Control Strategies for Energy Efficiency of Next-generation Cellular Networks with Hybrid Energy Sources

Resum

Large-scale systems are characterised by having a large number of components working in coordination. These systems can be composed of geographically distributed elements with resource limitations. In this way, control strategies for large-scale systems have challenges related to information flow, processing time and capacity, controller design, and energyresource optimisation. One particular large-scale system is the next-generation mobile communications cellular network, which will comprise hundreds of base stations interacting with thousands of users in milliseconds. One of the main challenges with next-generation cellular networks (NGCNs) is the higher energy consumption caused by the expected number of connected devices. Here, renewable energies are a good option to face the growing demand of energy consumption. However, there are still major challenges related to the appropriate control schemes to minimise ongrid consumption and optimise energy management in cellular networks with hybrid energy sources (grid and renewable energy). In this thesis, different control strategies for large-scale networks are proposed. These control strategies are assessed over an NGCN powered by hybrid energy sources to reduce grid consumption. The energy-efficiency problem is studied from the viewpoint of the energetic processes – i.e., on-place renewable energy is available, and mechanisms to reduce the gridenergy consumption should be developed. The proposed mechanisms are based on previous research that shows the relationship between the number of users connected to a cellular network base station (BS) and its energy consumption. For this reason, the study of optimal control mechanisms that balance the load of users over the available BSs according to the renewable energy available is a key element in the field of energy efficiency in cellular networks. These schemes are assessed through simulations and then compared with the scheme actually used to manage the user–BS association in cellular networks. The results show that the proposed control schemes improve grid-electricity consumption compared with the traditional association mechanism while still maintaining adequate quality-of-service (QoS) levels. The control schemes for the energy-efficiency problem were studied in two timescales. The short timescale (of the order of seconds) was used to analyse the user–BS association problem in a network configuration with hybrid power sources without an energy storage system. The long timescale (of the order of hours) was used to study load balancing of aggregated traffic in each BS with hybrid power sources and an energy storage system. Finally, the proposed controllers are of different types: (i) centralised, (ii) distributed at the base-station level, and (iii) distributed at the user level