ocedure) sub- layer is described in Figure 5.3. SERVICE L-STF L-LTF L-SIG VHT-SIG-A VHT-STF VHT-LTF VHT-SIG-A Figure 5.3. PLCP frame structure L-STF (Non-HT Short Training Field): this field is identical to the short training sequence of the 802.11a/g/n interfaces. L-LTF (Non-HT Long Training Field): this field is identical to the long training sequence of the 802.11a/g/n interfaces. The VHT-SIG-A, VHT-STF, VHT-LTF and VHT-SIG-B fields only exist for the VHT format. VHT-SIG-A: this field is used to interpret the PPDU data unit. Table 5.3 describes the information in this field. The main purpose of the VHT-STF field is to improve the estimation of automatic gain control for MIMO transmission. The VHT-LTF field allows the receiver to estimate the transfer function of the radio channel for MIMO transmission. The VHT-SIG-B field provides information on the length of the payload of the PPDU data unit (for SU-MIMO or MU-MIMO transmission) and on the modulation and coding scheme (only for MU-MIMO transmission). 802.1 11ac Interface Information Bit number Designation Bandwidth of the radio channel (20, 40, 80, 160 or 80+80 MHz) STBC (Space-Time Block Coding) Use of transmission diversity Identifier assigned to a mobile set in Group ID the case of a MU-MIMO transmission NSTS: number of space-time channels Partial AID Partial AID: part of the mobile identifier TXOP PS Entering the power-saving mode NOT_ALLOWED Bit to ONE if a short guard interval is Short GI (Guard Interval) Bit to ZERO if not Bit to ONE if a short guard interval is Short GI / NSYM used and if the number of symbols Disambiguation mod10 = 9 Bit to ZERO if not Bit to ONE for LDPC (Low-Density Parity Check) encoder SU/MU[0] Coding Bit to ZERO for BCC (Binary Convolutional Code) encoder LDPC Extra In the case of LDPC encoder, OFDM Symbol indication of an additional symbol used SU VHT MCS/ Modulation and coding scheme (MCS) MU[1-3] Coding Applying a direction matrix for the Beamformed beamforming Cyclic Redundancy Check Completion of the lattice of the convolut