how the data steam convolution with the channel matrix in the massive mimo ? is the data stream is sent through all the antennas in the base station ? or it is sent according to user scheduling and beamforming (spatial and space multipexing)?..
many thanks for efforts
The data stream is sent through all antennas, with different phase shifts and amplitudes, to form a beam at the location of the receiver. Multiple such transmissions can be done at the same time.
I recommend you to read the first chapter of my book Massive MIMO Networks, which you can download here: https://massivemimobook.com
No, space-time block codes are only used when there is a lack of channel state information, so one cannot focus the transmitted signals at the desired receiver. In Massive MIMO, we estimate the channel to each user and then use the antenna array to transmit a directive signal that is matched to the channel. Since each directive transmission only leads to signal amplification around the desired receiver, we can transmit to many users at the same time - as long as they are not located at the same physical point.
In massive MIMO, the transmitted data is sent through all the antennas at the base station. This is because the channel matrix in massive MIMO is typically large, with the number of antennas at the base station (BS) being much larger than the number of user equipments (UEs) being served. Thus, to take advantage of the large number of antennas and provide spatial diversity, the data is transmitted through all antennas.
However, the way the data is transmitted through the antennas depends on the precoding scheme used. Precoding is the process of multiplying the data with a complex weight vector to create a beamforming gain that enhances the received signal power at the UE. There are several precoding techniques that can be used in massive MIMO, including zero-forcing (ZF) and maximum ratio transmission (MRT).
In ZF precoding, the precoding matrix is designed to null out the interference between different UEs. The data is multiplied by this precoding matrix, which then determines how the data is sent through the antennas. In MRT, the precoding matrix is designed to maximize the signal power at the UE, and the data is again sent through all the antennas.
The exact way the data stream is convolved with the channel matrix also depends on the precoding scheme used. For example, in ZF precoding, the data stream is multiplied by the inverse of the channel matrix, while in MRT, the data stream is multiplied by the conjugate transpose of the channel matrix.
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