As the Internet of Things is ignited, how will wireless testing be disrupted?

　　1. Introduction to the Internet of Things

　　The Internet of Things (IOT) technology is a complex application technology. It not only covers microwave technology and electromagnetic theory, but also involves communication principles and semiconductor integrated circuits. It is an emerging application technology that integrates multiple disciplines. At present, IOT technology has become a new economic growth point. It is widely used in many fields such as industrial automation, commercial automation, and transportation control management. Therefore, the research and development of IOT technology has huge economic benefits and social significance. The research on IOT testing technology is also an indispensable part of IOT applications.

　　2. Principles and applications of the Internet of Things

　　At present, depending on different application scenarios, the wireless technologies covered by the Internet of Things include radio frequency identification RFID, near-field communication NFC, ZigBee, WLAN, and Internet of Vehicles 802.11p.

　　2.1 RFID

　　RFID radio frequency identification is a non-contact automatic identification technology that automatically identifies target objects and obtains relevant data through radio frequency signals. The identification work does not require human intervention and can work in various harsh environments.

　　RFID is divided into low frequency (LF), high frequency (HF), ultra high frequency (UHF), and microwave (MW) according to the different application frequencies. The corresponding representative frequencies are: low frequency below 135KHz, high frequency 13.56MHz, ultra high frequency 860M~960MHz, microwave 2.4G, 5.8G; RFID is divided into passive RFID, active RFID, and semi-active RFID according to the energy supply method. Passive RFID has a short reading and writing distance and a low price; active RFID can provide a longer reading and writing distance, but it needs battery power, which is more expensive and is suitable for long-distance reading and writing applications.

　　The basic working principle of RFID technology is not complicated: after the electronic tag enters the magnetic field, it receives the radio frequency signal sent by the reader and uses the energy obtained from the induced current to send out the product information stored in the chip; after the reader reads and decodes the information, it sends it to the computer control end for relevant data processing.

　　Figure 1 RFID system working principle diagram

　　2.2 NFC

　　NFC (Near Field Communication) is an integration of RFID and interconnection technology. The main promotion companies are NOKIA, SONY and NXP. Near field communication is a short-range high-frequency radio technology that operates at a frequency of 13.56MHz within a distance of 20 cm. Its transmission speed is 106 Kb/s, 212 Kb/s or 424 Kb/s.

　　NFC integrates contactless readers, contactless cards and peer-to-peer functions, creating countless new opportunities for consumers' lifestyles. It is an open interface platform that can quickly and actively set up wireless networks, and is also a virtual connector that serves existing cellular networks, Bluetooth and wireless 802.1l devices.

　　NFC has three operating modes:

　　1) Card emulation mode;

　　2) Read-write mode;

　　3) Point-to-point communication mode.

　　NFC has two communication modes: passive communication and active communication. It is worth noting that the communication mode has no necessary relationship with the working mode.

　　1) Passive communication

　　Passive communication means that one party of NFC communication generates a radio frequency field, and the other party obtains energy from the radio frequency field and communicates with the party generating the radio frequency field through load modulation. Passive communication is commonly used in card emulation mode and read-write mode.

　　2) Active communication

　　Active communication means that the RF field is generated alternately by both parties in NFC communication, that is, both parties generate their own RF field when communication is needed. Active communication is mainly used in point-to-point communication mode.

　　2.3 ZigBee

　　ZigBee is a low-power LAN protocol based on the IEEE802.15.4 standard. According to international standards, ZigBee technology is a short-range, low-power wireless communication technology. The name comes from the bee's figure-eight dance. Since bees (bees) rely on flying and "buzzing" (zig) to shake their wings to communicate with their companions about the location of pollen, bees rely on this method to form a communication network in the group. Its characteristics are short distance, low complexity, self-organization, low power consumption and low data rate. It is mainly suitable for use in the fields of automatic control and remote control, and can be embedded in various devices. In short, ZigBee is a cheap, low-power short-range wireless networking communication technology.

　　According to the IEEE 802.15.4 standard, the frequency bands in which ZigBee operates are free and open, namely 2.4GHz (global), 915MHz (USA) and 868MHz (Europe). Different technologies are used according to the frequency bands, as shown in the following table:

　　Table 1 IEEE 802.15.4 bandwidth, modulation type and pulse shaping filter

　　Phase modulation technology is used in 3 different frequency bands. 2.4GHz uses higher-order OQPSK modulation technology to achieve a rate of 250kbit/s and reduce working time to reduce power consumption. Compared with the 2.4GHz frequency band, 868MHz/915MHz is a low frequency band, using BPSK modulation technology, with less wireless propagation loss and longer transmission distance.

——This article is selected from the Change The World column of the November "Test and Measurement Special Issue" of Electronics Enthusiasts Network. Please indicate the source for reprinting!
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　　3. IoT testing requirements

　　According to the wireless technology used in the Internet of Things, its current testing needs are mainly reflected in the following aspects:

　　RFID testing

　　NFC test

　　Zigbee testing

　　Since the IoT product is a radio transceiver device, some special tests are needed to carry out the test work in the actual test process. For radio transceiver equipment, the commonly used test equipment mainly includes measurement receivers, spectrum analyzers, signal sources, comprehensive testers and oscilloscopes. In addition, the test antenna plays an important role in the test process of radio transmitting equipment. Without the assistance of the antenna, normal testing work cannot be carried out. It can be seen that the test antenna is also a very important test auxiliary equipment. In summary, the test requirements of the IoT mainly include the following aspects. [page]

　　3.1 RF test requirements

　　In April 2007, my country issued the technical specification for the type approval test of the radio frequency indicators of RFID reader equipment. There is no special standard to describe the UHF RFID radio frequency test in the world. It is generally included in the protocol consistency standard. At present, the reference standard for RFID radio frequency testing in the UHF band is my country's "800/900MHz Band Radio Frequency Identification (RFID) Technology Application Regulations (Trial)". Among them, the specified test items include carrier frequency tolerance, occupied bandwidth, transmission power, adjacent channel power leakage ratio, spurious emission and maximum dwell time. In addition, according to the test specifications of EPC Global standard Version 1.0.2, its test items also include: reader data encoding, radio frequency envelope, radio frequency switching time, preamble and frame synchronization information.

　　Since the Analog part of NFC continues the ISO 14443 and ISO 15693 radio frequency standards, the NFC radio frequency test requirements can refer to ISO/IEC 10373-6 and ISO/IEC 10373-7. NFC radio frequency testing requires the assistance of a dedicated test antenna, and parameters such as the test point location and test power are specified in detail in the test standards.

　　The ZigBee physical layer is defined using a standard low-power LAN protocol. Generally, conventional RF tests are sufficient for its transmitter and receiver.

　　3.2 Protocol Testing Requirements

　　For RFID technology, the reader and the tag, as the two parties of wireless communication, must comply with the mutually agreed communication protocol, otherwise the communication will not be possible. The RFID air interface actually refers to the wireless transmission specification between the tag and the reader. It covers a wide range, mainly including wireless resource management, wireless link control, media access control and physical layer. At present, the UHF frequency band RFID air interface protocol standards widely used in the world mainly adopt the ISO/IEC 18000 series, and its test standards correspond to the ISO/IEC 18047 series.

　　3.3 Performance Testing Requirements

　　With the widespread application of RFID systems, the performance test of RFID systems has become an important issue of great concern to RFID application units and system integrators. The performance of RFID application systems directly affects the deployment and cost investment of RFID equipment in application scenarios, as well as the satisfaction of system application customers. According to the system composition of RFID, the evaluation of RFID systems can be divided into three aspects: overall system performance test, tag performance test and reader performance test. The main test standards correspond to (ISO-IEC18046-1/2/3)

　　4. IoT Testing Solutions

　　The R&Sâ IoT test system can perform comprehensive tests on RFID readers or tags, NFC devices, Zigbee transmitters or receivers under test according to the standards.

　　For RFID readers or tags, the R&Sâ IoT test system is suitable for the 860-960MHz UHF frequency band to test their RF, protocol, and performance;

　　For NFC devices, the R&Sâ IoT test system is suitable for the 13.56MHz frequency band to test their RF and modulation characteristics.

　　For Zigbee transmitters or receivers, the R&Sâ IoT test system is suitable for the 2.4 GHz frequency band to test its RF and modulation characteristics;

　　4.1 Composition of IoT Test System

　　The core equipment of the R&Sâ IoT test system is the protocol processing unit, which is combined with the digital baseband interface EX-IQ-BOX, signal source SMBV100A, spectrum analyzer FSV, vector network analyzer ZNB, power supply NGMO, oscilloscope RTO, RF switching unit Switching Unit, test software, antenna and other accessories to complete the test of IoT products. And it can be used with a turntable to perform RF and performance tests in a darkroom. The figure below is a block diagram of the IoT test system.

　　Figure 2 Structural diagram of IoT test system

　　4.2 IoT Test Project

　　1) RF test

　　The RFID radio frequency test includes 6 test items, all of which are reader radio frequency index tests. The reference standard for the radio frequency test part is the "800/900MHz frequency band radio frequency identification (RFID) technology application regulations (trial)". The specific test items supported include: carrier frequency tolerance; occupied bandwidth; transmit power; adjacent channel power leakage ratio; spurious emission; dwell time; spectrum template.

　　There are many NFC radio frequency test items, and the reference standards are "ISO/IEC 10373-6 Identification cards - Test methods - Part 6: Proximity cards", "ISO/IEC 10373-7 Identification cards - Test methods - Part 7: Vicinity cards" and "NFC Forum-Test Cases for Analog Specification". There are many specific test items supported, which will not be described in detail here.

　　ZigBee RF test includes 11 test items, all of which are conventional test items for transceivers, and the reference standard is "IEEE Standard 802.15.4 for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements". Specific test items supported include: transmitter channel power; transmitter time domain power; transmitter occupied bandwidth; transmitter adjacent channel power leakage ratio; transmitter rise time and fall time; transmitter modulation characteristics; transmitter emission spurious; transmitter signal peak-to-average ratio; receiver sensitivity; receiver blocking test; receiver adjacent channel selectivity test.

　　2) Protocol testing

　　The RFID protocol test includes 14 test items, including 10 tests for tags and 4 tests for readers. The test is based on the EPCglobal C1G2 RFID air interface protocol in the UHF band, which is the "EPCglobal Class-1 Generation-2 UHF RFID Conformance Requirements". The ISO organization accepts it as the ISO/IEC18000-6C standard and promulgates ISO/IEC 18047-6. The test items included are: tag frequency range; tag demodulation capability; tag link frequency; tag link frequency tolerance; tag T1 time; tag link duty cycle; tag reflection signal preamble; tag anti-collision capability; tag storage content; tag state transfer capability; reader preamble time; reader envelope; reader T2 time; reader data encoding.

　　3) Performance Testing

　　RFID performance test includes 15 test items, including 11 tests for tags and 4 tests for readers. The test is mainly based on 18046-3: "Information Technology Radio Frequency Identification Equipment Performance Test Method Part 3: Tag Performance Test Method", "Information Technology Automatic Identification and Data Collection Technology Radio Frequency Identification Equipment Performance Test Method". Tag maximum recognition distance; tag maximum reading distance; tag maximum writing distance; recognition electromagnetic field threshold; reading electromagnetic field threshold; writing electromagnetic field threshold; sensitivity degradation; maximum working electromagnetic field; survival electromagnetic field; interference suppression; tag antenna pattern; reader sensitivity; reader BER; reader antenna pattern test; reader interference suppression.

　　4.3 IoT Automatic Testing Platform

　　The R&Sâ IoT test platform can control the instrument to automatically complete RF, protocol and performance tests, monitor the test process, display the test results to the user and automatically generate a test report. The test interface is shown in the figure below. [page]

　　Figure 3 IoT automatic test platform interface

　　The functions provided by the R&Sâ IoT test platform are shown in the figure below.

　　Figure 4 IoT automatic test platform functions

　　4.4 IoT Test Examples

　　Based on the R&Sâ IoT test system, RFID, NFC and ZigBee tests can be easily completed. The following figure shows the actual picture of the IoT test system and the RFID test results.

　　Figure 5 Actual photos of the IoT test system and RFID test results

　　5. Summary

　　As a special test equipment for IoT products, R&S IoT test system has the advantages of simple operation, strong pertinence and accurate testing, which can greatly reduce the time of development, certification and production of IoT products. At the same time, with the strong technical strength and excellent instrument performance of R&S, it can ensure the accuracy of test performance and further improve product quality. Therefore, IoT test system can be widely used in various links and fields such as development, production and certification of IoT products.