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For a given OFDM symbol, no subcarrier can be assigned to two users simultaneously. Each subcarrier is uniquely assigned to a unique user. Else you have to implement an Interference cancellation at receiver (which would require having channel knowledge of other users as well, meaning global CSI) or at the transmitter and extremely complex interference ...


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You are right, coherence bandwidth is the frequency domain counterpart of delay spread. However, to achieve diversity across antennas the spacing between the antennas is important "relative to the environment".Let me explain that a bit more. In a user mobile phone you would typically find the order of wavelengths seperation between antennas sufficient to ...


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MAI is when there is Interference due to multiple users accessing a common wireless media. So if you consider an OFDM system then as long as users are trasmiting in their allocated sub carriers there is no multi access interference irrespective of the MIMO technique used, delay spread etc. If each user is using the same frequencies to transmit ...


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The point of increasing the distance between receive antennas is not to reduce the interference; it is to uncorrelate the channels. In the system you're studying, the signal $x_1$ travels by two paths. One has gain $h_{11}$ and the other has gain $h_{12}$. Both of these gains are random. A channel is considered bad when the magnitude of its gain, $|h|$, is ...


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Stop thinking about the maths and just think about the reality. You have 1 receiver. That means there is a signal coming from the receiver into the processor. There is only one signal. You can't measure it twice and get two different signals. You may be thinking of the channel matrix, which has dimension 1x4 (not 4x1, sorry). That's because the channel ...


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Multi-input single-output (MISO) is describing the inputs and outputs of the system. In communication, this is the channel, so if you have a single-output it means that the received vector is $1 \times 1$. The general model for a MISO system is: \begin{split} y &= \mathbf{h^Tx}+\text{noise} \\ &= (h_1x_1+h_2x_2+...+h_Nx_N)+\text{noise} \end{split} ...


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In contrast to your previous question(Why multi-path channel has linear phase within the coherence bandwidth?), the coherence BW in mmWave may not be relevant considering delay spread alone. If you see eq (7) of the reference, the $H$ has contribution from all the $N_p$ paths, even though channel is mentioned as narrow band (flat fading). This is true till ...


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Looking at the equation you have posted, it seems $l$ is the variable for $N_p$ multipaths and for each path, there will be a constant delay $\tau_l$, an attenuation $\alpha_l$, a doppler shift in the carrier $\nu_l$ , angle of arrival at the receiver $\mathbb a_{\mathbf R}$ and angle of departure at transmission $\mathbb a_{\mathbf T}$. And both of these ...


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It is possible if the system supports MU-MIMO.


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The answer is simply orthogonalization of radio resources. For any given OFDM symbol, exactly one user will be allocated certain sub carriers. This allocation is dynamic and informed to the user in what is known as the DCI, in the downlink control channel. Each user will decode data only on the subcarriers on which it has a grant allocated by the base ...


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