Noncontiguous OFDM for Future Radio Communications

The Non‐contiguous Orthogonal Frequency‐Division Multiplexing (NC‐OFDM) technique is considered as a strong candidate for air‐interface definition in the future communication systems with cognitive capabilities. It possesses sufficient spectral agility in order to facilitate the transmission of data from unlicensed‐system users (Secondary Users (SUs)) across several fragmented frequency bands simultaneously even in the presence of licensed‐system users (Primary Users (PUs)) signals, thus, resulting in an increase of spectrum utilization. In addition to achieving a required level of Out‐of‐Band (OOB) emission power within a given spectrum mask, an SU transmitter must be capable of tailoring its spectral characteristics dynamically in order to avoid interference with the dynamically changing incumbent PU transmissions. Windowing (WIN) is a method usually applied to the OFDM symbol time‐domain samples containing Cyclic Prefix (CP). In the adaptive symbol transition (AST) method, similarly to WIN, the time‐domain samples in the transition region between consecutive symbols are chosen in order to minimize the OOB power.