Sight Channel Research Articles

NOMA Assisted Two-Tier VR Content Transmission: A Tile-Based Approach for QoE Optimization

Virtual reality (VR) provides users with an immersive and interactive experience through head-mounted devices, which has attracted increasing attention in recent years. Specifically, tile-based VR content transmission provides a promising approach to alleviate the conflict between limited bandwidth and high-performance requirements (e.g., high-resolution and low-delay). However, the tiling pattern affects the encoding efficiency and visual distortion of the VR content. Accounting for this issue, in this paper, a quality of experience (QoE)-aware cost minimization problem is investigated for a tile-based VR content transmission scenario. In particular, an edge server (ES) co-located at a cellular base station (BS) separates its generated VR content into several tiles according to the tiling pattern selection, and a weighted-to-spherically-uniform quality model is used to evaluate the effect of different tiling patterns on QoE. Moreover, to improve the transmission performance between the edge server and VR users (VRUs), unmanned aerial vehicles (UAVs) are leveraged as relay points to provide line of sight channels. Then, we formulate an optimization problem to minimize the sum of weighted total energy consumption and VR content distortion (i.e., QoE-aware cost) by jointly optimizing the tiling pattern selections, the VRUs-UAV grouping, partial computing decisions, and resource allocation. The formulated problem is a mixed integer non-linear programming problem, which is challenging to solve. To address this difficulty, we equivalently decompose the formulated problem into three subproblems and propose corresponding algorithms to solve them, respectively. Numerical results demonstrate that our proposed solution can effectively reduce the QoE-aware cost for VR content transmission in comparison with other baseline algorithms.

Performance of Static Power Allocation in Indoor Room on VLC-NOMA System Using Modulation PPM


 
 
 Visible light communication (VLC) is an emerging and promising technology that exploits the visible light spectrum for data transmission. However, one of the major challenges in VLC is how to efficiently allocate the scarce modulation bandwidth to multiple users while avoiding interference and maintaining signal quality. To tackle this challenge, we propose a novel scheme that combines non-orthogonal multiple access (NOMA) with static power allocation (SPA) and pulse position modulation (PPM) in VLC. We conduct simulations in a realistic indoor scenario with a 9x9x3 m room and a single 12-watt LED at the center, using a line of sight (LOS) channel with a field of view (FOV) of 70o. The results show that our scheme achieves superior performance, with user 1 and user 2 obtaining signal-to-interference noise ratio (SINR) values of 20 dB and 74 dB, respectively. Our scheme can effectively overcome the limitations of VLC, such as low data rate, limited coverage area, and high sensitivity to ambient light noise, and pave the way for future VLC applications.
 
 

Statistical LOS/NLOS Classification for UWB Channels

Ultrawideband (UWB) technology has attracted a lot of attention for indoor and outdoor positioning systems due to its high accuracy and robustness in non-line-of-sight (NLOS) environments. However, UWB signals are affected by multipath propagation which causes errors in localization. To overcome this problem, researchers have proposed various techniques for NLOS identification and mitigation. One of the approaches is statistical LOS/NLOS classification, which uses statistical parameters of the received signal to distinguish between LOS and NLOS channels. In this paper, we formulated several techniques which can be used for effectively classifying Line of Sight (LOS) channel from a Non-Line of Sight (NLOS) channel. Various parameters obtained from Channel Impulse Response (CIR) like Skewness, Kurtosis, Root Mean Squared Delay Spread (RDS), Mean Excess Delay (MED), Energy, Energy Ratio and Mean of Covariance Matrix are used for channel classification. In addition to this, the Joint Probability Density Functions (PDFs) of various parameters are used to improve the accuracy of UWB LOS/NLOS channel classification. Two different criteria-Likelihood Ratio and Hypothesis Test are used for the identification of channel.

The Degrees-of-Freedom in Monostatic ISAC Channels: NLoS Exploitation vs. Reduction

The degrees of freedom (DoFs) attained in monostatic integrated sensing and communications (ISAC) are analyzed. Specifically, monostatic sensing aims for extracting target-orientation information from the line of sight (LoS) channel between the transmitter and the target, since the Non-LoS (NLoS) paths only contain clutter or interference. By contrast, in wireless communications, typically, both the LoS and NLoS paths are exploited for achieving diversity or multiplexing gains. Hence, we shed light on the NLoS exploitation vs. reduction tradeoffs in a monostatic ISAC scenario. In particular, we optimize the transmit power of each signal path to maximize the communication rate, while guaranteeing the sensing performance for the target. The non-convex problem formulated is firstly solved in closed form for a single-NLoS-link scenario, then we harness the popular successive convex approximation (SCA) method for a general multiple-NLoS-link scenario. Our simulation results characterize the fundamental performance tradeoffs between sensing and communication, demonstrating that the available DoFs in the ISAC channel should be efficiently exploited in a way that is distinctly different from that of communication-only scenarios.

Achievable Energy Efficiency in Massive MIMO: Impact of DAC Resolution and PAPR Reduction for Practical Network Topologies at mm-Waves

This letter explores key parameters of a massive MIMO system and their impact on energy efficiency at transmission. In particular, the effect of the digital to analog converter resolution and peak to average power ratio reduction techniques are addressed, in the context of practical user location distributions for both line and non line of sight channels. Results show interesting design trade-offs, and highlight the relevance of an accurate model for the user locations for the correct evaluation of the achievable performance.

Performance Analysis of MIMO Techniques for a Pyramid Receiver in an Indoor MIMO-VLC System

In an indoor multiple-input multiple-output (MIMO) visible light communication (VLC) system, line of sight (LoS) channel links are present between a light-emitting diode (LED) based transmitter and a photodetector (PD) based receiver. The PDs in the receiver are closely packed resulting in a high channel correlation. To overcome channel correlation and improve the performance of the MIMO-VLC system, angle diversity receivers (ADRs) are commonly employed. The channel matrix entries depend on the normal vectors of the PDs, which in turn depend on the elevation angle (EA) of the PDs. Thus, by having normal vectors pointing in different directions, the channel correlation can be considerably reduced. This paper considers a special type of ADR called pyramid receiver (PR) and employs a 4x4 MIMO-VLC system. In this paper, different MIMO algorithms such as repetition coding (RC) and spatial multiplexing (SMP) are considered to exhibit and compare the bit-error-rate (BER) performance of the fixed and variable EA MIMO-VLC systems. The results show that an SMP-employed MIMO-VLC system outperforms the RC-employed MIMO-VLC system. SMP results in an spatial multiplexing gain that varies linearly with the number of LEDs whereas RC does not yield any spatial multiplexing gain. To attain the same spectral efficiency i.e. 4 bit/s/Hz, a larger signal constellation size is required for RC employed MIMO-VLC system to achieve the same BER as of an SMP employed MIMO-VLC system. Similarly, the BER performance of variable EA MIMO-VLC systems is better as compared to fixed EA MIMO-VLC systems.

Challenges of IEEE 802.11a technology and improving its performance using diversity technique

In this technology, <span>information can be transmitted through the air without the need for cables, wires, or other electronic connectors, using electromagnetic waves such as infrared, radio and satellite frequencies. In this research, the most important challenges and problems faced by wireless communication systems were identified and how to solve and address them. (IEEE 802.11aWLAN) was also simulated and tested using Mat lab program, where the signal generated in (IEEE 802.11aWLAN) was examined in the form of orthogonal frequency division multiplexing (OFDM) modulation by examining the performance of the bit error rate of this system using diversity technology to improve the performance of this system where we adopted the reception diversity technology, In the case of line of sight (LOS) channel and multipath channel using maximal ratio combining (MRC) method. We notice that the use of the MRC receiving diversity technique in the system reduces the bit error rate and increases the efficiency of the system and the performance improve with increase the number of receiving antenna with gain 6 dB.</span>

Energy-Efficient User Pairing for Downlink NOMA in Massive MIMO Networks

The motivations for deploying energy and spectral-efficient network architectures are the high energy consumption and the need for more spectral resources in modern cellular networks. The key method to solve the energy efficiency EE maximization problem of the downlink non-orthogonal multiple access (NOMA)-based massive MIMO system is to decouple it into user pairing and efficient power allocation problems. This work studies the performance of three main pairing methods in NOMA-based networks: Hungarian, Gale–Shapley, and correlation-based approaches. Firstly, we provide a mathematical analysis for EE of downlink NOMA in a massive MIMO system for the non-line of sight (NLoS) channel model with perfect successive interference cancellation (SIC). Finally, the sequential convex programming (SCP) approach is used to tackle the power allocation problem. Simulation results show that the Hungarian algorithm for pairing plus SCP for power allocation (Hungarian algorithm-SCP) achieves the highest energy efficiency among all the three pairing algorithms with an identical performance to joint user and resource block association with power allocation (joint user-RB PA) algorithm but with much lower computational complexity and outperforms the NOMA SCP greedy algorithm (NOMA-SCP-GA).

Optical investigations of Cu2CdSnS[formula omitted] quaternary alloy nanostructure for indoor optical wireless communications

The development of high-performance nano-luminophores based on luminescent nanomaterials, such as Carbon Nanotubes (CNT) and Quantum Dots (QDs), opens the doors for many potential improvements in luminescent systems and notably Optical Wireless Communication (OWC) systems. Other side, Cu2CdSnS4 quaternary alloy nanostructure has attracted attention in solar cell applications owing to the high optical absorption in visible range. This work presents the feasibility of the infrared uplink Visible Light Communication (VLC) system using Near Infrared Light Emitting Diode (NIR-LED) operating at 780 nm. The used NIR-LED-based Cu2CdSnS4 quaternary alloy nanostructure is to investigate the performance of NIR uplink transmission according to Line of Sight (LOS) channel model. In this transmission, the effect of transmitter orientation and transmitted optical power level with respect to Tx–Rx​ uplink distance are taken into consideration. For this purpose, performance evaluation will be achieved in terms of Bit Error Rate (BER) where we demonstrated satisfactory BER performance (BER≥10−9) over the entire typical room configuration. In addition, an optimal semi-angle interval and optimal Tx power level has been selected. We further investigated the performance improvement by using several transceivers, compared with a single one on the center of the ceiling.

Smart License Plate in Combination with Fluorescent Concentrator for Vehicular Visible Light Communication System.

Vehicle-to-vehicle communication based on visible light communication has gained much attention. This work proposes a smart license plate receiver incorporated with a fluorescent concentrator, enabling a fast vehicle-to-vehicle communication with a large field of view and high optical gain. Communication performance is experimentally analyzed using off-the-shelf light-emitting diode-based headlamps for low-latency direct line of sight channel. Additionally, a blue laser diode-based beam-steering and tracking system, through image processing of taillights with a steerable mirror, is investigated. Data rates of 54 Mbps from the headlamps and 532 Mbps from the beam-steering channel with ±25° are demonstrated. In addition, real-time video streaming through the beam-steering channel is presented.

Quantum key distribution with multiphoton pulses: an advantage

In this article, we introduce a quantum key distribution protocol for the line of sight channels based on coincidence measurements. We present a proof-of-concept implementation of our protocol. We show that using coincidence measurements to monitor multi-photon pulses results in a higher secure key rate over longer distances for such channels. This key rate is higher than popular implementations of quantum key distribution protocol based on BB84, for example, the GLLP analysis [ Quant. Info. Comput. 4, 325 (2004)10.26421/QIC4.5-1 ]. In the experiment, we could generate around 74% more key bits per signal pulse as compared to the GLLP analysis of BB84 protocol with similar parameters and equal value of mean photon number.

Machine Learning for CSI Recreation in the Digital Twin Based on Prior Knowledge

Knowledge of channel state information (CSI) is fundamental to many functionalities for mobile communication systems. With the advance of machine learning (ML) and digital maps, i.e., digital twins, we have a big opportunity to learn the propagation environment and design novel methods to derive and report CSI. In this work, we propose to combine untrained neural networks (UNNs) and conditional generative adversarial networks (cGANs) for MIMO channel recreation based on prior knowledge. The UNNs learn the prior-CSI for some locations which are used to build the input to a cGAN. Based on the prior-CSI estimates, their locations and the location of the desired channel, the cGAN is trained to output the channel expected at the desired location. This combined approach can be used for low overhead CSI reporting as, after training, we only need to report the desired location. Our results show that our CSI recreation method is successful in modelling the wireless channel under different configurations of prior-CSI spatial sampling. In addition, the results consider a real world measurement campaign for indoor line of sight and non-line of sight channels. The signal to noise ratio (SNR) achieved by our CSI recreation is better than the SNR reported by the measured campaign providers. Moreover, our CSI recreation provides means for low overhead CSI reporting as the UNN structure is underparameterized compared to the full explicit CSI, and only the desired location is needed for the cGAN to recreate the desired CSI.

Quantum key distribution with multiphotonpulses: An advantage

In this article, we introduce a quantum key distribution protocol for the line of sight channels based on coincidence measurements. We present a proof-of-concept implementation of our protocol. We show that using coincidence measurements to monitor multi-photon pulses results in a higher secure key rate over longer distances for such channels. This key rate is higher than popular implementations of quantum key distribution protocol based on BB84, for example, the GLLP analysis [Quant. Info. Comput.4, 325 (2004)10.26421/QIC4.5-1]. In the experiment, we could generate around 74% more key bits per signal pulse as compared to the GLLP analysis of BB84 protocol with similar parameters and equal value of mean photon number.

Analisis Kinerja Multiple Pulse Position Modulation terhadap Interferensi Lampu Neon pada Sistem VLC

Visible Light Communication (VLC) technology is a wireless communication system that transmit information using the visible light spectrum. VLC has the advantage of not being affected by electromagnetic interference, but can be affected by interference from ambient light. There are two types of interference in the VLC system, namely natural interference from sunlight and ambient light interference from fluorescent or incandescent lamps. This study discusses the effect of fluorescent light interference on the VLC system using Multiple Pulse Position Modulation (MPPM) in a 10x10x3 meter room with Line Of Sight (LOS) channel. There are two scenarios carried out in this study discusses. The first scenario is the delivery of information using the VLC system without interference, while the second scenario is the delivery of information with interference from fluorescent lights. The final results of the simulations show that the VLC system in scenario I has a better performance compared to the VLC system in scenario II. This is evidenced by the results of the BER value obtained in scenario I with 2-PPM modulation obtained a value of 0.416, in 4-PPM modulation obtained a value of 0.335, and with 8-PPM modulation obtained a value of 0.231. In scenario II the BER value obtained with 2-PPM modulation is 0.466, in 4-PPM modulation is 0.432 and with 8-PPM modulation is 0.384. It also shows that 8-PPM modulation is the best modulation to transmit data compared to 2-PPM and 4-PPM modulation.

Optimal UAV Deployment and Resource Management in UAV Relay Networks.

UAV equipped three-dimensional (3D) wireless networks can provide a solution for the requirements of 5G communications, such as enhanced Mobile Broadband (eMBB) and massive Machine Type Communications (mMTC). Especially, the introduction of an unmanned aerial vehicle (UAV) as a relay node can improve the connectivity, extend the terrestrial base station (BS) coverage and enhance the throughput by taking advantage of a strong air-to-ground line of sight (LOS) channel. In this paper, we consider the deployment and resource allocation of UAV relay network (URN) to maximize the throughput of user equipment (UE) within a cell, while guaranteeing a reliable transmission to UE outside the coverage of BS. To this end, we formulate joint UAV deployment and resource allocation problems, whose analytical solutions can be hardly obtained, in general. We propose a fast and practical algorithm to provide the optimal solution for the number of transmit time slots and the UAV relay location in a sequential manner. The transmit power at BS and UAV is determined in advance based on the availability of channel state information (CSI). Simulation results demonstrate that the proposed algorithms can significantly reduce the computational effort and complexity to determine the optimal UAV location and transmit time slots over an exhaustive search.

Efficient Performance Bound for Channel Estimation in Massive MIMO Receiver

In this paper, we present a new performance bound for uplink channel estimation (CE) accuracy in the Massive Multiple Input Multiple Output (MIMO) system. The proposed approach is based on noise power calculation after the CE unit in a multi-antenna receiver. We decompose a non-line of sight (NLOS) channel into separate taps and calculate the cross-covariance matrix between them. Then a linear minimum mean squared error (MMSE) method is applied with these taps to estimate residual CE error value for each unique scenario, assuming Gaussian distribution of tap amplitudes and antenna noise. An artificial CE is calculated as a sum of the ideal noiseless channel (pre-defined Quadriga model) and the leftover noise after the optimal estimate. The artificial CE is then utilized in the MIMO detector and decoder units to calculate performance bound. Our method outperforms the accuracy of a well-known Cramer-Rao lower bound (CRLB) due to considering more statistics (number of taps and correlation between them) since performance strongly depends on several channel taps and their power ratio. Additionally, we show that our bound can be obtained from the generalized Bayesian CRLB. Simulation results are presented for the 5G QuaDRiGa 2.0 NLOS channel.

High speed trains communication systems in 5G cellular networks

In this paper, a new transmitter-receiver structure for high speed train (HST) data transmission and detection in fifth generation (5G) communication systems is proposed. This structure employs a new Doppler shift frequency (DSF) estimation approach, projected in this paper, to calculate the channel taps' DSFs at the base station (BS) receiver. The estimated DSFs are used to calculate the channel taps' angle of departures (AoDs). Considering the estimated AoDs, the transmitter beamformer regulates its coefficients to suppress the non-line of sight channel taps (NLoSCTs) and a DSF compensation block is employed to alleviate the line of sight channel tap's (LoSCT's) DSF. The proposed DSF estimation approach is a two-phase scheme which obtains a coarse estimation of DSFs at the first phase and calculates DSFs more accurately at the second phase. While this two-phase DSF estimation approach is able to estimate DSFs in both multipath rich and Rician channel models, an alternative DSF estimation scheme for Rician channel models is proposed which can estimate the LoSCT's DSF with much lower computational complexity compared to the two-phase DSF estimation method. Simulation results indicate the fidelity of the proposed DSF estimation methods and the proposed transmitter-receiver structure.

АНАЛИЗ И РАЗРАБОТКА ПОЛЯ ОЦЕНКИ КАНАЛА ДЛЯ МОДУЛЯЦИИ С ОДНОЙ НЕСУЩЕЙ В IEEE 802.11AY

This paper describes structure of a channel estimation field for the single carrier (SC) modulation based on the IEEE 802.11ad standard supporting transmission of radio signals between devices with multiple antennas for transmission and reception (MIMO – Multiple Input Multiple Output). Channel estimation field design uses a developed set of reference sequences based on complementary Golay pairs having similar statistical characteristics. All sequences are orthogonal to each other and each complementary pair has a pair in the set with zero cross-correlation property between them. Usage of this property allows to cancel out interstream interference during channel estimation procedure. A key property of the developed set is a common hardware architecture for a generator and correlator. Proposed structure of the channel estimation field is flexible and can be extended to arbitrary number of spatial streams for transmission. To analyze influence of the proposed channel estimation field on system performance, dependence of packet error rate on signal to noise ratio (SNR) was simulated for MIMO configuration with two transmit and two receive antennas for real and ideal channel estimations. System performance is analyzed in two channel models: the line of sight channel and the Rayleigh channel corresponding to the best and worst case of the signal propagation. It was shown that degradation of the SNR operating points depending on a modulation-coding scheme is in range 0.6-1.1 dB for the line of sight channel model and 0.7-1.5 dB for the Rayleigh channel model. This solution is already adopted by the IEEE 802.11ay standardization group.

Efficient Placement of an Aerial Relay Drone for Throughput Maximization

Unmanned aerial vehicle (UAV) communication can be used in overcrowded areas and either during or postdisaster situations as an evolving technology to provide ubiquitous connections for wireless devices due to its flexibility, mobility, and good condition of the line of sight channels. In this paper, a single UAV is used as an aerial relay node to provide connectivity to wireless devices because of the considerable distance between wireless devices and the ground base station. Specifically, two path loss models have been utilized; a cellular‐to‐UAV path loss for a backhaul connection and an air‐to‐ground path loss model for a downlink connection scenario. Then, the tradeoff introduced by these models is discussed. The problem of efficient placement of an aerial relay node is formulated as an optimization problem, where the objective is to maximize the total throughput of wireless devices. To find an appropriate location for a relay aerial node that maximizes the overall throughput, we first use the particle swarm optimization algorithm to find the drone location; then, we use three different approaches, namely, (1) the equal power allocation approach, (2) water filling approach, and (3) modified water filling approach to maximize the total users’ throughput. The results show that the modified water filling outperforms the other two approaches in terms of the average sum rate of all users and the total number of served users. More specifically, in the best‐case scenario, it was observed that the average sum rate of the modified water filling is better than the equal power allocation and ensuring 100% coverage. In contrast, the water filling provides a very close average sum rate to the modified water filling, but it only provides a 28% user coverage.

Performance analysis of L-PPM modulated NLOS-VLC system with perfect and imperfect CSI

Visible light communication (VLC) has evolved in the last few years as an alternative to radio frequency communication technology. In this paper, the performance analysis of pulse position modulated (PPM) VLC system is presented over non-line of sight (NLOS) channel. Specifically, an L-PPM modulated VLC system is considered in which the communication occurs through single-order reflected components as there is no existence of line of sight (LOS) link between transmitter and receiver. The reflection points on the walls of the room are randomly distributed. The Gaussian approximation is used to derive the bit-error-rate (BER) of the proposed VLC system with perfect and imperfect channel state information available at the receiver. For the given transmitting power, L-PPM modulated NLOS-VLC system, (L > 2), improves the system BER significantly than that of on-off keying modulated NLOS-VLC system. The error performance of the L-PPM modulated NLOS-VLC system is also compared with that of L-PPM modulated LOS-VLC system. For the parameters of interest, the error performance of L-PPM modulated NLOS-VLC system is observed.