## What is Constellation in QAM?

A constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying. It displays the signal as a two-dimensional xy-plane scatter diagram in the complex plane at symbol sampling instants.

**What is the symbol rate of 16-QAM?**

Tabular difference between 16-QAM, 64-QAM and 256-QAM

Specifications | 16-QAM modulation | 64-QAM modulation |
---|---|---|

Number of bits per symbol | 4 | 6 |

Symbol rate | (1/4) of bit rate | (1/6) of bit rate |

KMOD | 1/SQRT(10) | 1/SQRT(42) |

### What is the difference between 16 PSK and 16 QAM?

More the distance between the constellation, lesser is the chance of a constellation point getting decoded incorrectly. This implies that for the same symbol error rate, 16QAM modulation requires only 4.19dB lesser signal to noise ratio , when compared with 16PSK modulation.

**What is the difference between 16 QAM and 64 QAM?**

The 16 qam bits per symbol are 4 (four). This means in 16-QAM each symbol represents 4 bits as mentioned in the 16-QAM constellation diagram above. The 64 qam bits per symbol are 6 (six). In 64-QAM, each symbol is represented by 6 bits as shown in the 64-QAM constellation diagram above.

## What are advantages of 16QAM?

The advantages of QAM are higher data rates, high noise immunity, low probability of error values, and increased bandwidth.

**How many different symbols are possible at the output of a 16QAM modulator?**

Each dot in Figure 1.8 is a symbol, as it represents a unique combination of amplitude and phase of the I and Q waves. So, in each symbol period, only one of the ‘dots’ is transmitted. As there are 16 symbols, this version of QAM is called 16-QAM. Figure 1.8 Constellation diagram for 16-QAM.