The Spectrum Split: 6GHz vs 80GHz

Microwave engineering is divided by the frequency of operation. Lower frequencies (6-11GHz) are used for Long-Haul links (30km+) due to their resilience to rain fade. Higher frequencies (60-80GHz, E-Band) provide Short-Haul 10Gbps+ capacity but are highly sensitive to oxygen absorption and heavy precipitation.

Link Budget Calculation ($P_{rx}$)

The success of a microwave link depends on the Link Budget. The received power ($P_{rx}$) must be greater than the receiver sensitivity ($S_{rx}$) plus a safety buffer called the Fade Margin.

$P_{rx} = P_{tx} + G_{tx} + G_{rx} - L_{fs} - L_{misc}$

Adaptive Modulation (ACM)

Modern microwave radios use Adaptive Coding and Modulation (ACM). In clear weather, the radio may use 4096-QAM for maximum throughput. When rain starts, the radio automatically 'steps down' to QPSK or 16-QAM. The link slows down, but it does not drop.

Polarization & XPIC

To double capacity without using more spectrum, engineers use Vertical and Horizontal polarization on the same frequency. XPIC (Cross-Polarization Interference Cancellation) technology allows the radio to distinguish between the two signals, providing 2x the throughput in the same bandwidth.