This blog post is the second part of the Wi-Fi front-end design puzzle series (two parts). The first part discusses related thermal issues.
There is a signal interference in Wi-Fi in the home. There are many ways consumers can solve this problem, such as the location of a mobile router, reconnecting to a Wi-Fi network, restarting the modem, and contacting the service provider when in trouble. However, as an RF Engineers, how can you design Wi-Fi access points to solve the most serious interference problems at the source?
This blog post will focus on the following factors that affect Wi-Fi interference: • The need to support multiple wireless standards at the same time • The types of interference are different • The important role of the edge • The importance of high-performance edge-edge coexistence filters
One access point, multiple wireless technology standards
When developing Wi-Fi access points, designers must consider a variety of wireless technology standards: • Medium-range and short-range standards, such as Bluetooth, Zigbee, and Z-Wave • High-power close- and distant standards, such as Wi- Fi, 3G/4G LTE and 5G Many of these standards may interfere with one another, causing problems with the user's connection.
In addition, unlicensed spectrum can also cause interference. As wireless communication expands capacity in order to divert data, the important role of licensed networks and unlicensed networks is increasing. In addition, the new Internet of Things (IoT) field is also heavily utilized. Licensed spectrum.
How to ensure that the licensed frequency band, unlicensed frequency band, and multiple protocols coexist without mutual interference? This is a problem we need to consider.
Different types of interference: Interference from the device to the interference of LTE and Bluetooth
Interference may occur between the device and the device. For example, the signals of the wireless carrier can interfere with each other, and the two wireless standards can also interfere with each other. Bluetooth, LTE and Wi-Fi are widely used in these three technologies, so Bluetooth and LTE are for Wi. -Fi interference is also the most common. Let's explore these interferences in detail:
Interference within the equipment
Multiple antenna architectures of the system may interfere with each other, thereby weakening the coupling effect between the victim antennas (antenna isolation). The transmission (Tx) signals of other antennas will increase the noise power of the victim receiver, and the signal noise The negative ratio has a negative effect. The sensitivity of the receiver (Rx) decreases, which causes the engineering designer to say 'desensitization'.
Desensitization, that is, the receiver is affected by an external noise source, the sensitivity is reduced. This phenomenon can lead to loss or interruption of the wireless connection. This problem is not modern, early radio equipment often encountered this problem - after other components start, The sensitivity of the receiver will be affected. However, as the wireless technology has been widely used in smart phones, Wi-Fi routers, Bluetooth speakers and other devices, if this problem is not properly handled, it will have a greater negative impact.
The 'desensitization' mainly occurs in the following three cases: • Two radio systems occupy adjacent frequencies and a carrier leak occurs. • The harmonics of one transmitter fall within the carrier frequency range of the other system. • The two radio systems share The same frequency range.
LTE and Wi-Fi
In the figure below, the three LTE bands in Band 40, Band 7 and Band 41 are very close to the channels in the Wi-Fi band. The 2.4 Ghz Wi-Fi radio band is very likely to leak into the adjacent band carrier at both ends. Inadequately designed, cellular channel 1 and Wi-Fi channel 11 may interfere with each other's send and receive capacity.
Bluetooth and Wi-Fi
Bluetooth and Wi-Fi transmit signals in different ways, using different protocols, but the operating frequency range is the same (as shown in the figure below). Therefore, if Wi-Fi works in the 2.4Ghz band, Wi-Fi and Bluetooth will affect the other party's transmission. Signals. Since Bluetooth and Wi-Fi radios often work in the same physical area, such as in the same access point, the two standards interfere with each other and may affect the performance and reliability of both wireless interfaces.
Bringing edge to the important role of Wi-Fi coexistence
The U.S. government has taken a variety of approaches to help consumers solve related problems. One of them is to introduce regulations to regulate the radiation and spectrum of various electronic devices. Consumer products must be tested for compliance.
The U.S. Federal Communications Commission (FCC) requires that most RF equipment be tested to demonstrate that the product meets FCC requirements. They specify that the equipment should have steep skirts in the lower and higher Wi-Fi frequency range in order to enforce the strict Banding requirements to ensure the coexistence of adjacent spectrum.
Wi-Fi access points can meet FCC requirements in two ways: 1. Reduce the power levels of Wi-Fi channels 1 and 11, because both are on the edge of the Wi-Fi spectrum. 2. The use of band edges is very steep filter.
Design Tips for Solving Interference Problems: Using High-Quality BAW Filters
We use high-performance coexistence band edge filters, Wi-Fi transmitters can work near the FCC high and low band edges.
High-quality BAW bandpass filters have been successfully adopted by many customers and demonstrate many advantages: • Skirts are extremely steep and can achieve low loss in the Wi-Fi band, in band edge and adjacent LTE/TD-LTE bands Achieve High Suppression Performance • Significantly reduced size to help designers create even smaller, more attractive end-user devices for home or office use • Enable coexistence of Wi-Fi and LTE signals on the same device or adjacent devices • Unique power handling Ability to use in high performance high power access points and small base stations
These filters solve temperature problems encountered in multi-user multiple-input/multi-output (MU-MIMO) systems without affecting harmonic compliance and radiation performance. This is critical if you want to fully cover the entire allocated spectrum.
However, why does the high-quality BAW filter perform so well in terms of FCC-specified banding?
1, Compared to SAW technology in the Wi Fi frequency range, BAW devices have lower insertion loss, steeper band edges, and more stable temperatures
After accessing a higher-bandwidth network such as Wi-Fi, the insertion loss of surface acoustic wave (SAW) devices will increase due to acoustic energy radiated into the substrate body. In the following figure, we can see that with increasing frequency (right The high-quality BAW has a lower loss of body radiation and is therefore the best choice for multiplexer filter design. In addition, BAW can also guarantee a steep band edge required by the FCC, and SAW cannot reach such high frequency range. This performance requirement.
BAW also has better temperature stability than other technologies, which has advantages in FCC certification testing. Most Wi-Fi designs are based on room temperature (20-25°C), but the actual operating temperature of the system may reach 60-80 °C. As the temperature increases, the insertion loss increases. If this is not taken into account in advance, problems may occur during product certification. Using BAW technology can reduce insertion loss and improve the passing rate of certification tests.
The more advantages of BAW over SAW can be found in our free eBook "RF Filter Technologies For Dummies®" (Vol. 1).
2, BAW filter can help engineering designers realize seamless transition of interference band
In the figure below, after using the filter, the band edge response is better than before use. The designer can use this technology to break the limit of the RF front end output power, without violating the FCC's regulations on power spectral density. Without the use of filtering technology In the future, some spectrum may not be available. Operators and manufacturers can make full use of these spectrums after using band-edge BAW filter technology to increase data transmission speed and increase bandwidth.
3, High-quality BAW edge filter can expand channel 1 and channel 11 two or three times
When setting the channel power, Wi-Fi designers usually must set the minimum power that meets band edge supervision requirements to the power of all channels of the entire device. For example, channel 1 meets regulatory requirements with a power of 15 dBm, although channel 6 can reach 23 dBm The designer will still set the overall power of the control scheme to 15 dBm. Designers using band-edge filtering can significantly increase the overall power of the control scheme, thus reducing the required RF link.
In addition, the BAW band edge filter's transmit power can reach 28 dBm, making the system performance increase by more than 15%, and 5G multi-user MIMO co-channel interference will also be reduced. If the CPE developer does not use band edge filtering, Wi Channel 1 and channel 11 in the -Fi band are difficult to comply with FCC regulations; and with the high quality BAW band edge filter, CPE designers can maintain the power of all channels (1 to 11) at a high level.
To understand the role of the band edge filter in detail, let's look at the differences in the user experience before and after using the band edge filter: • Before using the filter: Suppose you have multiple people in your room using Wi-Fi and mobile phones. Use the channel 5 Wi-Fi to watch live football matches without buffering or interruption. At this time, the room enters a mobile phone user and starts to occupy your Wi-Fi space in channel 5. The CPE device will be transferred after adjustment. Go to channel 1 to free up channel 5 space. If the Wi-Fi device does not have a fringe filter (as shown in the block diagram on the left), the Wi-Fi signal strength and live streaming quality will decrease, causing the program to appear Buffering. What is the reason? Because the CPE device must reduce the power of Channel 1 in order to comply with the FCC regulations, so as not to interfere with the adjacent cellular band. • After the filter is used: If the CPE device has a band edge filter (such as the right block As shown in the figure, channel 1 and channel 11 will not be affected and there is no need to reduce the power. You can continue to watch live football matches.
Learn more: How Qorvo's Wi-Fi Solution Can Help Solve Signal Interference
We have entered an era of interconnection. With more and more devices and wireless standards, the problem of coexistence and interference will inevitably persist. Wi-Fi design with high-quality BAW filters can enhance the performance of Wi-Fi access points. To make full use of each existing spectrum.
Want Qorvo experts to talk about other topics? Please send your suggestions to the Qorvo blog team via email, we may discuss them in a later post.
About the author
Wayne has more than 18 years of experience in the RF industry and can help customers around the world solve the design challenges created by the increasing complexity of Wi-Fi applications.