Current status and suggestions for power supply solutions for small-capacity wireless sites

With the large-scale construction of wireless small-capacity sites, especially indoor coverage sites, by the three major domestic operators in the past two years, the power supply problem that did not receive enough attention in the early construction has gradually become prominent. It is not uncommon for the network coverage quality to decline due to the power supply problem, and even affect the customer experience and cause customer complaints.

This article attempts to analyze this problem from the characteristics of wireless network construction and the status of power supply, and strives to put forward some practical suggestions.

Problems caused by delayed power supply

After the operator reorganization and the issuance of 3G licenses in 2008, the three major domestic operators all started large-scale network deployment to obtain better network coverage quality and gain advantages in the competition of wireless operation business. In this network construction, the operators generally reflected the following characteristics:
● Focusing on solving coverage and rapidly improving network coverage.
● Small investment per site. By reducing the investment amount per site, the number of sites can be maximized and the pressure of funding gap can be alleviated.
● Short construction period, tight time and heavy tasks.
Based on the above characteristics, the wireless construction departments of various operators all use small-station equipment when constructing networks. Whether it is 2G micro base stations, indoor coverage base stations, or 3G RRU equipment, the user capacity of a single station is not large, forming a pattern of large numbers, scattered sites, and small power consumption of a single station.
Most of these sites choose single-phase AC power supply, directly using the mains power without backup power considerations.
The problem of AC power supply without backup power gradually emerged after commissioning. The first problem exposed was the service interruption caused by the mains power outage. For example, Qinghai Unicom conducted a statistical analysis of the failures of base station decommissioning in 2009, and found that the base station decommissioning failures caused by power outages accounted for more than 90% of the total failures, and the frequency of base station decommissioning failures caused by micro base station power outages accounted for 97% of the total failures, and the failure duration accounted for 98.5% of the total duration, becoming an important reason for the decommissioning of base stations.
UPS backup power solutions have many problems
In order to solve the problem of business interruption caused by mains power outages, the power maintenance department will increase the backup power. Because the wireless side uses AC input, the simplest and most direct way to increase the backup power is UPS, and the backup time ranges from 8 hours to 20 hours.
Although this solution temporarily solved the power outage and service withdrawal problem of some sites, it also brought endless troubles to operators from the domestic operation situation in the past few years. Many provinces finally had to abandon this solution.
● Battery life is far lower than expected .
Most of the batteries configured in UPS use 12V monomers with a theoretical life of about 5 years. However, in actual applications, many sites have started to suffer a lot of battery damage in less than a year.
● Increased maintenance workload .
The failure rate of UPS host is high, and the battery damage rate is high. Maintenance personnel must frequently respond to maintenance at these sites.
● Substantial increase in electricity costs
DC power supply solution regains recognition
The main advantages of the DC solution are high system reliability, high efficiency, and perfect battery management functions, as shown in Table 1.
Table 1 Comparison of DC communication power supply and UPS