EC11 · Sem 6 · Digital communication

16-QAM and spectral efficiency

Aim: Compare 16-QAM with QPSK: more bits per symbol, but more noise sensitivity.

🧪 Live simulation🧊 Real-time 3D bench⚠ Simulated values, not physical measurements

🔬 Virtual lab

Starting the lab…

📘 Theory

16-QAM places 16 points on a grid, carrying 4 bits per symbol. The points are closer together for the same power, so it needs about 4 dB more Eb/N0 than QPSK for the same BER.

BER ≈ (3/8)·erfc(√(0.4·Eb/N0)) · 4 bits/symbol

🧰 Apparatus (virtual)

16-QAM modulator
AWGN channel
constellation display

📝 Procedure

Run at 12 dB and inspect the grid
Lower Eb/N0 and watch neighbours overlap
Compare BER with theory
Explain why Wi-Fi switches modulation with signal strength

Observations and result (kept on this device)

🎤 Viva questions

Why does Wi-Fi drop from 256-QAM to QPSK far from the router

Lower SNR needs points farther apart.

What is the trade-off

Spectral efficiency against noise robustness.

🛡️ Safety

Virtual lab. With real RF equipment, respect exposure limits, never transmit without a licence, and keep antennas away from people.