IBC Solutions Explained

Coverage refers to the availability of a cellular signal throughout an area. An area is considered ‘covered’ when signal is adequate.

A 4G or 5G signal is ‘available’ when it is of an adequate strength to be reliably detected by the mobile device. Signal strength is measured in RSRP, in dBm, and is a negative number between about -50 and -130 dBm. 

• Signal is considered adequately strong when it is above about -100 dBm. 
• Signal below -100 dBm will result in the mobile device operating with reduced capabilities, such as poor video call quality and low data speeds. 
• Signal below -110 dBm will cause a noticeable reduction in voice call quality, and internet speeds may become frustratingly slow. 
• Signal below -120 dBm voice calls will be extremely unreliable, and internet may not be available at all. 
• Most handsets will not establish any connection to the network at strengths below about -128 dBm.

Coverage can be provided by installing an IBC that strengthens the signal. Often these systems will use an antenna placed outdoors where a strong and clean signal can be received from the local cell tower. Repeaters are then to amplify this good quality signal so that it can be output over antennas placed throughout the building.

Capacity describes a 4G or 5G signal’s ability to handle ‘traffic’, which is generated when user sends or receives data. This can be making a voice call, accessing a web page, watching YouTube, etc. The term ‘traffic’ comes from the analogy where if a signal was thought of as a highway, data would be the vehicles travelling from the transmitter to the receiver. This is an important analogy because it helps us understand that a signal is a shared medium, where all devices are sharing the one signal. If too many users generate traffic, the highway can become congested.

Just like a highway, Capacity can be increased by adding more ‘lanes’, which in the context of cellular networks is equivalent to adding additional frequency bands to the cell tower. Capacity can also be increased by building new cell towers, which using our analogy would be equivalent to building a separate highway serving a specific area.

IBC systems must be designed by carefully considering the Capacity of the surrounding cell towers. In order to prevent a tower from being overloaded, an IBC design may be rejected by the network operator during the approval process if it results in an undue number of users being pushed onto one tower.

Powertec manages this concern by requesting the typical occupancy and foot traffic of the building, so that a system can be developed that has enough ‘lanes’ to support the expected traffic, or that implements a dedicated base station to create a separate ‘highway’ just for the users within the building.

There are two main types of IBC systems, which are classified based on the way they provide Capacity.

Off-Air IBC

Off-Air IBC are those systems which obtain their input signal from the local cell tower. These systems are found in small and medium sized buildings, such as medical facilities, office buildings, schools, aged-care facilities, apartment buildings, factories, and warehouses.

Typically, one or more antennas are mounted on the outside of the building where signal is naturally stronger and cleaner, which are then connected by cables to a group of repeaters placed inside the building. The job of the repeater is to boost the signal and output it over antennas strategically placed throughout the building.

These are highly flexible systems which can be built using the same technology to cover areas as small as a single room, to as large as a major logistics warehouse.

These are simple systems that do not modify the signal captured from the cell tower. Capacity is unchanged from what is available in the area. This means that an Off-Air IBC must share Capacity with hundreds or potentially thousands of other users in the surrounding area.

During the design phase, Powertec will use the occupancy / foot traffic details provided by the client combined with a typical usage profile based on the building’s function to determine the number of frequency bands to implement in the building. While this means there is no single figure used, the number of users per frequency band per network is typically between 50 and 125.

Where occupancy or foot traffic significantly exceeds this range a solution which provides dedicated Capacity is required.

Passive

For small to medium building sizes, Off-Air IBC are constructed using a Passive topology. This is the most simple and economical approach to resolving poor Coverage. Groups of repeaters are located throughout the building, each connecting to an externally mounted antenna. Internal antennas are typically placed every 20 to 40 metres, and connected back to the repeater using a large span of coaxial cable. This coaxial cabling is branched and split using Couplers which equalise the output power at each internal antenna, ensuring a balanced distribution of signal across the entire design area.

Passive systems can become less practical for very large building sizes, where large amounts of repeaters and roof mounted antennas become required. Coaxial cable is not well suited for large spans, as signal power is lost on a per-metre basis.

QUATRA

The Cel-Fi QUATRA 4000e system is a popular example of an Off-Air IBC repeater system. Its popularity is due to its Hybrid topology, where the transmit and receive functions of the repeater are split between a Network Unit (NU) and its Coverage Units (CUs).

The Network Unit’s role is to connect to the externally mounted antennas and encapsulate it into an intermediate digital signal, so that it can be sent to multiple Coverage Units over Cat6 Ethernet cabling. Each Coverage Unit then strips off the digital encapsulation so that it can be amplified and output as a full strength 4G-5G signal.

QUATRA is a multi-operator system. The Network Unit has one input connection per Mobile Network Operator and all input signals are combined onto a common output signal.

QUATRA 4000e is the go-to solution for medium to large-sized facilities. The key differentiator and advantage of QUATRA is its hybrid topology. Connection between the NU and CU is digital and uses Cat6 cabling, meaning the units can be separated by 150 metres (up to 2 km with a QFRE extender) without any loss.

By using standard Cat6 Ethernet cabling as the ‘arterial’ interconnections, QUATRA is more future-proofed than Passive systems as an upgrade can be performed by replacing the CUs without having to re-run large spans of cable.

Dedicated IBC

A Dedicated IBC solution appears very similar to an Off-Air IBC, in that it too consists of a series of antennas, cables, and transceivers. The primary distinction is that rather than obtaining their input signal from a local cell tower using a roof-mounted antenna, the cell tower hardware is installed inside the building itself. These types of systems are typically found in large high-rise buildings, shopping complexes, major hospitals, and stadiums.

As the name suggests, a Dedicated IBC provides dedicated Capacity as the building effectively has an entire cell tower to itself. Using the earlier analogy, this is the equivalent to constructing a new ‘highway’ just for the building. The Radio Units used in these systems are also significantly higher in output power than repeaters, meaning the system can cover significantly more building levels or floor area.

A dedicated fibre optic backhaul is typically installed by the Mobile Network Operator, enabling higher data speeds than would otherwise be available with a shared solution.

This type of solution requires a more substantial design process because the presence of this new ‘cell tower’ inside the building has the potential to adversely affect other users in the immediately surrounding area. Extensive planning must be undertaken to ensure there are clear boundaries (called handover zones) between the signal provided by the building’s base station, and signals provided by other cell towers. This makes sure that in any given area there is one signal that is ‘dominant’, and each device can clearly tell which tower it must connect to.

As the design must be closely scrutinised by the operator, the lead time on the implementation of a Dedicated IBC solution is significantly greater than an Off-Air IBC solution. The operator must also supply and install both the base station hardware and backhaul connection to their Core Network, the building owner is required to pay operator connection fees, which are typically several hundred thousand dollars per network.

For Australia, the different IBC solutions can be roughly compared below.