For most of the non-conventional scenarios that will be described in this section, it would be extremely useful if the user could just authenticate to the temporary network by using his commercial UE without needing to establish a connection with its home network first, in order to verify the USIM card credentials. However and after much research, it was confirmed that such a scenario is not possible to deploy (atleast according to the 3GPP’s specifications for LTE). It would only work if the temporary network’s database already contained the user’s USIM card information. This is because of LTE’s mutual authentication procedure, described in Appendix A, which basically consists on a comparison of keys generated by the UE and the network - if both groups of keys aren’t exactly the same, the procedure terminates -, followed by encryption and integrity protection algorithms.
There’s a specific type of attachment, named Emergency Attach, which authorizes the UE to attach to the network without authentication, but it is only allowed for IMS emergency calls. This is also explained in Appendix A. Any other functionalities are blocked, unless the mutual authentication procedure is completed.
Nevertheless, a workaround is possible and a connection to the LTE network can still be provided to nearby users, as is described in the next section.
4.3.1 Sharing the LTE network via Wi-Fi hotspot
A software-defined radio implementation of the UE, interfaced with an RF front-end platform, is attached to the created LTE network with access to the Internet. The UE is now able to share its LTE connection with the surrounding devices, either by Ethernet or a Wi-Fi hotspot, as in Figure 4.4. This way, only one UE is required to complete the mutual authentication procedure, while providing free Internet coverage to a specific location via Wi-Fi.
Figure 4.4: Non-conventional LTE deployment scenarios architecture. All of the subsequent scenarios will use this network sharing method.
It is common that in catastrophe scenarios, e.g. hurricanes and wildfires, damage is in- flicted to the existing telecommunications systems (as in Figure 4.5) and the coverage must be re-established as soon as possible, either for emergency purposes or ordinary communica- tions. The same can be said for war scenarios, where radio towers might be destroyed, for example, and communications become unavailable. The existence of an easily deployable UE that shares a free Internet connection in a certain area via a Wi-Fi hotspot would be very useful.
A possible implementation architecture is shown in Figure 4.4. In terms of radio configu- rations, the connection between the UE and the base station can be cabled, avoiding any air interface losses but requiring them to be close to each other, or wireless, using antennas.
4.3.3 Remote locations
There are still locations on the globe where no regular mobile network operator coverage is available. These can be third world countries, on board of cruise ships or just sporadic events in remote places. A temporary or even seasonal existence of a LTE mobile network that provides Internet access would be very interesting from an economic point of view.
A possible implementation architecture is shown in Figure 4.4. For remote or rural lo- cations, the utilization of FDD frequency band 31 should be explored. It is the lowest LTE frequency band on the spectrum, 450 MHz, which means that the coverage it provides is bigger than any other bands. The only disadvantage is that it only allows bandwidths up to 5 MHz. Band 31 is in the same frequency range as one of the Terrestrial Trunked Radio (TETRA) bands in Europe, used for emergency services.
4.3.4 Opportunistic use of TDD in frequency bands licensed for different purposes
Certain frequency bands are licensed for different purposes than LTE transmission. This is the case of TDD band 40. Such a premise should be taken advantage of, so the transmission on the TDD band 40 and similar frequency bands should be tested. Once again, the architecture of the system could be the one in Figure 4.4.
4.3.5 Unlicensed spectrum and custom frequency bands
LTE-Unlicensed (LTE-U) was created by cellular network operators in order to find a solution for the increasing demand in mobile data. The idea is that it offloads data traffic by accessing the unlicensed 5 GHz frequency band [LMRZ17].
Considering the flexibility of the UE implementation, LTE in the unlicensed spectrum or any other custom frequency bands are a possible and a non-conventional scenario that could be implemented. The proposed architecture is the one in Figure 4.4, with either radio configurations.
The two last proposed scenarios are the most conventional amongst the group.
4.3.6 Investigation infrastructures
For a different scenario, there could also be investigation infrastructures with the need for open-source and modular platforms that grant an elevated level of configurability and observ- ability of the LTE network system (e.g. university campuses with platforms for demonstration and validation of new systems and telecommunication services).
One of the possible architectures would be the same as in Figure 4.4, but considering it is a scenario for investigation purposes, it will be subject to change.
4.3.7 Network reinforcement
This is a very conventional scenario, when compared to the previous ones. A reinforcement of network coverage and signal might be required. Temporary installations for event support, such as conferences (in Figure 4.6), gatherings, festivals and sport events, where the number of users on the network is greater than usual and the existing deployments might not be enough are one example. Other possibilities are hotel rooms, where hotel owners might be interested in reinforcing the network coverage of their establishments.
Figure 4.6: Conferences, where a signal reinforcement might be required.
The proposed architecture for this scenario is also the one in Figure 4.4, using a cabled setup in between the UE and eNB and then sharing the network through the Wi-Fi hotspot. A cabled setup is preferred, as the air interface in such locations is surely overcrowded.
In this chapter, the framework-related deployments were presented, being that only one of them was relevant to this chapter, the software-defined radio UE implemented in a General Purpose Processor (GPP). Then, the network architecture to be used in all of the presented scenarios was defined, with differences only on the radio setup level. To finalize, several non-conventional LTE deployment scenarios were discussed.
In the following chapter, some of these scenarios will be implemented and explained in a more detailed way, along with the used network configurations and parameter changes.
In this chapter, the implementation of the setup is described. It begins with an introduc- tion showing the block diagram of the network components and their radio configurations, in section 5.1. Then, each network component is described: the UE in section 5.2, the eNB in section 5.3 and the EPC in section 5.4. The subsequent section 5.5 contains information on how the obtained LTE mobile data is shared by creating a free Wi-Fi hotspot.