  We investigate hp-stabilization for variational inequalities and boundary
element methods based on the approach introduced by Barbosa and Hughes for
finite elements. Convergence of a stabilized mixed boundary element method is
shown for unilateral frictional contact problems for the Lame equation. Without
stabilization, this may not converge because the inf-sup constant need not be
bounded away from zero for natural discretizations, even for fixed h and p.
Both a priori and a posteriori error estimates are presented in the case of
Tresca friction, for discretizations based on Bernstein or
Gauss-Lobatto-Lagrange polynomials as test and trial functions. We also
consider an extension of the a posteriori estimate to Coulomb friction.
Numerical experiments underline our theoretical results.
