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Design and Performance of Enhanced Spread Spectrum Aloha for Unsourced Multiple Access

Riccardo Schiavone, Gianluigi Liva, Roberto Garello

TL;DR

This work tackles scalable random access for many intermittently active devices under unsourced MAC constraints. It proposes an enhanced spread spectrum Aloha (E-SSA) protocol adapted to UMAC by wrapping asynchronous transmissions into frames, coupling short CRC-aided polar codes with a timing channel to boost energy efficiency. The receiver achieves linear complexity in the number of active users through iterative preamble detection, despreading, adaptive SCL decoding, CRC checks, and SIC, and the performance approaches the UMAC achievability bound for moderate loads. Numerical results in a GMAC setting demonstrate competitive energy efficiency and near-bound performance for up to roughly 100 active users, with practical transmitter simplicity and scalable receiver workload. These findings suggest E-SSA as a viable, implementable approach for next-generation ultra-dense random-access systems such as satellite IoT and 6G communications.

Abstract

We analyze the performance of enhanced spread spectrum Aloha (E-SSA) in the framework of unsourced multiple access (UMAC). The asynchronous, unframed transmission of E-SSA is modified to enable a direct comparison with framed UMAC schemes and with Polyanskiy's achievability bound. The design of E-SSA is tailored to the UMAC setting, resorting to short polar codes and the use of a timing channel to improve the energy efficiency of the protocol. We assess the impact of the preamble length and of the spreading factor on the system efficiency. The resulting scheme exhibits simplicity at the transmitter and linear complexity with respect to the number of active users at the receiver, approaching the UMAC achievability bound in close competition with the best known UMAC schemes.

Design and Performance of Enhanced Spread Spectrum Aloha for Unsourced Multiple Access

TL;DR

This work tackles scalable random access for many intermittently active devices under unsourced MAC constraints. It proposes an enhanced spread spectrum Aloha (E-SSA) protocol adapted to UMAC by wrapping asynchronous transmissions into frames, coupling short CRC-aided polar codes with a timing channel to boost energy efficiency. The receiver achieves linear complexity in the number of active users through iterative preamble detection, despreading, adaptive SCL decoding, CRC checks, and SIC, and the performance approaches the UMAC achievability bound for moderate loads. Numerical results in a GMAC setting demonstrate competitive energy efficiency and near-bound performance for up to roughly 100 active users, with practical transmitter simplicity and scalable receiver workload. These findings suggest E-SSA as a viable, implementable approach for next-generation ultra-dense random-access systems such as satellite IoT and 6G communications.

Abstract

We analyze the performance of enhanced spread spectrum Aloha (E-SSA) in the framework of unsourced multiple access (UMAC). The asynchronous, unframed transmission of E-SSA is modified to enable a direct comparison with framed UMAC schemes and with Polyanskiy's achievability bound. The design of E-SSA is tailored to the UMAC setting, resorting to short polar codes and the use of a timing channel to improve the energy efficiency of the protocol. We assess the impact of the preamble length and of the spreading factor on the system efficiency. The resulting scheme exhibits simplicity at the transmitter and linear complexity with respect to the number of active users at the receiver, approaching the UMAC achievability bound in close competition with the best known UMAC schemes.
Paper Structure (9 sections, 4 equations, 5 figures)

This paper contains 9 sections, 4 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Preliminaries
  3. Polar Codes
  4. Protocol Design
  5. Message Transmission
  6. Detection and Decoding
  7. Error Detection via Timing Channel
  8. Numerical Results
  9. Conclusion

Figures (5)

  • Figure 1: Structure of the transmission chain.
  • Figure 2: Effect of the spreading factor $s$ on the minimum $E_b/N_0$ required for $\epsilon^{\star}=5\times 10^{-2}$. Genie-aided preamble detection.
  • Figure 3: Effect of the channel load $K_a$ on the PUPE in a system with no preamble. Spreading factor $s=25$. Genie-aided preamble detection.
  • Figure 4: Minimum $E_b/N_0$ (above) and average number of decoding attempts (below) for $\epsilon^{\star}=5\times 10^{-2}$ as a function of the preamble loss, $s=15$.
  • Figure 5: $E_b/N_0$ required to achieve the target $\epsilon^\star=5\times 10^{-2}$.