This paper investigates over-the-air computation (AirComp) in the context of multiple-access time-varying multipath channels. We focus on a scenario where devices with high mobility transmit their sensing data to a fusion center (FC) for averaging. To combat the time-varying channel and Doppler effect, each device adopts orthogonal time frequency space (OTFS) modulation. After signals are received by the FC, the aggregated data undergoes demodulation and estimation within the delay-Doppler domain. We leverage the mean squared error (MSE) as a metric for the computational error of OTFS-based AirComp. We then derive the optimal transmit power at each device and signal scaling factor at FC for minimizing MSE. Notably, the performance of OTFS-based AirComp is not only affected by the noise but also by the inter-symbol interference and inter-link interference arising from the multipath channel. To counteract the interference-induced computational errors, we incorporate zero-padding (ZP)-assisted OTFS into AirComp and propose algorithms for interference cancellation. Numerical results underscore the enhanced performance of ZP-assisted OTFS-based AirComp over naive OTFS-based AirComp.

翻译：本文研究了多址时变多径信道环境下的空中计算（AirComp）技术。我们聚焦于高移动性设备将其传感数据传输至融合中心进行平均计算的场景。为对抗时变信道及多普勒效应，各设备采用正交时频空间（OTFS）调制。融合中心接收信号后，在时延-多普勒域对聚合数据进行解调和估计。我们以均方误差（MSE）作为衡量OTFS空中计算误差的指标，进而推导出各设备最优发射功率与融合中心最优信号缩放因子以最小化MSE。值得注意的是，OTFS空中计算的性能不仅受噪声影响，还受多径信道引起的符号间干扰与链路间干扰制约。为抑制干扰导致的计算误差，我们将零填充（ZP）辅助的OTFS引入空中计算，并提出干扰消除算法。数值结果验证了ZP辅助OTFS空中计算相比传统OTFS空中计算的性能提升。