BER Reduction Using Partial-Elements Selection in IRS-UAV Communications With Imperfect Phase Compensation

—This work considers minimizing the communications bit error rate (BER) of unmanned aerial vehicle (UAV) when assisted by intelligent reﬂecting surfaces (IRSs). By noting that increasing the number of IRS elements in the presence of phase errors does not necessarily improve the system’s BER, it is crucial to use only the elements that contribute to reducing such a parameter. To this end, we propose an efﬁcient algorithm to select the elements that can improve BER. The proposed algorithm has lower complexity and comparable BER to the optimum selection process which is an NP-hard problem. The accuracy of the estimated phase is evaluated by deriving the probability distribution function (PDF) of the least-square (LS) channel estimator, and showing that the PDF can be closely approximated by the von Mises distribution at high signal-to-noise ratios (SNRs). The obtained analytical and simulation results show that using all the available reﬂectors can signiﬁcantly deteriorate the BER, and thus, partial element selection is necessary. It is shown that, in some scenarios, using about 26% of the reﬂectors provides more than 10 fold BER reduction. The number of selected reﬂectors may drop to only 10% of the total elements. As such, the unassigned 90% of the elements can be allocated to serve other users, and the overhead associated with phase information is signiﬁcantly reduced.