Double symbol error rate and block error rate of MDPSK

The double symbol error rate (DSER) is calculated for an M-ary DPSK (MDPSK) system to show that double symbol errors are less likely to be produced when M>or=4 than for the binary case (M=2) and that MDPSK with M>or=4 provides similar conditional SER (defined as the SER when the previous symbol decision was in error) when compared at the same SER value. The block error rate (BKER) is also shown to be well approximated by that determined assuming independent symbol error when M>or=4.