询问关于LTE物理层上行链路接收端的均衡问题

littlelrc

在做LTE的物理层上行链路基于OFDM的仿真。接收端做信道估计和均衡。

在均衡的时候参考资料上是这样说的：

The nominal reference symbols and nominal OFDM data symbols are used to equalize the measured data symbols.

The nominal OFDM data symbols are created by a demodulation process. A demodulation process as follows is recommended:

1. Equalize the measured OFDM data symbols using the reference symbols for equalization. Result: Equalized OFDM data symbols

2. Decide for the nearest constellation point, however not independent for each subcarrier in the RB (Resource Block). 12 constellation points are decided dependent, using the applicable CAZAC sequence. Result: Nominal OFDM data symbols.

At this stage we have an array of Measured data-symbols and reference-symbols (MS(f,t))

and an array of Nominal data-symbols and reference symbols (NS(f,t))

其中我对小标2不是很理解，他是说什么意思呢？是说将接收端测到的偏移的实际点近似到最近的理想星座点吗？还是其他什么意思，不太理解。

如果情况如下面星座图所示：


图为QPSK星座图，黑色星点为理想的星座图的点。但接收端由于各种干扰使得接收到的点位红色星点。用matlab建一个从发送端到接收端的物理信道模型，计算一个表示理想发射点和实际接收点之间关系的参数EVM（错误矢量模）来表示调制质量。有个问题是上图中第1，2，3象限的理想点和接收点都在一个象限内，从接收点推断出相应的理想发射点很容易，但第四象限的理想发射点对应的接收点跑到了第一象限，这种情况用什么算法能够正确地推断出那个跑偏的点对应的是0.707-0.707i这个点呢？这个情况是否和上述的参考资料里的均衡要求冲突了呢？