Implications of Recent Spectrum Sharing Efforts within the U.S.

Recent efforts within the FCC and the NTIA focus on the opportunity of spectrum sharing as a means to open additional spectrum in a useful frequency range for wireless broadband services. A variety of technologies have made such coexistence models now feasible in ways previously difficult or impossible. This includes such concepts as geo-location databases, sensing and interference tolerance. These technologies allow for denser packing of services, hence spectrum policy can be more creative with sharing proposals and achieve increased spectrum utilization. This type of sharing has moved from academic thought to policy decisions in several recent rulemaking efforts, including the FCC Docket 12-354 which proposes a sharing regime for the 3550-3650 MHz band. The opportunities surrounding 100 MHz of shareable spectrum that is focused on small cell applications is exciting. This band presents a unique opportunity for the FCC, NTIA, DoD, academia and industry to experiment with novel sharing techniques from both technical and administrative perspectives. Of particular interest in this band is finding ways for commercial systems to coexist with radar systems. Therefore, it is imperative to develop appropriate sharing policy that supports both incumbent radar protection and spectrum utilization by small cell devices. One vital aspect of developing appropriate spectrum sharing policy is accurately modeling the interference potential between services. The focus of this work is modeling of the 3550-3650 MHz band spectrum sharing scheme, which entails the interaction between high powered and interference sensitive radar systems and low powered and interference tolerant small cell devices. Specifically, ship-borne radar exclusion zones were analyzed and compared to modeling work completed by the NTIA. Also, modeling of aggregate interference impacts from small cell devices to ship-borne radars was completed. The intent of this research is to demonstrate that appropriate interference modeling techniques support an increase in modeling granularity and accuracy therefore supporting more granular and informed policy making. The methodology used in the modeling exercises employed a mix of accepted NTIA techniques as well as introducing appropriate new methods that better enable the modeling of small cell system architectures. The novel methods used in this research consist of using higher resolution propagation modeling techniques for interference potential determination as well as site-specific aggregate impact analysis of small cell devices upon radar systems. The research found that ship-borne radar exclusion zones can be significantly reduced in ship-borne radar operation areas. In addition, it was found that there was insufficient information provided by the U.S. government in regards to radar equipment specifications to accurately model interference potential, therefore reducing the ability of the policy-maker to achieve appropriate sharing policy. Also, it was found that the ITM propagation model does not use land use data or building data along radio propagation paths, which is necessary for accurate modeling of small cell network deployment cases. Therefore, ITM is insufficient for modeling of radar and small cell system interaction studies. Correspondingly, to accurately model small cell systems in a site-specific manner, the use of higher resolution geographic data and a propagation model that can utilize this data is necessary. It was also found that small cell device loading for aggregate interference impact analysis can be accomplished through use of census, land use and building data and can be done in site-specific manner. This loading methodology can support more granular interference potential data that can better shape spectrum policy work.Finally, it was found that the advances in technology that support spectrum sharing discussed previously should not be bottlenecked by legacy interference modeling techniques when more granular methods are currently available.