While most operators are focused, for now, on mid-band spectrum for 5G roll-out, a few want to start using millimeter wave bands above 20 GHz in the near term. One of these is SK Telecom, which is digging into the detail of how to make mmWave systems work effectively despite the spectrum’s short range. Signals in the 28 GHz band, in which SK Telecom is testing 5G prototype equipment, travel over short distances and in straight lines. The company is focusing on relay technology, which is also being trialled by Softbank in Japan and others, to improve coverage and quality of service. The operator has been working with its own integration subsidiary, SK Telesys, and with High Gain Antenna, to…