Low SINR Synchronization for the DARPA Spectrum Challenge Scenario

The DARPA Spectrum Challenge (DSC) established a problem space that created a need for radio synchronization algorithms functional in environments with low signal-to-interference-plus-noise ratio (SINR). For the final DSC competitive event, forward link receiver SINR was commonly less than 0 dB and feedback link receiver SINR could be less than 5 dB, both in a 5 MHz channel. For the preliminary DSC competitive event, both forward and feedback link receiver SINR could be much less than 0 dB. Additional constraints led to the implementation of synchronization algorithms in accordance with the GNU Radio framework. As a result, the algorithms are written in software that executes on general-purpose Intel processors and requires minimal computational complexity. Additionally, the synchronization should not limit system error rate performance to ensure that the capability of implemented receiver signal processing is fully realized (e.g. Error control coding). A possible solution for the DSC competitive event includes time division duplexing (TDD) for channel access with a high data rate forward link and robust feedback link for automatic repeat request (ARQ). In support of this approach, multiple synchronization techniques were implemented. In this work, we present one of our implementations, a non-data aided symbol synchronization method that can be employed for both links. This paper includes a description of the synchronization algorithm along with its simulated and implemented performance for scenarios applicable to the DSC.