A New Software Defined Radio Communication System Using 256-QAM

In this paper a new software defined radio communication system using 256-QAM used for vehicular communications is presented. The proposed radio communication system simultaneously transmits an audio stereo signal and a data signal with 256-QAM modulation in the subsidiary FM bands. The radio receiver is based on a carrier synchronization loop operating at the baseband and a 256-QAM demodulator. The operating of the proposed radio communication system under conditions of carrier offset, as well as data rate offset on an AWGN communication channel is analyzed. In order to validate the proposed solution, the bit error rate depending on the $E_{b} / N_{0}$ ratio of the radiofrequency 256-QAM signal are plotted and compared with ideal BER curve for the $256-\mathrm{QAM}$. The input data rate of the proposed radiocommunication system is 152 kbits/sec and the minimum value of the $E_{b} / N_{0}$ ratio for the received radiofrequency 256-QAM signal for which a number of $\mathbf{3} \cdot 1 \mathbf{0}^{\mathbf{5}}$ bits are transmitted without any error is equal to 23 dB. The proposed radio communication system was implemented in Matlab/Simulink and the simulations performed confirmed the theoretical results. The experimental results were obtained under laboratory conditions using USRP type devices configured as transmitter and receiver.