# 16-QAM / 64-QAM / 256-QAM / 1024-QAM and Quizzes
###### tags: `elearning` `Multimedia Wireless Network`
###### Note Page : [:link:](https://hackmd.io/@YTL0307/HJEb6jWCo)

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## **16-QAM**
- The 16-quadrature amplitude modulation (16-QAM) increases the complexity of the modulation through adding amplitude as a new element of complexity to the modulation.
- It increases the complexity more than the QPSK modulation as it uses both peak points, as well as amplitude.
- In the 16-QAM modulation, you can transmit four bits at a time. Both phase modulation and amplitude shift keying modulation are combined to create the 16-QAM modulation.
- In the BPSK modulation, the size of the EVM box was half of the polar coordinate chart.
- In the QPSK modulation, the size of the EVM box was quarter of the polar coordinate chart.
- In the 16-QAM modulation, notice that the EVM box has shrunk further in size.
- In the BPSK and QPSK modulations, you could note the movement of landing points around the polar coordinate chart.
- In the 16-QAM modulation, you can note the position of the landing point around the polar coordinate chart, as well as their distance from the center of the chart to land on different boxes of the polar coordinate chart that represent the bits of transmission.
- Phase shift keying is used to indicate the peak point of the wave and amplitude is used to indicate the distance from the center where the wave peaks.
- The peak and their corresponding landing points on the polar coordinate chart for two sample wave transmissions are shown here.
- You can notice that the higher the complexity of the modulation, the smaller is the size of the EVM box.

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## **64-QAM**

- In the 64-QAM modulation scheme, you can transmit six bits of data at a given point of time.
- These bits together form bit structures, which are known as symbols.
- Different modulation schemes have different symbol sizes.
- Therefore, 16-QAM has a four-bit symbol, whereas the 64-QAM has a six-bit symbol.
- You can notice that the size of the EVM box is further reduced in this modulation.
- The wave transmitters and receivers are expected to understand the arrival angle of the wave and the amplitude of the received wave.
- This in turn helps to identify the landing point of the wave on the polar coordinate chart to understand which symbol or the set of bits is being transmitted here.

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## **256-QAM and 1024-QAM**

- In the 256-QAM scheme, you can transmit eight bits per symbol.
- With the 802.11ac standard, you can get a 256-QAM, where the size of the EVM box is very small.
- With the 802.11ax standard, you can also get a 1024-QAM modulation scheme.
- In this modulation scheme, you can transmit ten bits per symbol.
- The EVM box gets even more smaller in this modulation scheme.
- If you have ever done throughput testing with the 802.11ac access points, you will notice that you can get excellent data rates only when you are right on top of the access points.
- As you move away from the access points, your data rates begin to drop.
- This is due to QAM.
- When you are very close to an access point, your signal strength is very good, the signal-to-noise-ratio (SNR) is excellent, and the transceivers can decode with accuracy.
- Therefore, the Wi-Fi transceiver can place the symbols, as it lands in the EVM box.
- Whereas, when the signal drops, the Wi-Fi transceiver is unable to place the landing points inside the EVM box.
- This issue can be addressed by moving backwards to a larger EVM box.
- In this case, you should move back to the 256-QAM modulation, so that you can place most of the symbols inside the EVM box.
- As the signal strength drops, you need to move to a larger EVM box, to place the symbols within an EVM box.
- This backward process continues, as you move farther away from an access point and eventually you land in the BPSK with a large EVM box, but which can transmit only one bit at a time.

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## **Quizzes**