This paper investigates a grant-free non-orthogonal multiple access (NOMA) system where massive number of users wake up and send data right away without performing a grant-based initial access procedure. Since no scheduling grant is used in this system, the base station (BS) does not know which user is transmitting on each resource. Also, due to the lack of an uplink (UL) timing control process, multiple user's signals are asynchronously received at the BS. This causes asynchronous interference, or multiuser inter-carrier and inter-symbol interference. We propose two ideas to address these two problems. We first propose an auxiliary preamble structure to successfully detect the user activity, even in the presence of a massive number of users. We, then, propose a modification to the interleave-division multiple access (IDMA) receiver to mitigate asynchronous interference. The simulation results show that the proposed scheme significantly improves the preamble detection performance and BER performance compared to the conventional schemes. Furthermore, we show that the proposed grant-free NOMA system can achieve much better performance than the grant-based NOMA system in terms of transmission time and signaling overhead.
Bibliographical noteFunding Information:
Manuscript received April 20, 2018; revised August 25, 2018 and February 12, 2019; accepted June 18, 2019. Date of publication July 9, 2019; date of current version September 10, 2019. This work was supported in part by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MSIT) under Grant 2018R1A2A1A05021029, in part by Institute for Information and Communications Technology Promotion (IITP) grant funded by the Korea Government (MSIT) (2016-0-00181-004, Development on the core technologies of transmission, modulation and coding with low-power and low-complexity for massive connectivity in the IoT environment), and in part by the Samsung Research in Samsung Electronics under Grant IO160816-03854-01. The associate editor coordinating the review of this paper and approving it for publication was B. Natarajan. (Corresponding author: Daesik Hong.) S. Kim, H. Kim, and D. Hong are with the School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, South Korea (e-mail: firstname.lastname@example.org; email@example.com; firstname.lastname@example.org).
All Science Journal Classification (ASJC) codes
- Computer Science Applications
- Electrical and Electronic Engineering
- Applied Mathematics