Performance Evaluation of IEEE 802.11ah Networks With High-Throughput Bidirectional Traffic

Abstract

So far, existing sub-GHz wireless communication technologies focused on low-bandwidth, long-range communication with large numbers of constrained devices. Although these characteristics are fine for many Internet of Things (IoT) applications, more demanding application requirements could not be met and legacy Internet technologies such as Transmission Control Protocol/Internet Protocol (TCP/IP) could not be used. This has changed with the advent of the new IEEE 802.11ah Wi-Fi standard, which is much more suitable for reliable bidirectional communication and high-throughput applications over a wide area (up to 1 km). The standard offers great possibilities for network performance optimization through a number of physical- and link-layer configurable features. However, given that the optimal configuration parameters depend on traffic patterns, the standard does not dictate how to determine them. Such a large number of configuration options can lead to sub-optimal or even incorrect configurations. Therefore, we investigated how two key mechanisms, Restricted Access Window (RAW) grouping and Traffic Indication Map (TIM) segmentation, influence scalability, throughput, latency and energy efficiency in the presence of bidirectional TCP/IP traffic. We considered both high-throughput video streaming traffic and large-scale reliable sensing traffic and investigated TCP behavior in both scenarios when the link layer introduces long delays. This article presents the relations between attainable throughput per station and attainable number of stations, as well as the influence of RAW, TIM and TCP parameters on both. We found that up to 20 continuously streaming IP-cameras can be reliably connected via IEEE 802.11ah with a maximum average data rate of 160 kbps, whereas 10 IP-cameras can achieve average data rates of up to 255 kbps over 200 m. Up to 6960 stations transmitting every 60 s can be connected over 1 km with no lost packets. The presented results enable the fine tuning of RAW and TIM parameters for throughput-demanding reliable applications (i.e., video streaming, firmware updates) on one hand, and very dense low-throughput reliable networks with bidirectional traffic on the other hand.

Evaluating the Suitability of IEEE 802.11ah for Low-Latency Time-Critical Control Loops

“…They wake up periodically to receive the beacon indicating if there is buffered traffic at the AP. In order to prevent all the stations to wake up for the beacon, a power saving mechanism is introduced, called TIM segmentation [11].…”

“…It offers the same data rate for downlink and uplink traffic and, hence, could be used for high-throughput applications (e.g. firmware updates) and reliable monitoring (i.e., acknowledging every transmitted packet) [11].…”

Extension of the IEEE 802.11ah ns-3 simulation module

“…We evaluate the trade-off between the maximum attainable data rate per station and the total number of cameras in the network [8]. As Figure 11 illustrates, already for 10 stations adequate TIM and RAW configuration can achieve a 10 % higher data rate than EDCA/DCF.…”

“…Current research on the MAC layer of 802.11ah mainly focuses on performance of the RAW [5,[10][11][12] and TIM mechanisms [3,7,8]. Originally, much of this research was based on mathematical modeling of the saturated network state, which does not accurately capture real network behavior and is hard to adapt to non-saturated network conditions.…”

Interactive web visualizer for IEEE 802.11ah ns-3 module

“…We avoided the difficulty of post-processing and the limited visualization options by developing a tool that covers both, the ahVisualizer 1 . We extensively use ns-3 for our research on the new IEEE 802.11ah technology [7]. Thus, we needed an easy way to analyze the data obtained from thousands of simulations and to be able to show the evolution of interesting parameters over time while simulating very dense networks with thousands of nodes, which can take hours to complete.…”