Liability and Public Safety Broadband Networks

The objective of this paper is to describe and analyze the need for a regulatory framework that will enfranchise commercial wireless operators to share wireless networking infrastructure with Public Safety (PS) transmissions. There exists a liability concern by commercial operators in the case of a PS communications failure. We show that this proposed policy initiative is driven by a compelling technical need with examples of adjacent band interference between commercial 700 MHz LTE signals and PS 700 MHz LTE signals. Beyond the wireless concern outlined here, the need to mitigate liability concerns over commercial networking infrastructure is applicable to other areas of networking and we will dedicate a portion of this paper to illustrate this need. We also review historical PS service failures or interference issues to present relevant legal and business consequences.In testing with live systems, it has been observed that when receiving weak PS LTE (Band Class 14) signals that the User Equipment (UE) device struggles is close proximity to adjacent channel LTE base station (adjacent Band Class 13). None of these systems are operating outside of specifications or outside of their specified legal limits. This phenomenon occurs when the PS signal is weak, from a distant transmitting base station, and the UE receiver is close to an adjacent channel transmitter.The build-out of a commercial carrier will always be denser than that of the PS network for capacity reasons. Commercial operators have the business need and the budget to adopt a higher density of cells provide increased data rates and capacity. LTE networking technology will enable small cells, at a greater density, than we have seen with previous generations of cellular technology. The PS LTE network will not have the budget or the capacity motivation to build out cell sites as aggressively. These factors lead to an increase probability that a PS user will experience a weak PS LTE signal in the presence of a strong adjacent channel signal.In today’s networks, there are already a large number of existing environments that realize this scenario. Commercial LTE operators have invested heavily in indoor distributed antenna systems (DAS). As a result, these operators have strong signals in many indoor public spaces such as airports and sports stadiums. This equipment is part of their network infrastructure. PS signals are not always carried on the DAS. This is in large part due to the reluctance of wireless operators to carry PS signals from a perceived liability in the case of a communications failure. In these cases, the PS base station may be located outside of the facility attempting to penetrate the building for coverage. This PS LTE signal will be weak while the adjacent channel LTE signal will be strong as it is carried by the DAS.In this paper we will show through simulation that as the density of the PS network diminishes relative to the density of the adjacent channel LTE network that the probability of reduced throughput for the PS network will increase. We are planning live measurements of a PS band class 14 device in the presence of strong out band LTE interference to further characterize this effect. We will also compare the build out philosophies of the PS and commercial LTE networks to illustrate the likelihood of the phenomena. Possible solutions are to enfranchise wireless operators to admit and incorporate PS signals onto portions of their radio access network equipment. A second solution is to mandate improved adjacent channel receiver specification for PS user equipment. The full solution may be a combination of both as we will show.