In underwater communications, a system is wideband when the message bandwidth significantly exceeds the coherence bandwidth of the channel. MIMO (Multi-Input Multi-Output) has become an essential element of wireless communication. The main issue in MIMO is the occurrence of ISI (Inter-Symbol Interference) which results in degradation of performance. To attain bandwidth efficiency and ISI suppression ability, the Multi-band (MB) orthogonal frequency division multiplexing (OFDM) is a most reliable technique. In order to identify the unknown system with considerable computation complexity and accuracy, a novel Multichannel Adaptive Filter is employed with Group average clustering based Fast QR Decomposed Normalised Least Mean Square Algorithm and Normalised Sign Algorithm.