Sharif Digital Repository

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... 

Recent advances in unmanned aerial vehicles (UAVs) technology have made it possible to use them in wireless network applications. Intrinsic features of UAVs such as mobility, maneuverability and flight altitude adjustment, Provides the possibility of fast and low cost implementation of UAV-based telecommunications networks relative to their terrestrial counterparts.One of the applications of UAVs in free space optical (FSO) communications is their use as a relay in the network. Creating communications links when there is an obstacle in the way (such as mountainous areas or buildings in urban areas) or when natural disasters have damaged communications infrastructure are examples of this use... 

In the future mobile network 5G will offer high speed and low delay but millimeter wave link are poor at penetrating into solid objects. Thus future network will be a hybrid of traditional sub-6GHz macrocells and denser 5G small cells. We develop a general analytical model to derive delay and throughput in this network. First we analyse the initial access delay which is very important in Internet of things and machine to machine communication. Then we go into data delay of network. With the foreseeable explosive growth of small cell deployment, backhaul has become the next big challenge in the next generation network. We analyse two option of fiber and millimeter wave. At the end we have end... 

The growth of traffic in metro and core networks is not deniable today, in addition to the volume of traffic, their different requirement force operators to dimension IP over optical network for the peak traffics and also cares about requirements of the traffics. this multi-policy enabled network using new extended technology such as Elastic Optical Network and Bandwidth variable transponders is used to design network with minimum cost and resource. There is different quality of service parameter, in this work we focus on end to end latency and survivability. we present ILP formulation for the IP over elastic optical network and introduce these parameters to this formulation, as we know... 

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... 

Recently, elastic optical networks have attracted high interest to provide more efficiency and scalability in optical core networks. Due to the high transmission rates and the importance of the transmitted data in these networks, a failure may cause vast data losses. Thus, addressing the problem of survivability in these networks is of great importance. According to different time domain behaviors and reliability requirements of incoming traffic, supporting different quality of services is another important concern. On the other hand, using multi-core fibers is a way to scale the network capacity to provide high-speed transmission services but there is a concern that the inter-core crosstalk... 

The growth of broadband applications in networks such as IOT, video content sites, and 5G technology has called for an increase in the capacity of the network infrastructure. Free space optical channel has been proposed as an option to meet this need. The use of optical channels in free space, in comparison with fiber optic channels, has been considered to be used in 5G technology, due to presenting high bandwidth and low CAPEX. The availability of a free space optical channel is highly affected by weather conditions especially fog and snow particles. Hybrid radio and optical channels and deploying relays are two methods proposed to be used in free space optical communication networks, in... 

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...