Shota Ishimura

Eight-state trellis-coded optical modulation with signal constellations of four-dimensional M-ary quadrature-amplitude modulation.

We apply the eight-state trellis-coded modulation (TCM) using signal constellations of four-dimensional M-ary quadrature-amplitude modulation (4D-MQAM) to optical communication systems for the first time to our knowledge. In the TCM scheme, the free distance of the trellis diagram is equal to the minimum distance between constellation points in partitioned subsets, which enlarges the coding gain effectively. In fact, its asymptotic power efficiency is 3-dB larger than that of the set-partitioned 4D-MQAM (SP-4D-MQAM) format, while their spectral efficiencies are the same. Such theoretical predictions are confirmed through computer simulations on eight-state TCM with constellations of 4D-4QAM (i.e., 4D quadrature phase-shift keying: 4D-QPSK) and 4D-16QAM. In particular, eight-state TCM with 4D-QPSK constellations is practically important because of its simple encoder structure, relatively low computational cost, and high coding gain against dual-polarization QPSK (DP-QPSK) and SP-4D-QPSK. Through measurements of its bit-error rate (BER) performance, we confirm that the coding gain against DP-QPSK is about 3 dB at BER=10(-3).

Multi-dimensional permutation-modulation format for coherent optical communications

We introduce the multi-dimensional permutation-modulation format in coherent optical communication systems and analyze its performance, focusing on the power efficiency and the spectral efficiency. In the case of four-dimensional (4D) modulation, the polarization-switched quadrature phase-shift keying (PS-QPSK) modulation format and the polarization quadrature-amplitude modulation (POL-QAM) format can be classified into the permutation modulation format. Other than these well-known modulation formats, we find novel modulation formats trading-off between the power efficiency and the spectral efficiency. With the increase in the dimension, the spectral efficiency can more closely approach the channel capacity predicted from the Shannons theory. We verify these theoretical characteristics through computer simulations of the symbol-error rate (SER) and bit-error rate (BER) performances. For example, the newly-found eight-dimensional (8D) permutation-modulation format can improve the spectral efficiency up to 2.75 bit/s/Hz/pol/channel, while the power penalty against QPSK is about 1 dB at BER=10(-3).

Multi-dimensional Permutation Modulation Aiming at Both High Spectral Efficiency and High Power Efficiency

We analyze the performance of multi-dimensional permutation modulation formats. With the increase in the dimension of modulation, their spectral efficiencies can approach the Shannon limit even when their power efficiencies are kept high.

Fast decoding and LLR-computation algorithms for high-order set-partitioned 4D-QAM constellations

We propose digital-signal-processing algorithms that achieve fast decoding and LLR-computation for high-order set-partitioned 4D-QAM formats based on their parity-check functions. Computer-simulation results show that computational complexity of the decoder can significantly be reduced with negligible power penalty using such algorithms.

Broadband IF-Over-Fiber Transmission With Parallel IM/PM Transmitter Overcoming Dispersion-Induced RF Power Fading for High-Capacity Mobile Fronthaul Links

We demonstrate a broadband and long-distance intermediate frequency-over-fiber (IFoF) transmission scheme employing a transmitter composed of parallel intensity/phase (IM/PM) modulators with appropriate bandwidth allocations to IM and PM. Due to the proposed scheme, we can eliminate all the null frequencies caused by dispersion-induced RF power fading, which, in turn, enables us to significantly increase the available bandwidth. In addition, our system does not require any synchronization between IM and PM, which reduces complexity compared to conventional parallel transmitter architecture. We successfully transmitted 20

DSP technologies in the Stokes vector receivers for short-reach optical transmission systems

\times

Optical and wireless integrated technologies for mobile networks towards beyond 5G era

360 MHz filtered orthogonal-frequency-division-multiplexed signals corresponding to a common public radio interface equivalent data rate of 524.28 Gbps over a 30- and 40-km single-mode fiber satisfying the 8% threshold for the error-vector magnitude values for all the subcarriers. These results show that our proposed IFoF transmission scheme is scalable to long-distance mobile fronthaul links for 5G and beyond.

Blind polarization demultiplexing algorithm for multi-level modulation formats in stokes vector direct detection systems

Stokes vector receivers have attracted attention for their ability to enhance spectral efficiency due to the increase in the number of dimensions compared to conventional intensity-modulation and direct-detection (IM-DD) systems. One of the technical advantages of the Stokes receiver is that the original state-of-polarization (SOP) of a transmitted signal can be retrieved with digital signal processing (DSP) even if it is fluctuated during fiber transmission. In this paper, we review DSP technologies for SOP recovery, focusing on the modified constant modulus algorithm (CMA), and the radius directed equalization (RDE) algorithm in the Stokes space. Using computer simulations, we show that these algorithms can track random SOP fluctuations without any penalties.

Optical and wireless integrated technologies for future mobile networks

The peak rate of coming 5 G mobile services will be comparable to that of FTTH. In this paper, we will discuss integrated optical and wireless technologies, such as RoF, for efficient use of bandwidth of future mobile back/front-haul networks towards beyond 5G era.

Experimental demonstration of the 8-state Trellis-coded 4D-QPSK optical modulation format

In the Stokes vector direct detection (SV-DD) system, we extend a previously-proposed simple blind polarization demultiplexing (POL-DEMUX) algorithm for PSK constellations to QAM constellations. We numerically analyze the POL-DEMUX performance and confirm that the blind POL-DEMUX process can be successfully done with negligible power penalties for high-order modulation formats such as 8-PSK, 16-PSK and 16-QAM even under conditions with fast SOP fluctuation.