 with sub-carrier 0 being the central sub-carrier. 802. 11ac Interface For a radio channel of 40 MHz, the bandwidth is divided into 128 sub- carriers. The signal is transmitted on the sub-carriers -58 to -2 and 2 to 58. For a radio channel of 80 MHz, the bandwidth is divided into 256 sub- carriers. The signal is transmitted on the sub-carriers -122 to -2 and 2 to For a radio channel of 160 MHz, the bandwidth is divided into 512 sub- carriers. The signal is transmitted on the sub-carriers -250 to -130, -126 to -6, 6 to 126 and 130 to 250. For a non-contiguous radio channel of 80 + 80 MHz, each frequency segment of 80 MHz is divided into 256 sub-carriers. In each frequency segment, the signal is transmitted on sub-carriers - -122 to -2 and 2 to 122. 5.3.4. Spatial multiplexing On the 802. 1n interface, an access point can simultaneously transmit several streams spatially multiplexed to a single station using the SU-MIMO (Single User - Multiple Input Multiple Output) mechanism (Figure 5.18). SU-MIMO MU-MIMO Figure 5.18. SU-MIMO and MU-MIMO mechanism On the 802.11ac interface, the access point can also simultaneously transmit several spatially multiplexed streams to multiple stations using the MU-MIMO (Multi-User) mechanism (Figure 5.18). Wi-Fi Integration to the 4G Mobile Network 5.3.5. Modulation and coding scheme The value of the modulation and coding scheme (MCS) determines the rate value from the following parameters: - modulation of the sub-carriers, phase modulation (BPSK or QPSK) or a mixed phase and amplitude modulation (16-QAM, 64-QAM or 256-QAM); - coding rate of the error correcting code, which can take values of 1/2, 2/3, 3/4 or 5/6; - number of spatial flows of the MIMO mechanism, which can take values between 1 and 8; - bandwidth of the radio channel, which may be 20, 40, 80 or 160 MHz; - duration of the guard interval, short duration of 400 ns or long duration of 800 ns. Tables 5.4-5.7 respectively provide the rate values for a single spatial stream, for the MCS values between 0 and 9 and for bandwidt