# Interpreting QPSK Modulation Angles

• fran1942
In summary, the conversation discusses the interpretation of red and yellow dots in a diagram of QPSK modulation angles. Despite not being on the 4 distinct phase angles, it is understood that QPSK has a discrimination of 90 degrees. It is questioned whether the red dot equates to 45 or 135 degrees and the yellow dot to -45 or 45 degrees. It is confirmed that these dots are likely not valid due to low SNR or corruption, and a simple decoder may assign them to the closest location, resulting in symbol errors.
fran1942
Hello, I have attached a diagram of QPSK modulation angles. I was wondering how would the red and yellow dots be interpreted.
Those dots are not exactly on either of the 4 different phase angles. But I understand QPSK has a discrimination of 90 degrees so would the red equate to 45 degrees and the yellow to -45 degrees ? Is that how it works or would the red equate to 135 degrees and the yellow to 45 degrees ?

Thanks for confirmation.

#### Attachments

• qpsk.jpg
9.2 KB · Views: 449
Points at these locations only occur when the SNR is abnormally low or there is some kind of corruption, indicating that they are probably not valid. A simple decoder would assign them to the closest location, but it is likely that they will give symbol errors.

## 1. What is QPSK modulation and why is it used?

QPSK (Quadrature Phase Shift Keying) is a type of digital modulation technique used to transmit data over a communication channel. It uses four different phase shifts to encode data, allowing for twice the amount of information to be transmitted in the same bandwidth compared to traditional modulation techniques. QPSK is commonly used in wireless communication systems, such as satellite and cellular networks.

## 2. What are the angles used in QPSK modulation?

The angles used in QPSK modulation are 0°, 90°, 180°, and 270°. These angles represent the four different phase shifts used to encode data.

## 3. How are the angles chosen in QPSK modulation?

The angles used in QPSK modulation are chosen based on the representation of the data in binary form. Each angle represents a combination of two bits, with 00 being 0°, 01 being 90°, 10 being 180°, and 11 being 270°.

## 4. How is QPSK modulation different from other modulation techniques?

QPSK modulation differs from other modulation techniques in that it uses four different phase shifts to encode data, allowing for a higher data rate in the same bandwidth. This makes it more efficient compared to traditional techniques such as Amplitude Modulation (AM) or Frequency Modulation (FM).

## 5. What are the advantages of interpreting QPSK modulation angles?

Interpreting QPSK modulation angles allows for accurate decoding of data transmitted using this technique. It also allows for higher data rates, better signal-to-noise ratio, and improved system performance compared to other modulation techniques. Additionally, QPSK modulation is less susceptible to interference, making it more reliable for use in communication systems.

Replies
13
Views
3K
Replies
4
Views
5K
Replies
5
Views
2K
Replies
19
Views
2K
Replies
4
Views
1K
Replies
49
Views
3K
Replies
3
Views
1K
Replies
8
Views
1K
Replies
4
Views
2K
Replies
45
Views
4K