Abstract
One of the major challenges to cognitive radios is the synchronization of distributed radios onto the same spectrum white spaces which vary in time and space. In this paper, we propose a frequency-hopping spread spectrum transmission scheme which works reliably without any a priori handshaking assumption. Each cognitive radio independently detects white spaces, and then selects one of them to transmit or receive signals according to a pre-defined frequency hopping pattern. While exploiting the reliability of the white space detection capability of cognitive radios, the new scheme is robust to even large detection errors. According to the accuracy of the spectrum sensing, both the secondary data rate and the interference to primary users can be optimized by adjusting the spreading gain. Its performance is analyzed and demonstrated by simulations.