Design of receiver front-end with 25 kHz carrier frequency and 5 kHz symbol rate for communication system

In this paper, a front-end of digital receiver with 25 kHz carrier frequency, 5 kHz symbol rate, and any excess-bandwidth of pulse shaping filter is designed using two basic facts. The one is the analog-to-digital converting characteristics that the sampled sequence makes its replicas on the frequency domain and might not be suffered from the aliasing although its sampling rate is lower than the Nyquist sampling rate if the analog signal is a bandpass one. The other is that if the sampling rate is 4 times the center frequency of sampled sequence, the front-end processing complexity can be dramatically reduced due to the half of sampled sequence to be multiplied by zero in the demixing process. Furthermore, the designed front-end is simplified by introducing the sub-filters and sub-sampling sequences. The designed front-end is composed of an A/D converter, which takes samples of bandpass filtered signal at 20 kHz rate, a serial-to-parallel converter, which converts a sampled bandpass sequence to 4 paralleled sub-sample sequences, 4 sub-filter blocks, which act as a frequency shifter and lowpass filter for complex sequence, 4 synchronized switches, and 2 adders. The designed front-end dramatically reduces the computational complexity by more than 50% for frequency shifting and lowpass filtering operations since the conventional front-end requires a frequency shifting and two lowpass filtering operations to get one lowpass complex sample and the proposed front-end requires only four filtering operation to get four lowpass complex samples, which is equivalent to one filtering operation for one sample.