The Federal Communications Commission (FCC) spectrum auctions in 2015, resulted in significant rule changes to former federal spectrum bands, causing incumbent federal users to abandon, or share frequency allocations with commercial users. With these changes in licensed spectrum use and associated service rules, there is an interest in identifying new methods of frequency band sharing among users (as is the case in the AWS-3 band).
In a spectrum sharing scenario, low power uplink traffic from user equipment (UE) such as a cellphone could be susceptible to co-channel interference from a newly deployed communications system. This would lead to a compromised uplink signal for which an Long-Term Evolution (LTE) based cellphone tower (eNB) may not be able to implement a correction, resulting in an impact to link performance.
The NASCTN research project on “Advanced Co-channel Interference” addresses the need for a test methodology to quantify interference impacts between an uplink frequency division duplex (FDD) LTE link and incumbent or newly deployed communications waveforms. Immunity testing of communications systems is typically carried out in the presence of additive gaussian noise or amplitude modulated signals. However, these types of stand-in interference waveforms do not capture the dynamic nature of spectrum sharing candidate waveforms or rival waveforms that could be present in a band. Therefore, the NASCTN research test incorporated a limited set of frequency hopping interference signals that are parameterized by bandwidth, pulse repetition rate, pulse duration, jitter level, and hopping dynamics to better emulate potentially interfering waveforms.
A well-controlled conducted experiment verified the test methodology, as well as demonstrated the ability to measure LTE system response to co-channel interference based on statistically rigorous analysis of LTE provided measurands.