BER Performance Analysis of OTFS Systems with Power Allocation

Orthogonal time frequency space (OTFS),as a novel 2-D modulation technique, has been pro-posed to achieve better BER performances over delay-Doppler channels. In this paper, we propose two dif-ferent power allocation (PA) algorithms in OTFS sys-tems with zero forcing (ZF) or minimum mean squareerror (MMSE) equalization, where general formulaswith PA are derived in advance under the conditionof minimum BER (MBER) criterion. On one hand,a suboptimal MBER power allocation method is putforward to achieve better BER performances, and thenanalytical BER expressions are derived with proposedPA strategy. Considering the case of MMSE equal-ization, a combined subsymbol allocation (SA) andPA strategy is raised, where some subsymbols may beabandoned due to worse channel conditions, and thenit is proven effectively to improve BER performancesthrough theoretical and simulation results. Further-more, BER performances with proposed joint SA andPA strategy are also investigated in delay-Dopplerchannels, where an improved message passing (MP)receiver based on equivalent channel matrix with PAis given