Hou-Tzu Huang

1.1-Gb/s White-LED-Based Visible Light Communication Employing Carrier-Less Amplitude and Phase Modulation

We demonstrate 1.1-Gb/s visible light communication (VLC) employing carrier-less amplitude and phase modulation (CAP) and a commercially available phosphorescent white light emitting diode (LED). Optical blue filtering, precompensation, and decision feedback equalization are used to compensate the frequency response of the phosphor-based white LED. Various modulation orders of CAP signals are investigated to maximize the capacity of the VLC system. The record data rate of 1.1 Gb/s with the bit error rate performance below the FEC limit of 10-3 is successfully achieved >; 23-cm air-transmission via a 220-MBaud 32-CAP signal.

Performance Comparison of OFDM Signal and CAP Signal Over High Capacity RGB-LED-Based WDM Visible Light Communication

We experimentally demonstrate a visible light communication (VLC) system based on a single commercially available RGB-type LED. High spectrally efficient carrierless amplitude and phase (CAP) modulation and orthogonal frequency-division multiplexing (OFDM) are adopted in the intensity-modulation and direct-detection VLC system of limited bandwidth. In order to achieve higher capacity of the uneven-frequency-response LED-based VLC system, OFDM signals are combined with the bit- and power-loading techniques, and CAP signals of various modulation are pre-emphasized to modulate one of the RGB chips. To reach the BER of less than 10-3, CAP and OFDM signals demonstrate the maximum data rates of 1.32 and 1.08 Gb/s, respectively, employing the blue chip. In addition to spectrally efficient formats, the wavelength-division-multiplexing (WDM) scheme is applied to further increase the capacity. After individually optimizing RGB chips, the maximum aggregate data rates of CAP and OFDM are 3.22 and 2.93 Gb/s, respectively, in our RGB-LED-based WDM VLC system. Hence, compared with OFDM, the CAP scheme shows competitive performance and provides an alternative spectrally efficient modulation for next generation optical wireless networks.

High spectral efficient W-band OFDM-RoF system with direct-detection by two cascaded single-drive MZMs

W-band wireless transmission has attracted a lot of interest due to its wider available bandwidth (i.e. 75-110 GHz). In this article, we propose a direct-detection orthogonal frequency division multiplexing radio over fiber (OFDM-RoF) system via two cascaded single-drive MZMs at center frequency of 103 GHz. We discuss maximum bandwidth of different modulation formats under forward error correction (FEC) threshold (3.8 x 10(-3)). Up to 40-Gbps 16-QAM OFDM signals is achieved over 25-km fiber and 2-m wireless transmission. To overcome the penalty from uneven frequency response, bit-loading algorithm is applied to discuss data rate and spectral efficiency with signal bandwidth from 5 to 10 GHz. With 10-GHz bandwidth, 46.4-Gb/s data rate and 4.64-bit/s/Hz spectral efficiency was achieved. To achieve 40-Gbps data rate, the required bandwidth of OFDM signal with bit-loading is 2 GHz less than that without bit-loading.

100-GHz DD-OFDM-RoF system over 150-km fiber transmission employing pilot-aided phase noise suppression and bit-loading algorithm.

This study extended the transmission distance of a 100-GHz DD-OFDM-RoF system through the reduction of chromatic dispersion-induced phase noise. The implementation of a pilot-aided phase noise suppression (PPNS) scheme enabled the transmission of distance-insensitive 16.97-Gbps QPSK OFDM over 0~150-km fiber and 2-m air transmission via a DFB laser with linewidth of 1~10-MHz. We applied a bit-loading algorithm in conjunction with PPNS to maximize spectral efficiency, resulting in a 93% improvement in the data rate from 11.53 to 22.27 Gbps at a fiber transmission of 150 km.

2

Multiple-input-multiple-output (MIMO) technology is a promising method to increase spectral efficiency in wireless communications. In this paper, a 60-GHz orthogonal frequency-division multiplexing radio over fiber (OFDM-RoF) system employing 2 × 2 MIMO wireless technology is demonstrated. With the proposed equalizer employing least mean squares (LMS) algorithm, MIMO channel mixing and I/Q-mismatch can be compensated simultaneously. 16-QAM and 32-QAM OFDM signal transmissions under forward error correction (FEC) threshold ( 1×10-3) are demonstrated. A data rate of 76.3 Gb/s can be achieved with a bit-loading algorithm over 25-km fiber transmission and 3.5-m wireless transmission.

\times

This study experimentally investigated the impact of dispersion-induced phase noise (DPN) on the transmission performance of a 100-GHz DD OFDM-RoF system. We sought to extend the transmission distance through the reduction of DPN using two digital phase noise suppression (PNS) schemes, based on the assumption that all subcarriers suffer from common DPN. The decision-aided PNS (DA-PNS) scheme treats the OFDM signal as feedback to aid in the calculation of DPN without incurring additional overhead. Pilot-aided PNS (PA-PNS) estimates the common DPN by inserting an additional optical pilot tone with guard band. Although both schemes are able to extend fiber transmission distance to beyond 150 km, the PA-PNS scheme tends to be outperformed by the DA-PNS scheme due to additional power required for the pilot tone. Nonetheless, in the DA-PNS scheme, the bandwidth of the estimated DPN must be truncated to avoid error propagation, which can result in the relatively faster increment in the transmission penalty. In contrast, the PA-PNS scheme maintains the variation in penalty to <;1 dB, thereby achieving the performance that is insensitive to transmission distance.

2 MIMO OFDM-RoF System Employing LMS-Based Equalizer With I/Q Imbalance Compensation at 60 GHz

This paper investigates the efficacy of two methods for compensating I/Q imbalance, which causes serious performance problems in wideband (6.98-GHz spectrum) millimeter-wave systems employing MIMO signal transmission. A 60-GHz orthogonal frequency division multiplexing (OFDM) RoF system employing 2 × 2 MIMO technology is implemented using a commonly used training symbol arrangement and a proposed method. We experimentally demonstrate that the proposed training symbol arrangement performed significantly better than the commonly used approach. By combining the proposed training symbol arrangement with LMS I/Q compensation and bit-loading, we achieve an extremely high wireless data rate transmission of 75.211 Gb/s over both 50 km of standard single-mode fiber and 3.5-m wireless distance. The optical power penalty after 50-km fiber transmission was only ~1 dB.

Estimation and Suppression of Dispersion-Induced Phase Noise in W-band Direct-Detection OFDM Radio-Over-Fiber Systems

This paper proposes a 2x2 MIMO OFDM Radio-over-Fiber scheme based on optical subcarrier multiplexing and 60-GHz MIMO wireless transmission. We also schematically investigated the principle of optical subcarrier multiplexing, which is based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In our simulation result, combining two MIMO OFDM signals to drive DP-MZM gives rise to the PAPR augmentation of less than 0.4 dB, which mitigates nonlinear distortion. Moreover, we applied a Levin-Campello bit-loading algorithm to compensate for the uneven frequency responses in the V-band. The resulting system achieves OFDM signal rates of 61.5-Gbits/s with BER of 10(-3) over 25-km SMF transmission followed by 3-m wireless transmission.

Theoretical and Experimental Investigation of a 2 × 2 MIMO OFDM Radio-Over-Fiber System at 60-GHz With I/Q Imbalance Compensation

This paper presents a simple 2 × 2 multiple-input multiple-output (MIMO) 60-GHz radio-over-fiber system. Due to the proposed specific frequency arrangement of driving signals, each optical transmitter requires only a single-drive Mach-Zehnder modulator with 3-dB bandwidth of less than 35 GHz. This arrangement of frequencies can increase the tolerance of optical signals to dispersion-induced RF fading, thereby extending fiber transmission distance. Unfortunately, this scheme leads to signal-to-signal beating interference (SSBI), which can deteriorate system performance. Thus, we employed a 2 × 2 MIMO scheme to enhance data capacity by combining two data streams and two corresponding SSBIs prior to signal demodulation. We also developed a novel iterative equalization technique to mitigate SSBI in the MIMO system. The proposed system achieved a maximum capacity of 55.9-Gb/s in the transmission of 7-GHz orthogonal frequency division multiplexing signals over 12-km fiber and 3.5-m air transmission using a bit-loading algorithm.

60-GHz optical/wireless MIMO system integrated with optical subcarrier multiplexing and 2x2 wireless communication

This Letter proposes a W-band OFDM RoF system at 103.5 GHz employing power detector to support vector signal down-conversion. Additional RF tone is generated and transmitted from central office to replace the local oscillator at a wireless receiver. With a proper frequency gap and power ratio between the RF tone and the OFDM-modulated signal, the impact from signal-to-signal beating interference can be minimized. The data rate can achieve a 40 Gbps 16 QAM OFDM signal over 25 km fiber and 2 m wireless transmission.