Many national and international Public Safety organizations have endorsed or are considering LTE as the next generation technology either to augment their existing systems, or to provide a future migration path. Ensuring the continued ability of Public Safety users to communicate within mission critical situations is of the utmost importance even when the fixed infrastructure is compromised.
The IOPS feature as specified in the Stage 1 normative requirements  provides the ability to:
Maintain a level of communications for Public Safety users, via a fixed infrastructure eNB (or set of connected eNBs), following the total loss of backhaul communications.
Create a serving radio access network without backhaul communications from a deployment of one or more standalone deployable IOPS-capable eNBs forming a Nomadic EPS. A Nomadic EPS is intended for Public Safety use providing coverage or additional capacity where: 1) coverage was never present (e.g. forest fire or underground rescue) or 2) where, for example, due to natural disaster coverage is no longer present.
Create a serving radio access network, with and without backhaul communications, from a deployment comprising a combination of eNBs and deployable IOPS-capable eNBs.
Maintain or create a level of communications for Public Safety users in the scenario where set of eNBs or deployable IOPS-capable eNBs is without normal backhaul communications but has been provided with an alternative (non-ideal) limited bandwidth backhaul.
The Isolated E-UTRAN may comprise a single or multiple eNBs. An Isolated E-UTRAN comprising multiple eNBs, with connections between the eNBs, can provide communication between UEs across a wider area of coverage than can be provided by a single isolated eNB. The UEs in the coverage of the Isolated E-UTRAN are able to continue communicating and provide a restricted set of services supporting voice, data and group communications, to their Public Safety users.
An Isolated E-UTRAN may comprise a deployment of one or more deployable IOPS-capable eNBs. An Isolated E-UTRAN derived from deployable IOPS-capable eNBs exhibits similar behaviour to an Isolated E-UTRAN derived from eNBs including: support for Public Safety UEs in the coverage area, communication between deployable IOPS-capable eNBs and support for limited backhaul connectivity.
Furthermore an Isolated E-UTRAN may also comprise a combination of eNBs and deployable IOPS-capable eNBs where additional capacity or coverage is provided by deployable IOPS-capable eNBs in an Isolated eNB infrastructure network.
Realization of the IOPS feature must be able to manage the potentially dynamic nature of an Isolated E-UTRAN where:
Deployable IOPS-capable eNBs or eNBs form, join and leave the Isolated E-UTRAN in a secure manner;
UEs join and leave the Isolated E-UTRAN.
An Isolated E-UTRAN is characterized by having no, or a limited, backhaul connection. In particular, the IOPS feature enables services to be provided to Public Safety UEs in the following backhaul scenarios:
Limited bandwidth signalling only backhaul;
Limited bandwidth signalling and user data backhaul.
The architecture of a network for isolated operation of E-UTRAN in Public Safety is described in TR 23.797
and TS 23.401
, Annex K.
From a security point of view, it has been decided to have a USIM application dedicated exclusively for IOPS mode.
LTE security procedures are followed for IOPS networks as described in TS 33.401