Baseband Fusion Technique for Filter-Less Wideband Transmitters

The multi-band and spectrally flexible transmission requires a wideband transmitter system to cover a wider frequency band of interest. A wideband power amplifier (PA) is required to achieve the desired signal strength for covering long-distance communication. Due to PA's nonlinear characteristics, spectral growth and harmonics occur, which may cause interference with the other band of interest. This paper presents a linearization technique, denoted as baseband fusion technique (BFT), for the wideband filter-less transmission system. The proposed method simultaneously reduces the spectral growth around the fundamental frequency and cancels out harmonics. The presented technique uses the signal cancellation approach in baseband and avoids modeling as required in digital predistortion. This method may eliminate the need for bulky filters to suppress harmonics. The proposed method has much lower complexity in digital signal processor resources than the Volterra-based models and their derivatives. We have experimentally tested with long-term-evolution (LTE), four-tone, and 256-QAM signal to validate the proposed method. This method can also be useful for cognitive radios where PA's unwanted emission interferes with the other user transmission.