IoT and Low-Power Wireless

Circuits, Architectures, and Techniques

Christopher Siu

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351251648
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

The book offers unique insight into the modern world of wireless communication that included 5G generation, implementation in Internet of Things (IoT), and emerging biomedical applications. To meet different design requirements, gaining perspective on systems is important. Written by international experts in industry and academia, the intended audience is practicing engineers with some electronics background. It presents the latest research and practices in wireless communication, as industry prepares for the next evolution towards a trillion interconnected devices. The text further explains how modern RF wireless systems may handle such a large number of wireless devices.

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• Covers modern wireless technologies (5G, IoT), and emerging biomedical applications

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• Discusses novel RF systems, CMOS low power circuit implementation, antennae arrays, circuits for medical imaging, and many other emerging technologies in wireless co-space.

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• Written by a mixture of top industrial experts and key academic professors.

1
The Internet of Things—Physical and Link Layers Overview

Christopher Siu
British Columbia Institute of Technology (BCIT)

Kris Iniewski
Redlen Technologies Inc.

CONTENTS

1.1 Introduction

1.2 Radio and MAC Technologies for IoT

1.2.1 Physical layer with existing radio frequency (RF) standards

1.2.2 Physical layer with emerging radio frequency (RF) standards

1.2.3 Link layer considerations for WUR

1.2.4 Link layer example—6LoWPAN

1.2.5 Application layer protocols

1.2.6 Future directions

1.3 Conclusions

Bibliography

1.1 Introduction

The internet of things (IoT) has sometimes been referred to as the digitization of the physical world. It is a confluence of different technologies at low-enough costs that makes this possible. While different definitions of IoT exist, we will use the following description for this book:

A device embedded with a sensor and/or actuator, connected to the internet, that shares its information with other devices and hosts, with the potential to act on this information based upon some rules and intelligence.

In the simplified block diagram given later, sensors in an end node collect data at specified intervals. The data are framed into packets by the microcontroller, which also contains parts of the protocol stack to perform media access control (MAC). The packets are modulated and transmitted over the wireless link, which is received by a gateway connected to the internet. The gateway may have a rules engine to reduce the amount of data before it is stored. The sensor data may then be transferred to an end user for further analysis and report generation (Figure 1.1).

FIGURE 1.1
Simplified IoT system block diagram.

Note that while the gateway may be mains powered, the sensor nodes will be powered by battery and/or energy scavenging. Since it is not feasible to change the battery regularly on a large number of sensor nodes, there is great motivation to reduce the power consumption of end nodes as much as possible.

1.2 Radio and MAC Technologies for IoT

In conceptualizing computer networks, many of us have seen the 7-layer open systems interconnection (OSI) model. The 7 layers, from the lowest to the highest, are the physical, link, network, transport, session, presentation, and application layers. Over the past two decades, with the exponential growth of the internet running transmission control protocol/internet protocol (TCP/IP), the OSI model has been eclipsed by a 5-layer model, sometimes referred to as the TCP model or the IP stack [1]. Shown later is the TCP model with the corresponding standards and protocols for WiFi (Figure 1.2).

FIGURE 1.2
The 5-layer model in relation to WiFi.

The physical layer defines the hardware aspects of the communication link, such as the modulation method, voltage levels, and physical medium (e.g., copper wire, over-the-air). The link layer provides several services, typically implemented with a combination of hardware and software. If the physical medium is shared by multiple users, such as wireless communication on a certain frequency band, then orderly access to the medium must be controlled so that users don’t interfere with each. The mechanism for this is aptly named MAC, and it is a key function of the link layer. Other services provided by the link layer include framing of higher layer data and delivering the data reliably.

The focus of this book is on the physical and link layer technologies that are in development for IoT. As such, this chapter provides an overview of these technologies, but the higher layers will also be mentioned where it is appropriate.

1.2.1 Physical layer with existing radio frequency (RF) standards

One of the main energy consumers in mobile systems is the wireless transceiver. Hence, research into low-power circuit techniques is ongoing, but there are limits on using this approach alone. Additional innovations in MAC and network architecture have also been necessary to drastically reduce the transceiver power consumption. At the present time, there is no de facto RF standard for IoT; existing standards are repositioning themselves, and new standards are being introduced to support this new market. In the following, we will briefly survey some of these RF technologies and standards.

Bluetooth (IEEE 802.15.1) was conceived to be a wire replacement for computer peripherals, for example, the connection between a PC and a mouse. As such, it falls within the classification of a wireless personal area network (WPAN), for short-range point-to-point connections. Today, a large number of mobile devices like smartphones include Bluetooth capability, and the standard is constantly evolving to create Bluetooth low energy with mesh networking to support new market needs.

IEEE 802.15.4 was created as a lower power, lower data rate alternative to Bluetooth. In 802.15.4–2006, a 2.4 GHz physical layer using spread spectrum is specified at 250 kbps. Over the years, it has been used as the platform for Zigbee, Thread, and other proprietary solutions. It is also part of IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN), which supports IPv6 addressing for network nodes. Although there is no native support for mesh networking in 802.15.4, it has been implemented in the higher layers for various applications. Similar to Bluetooth, however, it is a short-range standard.

WiFi (IEEE 802.11) has become one of the most ubiquitous wireless standards on the planet. The standard is designed to support an ethernet-based wireless local area network (WLAN), and so the range and power consumption are necessarily higher than those of Bluetooth and 802.15.4. Although WiFi radio transceivers are not a popular choice for low-power wireless systems, a new task group called 802.11ba has been formed to address this. In particular, this task group is creating a new standard for low-power wake-up radio (LP-WUR) in WiFi, intended to make WiFi an attractive technology for IoT.

One of the key ideas for LP-WUR is to use an ultra-low power auxiliary receiver to detect a wake-up packet, while keeping the main WiFi radio transceiver in sleep mode most of the time. In fact, the auxiliary receiver itself may be duty-cycled between sleep and wake to further reduce power consumption (Figure 1.3).

FIGURE 1.3
Wake-up radio concept.

To make an ultra-low power receiver, some obvious tradeoffs such as performance, data rate, and modulation scheme need to be considered. For the IEEE 802.11ba initiative, on–off keying is used to allow for a simple demodulation. Furthermore, low-power radio circuits can be used, including techniques such as

• superregenerative receiver (Figure 1.4)

• envelope detection

• injection locking

• subsampling architectures

FIGURE 1.4
Superregenerative receiver: (a) block diagram and (b) internal waveforms.

Superregeneration is an idea developed by Edwin Armstrong in the early 1920s, and in its modern implementation, it removes the phase locked loop from a typical radio receiver. In conjunction with on–off keying, the oscillator start-up time depends on whether a signal is received by the low noise amplifier (LNA) or not. By detecting this time difference, the receiver decides whether a logic 0 or 1 was transmitted.

1.2.2 Physical layer with emerging radio frequency (RF) standards

The existing RF standards competing for market share in IoT have tended to be WPAN and WLAN standards, since the strict need for low power consumption favors these short-range applications. The architecture implied here is a large number of sensor nodes connected to gateway(s) either directly or via a mesh network. The short range of these standards also creates potential problems if one node is not in range of any other nodes and/or gateways.

Many of us are accustomed to a wide area cellular coverage; we never think about being near a gateway or base station before communicating on our mobile phones. A wireless wide area network (WWAN) is thus very attractive in terms of network access, but devices connected to a WWAN also have high power consumption. Just as the IEEE 802.x standards are evolving to meet IoT needs, so are the cellular standards. We will survey the following WWAN for IoT:

• Narrowband IoT (NB-IoT)

• Sigfox

• LoRaWAN

The 3rd Generation Partnership Project has been defining cellular standards since the third generation, and this now includes the 4th generation long term evolution (LTE) standard that is in use. LTE has undergone a number of revisions, and one of the latest releases (Rel 13) defines NB-IoT, which is a low-power, low-data rate service at 250 kbps.

Sigfox is a proprietary standard operated by a company of the same name. Sigfox uses a scheme called ultra narrow band modulation, which requires only 100 Hz of bandwidth per message, with a correspondingly low rate of 100–600 bps. At the present time, the coverage and deployment are much more extensive in Western Europe than in the United States.

LoRaWAN and LoRa are open standards for low-power WWAN; LoRaWAN specifies the MAC, and LoRa specifies the physical layer. LoRa uses spread spectrum modulation, and hence has built-in resistance to interference and multipath fading. LoRa also has a low-data rate in the tens of kbps, allowing the present integrated circuit implementations (SEMTECH SX127n series) to receive sensitivity in the – 140 to – 150 dBm range.

1.2.3 Link layer considerations for WUR

If radio duty cycling is fundamental to low-power wireless, then the MAC layer must be designed to support this need. For example, the 802.11ba LP-WUR uses a new wake-up packet to inform the wake-up receiver that the main radio needs to be taken out of sleep and prepare for data exchange (Figure 1.5).

FIG...

Table of contents

• Cover Page
• Halftitle
• Title Page
• Copyright
• Contents
• List of Figures
• List of Tables
• Preface
• Series Editor
• Editor
• List of Contributors
• 1 The Internet of Things—Physical and Link Layers Overview
• 2 Low-Power Wearable and Wireless Sensors for Advanced Healthcare Monitoring
• 3 Biomedical algorithms for wearable monitoring
• 4 Approaches and Techniques for Maintenance and Operation of Multisink Wireless Sensor Networks
• 5 Energy-Efficient Communication Solutions Based on Wake-Up Receivers
• 6 All-Digital Noise-Shaping Time-to-Digital Converters for Mixed-Mode Signal Processing
• 7 Power-Efficient CMOS Power Amplifiers for Wireless Applications
• 8 Injection-Locking Techniques in Low-Power Wireless Systems
• 9 Low-Power RF Digital PLLs with Direct Carrier Modulation
• 10 Frequency Synthesis Technique for 60 GHz Multi-Gbps Wireless
• 11 60 GHz Multiuser Gigabit/s Wireless Systems Based on IEEE 802.11ad/WiGig
• 12 Adaptive and Efficient Integrated Power Management Structures for Inductive Power Delivery
• Index