Redundant Residue Number System Assisted Multicarrier Direct-Sequence Code-Division Dynamic Multiple-Access for Cognitive Radios

A redundant residue number system assisted multicarrier direct-sequence code-division dynamic multiple-access (RRNS MC/DS-CDDMA) scheme is proposed for application in cognitive radios (CRs). Taking the advantages of both the multicarrier direct-sequence code-division multiple-access (MC/DS-CDMA) and the RRNS, the RRNS MC/DS-CDDMA has a low-complexity for implementation, a high-flexibility for reconfiguration and is robust to dynamic spectrums. Associated with the RRNS MC/DS-CDDMA, in this paper, the so-called receiver multiuser diversity aided multi-stage minimum mean-square error multiuser detector (RMD/MS-MMSE MUD) is considered for signal detection. Specifically, three types of RMD/MS-MMSE MUDs are proposed, which are the Type-I.1, Type-II.1 and Type-I.2 RMD/MS-MMSE MUDs. In these MUD schemes, the Type-I.1 MUD carries out the joint detection of all the subcarrier signals using both the observations and the channel state information (CSI) of all the subcarriers. In the Type-I.2 and Type-II.1 RMD/MS-MMSE MUDs, the embedded MMSE-MUDs are implemented subcarrier-by-subcarrier independently. Furthermore, in the Type-I.2 RMD/MS-MMSE MUD, the autocorrelation matrices used by the MMSE-MUDs are free from the CSI. Explicitly, both the Type-II.1 and Type-I.2 RMD/MS-MMSE MUDs are suitable for operation in dynamic spectrum environments. Furthermore, our simulation results show that the above three types of RMD/MS-MMSE MUDs are capable of making the RRNS MC/DS-CDDMA systems achieve similar error and throughput performance. Owing to the above merits, the RRNS MC/DS-CDDMA employing either Type-I.2 or Type-II.1 RMD/MS-MMSE MUD may be considered one of the highly promising DMA schemes for application in CR systems