Power Domain Multiplexing Research Articles

Non-Orthogonal Random Access for 5G Networks

The massive amounts of machine-type user equipments (UEs) will be supported in the future fifth generation (5G) networks. However, the potential large random access (RA) delay calls for a new RA scheme and for a detailed assessment of its performance. Motivated by the key idea of non-orthogonal multiple access, the non-orthogonal RA (NORA) scheme based on successive interference cancellation (SIC) is proposed in this paper to alleviate the access congestion problem. Specifically, NORA utilizes the difference of time of arrival to identify multiple UEs with the identical preamble, and enables power domain multiplexing of collided UEs in the following access process, while the base station performs SIC based on the channel conditions obtained through preamble detection. Our analysis shows that the performance of the NORA is superior to the conventional orthogonal RA (ORA) scheme in terms of the preamble collision probability, access success probability, and the throughput of RA. Simulation results verify our analysis and further show that our NORA scheme can improve the number of the supported UEs by more than 30%. Moreover, the number of preamble transmissions and the access delay for successfully accessed UEs are also reduced significantly by using the proposed RA scheme.

NOMA-Based Spatial Modulation

Spatial modulation (SM) has emerged as a low-complexity and energy-efficient multiple-input multiple-output transmission technique, where the information bits are not only transmitted by amplitude phase modulation but also conveyed by the index of activated transmit antenna (TA). By deploying SM in downlink multi-user (DL-MU) scenarios, conventional orthogonal multiple access-based SM (OMA-SM) allocates exclusive time-frequency resources to users, but suffers from low spectral efficiency. TA grouping-based SM (TAG-SM) divides TAs into sub-groups to serve different users independently, but suffers from severe inter-user interference. By introducing non-OMA (NOMA) into SM for DL-MU transmission, NOMA-based SM (NOMA-SM) is proposed to mitigate inter-user interference, while maintaining high spectral efficiency. Specifically, by applying successive interference cancellation at user side, the inter-user interference could be effectively eliminated with the sacrifice of increased computational complexity. Afterward, based on a symbol error rate analysis, a low-complexity power allocation scheme is provided to achieve high spectral efficiency through power domain multiplexing. When considering near-far effect from user distribution, user pairing issue is also discussed. Numerical simulation compares NOMA-SM with OMA-SM and TAG-SM, and verifies the effectiveness of the proposed low-complexity power allocation and user pairing methodologies.

Design of Joint Spatial and Power Domain Multiplexing Scheme for Massive MIMO Systems

Massive Multiple-Input Multiple-Output (MIMO) is one of the key techniques in 5th generation wireless systems (5G) due to its potential ability to improve spectral efficiency. Most of the existing works on massive MIMO only consider Time Division Duplex (TDD) operation that relies on channel reciprocity between uplink and downlink channels. For Frequency Division Duplex (FDD) systems, with continued efforts, some downlink multiuser MIMO scheme was recently proposed in order to enable “massive MIMO” gains and simplified system operations with limited number of radio frequency (RF) chains in FDD system. However these schemes, such as Joint Spatial Division and Multiplexing (JSDM) scheme and hybrid precoding scheme, only focus on multiuser transmission in spatial domain. Different from most of the existing works, this paper proposes Joint Spatial and Power Multiplexing (JSPM) scheme in FDD systems. It extends existing FDD schemes from spatial division and multiplexing to joint spatial and power domain to achieve more multiplexing gain. The user grouping and scheduling scheme of JSPM is studied and the asymptotic expression for the sum capacity is derived as well. Finally, simulations are conducted to illustrate the effectiveness of the proposed scheme.