J.J. O'Reilly

Radio-over-fiber distribution using an optical millimeter-wave/DWDM overlay

We demonstrate an optical MM-wave/DWDM overlay using optical suppressed-carrier modulation to simultaneously upconvert multi-wavelength subcarriers to 35 GHz. Performance of the system is analyzed for radio-over-fiber distribution.

Relationship between the saddlepoint approximation and the modified Chernoff bound (optical communication)

A comparison is made of two methods for the computation of the probability that the sum of a Gaussian and a nonGaussian random variable exceeds a certain threshold value. The two methods, the saddlepoint approximation (SAP) and the modified Chernoff bound, are closely related to one another. For the computation of error probabilities in digital optical communications where both methods can be applied, the modified Chernoff bound is found to lie close above the saddlepoint approximation for all cases of practical interest. The ratio of signal-dependent to additive noise has been established as the parameter dominating the bound tightness. Since the SAP has been reported to be extremely precise, this result indicates that the more versatile upper bound can be used with confidence both for performance evaluation and for optimization of optical communication systems. >

Broadband wireless systems and networks: an enabling role for radio–over–fibre

There has been a remarkable take up of wireless and mobile communications in recent years, such that in a number of countries the number of mobile phones now exceeds the number of fixed network connections. Alongside this, we are seeing dramatic growth in data on the network compared with voice: the so–called ‘data wave’. While much mobile network traffic is currently voice there is increasing use of the available data facilities with these now being enhanced (e.g. via evolution of the global system for mobile communications and subsequently the introduction of ‘third–generation’ systems such as the universal mobile telecommunications system). Accordingly, there is considerable interest and activity in the research community concerning possible technologies exploiting yet higher frequencies where truly broadband future wireless networks may be realized. This paper will review some of the technology options currently available or under examination for millimetre-wave broadband wireless networks and will go on to consider in some detail a specific example of ‘fixed-wireless’ technology synergies exploiting radio-over-fibre techniques to achieve flexible, reconfigurable broadband wireless networks.

System capacity for millimeter-wave radio-over-fiber distribution employing an optically supported PLL

We consider the performance of a hybrid radio-over-fiber distribution system with a remote phase-locked loop (PLL) providing the local oscillator for upconversion to millimeter (mm)-wave frequencies. The reference signal for the PLL is transmitted together with digitally modulated subcarriers over a fiber link, allowing centralization of radio processing. Through analysis and simulation, we identify the relationship between the phase noise requirement for the PLL and the data capacity of the fiber link. For a practical link, we provide an upper limit on system capacity for transmission of 16 quadrature amplitude modulation (QAM) subcarriers.

Extraction of semiconductor intrinsic laser parameters by intermodulation distortion analysis

A new technique is described for the extraction of the intrinsic semiconductor parameters from intermodulation measurement of composite second-order (CSO) and composite third-order (CTB) distortion products. The effect of the parasitics elements are eliminated, by taking the distortion measurements at constant optical modulation depth, which enables one to obtain the laser parameters on packaged laser diodes. An optimization algorithm is then described that extracts the relevant laser parameters from the distortion data. This method was applied to a commercially available packaged laser diode and very good agreement was obtained between the measured and theoretical results.

Accurate performance modeling of subcarrier multiplexed fiber/radio systems: implications of laser nonlinear distortion and wide dynamic range

In this paper, we present an analytical approach to accurately assessing the performance of subcarrier multiplexed optical systems for the delivery of future mobile radio broadband services. The existence of a wide dynamic range of power levels in the return link, together with laser nonlinear distortion, represents a major problem and makes performance evaluation difficult. By modeling laser nonlinear distortion using Volterra series analysis, we show that the performance assessment of these systems becomes not only tractable, but also that they can be can be optimized based on the worst case condition. This analysis is performed here for the case of continuous phase frequency shift keying (CPFSK) modulation, for which we calculate the power spectral density (PSD) of the intermodulation products. The overall system performance is that investigated, and its dependence on laser bias and RIN is examined. As an illustrative example we consider a specific 50 channel CPFSK system occupying the bandwidth of 2 to 2.1 GHz.

Optical amplifier noise figure reduction for optical single-sideband signals

This paper analyzes the amplification of optical single-sideband signals, highlighting the significance of the optical signal bandwidth in determining signal-amplified spontaneous emission (ASE) beat noise. It predicts that an electrical noise figure of one may be realized for single-sideband signals using appropriate optical filtering. It verifies noise figure reduction experimentally, demonstrating an electrical noise figure of 1.1/spl times/ the spontaneous emission factor of the amplifier, which is 2.6 dB below the limit for conventional intensity modulated signals.

A power efficient coding scheme for low-frequency spectral suppression

Multilevel coding schemes with simultaneous error control and low-frequency spectral suppression are compared to traditional cascaded error control and line coding systems. A new coding algorithm is introduced and an assessment in terms of error performance and low frequency spectral suppression is provided. Results show that significant performance benefits can be gained by employing the combined coding technique. >

A simple strategy for constructing a class of DC-free error-correcting codes with minimum distance 4

A class of DC-free codes with minimum distance 4 which offer very simple encoding and decoding procedures is presented. Spectral analysis shows that in addition to being DC-free they offer strong spectral suppression at low frequencies. A comparison with similar codes in the literature shows that they provide a good compromise solution to the design of practically realizable, high-rate, DC-free error-correcting codes with strong low frequency suppression. >

Performance assessment of optical subcarrier multiplexing systems: implications of laser distortion

The theory of nonlinear systems based on frequency domain analysis using Volterra series is shown to provide an appropriate means of assessing laser distortion which includes the effects of laser resonance. Hence, it is an appropriate and tractable means of assessing the performance of optical subcarrier multiplexed (SCM) systems. Based on this analysis the performance of SCM systems is examined, with calculation of the carrier-to-intermodulation ratio for an eight-channel SCM system providing an illustrative example.<<ETX>>