CTO Blog: Vehicular Network System (VNS)

October 21, 2015

UPDATE (October 2015) - FirstNet, in cooperation with the PSAC Executive Committee, has determined that the use of the term Mobile Communications Unit (MCU) might be confused with some existing or traditional nomenclature in the public safety arena. Thus, we will be using the term Vehicular Network System (VNS) in future blog postings and the final RFP. Note that they both refer to the same concept of a set of equipment that can be present in traditional first responder vehicles and provide range extension for the terrestrial network, as well as standalone network support when out of range. The basic architecture and functions described in the original MCU blog remain the same. Only the name is being changed to avoid confusion. As such, an updated blog will be posted based on feedback and input from the PSAC and public safety stakeholders.


The FirstNet Office of the Chief Technology Officer developed the following blog on the Mobile Communications Unit (MCU) and its role in incident deployment and coverage extension options. FirstNet anticipates that the MCU and other alternatives will play a role as coverage extension tools within the deployment of the nationwide public safety broadband network.

Since FirstNet was created under the Middle Class Tax Relief and Job Creation Act of 2012 (the Act), it has recognized that providing more network coverage for states and territories than commercial operators currently provide presents unique problems. While there are many deployable alternatives or solutions, such as High Power User Equipment (HP-UE), they have shortcomings.

The Mobile Communications Unit (MCU) is a product concept meant to address the needs of remote first responders when they are outside of terrestrial coverage. Figure 1 shows how the MCU relates to other alternatives, including deployable aerial communications architecture (DACA) such as balloons or drones, cell on light trucks (COLTS), cell on wheels (COWs), and system on wheels (SOWs), with respect to coverage and capacity:

There are two features that are key to the MCU. First, MCUs are built into first responder vehicles that are used every day, so MCUs are there when first responders need them, without calling for a conventional deployable to be sent to the incident. Second, the MCU also supports local and remote communications when first responders are outside of terrestrial coverage. MCUs can coordinate local communications if the size of the incident expands and additional first responders are needed. MCUs also have the flexibility to transition to support longer incident periods if required. Figure 2 shows how the MCU relates to other alternatives with respect to response time and incident duration:

MCU Technology Elements

The MCU concept is still being addressed by industry players, but it would likely comprise technologies such as:

  • In-Vehicle Router (IVR) – when the MCU is within terrestrial network coverage, it acts like every other IVR, using the terrestrial network as a wide area network connection for local area communications (which may include Land Mobile Radio (LMR) modems too).
  • Satellite modem and antenna – once the MCU is fully outside of terrestrial network coverage, it can automatically switch over to the satellite modem from the terrestrial network modem(s). New satellite technologies can improve some of the performance, physical installation, and cost of including a satellite option. A rugged antenna design which can withstand extreme environmental conditions will be key to the MCU platform.
  • Local eNodeB and antenna – when the MCU is outside of LTE coverage or when additional local coverage is needed, the MCU can automatically act like a remote base station to other users.
  • Local Evolved Packet Core (EPC) elements and applications –the level of EPC functionality and application content will vary depending on design and use cases to be support. New technologies in the area of compact EPC platforms and local application servers will impact the evolution of the MCU roadmap.

Note that there are minimal, if any, portable device (User Equipment, or UE) implications; in ideal scenarios the UE sees the MCU as just the regular network, and the arriving first responders to an incident operate their devices as they would normally.

Potential Functional Architecture

Putting these elements together, a functional architecture might look like figure 3:

FirstNet is currently coordinating with organizations researching deployable platforms and working to ensure that the MCU is prioritized as appropriate to support commercial availability of this critical platform. In addition, there are a couple of relevant standards efforts within 3GPP that FirstNet believes could be relevant to the MCU concept.

These include:

  • Isolated E-UTRAN Operations for Public Safety (IOPS, 3GPP TS 22.346) of Release 13 - Support for an isolated eNodeB configuration
  • Proximity-based Services (ProSe, 3GPP TS 23.303 and TS 23.703) of Releases 12 and 13 – Support of device to device (D2D) communication mode commonly called direct mode

These critical 3GPP development activities will be monitored closely to determine when support should be made available within the MCU platform.

The picture below illustrates the type of vehicle which could house an MCU and allow for the mounting of the antennas discussed.

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