Yuxi Han

Bio: Yuxi Han is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Decoding methods & Combustion. The author has an hindex of 3, co-authored 4 publications receiving 41 citations.

Weighted message passing algorithm for SCMA

Abstract: Sparse code multiple access (SCMA) is a new frequency domain non-orthogonal multiple-access technique which can make full use of limited spectrum resources in wireless communication system. In SCMA, multiple users share the same time-frequency resources of orthogonal frequency division multiple access (OFDMA). However, message passing algorithm (MPA) is used in the process of SCMA decoding. And when the iteration number of MPA is large, the decoding complexity of SCMA is very high. In this paper, we propose an algorithm to decrease the decoding complexity of SCMA by introducing weight factors to replace MPA algorithm iterative process. We give each codeword in the codebook an original probability value which is related to the distance between received signal and the codeword. We set a corresponding weight factor for each probability value to change the original probability distribution of each codeword in the codebook. Simulation shows that this algorithm can greatly decrease the decoding complexity of SCMA while suffering only a bit of performance loss.

Enabling High Order SCMA Systems in Downlink Scenarios With a Serial Coding Scheme

Abstract: In the future fifth generation communication systems, sparse code multiple access (SCMA) shows strong competitiveness as a novel non-orthogonal multiple access (NOMA) technique. Attributing to multi-dimensional codebooks, the SCMA can obtain shaping gain and provide a better performance than some other NOMA schemes, such as pattern division multiple access, low-density signature (LDS), and so on. However, under higher user load, each orthogonal resource in high-order SCMA systems is occupied by more users and the constellations of these systems possess smaller Euclidean distances, both of which will degrade the link performance. The iterative algorithm employed in SCMA decoding, namely message passing algorithm, will also bring an exponential growth of computational complexity. In this paper, a scheme with serial codes for system order reduction in downlink scenarios, namely serial SCMA, is proposed to tackle these issues. Based on the idea of hierarchical coding, the processes of encoding and decoding in a high-order system are decomposed into several processes in low-order systems. Specific mapping modules are designed to recover the original user binary bits. Simulation results show that serial SCMA will substantially cut down the detection complexity and enjoy better link performance while maintaining sparser codebooks. Besides, it still inherits the advantages of original SCMA systems such as overloading and average aggregate energy efficiency over OMA and other NOMA schemes.

Enabling SCMA long codewords with a parallel SCMA coding scheme

Abstract: Fifth generation (5G) wireless networks require massive connectivity with a large number of devices and ask for non-orthogonal multiple access which has been proposed as a paradigm shift of physical layer technologies. Among all the existing non-orthogonal technologies where the number of users can be larger than the spreading factor, recently proposed sparse code multiple access (SCMA) is shown to achieve a better link performance. However, the message passing algorithm (MPA) is used in SCMA decoding. And the decoding complexity of SCMA is very high and is increasing exponentially as the dimensions of the codebook increase. From this point of view, implementing SCMA long codewords in a real hardware environment with the high complexity MPA is intractable. A scheme to reduce the decoding complexity of SCMA is essential. In this paper, we propose a parallel SCMA system which can be called SCMA hierarchical coding to come through SCMA long codewords. We try to break the process of the encoding and decoding of a long SCMA codeword into several processes of encoding and decoding of short codewords. We also analyze the tradeoff between the performance and the decoding complexity of the parallel SCMA system. The simulation results show that the parallel SCMA system can greatly reduce the decoding complexity of SCMA long codewords while still keeping higher capacity and lower block error rate compared to long term evolution (LTE) and low density signature (LDS) respectively.

High-Performance TPE-S Modified by a Flame-Retardant System Based on Black Phosphorus Nanosheets

Abstract: Few-layer black phosphorus nanosheets (BPs) combined with melamine cyanurate and poly(phenylene oxide) were used to prepare a flame-retardant thermoplastic elastomer based on polystyrene (TPE-S) for the first time. Compared with neat TPE-S, BP-modified TPE-S with a phosphorus content of 7.98% (TPE-S/BP-7.98) passed the UL-94 vertical burning V-0 rating, and the limiting oxygen index value increased to 24.0%. The peak heat release rate (PHRR), total heat release, and the average combustion effective heat of TPE-S/BP-7.98 were decreased by 61.8, 26.0, and 35.3%, respectively. The time to PHRR was increased from 90 s (neat TPE-S) to 170 s. Scanning electron microscopy of frozen fracture sections showed favorable compatibility and dispersibility of BPs in TPE-S. In addition, the introduction of BPs showed the most negligible effect on the mechanical properties of TPE-S compared with other flame retardants (aluminum hypophosphite and red phosphorus).

Optimization of OTT small data services: Network capacity and cost analysis

Abstract: The popularity of smartphones and mobile applications has boosted over the top (OTT) services during the recent years, and this trend is expected to continue in the future. However, frequent connection reestablishments caused by OTT services which send or receive small amounts of data often lead to a heavy signalling load within the mobile networks. That has brought about signalling storm, which is a specific problem of mobile networks. It is mainly limited by the scarcity of wireless spectrum resources. Heartbeat mechanism is one of OTT services. Smartphones communicate with the mobile networks by the heartbeat mechanism to report whether they are online. Although heartbeat message belongs to small data services, it lead that users update their status frequently. The payload of update message can not be ignored. Thus, for OTT services such as Wechat, mobile QQ, the optimization of heartbeat mechanism has become one of the best methods to reduce the network payload. In this paper, we proposed a new concept visual user equipment (VUE) which can imitate some periodic information of user equipment (UE) and replace the UE to communicate with applications in the cable end. We also proposed a scheme to reduce the transmission of heartbeat signallings according to the state of OTT services. Under the same end-to-end payload condition our scheme has greater network capacity and higher throughput at the expense of a little rise in packet loss rate only when the arrival rate of service packets is high. On the other hand, our scheme can relieve the signalling storm of OTT services to a great extent.

A Survey of Non-Orthogonal Multiple Access for 5G

Abstract: In the fifth generation (5G) of wireless communication systems, hitherto unprecedented requirements are expected to be satisfied. As one of the promising techniques of addressing these challenges, non-orthogonal multiple access (NOMA) has been actively investigated in recent years. In contrast to the family of conventional orthogonal multiple access (OMA) schemes, the key distinguishing feature of NOMA is to support a higher number of users than the number of orthogonal resource slots with the aid of non-orthogonal resource allocation. This may be realized by the sophisticated inter-user interference cancellation at the cost of an increased receiver complexity. In this paper, we provide a comprehensive survey of the original birth, the most recent development, and the future research directions of NOMA. Specifically, the basic principle of NOMA will be introduced at first, with the comparison between NOMA and OMA especially from the perspective of information theory. Then, the prominent NOMA schemes are discussed by dividing them into two categories, namely, power-domain and code-domain NOMA. Their design principles and key features will be discussed in detail, and a systematic comparison of these NOMA schemes will be summarized in terms of their spectral efficiency, system performance, receiver complexity, etc. Finally, we will highlight a range of challenging open problems that should be solved for NOMA, along with corresponding opportunities and future research trends to address these challenges.

Low Complexity Iterative Receiver Design for Sparse Code Multiple Access

Abstract: Sparse code multiple access (SCMA) is one of the most promising methods among all the non-orthogonal multiple access techniques in the future 5G communication. Compared with some other non-orthogonal multiple access techniques, such as low density signature, SCMA can achieve better performance due to the shaping gain of the SCMA code words. However, despite the sparsity of the code words, the decoding complexity of the current message passing algorithm utilized by SCMA is still prohibitively high. In this paper, by exploring the lattice structure of SCMA code words, we propose a low-complexity decoding algorithm based on list sphere decoding (LSD). The LSD avoids the exhaustive search for all possible hypotheses and only considers signal within a hypersphere. As LSD can be viewed a depth-first tree search algorithm, we further propose several methods to prune the redundancy-visited nodes in order to reduce the size of the search tree. Simulation results show that the proposed algorithm can reduce the decoding complexity substantially while the performance loss compared with the existing algorithm is negligible.

Investigation on Evolving Single-Carrier NOMA Into Multi-Carrier NOMA in 5G

Abstract: Non-orthogonal multiple access (NOMA) is one promising technology, which provides high system capacity, low latency, and massive connectivity, to address several challenges in the fifth-generation wireless systems. In this paper, we first reveal that the NOMA techniques have evolved from single-carrier NOMA (SC-NOMA) into multi-carrier NOMA (MC-NOMA). Then, we comprehensively investigated on the basic principles, enabling schemes and evaluations of the two most promising MC-NOMA techniques, namely sparse code multiple access (SCMA) and pattern division multiple access (PDMA). Meanwhile, we consider that the research challenges of SCMA and PDMA might be addressed with the stimulation of the advanced and matured progress in SC-NOMA. Finally, yet importantly, we investigate the emerging applications, and point out the future research trends of the MC-NOMA techniques, which could be straightforwardly inspired by the various deployments of SC-NOMA.

On Fixed-Point Implementation of Log-MPA for SCMA Signals

Abstract: In this letter, we present a design framework for fixed-point implementation of the log-domain message passing algorithm (Log-MPA) for sparse code multiple access signals, and make a detailed comparative analysis on the complexity of Log-MPA and traditional MPA. We also investigate the impact of the number of massage-passing iterations within the Log-MPA decoding process on the performance of Log-MPA. Simulation results demonstrate that Log-MPA achieves favorable performance with low-complexity hardware implementation as compared to MPA. We also implement Log-MPA on FPGA evaluation board to verify the performance of Log-MPA.

Survey and Performance Evaluation of Multiple Access Schemes for Next-Generation Wireless Communication Systems

Abstract: Mobile communication systems are always in continuous evolution due to the demands of the end-users using this technology. Therefore, before the possible launch of 5G, some technologies have opened the way to the new mobile communication system. The need for technologies that provide more comfort to users has led to the construction of complex communication systems that were only science fiction decades ago. The information society in which we are now immersed has been the result of constant progress over time. In this paper, a survey of multiple access schemes for next-generation wireless communication systems is presented. Multiple access schemes are reviewed for possible use in next-generation wireless communication systems such as orthogonal multiple access (OMA), non-orthogonal multiple access (NOMA), and delta-orthogonal multiple access (D-OMA), etc. General comparisons of 1G to 6G are presented. Different types of OMA are explained, and then orthogonal frequency division multiple access (OFDMA) is chosen as an example of the OMA scheme to compare with NOMA and D-OMA. There are two types of NOMA: power-domain and code-domain, which are discussed and compared. Simulation results are presented, and a comparison among different access schemes is provided.