  Focusing on the increasing market of the sensors and actuators networks, the
IEEE 802.11ah Task Group is currently working on the standardization of a new
amendment. This new amendment will operate at the sub-1GHz band, ensure
transmission ranges up to 1 Km, data rates above 100 kbps and very low power
operation. With IEEE 802.11ah, the WLANs will offer a solution for applications
such as smart metering, plan automation, eHealth or surveillance. Moreover,
thanks to a hierarchical signalling, the IEEE 802.11ah will be able to manage a
higher number of stations (STAs) and improve the 802.11 Power Saving
Mechanisms. In order to support a high number of STAs, two different signalling
modes are proposed, TIM and Non-TIM Offset. In this paper we present a
theoretical model to predict the maximum number of STAs supported by both modes
depending on the traffic load and the data rate used. Moreover, the IEEE
802.11ah performance and energy consumption for both signalling modes and for
different traffic patterns and data rates is evaluated. Results show that both
modes achieve similar Packet Delivery Ratio values but the energy consumed with
the TIM Offset is, in average, a 11.7% lower.
