An Interpolator of Underwater Sensor Node with Enhanced Frequency Response Characteristic

Abstract

The digital part of the transmitter for acoustic wave communication must perform a sampling rate up conversion before converting the baseband signal to the acoustic wave band signal. Because acoustic wave communication operates at a low frequency, the digital part of most underwater communication devices is designed as software using DSPs. Since underwater sensor nodes among underwater communication devices are scattered in the sea, the power supply to the nodes is not smooth, so low-power design is important. In this paper, we designed the interpolator hardware for the low-power underwater communication sensor node chip. The requirements for frequency characteristics for acoustic wave communication of underwater sensor nodes and the operating frequency of the system to be implemented were identified, and an interpolator capable of meeting them was modeled using Matlab. Since a CIC interpolator is implemented without a multiplier and has a small area, we used CIC interpolators. However, the CIC interpolator has a wide transition band and a large passband droop. On the other hand, since the frequency of acoustic wave is low, both the data bandwidth and channel spacing are narrow, so filtering of the data signal is important. Therefore, complementary filters were added to satisfy the frequency specifications of the underwater sensor nodes. The structure of the entire interpolator hardware is designed so that additional filters operate at as low a clock rate as possible and have a low filter order. A hardware was designed using verilog hdl and verified using ModelSim. The simulation results of the designed hardware were compared with Matlab results to confirm that the frequency specifications were satisfied. The designed interpolator will be replaced by the interpolator of the previously tested underwater sensor node designed using DSP and used for distributed underwater observation control networks.