A Two-Level Control Channel Scheme in Cognitive Radio Networks Based on Cascaded Space-Time Interference Suppression

We propose a two-level control channel scheme to solve the setup problem of cognitive radio networks (CRNs). The scheme enables transmission of control bits between cognitive users (also referred to as the secondary users (SUs)), without introducing interference to the primary users (PUs). First, a hybrid waveform with low power spectrum density is utilized to establish a lower level control channel (LLCC) for all SUs. Limited by the channel capacity, SUs can only shake hands and exchange low rate control bits with each other via the LLCC. Once any two SUs find enough common frequency band in their spectrum-hole lists, the waveform can be reconfigured to setup a higher level control channel (HLCC) with higher bit-rate between them. Thus, spectrum information can be synchronized in CRN via opportunistic control channels, and the coexistence between PUs and SUs is guaranteed. We also present a cascaded space-time interference suppression algorithm for LLCC receiver, which can keep SU from narrow band interference transmitted by PU. The numerical results obtained from MATLAB simulations demonstrate that the interference from PUs located at various directions can be suppressed well within a wide range of signal-to-interference ratios.