Kenichi Murayama

MIMO for ATSC 3.0

This paper provides an overview of the optional multiple-input multiple-output (MIMO) antenna scheme adopted in ATSC 3.0 to improve robustness or increase capacity via additional spatial diversity and multiplexing by sending two data streams in a single radio frequency channel. Although it is not directly specified, it is expected in practice to use cross-polarized 2×2 MIMO (i.e., horizontal and vertical polarization) to retain multiplexing capabilities in line-of-sight conditions. MIMO allows overcoming the channel capacity limit of single antenna wireless communications in a given channel bandwidth without any increase in the total transmission power. But in the U.S. MIMO can actually provide a larger comparative gain because it would be allowed to increase the total transmit power, by transmitting the nominal transmit power in each polarization. Hence, in addition to the MIMO gains (array, diversity, and spatial multiplexing), MIMO could exploit an additional 3 dB power gain. The MIMO scheme adopted in ATSC 3.0 re-uses the single-input single-output antenna baseline constellations, and hence it introduces the use of MIMO with non-uniform constellations.

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.

Technology for next-generation digital terrestrial broadcasting — Field experiments of dual-polarized MIMO-OFDM transmission using LDPC codes

We have developed a transmission system using ultra-multilevel orthogonal frequency division multiplexing (OFDM) technology, dual-polarized multiple-input multiple-output (MIMO) technology, and Low-Density Parity-Check (LDPC) Codes for experimental purposes on the basis of the conventional digital terrestrial broadcasting transmission scheme, ISDB-T. We conducted two field experiments: one at 23 reception points around NHK Science & Technology Research Laboratories (STRL) using an experimental transmitter installed at NHK STRL, and the other on the lawn at NHK STRL using circularly or skew polarized waves in addition to a conventional polarization set, horizontal and vertical. As a result, we obtained the required field strength in an urban environment when using the 4096QAM carrier modulation scheme with a LDPC code. Furthermore, we confirmed the advantage of circularly or skew polarized waves in an environment in which the received power differed between the horizontally and vertically polarized waves.

Field experiments on dual-polarized MIMO transmission with ultra-multilevel OFDM signals toward digital terrestrial broadcasting for the next generation

We developed a transmission system using ultra-multilevel orthogonal frequency division multiplexing (OFDM) technology and dual-polarized multiple-input multiple-output (MIMO) technology for experimental purposes based on the conventional digital terrestrial broadcasting signal format, ISDB-T. We conducted field experiments at 27 reception points around NHK Science & Technology Research Laboratories (STRL) using an experimental transmitter installed at NHK STRL. As a result, we obtained quasi error free (QEF) operation in MIMO -OFDM transmission whose carrier modulation scheme was 4096QAM. We found that the average required field strength was about 60 dBµV/m for 4096QAM in the field experiments and there was a large difference in field strength at some reception points between both polarized signals that deteriorated the bit error rate characteristics, even if the average field strength was sufficiently high.

A study on advanced single frequency network technology using STC-SDM transmission

We have been conducting research on a transmission system using ultra-multilevel orthogonal frequency division multiplexing (OFDM) technology and dual-polarized multiple-input multiple-output (MIMO) technology based on the digital terrestrial broadcasting signal format, ISDB-T. As a technology of a single frequency network (SFN) for the next-generation of digital broadcasting, we studied a space time coding (STC) - space division multiplexing (SDM) transmission in which STC and dual-polarized MIMO-OFDM are used together. In this paper, we studied a scattered pilot (SP) scheme for the channel estimation in STC-SDM transmission and the coding schemes. Computer simulations confirmed the advantages of STC-SDM transmission compared with the conventional SFN scheme in environments in which the desired to undesired signal ratio (D/U) is low. We also show the results that STC-SDM transmission with space time block coding (STBC) and space frequency block coding (SFBC) has the same characteristics as transmissions under fixed reception conditions.

MIMO Scattered Pilot Performance and Optimization for ATSC 3.0

The next-generation U.S. digital terrestrial television (DTT) standard ATSC 3.0 is the most flexible DTT standard ever developed, outperforming the state-of-the-art digital video broadcasting-terrestrial 2nd generation (DVB-T2) standard. This higher flexibility allows broadcasters to select the configuration that better suits the coverage and capacity requirements per service. Regarding the selection of pilot patterns, whereas DVB-T2 provides eight different patterns with a unique pilot amplitude, ATSC 3.0 expands up to 16, with five different amplitudes per pattern. This paper focuses on the pilot pattern and amplitude performance and optimization for time and power multiplexing modes, time division multiplexing and layered division multiplexing (LDM), respectively, of ATSC 3.0. The selection of the optimum pilot configuration is not straightforward. On the one hand, the pilots must be sufficiently dense to follow channel fluctuations. On the other hand, as long as pilot density is increased, more data overhead is introduced. Moreover, this selection is particularly essential in LDM mode, because the LDM implementation in ATSC 3.0 requires that both layers share all the waveform parameters, including pilot pattern configuration. In addition, there is an error proportional to the channel estimate of the top layer that affects to the lower layer performance.

Technologies for the next generation of digital terrestrial television broadcasting-Decoding method of LDPC codes in dual-polarized MIMO transmission

NHK is conducting research on the next generation of digital terrestrial broadcasting to enable large-volume content services such as Super Hi-Vision (8K). In a previous study on dual-polarized MIMO transmission, we used low density parity check (LDPC) code for forward error correction (FEC) and developed a multi-dimensional interleaving scheme that reduces deterioration caused by the difference between the channel responses of both polarizations. In this study, we developed a decoding algorithm for LDPC code that iteratively uses the channel responses of dual-polarized MIMO transmission for the log likelihood ratio (LLR) calculation, and tested it in a computer simulation.

Performance of dual-polarized MIMO-high-order-modulation OFDM in deteriorated transmission channel

Japan Broadcasting Corporation (NHK) has been conducting research on high-order-modulation orthogonal frequency-division multiplexing (OFDM) schemes, such as 4096QaM, dual-polarized multiple-input multiple-output (MIMO), and low-density parity-check (LDPC) code schemes, for large-capacity transmissions of next-generation digital terrestrial broadcasting. In 2014, we conducted a field experiment on MIMO-OFDM transmission in Hitoyoshi-city, Kumamoto prefecture, Japan. In 2016, the technologies were tested in a field experiment in Rio de Janeiro (RJ), Brazil. In addition, we conducted a transmission simulation of MIMO-OFDM and a calculation of the MIMO channel capacity by using the deteriorated MIMO channel measurements from RJ. In our previous study, we reported that using weighted log likelihood ratios (LLRs) and an erasure process in each subcarrier improves the bit error rate (BER) performance in a single echo environment. The erasure process sets the LLR to 0 when the MIMO channel of a subcarrier deteriorates. In this study, we examined the BER performance in cases with or without the erasure process by using the deteriorated MIMO channel measurements from RJ. We found that the erasure process gives quasi-error free (QEF) results even when the MIMO demodulator uses a zero forcing (ZF) algorithm with a higher order modulation such as 4096QAM.

Performance evaluation of MIMO channel estimation for ATSC 3.0

ATSC 3.0, the latest Digital Terrestrial Television (DTT) standard, allows a higher spectral efficiency and/or a transmission robustness with Multiple-Input Multiple-Output (MIMO) technology compared to existing single-antenna DTT networks. Regarding MIMO channel estimation, two pilot encoding algorithms known as Walsh-Hadamard encoding and Null pilot encoding are possible in ATSC 3.0. The two MIMO pilot algorithms are standardized so as to have the same pilot positions and the same pilot boosting as SISO, but the performance has not been evaluated. This paper focuses on the performance evaluation of the two MIMO pilot encoding algorithms in ATSC 3.0 using physical layer simulations. Results can be used as guidelines or recommended practices to broadcasters to select the MIMO pilot encoding algorithm that better suits their service requirments. Several channel estimation algorithms have been evaluated in both mobile and fixed reception conditions. The simulation results show that Null pilot encoding provides slightly better performance than Walsh-Hadamard encoding for fixed reception but worse performance for mobile reception, especially at high signal-to-noise ratios.

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.