RF coexistence testing? Is it difficult?[Copy link]
The current development of the international epidemic is just like that in Wuhan a few months ago, facing severe challenges brought about by a surge in infected patients, a shortage of medical resources on the front line, and even the unfortunate infection of medical staff.
European countries such as France and Spain have also followed China's prevention and control measures, using IoT devices such as drones and monitors to build a remote prevention and control system. Medical staff can also monitor patients' vital signs such as body temperature and blood pressure in real time, directly reducing the risk of infection for frontline disease control workers.
The completion of the two mountains, Vulcan and Thunder, has shown the world China's speed and also allowed us to witness the implementation of the concept of "Internet of Things Hospital". However, before the Internet of Things medical equipment is put into use, there is still a problem that needs to be solved urgently, that is, the interference and coexistence between Internet of Things devices .
What is RF Coexistence?
Coexistence refers to the ability of wireless devices to maintain normal operation under the interference of other devices (using different working protocols or standards). Before understanding what RF coexistence is, let's look at the following scenarios.
Q1 Ward
At the hospital's remote monitoring station, the nurse Xiao Liu on duty found that the patient in bed 303 suddenly had no data. She hurriedly notified her colleague in charge of nursing, but her colleague said that the patient's vital signs and the readings of the monitor were normal, and the readings of the instrument at the monitoring station had also returned to normal. This made Xiao Liu very confused. Which of the following reasons do you think caused the failure to read the data?
After finishing a day's work, Xiao Liu returned to the dormitory from the ward. As usual, she was going to video chat with her parents to let them know she was safe, but the call quality, which was usually very good, was now stuck like a PPT. Based on the above picture, which of the following reasons do you think affected the video call?
With stable and sufficient logistical support, medical staff can overcome difficulties and achieve frequent successes on the front line. Today’s logistics distribution centers have also begun to use IoT devices to sort express parcels, which improves efficiency while reducing the possibility of cross-infection among staff.
The sorting robot in the warehouse in the picture (there is a wireless position control sensor in the robotic arm) cannot work properly and the position control always makes mistakes. Which of the following reasons is most likely to be the cause?
Coexistence is the ability of a wireless device to continue functioning despite interference from other devices that use different operating protocols or standards. When two wireless devices are close to each other and operate on the same or close frequencies, they will affect each other. The most densely used spectrum is the unlicensed "ISM" bands at 2.4 and 5 GHz. Bluetooth devices, microwave ovens, cordless phones, and wireless security cameras are examples of wireless devices that can cause interference.
Licensed spectrum, such as cell phone bands, is more tightly controlled, but its transmissions can affect users in nearby bands. There are four key factors that create coexistence issues. They are:
1) Increased use of wireless technology to connect key devices
2) Intensive use of unlicensed or shared spectrum
3) Deployment of more sensitive equipment, including medical devices (IV pumps, pacemakers) and emergency detection equipment (such as those in connected vehicles)
4) Large-scale deployment of sensors for smart cities, industrial applications and other applications These factors directly affect the communication reliability of IoT devices.
Wireless coexistence is critical for the Internet of Things (IoT) to achieve stable and reliable communications. Without coexistence, IoT devices will not be able to work properly in a crowded wireless environment, which may result in data loss or voice quality degradation, or a shorter operating range or battery life, or even accidents or dangers.
2. What is wireless coexistence testing?
Ensuring IoT devices support coexistence is a challenging problem that can be solved by performing coexistence testing . This testing helps determine your device’s tolerance to other radio signals and characterizes the device’s behavior in the presence of other radio protocols. Coexistence testing is the only way to accurately assess whether a device can maintain functional wireless performance (FWP) in the presence of expected and unexpected (interfering) signals.
Coexistence testing is not the same thing as electromagnetic interference (EMI) and electromagnetic compatibility (EMC) testing, nor is it the same thing as protocol conformance testing. There is no fixed pass/fail criteria. Coexistence testing evaluates the effects of expected signals and unexpected/interfering signals on the device.
Modeling the RF environment,To characterize the RF environment in which your device is expected to operate, you must perform field measurements in the frequency band of interest.You need to develop a model that includes the signals present in the target environment, the strength of those signals, and the frequency spectrum they use.
Traditional swept spectrum analyzers are often not able to perform this task efficiently. The digital transmission time of a device is so short that a transmission may complete before the analyzer has swept to the frequency in use, thus going undetected. For accurate field measurements, a real-time spectrum analyzer (RTSA) is recommended.
A real-time spectrum analyzer can help you continuously sample the spectrum using a high-speed analog-to-digital converter (ADC). Keysight's N99xx series portable spectrum analyzers are a powerful tool for field testing, quickly detecting the frequency, type, and strength of a signal.
Simulate the RF environment. After obtaining the interference signal model in the environment, you can use the RF signal generator to simulate and generate various RF signals in the environment.
For example, if there are 5G signals, LTE signals, WiFi signals, and Bluetooth signals in the environment, you need to use a signal generator to simulate and generate these signals. Sometimes there may be multiple signals of the same type. Using Keysight's vector signal generator and RF signal generator, you can simulate various RF signals.
In addition, sometimes we also need to establish the working status of the device under test, which requires some RF base station simulators, such as Keysight's LTE network simulator or 5G network simulator.
Defining Functional Wireless Performance , Functional Wireless Performance (FWP) is a measure of whether a device under test is qualified in a specific environment. This metric defines the important characteristics that the device under test must have in its wireless channel. Your device must be able to perform these functions in order to be considered functional and able to coexist with other devices. For example, these functions may include:
Ability to connect to the facility's wireless network within a specified time
Status reports are sent successfully and quickly
The bit error rate of the data cannot be lower than a certain range, etc.
These functional requirements depend on the type and application of the equipment and its defined “normal” operating characteristics.
There are four ways to configure the test equipment to perform coexistence testing. Each method requires:
Your device under test and the associated control software
Device connected or paired with the device under test
Other network simulation equipment and spectrum analyzers, etc., these instruments have test functions
Signal source and other interference simulation equipment
Other considerations include: Is the external antenna connection of the device under test (DUT) accessible? Will the device operate in a multiple-input multiple-output (MIMO) network? Does the device have a directional antenna?
Test method 1
As shown in the figure below, this test is performed by simulating the desired and unwanted signals and connecting them to the access port close to or located at the antenna location. The advantages of this test are:
Tests exclude antenna effects
MIMO and beamforming can be considered, but this can be challenging
This is the easiest test to replicate but the least realistic
There are two other methods. If you need to know more, please scan the QR code below to download our white paper . I will not introduce them one by one here.
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