The BOC-Gated-PRN (or “BOC-GPRN”) discriminator has been employed as an extended solution of BOC-PRN correlators to eliminate multipath and ambiguous tracking of Binary Offset Carrier (BOC) signals. The code multipath error mitigation of this DLL discriminator has been analysed and discussed in . However, the carrier phase multipath error for BOC (n, n) signals when utilizing this new DLL discriminator has not yet been discussed. Since the carrier phase loop cooperates with the code tracking loop in the receiver, a change of correlation process in the DLL could have a direct influence on the Phase Lock Loop (PLL) tracking performance and hence lead to different carrier phase biases in the presence of multipath. Therefore, the purpose of this paper is to investigate and validate the discriminator’s multipath mitigation performance for the BOC (1,1) signal, including code and carrier-phase tracking error envelopes in the presence of multipath in a Costas loop, based on a software receiver platform. The key finding of this paper is that the new BOCGPRN discriminator leads to different carrier phase multipath error behaviour depending on the architecture implementation of different ATAN type PLL discriminators.