叠加导频传输无标识随机接入方案研究

doi:10.19665/j.issn1001-2400.20230907

摘要/Abstract

摘要：

在无标识随机接入中,基站只需要恢复各个活跃设备发送的数据,而不需要识别活跃设备的信息。这使得大量活跃设备可以在无需事先请求资源的条件下,随时接入基站,从而极大地降低信令开销和传输时延,成为近期的研究热点。目前的研究大都采用基于前导序列来设计的随机接入方案,但这类方案在活跃设备数改变时的鲁棒性较差,且不能充分利用信道带宽,导致活跃设备数较大时系统性能较差。针对这一问题,提出一种叠加导频传输方案来提升信道利用率,并通过最优功率分配进一步提升不同活跃设备数下的系统性能,使系统在活跃设备数变化时具有良好的鲁棒性。在该方案中,首先将需要发送的消息序列的前B_p个比特做为索引,选择一对导频序列和交织器。然后,利用选中的交织器对消息序列进行编码、调制和交织,并将选中的导频序列与交织后的调制序列进行叠加来得到发送信号。针对该传输方案,提出基于最小错误概率的功率优化方案来得到不同活跃设备数下的最优功率分配比例,设计了叠加导频检测消除和多用户检测译码的两阶段检测方案。仿真结果表明,叠加导频传输方案可以使基于前导序列的无标识随机接入方案和基于前导的稀疏无标识随机接入方案的性能分别提升约1.6~2.0 dB和0.2~0.5 dB,可以灵活地改变所能承载的活跃设备数量,并具有较低的译码复杂度。

关键词: 无标识随机接入, 叠加导频, 多用户检测和译码, 功率分配

Abstract:

In unsourced random access,the base station(BS) only needs to recover the messages sent by each active device without identifying the device,which allows a large number of active devices to access the BS at any time without requiring a resource in advance,thereby greatly reducing the signaling overhead and transmission delay,which has attracted the attention of many researchers.Currently,many works are devoted to design random access schemes based on preamble sequences.However,these schemes have poor robustness when the number of active devices changes,and cannot make full use of channel bandwidth,resulting in poor performance when the number of active devices is large.Aiming at this problem,a superimposed pilots transmission scheme is proposed to improve the channel utilization ratio,and the performance for different active device numbers is further improved by optimal power allocation,making the system have good robustness when the number of active devices changes.In this scheme,the first Bp bits of the sent message sequence are used as the index,to select a pair of pilot sequence and interleaver.Then,using the selected interleaver,the message sequence is encoded,modulated and interleaved,and the selected pilot sequence is then superimposed on the interleaved modulated sequence to obtain the transmitted signal.For this transmission scheme,a power optimization scheme based on the minimum probability of error is proposed to obtain the optimal power allocation ratio for different active device numbers,and a two-stage detection scheme of superimposed pilots detection cancellation and multi-user detection decoding is designed.Simulation results show that the superimposed pilot transmission scheme can improve the performance of the unsourced random access scheme based on the preamble sequence by about 1.6~2.0 dB and 0.2~0.5 dB respectively,and flexibly change the number of active devices that the system carries and that it has a lower decoding complexity.

Key words: unsourced random access, superimposed pilots, multi-user detection and decoding, power allocation

中图分类号:

TN911.22

郝孟男, 李颖, 宋光辉. 叠加导频传输无标识随机接入方案研究[J]. 西安电子科技大学学报, 2024, 51(3): 1-8.

HAO Mengnan, LI Ying, SONG Guanghui. Superimposed pilots transmission for unsourced random access[J]. Journal of Xidian University, 2024, 51(3): 1-8.

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所比较的方案	译码复杂度
SP-based IDMA	O(M_pN_tot+(2K_a+1)N_tot)
基于前导的IDMA	O(M_pN_pT+(2K_a+1)N_c)
SP-based Sparse IDMA	O(M_pN_tot+K_aN_tot)
基于前导的稀疏IDMA^[8]	O(M_pN_pT+K_aN_c)