  The problem of underwater acoustic (UWA) channel estimation is the
non-uniform sparse representation that may increase the algorithm complexity
and the required time. A mathematical framework utilizing l21 constraint with
two-dimensional frequency domain is employed to enhance the channel estimation.
The frame work depends on both main and auxiliary channel information. The
simulation results have been demonstrated that the proposed estimation method
can improve some problems that are achieved with other norms like l1.
Furthermore, it can achieve a better performance in terms of mean square error
(MSE) and execution time.
