ion code Table 5.3. Structure of VHT-SIG-A field Wi-Fi Integration to the 4G Mobile Network 5.3. PMD sub-layer The PMD (Physical Medium Dependent) sub-layer improves the rate of the 802.11ac radio interface relative to the 802.11n interface from the following parameters: - aggregation of radio channels makes it possible to constitute a bandwidth of 80, 160 or 80 + 80 MHz. For the 802.11n interface, aggregation limits the bandwidth to 40 MHz. - 256-QAM modulation allows an OFDM symbol to carry eight bits. For the 802.11n interface, 64-QAM modulation limits the number of bits to 6. - spatial multiplexing MIMO can be performed on eight space-time flows. For the 802.11n interface, spatial multiplexing is limited to four space-time flows. 5.3.1. Transmission chain The transmission chain includes the function blocks described for the 802.11n interface in section 4.3.1. Figure 5.4 shows the transmission process for the L-SIG and VHT-SIG-A fields of a PPDU data unit. These transmit blocks are also used to generate the non-VHT fields of the VHT data unit. Figures 5.5 and 5.6 show the transmission process for generating the VHT-SIG-B field of a PPDU data unit for a single user (SU) and multi-user (MU), for radio channel bandwidths of 20, 40 and 80 MHz. Figures 5.7 and 5.8 show the transmission process for generating the VHT-SIG-B field of a PPDU data unit for a single user (SU), for radio channel bandwidths of 160 and 80 + 80 MHz. Figures 5.9 and 5.10 show the transmission process for generating the DATA field of PPDU data unit for a single user, for radio channel bandwidths of 20, 40 and 80 MHz, with BCC and LDCP encoders. A subset of these transmit blocks is also used to generate the VHT-LTF and VHT- STF fields. 802. 11ac Interface Figure 5.11 shows the transmission process for generating the DATA field of a PPDU data unit for multi-user (MU), for radio channel bandwidths of 20, 40 and 80 MHz, with BCC and LDPC encoders. Figures 5.12 and 5.13 show the transmission process for generating the DATA field of a PPDU data unit