Remote Radio Unit (RRU) DC feed protection

Distributed Base Stations (DBS) split the traditional Radio Base Station (RBS) antenna tower base equipment into two locations; a Base Band Unit (BBU) at the tower base and a Remote Radio Unit (RRU) mounted on the top of the tower. Normally the BBU and the RRU would be connected by a fibre optic cable to carry the signals and a DC feed to power the RRU. Towers are likely to be struck with lightning and so some form of protection is necessary to prevent damage to the DC powering feed and connected equipment. Several example protection methods and a worked example are given. Feed cable currents and protection stress levels are calculated for negative and positive lightning flashes. Clause 1 describes the DBS configuration with term definitions in clause 2. Clause 3 shows three possible protection configurations and clause 4 determines the circuit parameters. Clauses 5 through to 7 calculate DC feed cable currents and the Surge Protective Device (SPD) energy for four variants of lightning stroke. Clause 8 outlines two other forms of DC feed protection. Finally clause 9 summarises and comments on the results.