Zhixing Yang

Tsinghua University, Peping, Beijing, China

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Publications (146)84.25 Total impact

  • 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.
    IEEE Communications Letters 07/2015; 19(7):1-1. DOI:10.1109/LCOMM.2015.2426694 · 1.46 Impact Factor
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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.
    ICC 2014 - 2014 IEEE International Conference on Communications; 06/2014
  • 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.
    IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences 01/2014; E97.A(9):1994-1997. DOI:10.1587/transfun.E97.A.1994 · 0.23 Impact Factor
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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.
    IEEE Journal on Selected Areas in Communications 09/2013; 31(9):460-469. DOI:10.1109/JSAC.2013.SUP.0513041 · 4.14 Impact Factor
  • 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.
    IEICE Transactions on Communications 06/2013; E96.B(6):1551-1558. DOI:10.1587/transcom.E96.B.1551 · 0.33 Impact Factor
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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.
    IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences 04/2013; E96.A(4):807-813. DOI:10.1587/transfun.E96.A.807 · 0.23 Impact Factor
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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.
    IEEE Transactions on Broadcasting 03/2013; 59(1):168-173. DOI:10.1109/TBC.2012.2219231 · 2.65 Impact Factor
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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.
    IEEE Transactions on Information Theory 03/2013; 60(6). DOI:10.1109/TIT.2014.2313081 · 2.65 Impact Factor
  • 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.
    IEEE Transactions on Vehicular Technology 03/2013; 62(3):1216-1227. DOI:10.1109/TVT.2012.2228679 · 2.64 Impact Factor
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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.
    IEEE Transactions on Consumer Electronics 02/2013; 59(1):16-23. DOI:10.1109/TCE.2013.6490236 · 1.16 Impact Factor
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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.
    IEEE Journal on Selected Areas in Communications 02/2013; 31(2):251-263. DOI:10.1109/JSAC.2013.130213 · 4.14 Impact Factor
  • 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.
    Wireless Communications and Mobile Computing Conference (IWCMC), 2013 9th International; 01/2013
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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.
    Broadband Multimedia Systems and Broadcasting (BMSB), 2013 IEEE International Symposium on; 01/2013
  • 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.
    Wireless Communications and Mobile Computing Conference (IWCMC), 2013 9th International; 01/2013
  • 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.
    Broadband Multimedia Systems and Broadcasting (BMSB), 2013 IEEE International Symposium on; 01/2013
  • Ruifeng Ma · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: This letter presents a flexible signal structure supporting localization service for time domain synchronous OFDM (TDS-OFDM) in multi-service transmission applications. Localization is treated as one specific service and the corresponding data is allocated within the physical layer pipe (PLP) of the first subframe. The concept of variable sub-carrier spacing to combat Doppler spread is also introduced for the localization service. Simulation results indicate that the proposed scheme outperforms the conventional scheme and at the same time achieves high positioning accuracy.
    IEICE Transactions on Communications 12/2012; E95.B(12):3922-3924. DOI:10.1587/transcom.E95.B.3922 · 0.33 Impact Factor
  • Fang Wang · Yong Li · Zhaocheng Wang · Depeng Jin · Zhixing Yang
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    ABSTRACT: Wireless traffic has two features: people have common interests in the hottest contents, and a large amount of traffic belongs to non-realtime services. Exploiting these two features, we propose a content dissemination system, integrating broadcast network and opportunistic network. In the proposed system, popular contents are broadcasted through broadcast network and then disseminated to users through opportunistic network. Such system can significantly reduces the same contents repeated transmission and efficiently delivers contents to their clients. Using a Markov model, we theoretically analyze content dissemination delay of the proposed system.
    2012 IEEE 9th International Conference on Mobile Ad-Hoc and Sensor Systems (MASS); 10/2012
  • Qiuliang Xie · Zhixing Yang · Jian Song · Lajos Hanzo
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    ABSTRACT: We provide some examples of our proposed APSK constellations in this technique report, whereby the mutual information between the channels' inputs and outputs associated with such APSK constella-tions is also presented. Results show that well-designed APSK constellations according to our procedure have indistinguishable mutual information at low-to-median SNR, while the mutual information at high SNR is dominated by the minimum Euclidean distance between adjacent constellation points.
    Technical Report; 08/2012
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    Chao Zhang · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: An improved frame structure for TDS-OFDM systems is presented by adopting cyclic block shifted training sequences. The guard interval needed for the training sequences could be shortened while the ability to combat the maximum channel delay spread is not sacrificed. Therefore the spectrum efficiency is increased. The corresponding channel estimation and equalisation schemes are also illustrated.
    Electronics Letters 08/2012; 48(16):1024-1026. DOI:10.1049/el.2012.1537 · 1.07 Impact Factor
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    Qiuliang Xie · Zhaocheng Wang · Zhixing Yang
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    ABSTRACT: Amplitude phase shift keying (APSK) constellation is capable of outperforming quadrature amplitude modulation (QAM) in terms of both the mutual information and the error-control performance. However, the lack of simplified demapper prevents its potential applications due to the inherent high computation complexity. In this paper, the concept of APSK using product constellation labeling is introduced, and two simplified demappers are proposed. Theoretical analysis and simulations show that the performance degradation caused by these simplified demappers is negligible, while the complexity is significantly reduced, compared to the traditional Max-Log-MAP demapper.
    IEEE Transactions on Wireless Communications 07/2012; 11(7):2649-2657. DOI:10.1109/TWC.2012.051412.112055 · 2.76 Impact Factor

Publication Stats

780 Citations
84.25 Total Impact Points

Institutions

  • 1995–2014
    • Tsinghua University
      • • Department of Electronic Engineering
      • • Tsinghua National Laboratory for Information Science and Technology
      • • Department of Electrical Engineering
      Peping, Beijing, China
  • 2004
    • National Tsing Hua University
      Hsin-chu-hsien, Taiwan, Taiwan