چكيده به لاتين
Fifth-generation (5G) Mobile Networks has been investigated to support the high volume of data traffic, with the aim of reducing energy consumption and improving the quality of service. To achieve the fifth generation mobile networks, some key technologies such as heterogeneous networks, massive MIMO networks, energy harvesting networks and millimeter-wave techniques have been proposed. because of the ever-increasing data traffic, conventional cellular networks with a wide coverage area is not enough to satisfy high data rate demands; Therefore heterogeneous networks are employed to solve that problem and in this network base stations of each layer are located randomly and each one for satisfaction of mobile users has a different transmit power, pathloss exponent, number of antennas and spatial density. Heterogeneous networks, made up of macro base stations, that each macro base station is equipped with small cells. Small cells, such as Picocells, Femtocells and relays, have a more spatial density and they use lower power for data transfer. Also, the small cells are recognized as an important element for offloading the macrocell's traffic as well as for improving coverage. moreover using small cells result in increasing performance of the cell edge users, increase spectral efficiency and energy efficiency and reduce both of the operational and capital expenditures. In addition, user association has a great importance to increase load balancing, spectral efficiency and energy efficiency in this network; therefore, challenges and multiple opportunities are introduced for user association algorithm in 5G networks and that mechanism is: asigning a user to a specific base station before starting data transmission.
In this thesis, the mean utility of typical user in MIMO downlink heterogeneous networks is investigated and examined. The concept of that Utility is defined as a Logarithm of transmission rate. The thesis novelty is taking more than one antenna in each base station of layers to serve more than one user in each time slot. This novelty leads to complex mathematical analysis and derive an approximate equation for mean utility of typical user's function. The mathematically equation is studied under spectrum sharing and spectrum partitioning among tiers. Numerical results and simulation results also help to evaluate the proposed model, which validate the derived mathematically equation. The mean Utility Improvement of typical user by addition 2, 3 and 5 antennas to each base station at the first tier under optimal bias factor, is 0.312 log(R[Mb/s]), 0.525 log(R[Mb/s]) and 0.687 log(R[Mb/s]) respectively. The user outage probability decreases 0.15 by adding 5 antennas to the first tier.
Keywords: Heterogeneous Cellular Networks, MIMO Heterogeneous Networks, Stochastic Geometry, User Association, Spectrum Allocation, Downlink performance analysis, Utility optimization.
