Power Allocation and Cooperative Diversity in Two-Way Non-Regenerative Cognitive Radio Networks

In this paper, we investigate the performance of a dual-hop block fading cognitive radio network with underlay spectrum sharing over independent but not necessarily identically distributed (i.n.i.d.) Nakagami-$m$ fading channels. The primary network consists of a source and a destination. Depending on whether the secondary network which consists of two source nodes have a single relay for cooperation or multiple relays thereby employs opportunistic relay selection for cooperation and whether the two source nodes suffer from the primary users' (PU) interference, two cases are considered in this paper, which are referred to as Scenario (a) and Scenario (b), respectively. For the considered underlay spectrum sharing, the transmit power constraint of the proposed system is adjusted by interference limit on the primary network and the interference imposed by primary user (PU). The developed new analysis obtains new analytical results for the outage capacity (OC) and average symbol error probability (ASEP). In particular, for Scenario (a), tight lower bounds on the OC and ASEP of the secondary network are derived in closed-form. In addition, a closed from expression for the end-to-end OC of Scenario (a) is achieved. With regards to Scenario (b), a tight lower bound on the OC of the secondary network is derived in closed-form. All analytical results are corroborated using Monte Carlo simulation method

A Study Of Cooperative Spectrum Sharing Schemes For Internet Of Things Systems

The Internet of Things (IoT) has gained much attention in recent years with the massive increase in the number of connected devices. Cognitive Machine-to-Machine (CM2M) communications is a hot research topic in which a cognitive dimension allows M2M networks to overcome the challenges of spectrum scarcity, interference, and green requirements. In this paper, we propose a Generalized Cooperative Spectrum Sharing (GCSS) scheme for M2M communication. Cooperation extends the coverage of wireless networks as well as increasing their throughput while reducing the energy consumption of the connected low power devices. We study the outage performance of the proposed GCSS scheme for M2M system and derive exact expressions for the outage probability. We also analyze the effect of varying transmission powers on the performance of the system

Performance Analysis of AF Relaying With Selection Combining in Nakagami-m Fading

This paper investigates the performance analysis of a selection combining scheme, which utilizes a variable gain amplify and forward relay over a Nakagami-m fading channel. A selection combiner at a destination node chooses the better link between a relay channel and a direct channel. We derived exact closed-form expressions for moments of signal to noise ratio (SNR), ergodic capacity, and average symbol error probability. Simulation examples confirm that our exact formulas offer a more accurate analysis tool for selection combining than other prevailing approximations without extra complexity. The derived expressions serve as a useful tool for system design due to their validity for any SNR and arbitrary system parameters

Threshold-Based Relay Selection for Cooperative Wireless Network

Cooperative communication plays a vital role in the wireless domain recently due to its numerous benefits such as coverage extension, improvement in spectral efficiency, and throughput by increasing the complexity of the system. Furthermore, security becomes a key issue for implementing a cooperative communication system. In this thesis, the complexity is reduced by employing differential modulation as they do not require complete channel state information (CSI). Different threshold-based relay selection schemes are also proposed to reduce complexity. Furthermore, the security issue in the cooperative wireless network is addressed by enhancing the physical layer security using the proposed double threshold-based optimal relay selection scheme

Techniques de coopération dans les réseaux à radio cognitive : conception et évaluation des performances

RÉSUMÉ La technologie de radio cognitive permet aux usagers sans licence (appelés usagers secondaires) de transmettre dans les bandes de fréquences avec licence, sans dégrader la qualité de service des transmissions des usagers avec licence (appelés usagers primaires). Afin d’éviter l’interférence indésirable aux récepteurs primaires, les émetteurs secondaires doivent réduire leurs puissances de transmission. Cette limitation de puissance génère généralement des performances secondaires dégradées. Combiner la technologie à radio cognitive à d’autres technologies de transmission émergentes comme la coopération et la technologie des antennes multiples pourrait bénéficier aux transmissions primaires et secondaires. Dans cette thèse, nous proposons et étudions différentes techniques de coopération pour le réseau à radio cognitive. Certaines techniques exploitent la sélection d’antennes ou bien le pré-codage à un seul relai à plusieurs antennes, alors que d’autres utilisent la sélection de relai(s) lorsque plusieurs relais à une seule antenne sont disponibles pour assister la transmission primaire, la transmission secondaire ou les deux simultanément. Le problème d’allocation de puissance ou de pré-codage associé est étudié, et les expressions exactes des probabilités de blocage primaire et/ou secondaire ou de capacité ergodique secondaire sont dérivées. Pour certaines des techniques proposées, la connaissance imparfaite des canaux de transmission est prise en compte, modifiant ainsi la résolution du problème d’allocation de puissance ou de pré-codage associé. Nous montrons par analyse et simulation que chacune des techniques de coopération proposée est capable d’améliorer considérablement la performance secondaire, tout en respectant la qualité de service primaire. Ces performances dépassent d’une manière significative celles des techniques de transmission conventionnelles (techniques coopératives ou non) utilisées dans le contexte du réseau à radio cognitive.---------- ABSTRACT Cognitive radio technology allows unlicensed users (called secondary users) to transmit on the licensed frequency bands, without degrading the quality-of-service of the licensed users’ transmissions (called primary users). In order to avoid undesirable interference at the primary receivers, the secondary transmitters have to limit their transmit power. This limitation may cause performance degradation for the secondary transmissions. Combining cognitive radio with other emerging technologies, such as user cooperation and multiple antennas may have many benefits on both the primary and secondary transmissions. In this dissertation, we propose and investigate different cooperation techniques for the cognitive radio network. Some of the proposed techniques exploit antenna selection or precoding at one multi-antenna relay node, while the other proposed techniques use relay(s) selection when several single-antenna relay nodes are available to assist either the primary, the secondary or both transmissions simultaneously. The associated power allocation problem or pre-coding problem is investigated and the exact expressions of the primary and secondary outage probabilities or the secondary ergodic capacity are derived. For some of the proposed techniques, the imperfect knowledge of the channel states at the secondary transmitters is taken into account, hence modifying the power allocation or pre-coding process. We show by analysis and simulation that each of the proposed cooperation technique is able to improve significantly the secondary performance with respect to the primary Quality-of-Service. The realized performances outperform those of conventional transmission techniques used in the context of cognitive radio networks

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