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Performance Evaluation of a 60 GHz Radio-over-Fiber System Employing MIMO and OFDM Modulation

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Chia-Chien Wei, Sien Chi, and Anthony Ng’oma, Member, IEEE

Abstract—Multiple-input-multiple-output (MIMO) technique

for wireless communications is extensively used these days, especially to increase the spectral efficiency of new wireless communication systems like LTE, WiMAX, etc. MIMO in combination with robust modulation techniques like orthogonal frequency division multiplexing (OFDM) provides a good solution for high data rate wireless links. In this paper, the performance of MIMO for a 60 GHz OFDM radio over fiber link is analyzed. System performance of the MIMO system for different antenna spacing is also studied. Using the optimum system parameters, a MIMO OFDM wireless link of up to 51 Gb/s was successfully demonstrated at 60 GHz in a bandwidth of <7 GHz, with a wireless transmission distance of up to 4 m and optical fiber transmission of 1 km. To our knowledge this is the highest data rate demonstrated in the 7 GHz band of 60 GHz.

Index Terms—Millimeter wave communication, optical

modu-lation, radio over fiber, MIMO.

I. INTRODUCTION

D

EMAND for wireless data capacity is constantly in-creasing with the next generation smart mobile devices and new bandwidth-intensive user applications such Facebook, YouTube, Netflix, etc., which have revolutionized the way mobile communications are used. With the recent advances in cloud computing/network storage the requirement for high capacity bandwidth is increasing. Other than in mobile phones, wireless communications are also playing an important role in other consumer electronic devices like TVs, tablets, etc., where very high speed wireless links are required for applications such as HD-video streaming, instant back-up over the air, and other multi-media rich applications. The current wireless systems in the lower frequencies providing wireless services like LTE, and WiFi 802.11n, etc., have a bandwidth of few

Manuscript received June 18, 2012; revised October 31, 2012.

R. Sambaraju, H. Yang, and A. Ng’oma are with the Science and Tech-nology Dept., Corning Incorporated, Corning, NY, 14831, USA (e-mail: sambarajr@corning.com).

C.-H. Ho, T.-S. Lu, C.-Y. Wang, and C.-T. Lin are with the Institute of Photonic Systems, National Chiao Tung University, 301 Gaofa 3rd, Tainan Country 711, Taiwan (e-mail: jinting@mail.nctu.edu.tw).

W.-J. Jiang and W.-Y. Li are with the Dept. of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Taiwan.

C.-C. Wei is with the Dept. of Photonics, National Sun Yat-Sen University, Taiwan.

S. Chi is with the Dept. of Photonics Engineering, Yuan-Ze University, Chung-Li 320, Taiwan.

C.-H. Ho, W.-J. Jiang and W.-Y. Lee were with Corning Incorporated. Digital Object Identifier 10.1109/JSAC.2013.SUP2.12130010

tens of MHz. Consequently, these wireless systems use the most advanced techniques like multiple input multiple output (MIMO), OFDM, modulation formats of up to 256 QAM in an attempt to offer higher transmission data rates. However, the FCC and other regulatory bodies have freed up to 7 GHz of unlicensed spectrum in the millimeter wave (MMW) band of 60 GHz for wireless access. The huge bandwidth available in this band provides a promising solution for high capacity multi-Gb/s wireless communication, which far exceeds the performance of existing wireless systems.

One of the limitations of such high frequencies like 60 GHz is huge attenuation, which limits the wireless coverage and distribution of these wireless signals pose a challenge. Radio over fiber (RoF) technology with its huge bandwidth is a good solution for the generation and distribution of high bandwidth 60 GHz wireless links [1]–[6]. Until now several techniques were proposed to generate and distribute high capacity wire-less links in the 60 GHz band using several advanced modu-lation formats [2]–[6]. Till now, up to 31 Gb/s wireless links at 60 GHz using OFDM modulation was demonstrated [4]. It is well-known that multiple-input-multiple-output (MIMO) techniques can achieve system capacity that exceeds the Shan-non’s limit. MIMO is currently used in most of the wireless communication systems like LTE – the 4th generation cel-lular technology, WiMax, WiFi, etc., for providing increased capacity and robustness. MIMO can provide either increase in the wireless capacity by implementing multiple antennas at the receiver and transmitter sides and employing spatial multiplexing [7]–[9] or it can provide system robustness by employing antenna diversity [10]. Hence implementing MIMO for 60 GHz wireless systems can effectively increase the capacity or robustness of the systems.

MIMO for 60 GHz has attained considerable interest and recent results demonstrate several systems operating in MIMO mode at 60 GHz [11]–[14]. All these systems operate at only a few Gb/s and recent work reported up to 27.15 Gb/s using 60 GHz MIMO with a RoF system employing double sideband single carrier (DSB–SC) signals [6]. To the authors’ best knowledge, this paper is the first demonstration of a MIMO RoF system employing OFDM modulation at 60 GHz. The higher spectral efficiency of OFDM and its robustness to multi-path effects make it a highly suitable modulation format to be implemented in combination with MIMO. MIMO

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Fig. 1. Block diagram of the 2×2 MIMO system, and the schematics of the training symbol design of 2×2 MIMO-OFDM signals.

typically requires multi-path environment for providing the capacity gain, but recent studies [15]–[17] have proved that for optimum antenna spacing, MIMO performance in LOS can surpass a typical Rayleigh faded channels. In previous work we have demonstrated both OFDM and single carrier modulation formats based RoF systems, and we observed that OFDM is robust to the non-flat frequency response of the RoF link [6].

In this paper, we study the performance of a 2×2 spatially multiplexed MIMO-OFDM system employing a 60 GHz RoF system. Based on the optimum system parameters record wire-less data speeds of up to 51 Gb/s (2×25.5 Gb/s) were achieved using 16 QAM modulation within 6.375 GHz bandwidth. This result represents a very high spectral efficiency of 8 b/s/Hz.

II. OPERATINGPRINCIPLE OF2×2 MIMOFOROFDM In MIMO communication systems, multiple antennas are located at either side of the link; where anM ×N MIMO sys-tem consists ofM transmit antennas and N receive antennas. The M transmitted signals are received by the N receivers, where after MIMO decoding the transmitted signals can be re-covered. Uncorrelated wireless paths between the transmitters and the receivers are required for distinguishing the received signals and hence for proper operation of MIMO systems. When MIMO is implemented with spatial multiplexing, space-time codes provide increase in capacity for fixed power and bandwidth, and the maximum capacity increase is determined by the minimum number of antennas (min(M, N)) in the MIMO system [7]–[9].

Fig. 1 shows the block diagram of an M × N MIMO communication system using OFDM modulation with training symbols for wireless channel estimation. The transmitter and receiver are divided into two blocks, namely: the OFDM modulation/demodulation part and the MIMO decoding part. The blocks performing OFDM modulation and demodulation are similar to any OFDM based communication system [18], [19]. For the M × N MIMO-OFDM signal generation, M independent data streams were generated and each data stream mapped to a digital modulation format. These M serial data streams were converted to parallel followed by inverse fast Fourier transformation (IFFT), which was applied to generate multiple complex time domain streams, and form the OFDM carriers. In OFDM modulation, the cyclic prefix is inserted between each OFDM block to overcome inter symbol inter-ference. After the insertion of the cyclic prefix and subsequent

digital to analogue conversion, M independent RF streams each containing independent data are generated, representing H spatially multiplexed MIMO channels.

At the receiver,N antennas receive the combination of the M transmitted RF signals after transmission over the air and down converted to the desired IF (intermediate frequency) for digital signal processing, which involve MIMO decoding and OFDM demodulation. MIMO decoding includes FFT and Zero-Forcing (ZF) algorithm. In the M × N MIMO system, the OFDM signal for the ith transmit antenna at the kth sub-carrier is denoted by xi[k], while H denotes a channel matrix with(i, j)thentryhij for channel coefficients between the ith transmit antenna and jth receiver antenna, where i = 1, 2 . . . M and j = 1, 2 . . . N. The signal at the receiver antenna can be mathematically expressed as:

yi= Hij[k]xi[k] + wi[k] (1)

Where yj[k] represent received signal for the jth receiver antenna at the kth sub-carrier. wj[k] denote the additive complex Gaussian noise for the jth receiver antenna. Using the Zero-Forcing (ZF) algorithm [7], the transmitted data can be recovered by inversing the estimated channel matrix as:

˜x[k] = H[k]−1y[k] = x[k] + H[k]−1w[k] (2)

From the eqn. 2, the estimation of the channel matrix is the most important part of the MIMO-OFDM demodulation process. The channel estimation is performed by using training symbols. Considering an example of a 2×2 MIMO system, a special arrangement of training symbol is implemented by switching between the on-off positions as shown in Fig. 1 (left) [20]. The received signals then corresponding to either the first or the second training symbol time, which can be expressed as eqn. 3:  T S3[k] T S4[k]  =  h11[k] h21[k] h21[k] h22[k]   T S1[k] 0  + w[k]  T S5[k] T S6[k]  =  h11[k] h21[k] h21[k] h22[k]   0 T S2[k]  + w[k] (3) Form the above matrices in eqn. 3, the channel coefficients can be estimated by appropriate training symbols and the transmitted data can be recovered by using the ZF algorithm. The estimated channel matrix can be expressed as:

˜ H =  T S3/T S1 T S4/T S1 T S5/T S2 T S6/T S2  (4)

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CN =max(λi)

min(λi) (5)

Whereλi is singular value of channel matrix.H is said to be

well-conditioned if the CN is close to 1 and ill-conditioned if the CN is close to infinite. The CN impacts the MIMO performance, and for higher CN channels, the required SNR to achieve the same capacity increases, causing significant reduction in the performance of the MIMO system.

III. EXPERIMENTALSET-UP

Fig. 2 schematically depicts the experimental setup of the implemented 60 GHz RoF system [22] for generation and transmission of a 2×2 MIMO OFDM signal. Using an arbitrary waveform generator with a sampling rate of 12 GS/s the in-phase and quadrature-phase components of an OFDM signal were generated, with a maximum RF bandwidth of 3.5 GHz each. The OFDM QAM signal consists of 74 sub-carriers within the 7 GHz bandwidth, and 1/8 cyclic prefix to mitigate inter symbol inference induced by the system.

The OFDM signals were then up-converted to 25 GHz using an electrical I/Q mixer as shown in inset (i) of Fig. 2. In order to generate a 60 GHz OFDM signal from optical heterodyne in the photo detector, the 25 GHz OFDM signal was combined with another 35.5 GHz carrier signal as shown in inset (ii) and (iii) of Fig. 2. The RF signals were then used to modulate an optical carrier at 1550 nm generated using a Distributed Feedback (DFB) laser, in a Mach-Zehnder modulator with a 3-dB bandwidth of ∼50 GHz. To achieve the 60 GHz RF signal, the Mach-Zehnder modulator (MZM) was biased at its minimum point to generate a carrier suppressed optical signal, as shown in Fig. 3(a). The optical signal at the output of the MZM was amplified using an Erbium Doped Fiber Amplifier (EDFA) with a nominal gain of 20 dB. To generate two independent signals for a 2×2 MIMO system, the optical signal was split equally using a 3 dB coupler, and the two resulting signals de-correlated by delaying one of the signals using a 1 km optical fiber. The now de-correlated optical signals were individually photo-detected using a 60 GHz photo-detector to generate a 2×2 MIMO-OFDM signal at a carrier frequency of 60.5 GHz. The 60 GHz signals were radiated using standard horn antennas with a gain of∼24 dBi. To compensate for the uneven gain of the two RF paths, and to maintain the same RF output power at the two antennas, the optical power into the photo detectors for channel 1 and channel 2 were set to−2 dBm and −3.5 dBm respectively. At the receiver two horn antennas were used to receive the 2×2 MIMO signals, and later amplified using a low-noise amplifier. The two received signals were down-converted to two separate

Fig. 2. Schematic of the experimental set-up depicting a central office, remote wireless unit and a receiver unit.

Fig. 3. Optical spectrum for double-sideband carrier suppression scheme after EDFA (a). Electrical spectrum of MIMO-OFDM signal at 4.5 GHz carrier frequency after down-conversion at received unit (b).

IF signals at 4.5 GHz as shown in Fig. 2. The 4.5 GHz IF signals were later sampled at a rate of 40 GS/s using a digital sampling scope, and demodulated using a PC based offline digital signal processor.

IV. EXPERIMENTALRESULTS ANDDISCUSSIONS

Over the air wireless transmission measurements of 60 GHz 2×2 MIMO system were performed in a typical laboratory (dimensions: 7.5× 6.88 m). The floor plan of the laboratory and the possible signal radiation paths for a 2×2 MIMO system are shown in Fig. 4(a). The transmitters and receivers were placed on two tripods, at a height of 1.3 m above the floor. At the receiver side, the two antennas were separated by a fixed distance of∼5 cm, which was the minimum separation distance allowed by the bulk horn antennas employed, and which was sufficient to avoid coupling-induced correlation between the antennas [13]. From the geometrical calculations (for Tx antenna separation of 17 cm and Rx separation

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(a)

(b)

Fig. 4. Spatial arrangements for 2×2 MIMO RoF systems (a), and the corresponding geometrical interpretation of the radiated signal’s beamwidth (b).

of 5 cm) we found that the minimum beam width (θ1, θ2) as shown in Fig. 4(b), required for radiating on both the receiver antennas is far less than the 3-dB beam width of the antennas used, which is around 30 degrees. To ensure MIMO is correctly implemented, the transmit antennas were angled in such a way to receive strong 60 GHz signals at both the RF antennas from each transmitter antenna as depicted in Fig. 4(b).

During the whole experiment, both transmit antennas were angled such that they always faced towards the center of the two receive antennas. We investigated the impact of transmit antenna separation, the wireless transmission distance and optical fiber transmission on the performance of the MIMO system.

The effect of receiver antenna separation was modeled by calculating the condition number for different receiver and transmitter antenna spacing. From the simulation results shown in Fig. 5, it can be observed that the impact of the re-ceiver and transmitter antenna separation can be interchanged resulting in the same condition number. However, it should be noted that in practical implementations of 60 GHz wireless access systems, transmitter antennas will be integrated inside

Fig. 5. Simulated condition number values for varying receiver and transmitter antenna separation for different wireless transmission distances. 2.5 m (a), 3 m (b), 3.5 m (c), and 4 m (d).

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(b)

Fig. 6. The channel condition number for different transmitter antenna separations in a 2×2 MIMO 60 GHz wireless link at different receiver to transmitter distance evaluated experimentally (a) and using simulations (b).

the user equipment, providing for fixed and close antenna spacing. On the other hand, there may be more room in the 60 GHz access point to spread the transceiver antennas further apart as desired.

First, the optimum antenna separation between the transmit antennas was investigated. Fig. 6(a) shows the measured condition number of the 2×2 MIMO signal plotted against the

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Fig. 7. BER performance versus with data rate by QPSK, 8 QAM, 32 QAM in 7 GHz bandwidth and 16 QAM in 6.375 GHz.

Fig. 8. BER performance of 60 GHz 2×2 MIMO-OFDM QPSK signal as function of wireless received power with wireless distance from 2.5 m to 4 m.

separation between the transmit antennas for different wireless transmission distances. The CN obtained was the average of all the 74 sub-carriers and was calculated from the estimated parameters of the 2×2 MIMO channel matrix.

The effect of transmitter antenna separation was simulated for various wireless transmission distances and plotted as shown in Fig. 6(b). It can be observed that the lowest condition number was obtained anywhere between 12 cm to 18 cm of antenna separation, and variation in condition number over the 6 cm range was minimal. From these results we chose 17 cm to be the optimal antenna separation for most of the wireless transmission distances. Due to physical limitations of the experimental set-up transmitter antenna separation below 17 cm were not implemented.

With the transmit antenna separation fixed at 17 cm, wire-less transmission experiments using the 60 GHz 2×2 MIMO OFDM system were performed with different modulation formats like QPSK, 8 QAM, 16 QAM and 32 QAM over the whole 7 GHz of available bandwidth. Fig. 7 summarizes the bit-rates possible for the MIMO system with different mod-ulation formats and their corresponding calculated bit error ratios. From Fig. 7 it can be seen that for 7 GHz bandwidth, 28 Gb/s using QPSK modulation and 42 Gb/s using 8 QAM modulation were achieved with the BER complying with the FEC thresholds, whereas the higher modulation formats like 16 QAM (56 Gb/s) and 32 QAM (70 Gb/s) failed to meet the BER requirements. To overcome the distortion limitations faced by the 7 GHz wide spectrum, the bandwidth of the OFDM signal was reduced to 6.375 GHz. This allowed the

Fig. 9. BER performance as function of wireless received power through 4 m wireless transmission with BTB, 500 m and 1200 m fiber transmission with QPSK signal.

Fig. 10. BER performance as function of wireless received power through 4 m wireless transmission and 1200 m fiber transmission with 16 QAM signal.

OFDM-MIMO system with 16 QAM modulation to meet the minimum FEC BER performance requirement of < 10−3 with a higher data-rate of 51 Gb/s. This record wireless data transmission speed corresponds to a high spectral efficiency of 8 b/s/Hz.

To further understand the performance limitations of the proposed MIMO system, several experiments were performed for varying wireless transmission distances as well as different optical fibre transmission distances.

The wireless transmission distance was varied from 2.5 m to 4 m, whereas the fiber transmission distances of 500 m and 1200 m were considered. Fig. 8 shows the BER plots of the 60 GHz 2×2 MIMO-OFDM QPSK signal, plotted against the received RF power at different wireless transmission distances. The separation between transmit antennas was fixed at 17 cm from Fig. 6. From 2.5 m to 4 m of transmission distance, only 1 dB of received power penalty was recorded for a BER of 10−3. This result, in combination with the results shown in Fig. 5 indicates that the transmitter antenna separation had more impact on the performance of the MIMO system than the wireless transmission.

Fig. 9 shows the BER plots of the 60 GHz MIMO-OFDM QPSK signals with a wireless transmission of 4 m and with variable fibre transmission distances. Comparing no fibre

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(a) (b)

(c) (d)

Fig. 11. Constellation diagrams of MIMO-OFDM with 16QAM by transmitting (a) 2.5m (b) 3m (c) 3.5m (d) 4m wireless distance.

transmission case with 500 m and 1200 m fiber transmission as shown in Fig. 9, it can be observed that no significant penalty was induced by fibre transmission up to 1200 m. Fiber transmission of about 1 km is sufficient for typical indoor deployment scenarios. Similar tests were performed with the 51 Gb/s MIMO system, with 6.375 GHz bandwidth and 16 QAM modulation format, and a fiber transmission of 1200 m. Fig. 10 summarizes the BER results plotted against the RF received power. From Fig. 9 and Fig. 10 it can be observed that 16 QAM modulation format required 10 dB more received RF power compared to QPSK to achieve the same BER threshold of 10−3 but with almost twice the bit-rate. The received power levels indicate that there was sufficient RF power budget to accommodate longer wireless transmission distances. The slight difference (0.3 × 10−4)

in the BER between 2.5 and 4 m on one hand and 3 and 3.5 m on other hand as observed in Fig. 10 is attributed to the slight variations in the CN of the different wireless transmission distances for the same 17 cm transmitter antenna separation as shown in Fig. 6(b) in addition to the tolerance of the experimental set-up. In any case all wireless transmission distances achieved BER performance well below the FEC limit. The objective of this experimental investigation was not focused on quantifying the performance differences between various wireless transmission distances, but on demonstrating the feasibility of realizing RoF signal generation and

distribu-tion of high data-rate 60 GHz MIMO signals.

Fig. 11 shows the constellation diagrams of the MIMO-OFDM 16 QAM system for the wireless transmission dis-tances between 2.5 m to 4 m and BER < 10−3. As can be seen from the Fig. 11, the constellation diagrams were clear in all cases.

V. CONCLUSION

We experimentally investigated the performance of a 2×2 spatially multiplexed MIMO radio-over-fiber system operating at 60 GHz. The results show that the performance of the 60 GHz MIMO system depends on the antenna separation distance at the transmitter. A record wireless data transmission speed of 51 Gb/s over 4m wireless distance was success-fully demonstrated by using an optimal antenna separation of 17 cm at the transmitter. A high spectral efficiency of 8 b/s/Hz was achieved. Data-rates higher than 51 Gb/s were also tested, but their performance was found to be above the FEC coding threshold We investigated different fiber transmission distances and observed that there was no penalty for fiber transmission distances of up-to 1.2 km, which are sufficient for typical indoor deployments. The received power levels and their corresponding BER plots indicate that there was sufficient power budget to further increase the wireless transmission distance beyond 4 m.

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Wen-Jr Jiang received the B.S. degree in

elec-trophysics and M.S. degree in display from the Institute of Electro-Optical Engineering, National Chiao Tung University (NCTU), Hsinchu, Taiwan, in 2006 and 2008, respectively. He is currently working toward the Ph.D. degree at the Institute of Electro-Optical Engineering, NCTU. He is also currently with the Department of Photonics, NCTU. His research interests include radio-over-fiber sys-tems, digital signal processing, optical millimeter-wave generation, photonic vector signal generation, and hybrid access networks.

Rakesh Samabraju (M’09) received the bachelor’s

degree in technology from Jawaharlal Nehru Tech-nological University, Hyderabad, India, in 2002, the M.Sc. degree in telecommunications from the Tech-nical University of Denmark, Lyngby, Denmark, in 2006, and the Ph.D. degree from the Univer-sitat Politécnica de Valéncia, Valencia, Spain, in 2010, specializing in radio-over-fiber systems. From 2006 to 2010, he was a member of the Valencia Nano-photonics Technology Center, where he was involved in several European funded and Spanish national research projects. He is currently with Corning Incorporated, Corning, NY, as a Research Scientist. He has authored and co-authored more than 40 papers in international journals and conferences. His current research interests include 3G/4G mobile communications, millimeter-wave wireless, radio-over-fiber systems, and digital signal processing.

Dr. Sambaraju is a member of the IEEE Photonics Society and IEEE Communications Society.

Hejie Yang (M’11) received the M.Sc. degree in

telecommunications from the Technical University of Denmark, Copenhagen, Denmark, in 2006, and the Ph.D. degree in the area of future home network from the COBRA Research Institute, Eindhoven University of Technology, Eindhoven, The Nether-lands, in 2011. Since February 2011, he has been a research scientist in applied research at Corning Incorporated, Corning, NY. His current research interests include in-door distributed antenna systems and fiber-wireless technologies, including millimeter wave communications.

Chun-Ting Lin (M’07) received the B.S. and M.S.

degrees in material science and engineering from National Tsing Huang University, Hsinchu, Taiwan, in 1997 and 2001, respectively, and the Ph.D. de-gree in electro-optical engineering from National Chiao Tung University (NCTU), Hsinchu, Taiwan, in 2007. From 2007 to 2009, he was a Research Associate with the Department of Photonics, NCTU. In 2009, he joined the Faculty of NCTU, where he is currently an Assistant Professor with the Institute of Photonic Systems. His research interests include radio-over-fiber systems, optical millimeter-/sub-terahertz-wave generation and application, optical data formats, and optoelectronic packages.

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Chia-Chien Wei received his Ph.D. degree in

electro-optical engineering from National Chiao Tung University, Taiwan, and his Ph.D. degree in electrical engineering from the University of Mary-land, Baltimore County, USA, in 2008. In 2011, he joined National Sun Yat-sen University, Taiwan, where he is currently an assistant professor in the Department of Photonics. His current research inter-ests include optical and electrical signal processing, advanced modulation formats, optical access net-works, and radio-over-fiber systems.

Sien Chi received the B.S.E.E. degree from

Na-tional Taiwan University, Taipei, Taiwan, and the M.S.E.E. degree from National Chiao-Tung Uni-versity, Hsinchu, Taiwan, in 1959 and 1961, re-spectively. He received the Ph.D. degree in electro-physics from Polytechnic Institute, Brooklyn, NY, in 1971. From 1971 to 2004, he was a Professor at National Chiao-Tung University. From 1998 to 2001, he was the Vice President of National Chiao-Tung University. He is currently a Chair Professor at Yuan-Ze University, Chung Li, Taiwan. He is a Fellow of the Optical Society of America (OSA), His research interests are optical-fiber communications, fast and slow light, passive optical networks, and microwave photonics.

Anthony Ng’oma (M’02) Dr. Anthony Ng’oma

leads a team of scientists and engineers working on short reach communication networks and applica-tions at the main research center for Corning Incor-porated, which is located in Corning, NY. He has been actively involved in optical communications research in general and fiber-wireless technology research in particular, for more than 10 years, both in Europe and the United States.

Dr. Ng’oma holds a Ph.D. degree in optical fiber communications and a professional doctorate in en-gineering (PD.Eng.) in information and communication technology (ICT), both from Eindhoven University of Technology, The Netherlands. He also earned M.Eng. and B.Eng. degrees (with Merit) in electrical/electronics engineering from the University of Zambia, Zambia. He has authored and co-authored more than 60 peer-reviewed technical publications and journals and two book chapters in the field of fiber-optic communication.

Dr. Ng’oma is a member of the IEEE Photonics Society and the IEEE Microwave Theory and Techniques Society.

數據

Fig. 1. Block diagram of the 2 ×2 MIMO system, and the schematics of the training symbol design of 2×2 MIMO-OFDM signals.
Fig. 2. Schematic of the experimental set-up depicting a central office, remote wireless unit and a receiver unit.
Fig. 5. Simulated condition number values for varying receiver and transmitter antenna separation for different wireless transmission distances
Fig. 10. BER performance as function of wireless received power through 4 m wireless transmission and 1200 m fiber transmission with 16 QAM signal.
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Biases in Pricing Continuously Monitored Options with Monte Carlo (continued).. • If all of the sampled prices are below the barrier, this sample path pays max(S(t n ) −

For MIMO-OFDM systems, the objective of the existing power control strategies is maximization of the signal to interference and noise ratio (SINR) or minimization of the bit

This research used GPR detection system with electromagnetic wave of antenna frequency of 1GHz, to detect the double-layer rebars within the concrete.. The algorithm

The fist type of photonic crystal fiber is composed of a solid silica core with modulation core refractive index and a cladding with triangular lattice elliptical air holes,

The product of the luminescent nano materials on the film were illuminated with LED and luminance value were measured with incident angles of 0 o 、30 o 、45 o 、60 o 、90 o..