1
Introduction

This book began as a collection of observations and implementation experience that the author accumulated while researching wireless links used to enable the "Internet of Things" (IoT). Wireless communications engineers approach the challenge as a stack of layers, where the system has been decomposed into a stacked series of functions. Approaching the various wireless links used for IoT in this layered fashion helps cultivate an appreciation for the various standards that enable interoperability. This book will approach several standards for the wireless IoT from the layered perspective as found in a protocol stack. Organizing this book in the manner of a protocol stack will help the reader better navigate this book, and hopefully, shed some light on the purpose of the specifics within the different wireless standards that empower the IoT.

Let's begin with a question: What is the Internet of Things?

1.1 What is the Internet of Things?

The term "Internet of Things" has been around since the early 2000s [1]. This term refers to autonomous computing devices being networked together to perform various tasks. The term was coined by Kevin Ashton of the MIT Auto-ID center and was originally in reference to Radio Frequency Identifier (RFID) information being made available on the Internet [2]. RFID is a technology that allows objects to be tagged with devices that transmit identification information. RFID allows for the automatic identification and tracking of those tagged objects. This information can be sensed, gathered, parsed, and posted to the internet by way of automated and interconnected computing devices. The term "Internet of Things" has since grown to encompass far more applications and technologies than the original RFID reference.

There are a number of application areas that have either been adopted into or have grown from the Internet of Things, including:

• home automation
• medical devices
• industrial control
• smart grid
• distributed sensor networks
• and others

The Internet of Things is not a new concept, technology, or set of products, but is rather a natural evolution of networked computing technology, enabled primarily through affordable processing and connectivity. IoT is an extension of the "ubiquitous computing" concept popularized by Mark Weiser [3,4]. The size and cost of computing power is and has been decreasing for decades. This decrease in size and cost has resulted in small, inexpensive embedded devices, which are ideal for sensor and interface applications. Combined with the ease of connectivity provided by a robust and varied infrastructure consisting of wired, terrestrial cellular, satellite, and local wireless communication technologies, the rise of the Internet of Things is the natural consequence. While all of the technologies that comprise the Internet of Things are important, it is connectivity, particularly wireless connectivity, that is a fundamental component shaping many of the choices made in the implementation of IoT devices.

Figure 1.1 [5] illustrates the wide reach of this technology in both "vertical" and "horizontal" markets. The "vertical markets" address the needs of a specific group of consumers, and "horizontal markets" seek to address the needs of a wide group of consumers. By making use of technologies such as ubiquitous computing and wireless communications, the IoT transforms objects from being "traditional" to "smart." In Figure 1.1, these smart objects are grouped into domain-specific applications (vertical markets) while network-computing services form domain-independent services (horizontal markets).

Figure 1.1 The IoT Across Vertical and Horizontal Markets [5]

These network-computing services are sometimes called "The Cloud." What is "The Cloud"? There is a humorous answer to that question: "There is no cloud, just someone else's computer."

"The Cloud" is a collection of computation and data storage resources made available to end-consumers by a service provider. End-consumers gain access to these resources through the Internet. This collection of computation and data storage resources is shared across the large number of end-consumers with whom the service provider has some contract.

"Cloud Computing" is where computational tasks are offloaded from local devices and executed on remote, presumably larger and more powerful, devices. The local devices make requests of the remote, more powerful, "cloud" devices. The cloud devices execute the request and provide the results to the local, smaller, devices that directly interface with the end-user.

Wireless IoT technology interfaces with "The Cloud" and "Cloud Computing" to provide many different end-user applications. For example, an end-user may use their smart phone to access a cloud data center that is updated with the status of various sensors. In that example, the wireless IoT devices form a "device network" that sends information through a gateway to a server "in the cloud." The end-user can then access that information by using a personal wireless data device to log into the repository of sensor data stored on the remote server.

While the specific implementations of each of these application areas may be quite different, they all rely on the ability to remotely monitor, manage, and actuate distributed devices. IoT technology has enabled a wide variety of applications and is already deployed across markets as disparate as health care and power grids. World market analyses have made forecasts predicting the continuing rise of IoT applications and significant contributions to the world GDP [6].

An interesting trend within the IoT is the accessibility of development to individuals, which is a by-product of low-cost processing [7]. The availability of inexpensive general purpose embedded processing devices means that device and application development is no longer limited to companies with substantial development and manufacturing budget. Hobbyists and members of the Maker community are able to make use of these platforms to create their own devices for their own unique applications.

With so much development in this field, it is clear there is a risk of fragmentation and a lack of interoperability. Without interoperability, nothing in Figure 1.1 would function. Therefore, the future of IoT lies in interoperability. It is this interoperability that makes connectivity possible. This interoperability will be enabled and communicated through easy access to technology standards developed by the IEEE and others.

This book will focus on the wireless aspects of the IoT, and the standards that enable the necessary interoperability. To that end, there must be provided a disambiguation in what is being referred to as the "wireless" Internet of Things in this book.

1.2 What is the Wireless Internet of Things?

For applications of the IoT, as networks of increasingly autonomous computing devices performing some task, wireless connectivity is often essential. Consider Figure 1.2 [8]. Figure 1.2 shows disparate applications, all connecting to the internet by way of wireless access points. Those wireless access points alone demonstrate the importance of wireless connectivity to the IoT.

Figure 1.2 The IoT Application Areas and Wireless Connectivity [8]

Moreover, many of those application areas shown in Figure 1.2 would not be possible without locally networked devices. Wireline connectivity can establish a network of automated computing devices and connect those devices to cloud-based services. Wireless connectivity provides benefits in deployment that are unmatched by wireline solutions. Numerous sensor applications simply will not function without mobility, which requires wireless connectivity. For these reasons and others, wireless connectivity is a key element to the success of IoT.

Using the term "wireless Internet of Things" narrows the conversation to focus on that wireless connectivity as opposed to cloud-based services and other aspects of popular IoT applications.

1.3 Wireless Networks

Networking is essential for the wireless IoT. Different types of networks exist to satisfy the needs of different end-user applications. Therefore, while not the focus of this book, a brief discussion of the various types of wireless IoT networks is necessary to better understand the functions of the lower layers that will be covered in the subsequent chapters.

1.3.1 Network Topologies

A network topology is the organization of nodes in a given network of nodes. A common network topology for the wireless IoT is the "star" topology [9]. The star topology is illustrated in Figure 1.3. The star topology is called such because all network traffic converges onto a single point. If any data is intended to travel from one node to another, that data must still travel through the central point of the star topology. Under the star topology, the central point serves as a coordinator for all other nodes in the wireless IoT network.

Figure 1.3...