Bernard Caron

Transmitter identification using embedded pseudo random sequences

A transmitter identification system for DTV distributed transmission network using embedded pseudo random sequences is investigated. Different orthogonal pseudo random sequences and their suitability for transmitter identification are discussed. Code generators are developed to study the auto-correlation and cross-correlation properties of the Kasami sequences. To speed up the identification process, the embedded pseudo random sequence is preferred to be time-synchronized with the DTV frame structure. Therefore, the length of the identification code has to be truncated before it is fitted into each field of the ATSC DTV signal. The impact of truncation noise and in-band DTV interference on transmitter identification is also investigated. It is shown that the auto-correlation and cross-correlation properties are only slightly affected by truncation. It is also found that the dominant interference to the transmitter identification is the in-band DTV signal. The signal to truncation noise ratio and signal to DTV interference ratio in the correlation output are derived, and verified via simulation. It is further recognized that in-band DTV interference can only be mitigated by increasing the code length or by time-domain averaging technique to smoothen out the in-band interference.

Comparison of terrestrial DTV transmission systems: the ATSC 8-VSB, the DVB-T COFDM, and the ISDB-T BST-OFDM

This paper compares the performances of the ATSC 8-VSB, the DVB-T COFDM, and the ISDB-T BST-OFDM digital television terrestrial transmission systems under different impairments and operating conditions. First, a general system level description is presented. It is followed by comparisons based on laboratory test results and theoretical analyzes. The differences in the system threshold definitions are discussed. In addition, a performance and implementation analysis is also presented for the three transmission systems under different network infrastructures, whenever possible, the impact on the broadcasters or consumers is discussed. Possible performance improvements are also identified.

SER performance evaluation and optimization of OFDM system with residual frequency and timing offsets from imperfect synchronization

This paper deals with the effects of residual timing and frequency offsets on the symbol error rate (SER) performance of an orthogonal frequency division multiplexing (OFDM) system. The synchronization of an OFDM system generally consists of a coarse frequency and timing acquisition stage and a refine stage. Due to the presence of Gaussian noise, channel distortions and implementation losses of synchronization and equalization algorithms, residual frequency and timing offsets always exist for an OFDM receiver. The residual frequency and timing offsets are proven to be Gaussian distributed, with their corresponding variances determined. The reception process of an OFDM signal with frequency and timing offsets is analyzed. A closed-form analytical result on the SER of an OFDM system with residual synchronization errors is derived. Computer simulations and analyses show that the frequency and timing offsets affect the OFDM subcarriers differently. With this observation, a new technique is proposed to minimize the SER of the OFDM systems by adjusting the distribution of transmission power among the subcarriers.

On-channel repeater for digital television broadcasting service

This paper presents the results of tests performed by the Communications Research Center Canada (CRC) to investigate the on-channel repeater (OCR) for digital television broadcasting services using the ATSC-8VSB transmission standard. The focus has been to study the areas where the coverage of the OCR overlaps with the main transmitter. The factors involved in successful reception in these areas and their impact on the design and configuration of this kind of repeater are identified and discussed.

An ATSC DTV receiver with improved robustness to multipath and distributed transmission environments

This paper presents the design and implementation of an 8-VSB DTV receiver for indoor and distributed transmission environments. The receiver is designed to handle severe multipath distortion from indoor and Single Frequency Network (SFN) transmission conditions. The architecture of the receiver is first introduced. The adaptive equalizer structure and design are then discussed in detail. A channel-matched filter is employed as a pre-filter such that the signal energies from different echoes are combined optimally and the signal to noise ratio of the equalizer input is maximized. Feedforward and feedback equalizers are used to handle the pre-echo (pre-cursor) and post-echo (post-cursor), respectively. The feedforward filter is designed to minimize the pre-cursors or convert them into post-cursors, while the feedback equalizer is used to eliminate the post-cursors. Initial tap coefficients are computed to speed up the convergence of these two filters based on the channel estimation. Laboratory tests show that the new prototype DTV receiver has very robust performance in multipath environments. 0 dB echoes can be handled with this receiver due to the enhanced design of the equalizer. It can withstand a -10 dB single echo within a -29.5 to +38.5 microsecond range and a 0 dB echo within a 12 microsecond range.

A channel characterization technique using frequency-domain pilot time-domain correlation method for DVB-T systems

A new channel characterization technique using frequency-domain pilot time-domain correlation (FPTC) method for DVB-T systems is proposed in this paper. The proposed technique is based on the time-domain correlation between the received signal and the pilot sequence embedded in the DVB-T signal, which is derived from the frequency domain pilots and known to the receiver. Interruption to the broadcasting service can be avoided, since only regular DVB-T signal is needed for channel characterization. In comparison with other digital TV characterization techniques, the major advantages of this proposal are its implementation simplicity, large dynamic range, and the robustness against synchronization errors. Channel impulse responses can be accurately estimated without timing recovery. The impact of the non-perfect carrier recovery is very small, since the correlation is only computed on a short time period of the received signal. The proposed method has been verified through numerical simulations and lab tests. Possible ways of improving the estimation accuracy are also discussed.

Robust data transmission using the transmitter identification sequences in ATSC DTV signals

Transmitter identification (TxID, or transmitter fingerprinting) technique is used to detect, diagnose and classify the operating status of radio transmitters. Due to an ever-increasing number of transmitters, the need for transmitter identification is becoming an urgent issue, since it enables the broadcast authorities and operators to identify the source of interference. As a result, transmitter identification has been recognized as an important feature in the ATSC synchronization standard for distributed transmission. A new robust data transmission technique using the transmitter identification (TxID) sequences in the digital TV (DTV) signals is proposed in this paper. The major advantage of this low data transmission system is its robustness and extremely large coverage. The principle of the proposed data transmission system is presented. The modulation technique and throughput of the data transmission system is also evaluated.

The Implementation of a Return Channel for ATSC-DTV

In this paper, we describe how the transmission technologies developed for over-the-air digital television broadcasting could be used to offer interactive television and Internet multimedia service. We propose to use the ATSC-DTV system for the downlink and DVB-RCT standard to implement a wireless return channel. This paper will also present some technical aspects of the system implementation.

Using on-channel repeater to improve reception in DTV broadcasting service area

The paper presents the results of a series of tests performed by the Communications Research Centre Canada (CRC), to investigate the possibility of improving reception, by using an on-channel repeater (OCR), in areas already covered by an 8-VSB digital television transmitter. The results are then compared with those obtained at the same test locations using DVB-T transmission at various bit rates to study the impact of OCR versus reduced bit rate transmission. The results should show under which conditions it might be possible to use an OCR, instead of reducing the bit rate, to improve reception in parts of the coverage area of a main transmitter.

Transmitter identification using embedded spread spectrum sequences

A transmitter identification system using embedded spread spectrum sequence is proposed in this paper. Principles of the proposed technique is illustrated through an example of digital TV (DTV) transmitters identification. Code generators in Matlab are developed to study the auto-correlation and cross-correlation properties of the Gold and Kasami sequences. Spread spectrum sequences with different periods are generated and simulated. To speed-up the identification process, the embedded spread spectrum sequence is preferred to be time-synchronized with the DTV signal. By doing so, code length has to be truncated before it is fitted into each field of the ATSC DTV signal. The impact of truncation noise and in-band DTV interference on transmitter identification is also investigated in this paper. It is shown that the auto-correlation and cross-correlation properties are only slightly affected by truncation noise. It is also shown that the dominant interference to the transmitter identification is the in-band DTV signal. The signal to truncation noise ratio and signal to DTV interference ratio in the correlation output are derived and verified form the simulation results. It is further recognized that in-band DTV interference can only be mitigated by increasing the code length or by time-domain averaging technique to smoothen out the in-band interference.