What is IQ vector
It is representation of the signal in the complex form i.e. real and imaginary. I refers to real part and Q refers to imaginary part. The binary data after data mapping(modulation bpsk,qpsk,qam) becomes complex and refers as IQ vector signal.
Let us assume one sample of I/Q Data and analyze in the complex plane.
I = 0.70
Q = 0.42
From the rectangular plot of IQ data vector,following can be derived:
• Amplitude of real signal is 0.7
• From Pythagorus theorem,magnitude A is (0.72+0.422)0.5 = 0.816
• From graphy and trigonometry, angle φ is tan-1(0.42/0.7) i.e. 30.96 degree.
I = A cos(φ) and Q = A sin(φ)
IQ data vector signal can be represented in rectangular form(Cartesian form),polar form and Eulers form as follows.
As a complex number like I + Qi, and as a vector [I,Q].
In a polar form using Acos(φ) and Asin(φ)
I = Amplitude*cos(angle)
Q = Amplitude*sin(angle)
In the Eulers form as
Refer I/Q Data for Dummies>> with animation diagrams and figures by Mikael Q Kuisma.
IQ vector Signal Generation(VSG)
The IQ data is generated using advanced RF vector signal generator(VSG). The physical layer output is usually in the form of IQ data vector. Physical layers are different for different IEEE/3GPP standards such as WLAN,WiMAX,GSM etc.Hence various parameters such as bandwidth of the signal,modulation type,FEC technique and MAC payload are needed to generate the complex IQ data vector.
IQ vector Signal Analysis(VSA)
IQ data signal can be analyzed using vector signal analyzer(VSA). The most popular is Agilent's 89600 VSA. In order to analyze the IQ signal bandwidth and sampling rate at which IQ data is acquired is given as input to the VSA tool.
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