Four Key Factors for Wi-Fi Connectivity in IoT Product Design

Four Key Factors for Wi-Fi Connectivity in IoT Product Design

Whether the Wi-Fi connection is good or bad, the experience of using IoT products will have the difference between heaven and earth. A good Wi-Fi connection depends on four factors: long communication distance, high throughput, low packet error rate, and proper coexistence. And all of this can be enhanced by 802.11ac, which is explained in detail in this article.

Driven by the momentum of the Internet of Things (IoT), devices that we never thought could be connected in the past are becoming connected today. Now you don’t have to walk to the coffee machine to make coffee, you can simply send a command to the coffee machine from your mobile phone. The coffee machine even learns your preferences and prepares your coffee just the way you like it every time.

The number of connected devices and users continues to grow rapidly. This is really a good thing! However, for IoT infrastructure to be sustainable, IoT devices must be able to operate freely in any environment. IoT devices that cannot connect to a local access point (AP) are useless. When designing IoT products, system designers need to understand various Wi-Fi parameters such as transmit power, receive sensitivity, coexistence capability, and throughput. This article will describe some of the important characteristics of a successful IoT product.

The 2.4GHz band is crowded

Today, the wireless technologies commonly used by IoT devices are Wi-Fi and Bluetooth technologies operating in the 2.4GHz frequency band. But it’s not just IoT devices that use Wi-Fi. Wi-Fi technology is also widely used on TVs, laptops, tablets, and mobile phones in every home. Now, the 2.4GHz band is like a conference room where several people want to speak at the same time. However, if you want everyone to understand what is being said, only one device is allowed to “speak” at a time.

Now imagine a device that can’t communicate efficiently, but is still chattering. Other devices can’t open their mouths, and meaningful calls cannot be made in the conference room. In the past, Wi-Fi standards did not focus on performance and frequency band utilization. As the density of Wi-Fi devices continues to increase, the Wi-Fi Alliance needs to add strict performance requirements on the basis of compliance with the protocol, and products that meet the performance requirements can pass the certification.

IoT device makers need to move away from the “low-cost” approach and ensure they don’t design Wi-Fi connected devices that perform poorly or adversely affect other nearby Wi-Fi devices. Even a single device with poor performance can overwhelm a customer’s entire Wi-Fi network.

For IoT networks to last, system designers must be required to use high-reliability Wi-Fi connections. Suppliers must understand the consequences of poor design, as this directly affects the success or failure of the product and the reputation of the brand. IoT products that cannot connect to access points are useless to customers.

When customers experience any connectivity issues, they are likely to return the product or leave a bad review online. These issues can lead to product failure and negatively impact the brand. Even with a well-designed product, extensive technical support is necessary for customers unfamiliar with IoT.

Here are a few typical characteristics of a poor Wi-Fi connection:

• Short communication distance
• low throughput
• High packet error rate
• Poor coexistence

One of the bad Wi-Fi: short communication distance

Too short a communication distance limits how far IoT devices can connect to access points. Connecting a device to an access point is often the first impression a customer has of your product. If there is no way to connect, in most cases customers will return the product with a swipe of a pen to leave a bad review. The reason why your IoT product cannot connect to an access point at a certain distance may be due to low transmission power, poor sensitivity, or lack of support for beamforming transmission, as the Wi-Fi link requires the exchange of packets between the two devices to establish connect.

• Transmission power

The transmit power of an IoT device affects the ability of an access point to receive its signal. After the power exceeds a certain level, the output of the Wi-Fi power amplifier starts to distort. To solve this problem, most Wi-Fi devices limit the transmit power. Of course, there are other ways, Cypress uses a proprietary method to solve the distortion problem of the Wi-Fi power amplifier and increase the transmission power.

Another big issue with transmission power is the regulatory limits set by different countries. This requires controlling the maximum transmission power according to the requirements of the host country and complying with regulatory requirements. Therefore, the Wi-Fi subsystem must provide a convenient or automated method to control transmit power so that IoT devices can transmit at maximum transmit power levels while avoiding any regulatory (FCC, CE, etc.) violations.

• Receive Sensitivity

Receive sensitivity refers to the ability of the device to receive the signal from the access point. Excellent receiving sensitivity coupled with excellent transmission power is the key to ensuring communication distance. Some Wi-Fi devices have built-in algorithms that provide a better signal-to-noise ratio than others when processing the incoming signal. Therefore, when selecting Wi-Fi devices for IoT products, the receiving sensitivity should be fully considered.

• Link budget

Four Key Factors for Wi-Fi Connectivity in IoT Product Design

The link budget also has a significant impact on the communication distance.

Transmit power, receive sensitivity, and environmental factors together determine the link budget between two Wi-Fi devices. Assume that the transmission power of one device is +3dBm (decibel milliwatts) greater than another device, and the sensitivity is -3dBm. This improves the link budget by 6dBm. For every 6dBm increase in the link budget, the communication distance can be doubled (see figure).

• Beamforming transmission

Beamforming transmissions are used to directionally focus the transmission power, thereby helping to improve communication distances in the focused direction. For example, if IoT devices support beamforming transmissions, they can connect to access points over longer distances. However, not all Wi-Fi devices support beamforming transmissions. Beamforming technology first appeared in the 802.11n standard, but how it is ultimately implemented is up to the manufacturer. This creates interoperability issues. In the 802.11ac standard, this feature is well defined in the WLAN specification and is interoperable. Therefore, to increase the communication distance without repeaters, 11ac becomes a necessary condition.

Bad Wi-Fi No. 2: Low Throughput

Low throughput can have serious performance implications, including:

• Latency: The lower the throughput, the longer the latency. While most IoT devices only need to send a few bytes of data, time delays can also create a poor user experience. In addition, time extension can reduce the reliability of time-critical applications such as medical equipment and industrial equipment.

• Battery life: In the case of low throughput/modulation index, the device needs to transmit for a longer time, and there will be longer active time, which will directly shorten the battery life.

• Poor Band Utilization: Low throughput increases the airtime of communications. This will directly cause the 2.4GHz frequency band to be more crowded.

The throughput of a device is affected by several factors such as link budget, modulation index, and frequency band availability. Wi-Fi devices adapt to the link budget by adjusting their link data rates. A larger modulation index means higher throughput. Improvements in signal conditioning are required if higher modulation indices are to be supported. Therefore, some devices perform better at lower modulation indices than at higher modulation indices. It can provide excellent sensitivity and good transmission power under various modulation and coding schemes, so as to provide excellent data transmission rate under various communication distances.

To achieve excellent throughput, the throughput of the device under the various modulation indices and coding schemes supported must be examined. At the same time, it is also necessary to choose a device that can support a higher modulation index. The 802.11ac standard supports 256-QAM (Quadrature Amplitude Modulation). 802.11ac devices can achieve higher throughput than the 64-QAM supported by the 802.11n standard.

Additionally, the number of devices trying to communicate in a given area also directly affects throughput. The greater the number of devices, the less time each device takes to send/receive data. This limits the effective throughput. This problem becomes acute in the 2.4GHz band, where there are a lot of legacy Wi-Fi devices trying to communicate, along with other wireless devices like Bluetooth and Zigbee. So in addition to using a higher modulation index to improve throughput, the 802.11ac standard also supports the less crowded 5GHz band, which also helps improve throughput.

Bad Wi-Fi No. 3: High packet error rate

In Wi-Fi communication, once there is a packet error, it needs to be retransmitted. A device with a high packet error rate (PER) can cause poor performance for all devices in the network because it takes longer to transmit packets successfully. This may increase the number of collisions, causing other devices to also have to retransmit, further degrading the PER. The table shows the occupancy of talk time at different PERs. This table shows the percentage of talk time per second with 20 nodes transmitting 1,000 bytes of data at a rate of one packet per second.

Four Key Factors for Wi-Fi Connectivity in IoT Product Design

According to the table, a device with a 90% error rate took 900% of the talk time compared to a device with a 10% error rate. In addition, higher PER also increases latency. If the packet has errors, it needs to be retransmitted. This is a fatal problem for time-critical applications. Therefore, before selecting Wi-Fi devices for IoT applications, the PER of Wi-Fi devices should be mastered. The 802.11ac standard helps a lot because it supports the less crowded 5GHz band, which helps reduce the number of packet collisions.

Bad Wi-Fi No. 4: Poor Coexistence

IoT devices often need to use both Wi-Fi wireless technology and Bluetooth wireless technology. The problem is that they work in the same frequency band, and they are difficult to be compatible without coordination. Poor coexistence can severely degrade Wi-Fi throughput.

There are multiple coexistence schemes that can be used, but their performance varies widely. Hundreds of man-years of work are required to create a coexistence algorithm that can decide in real-time whether to grant a medium access to Wi-Fi and Bluetooth. The RF link of Wi-Fi and Bluetooth radios must be ideally controlled to minimize interference and maximize performance. Achieving coexistence requires a large amount of information from the Wi-Fi and Bluetooth cores to be fed to a high-performing arbiter.

Some Wi-Fi and Bluetooth combo devices have built-in coexistence capabilities, and the arbiter communicates with the Wi-Fi and Bluetooth cores over a parallel bus. The 802.11n and 802.11ac standards support Wi-Fi operating in the 5GHz band, which is helpful for applications that require both Wi-Fi and Bluetooth to work. Therefore, in addition to having a good coexistence mechanism, 5GHz-capable devices should be used for optimal coexistence.

At least 802.11ac (Wi-Fi 5)

A good Wi-Fi connection is the key to the success of IoT products. It is crucial to choose a device with long communication distance, high throughput, low PER, and good coexistence support. The 802.11ac standard transmits through beamforming, increases throughput (by increasing modulation index), reduces PER, enhances coexistence (by supporting the less crowded 5GHz band), and increases communication distance. Combining devices with proven coexistence capabilities can significantly increase Wi-Fi throughput, even if simultaneous use of Bluetooth is required. All of these factors should be taken into consideration when choosing a connectivity solution for an IoT product.

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