# Mobile Networks ## What is a Mobile Network A mobile network, also called a cellular network, is a wireless communications network distributed over land areas called cells, each served by at least one fixed-location transceiver known as a cell site or base station. A cell site provides the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A mobile network allows mobile devices to communicate wirelessly while moving between cells, with calls and data sessions handed off from one cell to another as the user moves. ## How Mobile Networks Work A geographic area is divided into cells, each typically hexagonal in shape. Each cell has a base station at or near its center. The base station communicates wirelessly with mobile devices within the cell. Base stations are connected to each other and to the core network through backhaul connections, which are typically fiber optic or microwave links. The core network handles call routing, authentication, billing, and interconnection with other networks including the internet. ## Cell Size and Frequency Mobile networks use different cell sizes for different purposes. Macrocells are large cells covering several kilometers, used in rural areas where population density is low. Microcells are smaller, covering a few hundred meters to a kilometer, used in urban areas with high user density. Picocells are even smaller, covering tens of meters inside buildings. Femtocells are home-based cells that provide cellular coverage inside a building using the home's broadband internet connection. Higher frequency radio waves support faster data speeds but cover smaller areas, requiring more densely placed base stations. ## Handover Handover, also called handoff, is the process of transferring an ongoing call or data session from one base station to another as the mobile device moves between cells. Without handover, a call would drop every time the user moved to a new cell. Hard handover disconnects from the old cell before connecting to the new one, causing a brief interruption. Soft handover, used in CDMA networks, maintains connections to multiple base stations simultaneously during the transition, providing seamless handover.