Gbit Radios for the Mobile Anyhaul

Abstract

Traditionally, the microwave and millimeter-wave (μ/mmW) links have been limited by thermal noise. Long microwave hops had to connect distant sites of several kilometers. The antennas were mounted on high altitude towers. Unwanted interference was eliminated with proper link design and frequency re-use plans. The link design focused on Free Space Loss, rain and atmospheric attenuation. Fading events (e.g., attenuation due to rain or multipath) can significantly reduce the received signal level and degrade the link performance. In worst case, the microwave connection is cut resulting in outage. In the last two decades we observed a rapid breakthrough in direct fiber-optical access. The very long microwave backbone links have been systematically replaced by fiber-optics wherever it was possible by terrain conditions. Consequently, the majority of μ/mmW links became shorter and shorter. In urban environments, the wireless hops are typically shorter than five-six kilometers. On the other hand, there is a huge demand for a flexible LTE, 5G and 6G front- and backhaul (commonly called anyhaul). In mobile systems the μ/mmW anyhaul became extremely dense. 5G and 6G mandate challenging user bit rate and latency requirements.To avoid radio interference and support high link throughputs, higher and higher carrier frequencies are introduced. State-of-theart radios offer excellent possibilities in the millimetric (E, V and W) bands. In the paper the long road to nowadays Gigabit radios is presented. Starting from the very early microwave experiments, the evolution of mobile networks and anyhaul is shown. Finally, some design examples are presented for the recent use of the E-band.