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What I understand in MIMO system, the user data is broken down into several chunks and transmitted over the antennas (say 3 Tx antennas) by using same frequency Fc. In order to use the interference as an advantage in this case.

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And what I know of OFDM, the large BW is divided into several smaller ones, with each having a specific frequency. For example, 2.4GHz BW is divided into 14 channels, each channel has a different central frequency (say the 6th channel has a frequency of 2.437 MHz).

Now the question is while we combine this 2 method of MIMO-OFDM for transmission, does that transmit in same frequency from each antenna? Or at different frequencies?

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For a given subcarrier, QAM symbols are transmitted on several antennas (MIMO). And an antenna can transmit several subcarriers (OFDM). One can imagine that QAM symbols are modulated on a 3-dimensional grid frequency-space-time.

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  • $\begingroup$ Still a bit confused. Can you provide an analogy for better understanding please. $\endgroup$ – Nusrat Feb 18 '18 at 19:06
  • $\begingroup$ Lets clarify what make you confused. What do you mean in saying "same frequency" ? $\endgroup$ – AlexTP Feb 19 '18 at 3:52
  • $\begingroup$ Let's take the example of the commercial routers in our home. Mine has 3 antennas, working at 2.4GHz radio (802.11n--> MIMO-OFDM) in channel 6 (2.437MHz). So what would be the frequency of each antenna as it is transmitting from? As from the concept of MIMO, it should be only 1 frequency (2.437 MHz), but I am confused as it is also under OFDM which has different sub-carrier frequencies. $\endgroup$ – Nusrat Feb 19 '18 at 19:16
  • $\begingroup$ It is true that 2.437MHz is only 1 frequency but channel 6 at 2.437MHz means a channel of 22MHz-bandwidth with center frequency 2.437MHz. Again, what do you mean in saying "same frequency" ? In clarifying what you wanna ask, you may answer your question by yourself. $\endgroup$ – AlexTP Feb 20 '18 at 4:47

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