Problem
Research questions and friction points this paper is trying to address.
Random Access
Localization
Frequency-Selective Fading
Cell-Free Networks
User-Centric
Joint Random Access and Localization in Cell-Free User-Centric Networks with Frequency-Selective Fading Channels
🤖 AI Summary
研究在频率选择性衰落信道下，通过联合检测和定位方法解决无蜂窝用户中心网络中的随机接入问题，提出基于多源近似消息传递的方法。
📝 Abstract
We study random access (RACH) schemes for cell-free (CF) user-centric networks to handle many geographically distributed users with sporadic traffic and intermittent activity. The RACH must allow the system to: 1) detect preambles sent by the (yet unknown) random access users in the RACH slot; 2) localize them for fast allocation of user-centric radio-unit (RU) clusters. Most prior work uses simplified models, neglecting frame-synchronous but chip-asynchronous transmission, possible line-of-sight (LoS) propagation for certain user-RU pairs, and multipath non-line-of-sight (NLoS) propagation yielding frequency-selective channels. Building on our previous work, we consider location-dependent partitioned random access codebooks where users in a geographic area (location) use the corresponding subset of random access preambles. We present a unified framework for joint detection and localization over a spatially consistent network-wide channel model, incorporating these neglected aspects. We evaluate two schemes: 1) a ``legacy'' scheme using Zadoff-Chu (ZC) sequences, extending the 3GPP 2-step RACH to the CF case; 2) our multisource approximate message passing (AMP) approach extended to multipath frequency-selective fading. For both schemes, we develop novel approximated GLRT preamble detection and Maximum-Likelihood position estimators with super-resolution refinement, implicitly exploiting received signal strength, angle of arrival, and time-difference of arrival information embedded into LoS components. Numerical results show that the AMP-based scheme achieves superior preamble detection, while both schemes have similar and excellent localization capability.
Innovation
Methods, ideas, or system contributions that make the work stand out.
location-dependent partitioned random access codebooks
spatially consistent network-wide channel model
multisource approximate message passing (AMP)
frequency-selective fading channels
approximated GLRT preamble detection
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