Shigeki Moriyama

A digital modulation method for terrestrial digital TV broadcasting using trellis coded OFDM and its performance

OFDM (orthogonal frequency division multiplexing) is regarded as an excellent digital modulation method for various future digital broadcasting systems, including digital audio broadcasting (DAB). The scope of applications of the OFDM can be further expanded by combining it with TCM (trellis coded modulation). This TCM-OFDM system can transmit a much larger number of data than conventional OFDM, causing almost no degradation of bit error rate performance within the same frequency bandwidth. The concept of the TCM-OFDM system for terrestrial digital TV broadcasting and a system configuration that needs no carrier recovery at the receiver and gives simulation results of the bit error rate performances under various receiving conditions are described.<<ETX>>

Digital transmission of high bit rate signals using 16DAPSK-OFDM modulation scheme

Radio transmission signals are distorted by multipath propagation and signal level fading in the channel. In the case of digital transmission systems, the distortion of signals causes a degradation of bit error performance. It is an especially severe problem with digital outside-broadcasting-link (OBL) which has to transmit, for example, digital HDTV signals at more than about 45 Mbps. The OFDM modulation scheme can mitigate the adverse effects of multipath fading. An experimental OFDM modem has been developed to enable stable transmission of digital HDTV sources in an OBL. The experimental modem distributes transmitting digital data to 688 carriers in a bandwidth of about 13.5 MHz using the 16DAPSK for each OFDM carrier. A combination of 8DPSK and 2DASK is adopted as the 16DAPSK and another combination of 8DPSK and coherent 2ASK instead of 2DASK is also considered. Indoor transmission experiments confirmed that the 16DAPSK-OFDM is feasible for transmitting high bit rate signals, even under severe propagation conditions.

Efficient use of frequencies in terrestrial ISDB system

Requirements for a terrestrial ISDB system and the schemes for efficiently using frequencies to fulfil the requirements are discussed. One requirement of a terrestrial ISDB system is the efficient allocation of frequencies using a SFN (single frequency network). The SFN incorporates the great advantages of OFDM, which has excellent performance under multi-path conditions. The transmission characteristics of 64QAM-OFDM and the SFN capability using 64QAM-OFDM in the Kanto area, including the Tokyo metropolitan area, are analyzed. The results show that more than a 97% coverage ratio can be obtained even by using a single channel while the same area is covered currently by more than 30 analog channels. The other requirement is a scheme for efficiently using the available frequency band for various services. A transmission scheme concept called BST-OFDM (band segmented transmission-orthogonal frequency division multiplexing) is proposed as a transmission scheme for meeting the requirements of a terrestrial ISDB system. In the BST-OFDM scheme, data are transmitted in a number of OFDM blocks called a BST-segment, for which channel coding and modulation schemes can be independently defined to provide robustness in the transmission environment according to stationary, portable and mobile reception.

Digital outside-broadcasting-link using OFDM modulation scheme

A study on digital broadcasting systems has been conducted for the multimedia era. Regarding program production, a digital outside-broadcasting-link (OBL), in particular, from mobile source is required to gather digital video and audio sources in severe multipath environments. The orthogonal frequency division multiplexing (OFDM) modulation scheme is robust under multipath fading conditions. A digital OFDM modem for OBL in the 800 MHz band has been developed to enable stable transmission of digital sources from moving vehicles. In the experimental OFDM-OBL, the compressed digital video and audio data are distributed to 572 carriers in the 9 MHz bandwidth, using differential quadrature phase shift keying (DQPSK) modulation for each carrier. In computer simulation and indoor/outdoor experiments, it is confirmed that digital OFDM-OBL can stably transmit signals, even under severe multipath fading conditions, while pictures transmitted with conventional FM-OBL are seriously degraded. This paper describes the features of the OFDM modem for the digital OBL which transmits program sources from moving vehicles, and also discusses aspects of gathering digital program sources.

TRAFFIC INFORMATION SERVICES USING FM MULTIPLEX BROADCASTING

NHK has developed an FM multiplex broadcasting system using a new digital modulation method called level controlled minimum shift keying (L-MSK) which is a kind of MSK. This system is multipath-proof, and has a transmission capacity of 16 kbps. Moreover, it has a compatibility with radio data system (RDS) because they use different frequency bands. Transmission tests were carried out to measure the performance of the 16 kbps L-MSK system in the service area of the NHK Tokyo FM station. These tests revealed that this system was superior to RDS in terms of the correct reception rates obtained in mobility. FM multiplex broadcasting using L-MSK has many merits for traffic information services.

Traffic Information Services Using FM Multiplex Broadcasting

A new traffic information service using FM multiplex broadcasting, which has a large transmission capacity, has been expected. The most difficult problem in mobile FM multiplexing broadcasting is multipath interference. To overcome this problem, a new modulation method called L-MSK( Level-controlled MSK ) has been developed. A transmission experiments have been carried out to confm the characteristics of the L-MSK modulation scheme. The results of transmission experiments indicate that the transmission system adopting L-MSK can achieve a transmission capacity of 16 kbps. This paper describes the transmis- sion quality of the new FM multiplex broadcasting system and applications for traffic information services.

Digital Broadcasting. Mobile Transmission Characteristics in UHF Digital FPU using DQPSK-OFDM Modulation Scheme.

The OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme is robust under multipath fading conditions. An experimental OFDM modem using the Differential Quadrature Phase Shift Keying (DQPSK) modulation scheme for each carrier has been developed to enable stable transmission of high-rate digital sources from moving vehicles. As one of the promising applications of the DQPSK-OFDM modulation scheme, a digital Field Pick-up Unit (FPU) is expected to be efficient in the case of mobile transmission. This paper describes the transmission characteristics of the DQPSK-OFDM modem in an urban area which transmits digital sources from vehicles in the UHF 800-MHz band, and also discusses the error protection scheme, the guard interval length, and the carrier spacing of the DQPSK-OFDM modem for mobile transmission.

Performance of an error correction scheme for PAL-TV teletext

The shortened (272, 190) difference set cyclic code has been adopted for the Japanese teletext system using NTSC vertical blanking periods. This system is known as BEST (burst and random error correction system for teletext) for NTSC-TV systems. A powerful error correction system adopting the (272, 190) code for PAL-TV teletext signals is described. To compare the error correction characteristics of this system to those of WST (World System Teletext), transmission experiments were carried out multiplexing both data packets with different lines during the vertical blanking period of the same TV signals. The validity of applying BEST to the PAL-TV signals was confirmed, particularly when there is ghost interference. >