In this paper an overview is given of some of the problems to be faced and the approaches to their possible solutions, in the design of a Doppler wind lidar. The emphasis is devoted to the causes of degradation of the heterodyne efficiency and to the line purity requirements for the local oscillator. Both the above aspects directly influence the signal to noise ratio and, as a consequence, the performance of the system. In particular, the first aspect refers to the number of speckles, to the alignment required between signal and local oscillator and to the beams matching characteristics in terms of wavefront and polarization; the second refers to the relative intensity and phase noise of the local oscillator and to the constraints in terms of its power level and in the position of the intermediate frequency stage. Although the receiver design characteristics are responsible for the system sensitivity, in the heterodyne system there are some direct links to the transmitter design specifications like the divergence and the tunability, that must be evaluated for the optimization of the overall system performance. For this reason a few aspects of the transmitter specifications are evidenced, in order to obtain a good trade-off between performance and real feasibility. A few suggestions are given in order to potentially improve the performance of a spaceborne Doppler wind lidar, considering that the technological impact on the system is at the boundary of the feasibility.