PTP (Point-to-Point Wireless Link)

In a point-to-point (PTP) link, two radios talk only to each other through high-gain directional antennas aligned on one another. PTP is used where laying fiber is costly, slow or impossible. Typical uses are building-to-building connections, cell-site and wireless ISP backhaul, and linking camera or SCADA sites to a control centre. Depending on frequency and antennas, links range from a few hundred metres to more than 50 km.

Frequency choice sets capacity and reach. The unlicensed 5 GHz band is flexible and widespread but exposed to interference. 60 GHz (V-band) offers very high capacity but is limited to a few kilometres by oxygen absorption and is affected by rain. Licensed microwave bands between 6 and 42 GHz and 70/80 GHz (E-band) provide carrier-grade reliability. In Türkiye, spectrum use and output power (EIRP) limits are governed by BTK regulations, and licensed bands require a right of use.

Design starts with a link budget: transmit power + antenna gains − cable losses − free-space path loss = expected received signal (RSSI). Free-space path loss is FSPL(dB) = 20·log10(d[km]) + 20·log10(f[MHz]) + 32.44, which is about 128 dB for 10 km at 5.8 GHz. Enough fade margin for rain and atmospheric variation must remain between the calculated signal and the receiver's sensitivity at the chosen modulation.

Link reliability depends on a clear line of sight (LOS) and on keeping the first Fresnel zone sufficiently free of obstructions. Precise antenna alignment, choosing channel width and modulation to suit the local noise floor, and selecting the channel after a spectrum scan all have a direct impact on performance.