We have developed a transmission test equipment based on draft specification of interim Digital Terrestrial Television Broadcasting System that was proposed last year. This paper describes the outline of test equipment, construction, block diagram and its functions.
The draft specification for digital terrestrial TV broadcasting adopts OFDM (Orthogonal Frequency Division Multiplexing) scheme that has robustness against multipath interference and can realize SFN (Single Frequency Network). It can also realize mobile reception and maximum four hierarchical transmissions that can set up the number of segments, modulation of carriers and convolutional coding rate. We have developed a transmission test equipment based on the draft specification to evaluate the transmission system. This paper describes transmission performances under Gaussian noise, multipath and Rayleigh fading. It is discussed required C/N, synchronization, phase noise and performance of hierarchical transmission.
OFDM is expected to be a suitable modulation method for digital terrestrial broadcasting systems. One of the reasons is that it makes it possible to provide services to an indoor/outdoor portable receiver with an in-built or set-top receiving antenna, which is major advantage compared with other media, such as satellite or cable. In this paper, a study on indoor portable reception model of coverage assesment and some planning criteria driven from field measurements carried out around Tokyo area are described. And coverage simulation results based on this model are also shown.
The coded OFDM (Orthogonal Frequency Division Multiplexing) system minimizes the effect of multipath mobile channels by using the time interleaving. But at lower speed there is possibility that a fade duration is longer than the time interleaving depth, and the time interleaving is not effective enough. Recently we reported the experimental results that the frequency diversity technique improves BER performances even at lower speed. This paper describes the effect of the diversity technique under correlative channels, with the relative gain of received signals and with doppler shift.
Generally, the multi-carrier signal is distorted by power amplifier (PA) with nonlinear characteristics. This paper describes the analysis of large number of distortions which are generated by the OFDM signal through the PA with third-order nonlinear characteristics. In particular, special attention is paid to the distortion components out of OFDM transmission band. Finally, investigation is discussed the evaluation of the most adjacent distortion due to back-off on PA operations.
The transmission method for the digital terrestrial TV system that uses an OFDM scheme has been developed in Japan. As a basic study of transmitting an OFDM signal over a cable TV system, we measured adjacent channel interference between an OFDM signal and a QAM signal so far being supposed to transmit through cable TV facilities. The BER's of a OFDM signal and a QAM signal are measured, respectively, and the allowable ranges of D/U ratio are studied.
Today's progress of degltal compression technology throw open the door to the new era of cable network. With this technology, the cable system comes to one of the best solution for the delivery of high-speed interactive servlces such as Internet access, Video-On-Demand (VOD) and telephony. The subscribers' dernand for the best media for the delivery of such servlces are growing rapldly, and Cable operators have ambitious plans to upgrade their existing networks or build new ones to satisfy the demand. The key factors that operators must consider when designing their networks are Scaiability. Reliability, and of course Cost. In this paper we analyse the upgr ading method of the existing networks to the reliable and scaiable architecture with minimal expense and disruption of sevices, and we introduce our new CATV equipment, that realize the future high-speed data communication via cable network in the cost-effective and reliable manner.
An optical double-sideband suppressed-carrier (DSB-SC) transmission with a frequency-shift-keyed (FSK) signal was proposed for fiber-optical transmission of microwave signals. The DSB-SC signal was obtained by Mach-Zehnder interferometric modulation with π optical phase difference. In the experiments at 13.6 GHz, the good bit-error performance of the transmitted 100 Mbps FSK signal was observed along the various lengths of single-mode optical fiber. The result proved that the scheme could overcome fiber-chromatic dispersion.
A direct optical DQPSK modulator is profitable as regards easy setup in a coherent fibre-optic transmission system. In this paper, we show transmission characteristics of an optical direct-modulated DQPSK signal. According to simulation results, DQPSK detection can be realized easier with a 100% rolloff filter than a 50% one and about 1000 waves can be multiplexed within 32nm with each filter.