As an ensemble scheme of solid-state NMR quantum computers the scheme based on the array of 31P donor atoms which are spaced lengthwise of the strip gates is considered. The possible planar topology of such ensemble quantum computer is suggested. The estimation of the output NMR signal is performed and it is shown that for the number N >= 105 of ensemble elements involving L ~103 qubits each, the standard NMR methods are usable. As main mechanisms of decoherence for low temperature (< 0.1  K), the adiabatic processes of random modulation of qubit resonance frequency determined by secular part of nuclear spin hyperfine interaction with electron magnetic moment of basic atom and dipole-dipole interaction with nuclear moments of neighboring impurity atoms was considered, Estimations of allowed concentrations of magnetic impurities and of spin temperature whereby the required decoherence suppression are obtained. Semiclassical decoherence model of two qubit entangled states is also presented.