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Iterative Receivers for Downlink MIMO-SCMA: Message Passing and Distributed Cooperative Detection

IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2018年第5期17卷 3444-3458页

作者： Yuan, Weijie Wu, Nan Guo, Qinghua Li, Yonghui Xing, Chengwen Kuang, Jingming Beijing Inst Technol Sch Informat & Elect Beijing 100081 Peoples R China Univ Wollongong Sch Elect Comp & Telecommun Engn Wollongong NSW 2522 Australia Univ Sydney Sch Elect & Informat Engn Ctr Excellence Telecommun Sydney NSW 2006 Australia

The rapid development of mobile communications requires even higher spectral efficiency. Non-orthogonal multiple access (NOMA) has emerged as a promising technology to further increase the access efficiency of wireless networks. Among several NOMA schemes, it has been shown that sparse code multiple access (SCMA) is able to achieve better performance. In this paper, we consider a downlink MIMO-SCMA system over frequency selective fading channels. For optimal detection, the complexity increases exponentially with the product of the number of users, the number of antennas and the channel length. To tackle this challenge, we propose near optimal low-complexity iterative receivers based on factor graph. By introducing auxiliary variables, a stretched factor graph is constructed and a hybrid belief propagation (BP) and expectation propagation (EP) receiver, named stretch-BP-EP, is proposed. Considering the convergence problem of BP algorithm on loopy factor graph, we convexify the Bethe free energy and propose a convergence-guaranteed BP-EP receiver, named conv-BP-EP. We further consider cooperative network and propose two distributed cooperative detection schemes to exploit the diversity gain, namely, belief consensus-based algorithm and the Bregman alternative direction method of multipliers (ADMM)-based method. Simulation results verify the superior performance of the proposed conv-BP-EP receiver compared with other methods. The two proposed distributed cooperative detection schemes can improve the bit error rate performance by exploiting the diversity gain. Moreover, Bregman ADMM method outperforms the belief consensus-based algorithm in noisy inter-user links.

关键词： sparse code multiple access multiple-input multiple-output belief propagation expectation propagation variational free energy distributed cooperative detection

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codehook Optimization for the Superposition Transmission of Uplink SCMA Systems

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2018年第10期67卷 10112-10117页

作者： Lim, Seung-Chan Park, Hyuncheol Korea Adv Inst Sci & Technol Sch Elect Engn Daejeon 34141 South Korea

For an uplink sparse code multiple access (SCMA) system, a codehook-domain superposition transmission can be applied to increase the multiplexing gain by efficient utilization of the codebooks as multiple access resources. However, the destructive collision of superposed codewords can restrict the performance improvement of the system because of the increasing interlayer interferences. In this paper, we analyze the effects of the interlayer interferences on the bit error rates, and optimize the SCMA codebooks that can mitigate the interlayer interferences. Simulation results show that the optimized codebooks can provide a noticeable gain to improve the performance of uplink SCMA systems applied with superposition transmission.

关键词： sparse code multiple access superposition transmission inter-layer interference codebook optimization

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Outage Probability Region and Optimal Power Allocation for Uplink SCMA Systems

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IEEE TRANSACTIONS ON COMMUNICATIONS 2018年第10期66卷 4965-4980页

作者： Chen, Jiaxuan Wang, Zhaocheng Xiang, Wei Chen, Sheng Tsinghua Univ Beijing Natl Res Ctr Informat Sci & Technol Dept Elect Engn Beijing 100084 Peoples R China James Cook Univ Coll Sci & Engn Cairns Qld 4878 Australia Univ Southampton Sch Elect & Comp Sci Southampton SO17 1BJ Hants England King Abdulaziz Univ Jeddah 21589 Saudi Arabia

As a promising non-orthogonal multiple access scheme, sparse code multiple access (SCMA) technology has attracted much attention. Because inter-user interference is present in code domain and multi-user iterative detection is required, user capacity and outage probability analysis for uplink SCMA systems are challenging and have not been presented in the literature. In this paper, the capacity region for uplink SCMA systems is analyzed, based on which the common and individual outage probability regions are calculated. Optimizing the outage probability within the outage probability region can be carted as an Lagrangian duality problem and solved by an iterative descent algorithm, which however imposes high complexity since the expectation operation is required in each iteration. To reduce the computational complexity of solving this Lagrangian duality problem, an adaptive algorithm is developed, which is capable of providing the optimal outage probability and adaptively updating it. Furthermore, a power allocation policy is naturally obtained to achieve the optimized outage probability in the outage probability region.

关键词： sparse code multiple access capacity region common outage probability region individual outage probability region power allocation policy

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Success Probability and Area Spectral Efficiency in SCMA Wireless Networks

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2018年第8期67卷 7764-7768页

作者： Liu, Lei Sheng, Min Liu, Junyu Wang, Xijun Li, Jiandong Xidian Univ State Key Lab Integrated Serv Networks ISN Xian 710071 Shaanxi Peoples R China

sparse code multiple access (SCMA) is emerging as a promising multiple access technology for the fifth-generation wireless networks. By leveraging user-specific SCMA codebooks, SCMA possesses the potential to enable non-orthogonal resource access, and thus leading to the overloading gain. Benefiting from this, SCMA can accommodate more users and achieve a higher throughput than orthogonal frequency division multiple access. In this correspondence, we propose a tractable analytical framework using tools from stochastic geometry to investigate the performance of SCMA wireless networks. In particular, we obtain explicit closed-form expressions for the success probability and the area spectral efficiency (ASE). Based on the derived results, we prove that the ASE is a quasi-concave function of the transmitter density. Moreover, we shed light on the impact of SCMA code-word dimension K and the number of non-zero entries in SCMA codeword N on the network performance. Specifically, we demonstrate that the optimal transmitter density and the maximum ASE scale super-linearly with rate K-N. Simulation results validate the accuracy of the presented analysis and exhibit the superiority of SCMA.

关键词： sparse code multiple access success probability area spectral efficiency stochastic geometry

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Gaussian Approximation-Based Belief Propagation Receiver for Uplink SCMA Systems With Imperfect CSIR

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IEEE COMMUNICATIONS LETTERS 2018年第12期22卷 2611-2614页

作者： Lim, Seung-Chan Park, Hyuncheol Korea Adv Inst Sci & Technol Sch Elect Engn Daejeon 34141 South Korea

For uplink sparse code multiple access (SCMA) systems, a channel estimation is required to support a multi-user detection in practice. Motivated by the conventional detection, called a Gaussian approximation-based belief propagation (GA-BP) with matched filtering, we propose an efficient receiver suitable for the uplink SCMA systems when exact channel state information is not available. By estimating matched filtered channels (rather than explicitly estimating actual channels), the proposed methods efficiently support the second-stage GA-BP detector with negligible increment of complexity. The simulation results show that the proposed receiver achieves the similar estimation and detection performance to the state-of-the-art receiver while the required complexity can be drastically reduced.

关键词： sparse code multiple access multi-user detection channel estimation belief propagation Gaussian approximation

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Feasibility analysis of non-orthogonal waveforms for multiple input multiple output passive radar application

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JOURNAL OF ENGINEERING-JOE 2019年第21期2019卷 7484-7488页

作者： Wang, Qing Li, Tong Dou, Tongdong Zhu, Weifeng Tianjin Univ Sch Elect & Informat Engn Tianjin Peoples R China Shanghai Jiao Tong Univ Dept Elect Engn Shanghai Peoples R China

New non-orthogonal multiple access technology is proposed with the development of 5G, which is expected to support higher spectrum efficiency and massive terminal access, it enables the communication system to achieve better bit error rate performance and alleviate the spectrum congestion problem effectively under limited resources. With the design of spectrum sharing for radar and communication getting more attention, 5G non-orthogonal signal has become potential passive radar illumination source. In this article, an orthogonal multiple input multiple output (MIMO) radar waveform design metric by minimising the integration sidelobe level, is introduced firstly. Then based on sparse code multiple access (SCMA) technology, the non-orthogonal waveform is designed as the passive radar illumination sources. The distance and Doppler resolution of non-orthogonal waveform are evaluated by a more generalised MIMO ambiguity function. Simulation results demonstrate that non-orthogonal SCMA signals have competitive performance with orthogonal code division multiple access signals.

关键词： MIMO radar radar signal processing radio links radio receivers MIMO communication multi-access systems orthogonal codes interference suppression radiofrequency interference code division multiple access error statistics passive radar nonorthogonal waveform multiple input multiple output passive radar application new nonorthogonal multiple access technology higher spectrum efficiency massive terminal access bit error rate performance spectrum congestion problem 5G nonorthogonal signal potential passive radar illumination source orthogonal multiple input multiple output radar waveform design sparse code multiple access passive radar illumination sources nonorthogonal SCMA signals orthogonal code division multiple access signals

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A Comparative Study on the Capacity of SCMA and LDSMA 14

A Comparative Study on the Capacity of SCMA and LDSMA

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14th IEEE International Wireless Communications and Mobile Computing Conference (IWCMC)

作者： Chen, Shuang Peng, Kewu Zhang, Yushu Song, Jian Tsinghua Univ Dept Elect Engn Beijing Natl Res Ctr Informat Sci & Technol Beijing 100084 Peoples R China

ISBN: (纸本)9781538620700

sparse code multiple access (SCMA) is a newly proposed non-orthogonal multiple access technique for the 5th generation (5G) of wireless communication systems. It improves low-density signature multiple access (LDSMA) by replacing the inherent repetition code with multi-dimensional constellations. In this paper, the Gaussian-input channel capacities as well as the constellation constrained (CC) capacities of SCMA and LDSMA are analyzed and compared for the cases of Gaussian multiple access channel (GMAC) with random phase rotation and GMAC with fast fading, which disclose the performance potential of SCMA over LDSMA.

关键词： non-orthogonal multiple access sparse code multiple access low-density signature multiple access channel capacity constellation constrained capacity

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Active User Detection of Uplink Grant-Free SCMA in Frequency Selective Channel 87

Active User Detection of Uplink Grant-Free SCMA in Frequency...

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87th IEEE Vehicular Technology Conference (VTC-Spring)

作者： Wang, Feilong Zhang, Yuyan Zhao, Hui Huang, Hanyuan Li, Jing BUPT Intelligent Comp & Commun Lab Key Lab Universal Wireless Commun Minist Educ Beijing Peoples R China

ISBN: (纸本)9781538663554

Massive machine type communication (mMTC) is one of the three fifth generation mobile networking (5G) key usage scenarios, which is characterized by a very large number of connected devices typically transmitting a relatively low volume of non-delay sensitive data. To support the mMTC communication, an uplink (UL) grant-free sparse code multiple access (SCMA) system has been proposed. In this system, the knowledge of user equipments' (UEs') status should be obtained before decoding the data by a message passing algorithm (MPA). An existing solution is to use the compressive sensing (CS) theory to detect active UEs under the assumed condition of flat fading channel. But the assumed condition is not suitable for the frequency selective channel and will decrease the accuracy of active UEs detection. This paper proposes a new simple module named refined active UE detector (RAUD), which is based on frequency selective channel gain analyzing. By making full use of the channel gain and analyzing the difference between characteristic values of the two status of UEs, RAUD module can enhance the active UEs detection accuracy. Meanwhile, the addition of the proposed module has a negligible effect on the complexity of UL grant-free SCMA receiver.

关键词： sparse code multiple access Uplink grant-free Active user equipments detection

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Low-Complexity Detectors for Uplink SCMA: Symbol Flipping and Dynamic Partial Marginalization-Based MPA 87

Low-Complexity Detectors for Uplink SCMA: Symbol Flipping an...

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87th IEEE Vehicular Technology Conference (VTC-Spring)

作者： Wei, Li Huang, Bo Zheng, Jianping Xidian Univ State Key Lab Integrated Serv Networks Xian Peoples R China

ISBN: (纸本)9781538663554

In this paper, two low-complexity detectors for uplink sparse code multiple access (SCMA) systems are proposed. The first, called symbol flipping algorithm (SFA), is an analogy of the bit-flipping decoding algorithm in the low-density parity check code field. Specifically, the local hard-decision detection is first performed at each resource node, and the decided signal in the least reliable resource node is flipped. The second is an improved partial marginalization (PM)-based message passing algorithm (MPA). Based on the reliability definition introduced in SFA, the variable nodes to be marginalized are determined dynamically during the MPA iteration procedure, and the resulted detector is termed as dynamic PM-based MPA. Simulation results show that the proposed hard-decision SFA can achieve a numerous complexity reduction and the proposed dynamic PM-based MPA has better performance than the conventional PM-based MPA.

关键词： sparse code multiple access multi-user detection bit flipping message passing algorithm complexity

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Decision Feedback for Channel Estimation in SCMA System with Diversity

Decision Feedback for Channel Estimation in SCMA System with...

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IEEE Conference of Russian Young Researchers in Electrical and Electronic Engineering (ElConRus)

作者： Klimentyev, Vyacheslav P. Sergienko, Alexander B. St Petersburg Electrotech Univ LETI Dept Theoret Fundamentals Radio Engn St Petersburg Russia

ISBN: (纸本)9781538643402

In this paper, we investigated channel estimation with decision feedback for sparse code multiple access (SCMA) system with diversity. In this scheme, symbols of SCMA codeword from J users are spread over K < J orthogonal resources with uncorrelated fading. For block fading model (flat fading) in uplink channel, it is required to estimate smaller number of channel coefficients per resource block than in the scheme without diversity where fading is identical for all orthogonal resources. The minimal length of orthogonal pilot signal for system with diversity can be decreased proportionally to the sparsity factor of SCMA codewords. Furthermore, the proposed scheme allows choosing flexible pilot lengths, while in a scheme without diversity this length should be a multiple of K. Data-feedback-aided algorithm with hard decisions from SCMA detector and from decoder of turbo code is used for channel estimation. The simulation results show performance gain when turbo decoder is included in feedback loop.

关键词： Non-orthogonal multiple access sparse code multiple access 5G mobile communications channel estimation data-feedback-aided estimation diversity turbo code Rayleigh channel

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