  We have studied the spin-orbit interaction in a high mobility two-dimensional
electron gas in a GaInAs/InP heterostructure as a function of an applied gate
voltage as well as a function of temperature. Highly sensitive magnetotransport
measurements of weak antilocalization as well as measurements of Shubnikov--de
Haas oscillations were performed in a wide range of electron sheet
concentrations. In our samples the electron transport takes place in the strong
spin precession regime in the whole range of applied gate voltages, which is
characterized by the spin precession length being shorter than the elastic mean
free path. The magnitude of the Rashba spin-orbit coupling parameter was
determined by fitting the experimental curves by a simulated quantum
conductance correction according to a model proposed recently by Golub [Phys.
Rev. B 71, 235310 (2005)]. A comparison of the Rashba coupling parameter
extracted using this model with the values estimated from the analysis of the
beating pattern in the Shubnikov--de Haas oscillations showed a good agreement.
