arXiv subjects

Mert Ozates

Publications and source records attributed to Mert Ozates.

7 recordsLinked to original sources

arXiv2026

Transceiver Design for Cell-Free Unsourced Random Access

We propose a low-complexity, energy-efficient solution for cell-free unsourced random access (URA), in which multiple distributed access points are connected to a central processing unit via a fronthaul. Assuming that each user transmits a pilot sequence followed by a polar codeword whose symbols are placed to the data part of the frame according to an on-off pattern, we utilize iterative decoding, including orthogonal matching pursuit (OMP)-based pilot detection and channel estimation, symbol estimation using a linear minimum mean square error (MMSE) solution, symbol combining, single-user decoding, and successive interference cancellation (SIC). We also present finite blocklength (FBL) performance and detailed complexity analyses. Numerical results demonstrate that the FBL analysis properly characterizes system performance and that the proposed cell-free URA scheme offers superior performance compared to existing low-complexity schemes. Namely, it offers a superior performance of up to 4.5 dB and can accommodate up to 1800 active users.

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arXiv2026

ETSI ISG MAT: Bridging Multiple Access Techniques Research and 6G Standardisation

Improved spectral efficiency and inter-user interference mitigation are important aspects of IMT-2030 and the ongoing 3GPP 6G study. ETSI established the Industry Specification Group on Multiple Access Techniques (ISG MAT) as a research and pre-standardisation activity to build wider consensus on downlink MAT for 3GPP-based 6G systems. Its first report, ETSI GR MAT 001 V1.1.1, provides a standards-oriented comparison of 3GPP-specified techniques, including OMA, MU-MIMO, and MUST, with candidate techniques comprising power-domain NOMA, RSMA, and cache-aided MU-MIMO. The report identifies operating conditions in which candidate MAT can improve spectral efficiency and assesses implications for transceiver processing, network assistance information, and reference-signal requirements. Ongoing work includes realistic 5G NR link-level evaluations and the study of MAT for non-terrestrial networks, providing timely technical evidence for 3GPP 6G standardisation discussions.

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arXiv2025

Fully Asynchronous Unsourced Random Access over Fading Channels

We examine unsourced random access in a fully asynchronous setup, where active users transmit their data without restriction on the start time over a fading channel. In the proposed scheme, the transmitted signal consists of a pilot sequence and a polar codeword, with the polar codeword distributed across the data part of the packet in an on-off pattern. The receiver uses a double sliding-window decoder, where the inner window employs iterative decoding with joint timing and pilot detection, channel estimation, single-user decoding, and successive interference cancellation to recover the message bits, while the outer window enhances interference cancellation. The numerical results indicate that the proposed scheme exhibits only a slight performance loss compared to the synchronous benchmark while being more applicable in practice.

cs.IT↗

arXiv2025

A Fully Asynchronous Unsourced Random Access Scheme

We investigate fully asynchronous unsourced random access (URA), and propose a high-performing scheme that employs on-off division multiple access (ODMA). In this scheme, active users distribute their data over the transmit block based on a sparse transmission pattern without any limitations on the starting time. At the receiver side, we adopt a double sliding-window decoding approach, utilizing a smaller inner decoding window of two block lengths within a larger outer window to enhance the interference cancellation process. Within the inner window, the receiver iteratively applies preamble-free joint starting time and pattern detection, single-user decoding, and successive interference cancellation operations. A notable feature of the proposed scheme is its elimination of the need for a preamble for starting time detection; this is achieved using ODMA transmission patterns. Numerical results demonstrate that the proposed asynchronous URA scheme outperforms existing alternatives.

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arXiv2025

ODMA-Based Cell-Free Unsourced Random Access with Successive Interference Cancellation

We consider the unsourced random access problem with multiple receivers and propose a cell-free type solution for that. In our proposed scheme, the active users transmit their signals to the access points (APs) distributed in a geographical area and connected to a central processing unit (CPU). The transmitted signals are composed of a pilot and polar codeword, where the polar codeword bits occupy a small fraction of the data part of the transmission frame. The receiver operations of pilot detection and channel and symbol estimation take place at the APs, while the actual message bits are detected at the CPU by combining the symbol estimates from the APs forwarded over the fronthaul. The effect of the successfully decoded messages is then subtracted at the APs. Numerical examples illustrate that the proposed scheme can support up to 1400 users with a high energy efficiency, and the distributed structure decreases the error probability by more than two orders of magnitude.

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arXiv2024

Unsourced Random Access: A Comprehensive Survey

Multiple access communication systems enable numerous users to share common communication resources, playing a crucial role in wireless networks. With the emergence of the sixth generation (6G) and beyond communication networks, supporting massive machine-type communications with sporadic activity patterns is expected to become a critical challenge. Unsourced random access (URA) has emerged as a promising paradigm to address this challenge by decoupling user identification from data transmission through the use of a common codebook. This survey offers a comprehensive overview of URA solutions, encompassing both theoretical foundations and practical applications. We present a systematic classification of URA solutions across three primary channel models: Gaussian multiple access channels (GMACs), single-antenna fading channels, and multiple-input multiple-output (MIMO) fading channels. For each category, we analyze and compare state-of-the-art solutions in terms of performance, complexity, and practical feasibility. Additionally, we discuss critical challenges such as interference management, computational complexity, and synchronization. The survey concludes with promising future research directions and potential methods to address existing limitations, providing a roadmap for researchers and practitioners in this rapidly evolving field.

cs.IT↗

arXiv2024

An ODMA-Based Unsourced Random Access Scheme with a Multiple Antenna Receiver

We investigate the unsourced random access scheme assuming that the base station is equipped with multiple antennas, and propose a high-performing solution utilizing on-off-division multiple access. We assume that each user spreads its pilot sequence and polar codeword to the pilot and data parts of the transmission frame, respectively, based on a transmission pattern. The iterative receiver operation consists of pilot and pattern detection followed by channel vector and symbol estimation, polar decoding, and successive interference cancellation. Numerical findings demonstrate that the proposed scheme has superior performance compared to the state-of-the-art in various antenna settings.

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