Adapting Mobile Devices to Private LTE/CBRS Networks

The potential for many new dedicated secure and private LTE/CBRS networks is on the rise. An important question is: how will commercially available mobile devices connect on these networks?

Three elements are needed for a private LTE network:

** From John Celentano in Inside Towers – See credit at the end**

  • Access to 3GPP LTE compatible spectrum, either owned or leased,
  • Dedicated infrastructure, radio access network (RAN), evolved packet core (EPC) equipment, either owned or leased, and
  • Private Subscriber Identity Module (SIM) cards with a Private Network Profile, encryption, and Network ID.

The global inventory of LTE spectrum is becoming more and more accessible. Not too long ago, there were about 30 LTE bands; today, there are over 70 bands. In the U.S., the newly created Citizens Broadband Radio Service (CBRS) in the 3.5 GHz range delivers outstanding possibilities, value, and ecosystem (see Strategies for Securing CBRS 3.5 GHz Spectrum). At the same time, many Enterprise and industrial organizations already own LTE spectrum, or they can arrange to subordinate (lease) spectrum that is not in use from public wireless service providers.

RAN equipment (radios, antennas, cables, power) is available from many large and small radio manufacturers alike. A fit-for-purpose dedicated EPC is critical for an LTE network to be Private. Per the 3GPP standard, the EPC is the intelligence of the LTE network, managing connections, services, QoS, and all the network traffic routing.

Keep in mind that most private LTE networks will be supporting hundreds to tens of thousands of devices versus the millions of subscribers on a public cellular network. Hence, a private LTE EPC does not need to be as broad and complex.

Consequently, private LTE network RAN and EPC can be scaled down from an expensive, extensive multi-rack configuration designed for large public networks, like those supplied by multinational carrier equipment vendors.

“The comprehensive end-to-end industrial-grade private LTE RAN, SIM Profile, EPC and even private push-to-talk application needed for a private network, can be affordable secure, dedicated, and hosted on a single small server, or even on a private or public cloud service,” said Louis Lambert, Redline Communications’ SVP Marketing & Business Development at a recent Entelec Conference.

The larger question relates to what fixed and mobile devices can be used on a private LTE/CBRS network. Many of the newer smartphones, tablets, and sensors used on public cellular communications are already capable of connecting to a private, dedicated CBRS LTE network.

Device support in the CBRS band comes with programming the SIM card incorporated into every cellular phone. The SIM stores the International Mobile Subscriber Identity (IMSI) number for each public cellular carrier and its corresponding authentication code. These data allows users to connect to the public cellular network to which they subscribe but does not allow unauthorized user access. 

In earlier cell phone versions, the SIM card, which is smaller than a postage stamp, would be programmed by the cellular carrier for use on its network then inserted into a slot on the side of the phone. Once programmed, the same SIM technically could be swapped between more than one phone to work in the same network.

Single SIM cell phones can be set for use in a private LTE/CBRS network, but the programming is hosted by the public carrier. As a result, users may incur roaming charges when they move off the public network and into the specified private network coverage area.

Today’s newer devices not only support the CBRS band on the radio side but most of the new user equipment (UE) also offers two SIM cards. The SIM cards can be either embedded SIM (eSIM) integrated into the phone as well as a removable SIM. 

This dual SIM arrangement allows a mobile device to be recognized and operated both in a private LTE/CBRS network as well as on a public cellular carrier when the user moves outside the private LTE/CBRS network coverage area.

This way, the private/public network identification, and authentication codes are kept separate with no roaming requirements. Enterprise or Industrial users can now build a Private LTE/CBRS network established in one or more sites with the same network ID 

Dual-SIM operation allows users to move seamlessly between public and private networks just as we do today when we step in and out of WiFi hotspots.

In the U.S., there are already over three dozen makes and models of dual SIM smartphones, mobile routers, fixed remotes, and sensors that are CBRS-ready with two SIM cards.

By John Celentano, Inside Towers Business Editor

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