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Open Access Issue
Performance analysis of a low-complexity nonorthogonal multiple access scheme in visible light communication downlinks using pulse modulations
Intelligent and Converged Networks 2021, 2 (1): 50-65
Published: 12 May 2021
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Although Successive Interference Cancellation (SIC) decoding is widely adopted in Nonorthogonal Multiple Access (NOMA) schemes for the recovery of user data at acceptable complexity, the imperfect SIC would cause Error Propagation (EP), which can severely degrade system performance. In this work, we propose an SIC-free NOMA scheme in pulse modulation based Visible Light Communication (VLC) downlinks, including two types of users with different data rate requirements. Low bit-rate users adopt on-off keying, whereas high bit-rate ones use Multiple Pulse Position Modulation (MPPM). The soft decision decoding scheme is exploited by high bit-rate users to decode MPPM signals, which could fundamentally eliminate the detrimental effect of EP; the scheme is also easier and faster to execute compared with the conventional SIC decoding scheme. Expressions of the symbol error rate and achievable data rate for two types of users are derived. Results of the Monte Carlo simulation are provided to confirm the correctness of theoretical results.

Open Access Issue
Convergence of Broadband and Broadcast/Multicast in Maritime Information Networks
Tsinghua Science and Technology 2021, 26 (5): 592-607
Published: 20 April 2021
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Downloads:51

Recently, the fifth-generation (5G) of wireless networks mainly focuses on the terrestrial applications. However, the well-developed emerging technologies in 5G are hardly applied to the maritime communications, resulting from the lack of communication infrastructure deployed on the vast ocean, as well as different characteristics of wireless propagation environment over the sea and maritime user distribution. To satisfy the expected plethora of broadband communications and multimedia applications on the ocean, a brand-new maritime information network with a comprehensive coverage capacity in terms of all-hour, all-weather, and all-sea-area has been expected as a revolutionary paradigm to extend the terrestrial capacity of enhanced broadband, massive access, ultra-reliable, and low-latency to the vast ocean. Further considering the limited available resource of maritime communication infrastructure, the convergence of broadband and broadcast/multicast can be regarded as a possible yet practical solution for realizing an efficient and flexible resource configuration with high quality of services. Moreover, according to such multi-functionality and all-coverage maritime information network, the monitoring and sensing of vast ocean area relying on massive Ocean of Things and advanced radar techniques can be also supported. Concerning these issues above, this study proposes a Software Defined Networking (SDN) based Maritime Giant Cellular Network (MagicNet) architecture for broadband and multimedia services. Based on this network, the convergence techniques of broadband and broadcast/multicast, and their supporting for maritime monitoring and marine sensing are also introduced and surveyed.

Open Access Issue
Analysis of Outage Capacity of NOMA: SIC vs. JD
Tsinghua Science and Technology 2016, 21 (5): 538-543
Published: 18 October 2016
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In fifth-generation wireless communication networks, Non-Orthogonal Multiple Access (NOMA) has attracted much attention in both academic and industrial fields because of its higher spectral efficiency in comparison with orthogonal multiple access. Recently, numerous uplink NOMA techniques have been proposed, some of which are based on Successive Interference Cancellation (SIC) and others on Joint Decoding (JD, or simultaneous decoding). In this study, we analyze the outage capacities of SIC and JD in the case of single-block transmission over a two-user Gaussian multiple-access channel with partial channel state information at transmitter from the perspective of information theory. Results of the analysis and numerals show that compared to SIC, JD can achieve a sum-rate gain of up to 10% or sum-power gain of 0.8 dB.

Open Access Issue
Non-Uniform APSK Optimization for BICM Systems
Tsinghua Science and Technology 2015, 20 (2): 175-181
Published: 23 April 2015
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Traditional Amplitude Phase Shift Keying (APSK) consists of rings with points uniformly spaced. By giving up this uniform-spacing feature, we propose an APSK optimization method based on the uniform APSK with Gray labeling (Gray-APSK). The aim of the optimization is to maximize the Generalized Mutual Information (GMI) of Bit-Interleaved Coded Modulation (BICM) for the targeted code rate and channel. We show that our optimized non-uniform APSK could offer further performance gain compared with the conventional uniform Gray-APSK and considerably outperforms the traditional quadrature amplitude modulation at the targeted SNR and channel.

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