Adaptive software modem technology

This paper presents a description of a new software modem technology. Our adaptive modem technology uses software algorithms for the modulation and demodulation process. A modem of this type can be designed with standard microprocessors and A/D and D/A devices or with special signal processors. We have developed a signal detection method which uses the discrete Fourier transform (DFT). Our prototype modem can be used both in radio communication channels and in PSTN networks because of the free selection of the modulation method parameters and the bandwidth used. The use of complex waveforms gives us the practical Shannon capacity in different cases. Basically we use AM, FM and PM modulations adaptively, which means that we can select the best modulation scheme (MFSK, MPSK, QAM) for different channels. We explain here the use of DFT and show some simulation results. We have made several field tests with the modem prototype and present our tests over radio channels. We show how the data transmission adapts to the narrow bandwidth. The most important feature of the adaptive modem is the data throughput and bit/Hz superiority. The band-limited data rate is higher than the rate of standard solutions of ITU-T or some military radio applications in use. With this technology, we can improve GSM and GPRS data transmission considerably. We believe that it is an alternative for EDGE and UMTS. We expect that the use of this technology will be in mobile Internet access (WLAN) and in tactical Internet.