Krasko O. Methods and algorithms for increasing the efficiency of convergent optical access networks.

The thesis is devoted to solving an actual scientific task of developing models, methods and algorithms for data flows transmission in converged optical networks, which integrate the fixed and mobile access segments in conditions of dynamic traffic intensity and variable requirements of data transmission quality. The main restrictions for network performance were assessed such as low efficiency of bandwidth utilization, high signaling overhead, complexity of adaptive resource management in conditions of dynamic traffic intensity and various traffic classes. The model or resource distribution in convergent optical access network has been proposed to improve the efficiency of bandwidth utilization. Proposed resource allocation method, called wavelength-time division multiple access separates the entire wavelength-time resource grid into resource blocks. Each resource block has of 8 symbols in time domain and 8 carriers in frequency domain. Carriers separation is 200 GHz that is equal to 1.6 nm interval between wavelengths in a single optical fiber. Time symbol has duration of 15 µs that allows fitting resource block into the 125 µs PHY time frame 10 GEPON. The advantage of this model is the high granularity of dynamic bandwidth allocation, when different amount of resource elements can be allocated to small cell. In this case, the minimal provided capacity is 1.25 Gbit/s per cell. Then the capacity can be gradually increased with 1.25 Gbit/s step until the maximum possible value of 80 Gbit/s per cell. For very large cells, it is also possible to aggregate four resource blocks in frequency domain, providing the total capacity of 320 Gbit/s. The model for convergence of fixed optical and mobile networks has been introduced to improve the efficiency of integrated access network. The novelty of this model is that it allows tunneling of radio signals between baseband processing unit and remote radio head over the optical network. This provides more flexibility of integration the Cloud-RAN and LTE mobile networks into converged infrastructure. The new method of load balancing between closely related segments of optical access network has been developed based on the wavelength-time resource grid. This model can estimate the load flows between different optical network units based on the previously known statistic about their relation among the nodes. Based on the proposed method, we have derived a new approach for handover in LTE networks. This approach takes into account the S1 and X2 traffic percentage in the backhaul. Proposed approach uses joint assignment of the resource elements for multiple optical network units during handover that allows to decrease the amount of backhaul traffic over X2 interface by 20%. New model of network function virtualization has been proposed to simplify the management of the convergent network infrastructure. The main novelty of this model is that it divides networks into four different elements. First, the high performance data centers provide the abstraction of the other network segments and are directly involved in the network functions virtualization according to the software-defined network paradigm. Second, the convergent optical access network is responsible for the transportation of the user data traffic. Finally, the two last mile segments are also considered as the important part of the overall access network infrastructure. Combination of the four above mentioned network segments into single convergent network architecture under software defined management provides a significant gain in terms of the energy and spectral efficiency and overall network performance.