Base Station Antenna Evolution for a 5G World

As 5G networks start commercial operations in countries including the United States, South Korea, China, and Japan, Base Station Antenna (BSA) vendors are innovating and coming to grips with the complex feature sets and performance demands required in a modern BSA.

In today’s converged Radio Access Network (RAN), which is expected to offer 3G, 4G LTE, and 5G communications deployed initially as Non-Standalone (NSA), fallback support for 4G LTE and even 3G Wideband Code Division Multiple Access (WCDMA) spectrum bands will be required. In addition, the trend toward higher orders of Component Carrier Aggregation (CCA) and dual connectivity (LTE-5G) will require multiple band support by the BSA for simultaneous connections to each network. The driver here is to converge all sub-2.7 GHz bands into one antenna and accommodate a second antenna or massive Multiple Input, Multiple Output (MIMO) antenna for mid-band (3.5 GHz) 5G to economize on cell tower space. The BSA must also support LTE-Advanced MIMO capabilities to their full potential and provide 4T4R for all LTE bands, particularly in the high band from 1,427 MHz to 2,690 MHz.

The technology roadmap for BSAs in a 5G world is a complex one, and is following three overarching drivers. Sectorization using multi-port/multi-band and/or multi-beam antennas is the first driver. By upgrading from a standard three sector cell site to six sectors or more, Mobile Network Operators (MNOs) reuse spectrum over an increased number of sectors covering a smaller angular spread. This increases overall cell site throughput and the number of simultaneous connections supported by the cell site. Sectorization also increases the number of sectors without increasing the number of antennas or radiation centers on the tower and represents important cost savings because towers are increasingly occupied by multiple BSAs and other equipment. Higher order sectorization for increased capacity gains is becoming available with tri-, penta-, and nona-beam BSAs now part of many vendors’ portfolios.

Active Antenna Systems (AASs) are the second driver. An AAS contains active radio electronics inside the BSA radome with the antenna/radio combination connected back to the to the baseband with fiber. Although more expensive than legacy passive antennas, AASs enable high-order and massive MIMO features for sector throughput enhancements. The AAS design is an attractive solution that streamlines deployment and scales to higher orders of MIMO, reduces cable losses, and reduces power consumption. Also, with AAS installation is simplified, and the equipment space required is reduced.

The third overarching driver is proactive cell shaping, wherein beamforming is used to shape or sculpt overall cell coverage. Sector sculpting in the cell shapes the Radio Frequency (RF) radiation pattern with directional antennas, which can be steered both in azimuth (horizontal direction) and elevation (vertical space). Sculpting delivers precise wireless coverage with minimal interference with neighboring cells. BSAs also come with various combinations of standards-based Remote Electrical Tilt (RET) mechanisms which in addition to assisting in sector sculpting using digital remote control can also be used for monitoring and control of the BSA.

However, repurposing a quote from Mark Twain, we can say that reports of the death of the passive antenna are greatly exaggerated.

In the evolution toward 5G, increasingly higher-order MIMO means that so many more antennas will be needed that new antenna designs and deployment options will be required. In the lower frequency bands, ABI Research expects that the passive antenna will remain the mainstream option because space limitations and regulations make it impractical for operators to deploy several single band AASs to replace the existing passive multiband antennas. However, passive single radome antennas will continue to evolve with increasing complexity to support more multiband sharing, with a gradual migration from 2x2 to 4x4 MIMO. Full Dimension-MIMO (FD-MIMO) and massive MIMO antennas are the next steps on this roadmap.

When considering 5G, massive MIMO increases spectral efficiency and cell capacity in the sector. Massive MIMO works on similar principles to TDD beam-forming, but in this case the antenna arrays are spaced out both horizontally and vertically. This allows the antenna beam to be steered in both planes by the baseband, using very narrow beams. Massive MIMO solutions accomplish 3D beamforming, which can provide high gain and adjustable beams that improve the signal coverage, while also reducing hardware costs because the sub-array needs less power and does not call for expensive high-power amplifiers. As an additional advantage, massive MIMO generates considerably less interference precisely because of the narrow beams and offers multi-path support, which enhances the reliability of the signal and increases channel capacity

Hybrid active/passive antennas are antenna systems that integrate massive MIMO antennas with passive antennas and are closely integrated, sharing electronics, radio frequency components, and chassis between the active and passive antennas. Hybrid active/passive antennas simplify adding and deploying massive MIMO systems on increasingly highly occupied towers. As a compact single unit, hybrid active/passive antennas reduce wind load and, since components are shared, offer a lower initial cost when compared to traditional options.

There are several methods of combining active and passive antenna arrays ranging from the simple side by side (SBS) configuration where all the passive and active arrays are placed inside a single radome to an intermediate configuration where the active or massive MIMO array is stacked with the high band arrays. The most compact form sees the massive MIMO array interleaved with the passive arrays such that the low band and the massive MIMO radiating layers can share common electrical and Radio Frequency (RF) components and share the physical structure of the passive arrays which acts as a heatsink for more efficient thermal management - a smaller lighter alternative than the bulky heatsinks that are typically used.

Competition and innovation in the mobile cellular antenna market are intense. Today’s BSAs now offer a complex portfolio of features and antennas needed to incorporate these technologies into the increasingly space-constrained cell tower and resist enormous stresses from the weather and environment in general.

The vendor ecosystem is rising to the challenge, with the top three vendors each accounting for double digit market shares and the top five vendors owning more than 80% of the market. As 5G rollouts continue to gain momentum, ABI Research anticipates a battle for the number two, three, and four spots in what is a very dynamic marketplace.

ABI Research’s Mobile Base Station Antennas (CA-1294) Competitive Assessment and 5G Antenna Innovations (AN-5100) Analysis Report offer a deeper assessment of the vendor ecosystem and examination of these trends.