FDMA and TDMA are not modulations, they are channel access methods. And it's QPSK, not OPSK.
C4FM, CQPSK, H-DQPSK (TDMA outbound), H-CPM (TDMA inbound) are a few examples of modulations used by P25. The specific modulation used depends on whether the site is standalone vs part of a simulcast cell, as well as whether the talkgroups are FDMA or TDMA. Standalone sites tend to use C4FM for the control channel and FDMA traffic. Simulcast cells will normally use CQPSK/LSM for the control channel and FDMA traffic. Phase II TDMA uses H-DQPSK for traffic channels regardless of whether the site is standalone or simulcast.
