V2X Meets NOMA: Non-Orthogonal Multiple Access for 5G Enabled Vehicular Networks

Benefited from the widely deployed infrastructure, the LTE network has recently been considered as a promising candidate to support the vehicle-to-everything (V2X) services. However, with a massive number of devices accessing the V2X network in the future, the conventional OFDM-based LTE network faces the congestion issues due to its low efficiency of orthogonal access, resulting in significant access delay and posing a great challenge especially to safety-critical applications. The non-orthogonal multiple access (NOMA) technique has been well recognized as an effective solution for the future 5G cellular networks to provide broadband communications and massive connectivity. In this article, we investigate the applicability of NOMA in supporting cellular V2X services to achieve low latency and high reliability. Starting with a basic V2X unicast system, a novel NOMA-based scheme is proposed to tackle the technical hurdles in designing high spectral efficient scheduling and resource allocation schemes in the ultra dense topology. We then extend it to a more general V2X broadcasting system. Other NOMA-based extended V2X applications and some open issues are also discussed.Comment: Accepted by IEEE Wireless Communications Magazin

SCMA Codebook Design

Multicarrier CDMA is a multiple access scheme in which modulated QAM symbols are spread over OFDMA tones by using a generally complex spreading sequence. Effectively, a QAM symbol is repeated over multiple tones. Low density signature (LDS) is a version of CDMA with low density spreading sequences allowing us to take advantage of a near optimal message passing algorithm (MPA) receiver with practically feasible complexity. Sparse code multiple access (SCMA) is a multi-dimensional codebook-based non-orthogonal spreading technique. In SCMA, the procedure of bit to QAM symbol mapping and spreading are combined together and incoming bits are directly mapped to multi-dimensional codewords of SCMA codebook sets. Each layer has its dedicated codebook. Shaping gain of a multi-dimensional constellation is one of the main sources of the performance improvement in comparison to the simple repetition of QAM symbols in LDS. Meanwhile, like LDS, SCMA enjoys the low complexity reception techniques due to the sparsity of SCMA codewords. In this paper a systematic approach is proposed to design SCMA codebooks mainly based on the design principles of lattice constellations. Simulation results are presented to show the performance gain of SCMA compared to LDS and OFDMA.Comment: Accepted for IEEE VTC-fall 201

Non-orthogonal multiple access for machine-type communications toward 6G

Abstract. Massive machine-type communications (mMTC) is one of the main focus areas in the fifth generation of wireless communications. It is also the fastest-growing field in terms of the number of devices. The massive increase in devices connected to the internet and global data traffic creates unprecedented requirements for future generations of wireless communications. One of the key technologies for the performance of the system is the utilized multiple access (MA) scheme. The conventional orthogonal MA (OMA) schemes from the earlier generations fail to satisfy the increasing demands for connectivity and spectral efficiency. On the contrary, non-orthogonal MA (NOMA) schemes offer the connectivity and spectral efficiency needed to enable mMTC. NOMA does this by allowing multiple users to transmit their data through the same resource blocks (RBs) simultaneously. NOMA is generally divided into two categories, namely power domain (PD-) NOMA and code domain (CD-) NOMA. PD-NOMA utilizes the power domain for the multiplexing, whereas CD-NOMA uses the code domain. This thesis focuses on the fundamentals of NOMA, MTC, and what NOMA can offer to MTC. We will also discuss the challenges and open problems that need to be solved. Finally, the thesis includes some simulations that demonstrate NOMA in practice.Ei-ortogonaalinen monikäyttö kone-tyyppisessä kommunikaatiossa kohti 6G:tä. Tiivistelmä. Massiivinen kone-tyyppinen kommunikaatio (mMTC) on yksi viidennen sukupolven langattoman viestinnän pääpainopisteistä. Se on myös nopeimmin kasvava osa-alue, kun katsotaan laitteiden lukumäärää. Internetiin yhdistettyjen laitteiden ja globaalin tietoliikenteen valtava kasvu luo ennennäkemättömiä vaatimuksia tuleville langattoman viestinnän sukupolville. Yksi avainteknologioista järjestelmän suorituskyvyn kannalta on käytetty monikäyttömenetelmä (MA). Tavanomaiset ortogonaaliset MA (OMA) -järjestelmät eivät saavuta yhdistettävyyden ja spektritehokkuuden kasvavia vaatimuksia. Sitä vastoin ei-ortogonaaliset MA (NOMA) -järjestelmät tarjoavat mMTC:n mahdollistamiseen tarvitun yhdistettävyyden ja spektritehokkuuden. NOMA saavuttaa tämän sallimalla usean käyttäjän lähettää dataa saman resurssilohkon kautta samanaikaisesti. NOMA voidaan yleisesti jakaa kahteen kategoriaan, tehoalueen NOMA:an ja koodialueen NOMA:an. Tämä työ keskittyy NOMA:n ja MTC:n perusteisiin ja siihen, mitä NOMA voi tarjota MTC-käyttökohteille. Työssä käydään myös läpi ratkaisuja vaativat haasteet ja avoimet ongelmat. Lopuksi työ sisältää simulaatioita, jotka mallintavat NOMA:n toimintaa käytännössä