  We study the variable-range hopping (VRH) of bosons in an array of sites with
short-range interactions and a large characteristic coordination number. The
latter leads to strong quantum interference phenomena yet allows for their
analytical study. We develop a functional renormalization group scheme that
repeatedly eliminates high-energy sites properly renormalizing the tunnelling
between the low-energy ones. Using this approach we determine the temperature
and magnetic field dependence of the hopping conductivity and find a large
positive magnetoresistance. With increasing magnetic field the behaviour of the
conductivity crossovers from the Mott's law to an activational behaviour with
the activation gap proportional to the magnetic field.
