Zhixing Yang

Tsinghua University, Peping, Beijing, China

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Publications (153)72.67 Total impact

  • Fang Wang · Zhaocheng Wang · Chen Qian · Linglong Dai · Zhixing Yang
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    ABSTRACT: Visible light communication (VLC) is a promising complementary technology to its radio frequency (RF) counterpart. Heterogeneous VLC-WiFi systems offer a solution for future indoor communications that combines VLC to support high data rate transmission and RF to support reliable connectivity. In such heterogeneous systems, vertical handover (VHO) is critical for improving the system performance. This paper investigates an efficient VHO scheme. We formulate it as a Markov decision process problem and adopt a dynamic approach to obtain a trade-off between the switching cost and the delay requirement. The proposed scheme determines whether to perform VHO given the queue length and the condition of the optical wireless channel (available or unavailable). The simulation results demonstrate that the proposed scheme is able to save about 50% of the signaling cost of the VHO process without an obvious loss in system performance. Moreover, the proposed scheme is adaptable to different scenarios.
    No preview · Article · Dec 2015 · Journal of Optical Communications and Networking
  • Tao Cheng · Kewu Peng · Fang Yang · Jian Song · Zhixing Yang
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    ABSTRACT: Multiple-input multiple-output (MIMO), which can provide ultrahigh data transmission rate, is one of the key technologies for the next generation digital terrestrial television broadcasting (DTTB) standards. This paper proposes a near-capacity MIMO bit-interleaved coded modulation scheme with either independent or iterative demapping (BICM/BICM-ID) for the DTTB system. First, the amplitude phase shift keying (APSK) constellation with Gray mapping is proposed to replace the conventional Gray quadrature amplitude modulation (QAM) counterpart. From the perspective of average mutual information analysis, Gray-APSK has certain shaping gain compared to Gray-QAM for both independent and iterative demapping schemes. Besides the APSK constellation, a novel bit interleaver named bit mapping, which takes into account the unequal error protection of both APSK constellations and low-density parity-check codes, is proposed to further improve the system performance. The tool of extrinsic information transfer chart is utilized to analyze and design the optimal bit mapping for the BICM/BICM-ID scheme. Bit error rate simulations are finally carried out to verify the superiority of the proposed MIMO coded modulation scheme.
    No preview · Article · Sep 2015 · IEEE Transactions on Broadcasting
  • Tao Cheng · KeWu Peng · Zaishuang Liu · ZhiXing Yang
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    ABSTRACT: The low-density parity-check (LDPC) coded bit-interleaved coded modulation with iterative demapping (BICM-ID) has excellent bit error rate (BER) performance, but with extremely high receiver complexity. This letter proposes a three-stage full-parallel receiver architecture in which each component decoder is separately but simultaneously iteratively decoded. This architecture can make full use of the computing resources and improve the system performance without sacrificing the throughput. Three-dimensional (3-D) extrinsic information transfer (EXIT) analysis and BER simulations are carried out to demonstrate the superiority of the proposed new receiver architecture.
    No preview · Article · Jul 2015 · IEEE Communications Letters
  • Fang Wang · Yong Li · Zhaocheng Wang · Zhixing Yang

    No preview · Article · Jan 2015 · IEEE Transactions on Vehicular Technology
  • Ruifeng Ma · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: The next generation wireless broadcasting systems combining with MIMO technology has drawn much attention recently. Considering the coexistence of receivers equipped with different numbers of antennas in these systems, there exists the special requirement to maximize the transmission rate for receivers having more antennas, while guaranteeing the normal rate for receivers having less antennas. In this letter, superposition coding is proposed to fulfill this requirement and the concept of broadcast cluster is introduced, wherein the optimized power allocation parameters are derived. The BER simulations for multiple services are provided to verify the significant SNR performance gap between receivers with various numbers of receive antennas.
    No preview · Article · Sep 2014 · IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences
  • Linglong Dai · Zhen Gao · Zhaohceng Wang · Zhixing Yang
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    ABSTRACT: Large-scale multiple-input multiple-output (MIMO) with high spectrum and energy efficiency is a very promising key technology for future 5G wireless communications. Although most research only considers training and channel estimation in the uplink based on the assumption of time division duplexing (TDD) protocol, downlink training and channel estimation is also necessary, especially for the dominated frequency division duplexing (FDD) protocol. Unlike conventional orthogonal pilots whose overhead prohibitively increases with the number of transmit antennas, we propose a spectrum-efficient superimposed pilot design based on the emerging theory of structured compressive sensing, whereby the frequency-domain pilots of different transmit antennas share common subcarriers instead of orthogonal subcarriers. Accordingly, we propose the structured compressive sampling matching pursuit (CoSaMP) algorithm to simultaneously recover multiple channels by exploiting the spatial and temporal correlations of large-scale MIMO channels. Simulation results verify that the proposed scheme can approach the performance bound of the exact least square algorithm.
    No preview · Conference Paper · Aug 2014
  • Tao Cheng · Kewu Peng · Fang Yang · Zhixing Yang
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    ABSTRACT: Digital video broadcasting-next generation handheld (DVB-NGH) is the first broadcasting standard that incorporates multiple-input multiple-output (MIMO) techniques to overcome the Shannon limit of single antenna systems. This paper contributes to analyze the performance of the DVB-NGH MIMO coded modulation system. The detailed performance degradation from information-theoretic limit to implementation by average mutual information and extrinsic information transfer analysis is presented, which provides an insight guideline for future system improvement. Finally, bit error rate simulations are carried out to verify the analysis.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: Compared with standard cyclic prefix OFDM (CP-OFDM), time domain synchronous OFDM (TDS-OFDM) can achieve a higher spectrum efficiency by using the known training sequence instead of CP as the guard interval. However, TDS-OFDM suffers from reduced energy efficiency and performance loss due to the existing mutual inferences. In this paper, based on the newly emerging theory of structured compressive sensing (SCS), we propose a reliable and energy-efficient TDS-OFDM transmission scheme with reduced guard interval power (which is impossible for CP-OFDM) by designing a channel estimation scheme with high accuracy. The wireless channel properties including channel sparsity and inter-channel correlation, which are usually not considered in conventional OFDM schemes, have been exploited. We further exploit the worst-case system design principle to extract multiple interference-free regions of small size to simultaneously reconstruct multiple channels of large size without iterative interference cancellation. In this way, the guard interval power in TDS-OFDM can be reduced to achieve a 20% higher energy efficiency than standard CP-OFDM, and the system reliability can be also improved in fast fading channels.
    Full-text · Conference Paper · Jun 2014
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    Linglong Dai · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: Time domain synchronous OFDM (TDS-OFDM) has higher spectral efficiency and faster synchronization than standard cyclic prefix OFDM (CP-OFDM), but suffers from the difficulty of supporting 256QAM in low-speed vehicular channels with long delay spread and the performance loss over fast time-varying vehicular channels. This paper addresses how to efficiently use the compressive sensing (CS) theory to solve those problems. First, we break through the conventional concept of cancelling the interferences if present, and propose the idea of using the inter-block-interference (IBI)-free region of small size to reconstruct the high-dimensional sparse multipath channel, whereby no interference cancellation is required any more. In this way, without changing the current signal structure of TDS-OFDM at the transmitter, the mutually conditional time-domain channel estimation and frequency-domain data detection in conventional TDS-OFDM receivers can be decoupled. Second, we propose the parameterized channel estimation method based on priori aided compressive sampling matching pursuit (PA-CoSaMP) algorithm to achieve reliable performance over vehicular channels, whereby partial channel priori available in TDS-OFDM is used to improve the performance and reduce the complexity of the classical CoSaMP signal recovery algorithm. Simulation results demonstrate that the proposed scheme can support the 256QAM and gain improved performance over fast fading channels.
    Full-text · Article · Sep 2013 · IEEE Journal on Selected Areas in Communications
  • Fang Wang · Yong Li · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: Orthogonal frequency division multiplexing (OFDM) is a promising technique for the broadband air interface and has been widely deployed in current wireless transmission systems. With the adoption of adaptive modulation and coding, OFDM system can support multi-services dissemination. However, since different services have different quality of service (QoS) requirements, efficient resource allocation while satisfying various QoS requirements remains a challenge in OFDM systems, especially when the resource is relatively small compared with the great demand of services. In this paper, we study the problem of how to allocate the resource for QoS-constrained multiple services in OFDM systems over time-frequency dimensions. We investigate two algorithms to sort an optimal service queue for resource allocation. One is greedy algorithm with low complexity, and the other one is genetic algorithm which is closer to the optimal solution. Simulation results demonstrate that genetic algorithm performs better than greedy algorithm but with longer computational time.
    No preview · Conference Paper · Jun 2013
  • Fang Wang · Yong Li · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: There has been an explosion in wireless devices and mobile data traffic, and cellular network alone is unable to support such fast growing demand on data transmission. Therefore, it is reasonable to add another network to the cellular network to augment the capacity. In fact, the dilemma of cellular network is mainly caused by that the same content is repeatedly transmitted in the network, since many people are interested in the same content. A broadcast network, however, could mitigate this problem and save wireless bandwidth by delivering popular content to multiple clients simultaneously. This paper presents a content dissemination system that combines broadcast and cellular networks. Using the model of Markov Decision Process (MDP), we propose an online optimal scheme to maximize the expected number of clients receiving their interested content, which takes clients' interests and queuing length at broadcast and cellular base stations into full consideration. Simulations demonstrate that the proposed scheme effectively decreases item drop rate at base stations and enhances the average number of clients who receive their interested content.
    No preview · Article · Jun 2013 · IEICE Transactions on Communications
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    Changyong Pan · Linglong Dai · Zhixing Yang
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    ABSTRACT: Time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) has higher spectral efficiency than the standard cyclic prefix OFDM (CP-OFDM) OFDM by replacing the random CP with the known training sequence (TS), which could be also used for synchronization and channel estimation. However, TDS-OFDM requires suffers from performance loss over fading channels due to the iterative interference cancellation has to be used to remove the mutual interferences between the TS and the useful data. To solve this problem, the novel TS based OFDM transmission scheme, referred to as the unified time-frequency OFDM (UTF-OFDM), is proposed in which the time-domain TS and the frequency-domain pilots are carefully designed to naturally avoid the interference from the TS to the data without any reconstruction. The proposed UTF-OFDM based flexible frame structure supports effective channel estimation and reliable channel equalization, while imposing a significantly lower complexity than the TDS-OFDM system at the cost of a slightly reduced spectral efficiency. Simulation results demonstrate that the proposed UTF-OFDM substantially outperforms the existing TDS-OFDM, in terms of the system's achievable bit error rate.
    Full-text · Article · Apr 2013 · IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences
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    Linglong Dai · Zhaocheng Wang · Jun Wang · Zhixing Yang
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    ABSTRACT: As the key technology of Chinese national digital television terrestrial broadcasting (DTTB) standard, time domain synchronous OFDM (TDS-OFDM) has high spectral efficiency at the cost of performance loss over fast fading channels. In this paper, a novel time-frequency signal structure is proposed to improve the system performance of TDS-OFDM over fast time-varying channels. Each TDS-OFDM symbol adopts the time-domain one-sample shifted training sequence (TS) and the frequency-domain grouped pilots as the time-frequency training information. The modulable orthogonal sequence (MOS) with perfect autocorrelation property is adopted as the TS, while each pilot group has only one non-zero central pilot surrounded by several zero pilots. The corresponding joint time-frequency channel estimation utilizes the time-domain TS for path delay estimation and the frequency-domain grouped pilots for path gain estimation, thus accurate tracking of the fast time-varying wireless channel could be achieved. Only about 1% of the total subcarriers will be occupied by the redundant grouped pilots, thus the loss in spectral efficiency is negligible. Simulation results demonstrate that the proposed scheme outperforms the conventional solutions over fast fading channels.
    Full-text · Article · Mar 2013 · IEEE Transactions on Broadcasting
  • Qiuliang Xie · Zhixing Yang · Jian Song · Lajos Hanzo
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    ABSTRACT: Bit-interleaved coded modulation with iterative decoding (BICM-ID) is investigated, wherein a novel method of designing amplitude phase-shift keying (APSK) constellations is proposed, which is capable of outperforming both traditional quadrature amplitude modulation (QAM) and nonuniformly spaced QAM (NU-QAM). It is shown that the channel capacity can be approached by the proposed M-APSK constellation as M tends to infinity. Additionally, a new algorithm is introduced for finding the best bit-to-symbol mapping. Furthermore, when signal space diversity is also employed, our extrinsic information transfer (EXIT) chart analysis and Monte Carlo simulations demonstrate that the proposed BICM-ID schemes exhibit a near-Shannon-capacity performance for transmission over both additive white Gaussian noise (AWGN) and Rayleigh fading channels. For a block length of 64 800 bits, the bit-error-rate (BER) curve of the proposed BICM-ID 16/64-APSK scheme is only about 0.8 and 1.0 dB away from the Gaussian-input Shannon limit over AWGN and Rayleigh fading channels, respectively, at the BER of 10-5 and for a code rate of 1/2.
    No preview · Article · Mar 2013 · IEEE Transactions on Vehicular Technology
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    Qiuliang Xie · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: A polar decomposition of mutual information between a complex-valued channel's input and output is proposed for a input whose amplitude and phase are independent of each other. The mutual information is symmetrically decomposed into three terms: an amplitude term, a phase term, and a cross term, whereby the cross term is negligible at high signal-to-noise ratio. Theoretical bounds of the amplitude and phase terms are derived for additive white Gaussian noise channels with Gaussian inputs. This decomposition is then applied to the recently proposed amplitude phase shift keying with product constellation (product-APSK) inputs. It shows from an information theoretical perspective that coded modulation schemes using product-APSK are able to outperform those using conventional quadrature amplitude modulation (QAM), meanwhile maintain a low complexity.
    Full-text · Article · Mar 2013 · IEEE Transactions on Information Theory
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    Changyong Pan · Linglong Dai · Zhixing Yang
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    ABSTRACT: Consumer electronics are expecting high-definition television (HDTV) services not only at home, but also in high-speed vehicles like cars, train, subways, etc. However, time domain synchronous OFDM (TDS-OFDM) could only provide HDTV services in static or low-speed channels, but not in fast fading channels due to the severe mutual interferences between the time-domain training sequence (TS) and the OFDM data block. Without changing the original TDS-OFDM signal structure, this paper firstly proposes the idea of regarding transmission parameter signaling (TPS) symbols embedded in the OFDM data block as frequency-domain pilots. This new perspective breaks the conventional concept that the training information of TDS-OFDM exists only in the time domain. Then, the two-dimensional channel estimation method jointly exploiting the time-domain TS as well as the frequency-domain pilots is proposed to improve the system reliability over fast fading channels. Simulation results demonstrate that reliable HDTV transmission could be achieved when the moving speed of consumer electronics is up to 120 km/h1.
    Full-text · Article · Feb 2013 · IEEE Transactions on Consumer Electronics
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    Linglong Dai · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: Large-scale orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) is a promising candidate to achieve the spectral efficiency up to several tens of bps/Hz for future wireless communications. One key challenge to realize practical large-scale OFDM MIMO systems is high-dimensional channel estimation in mobile multipath channels. In this paper, we propose the time-frequency training OFDM (TFT-OFDM) transmission scheme for large-scale MIMO systems, where each TFT-OFDM symbol without cyclic prefix adopts the time-domain training sequence (TS) and the frequency-domain orthogonal grouped pilots as the time-frequency training information. At the receiver, the corresponding time-frequency joint channel estimation method is proposed to accurately track the channel variation, whereby the received time-domain TS is used for path delays estimation without interference cancellation, while the path gains are acquired by the frequency-domain pilots. The channel property that path delays vary much slower than path gains is further exploited to improve the estimation performance, and the sparse nature of wireless channel is utilized to acquire the path gains by very few pilots. We also derive the theoretical Cramer-Rao lower bound (CRLB) of the proposed channel estimator. Compared with conventional large-scale OFDM MIMO systems, the proposed TFT-OFDM MIMO scheme achieves higher spectral efficiency as well as the coded bit error rate performance close to the ergodic channel capacity in mobile environments.
    Full-text · Article · Feb 2013 · IEEE Journal on Selected Areas in Communications
  • Tao Cheng · Kewu Peng · Changyong Pan · Zaishuang Liu · Zhixing Yang
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    ABSTRACT: Doping technique was employed to remove the high error floor in conventional bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID). This paper proposes a new look of the doping technique-BICM-ID with serial concatenated convolutional code (SCCC-BICM-ID). Unlike conventional doping decoding scheme which deems the doping decoder and the demapper as a whole doped demapper, we combine the doping code and the outer convolutional code together to form an SCCC, so that iterative demapping and decoding is performed between the demapper and the SCCC decoder. Extrinsic information transfer (EXIT) chart is used to analyze these two decoding schemes and reveals that they both can achieve near-capacity performance with no penalty of error floor. According to the results of EXIT analysis and BER simulations, SCCC-BICM-ID system can achieve the same or even better performance compared to the doping BICM-ID system with lower decoding complexity.
    No preview · Conference Paper · Jan 2013
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    Tao Cheng · Kewu Peng · Zhixing Yang · Jian Song
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    ABSTRACT: The performance degradation of each step from Shannon limit to implementation for the second generation digital video broadcasting - terrestrial (DVB-T2) system is analyzed in this paper, from three aspects: the time-frequency bandwidth loss, imperfect coded modulation scheme, and other implementation issues. The analysis results intuitively show the weak parts that still exist in the DVB-T2 system, and also provide guidelines for system improvement in the future.
    Full-text · Conference Paper · Jan 2013
  • Ruifeng Ma · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: Physical-layer security could efficiently prevent wiretapping for wireless communication from the information-theoretic perspective. However, most related works in this area are based on the assumption of Gaussian inputs, which are impractical for a practical communication system. In this paper, we study the physical-layer security with finite-alphabet inputs, wherein amplitude phase shift keying (APSK) constellation is considered to improve the achievable secrecy rate performance. It is concluded that the secrecy rate can be improved by using APSK, comparing to its quadrature amplitude modulation (QAM) counterpart, which is verified by both the minimum mean square error (MMSE) theoretic derivation and simulation results. A specific strategy of selecting constellation orders for secure communication is also presented.
    No preview · Conference Paper · Jan 2013

Publication Stats

961 Citations
72.67 Total Impact Points

Institutions

  • 1995-2015
    • Tsinghua University
      • • Department of Electronic Engineering
      • • Tsinghua National Laboratory for Information Science and Technology
      Peping, Beijing, China
  • 2004
    • National Tsing Hua University
      Hsin-chu-hsien, Taiwan, Taiwan