  The uncertainty principle sets a bound on our ability to predict the
measurement outcomes of two incompatible observables which are measured on a
quantum particle simultaneously. In quantum information theory, the uncertainty
principle can be formulated in terms of the Shannon entropy. Entropic
uncertainty bound can be improved by adding a particle which correlates with
the measured particle. The added particle acts as a quantum memory. In this
work, a method is provided for obtaining the entropic uncertainty relations in
the presence of a quantum memory by using quantum coherence. In the method,
firstly, one can use the quantum relative entropy of quantum coherence to
obtain the uncertainty relations. Secondly, these relations are applied to
obtain the entropic uncertainty relations in the presence of a quantum memory.
In comparison with other methods this approach is much simpler. Also, for a
given state, the upper bounds on the sum of the relative entropies of
unilateral coherences are provided, and it is shown which one is tighter. In
addition, using the upper bound obtained for unilateral coherence, the
nontrivial upper bound on the sum of the entropies for different observables is
derived in the presence of a quantum memory.
