multiple quantum well structures with different dopant concentration n . It is seen that for the sample with smaller concentration (Fig.2) the negative magnetoresistance is strongly enhanced with temperature decrease while for the sample with larger dopant concentration (Fig.3), in contrast, it is suppressed with a temperature decrease. FIG. 2: Temperature behavior of resistance for the structures of 10 GaAs wells of thickness 15 nm, separated by AlGaAs barriers with thickness 15 nm. The central parts of both wells and barriers were doped by p-type impurity Be with concentration 1 · 10 17 cm $^{−}$3. To our opinion, the difference of magnetoresistance curves for samples with different n is related to the following fact. The sample with smaller concentration is far from the metal- insulator transition and the localization length is relatively small, a ∼ 10 nm . Thus, in a view of small n and small a the 3-cite approximation for interference contribution holds, nr$_{h}$ ( ar$_{min}$ ) 1 / 2 ≤ 1. For heavily doped sample a ∼ 20 nm and n ∼ 10 $^{12}$cm − $^{2}$, correspondingly, nr$_{h}$ ( ar$_{min}$ ) 1 / 2 > 1. As a result, the 3-cite approximation for this sample does not hold and the interference loop includes large number of scatterers. As it was noted above, the spin statistical factor for each additional site with non-zero spin at H = 0 for acceptor impurities is ∼ 1 / 4. Correspondingly, the interference contribution for loops involving many intermediate scatterers vanishes at H = 0. As a result, the linear contribution to negative magnetoresistance is, in any case, much smaller than for weakly doped samples. In contrast, the quadratic positive magneroresistance resulting from the statistical factor given by Eq. 17 GLYPH<s48> GLYPH<s49>GLYPH<s48>GLYPH<s48>GLYPH<s48> GLYPH<s50>GLYPH<s48>GLYPH<s48>GLYPH<s48> GLYPH<s51>GLYPH<s48>GLYPH<s48>GLYPH<s48> GLYPH<s45>GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s54> GLYPH<s45>GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s52> GLYPH<s45>GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s50> GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s48> GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s50> GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s52> GLYPH<s48>GLYPH<s44> GLYPH<s48>GLYPH<s54> GLYPH<s32> GLYPH<s51>GLYPH<s46>GLYPH<s53>GLYPH<s75> GLYPH<s50>GLYPH<s46>GLYPH<s54>GLYPH<s75> GLYPH<s50>GLYPH<s75> GLYPH<s49>GLYPH<s46>GLYPH<s54>GLYPH<s75> GLYPH<s82>GLYPH<s47>GLYPH<s82> GLYPH<s72>GLYPH<s44>GLYPH<s32>GLYPH<s71>GLYPH<s115> GLYPH<s48>GLYPH<s46>GLYPH<s52>GLYPH<s75>