Masahiro Okano

8K Terrestrial Transmission Field Tests Using Dual-Polarized MIMO and Higher-Order Modulation OFDM

Japan Broadcasting Corporation (NHK) is conducting research on the next-generation of digital terrestrial broadcasting that will enable ultrahigh definition television such as 8K. Multiple-input multiple-output (MIMO) technology should be able to expand the single-input single-output channel capacity. 2x2 MIMO is adopted in ATSC3.0 as an optional method. In order to construct a next-generation terrestrial network using MIMO technology and to ensure an adequate link budget especially as regards the MIMO propagation parameters, two experimental stations have been installed in Hitoyoshi city, Kumamoto, Japan. This system is an extension of the conventional DTV system in Japan, called ISDB-T. NHK conducted 2x2 MIMO field tests using one station and 4x2 MIMO field tests using two stations composing a single frequency network (SFN). For the 4x2 MIMO test, an advanced SFN using space time coding was developed. The 2x2 MIMO field tests involved terrestrial 8K transmissions (91 Mb/s) over a single UHF band channel (6 MHz bandwidth). The degradation of required carrier to noise ratio compared to laboratory measurements in dual-polarized MIMO propagation was under 3 dB even in non-line-of-sight conditions. The 4x2 MIMO field tests indicated that the required received power of the SFN was up to 3 dB better than that of the conventional SFN.

Digital transmission scheme for ISDB-T and reception characteristics of digital terrestrial television broadcasting system in Japan

This paper introduces a transmission scheme for ISDB-T, and proposes a soft decision decoding technique for ISDB-T receivers to improve reception performance under multi-path distortion and interference from analog television signals.

Field experiments of dual-polarized MIMO-OFDM transmission using non-uniform constellations

We have been researching a transmission system that uses ultra-multilevel carrier modulation with orthogonal frequency division multiplexing (OFDM) and dual-polarized multiple-input multiple-output (MIMO) for 8K Super Hi-Vision terrestrial broadcasting. For the carrier modulation scheme, we studied a non-uniform constellation (NUC) to improve the transmission characteristics by optimizing the distance between signal points. Simulations demonstrated that the NUCs are advantageous compared with conventional uniform constellations (UC). We implemented the NUCs on a prototype MIMO-OFDM modulator and demodulator and investigated the bit error rate (BER) with laboratory and field testing. Results showed that the 4096-NUCs improved the required C/N by about 1 dB compared to the 4096-UC.

Evaluation of simplified demapping algorithm for NUQAMs using urban MIMO channel response

We have been researching a transmission system that uses high-order carrier modulation with orthogonal frequency division multiplexing (OFDM) and dual-polarized multiple-input multiple-output (MIMO) for 8K Super Hi-Vision terrestrial broadcasting. We evaluated the transmission performance of non-uniform QAMs (NUQAMs) with a simplified demapping algorithm that approximates the log-likelihood ratio (LLR) as a simple distance from a boundary of only the in-phase or quadrature component. Simulations using the MIMO channel response captured in an urban area demonstrated that the higher-order NUQAMs mitigate the degradation caused by the LLR approximation compared with conventional QAMs. The results show that the degradation in the simplified demapping algorithm in the required CNR is approximately 0.4 dB and that the LLR approximation is applicable to transmission systems with high-order NUQAMs.

Transmission performance evaluation of LDPC coded OFDM over actual propagation channels in urban area. Examination for next-generation ISDB-T

In Japan, the next generation of Integrated Services Digital Broadcasting — Terrestrial (ISDB-T) system is being developed for transmission of large-volume content services such as ultra high definition television (UHDTV). The system uses low density parity check (LDPC) code as the forward error correction (FEC) to improve its robustness. In particular, the performance of the systems FEC should be evaluated not only in additive white Gaussian noise (AWGN) environments, but also in multipath environments. Moreover, it would be desirable for the new FEC to have better performance than the previous one even in multipath environments. Previous research evaluated the transmission performance of LDPC code by using computer simulations of the propagation model. The actual propagation characteristics were not evaluated. In this paper, we describe the transmission performance of convolutional coded orthogonal frequency division multiplexing (CC-OFDM) and LDPC coded OFDM (LDPC-OFDM) in computer simulations using the same OFDM frame structure and propagation channels as measured in an outdoor experiment conducted in an urban area. We show that LDPC code outperforms CC in multipath environments and how the transmission performance depends on the code rate. In addition, we analyze the correlation between transmission performance and propagation channels.

4 × 2 MIMO field test of advanced SFN using space-time coding for 8K transmission

Japan Broadcasting Corporation (NHK) is aiming to broadcast ultra high definition television (UHDTV), such as 8K, terrestrially. To evaluate a next-generation terrestrial network, two experimental stations composed of an advanced single frequency network (SFN) using space-time coding technology were set up in the Hitoyoshi area of Kumamoto, Japan. The transmission capacity of each experimental station is a maximum of 91.8 Mbps when using dual-polarized multi-input multi-output (MIMO) and 4096QAM modulation. To evaluate an advanced SFN with a 4 × 2 MIMO system, we conducted experiments in a field test in the Hitoyoshi area to compare three SFN schemes: conventional SFN without coding, space-time coding (STC), and space-frequency coding (SFC). The results of the field tests show that the required received power of the STC-SFN and SFC-SFN are lower than those of the conventional SFN, and the amount of improvement averaged 2 dB. In this paper, we report on this field test.

A study on MIMO OFDM transmissions using inter-polarization spreading

The next generation of digital terrestrial broadcasting systems using dual-polarized SDM-MIMO technology is under development. The reception deteriorates under an AWGN channel when the XPD for the SDM-MIMO system is low. We describe a method for inter-polarization spreading in the SDM-MIMO transmission system that compensates for the deterioration and our investigation of the reception in a computer simulation. The simulation results show that applying the spreading can improve the reception in an AWGN and in TU6 channels. They also show that the reception was even improved when using a single receiving antenna.

Mobile reception performance of ISDB-T SB mobile multimedia broadcasting system using the VHF-low band

After analog television broadcasting was terminated in Japan, the frequency bands from 90 to 108 MHz (VHF-low band) and from 207.5 to 222 MHz (VHF-high band) were reallocated to mobile multimedia broadcasting (MMB). We propose three methods to improve the mobile reception performance with VHF-low MMB. These involve the extended time-interleaving length, space diversity reception technology, and iterative decoding technology between Viterbi decoding and Reed-Solomon decoding. This paper describes improvements of the mobile reception performance evaluated through laboratory and field experiments. As a result of laboratory experiments, the extension of time-interleaving length from I=4 (0.5 s) to I=32 (4 s) improved the mobile reception performance by 2.7 dB, three-fold iterative decoding improved it by 1 dB, and 2-branch space diversity reception improved it by 6.4 dB at a vehicle speed of around 30 km/h. Combining the three methods improved it by 8.9 dB. We conducted field experiments, and the results from these matched those from the laboratory experiments.

Digital Transmission Techniques that support Digital Broadcasting. Protection of Digital Terrestrial Television Signals Against Analog Signal Interference.

The draft standard for the Digital Terrestrial Television Broadcasting (DTTB) system of Japan using Orthogonal Frequency Division Multiplexing (OFDM) digital transmission was approved in 1998. DTTB services are provided along with analog television services, so that DTTB signals can be interfered with by analog signals.Various ratios for protecting DTTB signals against analog television signals, have been tested. The results show that co-channel protection ratios of 25 dB, and adjacent-channel protection ratios of no more than-20 dB are required when the DTTB signals are modulated by 64 QAM-OFDM and convolutionally coded at a rate of 7/8. The BER performance for co-channel interference was improved by using soft decision decoding with erasure.

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.