A Novel Method of Distributing the Spreading Sequence to Sub-Carriers in MC-CDMA

In Multi-carrier Code Division Multiple Access (MC-CDMA) systems, methods of distributing the spreading sequence to sub-carriers (spreading method) include discrete spreading (DS) and continuous spreading (CS), which have the superiority in obtaining frequency diversity and reducing MAI respectively, but both overall evaluations are not ideal. A novel method "twice spreading (TS)" is presented by combining DS and CS. In TS, the CS in which the sequence is distributed to sub-carriers next to each other is used to keep orthogonal among different users, then the DS in which the sequence is distributed to sub-carriers with a certain distance to each other is used to obtain frequency diversity. Theoretical analysis and Monte Carlo simulation results validate that TS has better trade-off performance than traditional method.