## 3 TXOP PSM-Based Mechanism Using Burst Transmissions  
This section describes the operation of the TXOP PSM-based mechanism in an infrastructure Basic Service Set (BSS) consisting of a finite and fixed number \(n\) of STAs associated to an AP. The STAs of the BSS and the AP exchange data with each other using a shared wireless channel. In addition, all the STAs can listen to all the transmissions between the STAs and the AP. In order to transmit data, the AP and the STAs access the channel following contention-based rules according to the 802.11 DCF specification. More specifically, they wait for the channel to be idle during a DCF Interframe Space (DIFS) period, or an Extended Interframe Space (EIFS) period after the end of a collision. The time that follows either a DIFS or an EIFS period is divided into slots. The AP and the STAs are allowed to initiate transmission only at the beginning of each slot time. Before transmitting, they also wait for a backoff time after a period in which the channel is busy, a consecutive transmission, or a failed transmission. The length of this period is initially obtained as a random number of slot times from a Contention Window (CW) of size ranging from a minimum size (\(CW_{min}\)) to a maximum size (\(CW_{max}\)), called backoff counter. When the channel is sensed idle during a slot time, the AP and the STAs decrement their backoff counters by one, and transmit when their backoff counters are equal to zero. Therefore, their actual backoff times can differ depending on the channel occupancy. As soon as the AP or an STA gets access to the channel, it takes the role of the source STA in the current transmission cycle. The STA addressed by the source STA becomes the destination STA and all other STAs behave as listening STAs, neither transmitting nor receiving frames. The source STA can send a burst of \(\alpha\) data frames to the destination STA, including the expected transmission duration in the MAC header of the transmitted data frames. Following the successful reception of each data frame, the destination STA responds with a positive Acknowledgment (ACK) frame after a Short Interframe Space (SIFS) period. In addition, the source STA can send a Request to Send (RTS) frame to the destination STA and wait for a Clear to Send (CTS) frame response after a SIFS period, prior to the actual transmission of data. Note that the transmission duration can also be attached to the RTS and CTS frames. When the listening STAs receive a frame addressed to the destination STA, they initiate the virtual carrier sense procedure defined by the DCF specification. More specifically, each listening STA maintains a Network Allocation Vector (NAV) specifying the channel occupancy time. This information is taken from the duration field contained in the MAC header of overheard RTS, CTS, data, and ACK frames. The listening STAs do not attempt to transmit for the time indicated by their NAVs and enable a microsleep operation until the NAV expiration. They can sleep as long as their NAVs are longer than the time they take in the transitions to go to sleep and wake up. If this condition is fulfilled, the time they can actually sleep is calculated as the time difference between their NAVs and their transition times between awake and sleep states. Allowing the source STA to send multiple data frames (\(\alpha>1\)) to the destination STA can facilitate microsleep operation due to longer transmission times, as compared to when only one frame transmission (\(\alpha=1\)) is performed. So as to increase the chances for multiple frame transmissions, the AP and the STAs can aggregate data frames during a certain time before transmission; this period of time is called holding time. If, prior to expiration of the holding time, they already have \(\alpha\) data frames with the same destination address, they can immediately attempt to transmit these frames.