P.M. Lane

Remote delivery of video services using mm-waves and optics

Advantages of a radio-based final drop for video delivery are outlined and spectral availability constraints that lead to the identification of the mm-wave region of the radio spectrum as the most appropriate for this application are discussed. The possibility of simultaneously supporting other broadband services, such as B-ISDN and traffic information systems (IVHS), enhance the attractiveness of a radio link. A large number of antenna units need to be served due to the limited propagation distances achievable at mm-wave frequencies, and therefore, a low-cost generation and delivery method has to be developed. In this paper, alternatives for the optical generation and distribution of mm-wave signals are reviewed and a new method is proposed that eases the bandwidth, and hence the cost, of the required optoelectronic components. An assessment of the relative merits of the methods is given. >

High-speed transmission of adaptively modulated optical OFDM signals over multimode fibers using directly Modulated DFBs

A novel optical signal modulation concept of adaptively modulated optical orthogonal frequency division multiplexing (AMOOFDM) is proposed, and a comprehensive theoretical model of AMOOFDM modems is developed. Numerical simulations of the transmission performance of the AMOOFDM signals are undertaken in unamplified multimode fiber (MMF)-based links using directly modulated distributed feedback (DFB) lasers (DMLs). It is shown that 28 Gb/s over 300 m and 10 Gb/s over 900 m transmission of intensity modulation and direct detection (IMDD) AMOOFDM signals at 1550 nm is feasible in DML-based links using MMFs with 3-dB effective bandwidths of 200 MHz/spl middot/km. Apart from a higher signal capacity, AMOOFDM also has a greater spectral efficiency and is less susceptible to different launching conditions, modal dispersion, and fiber types, compared with all existing schemes. In addition, a large noise margin of about 15 dB is also observed. The bits of resolution of analog-to-digital converters (ADCs) and the cyclic prefix of AMOOFDM symbols are the main factors limiting the maximum achievable performance, on which the influence of DMLs is, however, negligible under the optimum operating condition.

Transmission performance of adaptively modulated optical OFDM signals in multimode fiber links

A novel optical signal modulation concept of adaptively modulated optical orthogonal frequency-division multiplexing (AMOOFDM) is proposed and numerical simulations of the transmission performance of AMOOFDM signals are undertaken in unamplified multimode fiber (MMF)-based links using directly modulated distributed feedback lasers (DMLs). It is shown that 28 Gb/s intensity modulation and direct-detection AMOOFDM signal transmission over 300-m MMFs is feasible in unamplified DML-based links having 3-dB bandwidths of 150MHz/km. In addition, AMOOFDM is less susceptible to modal dispersion and variation in launching conditions when compared with existing schemes.

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.

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.

Design of high directivity directional couplers in multilayer ceramic technologies

Greater amalgamation of transceiver functionality is a way of addressing the commercial viability of forthcoming architectures. Multilayer Cofired Ceramics (e.g. LTCC/HTCC) is seen, as a potential integration platform offering size, cost and performance advantages. Monolithic integration of passive components, such as directional couplers, in Multilayer Integrated Circuit technologies is highly desirable. Microstrip broadside-coupled structures are well suited for tight coupling in a multilayer high integration environment. However, it is well known that such hybrids suffer from poor directivity due to the inhomogeneous nature of the substrate. Numerous compensation techniques have been proposed in the literature, which attempt to equalize the normal mode phase velocities. In this paper we address the equalization of couplers where the even mode phase velocity is greater than the odd mode, a case typically encountered in broadside-coupled microstrip structures. Simulation and measurement results of practical structures on LTCC technology show that the technique is well suited for multilayer design.

The WISDOM project: training primary care professionals in informatics in a collaborative 'virtual classroom'.

The WISDOM project applies Internet technologies to create a virtual classroom in health informatics for primary care professionals. Participants use a facilitated E‐mail discussion list supported by a web site which provides on‐line resources and an archive of teaching materials.

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.

Modelling of interferometric crosstalk in optical networks

Interferometric crosstalk due to imperfect component performance has been shown to have a dramatic impact on performance in optical networks. In this paper we assess the impact of incoherent interferometric crosstalk in terms of BER and power penalty (PP). We use a rigorous formulation based on the modified Chernoff bound (MCB) which provides an accurate upper bound on the BER and on the PP. We compare these results with the Gaussian approximation (GA) and identify the scenario for which the GA can be applied with confidence. The influence of the decision threshold level is also examined and we will show that optimisation of the threshold can provide up to about 5 dB of crosstalk isolation.

Assessment of the nonlinearity tolerance of different modulation schemes for millimeter-wave fiber-radio systems using MZ modulators

The nonlinearity tolerance of several higher order modulation schemes, which make efficient use of transmission bandwidth, such as 8-PSK, 16-QAM, and 64-QAM, has been assessed for millimeter-wave fiber-radio systems using a Mach-Zehnder (MZ) modulator for the modulation of an optical carrier. Some other deteriorating factors, such as a bias-point shift in the MZ modulator and optical carrier leakage at the MZ filter, which is used for the separation of the two optical carriers, have also been considered. The assessment was accomplished through computer simulations. It is found that the effect of the nonlinearity of the MZ modulator is less serious for a system using 8-PSK than for a system using 16-QAM or 64-QAM, and that in the latter case, an optimal drive level exists for the modulator to achieve the best system performance. A bias-point shift, required in some deployment scenarios, degrades system performance significantly. A leakage of optical carrier to the wrong port at the MZ filter further degrades the system performance, especially for systems using the 16-QAM or 64-QAM modulation scheme.