Yi Zhang

Non-Orthogonal Multiple Access in 5G Communications

Project description: Non-Orthogonal Multiple Access in 5G Communications

Sept. 2015 - Present, Institute of Information Engineering, School of Electronic and Information Engineering, Xi'an Jiaotong University, China.
Research Assistant supervised by Prof. Hui-Ming Wang.

As an emerging technology to enhance spectrum sharing, NOMA has been widely recognized as a promising technology for 5G wireless systems. Different from conventional orthogonal multiple access (OMA), NOMA realizes the simultaneous transmission of multiple data streams via power domain division. At a transmitter, a superposition of different messages is broadcasted. At the receivers, the successive interference cancellation (SIC) technique is used to realize multi-user detection.

Much of my master's work focuses on the algorithm design and convex optimization in NOMA from the perspective of physical layer security, energy efficiency, and spectrum sharing:

Publications:

H.-M. Wang, Yi Zhang, and Z. Ding, ''Physical Layer Security in Non-orthogonal Multiple Access," in Trusted Communications with Physical Layer Security for 5G and Beyond, IET, chapter 15, 2017. [Link]
Yi Zhang, H.-M. Wang, Q. Yang, and Z. Ding, "Secrecy sum rate maximization in non-orthogonal multiple access," IEEE Communications Letters, vol. 20, no. 5, pp. 930-933, May 2016. [Link]
Yi Zhang, H.-M. Wang, T.-X. Zheng, and Q. Yang, "Energy-efficient transmission design in non-orthogonal multiple access,'' IEEE Transactions on Vehicular Technology, vol. 66, no. 33, pp. 2852-2857, Mar. 2017. [Link]
Yi Zhang, H.-M. Wang, Z. Ding, and M. H. Lee, "Non-orthogonal multiple access assisted multi-region geocast,'' IEEE Access, vol. 6 pp. 2340-2355, no. 99, 2018. [Link]
Yi Zhang, Q. Yang, T.-X. Zheng, Y. Ju and H.-M. Wang, "Energy efficiency optimization in cognitive radio inspired non-orthogonal multiple access,'' IEEE Annual Symposium Personal, Indoor and Mobile Radio Communications (PIMRC), Valencia, Spain, Sep. 2016. [Link]
Yi Zhang, T.-X. Zheng, Q. Yang, H.-M. Wang, B. Wang and Z. Li, "The application of non-orthogonal multiple access in 5G physical-layer multi-region geocast,'' IEEE Wireless Communications and Networking Conference (WCNC), San Francisco, US, Mar. 2017.[Link]

Physical Layer Security in NOMA

Abstract----This work is to study physical layer security in a single-input single-output (SISO) NOMA system consisting of a transmitter, multiple legitimate users, and an eavesdropper. The aim is to maximize the secrecy sum rate (SSR) of the NOMA system subject to the users' quality of service (QoS) requirements. We firstly identify the feasible region of the transmit power for satisfying all users' QoS requirements. Then we derive the closed-form expression of an optimal power allocation policy that maximizes the SSR. Numerical results are provided to show a significant SSR improvement by NOMA compared with conventional orthogonal multiple access (OMA).

System model for a SISO NOMA system with an eavesdropper

Energy Efficient Transmissions in NOMA

Abstract----In this work, we study the benefit of NOMA in enhancing energy efficiency (EE) for a multi-user downlink transmission, where the EE is defined as the ratio of the achievable sum rate of the users to the total power consumption. Our goal is to maximize the EE subject to a minimum required data rate for each user, which leads to a non-convex fractional programming problem. To solve it, we first establish the feasible range of the transmitting power that is able to support each user's data rate requirement. Then, we propose an EE-optimal power allocation strategy that maximizes the EE. Our numerical results show that NOMA has superior EE performance in comparison with conventional OMA.

System model for a SISO NOMA system

NOMA-assisted Geocast

Abstract----The availability of wireless spectrum is severely limited for emerging wireless services, which inspires continuous innovation in designs of highly efficient spectrum sharing schemes. This work proposes a novel location-based spectrum sharing framework by extending the traditional multi-region geocast into the physical layer and reinforcing it with the NOMA technology. This novel scheme exploits NOMA to realize the simultaneous delivery of different messages to user groups characterized by their different geographical locations. The essence of the proposed scheme is that the geographical information of users plays a critical role in supporting both physical-layer multi-region geocast and NOMA to enhance the spectral efficiency (SE) and energy efficiency (EE) of wireless transmissions. In particular, we investigate downlink beamforming designs and optimizations in three multi-region geocast scenarios for a multiple-input single-output (MISO) NOMA system. Efficient algorithms are proposed based on the sequential convex approximation (SCA) method to solve the non-convex problems therein. Comprehensive numerical experiments are further provided to validate our proposed algorithms. Compared with conventional multi-group multicast and single-group multicast using orthogonal multiple access (OMA), physical-layer multi-region geocast using NOMA holds tremendous promise for improving spectrum sharing in terms of both SE and EE.

System model for a MISO NOMA system with geocast design

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