To communicate with a plurality of non-AP stations (STAs) within synchronized transmission opportunities (S-TXOPs), an access point station (AP) performs an initial management frame exchange with the STAs. During the initial management frame exchange, one or more sets of semi-static allocation parameters are signalling to the STAs. Each set of semi-static allocation parameters is associated with an allocation index (IDx). The AP may communicate data with the STAs during S-TXOPs that follow the initial management frame exchange. Each of the S-TXOPs may include an S-TXOP trigger. The S-TXOP trigger may be encoded to include one of the allocation indices to indicate a known allocation for use during the associated S-TXOP when a set of the predetermined semi-static allocation parameters are to be used. The S-TXOP trigger may be encoded to include full allocation information to indicate a new allocation for use during the associated S-TXOP when the predetermined semi-static allocation parameters are not used.