10-13U

We consider a hard-core boson model and obtain an analytical expression for conductivity. The pseudo-spin representation is used which allows one to take into account the effect of hard-core of particles upon their scattering processes. The diagrammatic series is constructed for the "current-current" correlation functions in normal phase at low temperature. We show how to sum up the main classes of diagrams in approximation of calculating up to one sum over $\mathbf{q}$. Method can be extended to whole temperature interval and does not depend on concentration of particles.