An apparatus of a high-efficiency "HE" station "STA", "HE-STA", (102,104) the apparatus comprising: processing circuitry; and memory (504, 506, 516), the processing circuity configured to: encode a HE physical layer convergence protocol "PLCP" protocol data unit "PPDU", "HE PPDU", to include a high-efficiency signal A field "HE-SIG-A", the HE-SIG-A comprising a first high-efficiency signal A field "HE-SIG-A1" and a second high-efficiency signal A field "HE-SIG-A2", the HE-SIG-A1 to include a dual carrier modulation "DCM" field and a field to indicate a guard interval "GI" duration and an HE long training field "LTF", "HE-LTF" size, the HE-SIG-A2 to include a space-time block coding "STBC" field; wherein if the field to indicate the GI duration and the HE-LTF size is set to indicate a 4x HE-LTF size, the processing circuitry is configured to set both the DCM field and the STBC field to one to indicate a 0.8 μs GI duration; and wherein for the 4x HE-LTF size, a 3.2 μs GI duration is indicated when the DCM field and the STBC field are not both set to one; and configure the HE-STA to transmit the HE PPDU, wherein neither DCM nor STBC are applied when both the DCM and STBC fields are set to one. processing circuitry; and memory (504, 506, 516), the processing circuity configured to: encode a HE physical layer convergence protocol "PLCP" protocol data unit "PPDU", "HE PPDU", to include a high-efficiency signal A field "HE-SIG-A", the HE-SIG-A comprising a first high-efficiency signal A field "HE-SIG-A1" and a second high-efficiency signal A field "HE-SIG-A2", the HE-SIG-A1 to include a dual carrier modulation "DCM" field and a field to indicate a guard interval "GI" duration and an HE long training field "LTF", "HE-LTF" size, the HE-SIG-A2 to include a space-time block coding "STBC" field; wherein if the field to indicate the GI duration and the HE-LTF size is set to indicate a 4x HE-LTF size, the processing circuitry is configured to set both the DCM field and the STBC field to one to indicate a 0.8 μs GI duration; and wherein for the 4x HE-LTF size, a 3.2 μs GI duration is indicated when the DCM field and the STBC field are not both set to one; and encode a HE physical layer convergence protocol "PLCP" protocol data unit "PPDU", "HE PPDU", to include a high-efficiency signal A field "HE-SIG-A", the HE-SIG-A comprising a first high-efficiency signal A field "HE-SIG-A1" and a second high-efficiency signal A field "HE-SIG-A2", the HE-SIG-A1 to include a dual carrier modulation "DCM" field and a field to indicate a guard interval "GI" duration and an HE long training field "LTF", "HE-LTF" size, the HE-SIG-A2 to include a space-time block coding "STBC" field; wherein if the field to indicate the GI duration and the HE-LTF size is set to indicate a 4x HE-LTF size, the processing circuitry is configured to set both the DCM field and the STBC field to one to indicate a 0.8 μs GI duration; and wherein for the 4x HE-LTF size, a 3.2 μs GI duration is indicated when the DCM field and the STBC field are not both set to one; and configure the HE-STA to transmit the HE PPDU, wherein neither DCM nor STBC are applied when both the DCM and STBC fields are set to one.