Chinese Digital Television Terrestrial Broadcasting Research Articles

Joint Time-Frequency Channel Estimation for Time Domain Synchronous OFDM Systems

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.

A novel algorithm for side peaks suppression of ambiguity function for passive radar based on chinese DTTB signal

The ambiguity function of Chinese standard Digital Television Terrestrial Broadcasting (DTTB) signals for passive radar contains one main peak and many side peaks. The side peaks may cause the false alarms. The relative positions and the reasons for the side peaks are analyzed and a new algorithm for side peaks suppression is proposed in this paper. The algorithm, in consideration of the characteristics of the structure of the frame, can eliminate the side peaks completely in the valid Doppler observation interval by setting the reference signals to zero at equal intervals. Both the simulative and experimental results show that this algorithm can improve the performance of target detection of the passive radar based on DTTB signal.

Iterative Channel Estimation for the Chinese Digital Television Terrestrial Broadcasting Systems with the Multiple-Antenna Receivers

Orthogonal frequency division multiplexing is an effective against multipath fading and high data throughput wireless channel transmission technology. Assistance with the inverse fast Fourier transform and fast Fourier transform operation, orthogonal frequency division multiplexing modulation and demodulation operations of the system convenient and convenient hardware implementation, orthogonal frequency division multiplexing, so in the modern digital television terrestrial broadcasting the system is widely used to support high performance bandwidth-efficient multimedia services. Broadband multi-carrier orthogonal frequency division multiplexing with multi-antenna and multi-antenna receiving system, to increase the diversity gain and improve the capacity of the system in different multipath fading channel. Accurate channel estimation in a simple channel equalization and decoding of broadband multi-carrier orthogonal frequency division multiple-antenna receiver and channel estimation accuracy and multiplexing system is very important, is the key to the performance of the overall broadband multi-carrier orthogonal frequency division multiplexing system in the multi-antenna receiver bit error rate. In this paper, iterative channel estimation to plan for digital terrestrial television broadcasting broadband multi-carrier orthogonal frequency division multiple antenna receiver multiplexing system proposal.

TDS-OFDMA: a novel multiple access system based on TDS-OFDM

As the key technology of Chinese national digital television terrestrial broadcasting (DTTB) standard, time domain synchronous OFDM (TDS-OFDM) utilizes known training sequence instead of cyclic prefix (CP) as the guard interval between adjacent inverse discrete Fourier transform (IDFT) blocks to achieve better system performance. Until now, TDS-OFDM was primarily used in downlink broadcasting. When TDS-OFDM is directly used in the uplink, it is difficult to eliminate the superposed interferences caused by different training sequences and IDFT blocks from multiple users. To solve this problem, a novel scheme called time domain synchronous orthogonal frequency division multiple access (TDS-OFDMA) is proposed in this paper. The novel space-time frame structure of the TDS-OFDMA scheme is proposed to achieve joint cyclicity reconstruction as well as joint channel estimation at the receiver. Simulation results show that the proposed scheme can achieve better bit error rate (BER) performance than conventional OFDMA system under highspeed mobile environments.

Interference Elimination for Chinese DTMB System With Transmit Diversity

When adopting transmit diversity in the Chinese digital television terrestrial broadcasting (DTTB) system, there exists two kinds of interference: training sequences (TSs) from different transmit antennas are overlapped; and the TSs are interfered with OFDM data due to multipath fading. In order to distinguish different TSs, this paper proposes a method to design orthogonal TS set, which also have good correlation characteristic. Subsequently, an iterative algorithm to eliminate the interference between TSs and data is proposed and theoretically analyzed. Finally, simulations are performed and the results show that the system with the proposed scheme can achieve great diversity gain under acceptable computational complexity.

A Novel Scheme of Joint Channel and Phase Noise Compensation for Chinese DTMB System

In broadband wireless communication systems, orthogonal frequency division multiplexing (OFDM) will suffer from severe performance degradation in the presence of phase noise (PHN) especially for the applications with narrow subcarrier spacing to support high bit rate. In the Chinese digital television terrestrial multimedia broadcasting (DTMB) system the time-domain synchronous OFDM (TDS-OFDM) is adopted in which the time-domain pseudo noise (PN) sequences and OFDM data block are combined into a signal frame. Continuous transmission parameter signaling (TPS) symbols are inserted into OFDM data blocks in the frequency domain which can be used for phase noise estimation. In this paper, joint channel estimation and phase noise reduction algorithms are investigated for DTMB systems using the common phase error (CPE) of PN sequences as an intermediate variable of channel frequency response (CFR) during estimation stage and removing it at compensation stage. A simplified channel and phase noise equalization method performed in both frequency and time domain is studied to suppress the distortion. Simulations prove that this proposed scheme has low complexity and works well under additive white Gaussian noise (AWGN) and multipath fading channels.

Channel Estimation for the Multiple-antenna Chinese Digital Television Terrestrial Broadcasting Systems

Channel Estimation for the Multiple-antenna Chinese Digital Television Terrestrial Broadcasting Systems

Channel Equalization With Phase Error Mitigation for the Chinese Digital Television Terrestrial Broadcasting Systems

OFDM is extensively used in modern digital television terrestrial broadcasting (DTTB) systems to support high performance bandwidth-efficient multimedia services, such as the Digital Video Broadcasting for Terrestrial Television (DVB-T) proposed as the European DTTB standard and the Digital Television/Terrestrial Multimedia Broadcasting (DTMB) proposed as the Chinese DTTB standard. System based on OFDM is sensitive to the phase error produced due to not only the tuner phase noise but also the phase deviation of residual sampling clock offset, frequency offset estimation error and Doppler spread in the mobile applications. In this paper, a channel equalization with phase error mitigation scheme is proposed for the time domain synchronous OFDM (TDS-OFDM) based Chinese digital television terrestrial broadcasting systems. In the proposed channel equalization scheme, the influence of the phase error on the performance of the TDS-OFDM based Chinese DTTB systems is split into a multiplicative part (which is common to all sub-carriers and is referred to as the common phase rotation (CPR)) and an additive part (which is referred to as the inter-carrier interference (ICI)). Both the CPE and the ICI are estimated and compensated in the proposed scheme. Simulation results for system with phase error and under mobile environment are presented to illustrate the effectiveness of the proposed scheme.

Low cost VLSI architecture of resisting long echo channel estimation for DTMB system

Digital television/terrestrial multimedia broadcasting (DTMB) was announced as the Chinese digital television terrestrial broadcasting (DTTB) standard in August, 2006. It adopts TDS-OFDM (time-domain synchronous-orthogonal frequency division multiplexing) as the baseline modulation technology. There is not pilot information in order to avoid reduction of channel throughput. It uses pseudo-noise (PN) sequence as guard interval (GI) and the training sequence for both multi- and single-carrier block transmissions which makes the synchronization faster than CP-OFDM (cyclic prefix-orthogonal frequency division multiplexing) systems. It can resist the inter-symbol interference (ISI) and can be used for channel estimation and synchronization. In this paper, a full-mode channel estimation scheme for DTMB demodulator is developed. This method utilizes the PN sequence to obtain channel estimation and equalization both in three kinds of frame head (FH) mode as well as in single and multi-carrier modulation transmission mode. To implement on hardware realization, interference cancellation is predigested, then equalization and filter for channel impulse response are optimized. A low cost VLSI architecture for channel estimation and equalization is proposed which works effectually and achieves low complexity as well. Computational simulation results show that the proposed scheme has little BER loss in performance.

Secure communication in TDS-OFDM system using constellation rotation and noise insertion

Time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) is the key technology of Chinese digital television terrestrial broadcasting (DTTB) standard. However, the issue of security was not considered, and this limits its application in commercial or military scenarios where secure communication is very important. This paper proposes an encryption scheme based on pseudo random constellation rotation and weak artificial noise insertion, which jointly utilizes the pseudo random key and the irreversible property of wireless channel to guarantee the physical layer security of TDS-OFDM system. Simulation results show that the proposed security scheme can protect the system from eavesdroppers, while the legal receivers only suffer a negligible bit error rate (BER) performance loss compared with the conventional TDS-OFDM system without security.

Multi-GI detector with shortened and leakage correlation for the Chinese DTMB system

As Guard Interval (GI), Pseudo Noise (PN) sequence is padded between adjacent data symbols in Chinese digital television terrestrial broadcasting (DTTB) standard. In order to accommodate with versatile applications, three GI modes are recommended with different lengths and formats. Obviously, a robust multi-GI detecting method is a prerequisite for further demodulation, such as frame synchronization, timing recovery, carrier recovery, and channel estimation. A novel multi-GI detector with shortened and leakage correlation (SLC-MGI) is proposed, which adopts a modified Pre-Pos correlation to overcome variable phases defined in DTMB system. Simulation results show that the proposed scheme outperforms the conventional Mixed-MMLS algorithm over both AWGN and multi-path channels, and is robust to frequency offset.

Low Complexity Soft Decoder for Nordstrom-Robinson Code With Application to the Chinese DTTB Standard

Nordstrom-Robinson (NR) code followed by 4 quadrature-amplitude modulation (4QAM) mapping is one of the working modes in the Chinese digital television terrestrial broadcasting (DTTB) standard, where the outer code is a low-density parity-check (LDPC) code. Since LDPC decoders usually accept soft rather than hard inputs for better error performance, soft NR decoders are highly recommended. In this paper, several novel low-complexity soft NR decoders are proposed with excellent error performance. Simulation results show that the proposed algorithm based on the maximum, second and third maximum (MST) cross correlation values achieves very low complexity at the cost of performance loss only about 0.1 dB at bit error rate (BER) of 10-6, under both additive white Gaussian noise (AWGN) and independent Rayleigh fading channels, compared to the ideal maximum a posteriori (MAP) decoder.

Low complexity channel estimation method for TDS-OFDM based Chinese DTTB system

The Chinese digital television terrestrial broadcasting (DTTB) standard uses pseudo-noise (PN) sequence as guard interval (GI) and the training sequence. This PN sequence is used to do channel estimation and synchronization in the system. The existing channel estimation methods often have to adopt iterative scheme when the length of channel impulse response (CIR) is long, which will increase the receiver complexity dramatically. In this paper, a channel estimation scheme for time domain synchronous OFDM (TDS-OFDM) systems is proposed. Interference free CIR information can be obtained by constructing special correlation windows, rather than removing interference from the time domain sequences through iteration. Moreover, the estimation can be achieved by using correlation process. Comparing to conventional schemes, the proposed algorithm greatly reduces the computational complexity. Simulation results show that the proposed method can meet the requirement of the Chinese DTTB systems. And the scheme is also suitable for other communication OFDM systems with time domain sequence headers.

Analysis and side peaks identification of Chinese DTTB signal ambiguity functions for passive radar

Passive radar is one of the current research focuses. The implementation of the Chinese standard digital television terrestrial broadcasting (DTTB) creates a new opportunity for passive radar. DTTB system contains single-carrier and multicarrier application modes. In this paper, ambiguity functions of the DTTB signals in the single-carrier and multicarrier application modes are analyzed. Ambiguity function of the DTTB signal contains one main peak and many side peaks. The relative positions and amplitudes of the side peaks are derived and the reasons for the occurrence of the side peaks are obtained. The side peaks identification (SPI) algorithm is proposed for avoiding the false alarms caused by the side peaks. Experimental results show that the SPI algorithm can indentify all the side peaks without the power loss. This research provides the foundation for designing the DTTB based passive radar.

High-Throughput QC-LDPC Decoders

High-throughput design approaches for quasi-cyclic (QC) low-density parity-check (LDPC) decoders are presented in this paper. Three novel schemes for the horizontal process in min-sum algorithm and its revisions are derived to reduce design and implementation complexity. The schemes can be directly applied for variant QC codes and easily pipelined to increase the operating frequency of the decoder. Some improvements of the semi-parallel architecture are proposed to enhance throughput performance and hardware efficiency. Employing the proposed approaches, QC-LDPC decoders for Chinese Digital Television Terrestrial Broadcasting (DTTB) standard are implemented using field programmable gate array (FPGA). As shown in the results, the proposed approaches can substantially improve the throughput performance, as well as the throughput-and-hardware tradeoff, of decoders with semi-parallel architecture.

Phase Noise Correction Based on TPS Symbols for the Chinese DTTB System

In orthogonal frequency division multiplexing (OFDM) system, phase noise (PHN) from oscillator can severely reduce the performance by causing: common phase error (CPE) and inter-carrier interference (ICI). The impact of PHN on received signal can be characterized by the circular convolution of the transmitted signal and the discrete Fourier transform (DFT) of PHN signal in frequency domain. Digital television/terrestrial multimedia broadcasting (DTMB), announced as the Chinese digital television terrestrial broadcasting (DTTB) standard, adopted the time-domain synchronous OFDM system (TDS-OFDM) system which has 36 continuous transmission parameter signaling (TPS) symbols in frequency domain which be used for PHN suppression. Based on a linearized parametric model for PHN, least squared (LS) estimation and fast Fourier transform (FFT) approaching method for PHN correction are proposed in this paper. The effects of the PHN on channel estimation in both TDS-OFDM system and conventional cyclic prefix OFDM (CP-OFDM) are also investigated. Simulations show that the proposed algorithm can effectively reduce the PHN and improve the symbol error rata (SER) of TDS-OFDM systems over both additive white Gaussian noise (AWGN) and broadcasting multipath channel. In practice, the FFT-approaching method can be applied to the DTMB receiver-chip design directly with low implementation cost.

Two-Way Digital Video Transmission over Medium-Voltage Power-Lines Using Time-Domain Synchronous Orthogonal Frequency Division Multiplexing Technology

This paper describes field trials of two-way digital video transmissions over a 700-m long medium-voltage power cable using a frequency division duplex scheme. The purpose is to check the feasibility of using time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) technology in powerline communication (PLC). TDS-OFDM is the core technology in digital multimedia broadcasting-terrestrial (DMB-T), developed by Tsinghua University for digital television terrestrial multimedia broadcast applications and successfully adopted in the Chinese Digital Terrestrial Television Broadcasting Standard. PLC systems are widely believed to be bandwidth or data throughput limited. However, the use of known pseudo random sequences as guard intervals for synchronization and channel estimation in TDS-OFDM greatly reduces the system overhead and increases the spectrum efficiency. These experiments show that TDS-OFDM is appropriate not only for broadcasting but also for PLC applications with appropriate modifications.

Novel channel estimation method based on PN sequence reconstruction for Chinese DTTB system

Digital television/terrestrial multimedia broadcasting (DTMB), announced as the Chinese digital television terrestrial broadcasting (DTTB) standard, uses pseudo-noise (PN) sequence as guard interval (GI) and the training sequence for both multi- and single-carrier block transmissions. The conventional channel estimation methods can be performed through either the subtraction of the PN sequence or the cancellation of residual inter-symbol interference (ISI). In this paper, a novel iterative method is introduced to estimate the overlapping part of PN sequence, meanwhile the channel impulse response (CIR) estimation can be obtained and updated via the reconstruction of the PN sequence in an iterative manner. Simulations show that the proposed algorithm can effectively reduce the ISI and improve the symbol error rata (SER) of DTMB system over slowvarying broadcasting multipath channel even with long delay spread. In practice, the proposed algorithm can be applied to the DTMB receiver-chip directly with low-complexity cost.

Robust Frame Synchronization for Chinese DTTB System

Digital terrestrial multimedia/television broadcasting (DTMB), which is the recently released Chinese digital television terrestrial broadcasting (DTTB) standard, uses guard intervals padded with known pseudo-noise (PN) sequences for multi-carrier or single-carrier block transmission. Well designed synchronization algorithms are a prerequisite for achieving high-quality multimedia transmission. In this paper, a novel frame synchronization technique, which is robust to carrier frequency offset (CFO), is proposed for DTMB systems. This technique is derived through segmenting the local PN sequence into M contiguous blocks and performing multiple cross-correlations with the received signal. The metric for peak detection is defined as the non-coherent summation of the M cross-correlation magnitude outputs. Moreover, a low-complexity frame synchronizer based on segment-based full correlation for PN420 mode in DTMB system is proposed. It is shown through computer simulation that the proposed techniques generally outperform the conventional ones when CFO occurs, over both AWGN and frequency-selective fading channels. For a DTMB system using PN420 mode, the maximal allowed CFO to keep system still working normally of our proposed schemes are more than 3 times larger than that of the conventional method.

A Robust and Adaptive Carrier Recovery Method for Chinese DTTB Receiver

This paper presents a robust and adaptive carrier recovery method for Chinese digital terrestrial television broadcasting (DTTB) system in which pilot signal and pseudonoise (PN) sequence are adopted to help carrier recovery. The conventional methods utilize pilot or PN sequence respectively. In this paper, we try to combine the advantage of each method together and propose a well designed state machine to control system state automatically. Moreover, as for using PN sequence, a fine PN tracking state is introduced to ensure the robustness of the proposed method. Software simulations show that the proposed method can provide large acquisition range, short acquisition time and small tracking jitter in severely distorted static and dynamic channels. Lab tests and field trials also prove its good performance in real propagation environments.