1、IEEE Technology Report on Wake-Up Radio: An Application, Market, and Technology Impact Analysis of Low-Power/Low-Latency 802.1 1 Wireless LAN InterfacesTrademarks and Copyright Analog Devices is a registered trademark of Analog Devices, Inc. () ANT+ is a registered trademark of Garmin Switzerland GM
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10、y, NJ, 08854 2017 IEEE ISBN 978-1-5044-4234-3Table of Contents Trademarks 1 Introduction 1.1 Wake-Up Radio and the Internet of Things (IoT)1.2 Battery Life: The Critical Factor 1.3 Wake-Up Radio Concepts 1.3.1 Efficiency is in the Details1.4 Economic Impact of Battery Life 2 Context: Market Opportun
11、ities in the Remote IoT 2.1 IoT Market Forecasts2.1.1 Regional Variation2.1.2 Sensors and Remote Devices3 Wake-Up Radio: IoT Use Cases and Challenges3.1 Coming Soon to a Thing Near You 3.1.1 Happening Now: Microgrids 3.1.2 Transportation the market opportunity and technical challenges of selected us
12、e cases; the magnitude of the aggregated IoT market; how IEEE 802.11 Wi-Fi communications fits into the scheme of IoT things; and details TGbas approach to Low-Power Wake-Up Radio. 1.2 Battery Life: The Critical Factor Todays smartphones usually have at least three main radios: the medium-range wire
13、less local area network (WLAN or Wi-Fi), the longer range cellular radio, and the short-range Bluetooth personal area network. These may be joined by near field communications and Global Positioning System radios, and accommodate an increasing number of legacy protocols for each radio (Figure 1-2).
14、FIGURE 1-2. ON YOUR PHONE: AN INCREASINGLY COMPLEX WEB OF STANDARDS AND PROTOCOLS. The growing number of communications protocols implemented on smart devices. Source: Eric Starkloff, National Instruments. Used by permission. 143 The Wi-Fi, cellular, and Bluetooth protocols are also the three main c
15、andidates for connecting the Internet of Thingsand each has strengths and weaknesses. Wi-Fi (IEEE Std 802.11) fits seamlessly into the IEEE 802 ecosystem that includes Ethernet (IEEE Std 802.3)and between the two, carry the lions share of the worlds digital data and offer straightforward integration
16、 with the Internet and web-based services. See Appendix 2 for a table of the principle IEEE 802 working groups and a quick review of some IEEE 802.11 Wi-Fi amendments that have expanded the standard over the past two decades. Wi-Fi and Ethernet are designed to accommodate high-bandwidth data, such a
17、s streaming videos and file sharing systems. Wi-Fi can operate through user-owned equipment and transmits on unlicensed radio frequencies. This makes it relatively easy and economical to set up wireless LANs. By the same token, setting up a Wi-Fi network can require some configuration. Until now, Wi
18、Fi has had a reputation for high power consumption, which has limited the service lives of remote devices in the field. Low-Power Wake-Up Radio is aimed at provided a well-integrated power- conservation tool to remedy this shortcoming. Cellular radiosincluding data-oriented 4G and 5G servicesoffer
19、long reach over licensed frequencies via commercially owned and maintained infrastructure. Cell service is highly reliable with low latency over wide areas, though users must generally use cell-system providers equipment and pay access fees. Cellular communication remains focused on the base station
20、 the cell tower. While there are proposals for supporting direct device-to-device communication on the edge, those standards are still being drafted and it is unclear whether and how this will be implemented. Bluetooth offers a short-distance, low-power connection. It was originally designed to con
21、nect cell phones with wireless peripherals like headsets, and has been oriented towards lower-bandwidth applications. Smartphone users know that leaving the phones screen and radios active can drain a battery in just a few hours. For example, an iPhone 7 with a 1,960 milliamp-hour battery may delive
22、r about 15 hours of 3G phone talk time, 12 hours of Internet browsing over an LTE cell connection, or 15 hours of Internet access over Wi-Fi. Short-range Bluetooth radios transmit at 1 to 2.5 milliwatts. Cellular and Wi-Fi radios generally broadcast at anywhere from 100 to a maximum of 1,000 milliwa
23、tts. But they clearly do not transmit constantly at full power; if they did, that 1,960 milliamp-hour battery would last no more than five or six hours, even if the phone used no power for anything else. Various amendments to the IEEE 802.11 standard (e.g., 802.11a, 802.11b, 802.11g, etc.) call for
24、transmitting at lower power where appropriate (or where required by a complex web of regulatory and engineering requirements) at around 20 to 100 mW EIRP (equivalent isotropically radiated power, a figure that takes the antennas signal boost into account). These are estimated figures as actual power
25、 usage can vary in response to the details of the protocol and environmental conditions. 4 There are always trade-offs when trying to conserve power. Lower-power transmissions, for example, may also reduce the signal-to-noise ratiolowering data rates and necessitating longer transmissions. Longer tr
26、ansmission times require more power, negating some of the apparent economy of switching to lower power. Duty-cycling is a frequent solution for power conservation. The radio turns off and goes to sleep when not in use, waking up for just a few milliseconds at intervals from a tenth of a second to an
27、 hour, to see if anybody is trying to get through. Early in the LP-WUR process, TGba Chair Minyoung Park calculated that running a Wi-Fi radio at a 2% duty cycle in “legacy power saving mode”having it wake up for 2 milliseconds out of every 100 should reduce average idling power drain from about 100
28、 mW to about 1.6 mW 4. This would stretch the idling time of a 130 mAh battery life from a few hours to about three days. The exact power saving depends on a variety of factors; this example illustrates the general kinds of improvement LP-WUR should produce, rather than predicting specific performan
29、ce. FIGURE 1-3. OVERVIEW OF LOW-POWER WAKE-UP RADIO FOR 802.11. The proposed IEEE 802.11ba Low-Lower Wake-Up Radio design adds a second radio, drawing less than 100 microwatts when it is active, to the more powerful main radio to remain asleep until needed to transfer data. Source: LP-WUR (Low-Power
30、 Wake-Up Receiver): Enabling Low-Power and Low-Latency Capability to 802.11(IEEE 802.11-16/0027r0) 4. The IEEE 802.11ba Wake-Up Radio plan adds a second, low-power radio receiver to the device (Figure 1-3). The low-power radio listens silently, waiting for the network to call its name. Only then doe
31、s the device turn on its main Wi-Fi radio and begin exchanging data. This is not a new technique by any means, observers point out, as it has been used on an ad hoc basis many times in the past 58; 5 TGba is new, however, in adding Low-Power Wake-Up Radio to the 802.11 standard. In Parks analysis, a
32、n always-on Low-Power Wake-Up Radio (LP-WUR) would consume about 0.105 mW. Applying a 2% duty cycle to a LP-WUR would drop radio power consumption to about 0.007 mW (Figure 1-4). FIGURE 1-4. REDUCING DEMAND FOR BATTERY POWER. Legacy power-saving mode (2% duty cycling, with Wi-Fi main radio waking up
33、 for 2 milliseconds every 100 milliseconds) cuts power usage to about 1.6 mW. Low-Power Wake-Up Radio in constant operation would use only about 0.105 mW, and LP-WUR on a 2% duty cycle would cut power demand to just 0.007 mW. U-APSD: unscheduled automatic power save delivery. TWT: Target Wake Time (
34、Duty-Cycle). PS Poll: An 802.11 control frame Source: LP-WUR (Low-Power Wake-Up Receiver): Enabling Low-Power and Low-Latency Capability for 802.11 (IEEE 802.11-16/0027r0) 4. The impact on battery life is dramatic. An always-on 100 mW Wi-Fi main radio might drain a 3-volt, 130 milliamp hour (mAh) ba
35、ttery in under four hours. Duty-cycling the same radio might increase battery life to more than 3 days. Operating a Low-Power Wake-Up Radio on the same duty cycle, though, could stretch battery life to 694 days 4 (Figure 1-5). Reduce the duty cycle still further and add engineering expertise to stre
36、amline signal handling, and engineers can look forward to thousand-fold increases in battery life and years of operation on a single charge.6 FIGURE 1-5. POWER CONSUMPTION AND BATTERY LIFE. A theoretical example of possible improvements in battery life, comparing power consumption and service time u
37、sing Low-Power Wake-Up Radio with savings possible using legacy duty-cycling techniques with the remote devices main Wi-Fi radio. Source: LP-WUR (Low-Power Wake-Up Receiver): Enabling Low-Power and Low-Latency Capability for 802.11 (IEEE 802.11-16/0027r0) 4. Engineers working on LP-WUR point out an
38、interesting trade-off in coordinating wake-up periods for duty-cycling applications: highly accurate clocks consume more power. Lower-power clocks, like those chosen to extend battery life in a remote device, tend to drift more over time. Access points will have to make allowances for this drift and
39、 open longer check-in windows in order to catch the Wake-Up Radio (WUR) when it is awake and resynchronize its clock. The accommodation could theoretically work the other way, with the WUR starting its own duty cycle early to be sure to catch a very punctual access point. This would increase WUR pow
40、er consumption, and negate some of the advantages of LP-WUR. 1.3 Wake-Up Radio Concepts The Low-Power Wake-Up Radio standard is still being drafted, and it is still too early for detailed discussion of its provisions. Summaries of a few of the Task Groups technical analyses can, however, supplement
41、the general information contained in the IEEEs Project Authorization Request (PAR). The PAR is the means by which standards projects are started within the IEEE Standard Association. PARs define the scope and purpose of the project. Summaries of the PAR and Specification Framework follow. 1.3.1 Effi
42、ciency is in the Details On-Off Keying. The Wake-Up Radio Task Group decided early on to build the system around on-off keying. Simple as a light switch: when there is a signal from the access points low-power radio, the station will turn on. The situation rapidly gets more nuanced, however. How does the remote device
