  We elucidate the origin and nature of the D'yakonov-Perel' spin relaxation in
a quantum wire structure, showing (analytically) that there are three necessary
conditions for it to exist: (i) transport must be multi-channeled, (ii) there
must be a Rashba spin orbit interaction in the wire, and (iii) there must also
be a Dresselhaus spin orbit interaction. Therefore, the only effective way to
completely eliminate the D'yakonov-Perel' relaxation in compound semiconductor
channels with structural and bulk inversion asymmetry is to ensure strictly
single channeled transport. In view of that, recent proposals in the literature
that advocate using multi-channeled quantum wires for spin transistors appear
ill-advised.
