Dynamic Breathing Networks with RRU Power Pooling

In the early stage of 2G and 3G wireless communication development, the carrier bandwidth was narrow, and the number of carrier systems and carriers transmitted by base stations was small, with relatively low requirements for RRU cabinet-top output power. With the development of 4G and 5G services, carrier bandwidth has become larger and larger, while 2G and 3G still have certain service requirements. RRU needs to support 2G, 3G, 4G, and 5G simultaneously, increasing the demand for cabinet-top output power. Moreover, as network sharing between operators becomes more common, the need for high RRU output power has further increased. This higher RRU cabinet-top output power complicates the design and increases RRU costs, which conflicts with operators' efforts to reduce equipment costs.

ZTE's Three-Sector Power Pooling

In a traditional mobile cellular network, a communication site usually consists of three or more sectors. Due to differences in coverage, user groups, and the number of users, the load between sectors is not exactly the same at any given time and varies over time. As a result, the inter-sector RRU cabinet-top output power is unbalanced：some RRUs operate below their maximum power, while some operate at their maximum. However, RRU resources in different sectors are independent of each other and have no physical connection. Even if an RRU resource has redundant power, it cannot be transferred to the sector in need of more power, preventing power sharing.

In recent years, ZTE has launched a series of simplified site solutions, among which the three-sector integrated solution is especially favored by operators. For the first time in the industry, this solution combines multiple frequency bands, three sectors, and 4T MIMO to form an all-around product, which has been deployed or will be deployed in many regions worldwide. In addition to these traditional highlights, this solution achieves power sharing between RRU power sectors for the first time, solving the long-standing issue of power sharing failure between sectors.

How Power Pooling Works

A single RRU supports three sectors, creating physical channels for power sharing between sectors and preliminarily meeting the conditions for sharing. The total output power of the RRU across three sectors can considered a resource pool. Each sector draws power from this resource pool on demand, enabling power sharing among the three sectors. This power sharing mechanism saves RRU hardware resources by about 20%, effectively lowering operators’ equipment investment costs.

The power sharing architecture is shown in Fig. 1. The network consists of the RRU, EMS, and baseband controller. The sharing switch and the sharable power for each sector are set on the EMS. The baseband controller calculates the remaining power for each carrier based on the service load of each sector and flexibly allocates the remaining power to one or more sectors as needed. As the transmit power of the borrowing sector increases, the signal-to-noise ratio (SNR) of the users within the sector is enhanced, boosting the throughput of a single user and the total sector capacity by 10% to 20%. Inter-sector power allocation can adjust at transmission time interval (TTI) levels as needed, ensuring that power can be borrowed and returned with no impact on the power requirements of burst services in the sector.

Extreme Function: Over-Provisioning of Power

We have conducted data research in several provinces and cities with high domestic load, as well as in countries with high international load. It was found that multiple sectors of the same site rarely reaches the maximum service load simultaneously. For sites with less than 80% load, the maximum load at any given time is only about 60% to 70% of the site’s theoretical maximum load.

Based on this survey data, another extreme function of inter-sector power sharing is the over-provisioning of the sector’s maximum rated power. The total power of the three-sector RRU resource pool remains unchanged. The maximum rated power of one or all sectors can be configured to the maximum hardware power of a single sector. Although the total configured power for the three sectors exceeds the total power of the resource pool, as long as the service load of the entire site is not high, even if one sector reaches its maximum power output due to a high service load, the actual total output power of the three-sector RRU does not exceed the resource pool limit. This function is especially applicable to general urban and rural areas with low service loads. Base station coverage and services can be implemented in accordance with the maximum power of each sector, effectively improving coverage and cell capacity.

Use Cases for Power Pooling

Three-sector power pooling is especially applicable to scenarios where three-sector coverage is unbalanced. For example, in a coastal site, the sectors covering land are usually tourist attractions with a small cell radius, and the power required for coverage is far less than the RRU’s maximum rated value. In contrast, the sectors covering the sea should be as far as possible, and the required power should be as large as possible. Traditional solutions usually use RRU with different power levels to deal with the problem, resulting in several RRU models in a single site, which makes configuration and commissioning inconvenient.

The three-sector RRU using a power pool can easily handle this problem. For example, if the total power of the RRU resource pool is 100W, the power can be divided as 20W+20W+60W, meeting the unbalanced power requirements of the three sectors without the need for dynamic adjustments by the baseband scheduler.

The urban-rural fringe is another typical scenario with uneven power requirements where the power pool can perfectly adapt. Even with future economic development and urban expansion, which may require adjustments to base station deployment, cell radius, and increased cell capacity, the power ratio between sectors can also be adjusted through software without the need for hardware changes. This truly enables smooth upgrade, saving operators' reconstruction costs and time.

The power pooling function uses the unbalanced service load across sectors and the RRU hardware that integrates the three sectors, and considers the output power of the entire device as a resource pool. Through flexible TTI-level scheduling by the baseband scheduler, the power can be shared and utilized to its maximum extent. Each watt of power is converted into bit traffic, helping operators enhance network benefits.