How much do you know about Wi-Fi throughput and various variables?

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Knock on the blackboard: the focus of this article:

1. What is throughput

2. Hardware influence factors

3. Software influence factors

4. Influencing factors of antenna

5. Test related influence factors

1. What is Wi-Fi throughput

a) In layman's terms, Wi-Fi throughput is the actual maximum rate supported by Wi-Fi devices (AP/STA) on the uplink and downlink. It is a kind of limit test and is closer to the actual user scenario, especially Today, when products are becoming more and more wireless and wired network port designs are gradually fading out, this is particularly important. The Wi-Fi throughput mentioned in this article is a Wi-Fi throughput test at the application layer, which is suitable for high data transmission application scenarios.

b) Wi-Fi throughput is a more general concept. In the actual test, it needs to be divided into modes and channels.

Such as IEEE 802.11n HT40 mcs7 ch1, IEEE 802.11ac HT80 mcs9 ch36 and so on.

Note: MCS is Modulation and coding scheme. Different numbers represent different modulation and coding schemes. Different modulation schemes correspond to different rates. You can check the 802.11n/ac protocol for details.

c) According to different verification purposes (application scenarios) of Wi-Fi throughput, there are multiple methods

1. For example, when verifying the Wi-Fi throughput inflection point, different attenuation values â€‹â€‹need to be set through the attenuator;

2. For example, several typical scenarios for verifying the coexistence performance of wireless systems:

1) Verify the coexistence performance of the product using Wi-Fi+Bluetooth combo chip (verify the product Wi-Fi and Bluetooth time slot allocation and channel avoidance mechanism, the principle is the same as 4G and Wi-Fi coexistence), the Bluetooth function of the product needs to be switched on and tested;

2) When testing the throughput of a single Wi-Fi device, plus a Bluetooth device, it can be subdivided into two states: Bluetooth only connection and data transmission;

3) The Wi-Fi device and Wi-Fi device coexistence scenario is to add other Wi-Fi devices during the test. The device can work on the same channel/adjacent channel currently being tested. It can also be subdivided into only connection and data transmission. Kind of state

3. For example, verify the influence of Wi-Fi driver, which is more obvious at close range;

4. For example, to verify antenna performance, different directions, angles and distances need to be distinguished.

5. For example, verify the influence of temperature on throughput. Various permutations and combinations of the above types can also be performed as needed.

d) How to judge whether Wi-Fi throughput is good

If you want to keep improving, compare the data of the same specifications and models in a clean and stable environment as a benchmark.

Generally speaking, the measured value at close range and zero attenuation needs to reach more than half of the theoretical value of the RF chip. For example, the theoretical rate is 150Mbps, and the maximum test value needs to be above 75Mbps; the measured value under close distance with attenuation is the same as the power and sensitivity of Wi-Fi OTA Related to antenna performance, its performance needs to be compared with the data under the same test state to determine.

In addition, when designing and selecting the product, it is necessary to consider the application scenarios of the product's own data transmission requirements and the maximum theoretical rate of the communication interface used in the product design. Do not blindly pursue a Wi-Fi solution with a high specification rate, resulting in waste of design costs, such as 802.11ac The maximum theoretical rate of the HT80 1T/R can reach 433.3Mbps, but the product uses the SDIO V2.0 communication interface, which is actually unable to reach half of the theoretical value.

2. Hardware influence factors

The impact of hardware on throughput can be distinguished from chip selection, layout design, RF index debugging, and mold structure. Only a brief overview can be made here.

a) Chip selection---choose the chip suitable for the product application

The parameters related to throughput include PHY layer data rate, support interface, typical conducted Tx power, typical EVM, etc. In addition, the ability of the chip to resist packet loss needs to be measured. The theoretical rate of the physical layer and the type of communication interface supported will directly determine the throughput of the product designed with this chip, the power determines the transmission distance, and the EVM determines the signal modulation quality.

b) Layout design (not detailed here)

Here is mainly focused on using SI9000 (or other tools) to select the reference layer, the length of the microstrip line of 50 ohm, the bend and the impedance control of the trace, the isolation of multiple Wi-Fi signals, the processing of the Wi-Fi part of the power supply, and interference Device layout, thermal design, shielding design, etc. will affect Wi-Fi radio frequency indicators.