25101中对相位不连续的测试到底是怎么回事？

onepercent

只知道相位不连续会引起频域杂散，协议中是这么说的：Phase discontinuity is the change in phase between any two adjacent timeslots. The EVM for each timeslot (excluding the transient periods of 25 ms on either side of the nominal timeslot boundaries), shall be measured according to subclause 6.8.2. The frequency, absolute phase, absolute amplitude and chip clock timing used to minimise the error vector are chosen independently for each timeslot. The phase discontinuity result is defined as the difference between the absolute phase used to calculate EVM for the preceding timeslot, and the absolute phase used to calculate EVM for the succeeding timeslot.
我不太理解的地方是，一个时隙的相位怎么和evm扯上关系的呢？首先一个时隙内有若干个符号，每个符号的相位是不一样的，用哪个做为这个时隙的相位呢？其次假设是qpsk，那么相位偏差怎么说也是90度以上，和协议要求小于30度不符合阿。我肯定理解错了，是不是说的载频上的相位？但是evm又是星座图的概念，联系不起来阿。
有没有朋友能说得具体些，具体是怎么计算的呢？