A Case Study of a Remote Line Powered Small Cell Network

In 2016, a neutral host carrier in Southern California, USA initiated a wireless network densification project that would ultimately involve several thousand small cells. While the service provider grappled with the obvious issues of backhaul, siting, and permits, one of the biggest issues was getting a usable source of power to each site. The provider found that the optimal site for RF coverage did not always coincide with the availability of power. The service provider had limited options. Compromising on the RF coverage would mean more sites would be needed. Electrical utility construction projects to reach each site would have jeopardized the project timeline, plus the potential cost overruns would have crippled the return on investment. The service provider was forced to seek an alternative solution. The resourceful neutral host considered various means of powering the devices, eventually deciding on Remote Line Power (RLP) using Twisted Pair Copper Cable to energize the small cells. The RLP method used a centralized power source to deliver power to the remote devices over copper cables. Sometimes, the sources were located in buildings, but more often they involved an outside plant electronics cabinet. In either case, utility AC provided at the central site connected to a conventional -48Vdc rectifier plant. The rectifier output in turn connected to a special DC-DC converter, called an Up-converter, that elevated the voltage to ±190Vdc for transport over the copper cables. The rectifier also charged batteries when backup power was required for critical circuits. At the small cell site another special DC-DC converter, called a Down-converter, changed the ±190Vdc back to 48V for powering the remote device. There were several requirements for this alternative approach to work, including: (1) the RLP equipment had to supply enough power to energize the small cells and backhaul equipment; (2) the down-converter had to be small, lightweight and able to mount on a strand near or alongside the small cell equipment; (3) the RLP system had to reach the worst-case distances while using the smallest standard OSP telecommunications cable; (4) the copper cable had to be installed along with the fiber to reduce the installation labor costs; and (5) the centralized power had to be placed at intermediate sites to minimize cable runs and lower the overall cost of equipment. This paper describes how the carrier met these requirements and successfully deployed a remote line powered small cell network that now consists of over 5000 end points. It describes the overall network architecture, including placement of the centralized sources and mounting for the down-converters. The paper also depicts the methods for accessing the copper cable networks. It concludes with a discussion of how the RLP technique met the timeline requirements.