Takuya Shitomi

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.

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.

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.

MIMO Sphere Decoding With Successive Interference Cancellation for Two-Dimensional Non-Uniform Constellations

Non-uniform constellations (NUCs) have been introduced to improve the performance of quadrature amplitude modulation constellations. 1D-NUCs keep the squared shape, while 2D-NUCs break that constraint to provide robustness. An impending problem with multiple-input multiple-output (MIMO) is the optimum demapping complexity, which grows exponentially with the number of antennas and the constellation order. Some well-known sub-optimum MIMO demappers, such as soft fixed-complexity sphere decoders (SFSD), can reduce that complexity. However, SFSD demappers do not work with the 2D-NUCs, since they perform a quantization step in separated I/Q components. In this letter, we provide an efficient solution for the 2D-NUCs based on Voronoi regions. Both complexity implications and SNR performance are also analyzed.