A survey on IEEE 802.11ah: An enabling networking technology for smart cities

Highlights

• We study carefully the IEEE 802.11ah draft standard published in July 2014.

• We overview use cases of .11ah, especially related to smart cities scenarios.

• We describe in details novel mechanisms and explain why they are needed in .11ah.

Abstract

Smart technologies play a key role in sustainable economic growth. They transform houses, offices, factories, and even cities into autonomic, self-controlled systems acting often without human intervention and thus sparing people routine connected with information collecting and processing. The paper gives an overview of a novel Wi-Fi technology, currently under development, which aims to organize communication between various devices used in such applications as smart grids, smart meters, smart houses, smart healthcare systems, smart industry, etc.

Introduction

At the end of the last century computers replaced people in many areas facilitating routine actions. Connected together, computers broke the boundaries limiting information dissemination.

In early 2000s, social networks and mobile gadgets connected people all over the world. Having replaced face-to-face communications, they gave us the Internet of people. Although the amount of data transmitted over the Internet is continuously growing, the number of active users in such a network is limited to the number of people on the Earth.

Both phenomena, computers and Internet, have unpredictably changed our life, making people check mail before washing up in the morning. No doubt that the desire to automate whatever possible will definitely revolutionize economics, politics, and social life. New application and services of scalable smart systems – grids, factories, and cities – require myriads of smart things (sensors, robots, controllers, etc.) connected together. Analysts forecast that the total number of devices in such a network, called Internet of Things (IoT), will reach 50 billion by 2020 [1]. Apparently, the best way to connect such a huge number of devices is by wireless.

While futurologists predict our life in 2020, networking engineers inquire whether state-of-the-art wireless technologies are able to provide connectivity for such a huge number of devices, most of which are battery supplied. Although a number of solutions based on RFID, ZigBee, Bluetooth, or other WPAN technologies already support low power device communication, their capabilities are limited by the number of devices, throughput, transmission range, etc. On the other hand, such technologies as WiMAX and LTE are also not suitable because of high energy consumption.

3GPP, IEEE and other international organizations adopt their technologies to the emerging market of the IoT. For example, IEEE 802.11 aka Wi-Fi, used everywhere nowadays, is not suitable for the IoT, since this wireless technology is originally designed to offer high throughput to a limited number of stations located indoor at a short distance between each other. To meet IoT requirements, IEEE 802 LAN/MAN Standards Committee (LMSC) has formed IEEE 802.11ah Task Group (TGah) to extend the applicability area of .11 networks by designing an energy efficient protocol allowing thousands of indoor and outdoor devices to work at the same area.

This paper addresses the activities of TGah, its challenges and the key mechanisms of the upcoming IEEE 802.11ah (.11ah) standard amendment. Although the work is expected to be finished by 2016 [2], draft standard IEEE 802.11ah-D1.0 [3] adopted in October 2013 provides us with the entire view of the novel solutions developed in the Task Group. Because of the refinement process of the draft standard, all the solutions will hardly stay unchanged, however, it is very unlikely that they will be excluded from the final version, the more so, that in May 2014 TGah estimates that 90% of the draft is stable [4].

Thus, the early acquaintance with .11ah is useful for both industry and academical sides. Dozen of papers studying .11ah confirm this idea [5], [6], [7], [8], [9], [10], [11], [12]. Written at the beginning of the standard development process, they provide only a brief overview of some solutions discussed in TGah at that time, leaving many interesting issues without consideration. Having waited for the work on version D1.0 to be finished¹ and seeing obvious difficulties to explain MAC and PHY protocols described in the 394-page draft standard, its motivation and necessity for smart scalable system in a single paper, we try to do it, focusing on the MAC layer aspects.

The rest of the paper is organized as follows. Section 2 describes the set of use cases considered by TGah, their relevance to scalable smart systems (such as smart cities) and problems to be solved in .11ah. Section 3 provides a brief overview of the PHY layer needed to understand MAC solutions. In Section 4, we describe MAC solutions developed in the Task Group to address all problems related to challenges of smart city implementation. For each solution, we provide an explanation² why it was included into draft standard and what benefits it brings. Finally, Section 5 concludes the paper.