Simple DC removers for digital FM direct-conversion receiver

Direct-conversion radio transceivers have been applied in digital mobile communications because they provide several desirable features such as reduced power consumption, and reduced hardware complexity and size. However, the undesirable direct current (DC) components are introduced after the direct conversion due to the parasitic coupling between the receiver antenna and the local oscillator. In this paper, two simple DC removing schemes, which can estimate the DC components within only several information bit intervals, are proposed, and placed before the baseband demodulator. For signaling, a digital FM modulation with parameters, which may be applicable to the FLEX paging system, is considered. For demodulation, the conventional cross-differentiate multiply (CDM) is employed. Bit error rate (BER) simulation results with and without the DC removers are compared for the two-level and four-level digital FM signaling with modulation index h=1 and 1.5, under both additive white Gaussian noise (AWGN) and Rayleigh mobile fading environments. The simulation results show that the proposed simple DC removers can almost perfectly remove the DC components even if the DC component has a 40 dB larger power than the signal component