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.
Highlights
The Internet of Things (IoT) is advancing towards 26 billion connected units by 2020 according to estimations [1]
Modulation and Coding Schemes (MCSs) and configurations of Restricted Access Window (RAW), Traffic Indication Map (TIM) and Transmission Control Protocol (TCP) through more than 40,000 simulations in the ns-3 network simulator in two scenarios: (1) Video streaming that needs reliable and high-throughput (Section 4.2) and (2) Reliable monitoring scenario (Section 4.3) where each packet is acknowledged at the application layer
We demonstrated that IEEE 802.11ah can support legacy Internet traffic by way of verbose TCP that is rarely suitable for IoT applications
Summary
The Internet of Things (IoT) is advancing towards 26 billion connected units by 2020 according to estimations [1]. Modulation and Coding Schemes (MCSs) and configurations of RAW, TIM and Transmission Control Protocol (TCP) through more than 40,000 simulations in the ns-3 network simulator in two scenarios: (1) Video streaming that needs reliable and high-throughput (Section 4.2) and (2) Reliable monitoring scenario (Section 4.3) where each packet is acknowledged at the application layer. Detailed analysis of the influence of RAW and TIM grouping (in parallel) on attainable scalability, throughput, latency and energy-efficiency considering bidirectional communication, Insights in the trade-off between scalability and throughput, along with configuration best-practices for achieving the desired performance, An immediate reply mechanism at the Access Point to reduce downlink latency, An extension of the ns-3 IEEE 802.11ah module [4], namely implementation of:.
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