جلسه دفاع از رساله دکتری
تخصیص منابع در شبکه های مخابرات بی سیم دوطرفه
دکتر سیدعلی قرشی
دکتر محمد شیخ بهایی
امیرحسین حاجی حسینی گزستانی
شنبه 18 بهمن 1399 ساعت 16
Zahra Ezzati Khatab, Amirhosein Hajihoseini Gazestani, Seyed Ali Ghorashi, Mohammad Ghavami
In recent years, because of the growing demand for location based services in indoor environment and development of Wi-Fi, fingerprint-based indoor localization has attracted many researchers’ interest. In Wireless Sensor Networks (WSNs), fingerprint based localization methods estimate the target location by using a pattern matching model for the measurements of the Received Signal Strength (RSS) from the available transmitter sensors, which are collected by a smartphone with internal sensors. Due to the dynamic nature of the environment, the fingerprint database needs to be updated, periodically. Hence, it is better to add new fingerprint data to the primary database in order to update them. However, collecting the labeled data is time consuming and labor intensive. In this paper, we propose a novel algorithm, which uses high level extracted features by an autoencoder to improve the localization performance in the classification process. Furthermore, to update the fingerprint data base, we also add crowd-sourced labeled and unlabeled data in order to improve the localization performance, gradually. Simulation results indicate that the proposed method provides a significant improvement in localization performance, using high level extracted features by the autoencoder, and by increasing the number of unlabeled training data.
Unmanned aerial vehicles (UAVs) can be used as aerial base stations (BSs) for future small cells. They can increase the spectral efficiency of the small cells due to their higher probability to have line-of-sight (LOS) connections and their mobility as a BS. In this article, in order to show the effectiveness of using full-duplex (FD) technology in UAV networks, we consider a UAV equipped with FD technology (FD-UAV) with imperfect self-interference cancelation as an aerial BS that serves both uplink (UL) and downlink (DL) users simultaneously in a small cell network. We aim to maximize DL sum-rate, whilst prescribing a certain quality of service for UL users, by optimizing the location of FD-UAV and available resources. The problem is nonconvex; so we propose an iterative method by exploiting the difference of convex functions programming to jointly optimize transmission power of users, FD-UAV location, and FD-UAV transmission power. Simulation results are illustrated to show the effectiveness of the proposed method for FD-UAV in comparison with ground BS, in both FD and half-duplex modes.
Amirhosein Hajihoseini Gazestani; Seyed Ali Ghorashi; Zhaohui Yang; Mohammad Shikh-Bahaei
Flying platforms such as Unmanned Aerial Vehicles (UAVs) are a promising solution for future small cell networks. UAVs can be used as aerial Base Stations (BSs) to enhance coverage, capacity and reliability of wireless networks. Also, with recent advances of Self Interference Cancellation (SIC) techniques in Full-Duplex (FD) systems, practical implementation of FD BSs is feasible. In this paper, we investigate the problem of resource allocation for multi-small cell networks with FD-UAVs as aerial BSs with imperfect SIC. We consider three different scenarios: a) maximizing the DL sum-rate, b) maximizing the UL sum-rate, and finally c) maximizing the sum of UL and DL sum-rates. The aforementioned problems result in non-convex optimization problems, therefore, successive convex approximation algorithms are developed by leveraging D.C. (Difference of Convex functions) programming to find sub-optimal solutions. Simulation results illustrated validity and effectiveness of the proposed radio resource management algorithms in comparison with ground BSs, in both FD mode and its half-duplex (HD) counterpart. The results also indicate those situations where using aerial BS is advantageous over ground BS and reveal how FD transmission enhances the network performance in comparison with HD one.
Amirhosein Zarif, Sajad Mohammad-Ali-Nezhad, Sajad Tijeri-Mofrad, Amirhosein Hajihoseini Gazestani
In this paper, a compact RFID chipless structure is designed, simulated, and fabricated. Image theory has been used to reduce the structure of the RFID tag so that it halves the tag and creates a PEC wall having the same resonant frequencies. In other words, each symmetric structure by this method is half the size with features similar to the original structure. The proposed structure has a ratio of area to lambda equal to 0.05 in which there are nine resonances in a frequency band of 4.3–8.5 GHz with dimensions of 14 × 7 mm2 in a bit density of 9.18 bit/cm2 and fabricated on Rog4003 substrate. The bit density for the full structure was equal to 4.59 bit/cm2. The original and proposed structures have similar resonances that indicate the accuracy of the proposed method. Also, this method can be used to create a label with a higher number of bits. The simulation results using HFSS software were in good agreement with the measurement results. Furthermore, the calculated detection error rate of the proposed structure was lower than the original one.
Behnaz Mousavinasab, Amirhosein Hajihoseini Gazestani, Seyed Ali Ghorashi, Mohammad Shikh-Bahaei
Hybrid duplex wireless networks, use half duplex (HD) as well as full duplex (FD) modes to utilize the advantages of both technologies. This paper tries to determine the proportion of the network nodes that should be in HD or FD modes in such networks, to maximize the overall throughput of all FD and HD nodes. Here, by assuming imperfect self-interference cancellation (SIC) and using ALOHA protocol, the local optimum densities of FD, HD and idle nodes are obtained in a given time slot, using Karush–Kuhn–Tucker (KKT) conditions as well as stochastic geometry tool. We also obtain the sub-optimal value of the signal-to-interference ratio (SIR) threshold constrained by fixed node densities, using the steepest descent method in order to maximize the network throughput. The results show that in such networks, the proposed hybrid duplex mode selection scheme improves the level of throughput. The results also indicate the effect of imperfect SIC on reducing the throughput. Moreover, it is demonstrated that by choosing an optimal SIR threshold for mode selection process, the achievable throughput in such networks can increase by around 5%.
بهناز موسوی نسب، امیرحسین حاجی حسینی گزستانی، سید علی قرشی، محمد شیخ بهایی
با پیشرفت روزافزون فناوری های الکترونیک و ارتباطات، سامانه های بیسیم به عنوان یکی از اجزای جدانشدنی زندگی روزمره مطرح شده و به دنبال آن نیاز به منابع طیفی برای پشتیبانی از تعداد کاربران بیشتر در شبکۀ بیسیم، روز به روز افزایش می یابد. با توجه به این افزایشِ نیاز به پهنای باند و جهت استفادۀ کارآمد از ظرفیت های شبکه های بیسیم مخابراتی، فناوری «ارتباط دوطرفه» اخیراً در کانون توجه پژوهشگران قرار گرفته است. این فناوری با ارسال و دریافت اطلاعات به صورت همزمان و در یک باند فرکانسی، می تواند بازدهی طیفی را تا دو برابر نسبت به سامانه های یک طرفۀ سنتی بهبود بخشد. از سوی دیگر در سال های اخیر سامانه های برداشت کنندۀ انرژی به عنوان یک راه حل برای رفع مشکل توان مصرفی گره های موجود در شبکه های بیسیم مطرح شده اند. در این مقاله ابتدا سناریوهای مختلف به کارگیری فناوری ارتباطات دوطرفه در سامانه های برداشت انرژی مورد بررسی و مقایسه قرار می گیرد، سپس توابع هدف مورد استفاده در طراحی این سامانه ها بررسی می شوند. در انتها نیز چالش های به کارگیری فناوری ارتباط دوطرفه در سامانه های برداشت انرژی مرور خواهد شد.
Amirhosein Hajihoseini Gazestani, Seyed Ali Ghorashi, Behnaz Mousavinasab, Mohammd Shikh-Bahaei
Nowadays, wireless networks play an important role in our daily life. Hence, radio frequency (RF) spectrum which is required to support the large number of users of these networks, have become a very valuable resource. Full Duplex(FD) communications, in which data can be sent and received using the same frequency band at the same time, is a promising solution for satisfying, at least in part, the ever increasing demand for wireless spectrum. Theoretically, FD could double the spectral efficiency and capacity. However, in order to harvest these benefits, it has to combat/suppress self-interference (SI) caused by transmitting and receiving data, simultaneously. FD systems should use SI cancellation methods to deal with this important challenge. Due to the significant benefits of FD communication, this research area has recently attracted much attention among the research community. In this paper, we review the applications and implementation challenges of FD communication in different subject areas such as energy harvesting, vehicular communication, massive Multiple-Input Multiple-Output (MIMO), small cells, practical implementation, millimeter wave and military applications. We also study the tradeoffs in deploying FD communication in each of the applications.
Amirhosein Hajihoseini Gazestani and Seyed Ali Ghorashi
Wireless sensor networks (WSNs) typically use license free industrial, scientific and medical (ISM) frequency bands and by increasing the demand for different usages of WSNs, it is anticipated that this band gets saturated. One solution to deal with this spectrum scarcity in WSNs is utilizing the cognitive radio concept, called cognitive radio sensor networks (CRSNs). One of the most critical challenges in CRSNs is spectrum sensing, which can be implemented by centralized, cluster based or distributed methods. In CRSNs, distributed methods have better spectrum sensing performance due to their fast adaptation to the network changes. Also they have lower power consumption level, which is critical in CRSNs. In this paper, we propose a novel distributed diffusion based spectrum sensing method for CRSNs that improves the robustness of the spectrum sensing method against link failure and network topology changes. It also increases the algorithm’s convergence rate while its accuracy is acceptable. We prove the proposed method convergence and calculate its mean square error, considering link failure assumption. Simulation results confirm that the proposed method improves the convergence rate compared with conventional distributed methods, and using the proposed method increases the convergence rate and needs less communications to make a decision about absence or presence of the primary user.