Multi-Antenna Technologies for Unlicensed Private Network Deployments

With the rapid growth of data traffic, Mobile Network Operators (MNOs) are looking for new ways to cope with their soon-to-be-overloaded networks. One promising strategy is to offload their best-effort traffic to unlicensed and shared spectrums, using technologies such as pro Long-Term Evolution-Wireless Local Area Networks (LTE-WLANs) Aggregation (LWA) and Licensed Assisted Access (LAA). For the LWA technology, MNOs are required to own WLANs and reuse their large numbers of installed WLAN Access Points (APs) to assist cellular communications. However, according to ABI Research’s latest Wi-Fi Customer Premises Equipment SOHO/Consumer and Enterprise Market (MD-WLEQ-163) Market Data, 95% of MNOs today do not have Carrier WLANs; therefore, the native cellular-based LAA technology becomes their preferred option. Due to the dynamic spectrum access nature of both technologies (e.g., licensed access can take over when unlicensed access fails), communication reliability can be guaranteed.

On the other hand, to seek more cost-effective network solutions, many industrial enterprise users in collaboration with MNOs or Communications Service Providers (CSPs) set out to build private networks that operate solely in unlicensed and shared spectrums. Given the broad range of advanced radio access technologies operating in the spectrums, guaranteeing seamless inter-technology coexistence, improving communication reliability becomes a pivotal issue. Multi-antenna technologies, such as Coordinated Multi-Point (CoMP) and massive Multiple Input, Multiple Output (MIMO), combined with Time-Sensitive Networking (TSN), are envisioned to boost the standalone unlicensed and shared spectrum use. However, in compliance with the strict regulatory rules for fairly sharing the spectrum, e.g., Listen Before Talk (LBT), can these technologies offer real economic benefits to enterprise verticals?

As it considers public cellular network deployment scenarios, MIMO beamforming technology is commonly adopted by MNOs at base stations to improve communication performance for User Equipment (UE) located in a cell center without much interference being generated from the adjacent cell(s). However, if a network is deployed densely, throughput improvement is insignificant for UE near the cell edge due to inter-cell interference. By allowing clustered base stations to serve single UE cooperatively, CoMP technology is well-positioned to solve the inter-cell interference problem. Depending on capacity constraints on backhaul links and latency requirements, the clustered base stations actually form a distributed MIMO system in a virtual cell to achieve different levels of network performance. As the technology is well cognized in the public network domain, CoMP’s unique feature can also be beneficial for industrial enterprise verticals to build private cellular networks, especially for using unlicensed and shared spectrums. Taking manufacturing as an example, typical implementation scenarios include remote mobile production control and smarter logistics, where multiple APs can be connected simultaneously to ensure robust connectivity and avoid interference.

To guarantee fair use of unlicensed and shared spectrum, standardization bodies and relevant regulators designed strict radio access rules—e.g., LBT. This discontinuous transmission strategy does not allow simultaneous transmissions between two different technologies, resulting in suboptimal network operation with reduced data rate performance. Multi-antenna technologies can overcome this hurdle by placing nulls in certain radiation directions or channel subspaces where other spectrum access technologies are operating. In this case, the AP that performs multi-antenna technologies does not need to listen to the directions or channel subspaces during the LBT phase, therefore resolving the multi-technology coexistence problem. For an enterprise company relying on multi-technology to serve diverse connectivity requirements, this implementation strategy offers a lot to the factory floor while enabling the guaranteed performances. Moreover, combined with TSN the technologies can help further improve communication reliability by introducing synchronized spectrum access.

The performance gains of the technologies discussed above come at the cost of stringent hardware requirements. Specifically, to enable multiple APs to serve a single UE cooperatively, high capacity backhaul links with ultra-low transmission delays between APs are required. Apart from that, UE also needs to be specifically designed so that it is capable of identifying different APs’ IDs and performing relative processing algorithms. Moreover, spatial awareness via multi-antenna technologies relies on performing accurate estimations of channel links between the AP and the devices from other radio access technologies. All of these will incur an overhead and generate a high Total Cost of Ownership (TCO) for the industrial enterprise users to build their private networks.

In consideration of the above challenges and the current stage of technology evaluations, ABI Research believes the multi-antenna technologies have the potential to help industrial enterprise verticals deploy small or medium-size private networks with moderate data traffic and latency requirements. To fully exploit the advantages of these technologies and pave the way to access their transformative benefits, however, industrial enterprise users and their network deployment partners still need to clearly understand the cost and carry out comprehensive analysis of Return on Investment (ROI) before the network is deployed. For example, they need to clarify the exact reliability levels they are expecting and what the additional cost of infrastructure deployment and network operations will generate to meet the reliability requirements.

The promotion of multi-antenna technologies is a long-term initiative. With more successful advanced technology development and a broader device ecosystem, the industrial enterprise verticals in collaboration with the network deployment partners will become confident to build cost-effective and highly performed private networks in unlicensed and shared spectrums.