The challenge of deploying 5G networks inside buildings Providing high-performing, reliable 5G coverage and capacity inside large buildings is becoming a priority for enterprise CIOs, venue owners and mobile network operators (MNOs). MNO macro network signals struggle to penetrate deeply inside buildings - an effect that is exacerbated further by the higher frequency bands allocated for 5G. To overcome these difficulties, industry has sought to develop dedicated solutions for deploying 5G inside buildings. Deploying a dedicated 5G network inside a building using existing solutions comes at significant cost and has its own challenges and compromises. Fortunately, a new approach is emerging which blends the best attributes of existing solutions, while overcoming their key challenges. In-building 5G architectures -two current options Historically, there have been two alternative architectures for in-building cellular networks:
Small Cells
Distributed Antenna System (DAS)
This short paper we will present anew alternative approach based on O-RAN Shared Cell architecture that provides a combination of the best aspects of both of these options at a significantly lower cost compared with either. In-building 5G use cases - private networks v public (neutral host) networks It’s important to recognise that there are two different deployment use cases for in-building 5G coverage:
5G Private Networks
5G (Public) Neutral Host Networks
5G Private Networks (5GPN) Use dedicated radio spectrum and serve the internal wireless connectivity needs of an enterprise customer, ranging from employees with mobile phones to Internet of Things devices with 5G modems. 5GPN is an enabler for ultra-reliable, low latency use cases such as factory & warehouse automation or wireless connectivity in hospitals.
5G Neutral Host Networks (5GNHN) Extend public MNO 5G coverage deep inside buildings, to serve the public users of one or more MNOs while they are inside the building. This tends to be a strong requirement in large public venues such as transport hubs, shopping malls, concert halls, sports stadiums, and large, multi-tenanted, mixed-use real estate properties. Matching available solutions to deployment use cases Small Cells have been the de-facto choice for Private 5G Networks whereas DAS was developed in response to the Neutral Host deployment scenario.
Each of today’s options has its own drawbacks
In a Small Cells architecture, radio units are distributed throughout a building, often attached to ceiling tiles or internal walls. Each radio unit (RU) – or wireless access point - is operating on its own frequency, which must be configured carefully so as not to interfere with its neighbouring RUs. However, due to the scarcity of available spectrum, frequency re-use is inevitable within medium to large Small Cell networks and the risk of inter-cell interference caused by “over-shooting” becomes a significant risk, as shown in Figure 1. From this we see that managing “inter-cell interference” is a major challenge in Small Cell networks and leads to a huge amount of complexity in setting up and managing these types of networks.
Figure 1: Traditional Small Cells suffer from Inter-cell Interference
Also, as users move around inside a building served by Small Cells, their connectivity needs to be
handed over between adjacent cells. Cell handover is a complex mechanism and often leads to
connectivity issues. Much innovation is applied to try to tackle these interference and handover
challenges which are inherent within Small Cell networks. One will come across solutions that employ “self-organising networks (SON)” techniques, or more recently another terminology has arisen, namely the use of xApps and rApps within a “RAN Intelligent Controller (RIC)”. Inevitably, this type of complexity requiring sophisticated AI-based control often comes at a cost premium and never guarantees to eradicate the problems it aims to solve.
Also, in a traditional Small Cells architecture, the entire radio functionality is duplicated in every radio
unit making each radio relatively expensive and power-hungry.
Conversely, in a DAS architecture the radio signals from a single cell (served by a single macro base
station) are divided up and distributed within a building. In this case, all of the RUs are operating on the same frequency, thereby eliminating inter-cell interference within the venue. Distributing and
recombining signals to/from user equipment is the task of the DAS equipment. At significant expense, a macro base station and associated backhaul connectivity is deployed at the venue by each MNO wishing to provide its users with coverage. The DAS system connects to the radio frequency (RF) interface on each MNO base station, attenuates and then processes the RF signals, converting them into digital signals for distribution over copper or fibre cabling to/from the multiple RUs that are deployed throughout the building.
The problems of inter-cell interference and handover failure so endemic within a Small Cell network are not prevalent in a DAS solution, because DAS operates as a “single cell” and therefore there are no intercell interference or handover issues arising.
Figure 2: Traditional DAS System - "donor base stations" are costly and energy inefficient
On the downside, DAS can be an expensive, power-hungry architecture that arose organically out of pragmatism rather than perfectionism. Taking a regular MNO-grade outdoor macro base station (at considerable expense) and deploying it in the basement of a large building (see Figure 2) and then fitting attenuators to reduce the output signal for internal distribution generates large amounts of heat, wasting most of the energy generated by the base station. Energy efficiency is becoming a prime concern for enterprise CIOs who are coming under increasing pressure to find innovative solutions to maintain compliance with their organizations' environmental policies.
Fortunately, a third approach is now emerging: O-RAN Shared Cell
The Open Radio Access Networks Alliance (O-RAN Alliance) has standardised a new architecture known as O-RAN Shared Cell to address the abovementioned shortfalls of Small Cells and DAS systems, producing an alternative hybrid approach that exhibits the “best of both worlds with the downsides of neither”. Within this new architecture, O-RAN has defined a new network element – the Fronthaul Multiplexer (FHM) – which provides the DAS-like signal copying and combining functionality of a DAS system. However, instead of being installed at the analogue RF interface of a conventional macro base station, the FHM is inserted into the digital open fronthaul interface employing the 7-2x Split defined by O-RAN. By integrating at the open fronthaul interface, O-RAN Shared Cell reduces the cost and energy consumption of the donor base station typical of a large DAS installation, while offering the cost and manageability advantages of highly simplified remote radios compared with traditional small cells. A full comparison of the benefits of O-RAN Shared Cell versus traditional Small Cells and DAS is shown in Figure 3.
Figure 3: O-RAN Shared Cell presents a new option for in-building 5G - best of both worlds
In-building 5G using O-RAN Shared Cell - the best of both worlds
The new O-RAN Shared Cell architecture exhibits the functionality of a DAS system without its costly and power-hungry architectural drawbacks. Meanwhile the O-RAN Shared Cell approach eliminates the intercell interference and handover issues that compromise and complicate the management of an enterprise Small Cell network. Furthermore, by employing the O-RAN Split 7-2x interface, the RU design can be massively simplified compared to a typical Small Cell, thus reducing drastically the unit cost and therefore the bill of materials for the solution cost.
About Antevia Networks
Antevia Networks design and develop 5G in-building Solutions for enterprises. Antevia Networks Ltd was formed in March 2021 and is based in Reading, UK, with research and development teams in Vancouver, Canada. Antevia’s leadership team have significant experience in 2G, 3G and 4G in-building coverage and is using new Open-RAN based technology to pioneer a new class of in-building 5G coverage and capacity for enterprises.