Sharif Digital Repository

Regarding the increasing trend of network costumers and services, requirement of high-speed and high quality seems to be inevitable. Therefor much effort has been put to issue the problem properly in recent years. Optical fiber networks are attending more attention and optical fiber channels are dominating the world of networking and data. Applying new methods such as CDMA and OFDM raise the issue of maximum achievable rate and quality of these systems.These include the main concentration of this project. First, optical channels are modeled.Then, applying OFDM and CDMA methods, lower and upper bound of channel capacity will be determined  

Fiber optic networks are the most attractive technology to deal with the ever increasing demands for high rate transmission with guaranteed quality of service and affordable costs. Optical-to-electrical (O/E) and electrical-to-optical (E/O) conversion at intermediate routers are the restricting processes in current optical networks. There is a great interest to remove O/E and E/O conversion at intermediate routers to achieve an all-optical transmission between source and destination. Optical circuit switched (OCS) networks are the first generation of all-optical networks, which are restricted due to its limitation such as being connection oriented, low bandwidth utilization, and coarse... 

With the explosive increase in the amount of information in the today's world, the need for high-speed data transmission is felt more and more. According to Cisco's forecast, the traffic explosion in real wireless networks will continue. According to the forecast, the volume of data traffic on wireless networks will be about one hundred and ninety exabytes in the next two years, and in the next four years will reach over five hundred exabytes per year. On the other hand, the advent of new technologies, such as the Internet of Things and the Tactile Internet, pushes us to make it possible to transmit with very low delays and high reliability in future generation networks. In this project, we... 

The increasing tendency to offshore exploration is making the need to design efficient methods for secure underwater wireless transmission increasingly highlighted. Radio frequency used for wireless communications in open space may not be suitable for data transfer due to their extensive drop in the water. On the other hand, since sound propagates well in water, now the majority of underwater communication systems are using audio frequencies. Limited bandwidth, low emission speed, and low security are the most important disadvantages of audio systems in comparison with optical systems. Therefore, optical systems, could be appropriate alternatives for audio systems to achieve secure,... 

Two major category of protocols suggested for quantum key distribution (QKD) are prepare and measure protocols and entanglement based protocols. One of the most challenging problem of these two categories is that they are not immune against attacks to measurement devices. For addressing this problem, measurement device independent protocol (MDI-QKD) was proposed in 2012; in which measurement device can be in hands of untrusted party. The idea of MDI-QKD is based on time-reversed EPR protocol. Still low secure key exchange rate has provoked many efforts, one of these efforts was to improve the key rate by means of quantum memories. In this thesis different proposed structures for memory... 

With the rapid development of communication technology, the importance of information security is growing daily. Data Encryption, as one of the most important tools of secure communication, has attracted a lot of attention. Most conventional cryptography methods are based on computational complexity assumptions. Hence, they are threatened by computational power enhancements. One of the most important approaches of cryptography that does not have this drawback is quantum cryptography. The unconditional security of this method has been proved by laws of quantum mechanics. One application of quantum cryptography is quantum key distribution that enables secret key exchange between two users. The... 

Demands on wireless access networks are growing enormously, thanks to deploying new generations of wireless communication systems—such as LTE, 4G, and in the near future 5G—and especially promoting new technologies, like Internet-of-Things (IoT). With the help of visible light communication (VLC) systems, networks have been developed the capacities of which can go beyond some Mbps, but this is not satisfying enough. Therefore, a newer version of VLC systems has been investigated, called Light-Fidelity (LiFi), which is complement to WiFi (in radio frequency networks(. Two main purposes of LiFi networks are obtaining a high-capacity wireless access network and using them for illumination... 

In this dissertation, the statistical analysis of ultrashort light pulse detectors, in presence of different noise sources, is presented. By investigating performance degradation of ultrashort light pulses detection based on linear conventional detectors, the necessity of all optical preprocessors prior to the low speed photodetectors is approved. By using these preprocessors, we achieve high discrimination between noise and ultrashort light pulses at the photodetector input, for simplicity in detection of light pulses by conventional low speed photodetectors. Among various types of preprocessors, in this dissertation, we focus on optical crystals with dominant imposed nonlinear second... 

Today's interest growth to the underwater explorations and navigations demands to design appropriate underwater communication methods and systems is strongly felt. Although radio frequencies which are widely used in free space communications, they cannot be a decent candidate for underwater wireless communications, due to their sever attenuation in water environment. On the other hand, underwater acoustic communications has been widely studied and implemented in past decades, because of little attenuation in comparison with other means of communications in water environment. However, acoustic communications suffer from limited bandwidth, low propagation speed, and low security in compared... 

Ever-increasing appetite for wireless data traffic is insatiable. Mobile data traffic was about 3.7 Exabytes per month in 2015. Owing to Cisco’s prognostications, this data traffic will surpass 30 Exabytes per month in 2020, which unveil exponentially growth in that. On the other hand, however, precedent techniques have undertaken this appetite till now, but most of them will not hold off this exponentially increasing demand in near future. Accordingly, one of the most precious resources for near future is millimeter Wave (mmWave). In this thesis, we present a cell planning problem for a cellular network containing two types of base stations (BS), to distinguish between them, BSs which have... 

Visible light communication networks provide wide bandwidth due to the use of visible light. In these networks, high efficiency can be achieved with proper system design and the use of space division multiplexing, effectively utilizing the existing bandwidth. Design issues in these networks are usually raised in the form of optimization. In this thesis, we optimize the energy efficiency of a visible light communication network with space division multiplexing in the transmitter by determining how to allocate LEDs to users and the amount of power for each LED. To accomplish this, we first propose two heuristic algorithms for determining how to allocate LEDs, and then we use a global... 

Increasing the demands for different services over the Internet, need for modern network designs and protocols to meet the required necessities is more appreciated. Therefore GMPLS protocol which can guarantee the Quality of Service has been introduced. Afterwards code-based GMPLS networks have been introduced which can provide different services with multi length variable weight codes for multimedia applications. In order to investigate network behavior, a comprehensive traffic model is required.
In this thesis an accurate and efficient model for the discussed networks using state dependent queuing network theory is introduced. By calculating the steady state probability of network, it... 

Elastic optical networks, due to their key features including flexible spectrum allocation, ability to convey high bitrates, and distance adaptive modulation assignment are considered as a promising solution for providing higher capacity, more efficiency, and scalability in core optical networks.Furthermore, Multi-Core Fibers (MCFs) and Space Division Multiplexing (SDM) technique can be utilized to overcome the capacity limitation of the conventional Single Mode Fibers (SMFs). However, the inter-core crosstalk issue in MCFs should be addressed in the design of these networks.With the use of these technologies and, as a result, increasing the transmission rate in optical networks, the issue... 

In this dissertation, the optimization problem of visible light communication (VLC) access networks is discussed and investigated. Firstly, by examining the fundamental concepts in VLC systems, the channel capacity is analyzed, and the concept of capacity per unit cost is introduced to improve energy consumption. The appropriate relationship for channel capacity in optimization studies is also explored. In this regard, we reached a new distribution for transmitted signals, which, by reducing up to approximately 92% of the additional energy required for data communication, increases energy efficiency in visible light communication systems up to 98%, bringing the energy consumption of the...