A method of wireless communication through a wireless local area network, in the following also referred to as WLAN, the method comprising: at a transmitter, acquiring a first transmission opportunity, TXOP; after a clear channel assessment, in the following also referred to as CCA, process, setting a first field in an initial high efficiency, in the following also referred to as HE, Physical Layer Convergence Protocol, in the following also referred to as PLCP, protocol data unit, in the following also referred to as PPDU, to specify a first duration value for Network Allocation Vector, in the following also referred to as NAV, setting and protection of said first TXOP, wherein said first field is defined to specify one of: a plurality of duration values comprising said first duration value; and a value indicating duration unspecified; setting a second field in said initial HE PPDU to specify a first channel bandwidth of said initial HE PPDU; transmitting said initial HE PPDU; after said initial HE PPDU is transmitted and responsive to a determination that said first TXOP comprises no transmission of any non-high throughput, in the following also referred to as non-HT, PPDU, setting said second field in a second HE PPDU to specify a second channel bandwidth of said second HE PPDU, wherein second channel bandwidth is equal to or narrower than said first channel bandwidth; and transmitting said second PPDU in said first TXOP using said second channel bandwidth, wherein said second HE PPDU comprises multiple frames; acquiring a third TXOP; after a CCA process and responsive to determination that: said third TXOP comprises no non-HT PPDU transmission; and each PPDU that has been transmitted in said third TXOP has in said first field said value indicating duration unspecified for NAV setting and protection of said third TXOP, setting said second field in a third HE PPDU to indicate a fourth channel bandwidth of said third PPDU, wherein said fourth channel bandwidth is equal to or narrower than a channel bandwidth of a preceding HE PPDU that has been transmitted in said third TXOP; and transmitting said third HE PPDU in said third TXOP using said third channel bandwidth. at a transmitter, acquiring a first transmission opportunity, TXOP; after a clear channel assessment, in the following also referred to as CCA, process, setting a first field in an initial high efficiency, in the following also referred to as HE, Physical Layer Convergence Protocol, in the following also referred to as PLCP, protocol data unit, in the following also referred to as PPDU, to specify a first duration value for Network Allocation Vector, in the following also referred to as NAV, setting and protection of said first TXOP, wherein said first field is defined to specify one of: a plurality of duration values comprising said first duration value; and a value indicating duration unspecified; setting a second field in said initial HE PPDU to specify a first channel bandwidth of said initial HE PPDU; transmitting said initial HE PPDU; after said initial HE PPDU is transmitted and responsive to a determination that said first TXOP comprises no transmission of any non-high throughput, in the following also referred to as non-HT, PPDU, setting said second field in a second HE PPDU to specify a second channel bandwidth of said second HE PPDU, wherein second channel bandwidth is equal to or narrower than said first channel bandwidth; and transmitting said second PPDU in said first TXOP using said second channel bandwidth, wherein said second HE PPDU comprises multiple frames; acquiring a third TXOP; after a CCA process and responsive to determination that: said third TXOP comprises no non-HT PPDU transmission; and each PPDU that has been transmitted in said third TXOP has in said first field said value indicating duration unspecified for NAV setting and protection of said third TXOP, setting said second field in a third HE PPDU to indicate a fourth channel bandwidth of said third PPDU, wherein said fourth channel bandwidth is equal to or narrower than a channel bandwidth of a preceding HE PPDU that has been transmitted in said third TXOP; and said third TXOP comprises no non-HT PPDU transmission; and each PPDU that has been transmitted in said third TXOP has in said first field said value indicating duration unspecified for NAV setting and protection of said third TXOP, setting said second field in a third HE PPDU to indicate a fourth channel bandwidth of said third PPDU, wherein said fourth channel bandwidth is equal to or narrower than a channel bandwidth of a preceding HE PPDU that has been transmitted in said third TXOP; and transmitting said third HE PPDU in said third TXOP using said third channel bandwidth.