A novel cognitive modulation method considering the performance of primary user

This paper proposes a new modulation method for an uncoded cognitive transmission (secondary user transmission) in presence of a Primary User (PU) for the AWGN channel. Interference of the PU is assumed to be known at the transmitter of Cognitive User (CU) non-causally. Based on this knowledge, for the design of the modulator and demodulator of the CU, a symbol by symbol approach is studied which can fulfill the coexistence conditions of the CU and the PU of the band. In this scheme, the modulator and demodulator of CU are designed jointly by solving an optimization problem to mitigate the interference of the PU and minimize the symbol error probability (P_e) in CU´s communication link without increasing the symbol error probability (P_e) of the PU. The proposed method is a modulation approach in a single (complex-valued) dimension rather than a high dimensional coding scheme. Although this one-dimensional method is not capacity achieving, we show it still has a remarkable performance with low amount of complexity. An implementation algorithm for our modulation method is also presented and the performance of this method is evaluated by experimental results.