Early results on the design of adaptive equalizer for HF communications system on equatorial region

Wideband HF channel (3-30 MHz) using Ionosphere layer as a reflection medium is very potential for an affordable long-distance communication system. The main challenge to realize HF communication is its time-variant multipath characteristic which causes fading, Doppler spread, and ISI (Inter-Symbol Interference) at the received signal. Consequently, adaptive signal processing in HF receiver system plays its important role to reconstruct transmitted signal that has gone through multipath fading. Our study focuses on the design of adaptive DFE (Digital Feedback Equalization) for HF communications based on channel estimation. The performance of adaptive DFE is measured in MSE (Mean Square Error) and convergence rate using either the LMS (Least Mean Square) or RLS (Recursive Least Square) algorithm. The design is to be based on HF channel impulse response measurement made in Indonesia, a typical equatorial region, on a 3036 km link.