The Constraints Satisfied to Suppress the Interferences Caused by MB-OFDM UWB Based Cognitive Radio Systems; One Type of Low Density Parity Check(LDPC)-like Modulation Scheme

A mathematical expression of side-band interferences caused by sub-carriers of multi-band (MB)-OFDM UWB based cognitive radio is derived. Based on this expression, the constraint relationship among transmitted symbols, which is satisfied to suppress the interferences, is obtained. Combined with this constraint, the design process of a type of LDPC-like modulation scheme is described. With modulation schemes of this type, the bit rate error (BER) performance of MB-OFDM UWB based cognitive radio systems is improved, and simultaneously, the side-band signals decrease more quickly. As a result, by the only measure of tuning off the sub-carriers at the corresponding position a deeper spectral notch can be generated. The interferences to other protected services are suppressed sufficiently and finally the coexistence is achieved between MB-OFDM UWB based cognitive radio system and other narrow band radio systems.