A base station transmits, in a repetitive first sequence (501) of transmission frames (202) of a wireless channel, first positioning reference signals (551). The base station transmits, in a repetitive second sequence (502) of transmission frames (202) of the wireless channel, second positioning reference signals (552). The first positioning reference signals (551) and the second positioning reference signals (552) each facilitate determining a time of arrival of signals communicated on the wireless channel.