UNSOURCED RANDOM ACCESS WITH USER LOCALIZATION AND SENSING

Abstract

Future wireless networks must support massive numbers of sporadic transmissions while meeting strict spectrum and energy limits. Unsourced random access (URA) provides a grant-free model in which devices transmit without pre-allocated resources and user identifiers and the receiver jointly detects user activity and decodes messages from a large number of users. This thesis advances URA by enabling sensing and localization within the communication process to build scalable frameworks that remain reliable and energy-efficient under heavy loads. It also contributes URA designs that tolerate relaxed synchronization and support longer payloads when needed. Amulti-antenna preamble–payloadURAarchitecture is developed that fuses compressedsensing (CS)-based activity detection with iterative multiuser detection (MUD), decoding, and channel refinement on Rayleigh fading channels. The design is extended to lowscattering regimes through channel models that account for array geometry, consistent with high-frequency environments. Building on this foundation, the thesis applies integrated sensing and communication (ISAC) principles. A location-based URA framework is introduced in which the base station (BS) localizes active users while detecting and decoding their data using only uplink signals. The method ties user transmission features to angle-ofarrival (AoA) and partitions space into sectors with sub-pool allocation and reuse to reduce collisions and complexity. Localization improves communication by providing spatial information that helps separate multiple packets. The concept is further generalized in the random-access procedure. The thesis also demonstrates environment sensing where user uplink signals act as opportunistic illuminators for multi-object sensing at the BS, revealing the synergy and trade-offs between sensing and communication. Some structural challenges of URA are also addressed. Scalability under timing uncertainty is achieved through a fully asynchronous URA design that removes slot and beacon requirements and performs sliding window timing acquisition together with MUD on the Gaussian channel. For longer messages a multi-segment URA structure is proposed that stitches decoded segments across consecutive slots and employs a dual preamble pool to identify the first segment and reduce collisions. Together, these studies show how URA can jointly deliver reliable data detection, user localization, and environmental sensing with high scalability, paving the way for intelligent and spectrum efficient random-access in future networks.