ed for the 802. 11n interface. The HT Control field has two forms: the HT variant and the VHT variant. These two forms differ according to the HT Control Middle field format. For the HT variant, the first bit is ZERO, whereas for the VHT variant, the HT Control field starts with a bit at ONE. The MAC header, described in Figure 5.2, has the following fields. Bit 0 Bit 1-29 Bit 30 Bit 31 HT Control Middle AC Constraint More PPDU Frame Frame Duration Address 1 Address 2 Address 3 Address 4 Control Control Control byte 2 0 2304 Figure 5.2. MAC header structure 802.11ac Interface The information provided by the HT Control Middle field is described in Table 5.2. Information Designation Request regarding the recommended value of MRQ (VHT-MCS feedback Request) the modulation and coding scheme MSI: MRQ request identifier MSI (MRQ Sequence Identifier) STBC: indicates whether the estimate in the STBC indication MFB subfield is calculated based on a PPDU data unit using STBC MFSI: identifier of the sequence relating to a request for a recommendation on the value of the modulation and coding scheme (MCS) MFSI (MCS Feedback Sequence Identifier) GID-L: part of the group identifier (GID) the GID-L (see note) PPDU data unit used to determine the value of the modulation and coding scheme indicated in the MFB field Recommended modulation and coding scheme (MCS) Complementary part of the group identifier GID-H (GID) of the PPDU data unit Type of error correction code Coding Type BCC (Binary Convolutional Code) LDPC (Low-Density Parity Check) Transmission type of the measured PPDU FB Tx Type data unit Indication of unsolicited information relating Unsolicited MFB to a recommendation on the value of the modulation and coding scheme Note: the group identifier (GID) is assigned to the mobile in the case of a MU-MIMO (Multi-User - Multiple Input Multiple Output) transmission Table 5.2. Subfields of Control Middle field Wi-Fi Integration to the 4G Mobile Network 5.2. PLCP sub-layer The structure of the PLCP (Physical Layer Convergence Pr