Little knowledge (thirty-eight) MPSK and MQAM modulation to achieve - using the IQ modulation

IQ modulation principle

(A) the basic principles of modulation

(B) the basic principles of modulation

 

 

 

 

IQ modulation achieved using MPSK (QPSK 8PSK BPSK) and MQAM (16QAM 64QAM) modulation

 

 

(A) using IQ modulation achieved QPSK modulation

 

QPSK constellation modulation

 

 

 

Constellation, that is a coordinate, such as the unit circle high school, I is the abscissa, the ordinate is Q, the projection corresponding to the I axis, called the in-phase component, similarly to the projection axis called the quadrature component Q. Since the signal amplitude difference, then it may fall within the unit circle. Specifically, 64QAM, a symbol 64, is equal to the sixth power of 2, so that each require 6 binary symbols to represent was enough. This falls within 64 symbols on the unit circle, depending on where the different colonies of different amplitude and phase. Jump from one point to another point, it means that the phase modulation and amplitude modulation can be done. "

 

QPSK mapping relationship can be arbitrarily set it?

Also to send data 11 as an example, the probability of miscarriage of justice to receive data 10 and 00 is higher than the probability of miscarriage of justice 01. 11 10 wrong mistaken for a bit, but 11 to 00 misjudgment was wrong two bits.
In summary, under the same channel conditions, using 00↔π / 4,01↔3π / 4,10↔5π / 4,11↔7π / 4 mapping relationship between the bit error rate is higher than the QPSK modulation using 00 ↔π / 4,01↔3π / 4,11↔5π / 4,10↔7π / 4 mappings.
Such as 00,01,11,10, between adjacent two code only one digit different encoding is called Gray code . QPSK modulation is used in the Gray code.

(B) the use IQ modulation achieved 8PSK modulation

How to use IQ modulation to achieve 8PSK ?

 

(C) using IQ modulation achieved 16QAM modulation

 

注：前面讲的PSK调制（QPSK、8PSK），星座图中的点都位于单位圆上，模相同（都为1），只有相位不同。而QAM调制星座图中的点不再位于单位圆上，而是分布在复平面的一定范围内，各点如果模相同，则相位必不相同，如果相位相同则模必不相同。星座图中点的分布是有讲究的，不同的分布和映射关系对应的调制方案的误码性能是不一样的，这里不再展开去讲。

 

（四）利用IQ调制实现BPSK调制