面向6G的新型多址与波形技术

New multiple access and waveform technology for 6G

随着互联网终端海量接入,传统正交多址接入(orthogonal multiple access,OMA)技术接入效率低,5G NR系统面临拥塞及高时延问题,并且在高速场景下,基于正交频分复用(orthogonal frequency-division multiplexing,OFDM)的系统由于多普勒效应性能严重恶化。为满足6G在高速移动场景下低时延、高可靠、海量接入需求,首先,结合正交时频空间(orthogonal time frequency space,OTFS)和图样分割多址接入(pattern division multiple access,PDMA)技术,提出了一种OTFS-PDMA联合方案;然后,推导PDMA传输码字在时延-多普勒(delay-Doppler,DD)域采用不同分配方式的系统输入-输出关系;最后,提出了一种基于期望传播算法(expectation propagation algorithm,EPA)的低复杂度接收机。仿真结果表明,OTFS-PDMA较传统的OTFS-OMA技术能够显著提升误码率性能;对于规则码本,不同码字分配方案性能相似,而对于非规则码本,发送信号采用集中式扩频优于离散式扩频,且对于离散式扩频,PDMA扩频信号沿多普勒轴分配,系统可取得较好性能;此外EPA接收机性能优于其他传统接收机。

With the explosive growth of Internet devices,the 5G new radio(NR)system faces congestion and high latency issues due to the low access efficiency of traditional orthogonal multiple access(OMA).Besides this,the performance of the orthogonal frequency-division multiplexing(OFDM)-based system is severely degraded due to the Doppler effect in high-speed scenarios.To meet the low-latency,high-reliability,and massive connection requirements of 6G communication in high-mobility scenarios,firstly,a novel orthogonal time frequency space(OTFS)-based pattern division multiple access(PDMA)scheme,shortened as OTFS-PDMA,was proposed.Then,the system input-output relationship of different types of PDMA codeword allocation schemes in the delay-Doppler(DD)domain was derived.Finally,a low-complexity expectation propagation algorithm(EPA)-based receiver was proposed.Simulation results illustrate that the proposed OTFS-PDMA scheme achieves significant performance gains over the conventional OTFS-OMA scheme.For regular PDMA patterns,the PDMA codeword allocation has a slight impact on the system performance.For irregular patterns,the centralized spreading method outperforms the discrete one.For discrete spreading scheme,the system can achieve better performance by assigning irregular PDMA spread signals along the Doppler direction.In addition,the proposed EPA receiver outperforms its conventional counterparts.