On the Higher Order Statistics of the Channel Capacity in Dispersed Spectrum Cognitive Radio Systems Over Generalized Fading Channels

This work is devoted to the study of dispersed spectrum cognitive radio (CR) systems over independent and nonidentically distributed (i.n.i.d.) generalized fading channels. More specifically, this is performed in terms of the high-order statistics (HOS) of the channel capacity over η-μ fading channels. A generic analytic expression is derived for the corresponding nth statistical moment, which is subsequently employed for deducing exact closed-form expressions for the first four moments

An Energy Efficient Data Collection Using Multiple UAVs in Wireless Sensor Network: A Survey Study

   اليوم، مع التقدم العلمي والتكنولوجي في الروبوتات، والذكاء الاصطناعي، والسيطرة والحواسيب، المركبات البرية والجوية والبحرية قد تم الاهتمام بها. كما تم تحسين الطائرات بدون طيار (UAVs) بشكل كبير وهي مفيدة جدا للعديد من التطبيقات الهامة في الأعمال التجارية والبيئة الحضرية والعسكرية. أحد أهم استخدامات الطائرات بدون طيار في شبكات الاستشعار اللاسلكية (WSNs)  التي لديها طاقة منخفضة وقد لا تكون قادرة على الاتصال في مناطق واسعة. في هذه الحالة ، يمكن أن توفر الطائرة بدون طيار وسيلة لجمع بيانات WSN من جهاز واحد ونقلها إلى المستلم المقصود تركز هذه المقالة على مجال البحث في التطبيقات العملية للطائرات بدون طيار كجامع متنقل لشبكات الاستشعار اللاسلكية. أولا التحقيقات حول الطائرات بدون طيار المقترحة تم دراستها ومقارنة نقاط ضعفها مع بعضها البعض. وكذلك التحديات التقنية لتطبيقات الطائرات بدون طيار في شبكة الاستشعار اللاسلكية تم استكشافها.Today, with scientific and technological advances in robotics, artificial intelligence, control and computers, land, air, and sea vehicles, they have been considered. Unmanned aerial vehicles (UAVs) have also significantly improved and are very useful for many important applications in the business, urban and military environment. One of the important uses of UAVs in Wireless Sensor Networks (WSNs) is that devices with low energy and may not be able to communicate in large areas. Nevertheless, a UAV can provide a tool for collecting the data of WSN from one device and transmitting it to another device. This article focuses on the field of research on practical applications of UAVs as mobile collectors for wireless sensor networks. First, the investigations of the proposed UAV were studied and compared their weaknesses with each other. Then, the technical challenges of the applications of UAVs in the wireless sensor network were explored

Simulação a nível de sistemas 5G através da utilização de ondas milimétricas

Devido à necessidade de atender aos requisitos associados ao mercado móvel cada vez mais exigente, a quinta geração (5G) de comunicações sem fio é caracterizada por proporcionar alta eficiência espectral (SE) e elevada eficiência energética (EE). Neste enquadramento, surgem tecnologias fundamentais para redes de próxima geração, como os sistemas massivos com múltiplas entradas e múltiplas saídas (M-MIMO) baseados em modulação espacial generalizada (GSM), a qual constitui um caso específico de modulação de índices (IM). Nestes sistemas, torna-se possível a utilização de ondas milimétricas (mmWave), as quais permitem providenciar taxas de dados mais elevadas, embora introduzam limitações na cobertura, devido ao aumento da atenuação do sinal. Com o intuito de avaliar o desempenho da comunicação milimétrica em sistemas 5G, efetuou-se o desenvolvimento e atualização de um simulador a nível de sistema, de forma a simular uma rede 5G New Radio (NR), incluindo a implementação de três cenários tridimensionais distintos (UMa, UMi - Street canyon e InO), aplicando diferentes modulações e a mesma numerologia e faixa de frequência. Numa segunda etapa, procedeu-se à análise e discussão dos resultados obtidos, derivados das diversas simulações elaboradas, tanto a nível de "throughput", em função do número de utilizadores e do número de antenas TRP ativas, como a nível de cobertura. Assim, os resultados indicam que os cenários "outdoor", particularmente o cenário UMa, apresentam melhor desempenho e, a nível de "throughput", a modulação 64QAM permite alcançar resultados mais elevados, enquanto que, a nível de cobertura, a modulação QPSK apresenta a melhor performance.Due to the need to meet the requirements of the increasingly demanding mobile market, the fifth generation (5G) of wireless communications is characterized by providing high spectral efficiency (SE) and high energy efficiency (EE). Therefore, there are emerging fundamental technologies used for the next generation networks, such as massive multiple-input multiple-output systems (M-MIMO) based on generalized spatial modulation (GSM), which constitutes a particular case of index modulation (IM). In these systems, it is possible to use millimeter waves (mmWave), which provide extreme data rates, although limitations in coverage are introduced due to the increased signal attenuation. With the purpose of evaluate the performance of millimeter wave communication in 5G systems, a system-level simulator was developed and updated, in order to simulate a 5G New Radio (NR) network, where three different three-dimensional scenarios (UMa, UMi – Street canyon and InO) were employed, using different modulations and the same numerology and frequency range. In a second phase, the results obtained from the system level simulations were analysed and discussed, both in terms of throughput, depending on the number of users and the number of active TRP antennas, and in terms of coverage. Consequently, the results indicate that outdoor scenarios, particularly the UMa scenario, can achieve an improved performance and, in terms of throughput, 64QAM modulation is able to obtain superior results, while, in terms of coverage, QPSK modulation presents the best performance

Optimal Power Allocation for Energy Efficient MIMO Relay Systems in 5G Wireless Communication

Wireless communication has undergone a significant growth to meet the unexpected demand of wireless data traffic over the past two decades. As manifested by the revolution of the third and fourth generations and long-term evolution advanced (LTE-A), engineers and researchers have been devoted to the development of the next-generation (5G) wireless solutions to meet the anticipated demand of 2020. To this end, cooperative relay communication has been introduced as an enabling technology to increase the throughput and extend the coverage of the broadband wireless networks. Decode-and-forward (DF) has been known as an effective cooperative relaying strategy for its outstanding features. On the other hand, merging massive multi-input-multi-output (MIMO) with cooperative DF relay is considered as a key technology for 5G wireless networks to improve the quality-of-service (QoS) in a cost-effective manner. The objective of this thesis is to establish and solve a power allocation optimization problem for energy efficient multi-pair DF relay systems integrated with massive MIMO. The first part of the thesis is focused on a constrained optimization problem to minimize the total transmit power for each transmission phase of the DF relay. Due to the non-convexity characteristic, the objective function is approximated as a convex function by means of complementary geometric programming (CGP) which is then solved by a sequence of geometric programming (GP). A lower bound of average SINR is also introduced by adopting the MMSE channel state information (CSI) to relax the constraint functions in the standard GP form. Finally, we proposed a homotopy or continuation method based algorithm to solve the optimization problem via popular CVX optimization toolbox. MATLAB simulations are conducted to validate the proposed algorithm. In the second part, another optimization problem is presented for the entire two-hop transmission of the DF relay to improve the global energy efficiency (GEE) under different channel conditions. Here, we estimate the channel by maximum likelihood (ML) criterion and investigate a closed-form expression of GEE. Further, GEE is approximated in a convex form by applying CGP due to the difficulty arising from the non-convexity and a lower bound of the average SINR expression is also derived to relax the constraint functions in the GP problem. Numerical results showing a detailed comparison of GEE under ML and MMSE channel estimation conditions and the performance improvement from the proposed algorithm are provided

Cognitive radio adaptive rendezvous protocols to establish network services for a disaster response

Disasters are catastrophic events that cause great damage or loss of life. In disasters, communication services might be disrupted due to damage to the existing network infrastructure. Temporary systems are required for victims and first responders, but installing them requires information about the radio environment and available spectrum. A cognitive radio (CR) can be used to provide a flexible and rapidly deployable temporary system due to its sensing, learning and decision-making capabilities. This thesis initially examines the potential of CR technology for disaster response networks (DRN) and shows that they are ideally suited to fulfill the requirements of a DRN. A software defined radio based prototype for multiple base transceiver stations based cellular network is proposed and developed. It is demonstrated that system can support a large number of simultaneous calls with sufficient call quality, but only when the background interference is low. It is concluded that to provide call quality with acceptable latency and packet losses, the spectrum should be used dynamically for backhaul connectivity. The deployment challenges for such a system in a disaster include the discovery of the available spectrum, existing networks, and neighbours. Furthermore, to set up a network and to establish network services, initially CR nodes are required to establish a rendezvous. However, this can be challenging due to unknown spectrum information, primary radio (PR) activity, nodes, and topology. The existing rendezvous strategies do not fulfill the DRN requirements and their time to rendezvous (TTR) is long. Therefore, we propose an extended modular clock algorithm (EMCA) which is a multiuser blind rendezvous protocol, considers the DRN requirements and has short TTR. For unknown nodes and topologies, a general framework for self-organizing multihop cooperative fully blind rendezvous protocol is also proposed, which works in different phases, can terminate when sufficient nodes are discovered, and is capable of disseminating the information of nodes which enter or leave a network. A synchronization mechanism is presented for periodic update of rendezvous information. An information exchange mechanism is also proposed which expedites the rendezvous process. In both single and multihop networks, EMCA provides up to 80% improvement in terms of TTR over the existing blind rendezvous strategies while considering the PR activity. A simple Random strategy, while being poorer than EMCA, is also shown to outperform existing strategies on average. To achieve adaptability in the presence of unknown PR activity, different CR operating policies are proposed which avoid the channels detected with PR activity to reduce the harmful interference, provide free channels to reduce the TTR, and can work with any rendezvous strategy. These policies are evaluated over different PR activities and shown to reduce the TTR and harmful interference significantly over the basic Listen before Talk approach. A proactive policy, which prefers to return to channels with recent lower PR activity, is shown to be best, and to improve the performance of all studied rendezvous strategies