Achievable Data Research Articles

Hybrid Power Line/Wireless System With Optimal Subcarrier Permutation Under Uniform or Optimal Power Allocation

This article studies optimal subcarrier permutation in hybrid power line/wireless systems to either maximize the achievable data rate or minimize the average bit error probability (BEP). In order to better exploit the frequency selectivity of power line and wireless media, subcarrier permutation is optimized under uniform or optimal power allocation over an orthogonal frequency-division multiplexing scheme using maximal-ratio combining. Different from previous works, we demonstrate that the normalized signal-to-noise (nSNR) must be considered instead of the SNR and prove that it can be extended to cases where the minimization of the average BEP and optimal power allocation are considered. Moreover, we show that subcarrier permutation and power allocation problems can be assumed to be decoupled. Numerical results show that performance gains associated with subcarrier permutation become more relevant as the frequency selectivity of the nSNRs increases. In addition, the optimal subcarrier permutation is more effective for minimizing the average BEP than maximizing the achievable data rate and yields similar improvement under the usage of uniform and optimal power allocations.

Communication by means of modulated Johnson noise

We present the design of a passive wireless communication method that does not rely on ambient or generated RF sources. Instead, the method modulates the Johnson (thermal) noise of a resistor to transmit information bits wirelessly. By selectively connecting or disconnecting a matched resistor to an antenna, the system can achieve data rates of up to 26 bps and distances of up to 7.3 m. This communication method operates at very low power, similar to that of an RFID tag, with the advantage of not requiring a preexisting RF signal to reflect.

Coverage Analysis of mmWave and THz-Enabled Aerial and Terrestrial Heterogeneous Networks

Heterogeneous networks (HetNets) are becoming a promising solution for future wireless systems to satisfy the high data rate requirements. This paper introduces a stochastic geometry framework for the analysis of the downlink coverage probability in a multi-tier HetNet consisting of a macro-base station (MBS) operating at sub-6 GHz, millimeter wave (mmWave)-enabled unmanned aerial vehicles (UAVs) operating at 28 GHz, and small BSs operating both at mmWave and THz frequencies. The analytical expressions for the coverage probability for each tier have been derived in the paper. Monte Carlo simulations are then performed to validate the analytical expressions. The effectiveness of the HetNet is analyzed on various performance metrics including association and coverage probabilities for different network parameters. We show that the mmWave and THz-enabled cells provide significant improvement in the achievable data rates because of their high available bandwidths, however, they have a degrading effect on the coverage probability due to their high propagation losses.

Conditional Contact Angle Distribution in LEO Satellite-Relayed Transmission

This letter characterizes the contact angle distribution based on the condition that the relay low earth orbit (LEO) satellite is in the communication range of both the ground transmitter and the ground receiver. As one of the core distributions in stochastic geometry-based routing analysis, the analytical expression of the Cumulative Distribution Function (CDF) of the conditional contact angle is derived. Furthermore, the conditional contact angle is applied to analyze the inaccessibility of common satellites between the ground transmitter and receiver. Finally, with the help of the conditional contact angle, coverage probability and achievable data rate in LEO satellite-relayed transmission are studied.

Enabling Cell-Free Massive MIMO Systems With Wireless Millimeter Wave Fronthaul

Cell-free massive MIMO systems have promising data rate and coverage gains. These systems, however, typically rely on fiber based fronthaul for the communication between the central processing unit and the distributed access points (APs), which increases the infrastructure cost and installation complexity. To address these challenges, this paper proposes two architectures for cell-free massive MIMO systems based on wireless fronthaul that is operating at a higher-band compared to the access links. These dual-band architectures ensure high data rate fronthaul while reducing the infrastructure cost and enhancing the deployment flexibility and adaptability. To investigate the achievable data rates with the proposed architectures, we formulate the end-to-end data rate optimization problem accounting for the various practical aspects of the fronthaul and access links. Then, we develop a low-complexity yet efficient joint beamforming and resource allocation solution for the proposed architectures based on user-centric AP grouping. With this solution, we show that the proposed architectures can achieve comparable data rates to those obtained with optical fiber-based fronthaul under realistic assumptions on the fronthaul bandwidth, hardware constraints, and deployment scenarios. This highlights a promising path for realizing the cell-free massive MIMO gains in practice while reducing the infrastructure and deployment overhead.

A Reflection Self-Canceling Design Technique for Multidrop Memory Interfaces

We propose a reflection self-canceling design technique for multidrop memory interfaces. In this technique, lengths of branch lines are designed, so that dominant multiple reflections become self-canceling. As a result, reflective intersymbol interferences (ISIs) can be greatly reduced to increase the bandwidth without utilizing serial resistor insertion, reflection compensation lines (RCLs), or advanced circuits, such as equalization circuits. Using the proposed and the conventional techniques, two eight-drop channels were designed with 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> microstrip lines on FR-4 printed circuit board (PCB) and tested with the pseudo-random binary sequence (PRBS) 31 pattern for comparison. At 10.5 Gb/s, the worst eye height was measured 28.0 mV in the proposed design, while the worst eye diagram of the conventional design was closed. The proposed design achieved the maximum data rate of 12.5 Gb/s and achieved the worst eye height of 10.0 mV. The achieved data rate of 12.5 Gb/s is 95.3% faster than the prior art measured with an eight-drop channel without equalization circuits.

3×3 MIMO 60-GHz OFDM-RoF System With Long-Distance Wireless Transmission Enabled by MIMO Volterra Filtering

A 3×3 60-GHz multiple-input multiple-output (MIMO) radio-over-fiber system with an MIMO Volterra filter was demonstrated. The main objective of the proposed scheme is to compensate for the nonlinear distortion caused by radio frequency (RF) power amplifiers (PAs) before the signals reaches the transmitter antennas—particularly when the PAs operate with a high input power to achieve a high output RF power for long-distance wireless transmission. When the required wireless transmission distance is only 7 m, the 3×3 MIMO system with careful control of the PA input power can achieve a data rate of 126 Gbps. However, the data rate decreases rapidly over a longer wireless distance because of the larger loss. By eliminating nonlinear distortion and interchannel interference simultaneously, MIMO Volterra filtering can significantly increase the achievable data rate of a long-distance system. When the required data rate is 90 Gbps (or 100 Gbps), the maximum wireless transmission distance is 118 m (or 70 m) with the aid of MIMO Volterra filtering, but it is only 74 m (or 40 m) without MIMO Volterra filtering.

Injection Locking Properties of an Dual Laser Source for mm-Wave Communications

We for the first time, the optical injection locking (OIL) to a frequency comb of a hybrid <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{{InP-Si}}_{3}\text{{N}}_{4}$</tex-math></inline-formula> dual laser source for high-purity mm-wave generation through optical heterodyning. Key performance parameters of the comb line demultiplexing functionality provided by this source under OIL – such as adjacent-comb-line side mode suppression ratio (SMSR) and locking range – are reported. It is also shown that the amount of free-running drift exhibited by the hybrid lasers (which should be as little as possible to keep them within the locking range) can be minimized by reducing the amount of bias level applied to the heater-based phase actuators present in such lasers. According to the measured drift, locking range and SMSR, these lasers have potential to achieve continuous locking with SMSR levels of more than 45 dB at comb line separations higher than 9 GHz. Successful carrier generation at 93 GHz is demonstrated by locking the two lasers to an optical frequency comb achieving an ultra-stable International Telecommunication Union (ITU)-compliant signal. Both real-time and DSP-aided data transmissions are demonstrated at this frequency achieving data rates of 12.5 and 28 Gbit/s, respectively.

Low-Power High-Bandwidth Non-Polar InGaN Micro-LEDs at Low Current Densities for Energy-Efficient Visible Light Communication

Recently, the rapidly developing Internet of Things (IoT) needs to support massive connectivity with high transmission data rate, which requires IoT transmitters with high speed and low power consumption. In this work, non-polar micro-LED operating at low current density of 10 A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> can still maintain a high bandwidth of 508 MHz and near-peak external quantum efficiency (EQE), making it promising for low-power, energy-efficient visible light communication (VLC) to address the challenge. At 10 A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> , non-polar micro-LEDs can achieve a low power consumption and high energy efficiency, still maintaining the data rate of 0.25 Gbps. In addition, data rates of 2 Gbps and 1.1 Gbps were also successfully achieved for non-polar micro-LED operating at 320 and 50 A/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> , respectively, to evaluate the relationship between power consumption and achievable data rate. The capability of non-polar micro-LED that can realize low-power consumption and high bandwidth at low current density is expected to play a great role in the field of energy-efficient VLC, multi-function display and IoT in the future.

Enhancing underwater Acoustic Identification Tag design using concurrent wireless ultrasonic power transfer and backscatter communication

Improvements in undersea localization and navigation of Autonomous Underwater Vehicles (AUVs) is critical. However using conventional active transponders as navigation aids is limited by powering constraints. Passive backscatter devices such as Acoustic Identification (AID)Tags are an alternate solution to this energy limitation [Satish et al., JASA 149 (2021)], but offer limited information content. To address this limitation, adding a wireless ultrasonic power transfer capability to these passive AID tags can be used to enable backscatterer uplink communication between the AID tag and an interrogating compact high-frequency SONAR system (which can be mounted on an AUV). Our design comprises a piezoelectric transducer impedance matched to a connected electrical load across two frequency ranges: a narrowband energy harvesting range, and a broadband data range. Onboard electronics harvest acoustic energy in the narrowband to power an onboard microcontroller, which can be used to simultaneously modulate the transducer broadband acoustic impedance by switching the electrical load connected to transducer during backscatter uplink communication. Water tank experiment using custom transducers, operating either around 1 MHz or 350 kHz, were conducted to quantify-amongst others-the operational source to tag distance, system power requirements and achievable communication data rates using the proposed concurrent ultrasonic power and data transfer approach.

Improved Hierarchical Codebook-Based Channel Estimation for mmWave Massive MIMO Systems

A novel approach is proposed to improve channel estimation accuracy in hierarchical codebook-based beam search for millimeter-wave (mmWave) massive multiple-input and multiple-output (MIMO) transmissions with channels that are accessible only through analog beamforming. Our approach is targeted at overcoming the resolution limit of directional angle estimation. In the proposed method, the data transmission beam is determined based on either two or three candidate codewords in the bottom layer and their beamforming gains. Design of the optimal beam is derived by exploiting the analytic structure of codewords in the bottom layer of the hierarchical codebook. Compared to conventional schemes used to increase the angle estimation resolution, the proposed scheme presents a higher achievable data rate in practical signal-to-noise ratio (SNR) ranges as well as superior channel estimation accuracy. This is verified through simulation results. The proposed method requires fewer codewords to be probed for beam training compared to the conventional methods, which reduces complexity.

A Novel Approach for Modeling and Digital Generation of RF Signals Distorted by Bandlimited Phase Noise

In radar and communication systems, phase noise is one of the main causes of performance degradation. Phase noise increases the uncertainty in radar measurements and limits the achievable data rates in communication systems. When radio frequency (RF) signals distorted by bandlimited phase noise are modeled, the phase noise power spectral density (PSD) is usually approximated by a scalar root-mean-square (RMS) phase error derived from a simple integration of the PSD. This disregards the close-to-carrier noise excess. In this article, we show that this convention simplification describes the real behavior of phase noise inadequately. In addition, we present a simulation of realistic phase noise behavior. The novel additive colored noise (ACN) model requires a representative phase noise PSD of the phase-locked loop (PLL) signal generator phase noise to be modeled. The developed ACN approach is validated by comparing the measured PSD of different PLL signal generators with the respective simulated RF signals distorted by phase noise. As a simple metric for assessing the quality of the phase noise models, we use the influence of phase noise on carrier frequency estimation. It is shown that the novel approach shows a significant improvement in the agreement between the simulated and measured precision compared to standard additive white Gaussian noise (AWGN) models. The results show that advanced phase noise models, as proposed in this paper, are necessary to adequately model and predict the performance of radar and communication systems.

IRS-aided network scheme supports unmanned aerial vehicle communication

Intelligent reflecting surface (IRS) and unmanned aerial vehicle (UAV) are forecasted to be extensively used in the forthcoming wireless system. In order to enhance the operational efficiency of UAVs in the urban areas, this paper proposes employing IRS equipped on the rooftop of buildings to create ground-to-air data links between the terrestrial base stations (BSs) and UAVs without any change in the terrestrial infrastructure. An optimization problem aiming to maximize the cumulative achievable data rate (CADR) and minimize the UAV's operational duration via altering the configuration of the IRS network, i.e., the phase profiles and reflecting angles, and the UAV's trajectory has been investigated. To deal with this optimization problem, firstly, we analyze the far-filed radiation pattern of all IRSs to construct the received signal strength (RSS) map over the considered region for a given setup of the activated BS and IRS networks. Then, this map is used to construct the designated BS-IRS-UAV paths (DBIUPs) that are the best paths between neighboring BSs obtained through optimizing the IRS network. Secondly, we develop heuristic algorithms (HAs) to select appropriate DBIUPs to build the optimize UAV's trajectory for any departing and landing positions. The simulation results show that the proposed scheme significantly improves the CADR and reduces the disconnected distance/duration (DD) of considered UAV communication, and the proposed algorithm has a good convergence.

Deep Federated Learning Based Convergence Analysis in Relaying-Aided MEC-IoT Networks

Recently, deep federated learning has attracted much attention from researchers in the fields of wireless communications, where the relaying technique has been shown as a powerful technology to assist the wireless signals and enhance the transmission quality, which is very important to the development of mobile edge computing (MEC) based Internet of Things (IoT) networks. In a relaying-aided MEC-IoT system, it is of vital importance to deeply investigate the system signal-to-noise ratio (SNR) at the receiver side, as it mainly determines the system performance metrics, such as capacity (or achievable data rate), outage probability, and bit-error-rate (BER). To this end, we first investigate the instantaneous convergence error, by deeply studying the relationship between the instantaneous two-hop relaying channels. We then investigate the statistical convergence error, by performing the statistical expectation with respect to the two-hop relaying channels. We finally present some results to show that the analysis of the convergence error is effective. The work in this paper can provide some theoretical foundation for deep federated learning and computing networks.

On performance of full-duplex UAV system with multiple NOMA users and millimeter-wave communications

This article considers millimeter-wave (mmWave) communications in a full-duplex (FD) unmanned aerial vehicle (UAV) system with multiple non-orthogonal multiple access (NOMA) users. In particular, a UAV operates in an FD transmission mode and acts as a decode-and-forward (DF) relay to aid communications between a ground base station and multiple ground users. Unlike previous works on the UAV-aided NOMA systems, where the specific carrier frequencies are often ignored, this work investigates the effect of a specific carrier frequency in the mmWave band and the channel model proposed for the fifth and beyond generations (5G and B5G) of mobile communications. The closed-form expressions of outage probability (OP) and achievable data rate (ADR) of the FD-UAV-NOMA system with mmWave communications (called as the MW-FD-UAV-NOMA system) are successfully derived over Nakagami-m fading channels. Numerical results clearly indicate the strong effects of the residual self-interference (RSI), high frequency, far distances between transmitters and receivers, wide bandwidth, and the altitude of the UAV on the OP and ADR of the MW-FD-UAV-NOMA system. Since the mmWave communications are used, an increase in the frequency, distances, bandwidth, and/or altitude of the UAV will significantly reduce the performance of the MW-FD-UAV-NOMA system. Importantly, when the UAV flies nearer the base station, the performance of the MW-FD-UAV-NOMA system can be better than when the UAV flies nearer the users. Finally, the exactness of the obtained expressions is confirmed via Monte-Carlo simulations.

Combining multi-RIS and relay for performance improvement of multi-user NOMA systems

In this paper, we propose a theoretical framework to examine the performance of a non-orthogonal multiple access (NOMA) system with multiple users under the support of multiple advanced reconfigurable intelligent surfaces (RISs) and a traditional relay. We derive the analytical expressions of main performance metrics of the proposed multi-RIS-and-relay aided multiple-user NOMA system (so called the RIS-R-NOMA system), including the outage probability (OP) and the achievable data rate (ADR) over Nakagami-m fading channels. We conduct the Monte-Carlo simulations to confirm the exactness of our mathematical expressions. Numerical results reveal that the OP of the proposed RIS-R-NOMA system is significantly lower than the OPs of the traditional NOMA systems without either RIS or relay (the R-NOMA and RIS-NOMA systems), and the ADR of the proposed RIS-R-NOMA system is much higher than the ADR of the R-NOMA system. Importantly, at high transmit power, the ADRs of both RIS-R-NOMA and R-NOMA systems are similar due to the property of NOMA. Additionally, the effects of various parameters such as the number of reflecting elements (REs), the locations of the RISs, the power allocation coefficients, and the data transmission rates on the performance of the RIS-R-NOMA system are demonstrated.

Terabit Optical Wireless-Fiber Communication With Kramer-Kronig Receiver—Part II

A high speed optical wireless-fiber solution was proposed in part I of this research with applications such as network backhaul and data center links. The proposed system is based on the utilization of state-of-the-art modulation and multiplexing techniques in optical fiber and optical wireless communications, including multicore fibers (MCFs) and coherent detection based on Kramer-Kronig (KK) receivers. In this letter, we analyze the performance of the proposed system and compare it with an intensity modulation and direct detection (IM/DD) system. Superior performance of the KK receiver is shown for various modulation formats and optical amplification schemes. We also consider the eye-safety constraint for the optical power as a practical design factor. It is demonstrated that the position of optical amplifiers affects the multiplexing gain and achievable data rate when eye-safety constraint is imposed. Further important challenges for the practical deployment of the system are discussed.

Dual-Hop Mixed FSO-VLC Underwater Wireless Communication Link

Underwater optical wireless communications (UOWCs) are promising and potential wireless carriers to envisage underwater phenomenal activities for various applications towards the futuristic 5G and beyond (5GB) wireless systems. The main challenges to deploy underwater applications are the physicochemical properties and strong turbulence channel conditions. In this regard, the end-to-end (E2E) performance analysis of a dual-hop mixed FSO/UVLC system under the intensity modulation/direct detection (IM/DD) technique in consideration of pulse amplitude modulation (PAM) scheme is investigated. Throughout this study, to tackle the issues of moderate-to-strong turbulence channel conditions, this work deploys the Gamma-Gamma (GG) distribution fading model and the links are designed by unifying plane wave models in the corresponding links, respectively. This investigation outperforms higher achievable data rate with minimal delay response and enhance network connectivity in real-time monitoring scenarios as compared with the traditional underwater wireless communication technologies. In more contrast, the probability distribution function (PDF), cumulative distribution function (CDF), and closed-form expression of the system are derived and presented in terms of Meijer-G function as well as Extended Generalized Bivariate Meijer-G Function (EGBMGF). The significant E2E performance metrics are obtained by employing the decode-and-forward (DF) relay protocol in hostile channel conditions. In aggregating this work, we combine the analytical expressions that present an efficient tool to depict the impact of channel parameters on the system. The simulation results are plausible of the system performance metrics as average BER (ABER) and outage probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(P_{out})$ </tex-math></inline-formula> in the presence of pointing and without pointing error events. Finally, in this work, we use the Monte-Carlo approach for the best fitting curves and validate the numerical expression yields simulation results.

Joint power and blocklength optimization for RIS‐aided multiple‐access downlink ultra‐reliable low‐latency communication

Ultra-reliable low-latency communication (URLLC) has gained significant interest since it deals with short packet transmission adopted to reduce latency; however, this implies that the conventional Shannon capacity formula is not applicable, and the achievable data rate becomes a complex function of the decoding error probability and blocklength. This paper studies URLLC transmission using a time-division multiple access scheme with an arbitrary number of actuators utilising a reconfigurable intelligent surface. The authors optimisze the weighted sum rate of this system subject to reliability, total energy, and latency constraints. For the blocklength allocation in a scenario where each actuator is allocated equal power, a closed-form analytical solution is provided. Also, for the case of joint optimization of the blocklength and power of each actuator, an analytical solution is provided for the case of two actuators, while an iterative sequential quadratic programing method is adopted for the case of an arbitrary number of actuators. The proposed methodology provides a low-complexity, fast solution, which is more efficient than using exhaustive search techniques. The results show that in some cases, optimization of the blocklength provides a near-optimal solution at low complexity, while jointly optimising the blocklength and the power per actuator has an improved performance at the cost of additional complexity.

Improvement for a full-spectrum modulated nonlinear frequency division multiplexing transmission system.

Nonlinear frequency division multiplexing (NFDM), as a possible technique to overcome the limit imposed by Kerr nonlinearity in conventional coherent optical communication systems, has attracted widespread attention in the communication community in recent years. In order to fully utilize the available degrees of freedom in the nonlinear spectrum, this paper focuses on the full-spectrum (FS) modulated NFDM system. First, we maximize the data rate of discrete spectrum (DS) by optimizing the distribution of eigenvalues in DS part of FS. Then through introducing the probabilistic shaping (PS) into the FS system, and combined with linear minimum mean square (LMMSE) estimators, a 1120 km transmission with BER below the hard decision forward error correction (HD-FEC) threshold at 112 Gbps is achieved, where 128 subcarriers with PS-64QAM are used in the continuous spectrum (CS) and 13 eigenvalues with 64QAM are adopted in the discrete spectrum (DS). The achievable data rate is about 12% higher than that of pure CS modulation. Our work achieves the current FS NFDM system with the largest number of multiplexed eigenvalues, and provides a way to improve the performance of FS systems.