Tractable Approach to MmWaves Cellular Analysis with FSO Backhauling under Feedback Delay and Hardware Limitations

In this work, we investigate the performance of a millimeter waves (mmWaves) cellular system with free space optical (FSO) backhauling. MmWave channels are subject to Nakagami-m fading while the optical links experience the Double Generalized Gamma including atmospheric turbulence, path loss and the misalignment between the transmitter and the receiver aperture (also known as the pointing errors). The FSO model also takes into account the receiver detection technique which could be either heterodyne or intensity modulation and direct detection (IM/DD). Each user equipment (UE) has to be associated to one serving base station (BS) based on the received signal strength (RSS) or Channel State Information (CSI). We assume partial relay selection (PRS) with CSI based on mmWaves channels to select the BS associated with the highest received CSI. Each serving BS decodes the received signal for denoising, converts it into modulated FSO signal, and then forwards it to the data center. Thereby, each BS can be viewed as a decode-and-forward (DF) relay. In practice, the relay hardware suffers from nonlinear high power amplification (HPA) impairments which, substantially degrade the system performance. In this work, we will discuss the impacts of three common HPA impairments named respectively, soft envelope limiter (SEL), traveling wave tube amplifier (TWTA), and solid state power amplifier (SSPA). Novel closed-forms and tight upper bounds of the outage probability, the probability of error, and the achievable rate are derived. Capitalizing on these performance, we derive the high SNR asymptotes to get engineering insights into the system gain such as the diversity order.Comment: arXiv admin note: substantial text overlap with arXiv:1901.0424

Asymmetric RF/FSO Relaying with HPA non-Linearities and Feedback Delay Constraints

In this work, we investigate the performance of a dual-hop multiple relays system consisting of mixed Radio-Frequency (RF)/Free Space Optical (FSO) channels. The RF channels are subject to Rayleigh fading while the optical links experience the Double Generalized Gamma including atmospheric turbulence, path loss and the misalignment between the transmitter and the receiver aperture (also known as the pointing error). The FSO model also takes into account the receiver detection technique which could be either heterodyne or intensity modulation and direct detection. Partial Relay Selection with outdated Channel State Information is assumed based on the RF channels to select a relay and we also consider fixed and variable Amplify-and-Forward relaying schemes. In addition, we assume that the relays are affected by the high power amplifier non-linearities and herein we discuss two power amplifiers called Soft Envelope Limiter and Traveling Wave Tube Amplifier. Furthermore, novel closed-forms and tight upper bounds of the outage probability, the bit error probability, and the ergodic capacity are derived. Capitalizing on these performance, we derive the high SNR asymptotic to get engineering insights about the system gains such as the diversity and the coding gains. Finally, the mathematical expressions are validated using the Monte Carlo simulation

Impact of Non-Linear High-Power Amplifiers on Cooperative Relaying Systems

In this paper, we investigate the impact of the high-power amplifier non-linear distortion on multiple relay systems by introducing the soft envelope limiter, traveling wave tube amplifier, and solid-state power amplifier to the relays. The system employs amplify-and-forward either fixed or variable gain relaying and uses the opportunistic relay selection with outdated channel state information to select the best relay. The results show that the performance loss is small at low rates; however, it is significant for high rates. In particular, the outage probability and the bit error rate are saturated by an irreducible floor at high rates. The same analysis is pursued for the capacity and shows that it is saturated by a detrimental ceiling as the average signal-to-noise ratio becomes higher. This result contrasts the case of the ideal hardware where the capacity grows indefinitely. Moreover, the results show that the capacity ceiling is proportional to the impairment's parameter and for some special cases the impaired systems practically operate in acceptable conditions. Closed-forms and high SNR asymptotes of the outage probability, the bit error rate, and the capacity are derived. Finally, analytical expressions are validated by the Monte Carlo simulation

Mixed RF/FSO Cooperative Relaying Systems with Co-Channel Interference

In this paper, we provide a global framework analysis of a dual-hop mixed Radio Frequency (RF)/Free Space Optical (FSO) system with multiple branches/relays wherein the first and second hops, respectively, consist of RF and FSO channels. To cover various cases of fading, we propose generalized channels' models for RF and FSO links that follow the Nakagami-m and the Double Generalized Gamma (DGG) distributions, respectively. Moreover, we suggest Channel State Information (CSI)-assisted relaying or variable relaying gain based Amplifiy-and-Forward (AF) amplification. Partial relay selection with outdated CSI is assumed as a relay selection protocol based on the knowledge of the RF CSI. In order to derive the end-to-end Signal-to-Interference-plus-Noise Ratio (SINR) statistics such as the Cumulative Distribution Function (CDF), the Probability Density Function (PDF), the higher order moments, the amount of fading and the Moment Generating Function (MGF), the numerical values of the fading severity parameters are only valid for integer values. Based on these statistics, we derive closed-forms of the outage probability, the bit error probability, the ergodic capacity and the outage capacity in terms of Meijer-G, univariate, bivariate and trivariate Fox-H functions. Capitalizing on these expressions, we derive the asymptotic high SNR to unpack valuable engineering insights of the system performance. Monte Carlo simulation is used to confirm the analytical expressions

Aggregate Hardware Impairments Over Mixed RF/FSO Relaying Systems With Outdated CSI

In this paper, we propose a dual-hop RF (Radio-Frequency)/FSO (Free-Space Optical) system with multiple relays employing the Decode-and-Forward (DF) and Amplify-and-Forward (AF) with a Fixed Gain (FG) relaying scheme. The RF channels are subject to a Rayleigh distribution while the optical links experience a unified fading model emcopassing the atmospheric turbulence that follows the M\'alaga distribution (or also called the $\mathcal{M}$-distribution), the atmospheric path loss and the pointing error. Partial relay selection (PRS) with outdated channel state information (CSI) is proposed to select the candidate relay to forward the signal to the destination. At the reception, the detection of the signal can be achieved following either heterodyne or Intensity Modulation and Direct Detection (IM/DD). Many previous attempts neglected the impact of the hardware impairments and assumed ideal hardware. This assumption makes sense for low data rate systems but it would no longer be valid for high data rate systems. In this work, we propose a general model of hardware impairment to get insight into quantifying its effects on the system performance. We will demonstrate that the hardware impairments have small impact on the system performance for low signal-to-noise ratio (SNR), but it can be destructive at high SNR values. Furthermore analytical expressions and upper bounds are derived for the outage probability and ergodic capacity while the symbol error probability is obtained through the numerical integration method. Capitalizing on these metrics, we also derive the high SNR asymptotes to get valuable insight into the system gains such as the diversity and the coding gains. Finally, analytical and numerical results are presented and validated by Monte Carlo simulation

Performance of wireless optical telecommunication systems in the presence of fading and interference

Postojeći komunikacioni sistem u domenu RF elektromagnetnog spektra nije u mogućnosti da zadovolji sve potrebe brzog i obimnog prenosa podataka, koje se javljaju usled ekspanzije i sve veće upotrebe IoT uređaja, 5G i B5G mreža, kao i raznovrsnih aplikacija i multimedijalnog sadržaja. Optička bežična komunikacija (OWC), koja koristi veliki opseg nelicenciranog dela spektra, se pokazala kao dobra alternativa za ublažavanje nedostataka konvencionalnog sistema za prenos podataka koji radi u RF domenu. FSO (Free Space Optics) tehnologija predstavlja jednu od vrsta optičkih bežičnih komunikacija, ima veliku upotrebu u LAN i MAN mrežama , bežičnom video nadzoru, koristi se u medicinske svrhe, u svemirskoj komunikaciji, za rešavanje problema poslednje milje itd. Primena bežičnih komunikacija, znatno može da doprinese performansama sistema, i to u smislu spektralne i energetske efikasnosti kao i u smislu pouzdanosti. U disertaciji je u cilju utvrđivanja optimalnog scenarija prijema signala, kao i određivanja optimalnih vrednosti parametara takvog prenosa, izvršena analiza karakteristika bežičnog optičkog prenosa signala u prisustvu turbulencije i efekta greške pozicioniranja, koji se odvija pod kompozitnim uticajem navedenih smetnji. Za posmatrane scenarije prenosa razmatrane su standardne mere performansi sistema, kao što su srednja verovatnoća greške po bitu, posmatrana za odgovarajuće modulacione formate, kao i verovatnoća otkaza. Predstavljena su analitička i numerička rešenja problema, a uticaji pojedinih parametara sistema na performanse bežičnog optičkog prenosa prikazani su i grafički