I have no background in telecommunication. Could anyone please explain to me what is the IQ data in telecommunication? It will be best to explain it with some basic analogies. Many thanks!!

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    $\begingroup$ Have a look at this discussion dsp.stackexchange.com/questions/7612/i-and-q-channels/7613#7613. Also understand what complex baseband representation of passband signal is. That will help you understand it. $\endgroup$ Dec 28, 2013 at 6:43
  • $\begingroup$ I have a follow up question really. I used a signal analyzer to get IQ sample data from a blue tooth device. The IQ data received is in the form of a .MAT file and I examined the file contents and see an + ibn samples where a, b are constants, n is the sample number and the format is a complex number. I was told the real part is the I and the imaginary part is the Q. Are these samples received baseband I Q data? I am trying to determine the carrier frequency offset. I was trying to determine the frequency of the signal. I felt I could measure the phase difference between samples per time. Howe $\endgroup$
    – Peter E
    Sep 2, 2019 at 14:21
  • $\begingroup$ @PeterE Please ask a new question! You have "answered" the original question with a non-answer. $\endgroup$
    – Peter K.
    Sep 2, 2019 at 16:14

3 Answers 3


Here is a good article from National Instruments. In general, we ask on this site that you put in more effort into your question, e.g. links to articles that you've already looked at and things you haven't understood. Otherwise, you'll simply get an answer which is the first link you get from Google when typing in your question.

In a nutshell, I/Q takes advantage of sine and cosine signals being mathematically orthogonal to each other, and therefore separable with very little amount of effort. This means that with appropriate care taken, you can modulate one signal with a sine wave, another one with a cosine wave (they are simply delayed versions of each other), and still be able to separate these two signals at the receiver even though their frequency spectrum overlaps.

If this is either completely over your head, or completely obvious to you, edit your question with clarifications of how much you understand. Otherwise it's impossible to give you the exact answer you're looking for.


A simple answer is that I/Q are the real and imaginary components of the complex-valued transmitted baseband signal. In communication systems "I/Q data" usually refers to the real (I) and imaginary (Q) samples of the constellation for the modulation type used. There are usually a lot of I/Q "samples" (rather than "data") that happen during interim processing.


I and Q signal concept is relatively complex topic to explain without signal background, you first need a basic knowledge about Passband and Baseband real and complex signals. if you are familiar whith these topics, you can jump to the last paragraph.

In short signals are any representations of real life quantitative parameter value versus to another variable mostly "time", i.e. values of room temperature in every hour is a signal.

Any signal with real values is type of real signal, e.g. all of physical signals are real, and signals which include imaginary values are complex signal. complex signals are widely used when processing real signals.

Another topic here is baseband and passband signal. first you should know every signal based on it's nature occupies specific frequencies in its spectrum. when a signal only occupies low frequencies (near or include zero) it called baseband signal. most of the signals in nature are baseband. and when a signal occupies higher frequencies far enough from zero (dc), they called passband, in telecommunication passband signals are created from baseband signal (modulating) when trying to send data through a medium which doesn't works well on baseband signals, such as Air, i.e GSM, UMTS signals are passband.

In telecommunication theory and applications, I and Q signals are respectively Inphase and Quadrature component of a passband (or aka RF/IF) signal, which both of them perfectly represent the passband/RF/IF signal. I/Q signals both are in baseband and easy to work when modulating, demodulating, manipulating or examining the passband/RF/IF signal.

Welcome to the complexity :))


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