Anthony Ng'oma

Radio-over-Fiber Distributed Antenna System for WiMAX Bullet Train Field Trial

Wireless broadband access for mobile applications is an area of increasing growth. An international collaboration, led by the Taiwan Industrial Technology Research Institute (ITRI), has been working to implement a dedicated WiMAX network for a user field trial on the Taiwan High Speed Rail (THSR) bullet train system. Continuous wireless coverage at train speeds up to 300km/hr is challenging due to a number of critical issues, including handover at high speeds and coverage in challenging terrain such as tunnels. A Radio-over-Fiber (RoF) Distributed Antenna System (DAS) was developed by Corning Incorporated to address the critical issue of handover and increase the coverage for each WiMAX basestation. For a DAS deployment consisting of multiple discrete antennas, proper signal strength management is required because the maximum delay spread allowed by the WiMAX protocol is easily surpassed at realistic fiber ranges up to 9km. This paper reviews some of the initial results of the RoF DAS experiments in SongShan tunnel in Taipei. Error-free signal transmission was achieved when the difference in received power from two consecutive antennas was greater than 10dB.

2 × 2 MIMO radio-over-fiber system at 60 GHz employing frequency domain equalization.

This work experimentally demonstrates the efficacy of the 2 × 2 multiple-input multiple-output (MIMO) technique for capacity improvement of a 60-GHz radio-over-fiber (RoF) system employing single-carrier modulation format. We employ frequency domain equalization (FDE) to estimate the channel response, including frequency response of the 60 GHz RoF system and the MIMO wireless channel. Using FDE and MIMO techniques, we experimentally demonstrate the doubling the of wireless data capacity of a 60 GHz RoF system to 27.15 Gb/s using 16-QAM modulation format, with transmission over 25 km of standard single-mode fiber and 3 m wireless distance.

Performance of a Multi-Gb/s 60 GHz Radio Over Fiber System Employing a Directly Modulated Optically Injection-Locked VCSEL

A multi-Gb/s 60 GHz radio over fiber (RoF) system employing direct modulation of an optically injection locked vertical-cavity surface-emitting laser is successfully demonstrated. Experimental results show that the RoF system is tolerant to fiber chromatic dispersion due to inherent single-sideband modulation produced by injection locking. A simple carrier-to-sideband equalization method is used to substantially improve the sensitivity of the RoF system by 18 dB, enabling both successful wireless signal transmission and multilevel signal modulation formats such as quadrature phase shift keying (QPSK). At least 3 Gb/s ASK-modulated data and 2 Gb/s QPSK-modulated data is transported over up to 20 km standard single-mode fiber and 3 m wireless distance with no penalty.

Simple 14-Gb/s Short-Range Radio-Over-Fiber System Employing a Single-Electrode MZM for 60-GHz Wireless Applications

This paper demonstrates the feasibility of a simple multigigabit-per-second (Gbps) radio-over-fiber (RoF) system employing multilevel orthogonal frequency-division-multiplexing (OFDM) signal modulation at 60 GHz and a single-electrode Mach-Zehnder modulator (MZM). In this paper, the impact of fiber chromatic dispersion and OFDM beat noise on the performance of the RoF system are investigated by theoretical analysis, VPI WDM-TransmissionMaker simulation and experimental demonstration. A 13.875-Gb/s QPSK OFDM signal occupying the full 7-GHz license-free band at 60 GHz with frequency multiplication for the RoF link is demonstrated. After 3 km of standard single-mode fiber transmission with no dispersion compensation, the power penalty is less than 3 dB.

Simple multi-Gbps 60 GHz radio-over-fiber links employing optical and electrical data up-conversion and feed-forward equalization

We show that optical up-conversion performs better than electrical up-conversion in simple IMDD-based 60 GHz radio-over-fiber links. Feed-forward equalization improved the performances of both systems, enabling error-free transmission of 4 Gbps over 500 m of single-mode fiber.

31 Gbps RoF system employing adaptive bit-loading OFDM modulation at 60 GHz

Record wireless data transmission of 31.4 Gbps within 7 GHz license-free band at 60 GHz is experimentally demonstrated using adaptive bit-loading OFDM modulation. Adaptive bit-loading OFDM also enables extended fiber transmission distances beyond 5km.

50-Gb/s Radio-over-Fiber system employing MIMO and OFDM modulation at 60 GHz

Record 50-Gb/s wireless signal transmission over 4 m is experimentally demonstrated using a 2×2 MIMO Radio-over-Fiber system at 60 GHz. MIMO spatial multiplexing and 16-QAM OFDM modulation were used to achieve a high combined spectral efficiency of up-to 8 b/s/Hz.

Transmission of 20-Gb/s OFDM signals occupying 7-GHz license-free band at 60 GHz using a RoF system employing frequency sextupling optical up-conversion

This work describes a proposed 60-GHz radio-over-fiber (RoF) system employing a frequency sextupling optical up-conversion scheme. Based on the modified single sideband modulation scheme, spectrally efficient vector signals were transmitted with no performance degradation due to dispersion-induced fading. Wavelength-division- multiplexed optical up-conversion can be realized using the proposed system. Since the required transmitter bandwidth is significantly reduced, radio-frequency components with lower bandwidth and higher reliability can be utilized. Both 13.75-Gb/s QPSK-OFDM and 20.625-Gb/s 8QAM-OFDM signals were experimentally demonstrated. After transmission over 25-km of standard single mode fiber, no significant received power penalty was observed.

Radio-over-fiber technologies for high data rate wireless applications

The paper discusses two approaches for increasing data throughput needed for the delivery of bandwidth-hungry services to wireless users. Small radio cells are a stop-gap solution for dealing with todays capacity-limited wireless systems. However, the ultimate path towards wireless communication at gigabit-per-second data rates is millimeter-wave frequencies such as 60 GHz. We discuss the benefits of using radio-over-fiber (RoF) technologies to feed the high-density of remote antenna units present in small-cell wireless systems operating at either low frequencies or mm-wave-frequencies. We investigate the performance of a simple 60 GHz RoF link transmitting 4 Gbps (single carrier), and show that the severe impact of ripples in the link response can be minimized by using simple linear feed-forward equalization, resulting in tremendous system performance improvement. We further demonstrate the use of a RoF system to generate a 7 Gbps QPSK-modulated 60 GHz signal.

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.