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Unsourced Multiple Access: A Coding Paradigm for Massive Random Access

Gianluigi Liva, Yury Polyanskiy

TL;DR

This paper introduces unsourced multiple access (UMAC) as a coding-theoretic framework for massive uncoordinated uplink access, tying together the physical and MAC layers through a common codebook and the PUPE performance metric. It surveys the historical evolution from Aloha to coding-based schemes, and categorizes current architectures into MPR slotted Aloha, coded compressive sensing (CCS), preamble-based, and spreading-based approaches, discussing their mechanisms and deployment maturity. It also analyzes grant-free cellular integration, notably 5GNR two-step random access, showing that targeted architectural refinements can yield substantial energy efficiency gains and support higher user counts, with concrete results on both Gaussian and fading channels and suggestions for improved preamble design and access patterns. The paper emphasizes the need for cross-disciplinary collaboration to identify a practical, scalable, and robust architecture for future wireless standards, highlighting the potential of simple, battery-friendly modifications to existing protocols to unlock massive, unsourced connectivity.

Abstract

This paper is a tutorial introduction to the field of unsourced multiple access (UMAC) protocols. We first provide a historical survey of the evolution of random access protocols, focusing specifically on the case in which uncoordinated users share a wireless broadcasting medium. Next, we highlight the change of perspective originated by the UMAC model, in which the physical and medium access layer's protocols cooperate, thus reframing random access as a novel coding-theoretic problem. By now, a large variety of UMAC protocols (codes) emerged, necessitating a certain classification that we indeed propose here. Although some random access schemes require a radical change of the physical layer, others can be implemented with minimal changes to existing industry standards. As an example, we discuss a simple modification to the 5GNR Release 16 random access channel that builds on the UMAC theory and that dramatically improves energy efficiency for systems with even moderate number of simultaneous users (e.g., $5-10$ dB gain for $10-50$ users), and also enables handling of high number of users, something completely out of reach of the state-of-the-art.

Unsourced Multiple Access: A Coding Paradigm for Massive Random Access

TL;DR

This paper introduces unsourced multiple access (UMAC) as a coding-theoretic framework for massive uncoordinated uplink access, tying together the physical and MAC layers through a common codebook and the PUPE performance metric. It surveys the historical evolution from Aloha to coding-based schemes, and categorizes current architectures into MPR slotted Aloha, coded compressive sensing (CCS), preamble-based, and spreading-based approaches, discussing their mechanisms and deployment maturity. It also analyzes grant-free cellular integration, notably 5GNR two-step random access, showing that targeted architectural refinements can yield substantial energy efficiency gains and support higher user counts, with concrete results on both Gaussian and fading channels and suggestions for improved preamble design and access patterns. The paper emphasizes the need for cross-disciplinary collaboration to identify a practical, scalable, and robust architecture for future wireless standards, highlighting the potential of simple, battery-friendly modifications to existing protocols to unlock massive, unsourced connectivity.

Abstract

This paper is a tutorial introduction to the field of unsourced multiple access (UMAC) protocols. We first provide a historical survey of the evolution of random access protocols, focusing specifically on the case in which uncoordinated users share a wireless broadcasting medium. Next, we highlight the change of perspective originated by the UMAC model, in which the physical and medium access layer's protocols cooperate, thus reframing random access as a novel coding-theoretic problem. By now, a large variety of UMAC protocols (codes) emerged, necessitating a certain classification that we indeed propose here. Although some random access schemes require a radical change of the physical layer, others can be implemented with minimal changes to existing industry standards. As an example, we discuss a simple modification to the 5GNR Release 16 random access channel that builds on the UMAC theory and that dramatically improves energy efficiency for systems with even moderate number of simultaneous users (e.g., dB gain for users), and also enables handling of high number of users, something completely out of reach of the state-of-the-art.
Paper Structure (18 sections, 10 equations, 8 figures, 1 table)

This paper contains 18 sections, 10 equations, 8 figures, 1 table.

Table of Contents

  1. Introduction
  2. Objective and Main Contributions
  3. Outline
  4. From Aloha to Codes for Unsourced Multiple Access
  5. First Period (1970--2007): Aloha and Collision Models
  6. Second Period (2007--2017): Aloha-like protocols with Multi-User Detection
  7. Third Period (2017--): Random Access as a Coding Problem
  8. Random access from an information-theoretic perspective
  9. Prominent Unsourced Multiple Access Architectures
  10. Multi-Packet Reception slotted Aloha Architectures
  11. Coded Compressive Sensing Architectures
  12. Preamble-based Architectures
  13. Spreading-based Architectures
  14. Maturity
  15. Grant-Free Access in Cellular Networks
  16. ...and 3 more sections

Figures (8)

  • Figure 1: Timeline of the development of random access protocols.
  • Figure 2: Coded compressive sensing architectures.
  • Figure 3: Preamble-based: $\bm{x} = (\bm{x}_1,\bm{x}_2)$.
  • Figure 4: Spreading-based architectures.
  • Figure 5: Minimum SNR required to achieve a $\mathsf{PUPE} = 5 \times 10^{-2}$, over the Gaussian MAC channel. The frame length is $n=30000$ real channel uses. For the 5GNR two-step random access protocol, $n=32556$.
  • ...and 3 more figures

Theorems & Definitions (1)

  • Example 1: Slotted Aloha as UMAC code