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Joint Message Detection, Channel, and User Position Estimation for Unsourced Random Access in Cell-Free Networks

Eleni Gkiouzepi, Burak Çakmak, Manfred Opper, Giuseppe Caire

TL;DR

This work considers unsourced random access (uRA) in user-centric cell-free (CF) wireless networks and proposes to partition the network coverage area into zones and assign an uRA codebook to each location, such that users in a certain location make use of the associated codebook.

Abstract

We consider unsourced random access (uRA) in user-centric cell-free (CF) wireless networks, where random access users send codewords from a common codebook during specifically dedicated random access channel (RACH) slots. The system is conceptually similar to the so-called 2-step RACH currently discussed in 3GPP standardization. In order to cope with the distributed and CF nature of the network, we propose to partition the network coverage area into zones (referred to as ''locations'') and assign an uRA codebook to each location, such that users in a certain location make use of the associated codebook. The centralized uRA decoder makes use of the multisource AMP algorithm recently proposed by the authors. This yields at once the list of active uRA codewords, an estimate of the corresponding channel vectors, and an estimate of the active users' position. We show excellent performance of this approach and perfect agreement with the rigorous theoretical ''state evolution'' analysis. We also show that the proposed ''location-based'' partitioned codebook approach significantly outperforms a baseline system with a single non-partitioned uRA codebook.

Joint Message Detection, Channel, and User Position Estimation for Unsourced Random Access in Cell-Free Networks

TL;DR

This work considers unsourced random access (uRA) in user-centric cell-free (CF) wireless networks and proposes to partition the network coverage area into zones and assign an uRA codebook to each location, such that users in a certain location make use of the associated codebook.

Abstract

We consider unsourced random access (uRA) in user-centric cell-free (CF) wireless networks, where random access users send codewords from a common codebook during specifically dedicated random access channel (RACH) slots. The system is conceptually similar to the so-called 2-step RACH currently discussed in 3GPP standardization. In order to cope with the distributed and CF nature of the network, we propose to partition the network coverage area into zones (referred to as ''locations'') and assign an uRA codebook to each location, such that users in a certain location make use of the associated codebook. The centralized uRA decoder makes use of the multisource AMP algorithm recently proposed by the authors. This yields at once the list of active uRA codewords, an estimate of the corresponding channel vectors, and an estimate of the active users' position. We show excellent performance of this approach and perfect agreement with the rigorous theoretical ''state evolution'' analysis. We also show that the proposed ''location-based'' partitioned codebook approach significantly outperforms a baseline system with a single non-partitioned uRA codebook.
Paper Structure (11 sections, 23 equations, 7 figures)

This paper contains 11 sections, 23 equations, 7 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Received signal and SNR normalization
  4. Multisource AMP algorithm
  5. Denoising function
  6. Message detection
  7. Active UEs position estimation
  8. Channel estimation comparison AMP/genie aided MMSE
  9. Numerical Results
  10. Conclusion
  11. Acknowledgements

Figures (7)

  • Figure 1: a) Conventional 4-step RACH; b) Novel 2-step RACH.
  • Figure 2: Hexagonal network topology with equilateral triangle tiles used in the numerical results of this paper.
  • Figure 3: AMP total normalized MSE and its theoretical deterministic prediction.
  • Figure 4: MD and FA probability tradeoff curves for the LB (matched, mismatched) and the SC case.
  • Figure 5: CDF of the absolute position error for the location based and the single codebooks schemes, using the proposed MAP position estimator for the active messages.
  • ...and 2 more figures