When SDR meets a 5G candidate waveform: providing efficient use of fragmented spectrum and interference protection for PMR networks

Filter bank multi carrier (FBMC) is a candidate modulation scheme for the fifth generation (5G) cellular mobile broadband networks. A specific domain where FBMC offers a clear advantage over other multicarrier solutions is the efficient occupancy of underutilized and fragmented spectrum. This is due to the rich spectral containment of the FBMC technology, which guarantees superior interference protection to the primary coexisting transmissions. These
features of FBMC could play an important role for the economic delivery of 5G services in licensed and unlicensed bands.
This paper focuses on the public safety domain where existing professional mobile radio (PMR) users are planning to add broadband services at the 400 MHz band, aiming to occupy the spectral holes left by current narrowband transmissions.
In this respect an agile software defined radio (SDR) broadband downlink FBMC system, aimed at exploiting unused licensed PMR spectrum, was developed and experimentally validated. The FBMC frame structure shared key similarities
with the long term evolution (LTE) specification. Two different SDR design methodologies were used to build the realtime baseband prototype. The level of interference protection offered by a broadband FBMC system to a coexisting
primary narrowband PMR transmission was practically demonstrated and compared to that of an equivalent LTE
system. This was made feasible by evaluating the performance of a PMR terminal under different mobile channels and FBMC waveform configurations. The applicability of this work to other 5G spectrum cohabitation scenarios is discussed.
Finally, the paper highlights the need to extend the SDR design paradigm, in order to tackle the challenges of real-time baseband processing in 5G broadband cellular systems.