Understanding modulation in transmiting of wireless communication

Hi everyone ^^

I have a question about modulation in transmition of singular antenna device as follow.

As I understand, for example, we are working with an OFDM system with 64 subcarriers.

We need to break our sequence of bits into blocks of 64 symbols to transmit at a time. So we need to transmit 64 symbols (=8*64 bits in 64-QAM, or 4*64 bits in 16-QAM) at a time.

We feed these 64 modulated values into 64 frequencies according to 64 subcarriers and then transmit them.

To work with the convolution , we need to represent our signal (from frequency domain) into time domain using IDFT.

The above is what I understand after reading the example Equalization, Convolution, and Cyclic Prefix AdditionOpen in MATLAB OnlineCopy Code  Copy Command.

But I have questions like:

1. How can we transmit those 64 symbols in 64 subcarriers at one time with a single antenna device? does the device have to transmit those symbol in 64 time slots, as it just can transmit 1 symbol at a time?
2. How should I understand the signal after IDFT? as I understand, the chain of signals in 64 frequencies became a chain of signals in 64 time slots. But I think it is not really correct. Or they are just "imaginary" time slots?

(Now I do not see that the example mention the assumtion of 1 single antenna). I am very confused about these questions as I am new to this signal processing.

Thank you in advance ^^

[Walter Roberson]

Wikipedia:

In OFDM, the incoming bitstream representing the data to be sent is divided into multiple streams. Multiple closely spaced orthogonal subcarrier signals with overlapping spectra are transmitted, with each carrier modulated with bits from the incoming stream so multiple bits are being transmitted in parallel

... In other words, something is effectively adding all of the signals together and the sum is what the antenna is asked to transmit.

[Thien Hieu]

Oh I see. Thank you for your answer ^^

Now I will look up how can we add the signals from different subcarriers for the antenna to transmit ^^

[Thien Hieu]

Oh I see this video OFDM and the DFT and realize my problem in my understanding ^^

In the matlab code we save 64 amplitudes (for example ) of 64 signals into 64 elements of a transmit vector (that's why i thought we can not add those values up because they are in different frequency).

Actually we really can not add those amplitudes but we can add the signals, because they are just simply represent as , then the transmiter transmit the sum of them (and as we know, these 64 subcarriers are orthogonal so at the receiver side, the signal can be simply detected by a mixer). Hence, even a single-antenna device can do this ^^