Mobil haberleşme sistemlerinde karıştırıcıların bozucu etkisinin azaltılması
Reducing the effects of jammers in wireless communications systems
Yazar: AZİZ GEDİZ SEZGİN
Danışman: PROF. DR. GÜNEŞ ZEYNEP KARABULUT KURT
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Elektronik ve Haberleşme Mühendisliği Ana Bilim Dalı / Telekomünikasyon Mühendisliği Bilim Dalı
Derece: Doktora, 2019
Konu: Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering

Özet:
Kablosuz haberleşme sistemlerindeki hızlı gelişmeler bilginin coğrafi sınırlarının ortadan kalkması için çok önemli bir etkendir. Bu sayede tüm ihtiyaçlarımız için bu teknolojinin sağladığı çözümlerden faydalanabiliyoruz. İhtiyaç kümemizdeki değişim nedeni ile kablosuz haberleşme sistemlerinde ortalama her on yılda bir yeni teknoloji hayatımıza girmektedir. Ses haberleşmesi ile başlayan teknolojik dönüşüm serüveni düşük hızlı veri iletimi ile devam etmiş, sonrasında geniş bant kablosuz internet deneyiminin sağladıkları ile yüksek ve çok yüksek hızlı veri iletimi gereksinimi ortaya çıkmış, devamında da veri iletim gecikmesinin neredeyse gerçek zamanlı olmasını gerektiren ihtiyaçlarımız dönüşümü şekillendirmiştir. 

Bugün neredeyse dünya nüfusu kadar olan mobil bağlantı sayısı, kablosuz haberleşme teknolojilerinin hayatımızın vazgeçilmezi olduğunu net olarak göstermektedir. Bu rakam aynı zamanda sağlıklı bir şekilde bağlanmanın ne derece kritik olduğunu da ifade eder. Çünkü en önemli doğal kaynak ihtiyaç duyulan ve sahip olunan bilgidir. Daha fazla kullanıcı bağlı hale geldikçe kötü niyetli girişimlerin de etki alanı artacaktır. Özellikle bilgiye erişimin engellenmesi amaçlı harici girişimlere günümüzde sıkça karşılaşılmaktadır. 
Kablosuz haberleşme sistemleri, harici girişimleri engellemek konusunda kendini geliştiren çözüm mekanizmaları üretmekte ne yazık ki çok esnek değildir. Bu nedenle araştırmacılar için çok önemli bir alan olarak görülen bu alanda yapılan çalışmalar yine de teorik çalışmalardan öteye gidememiştir. Yapılan çalışmaların şebeke uygulamaları, başarım ölçümlemesi ve klasik bağlantı modelleri ile karşılaştırılması da neredeyse yok denecek kadar azdır. 

Bu tez çalışmasında kablosuz haberleşme sistemlerine yapılacak harici girişimleri önlemek adına literatürde ilk olarak hem donanımsal hem de yazılımsal öneriler sunulmuştur. Bu önerilerin sağlayacağı katkı açıklanmış ve saha denemeleri ile de önerilerin gerçek şebeke trafiği altındaki performansları incelenmiştir. Donanımsal çözümde saha mimarisi gelişimine uygun akıllı anten teknolojilerinin kullanımı sağlanmıştır. Bu çözüm önerisinin klasik şebeke saha mimarisine göre çok daha yüksek oranda harici girişim bağışıklığı gösterdiği gözlenmiştir. Ayrıca kablosuz haberleşme teknolojisi standartları ile çakışmayan, cihaz donanımında da bir değişim gerektirmeyen yeni bir yazılımsal çözüm önerisi ile de harici girişime karşı hızlı bir dönüşümün sağlanması ve bağlı olan terminallerin hızlıca bu girişimden izole edilmesi önerilmektedir.
Günümüzde en değerli varlığımız olarak kabul ettiğimiz verilerimizin sağlıklı bir şekilde kablosuz şebeke üzerinden iletimi için sunduğumuz alternatif öneriler ile yüksek verimlilikle bağlantının sağlanması ve harici bozucu girişimlere karşı hızlı önlem alınması sağlanacaktır.

Abstract:
Rapid developments in wireless communication systems are a very important factor for the elimination of geographical boundaries of information. For all our data transmission needs, we can take advantage of the solutions provided by these technologies. Due to the change in our basic requirement set, new technology, which called as generation, is entering our lives in wireless communication systems on average every ten years. The technological transformation adventure started with the voice communication continued with low speed data transmission, and then the need for high and higher-speed data transmission emerged with the broadband wireless internet experience, and then our needs, which require the data transmission delay to be almost real-time, have shaped the transformation.
First Generation, referred to 1G, established the foundation of mobile connectivity by the early 80s, providing analog mobile voice services. The popularity of 1G led to a call for more - more applications and improved speeds. 2G digital wireless communications technologies increased voice capacity and supported low speed basic data transfer. For the first time mobile was available on a broad scale, 3G soon followed by millennium. It optimized mobile for data, which enabled broadband services, offered better connectivity and a focus on multimedia applications. 4G LTE announced in 2009 by standard bodies, delivers greater capacity for faster and improved mobile broadband experiences. Finally, 5G announced recently in 2018, offers not only higher speed but also lower latency to provide online gaming and real time video applications. As users' expectations have grown from the early 80s to the present day, wireless communications technology has advanced through the generations at a similar rate. Today, the latest technology satisfies the demand for faster connectivity, increased capacity and an overall improved user experience.
The number of mobile connections that almost as much as the world population, clearly shows that wireless communication technologies are indispensable to our lives. This figure also indicates how critical it is to connect in a correct way. Because the most important natural resource is the information needed and owned. The more users become connected, the more malicious attempts issued. We often encounter external jammer attempts to prevent access to information.
There are many attack types in the literature. Among these, the denial of service attacks are expected to be critical in different mobile network layers and they have to be considered. Similarly, signalling amplification attacks are also important for mobile networks, particularly in the signalling plane due to the scarcity of resources. In addition to these, physical layer attacks are also critical threats, which pollute the air interface by jamming attacks.
Unfortunately, wireless communication systems are not flexible in developing the self-improving solution mechanisms to prevent external jammer related interference, generated by undesired attacks. Therefore, studies in this area could not go beyond theoretical studies, even the problem is considered to be a very important for researchers. It is observed during the legacy network field tests that the terminal being served from the base station is either disconnected or the connected with very low quality. If the attack target is signalling channels between the base station and terminal, the call is dropped due to the loss of signalling between these two entities. Else, if the attack target is data channels, the call remains connected but not provide high quality services, and effect the mobile experience as negative. 
In this thesis, legacy network field tests are not only provided, but also both hardware and software suggestions are first presented in the literature in order to prevent external interference to wireless communication systems. The contribution of these suggestions are detailed. Performance output of suggested models observed at the field trials under the actual network traffic. In the hardware solution, intelligent antenna technologies, which is also called as Massive-MIMO antenna systems are used. It has been observed that this suggestion shows a much higher external jamming interference immunity than the conventional network field architecture including passive antenna solution. In addition to hardware solution, it is recommended a new software solution, which does not interfere with the wireless communications technology standards and does not require any change in device hardware. This software solution provides a fast conversion against external jamming interference and isolate the connected terminals quickly from this external interference.
This thesis consists of six chapters, briefly described below.
•	Chapter 1: In the introduction chapter, the historical development of wireless communication systems, the definition of the problem which is the subject of the thesis study, the aim and the benefits of this study, the studies on the solution of this problem in the literature and along with the organization of the thesis will be shared.
•	Chapter-2: A brief architectural summary of LTE systems will describe in here and theoretical evaluation of the use of multiple antennas, OFDM features, protocol architecture, physical and logical channels are going to be discussed in this chapter.
•	Chapter-3: In this section, we are going to describe how data obtained from different network layers are analyzed, how often it is received, validated and shared as the meaningful output.
•	Chapter-4: Field topologies of LTE systems, which designed in our country, will be presented in this part of the study, which are trying to overcome against the external jammer attack. Network immunity and data transmission performance against different types of disturbing sources will also be discussed in detail in this section. In order to understant the effect of external jammer attack on the network capability, basic network performance results are obtained from stationary and mobile drive tests. It is also going to explain how wireless communications systems are inevitable under the external undesired jammer attacks.
•	Chapter-5: We are going to offer two innovative methods to keep robust network performance against to external jammer attack. When selecting the methods, we will strive to stay true to the existing network architecture, data frame structure and 3GPP standards. First offered method will try to keep the network performance by having the hardware based solution, however second offered method have totally different perspective to the problem, and offer the rearrangement of signalling resource blocks under the some calculation based rules.
•	In the Results and Recommendations section, the results obtained from the different studies are evaluated and the contributions of the study to the science and industry will discussed. Also, some suggestions will make for future studies.