Remote Radio Head systems - Requirements and concept of lightning and overvoltage protection

The exponential growth of the mobile data traffic will continue furthermore in the course of the increasing distribution of smartphones, Tablet-PCs and terminal equipment which are always online. Network operators are faced with the challenge to fulfil this increasing demand for data. A change of the system-architecture is necessary, not only to make the use of the new 4th generation mobile network (4G) possible but also to keep the explosively growth of the legacy 3G-networks under control. The 4G technology or also called LTE - Long Term Evolution - provides the structure to make the huge amount of data available over radio interface. So called Remote Radio Head (RRH) systems establish the basis of this new system-architecture. This new cell site architecture has been evolving from the legacy cell site architecture where large radio components are located remote from the antennas, to an architecture wherein a separate radio frequency (RF) portion of the radio can be located more closely to the antennas. This separation of the digital radio (Base Band Unit - BBU), from the analog radio, Remote Radio Head technology, allows the reduction of the equipment foot print at the site and more efficient operation of the network. This new architecture makes it possible to reduce and optimize the operation costs (OPEX) e.g. the energy demand, foot print rental or less air-conditioning costs. Conventional base station systems use coaxial cable to transmit the high-frequency signal from the base station to the remote mast antenna. An advantage of remote radio systems is the use of optical fiber connections, called fiber-to-theantenna (FTTA), to link the RRH to the base band unit. Remote Radio Head systems are typically supplied with 48V DC. This implicates an additional modification in comparison with conventional base station systems. A long copper connection has to be installed from the 48V DC power supply at the BBU to the Remote Radio Head near to the antennas. The line length could be easily more than 30 meters. Lightning and overvoltage events are one of the main challenges of network operators regarding to the installation of radio equipment at mobile base stations in exposed positions. To ensure a high availability of the mobile cells and to reduce their downtime, for example caused by a lightning strike, there are specific requirements placed on the lightning and overvoltage protection concept and especially to its components.