BRS( Beam reference signal) is a special reference signal to let UE knows of the identification of each Beam that the network transmit. It also functions as DMRS for xPBCH.
It occupies 8 subcarriers(5th~12th subcarrier) in every RB(resrouce bloc) except the 18 RBs at the center of the frequency (Note : The 18 RBs at the center is reserved for PSS, SSS, ESS). It is transmitted at every symbols (i.e, symbol 0 ~ 13) in subframe 0 and 25 as shown below. The data is based on Pseudo Random Data (Gold Sequence).