Because of advances in the wide and two way characteristics, cable television (CATV) has been noted as a telecommunications infrastracture. So we constructed a digital NVOD experimental system using CATV networks with CATV operators in Tokyo, Yokohama and Kofu. This System will attempt to broadcast 4 programs simultaneously per analogue channel through the existing CATV network. 1,500 digital set top boxes will be distributed to the subscribers for this experiments. This paper repotrs on overview of the digital NVOD experimantal system.
According to the requirements for satellite ISDB transmission, both high transmission capacity and high service availability are the essential factors to be accomplished in order to realize excellent quality services such as HDTV, as well as multi-channel TV services. Hierarchical transmission scheme against rain attenuation and TC8PSK modulation scheme are powerful candidates to be employed. In this paper, first, a structure and a method for generating the ISDB transmission signal are discussed. Then, performances of the transmission system developed as prototype are examined by indoor experiments using a simulated typical DBS channel. It is consequently revealed that a flexible digital satellite transmission system can be achieved by using the combination of TC8PSK for High Quality Layer and QPSK coded with coding rate 1/2 convolutional code for Low Quality Layer.
SFN (Single Frequency Network) by using OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme is an important technology for digital terrestrial broadcasting to ensure the effective use of frequencies. Field trials were conducted to investigate the transmission characteristics in SFN using two transmitters. This paper describes the specifications of the experimental SFN facilities, and the results of the transmission experiments were discussed in comparison with the conventional network using two different frequencies. The results show that receivers with powerful error correction achieve to secure almost the same coverage area under SFN as that under conventional network.
As the popularity of the coplanar waveguide (CPW) has increased significantly in recent years, antenna elements which are suitable for a CPW-feed configuration have also become important. In this paper, we investigated the characteristics of the cicularly polarized printed array antenna fed by CPW using the FDTD method.
Experiment and calculation of 64QAM signal transmission by tentative specifications of Ministry of Posts and Telecommunication with single carrier interference and reflection in a transmission line was described. Degradation of bit error rate started from where the single carrier interference level was more than -20 dB of a desired QAM carrier signal level, and where the reflection signal level was more than -25.5 dB of a desired QAM signal level. Equalizer was not needed for reflection signals of more than 0.6 μ s.
Experiment of 64QAM signal transmission by tentative specifications of Ministry of Posts and Telecommunication with clipping distortion in an optical transmission line was described. Maximum optical modulation index, that is sum of optical modulation index of each signal, was applicable to use as expression of limitation based on the number of signals and modulation index. Maximum clipping distortion signal level in a desired channel should be less than the desired QAM carrier level by 30〜40 dB.
Orthogonal frequency division multiplex (OFDM) is a suitable digital modulation method for terrestrial digital broadcasting systems. It is important to reduce a phase noise in an OFDM receiver, because the phase noise disturbes orthogonality among the OFDM sub-carriers. This report describes design of a wideband tunable local oscillator with low phase noise characteristics for OFDM receivers. We have newly developed a balanced type oscillator with an L-C pararell resonance circuit between the transistor emitter ports, which has wide band frequency range of 1.15〜2.2GHz and low phase noise performances of-66dBc/Hz (1KHz offset) or less. Also, we calculated the SNR at the output of the tuner of OFDM sub-carriers by using above balanced type oscillator, and the results show that the SNRs of 33dB or more are achievable even for the 1KHz sub-carrier spacing system.
We have studied FFT circuit for OFDM modulation system, which guarantees the final S/N more than 40dB even though there exists input level variation about 10dB. Any circuit parameters, especially the accuracy of A/D converter and Butterfly operator are described. And the circuit structure is also described.
A lot of works have been performed for the digital terrestrial television systems using orthogonal frequency division multiplexing (OFDM). One of important points to realize a robust system against noise and disturbance is an error-correcting code and its decoding technique. A punctured convolutional code with the constraint length of 7 is already decided as the inner error-correcting code of the European digital terrestrial TV system. This paper discusses basic characteristics of the code, combined with QAM or DAPSK systems, under the additive white Gaussian noise (AWGN) channels. The bit error rates (BERs) are compared between the hard and soft-decision methods for the QAM and DAPSK systems. Especially, a few different types of soft-decision techniques are numerically examined for the DAPSK systems. The results show that the punctured convolutional code attains the coding gains of 2〜5 [dB] for the QAM systems. However, in some cases, the code can only realize very small or even negative gains for the DAPSK systems.
This paper proposes an adaptive equalization technique for OFDM (Orthogonal Frequency Division Multiplexing) demodulation. This technique estimates a channel response with using pilot signals embedded in OFDM symbols. A two dimensional filter used for interpolating the response estimates the channel response accurately, and also improves the C/N by reducing noise bandwidth. The bit error rate performance of the system in various channels is calculated by computer simulation, and the relative C/N improvement to differential demodulation is about 2.5 dB. And the result shows that the optimum filter can be determined by the maximum path delay time and the maximum doppler frequency of the channel.
In this paper we propose a new frequency synchronization scheme for OFDM (Orthogonal Frequency Division Multiplexing) demodulation. The synchronization scheme permits simultaneous frequency error estimate of a carrier frequency and sampling frequency error in a single estimator. The frequency error estimation is based on correlation vectors of OFDM signals and the portion of its replica placed on guard interval. The carrier frequency and sampling frequency errors are determined by an arithmetic process using the phase of each correlation vectors, which are output signals of correlators each operating in positive frequency and negative frequency respectively.