Sampling Bandlimited Signals: Why are the Samples 'Complex'?

Explains the process of sampling a band limited signal by down converting to baseband, and compares it to the sample rate required for a direct sampling approach.

[Kabodtubeofficial]

Hello prof. could you make a video on RIS aided cell-free massive MIMO system.

[ZiglioUK]

Very clear explanation, just a few thoughts: if you use a complex sinusoid to demodulate, there's no need for low pass filtering as the replicas at twice the frequency cancel themselves out. Then, the reason why we need sin and cos is because the signal at RF is not symmetrical around the carrier frequency. If it was, like in the case of an AM transmission, we could just demodulate with a cosine and the signal at baseband would be real.

[hariharannair]

Sir after 6:12 nothing is clear. Please explain

[zeuljakim]

Always very thank you !!!! Today I reading a sampling theory book from beyond bandwidth. If possible please explain what it is.

[mordehaym]

Hello,
Why do I need the sin multiplication? If I did the modulation with cos wave so I returned back to my original signal(they look the same on the frequency domain)

[vetrivelcheliant]

Sir, In OFDM systems we complex sample exactly at the same rate as bandwidth? but here we sample at twice the bandwidth! confused!

[stringstoparadise]

sir can i conclude that when we are transmitting the signal its a real signal i.e is either a sine or cosine component but at the receiver due to delay and fading and constructive and destructive interference its become a complex-valued signal which means both sine and cosine components are present in the signal at the receiver therefore we have to multiply it with sine and cosine wave both

[johnaweiss]

So, this wouldn't apply to FM RF?

[johnaweiss]

2:33 Unclear. Why are you adding your carrier to your modulator? Unclear what "sample rate" means with AM.

[amitpalkar]

Excellent video prof Iain. One thought. Issue of high sampling of bandpass signals may not be related to using sin and cos for demodulation I feel. Bandpass signals can be sampled at much lower rate (say for e.g. at twice the bandwidth under certain conditions) .

[eswnl]

I think this is how software defined radios work.

[sk.samiulreza]

There are gaps in the explanation. Please do not skip the intermediary steps.