Nonlinearity and Noise Effects in Multi-level Signal Millimeter-Wave over Fiber Transmission using Single- and Dual-Wavelength Modulation

We transmit multilevel quadrature amplitude modulation (QAM) data-IEEE 802.16 schemes-at 20 MSps and an orthogonal frequency-division multiplexing (OFDM) 802.11 g signal (54 Mbps) with a 25 GHz millimeter-wave over fiber system, which employs a dual wavelength source, over 20 km of single mode fiber. Downlink data transmission is successfully demonstrated over both optical and wireless (up to 12 m) paths with good error vector magnitude. An analysis of two different schemes, in which data is applied to one (single) and both (dual) of the wavelengths of a dual wavelength source, is carried out. The system performance is analyzed through simulation and a good match with experimental results is obtained. The analysis investigates the impact of Mach-Zehnder modulator (MZM) and RF amplifier nonlinearity and various noise sources, such as laser relative intensity noise, amplified spontaneous emission, thermal, and shot noise. A comparison of single carrier QAM IEEE 802.16 and OFDM in terms of their sensitivity to the distortions from MZM and RF amplifier nonlinearity is also presented

Organisational Commitment in the Public Service of Ghana: An Empirical Study

Overall performance of an organisation depends on several factors including organisational commitment. This phenomenon is a valuable factor that affects policy direction of organisations of today. The current study examines commitment of workers in the civil/public service of Ghana. In the process, the researchers also investigated differences in commitment in terms of age and length of service. Subjects were 343 male and female civil/public servants, drawn from various ministries, departments and agencies. Analyses show that males are more committed than their female counterparts. It was further revealed that age is positively associated with employee commitment, and that longer serving employees are more committed than staff with short tenure in an organisation. The implications were discussed and recommendations made. Keywords: Civil Service, Ghana, Organisational Behaviour, Organisational Commitment, Public Service

RFID over Low Cost VCSEL-based MMF Links: Experimental Demonstration and Distortion Study

Radio-over-Fibre (RoF) Distributed Antenna System (DAS) technology has been investigated for the distribution of ultra-high frequency (UHF) radio frequency identification (RFID) signals. RoF DAS allows for reduced number of readers and centralized placement of readers which facilitates easy system maintenance, but it is important to find a low-cost solution that can achieve comparable performance to a conventional RFID system. In this work, a lowcost vertical cavity surface-emitting laser (VCSEL)-based multimode fibre (MMF) link has been developed and demonstrated for passive UHF RFID applications. The reported results show almost the same performance when compared with a conventional RFID system. In addition, simple spatial antenna diversity schemes are tested, with improved performance reported in comparison with a RFID-RoF system without diversity. Also, an investigation of RFID over fibre with RoF nonlinearity is carried out showing that PR-ASK RFID modulation allows for higher levels of RF carrier and modulated signal power than the ASK RFID, for low levels of nonlinearity

Statistical Distribution of EVM Measurements for Direct-Modulation Radio-Over-Fiber Links Transporting OFDM Signals

The effect of distortion on the error vector magnitude (EVM) performance of orthogonal frequency-division multiplexing (OFDM) signals with different numbers of subcarriers and the connection to the peak-to-average power ratio (PAPR) of such signals is investigated. A low-cost and low-complexity directly modulated radio-over-fiber link is used in experiments as an example of a link limited by distortion. Statistical distributions of the EVM over a large number of transmitted OFDM frames are gained from experimental measurements and analyses of idealized processes. The measurement results show that as the number of subcarriers is reduced, the distribution means are more affected by extreme values. This effect results in mean EVMs for signals with different numbers of subcarriers that are not dependent in the expected way on the statistical PAPR of the transmitted OFDM signals. Instead, it is shown that in regions of moderate distortion, the median of the EVM is more closely related to the statistical PAPR and to the required back-off for signals with different numbers of subcarriers

Multilevel modulated signal transmission over serial single-mode and multimode fiber links using vertical-cavity surface-emitting lasers for millimeter-wave wireless communications

Quadrature phase-shift keying, 16 quadrature amplitude modulation (QAM), and 64-QAM data transmission-Worldwide Interoperability for Microwave Access modulation schemes-at 6 and 20 MS/s is demonstrated for a link that emulates a cost-effective 1.55-m vertical-cavity surface-emitting laser based radio. over fiber millimeter-wave indoor picocellular system. The system consists of a concatenation of 20-km single-mode fiber and 300-m multimode fiber links between a central office and remote antenna unit and employs remote 30-GHz local oscillator delivery. Successful transmission over both optical and wireless paths is achieved with good error vector magnitude performance recorded for both uplink and downlink. The performance is compared to other demonstrations of multilevel signal transmission in millimeter-wave over fiber systems

Multilevel modulated signal transmission over serial single-mode and multimode fiber links using vertical-cavity surface-emitting lasers for millimeter-wave wireless communications

Quadrature phase-shift keying, 16 quadrature amplitude modulation (QAM), and 64-QAM data transmission-Worldwide Interoperability for Microwave Access modulation schemes-at 6 and 20 MS/s is demonstrated for a link that emulates a cost-effective 1.55-m vertical-cavity surface-emitting laser based radio. over fiber millimeter-wave indoor picocellular system. The system consists of a concatenation of 20-km single-mode fiber and 300-m multimode fiber links between a central office and remote antenna unit and employs remote 30-GHz local oscillator delivery. Successful transmission over both optical and wireless paths is achieved with good error vector magnitude performance recorded for both uplink and downlink. The performance is compared to other demonstrations of multilevel signal transmission in millimeter-wave over fiber systems

Indoor Pico-Cellular Network Operation based on a Simple Optical Millimetre-Wave Generation Scheme

Experimental demonstrations of modulated signal transmission and pico-cellular network operation at millimeter-wave frequencies, which are based on a simple technique for millimeter-wave generation using an optical phase modulator and optical filtering, are reviewed

Radio Over Fibre Link Design for Next Generation Wireless Systems

The performance of radio over fiber (RoF) links using low cost optoelectronic components is assessed for distributed antenna applications in next generation wireless systems. Important design issues are discussed and an example link design is presented for a wireless system requiring the transmission of four radio channels per link direction, each with 100 MHz bandwidth, modulation complexity of 256-QAM and 2048 OFDM subcarriers. We show that the noise introduced by the RoF links does not have a significant impact on wireless range, provided the wireless system has uplink power control. Finally, we compare the cost and performance of RoF links for this application with alternative link types that use digitized radio transmission and show that RoF is the optimum choice from a cost perspective

Radio-Over-MMF Techniques-Part I: RF to Microwave Frequency Systems

Recent work on radio-over-multimode-fiber (MMF) transmission, for the support of wireless LANs and current cellular systems, operating at below 6 GHz, has shown that excellent performance (e.g., spur-free dynamic range well in excess of 100 dB.Hz(2/3)) can be achieved. However, it is shown here that for multisystem operation, spurious emissions may be more of a restriction than meeting good signal quality requirements (such as low error vector magnitude). Initial results are reported for error vector magnitude and adjacent channel leakage for UNITS transmission over a radio-over-MMF link with a multisystem remote antenna unit with conformance to standards being demonstrated