  The topological insulators have a gap in the bulk but extended states at the
edge that can carry current. We study a geometry in which such edge states will
manifest themselves through periodic oscillations in the magnetoconductance of
a singly connected sample coupled to leads through narrow point contacts. The
oscillations occur due to quantum interference of helical edge states of
electrons traveling along the circumference of the sample, and have a period of
B_0=h/eA_{eff}, where A_{eff} is the effective area enclosed by the edge states
of the sample. Our calculation indicates the possibility of a large change in
the magnetoresistance at small B, termed giant edge magnetoresistance, which
can have potential for application. The zero field conductance also exhibits
oscillations as a function of the Fermi energy due to interference between edge
states. The amplitude of the oscillations is governed by, and therefore can be
used to investigate, the transverse width of the edge channels.
