EV Engineering & Infrastructure

Why is Wi-Fi 802.11n the preferred wireless charging standard for EV charging?

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IEEE Wi-Fi 802.11n is the technology selected for wireless communication for EV charging in Part 8 of the ISO 15118 standard. This article explains why Wi-Fi 802.11n is the preferred wireless network protocol for wireless charging of EVs. We also present an interesting case study to conclude how the 802.11n standard has emerged on top among six other wireless network standards.

When referring to wireless charging of EVs, many address the wireless power transfer, forgetting that we also need a standard protocol for wireless communication during the power transfer. Such a wireless network protocol is necessary for front-end and back-end communication during EV charging and communication. 

Figure 1 illustrates the block diagram of a complete wireless EV charging system. The system is divided into three phases. The first phase is connected to the grid and draws power directly from the grid. The wireless charging pads are between the first and second phases, where the related standards are listed, including IEEE 802.11n. After the rectification and control process in phase two, the power is delivered to the battery in phase three.

Figure 1. The use of Wi-Fi 802.11n during EV wireless charging. (Image: E-Mobility Engineering)

Is Wi-Fi necessary for EV charging?

Recent regulations by the governments of various countries mandated Wi-Fi (or some form of wireless network) as an essential feature for EV charging. Whenever we hear of smart EV charging, we understand that the charging ecosystem includes a standard wireless network protocol.

To this extent, the ISO 15118 standard for EV charging has adopted Wi-Fi as the only wireless charging technology for communication purposes. More specifically, Wi-Fi 802.11n is the preferred protocol among Wi-Fi 802.11n, g, and p.

But why is 802.11n preferred over others?

You see, we have come a long way in the evolution of Wi-Fi standards. The IEEE designed the 802.11 standard exclusively for Wi-Fi technology. Figure 2 shows the various IEEE 802.11 standards arranged in chronological order.

Figure 2. Chronological order of Wi-Fi 802.11 evolution. (Image: Android Authority)

One can observe from Figure 2 that after 802.11n, we have newer standards with better speed, a better frequency band, and more MIMO channels. But why is 802.11n still the preferred way? Well! Here is the answer to it. 

Whenever the frequency band of a wireless network increases, it offers better data transfer, but the signal strength goes down quickly with obstacles in the network path. 

The Wi-Fi 5 and later versions have 5 GHz or above as their preferred frequency bandwidth. It means that their signal strength is more susceptible to disturbance due to obstacles in their network path. 

When it comes to Wi-Fi 4, their preferred frequency bandwidth is 2.4 GHz. So, although they offer a lower data transfer rate, they are better at handling signal strength compared to Wi-Fi 5 and later. This has become a deciding factor among consumers and manufacturers to opt for Wi-Fi 4.

Now, Wi-Fi 4 itself has three versions: 802.11b, g, and n. However, referring to Figure 2, you will notice that 802.11n offers MIMO options for the first time in the history of Wi-Fi evolution. With the help of MIMO, more than one antenna can be used by Wi-Fi devices to improve data transfer rates.

Case study

Here is an interesting case study conducted jointly by Carnegie Mellon University (Pittsburg, USA) and Jamia Millia Islamia (New Delhi, India) on using wireless technologies for EV charging. 

A total of seven different wireless networks were simulated to study the end-to-end (ETE) communication delay between EVs and roadside units (RSU). The networks under study were:

  • WiMAX 802.16 
  • Wi-Fi 802.11g 
  • Wi-Fi 802.11p 
  • Wi-Fi 802.11n 
  • Zigbee 802.15.4 (868 MHz) 
  • Zigbee 802.15.4 (915 MHz) 
  • Zigbee 802.15.4 (2.45 GHz)

Following were the three observations from the collaborative research study:

  • The first observation was that the average ETE delays of the Wi-Fi networks were lower than the ZigBee networks. 
  • During the second observation, researchers found that the Doppler effect caused the most spread in Wi-Fi 802.11n/p. 
  • The third observation concluded that Wi-Fi 802.11n/g had lower ETE delays compared to 802.11p. 

From the above three observations, it is clear that Wi-Fi 802.11n is well suited to EV charging on the grounds of better signal spread and lower ETE delays compared to other wireless sensor networks.

If you are wondering what the ETE delay is when you send a message from EV to RSU or vice versa, the ETE delay is the time it takes to be processed and sent across the network.

Summary and future scope

We have seen the importance of the IEEE Wi-Fi 802.11n wireless network standard for EV charging. At this point, you may be aware of the reason for choosing 802.11n over a few other standards.

In the future, we will find it interesting to see if we can use Wi-Fi 5 and later versions for wireless EV charging. EVs and charging stations are expected to experience fewer obstacles along the network. And Wi-Fi 5 and later work well when there are no obstructions in a network.

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