Over the past decade, wireless data communication has experienced a phenomenal growth, which is driven by the popularity of wireless devices and the growing number of bandwidth hungry applications. During the same period, various advanced communication technologies have emerged to improve network throughput. Some examples include multi-input multi-output (MIMO), full duplex, cognitive radio, mmWave, among others. An important research direction is to understand the impacts of these new technologies on network throughput performance. Such investigation is critical not only for theoretical understanding, but also can be used as a guideline to design algorithms and network protocols in the field. The goal of this dissertation is to understand the impact of some advanced technologies on network throughput performance. More specifically, we investigate the following three technologies: MIMO, full duplex, and mmWave communication. For each technology, we explore the performance envelope of wireless networks by studying a throughput maximization problem. / Ph. D. / As everyone knows, we are now living in a connected world, where network access is available anytime and anywhere. According to Cisco’s report [97], global Internet traffic is expected to reach 2.3 zettabytes per year by 2020, and wireless data traffic will account for 65% of the total Internet traffic. There are three primary contributors for the explosive growth of wireless data demand: the rising number of wireless devices, the increasing number of new applications, and the evergrowing amount of video traffic. Each year, all kinds of smart devices with increased intelligence are introduced in market. The number of wireless devices is predicted to reach 11.6 billion by 2020 [97]. The smart devices enable people to enjoy mobile applications for entertainment, such as social networking, video streaming, and gaming. Such bandwidth hungry applications have changed the wireless data consumption pattern. According to Ericssons report [98], video traffic dominates the mobile data consumption for all kinds of mobile devices. Moreover, the amount of video traffic is still growing more than 50 % annually. To meet the ever-growing traffic demand, innovative technologies have been developed to expand the capacity of wireless networks. Some examples include multi-input multi-output (MIMO), full duplex, cognitive radio, mmWave, ultra-wideband, among others. In this dissertation, we aim to investigate the impact of such advanced technologies on network throughput performance. Such theoretical study is critical since it can be used as a guidline to design real-world network protocols.

Millimeter-wave (mmWave) is widely investigated for indoor communication scenarios thanks to the available rich spectrum. However, the shortened antenna size and the high frequency make mmWave extra sensitive to blockages. Indoor dense space (IDS) is a specific type of indoor environment, where the compact geometry together with a high number of blocking objects and users make it hard to fulfill the data rate required by all of the users in the mmWave network. With the capability of redirecting signals, the reconfigurable intelligent surface (RIS) has the potential to overcome the attenuation brought by the blockage. Aside from the promising improvement in data rate brought by the RIS, the power supply for RIS is also a major concern in IDS due to the cabling and the batteries. Dynamic RIS has the capability of reconfiguring its phase-shifts to offer a higher gain in data rate with the price of consuming power. In comparison, by sacrificing the reconfigurability, static RIS does not require any power, cabling, or batteries but is expected to provide lower data rates. To find the balance between the performance and cost trade-off, the concept of self-sustainable RIS in IDS is proposed. This approach involves the utilization of specific RIS elements to harvest energy, thereby providing support for the power requirements of the RIS operation, consequently reducing the reliance on traditional cabling infrastructure. In this work, we compare the coverage extension effect brought by deploying static, dynamic, and self-sustainable RISs in the aircraft cabin which is a typical example of an IDS. To capture the propagation characteristics of a RIS in IDS, we first provide guidelines for modeling the RIS in the ray tracing (RT) simulator, and then we select the best locations to deploy RISs among three candidates. For each type of RIS deployment, we propose an optimization algorithm, which jointly configures the RIS phase-shifts and the time resources to provide the maximum equal achievable data rate for all of the users. Additionally, for the self-sustainable RIS, the working mode of each RIS element is also jointly configured such that each element is used either to reflect the incoming signal or to use the signal for energy harvesting. Based on the results, the signal propagation of a single base station (BS) can be extended from 3 rows to 11 rows by deploying static or dynamic RISs. The minimal achievable data rate is 35.4 Mbps with the static RISs and 45.3 Mbps with the dynamic RISs. The results indicate that due to the limitation of self-sustainable constraints, RISs with 16 elements are hard to cover the whole 11 rows in the considered cabin. Nevertheless, with self-sustainable RIS, 10 more UEs are covered compared to the case where no RIS is deployed. The minimal data rate with the help of the self-sustainable RISs within the coverage is 0.75 Mbps. The feasibility study shows that this energy requirement has a greater likelihood of being fulfilled as the number of elements in RIS increases. / Millimetervåg (mmWave) är allmänt undersökt för inomhuskommunikationsscenarier tack vare det tillgängliga rika spektrumet. Den förkortade antennstorleken och den höga frekvensen gör dock mmWave extra känslig för blockeringar. Indoor dense space (IDS) är en specifik typ av inomhusmiljö, där den kompakta geometrin tillsammans med ett stort antal blockerande objekt och användare gör det svårt att uppfylla den datahastighet som krävs av alla användare i mmWave-nätverket. Med förmågan att omdirigera signaler har reconfigurable intelligent surface (RIS) potentialen att övervinna dämpningen av blockeringen. Bortsett från den lovande förbättringen av datahastigheten som RIS ger, är strömförsörjningen för RIS också ett stort problem inom IDS på grund av kablarna och batterierna. Dynamic RIS har förmågan att omkonfigurera sina fasförskjutningar för att erbjuda en högre förstärkning i datahastighet med priset för att förbruka energi. I jämförelse, genom att offra omkonfigurerbarheten, kräver statisk RIS ingen ström, kablar eller batterier utan förväntas ge lägre datahastigheter. För att hitta balansen mellan prestanda och kostnadsavvägning föreslås konceptet med självförsörjande RIS i IDS. Detta tillvägagångssätt involverar användningen av specifika RIS-element för att skörda energi, vilket ger stöd för strömkraven för RIS-driften, vilket minskar beroendet av traditionell kabelinfrastruktur. I det här arbetet jämför vi den täckningsförlängningseffekt som uppstår genom att installera statiska, dynamiska och självförsörjande RIS i flygplanskabinen, vilket är ett typiskt exempel på en IDS. För att fånga utbredningsegenskaperna för en RIS i IDS ger vi först riktlinjer för modellering av RIS i ray tracing (RT)-simulatorn, och sedan väljer vi de bästa platserna för att distribuera RIS bland tre kandidater. För varje typ av RIS-distribution föreslår vi en optimeringsalgoritm, som gemensamt konfigurerar RIS-fasförskjutningarna och tidsresurserna för att tillhandahålla den maximalt lika möjliga datahastigheten för alla användare. Dessutom, för den självförsörjande RIS, är arbetsläget för varje RIS-element också gemensamt konfigurerat så att varje element används antingen för att reflektera den inkommande signalen eller för att använda signalen för energiskörd. Baserat på resultaten kan signalutbredningen av en enda base station (BS) utökas från 3 rader till 11 rader genom att distribuera statiska eller dynamiska RIS:er. Den minsta möjliga datahastigheten är 35,4 Mbps med statiska RIS och 45,3 Mbps med dynamiska RIS. Resultaten indikerar att på grund av begränsningen av självförsörjande begränsningar är RIS med 16 element svåra att täcka hela 11 rader i den övervägda kabinen. Ändå, med självförsörjande RIS, täcks 10 fler UE jämfört med fallet där ingen RIS är utplacerad. Den minimala datahastigheten med hjälp av de självförsörjande RIS:erna inom täckningen är 0,75 Mbps. Förstudien visar att detta energibehov har större sannolikhet att uppfyllas i takt med att antalet element i RIS ökar.

Dynamic Spectrum Access (DSA), also known as Dynamic Spectrum Management, is the method of utilizing a set of spectrum techniques in real time to provide the ability to share wireless channels between Primary (or licensed) users (PUs) and Secondary (or unlicensed) users (SUs). The system is so designed that under normal circumstances, the PUs always get priority, but DSA enables the SUs to use the licensed bands as long as they do not create any interference on the PUs. Hence, the goal of utilizing the spectrum more efficiently can be achieved. Though DSA has been researched extensively as a new concept, it is still under development and several challenges remain unsolved. DSA is recognized as a vital component in 5G-and-beyond network deployment scenarios. Although 5G networks can work in sub-6GHz bands, higher frequency bands (like 28 GHz and 60 GHz) are particularly of interest as they offer much larger bandwidth and regulatory agencies have been announcing licensing plans for these emerging bands. These higher frequency bands could enable extremely high-speed wireless communication by leveraging the gains of highly directional antennas. Smart devices used worldwide has already surpassed 22 billion and is only going to increase in the coming years. Channel allocation and high-speed communication will be the backbone to drive this enormous network of devices, and DSA and directional antenna communication mechanisms will be the key factors governing the future communication infrastructure. In this dissertation, we show how omnidirectional DSA techniques can be applied towards directional cases, i.e., replacing the omnidirectional antennas with directional antennas working in the millimeter wave (mmWave) bands. MmWave enables ultra-high speed transmission and reception, but with some caveats; these antennas should be deployed in line-of-sight (LOS) and a lot of transmission and reception properties depend on how the antennas are aligned, their steering angle, beamwidth and field-of-view (FOV). It is a challenge to take into consideration all of these factors and come up with a solution of ideal signal-to-interference-plus-noise-ratio (SINR) combination between a set of transmitters and receivers. This dissertation sets a guideline on how small cell mmWave transmitters and receivers can be deployed in a densely populated area by working in a coalition (such as by smartly allocating channels to coalitions with more users). Mobility and varying orientations of mmWave as part of dynamic coalitions present new challenges we undertake. Hence, an area where this research can be very apt is vehicular networks, leveraging the high-speed communication provided by mmWave networks. Since the nodes in this case, the vehicles, will be primarily in motion, our research can be applied especially, because we are investigating the antenna designs by considering their beamwidths, steering angles power budgeting.