For doubly-selective channels, delay-Doppler (DD) modulation, mostly known as orthogonal time frequency space (OTFS) modulation, enables simultaneous compensation of delay and Doppler shifts. However, OTFS modulated signal has high peak-to-average power ratio (PAPR) because of its precoding operation performed over the DD domain. In order to deal with this problem, we propose a single-carrier transmission with delay-Doppler domain equalization (SC-DDE). In this system, the discretized time-domain SC signal is converted to the DD domain by discrete Zak transform (DZT) at the receiver side, followed by delay-Doppler domain equalization (DDE). Since equalization is performed in the DD domain, the SC-DDE receiver should acquire the channel delay-Doppler response. To this end, we introduce an embedded pilot-aided channel estimation scheme designed for SC-DDE, which does not affect the peak power property of transmitted signals. Through computer simulation, distribution of PAPR and bit error rate (BER) performance of the proposed system are compared with those of the conventional OTFS and SC with frequency-domain equalization (SC-FDE). As a result, our proposed SC-DDE significantly outperforms SC-FDE in terms of BER at the expense of additional computational complexity at the receiver. Furthermore, SC-DDE shows much lower PAPR than OTFS even though they achieve comparable coded BER performance.

翻译：对于双选择性信道，时延-多普勒调制（通常称为正交时频空间调制）能够同时补偿时延和多普勒频移。然而，OTFS调制信号因其在时延-多普勒域进行预编码操作，具有较高的峰均功率比。针对此问题，本文提出一种单载波传输与时延-多普勒域均衡方案。在该系统中，接收端通过离散Zak变换将离散时域单载波信号转换至时延-多普勒域，随后进行时延-多普勒域均衡。由于均衡在时延-多普勒域中执行，SC-DDE接收机需获取信道时延-多普勒响应。为此，我们引入一种专为SC-DDE设计的嵌入式导频辅助信道估计方案，该方案不会影响发射信号的峰值功率特性。通过计算机仿真，将所提系统的PAPR分布和误码率性能与传统OTFS及频域均衡单载波方案进行对比。结果表明，尽管接收端计算复杂度有所增加，但所提SC-DDE在误码率方面显著优于SC-FDE。此外，即便两者在编码误码率性能上相当，SC-DDE的PAPR仍远低于OTFS。