Multiple Access it is a combination of OFDMA (orthogonal frequency-division multiple access), TDMA (Time-division multiple access), and SDMA (Space Division Multiple Access).
Where:
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OFDMA is based on Orthogonal Frequency Division Multiplexing (OFDM) with a cyclic prefix (CP); the transmission to/from different UEs uses mutually orthogonal frequency assignments. With granularity in frequency domain assignment equal to one resource block consisting of 12 subcarriers as illustrated by this grid.
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TDMA is based on the transmission to/from different UEs with separation in time. The granularity in the time domain is equal one slot consisting of 14 OFDM symbols, or 2, 4, 7 OFDM symbols within one mini-slot. The physical length of one slot ranges from 0.125ms to 1ms depending on the sub-carrier spacing.
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The SDMA , also known as multi-user MIMO, is referring to the possibility to transmit to/from multiple users using the same time-frequency resource as part of the advanced-antenna capabilities.
