We characterize multiple-access interference for cellular mobile networks, in which users are assumed to be Poisson-distributed in the plane and to employ frequencyhopped spreadspectrum signaling with a transmitter-oriented assignment of frequencyhopping patterns. Exact expressions for the bit error probabilities are derived for binary coherently demodulated systems without coding. Approximations for the packet error probability are derived for coherent and noncoherent systems and these approximations are applied when forward-errorcontrol coding is employed. In all cases, the effects of varying interference power are accurately taken into account according to some propagation law. Numerical results are given in terms of bit error probability for the exact case and throughput for the approximate analyses. Comparisons are made with previously derived bounds and it is shown that these tend to be very pessimistic.