# Performance Evaluation of IEEE 802.11 ah Networks With High-Throughput Bidirectional Traffic
## 2 Related Work
[25] proposed a load-balanced sensor grouping for RAW based on set partitioning that assumes that the Access Point (AP) knows the (static) traffic demand of each station. [PERSON] et al. [28] analyzed RAW performance in the non-Cross Slot Boundary use case under various holding schemes. They also proposed new holding schemes for RAW based on back-off states of the stations. [PERSON] et al. [27] developed a mathematical model that allows for finding (1) the distribution of time required for an arbitrarily chosen station to transmit its frame, and (2) the distribution of time required for all stations to transmit their frames in a RAW slot. They assumed that the AP does not transmit anything except acknowledgements (ACKs), there are no hidden nodes and transmission errors can only be caused by collisions. This model enables calculating the minimal RAW slot duration required for (1) an arbitrary chosen station to successfully transmit its frame with some predefined probability, and (2) all stations to successfully transmit their frames with some predefined probability; thus, it is only valid for WSN - scenarios. One could expect downlink traffic in hidden node mitigation studies. However, only [PERSON] et al. [16] assume the network is saturated with downlink traffic (limiting transmission to a device once per RAW) and propose RAW grouping based on a previously constructed carrier-sensitivity table, whereas [PERSON] et al. [23] identify hidden nodes by non-acknowledged Power-Saving-Poll (PS-Poll) transmissions (i.e., uplink). [PERSON] et al. [24] also assume that the network is saturated with uplink traffic and groups the stations according to their geographical position. An actuation scenario is investigated by [PERSON] et al. [15] who analyzed performance of IEEE 802.11 ah in a connected lightning use case considering latency and power consumption at the actuator. They investigated how MCS, TIM segmentation and DTIM period influence DL latency and energy consumption and concluded that 2 MHz channel bandwidth leads to lower DL latency compared to 1 MHz, that there is a trade-off between latency and power consumption in terms of DTIM period (i.e., short DTIM period contributes to lower latency, but increases power consumption) and that using broadcast/multicast for groups of actuators lowers the latency compared to serving the same group with unicast transmissions. [PERSON] et al. [13] proposed a solution for choosing a suboptimal Protected Interval (PI) duration, where PI represents a time interval within a beacon interval reserved for Power-Saving (PS) stations, whereas the rest of the beacon interval represents the Shared Interval in which all stations (both PS and active stations) can transmit their data. PI is merely an abstraction of time-restricting mechanisms such as RAW. They consider heterogeneous UL/DL traffic; however, they validated their model with a small number of stations without TIM segmentation. [PERSON] and [PERSON] [12] and [PERSON] et al. [14] optimized the energy consumption in IEEE 802.11 ah networks that support bidirectional traffic patterns. [PERSON] et al. [14] proposed a novel channel access protocol for IEEE 802.11 ah based on a smart use of Channel Access Slots, in which the RAWs can be divided. However, this study is based on an outdated draft of the IEEE 802.11 ah standard. The standard published in December 2016 defined RAW in a somewhat different way. [PERSON] and [PERSON] [12] investigated the TIM and page segmentation scheme and proposed a method that (selectively and dynamically) temporarily changes the TIM group membership of nodes and rearranges their traffic to maximize overall sleeping intervals without causing delay to data delivery. Finally, [PERSON] et al. [11] studied the energy efficiency of 802.11 ah in a heterogeneous Wi-Fi network and proposed a simple and fairly accurate mathematical model to calculate the average throughput and energy consumption of a 802.11 ah network, considering both TIM segmentation and RAW.