-carrier and power allocation to both types of devices and investigate novel questions related to interference, which reduces network capacity but improves the amount of harvested energy by EH devices. To study these questions, we formulate a mixed-integer non-linear program (MINLP) and propose three linear approximations to the MINLP where devices are either assigned one or multiple sub-carriers. Numerical results show that EH devices will not affect network capacity if they can harvest sufficient energy from data transmissions to legacy devices. In addition, if multiple sub-carriers can be assigned to devices, our results show that the sum transmit power decreases by approximately 15% as compared with assigning a single sub-carrier to these devices.

Over the last decade, short-range communications in the THz (Terahertz) band have been extensively studied as a technology-enabler for dense and ultra-dense wireless networks. The increasing demand for high data rates for wireless communication systems will inevitably lead to the extension of operation frequencies with larger bandwidths. THz range enables bandwidths on the order or hundreds of GHz. Thus, THz Band communication will alleviate the capacity limitations and spectrum scarcity of current wireless systems, and enable new classical networks and novel nanoscale networks applications. The main aim of this paper is to provide design guidelines for close proximity links with transmission capacity beyond 100 Gbit/s. We present the path loss, absorption loss, signal to noise ratio (SNR) and capacity of propagating electromagnetic waves at THz Band in different air medium types. The channel capacity and SNR properties are calculated according to transmit power estimation. In this paper, five air medium types are investigated which are average latitude—summer, high latitude—summer, average latitude—winter, high latitude—winter and tropics. [ABSTRACT FROM AUTHOR]

We investigate the joint selection problem of the transmit power level and the best access point for multi-access points. We further reduce the transmit power by jointly optimizing the transmit power and the access point selection. Our aim is to minimize the total transmit power, while each terminal maintains minimum signal to interference ratio requirement. We observe that the optimum solution can be achieved through proposed iterative algorithm for both TA link and AT link. Simulation results show that proposed algorithm (joint optimization of transmit power level and access point) outperforms the algorithm which optimizes the transmit power only. We also observe that the duality between the TA link and AT link does not hold in multi-access points environment. Accordingly, the resulting power vectors and the access point vectors for TA link and AT link are different in general. [ABSTRACT FROM AUTHOR]

With the rapid development and evolvement of unmanned aerial vehicle (UAV) technology, UAV aided wireless communication technology has been widely studied recently. In this paper, a buffer aided multi-UAV relaying network is investigated to assist blocked ground communication. According to the mobility and implementation flexibility of UAV relays, it is assumed that the communication link between air-to-ground is the Rician fading channel. On the basis of information causality, we derive the state change of the information in the buffer of UAV relays and maximize the end-to-end average throughput by join the relay selection, UAV transmit power, and UAV trajectory optimization. However, the considered problem is a mixed integer non-convex optimization problem, and therefore, it is difficult to solve directly with general optimization methods. In order to make the problem tractable, an efficient iterative algorithm based on the block coordinate descent and the successive convex optimization techniques is proposed. The convergence of the proposed algorithm will be verified analytically at the end of this paper. The simulation results show that by alternately optimizing the relay selection, UAV transmit power, and UAV trajectory, the proposed algorithm is able to achieve convergence quickly and significantly improve the average throughput, as compared to other benchmark schemes. [ABSTRACT FROM AUTHOR]

In hostile environments, localization often suffers from malicious attacks that may distort transmit power and degrade positioning accuracy significantly for wireless sensor network. A robust semidefinite relaxation secure localiza-tion algorithm RSRSL was proposed to improve the location accuracy against malicious attacks. On the assumption of unknown transmit power, which is undoubtedly approximate to the fact of WSN, a novel secure location probability model was introduced for single-target and multi-target sensor networks, respectively. Taking the computational complexity of RSRSL into account, the nonlinear and non-convex optimization problem was simplified into a semidefinite programming problem. According to the results from both simulations and field experiments, it is clearly demonstrated that the proposed RSRSL has better performance on location accuracy, in contrast to the conventional localization algorithms.

Unmanned aerial vehicles (UAVs) have been generally applied in the field of communication due to their small size, flexible mobility, and convenient deployment. As a mobile base station, the UAV node can quickly establish a line-of-sight link with the ground node, thereby improving communication performance. In this paper, we study a multi-UAV assisted data collecting system. Specifically, in the case of limited system energy consumption, UAV flight energy consumption and ground node data transmission energy consumption are considered as an general limitation, and considering the channel interference between nodes, a multi-UAV assisted data collection model is studied. An non-convex problem that maximizes the minimum amount of data collected from ground nodes is further formulated. Since the original optimization problem is non-convex that difficult to solve directly, the problem is first decomposed into four sub-problems, and then the solution of each sub-problem is obtained by using successive convex approximation and block coordinate descent method. Finally, based on the solution of the four subproblems, an iterative algorithm for joint optimization of data transmission planning, transmission power, UAV trajectory and mission time is proposed. Simulation experiments show that the proposed algorithm can obtain more transmission data than the baseline algorithms., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

This paper considers covert communications in the context of unmanned aerial vehicle (UAV) networks, aiming to hide a UAV for transmitting critical information out of an area that is monitored and where communication is not allowed. Specifically, the UAV as a transmitter intends to transmit information to a legitimate receiver (Bob) covertly while avoiding being detected by a warden (Willie), where location uncertainty exists at Bob and/or Willie. In order to enhance the considered covert communication performance, we jointly optimize the UAV's trajectory and transmit power in terms of maximizing the average covert transmission rate from the UAV to Bob subject to transmission outage constraint and covertness constraint. The formulated optimization problem is difficult to tackle directly due to the intractable constraints. As such, we first employ conservative approximation to transform a constraint into a deterministic form and then apply the first-order restrictive approximation to transform the optimization problem into a convex form. By applying the successive convex approximation technique, an efficient iterative algorithm is developed to solve the optimization problem. Our examination shows that the developed joint trajectory and transmit power optimization scheme achieves significantly better covert communication performance as compared to a benchmark scheme. [ABSTRACT FROM AUTHOR]

Abstract In vehicular ad-hoc networks, a large number of vehicles in mix-zones can increase privacy but at the expense of losing communication quality. Thus, it is necessary to harmonize these two conflicting goals for privacy protection. In this study, we propose an internal optimization model and an external anonymity updating game to cross-layer joint the physical layers transmit power and MAC layers delay into a two-step non-cooperative game model, by which the communication and privacy players respectively enjoy one utility function. The first step is to establish an internal optimal model aiming to balance privacy and delay, where we can obtain the optimal transmit power. The optimal number of neighbor vehicles can be obtained by selecting the transmitting power, which can be used as the input of the second step. For the second step, we present a non-cooperative external anonymity updating game model to analyze the non-cooperative behavior of vehicles, all of which together strive to maximize the utility function at the minimum cost. We analyze the Nash equilibrium in n-player complete information game, we also derive the pure strategy Nash equilibrium. Extensive numerical calculations are conducted to comprehensively investigate the reaction of the Nash equilibrium to various combinations of parameters. The results show that the two-step non-cooperative game of anonymity updating is capable of self-adapting to the vehicular context and improving the privacy without compromising on communication quality. [ABSTRACT FROM AUTHOR]

Abstract In this work, we study unmanned aerial vehicle (UAV) relaying networks with multi-hop, where one source communicates with one destination through the help of L relay hops. Cache is employed at the relay nodes nearby the destination. Then the destination can acquire the data directly through the cache instead of communicating with the source. For the multi-hop relaying networks with cache, we not only analyze the transmission performance of the considered system by deriving the analytical expressions for the outage probability as well as symbol error rate (SER), but also provide the asymptotic outage probability and SER, in the large region of transmit power. The proposed caching method is proved by simulation and numerical results, and validates that the usage of cache can provide ultra-reliable and low-latency communications for UAV systems. [ABSTRACT FROM AUTHOR]

Improved Spectral Efficiency (SE) is a prominent feature of Massive Multiple-Input and Multiple-Output systems. These systems are prepared with antenna clusters at receiver (Rx) and transmitter (Tx). In this paper, we examined a massive MIMO system to increase SE in each cell that ultimately improves the area throughput of the system. We are aiming to find appropriate values of average cell-density (D), available bandwidth (B), and SE to maximize area throughput because it is the function of these parameters. Likewise, a SE augmentation model was developed to attain an increased transmit power and antenna array gain. The proposed model also considers the inter-user interference from neighboring cells along with incident angles of desired and interfering users. Moreover, simulation results validate the proposed model that is implementable in real-time scenarios by realizing maximum SE of 12.79 bits/s/Hz in Line of Sight (LoS) and 12.69 bits/s/Hz in Non-Line of Sight (NLoS) scenarios, respectively. The proposed results also substantiate the SE augmentation because it is a linear function of transmit power and array gain while using the Uniform Linear Array (ULA) configuration. The findings of this work ensure the efficient transmission of information in future networks.

Reducing the energy consumption of the wireless networks is significantly important for the economic and ecological sustainability of the ICT industry, as high energy consumption may limit the performance of wireless networks, and is one of the main network costs. To solve the energy consumption problem, especially on the terminal side, a scheme known as distributed mobile cloud (DMC) is considered to be a potential solution. Multiple mobile terminals (MTs) can cooperatively take advantage of good quality links among the MTs to save energy when receiving from the Base Station. In this paper, we aim to find the optimal transmit power to further reduce the energy consumption of DMC. From simulation studies, it is shown that up to 80% energy savings can be accomplished when using optimal transmit power, compared to using the standard DMC without exploring the optimal transmit power. [ABSTRACT FROM AUTHOR]

Vehicular ad-hoc networks pose stringent requirements on quality-of-service (QoS) and security strength in parallel because of their open channels and highly dynamic topology. Harmonizing these two conflicting goals is an urgent challenge, especially in VNs that are characterized by restrictive resources, e.g. bandwidth and link lifetime. This paper aims to balance the anticipated QoS and security strength in context to fully utilize limited network and computing resources to attain a satisfactory performance rating without compromising any security. To this end, we use non-cooperative game theory to formulate node utility, synthesizing the channel capacity and security strength from the perspective of adaptively controlling the transmit power and encryption block length in Nakagami multipath fading (NMF) channels. Moreover, we analyze the non-cooperative behavior of a “communication player” in controlling the transmit power and a “security player” in deciding the encryption block length, both of whom together strive to maximize the utility function at minimum cost. We then theoretically derive the pure strategy Nash equilibrium. Extensive numerical calculations are conducted to comprehensively investigate the reaction of the Nash equilibrium against the various combinations of the considered parameters. The results show that the proposed joint optimization method is capable of self-adapting to the vehicular context and improving the communication quality without compromising on security. [ABSTRACT FROM AUTHOR]

Heterogeneous cellular networks (HCNs) have emerged as the primary solution for explosive data traffic. However, an increase in the number of base stations (BSs) inevitably leads to an increase in energy consumption. Energy efficiency (EE) has become a focal point in HCNs. In this paper, we apply tools from stochastic geometry to investigate and optimize the energy efficiency (EE) for a two-tier HCN. The average achievable transmission rate and the total power consumption of all the BSs in a two-tier HCN is derived, and then the EE is formulated. In order to maximize EE, a one-dimensional optimization algorithm is used to optimize picocell BS density and transmit power. Based on this, an alternating optimization method aimed at maximizing EE is proposed to jointly optimize transmit power and density of picocell BSs. Simulation results validate the accuracy of the theoretical analysis and demonstrate that the proposed joint optimization method can obviously improve EE.

In this letter, we investigate the problem of sum-power minimization for the users in orthogonal frequency division multiple access (OFDMA) networks subject to the target rate constraint. To address this problem, two fast water-filling (WF) methods are developed under two scenarios: without and with considering the peak-power constraint on the subchannels, which are referred to as FWF and FWF-PP, respectively. We show that our proposed methods converge to the optimal solution, while the computational complexity is reduced compared to the existing WF methods. Our results are also confirmed via simulations. [ABSTRACT FROM AUTHOR]

Non‐orthogonal multiple access (NOMA) has been considered as one of the key enabling techniques for next‐generation wireless networks and the overall performance of these systems largely depends on the power allocation (PA). In this Letter, the authors address the PA problem in a downlink cellular NOMA network. They propose an auction‐based mechanism in which the users compete for the transmit power being sold by the base station. Each user places his bid iteratively in order to maximise his own utility. Further, the authors prove the existence of an unique Nash equilibrium theoretically. Simulation results demonstrate the effectiveness of the proposed scheme in terms of the average sum rate of users as compared to an existing algorithm. [ABSTRACT FROM AUTHOR]

To solve the issue that new femtocells deployed in hierarchical networks would introduce a series of interference,a power self-configuration scheme was proposed.Various kinds of interference that femtocell base station might receive from other base stations were analyzed.Then an optimal power issue was formulized,as was able to maximize the femtocell system capacity on the condition guaranteeing the existing users'normal communication.And the optimal solution was also obtained with lagrange multiplier method.The simulation results show that the proposed scheme cuts down the transmit power of femtocell,increases the throughput and reduces interference for existing users,comparing with the scheme based on received signal strength.

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The localization of a sensor in wireless sensor networks (WSNs) has now gained considerable attention. Since the transmit power and path loss exponent (PLE) are two critical parameters in the received signal strength (RSS) localization technique, many RSS-based location methods, considering the case that both the transmit power and PLE are unknown, have been proposed in the literature. However, these methods require a search process, and cannot give a closed-form solution to sensor localization. In this paper, a novel RSS localization method with a closed-form solution based on a two-step weighted least squares estimator is proposed for the case with the unknown transmit power and uncertainty in PLE. Furthermore, the complete performance analysis of the proposed method is given in the paper. Both the theoretical variance and Cramer-Rao lower bound (CRLB) are derived. The relationships between the deterministic CRLB and the proposed stochastic CRLB are presented. The paper also proves that the proposed method can reach the stochastic CRLB. [ABSTRACT FROM AUTHOR]

In this letter, we study the coverage of base stations (BSs) in heterogeneous cellular networks, where BSs with different transmit powers are randomly deployed. Specifically, the boundary of coverage is formulated analytically as the intersection of circles when a multiplicative bias is applied for BS association. Moreover, the effect of the transmit power and the path loss exponent on the coverage is investigated. Furthermore, for femto BSs with low transmit powers which are deployed to offload the traffic of the cellular system, it is shown that the expected number of offloaded users is concave with respect to the transmit power. Finally, the coverage of BSs is evaluated through simulations, which verify the accuracy of the presented analysis. [ABSTRACT FROM PUBLISHER]

This letter is concerned with the optimal power allocation in femtocell networks using a new technique based on multiobjective optimization. In this letter, we consider a cochannel framework for the coexistence of orthogonal frequency division multiple access (OFDMA)-based macrocell and femtocell networks. We jointly maximize the total rate of OFDMA femtocell network and minimize the total transmit power of femtocell base stations while satisfying a target constraint on transmit power when either the cross femtocell interference is included or excluded. Additionally, the results show that the proposed method for power transmission contributes toward improving the energy efficiency of femtocell networks. [ABSTRACT FROM PUBLISHER]