Millimeter-Wave Fiber-Radio Systems for Broadband Wireless Access Applications:

Future generation wireless access systems will have the capacity to offer broadband integrated services. The high bandwidth demand for these services via wireless access networks has caused spectral congestion at lower microwave frequencies. Millimeter-wave fiber-radio systems have the potential to resolve this spectral congestion and the scarcity of transmission bandwidth, and, are considered for the future delivery of broadband services. In these systems multiple remote antenna base stations (BSs), suitable for untethered connectivity for the broadband wireless access services, are directly interconnected to a central office via an optical fiber feeder network dedicated for performing all the switching and signal processing functionalities. The higher propagation losses of mm-wave signals, however, shrinks the radio coverage of the BSs to micro and pico cells, which implies the need for a large number of antenna BSs to cover a certain geographical area. Therefore, the BS architecture has to be simplified and cost effective, whereas, the fiber feeder network has to be able to support a large number of BSs required to service a certain geographical area. Since the inception of my PhD research in 2002, with my co-authors I have demonstrated novel system technologies and architectures and resolved various challenges towards its practical deployment. The future plan is to extend the current investigations to further simplify the demonstrated technologies, develop and implement novel methods to engage high impact research in the area both in physical as well as in link/network layers. Selected recent publications can be seen via the following links.

1. M. Bakaul, A. Nirmalathas, and C. Lim, “Multifunctional WDM optical interface for millimeter-wave fiber-radio antenna base station,” IEEE/OSA Journal of Lightwave Technology, vol. 23, no. 3, pp. 1210-1218, 2005.
2. M. Bakaul, A. Nirmalathas, C. Lim, D. Novak, and R. Waterhouse, “Efficient multiplexing scheme for wavelength-interleaved DWDM millimeter-wave fiber-radio systems,” IEEE Photonics Technology Letters, vol. 17, no. 12, pp. 2718-2720, 2005.
3. M. Bakaul, A. Nirmalathas, C. Lim, D. Novak, and R. Waterhouse, “Simultaneous Multiplexing and Demultiplexing of Wavelength-Interleaved Channels in DWDM Millimeter-Wave Fiber-Radio Networks,” IEEE/OSA Journal of Lightwave Technology, vol. 24, no. 9, pp. 3341-3352, 2006.
4. M. Bakaul, A. Nirmalathas, C. Lim, D. Novak, and R. Waterhouse, “Investigation of Performance Enhancement of WDM Optical Interfaces for Millimeter-Wave Fiber-Radio Networks” IEEE Photonics Technology Letters, vol. 19, no. 11, pp. 843-845, Jun. 1, 2007.

Convergence of Optical and Wireless Technologies in ‘Last-mile’ Telecommunication Access Networks:

The demand for higher bandwidth necessitated by data-intensive multimedia and real-time applications is increasing in the ‘last mile’ access networks. To meet this bandwidth demand, a variety of access technologies such as digital subscriber line (xDSL), fiber-to-the-curve (FTTC), fiber-to-the-home (FTTH), ultra mobile broadband (UMB), worldwide interoperability for microwave access (WIMAX) etc. have been evolved, incorporating both wireless and wired media. Among these solutions, passive optical networks (PON) based wired solutions (e.g. FTTC/FTTH) remain the most future proof technology for the delivery of broadband to the users, as they offer higher bandwidths at longer distances. Also, due to fixed physical connections, they are more secure and reliable. On the other hand, wireless based access solutions are also very attractive due to their inherent advantage of portability and flexibility. In order to exploit the benefits of both of these transmission media, carriers and service providers are actively seeking a convergent network architecture that can facilitate a rich mix of value added and differentiated services via an integrated wireless and wired network, so that the demand for mobility, bandwidth, reliability, security and flexibility can be met. A generic integrated network incorporating both wireless and wired transmission media is shown in Fig. 1. In this concept, multiple wireless signals from customers come across the remote BS, processed through an optical network unit (ONU) and transported over fiber to the remote access node (RAN) to combine with the wired signals depending on the network architectures. Currently we are exploring the novel methods to overcome the physical layer challenges of such systems. The investigation will be extended in the network link/layer in the near future. Selected recent publications in this area can be seen via the following links.

1. M. Bakaul, A. Nirmalathas, C. Lim, D. Novak, and R. Waterhouse, “Hybrid Multiplexing of Multiband Optical Access Technologies Towards an Integrated DWDM Network” IEEE Photonics Technology Letters, vol. 18, no. 21, pp. 2311-2313, 2006.
2. M. Bakaul, A. Nirmalathas, C. Lim, D. Novak, and R. Waterhouse, “Hybrid demultiplexing towards the integration of millimeter-wave fiber-radio systems in DWDM Access Networks” Proc. MWP’2006, Grenoble, France, October, 2006.
3. M. Bakaul, N. Nadarajah, and A. Nirmalathas, “Source-free, inter-networking hybrid base stations towards the convergence of wireless and wireline access networks” Proc. Conference on Optical Internet Network/ Australian Conference on Optical Fibre Technology (COIN/ACOFT’2007), Melbourne, Australia, June, 2007.
4. Bakaul M., Nadarajah N., and Nirmalathas A., “Inter-networking, VCSEL-Based Low-Cost Hybrid Base Stations Towards the Integration of Wireless and Wireline Access Networks,” accepted for publication in proceedings MWP2007, will be held in Victoria, Canada, 3-5 Oct., 2007.

Optical performance monitoring (OPM) plays a fundamental role in the evolution and deployment of optical communication systems. The main objectives of OPM are to develop new techniques and interfaces to monitor the performance and degradation of signals in optical network avoiding the requirement of optoelectronic-optic (OEO) conversion in the data path, while having minimum knowledge about the data transportation history. The introduction of wavelength division multiplexing (WDM) optical networks has further spurred the need to develop new techniques to monitor channel performance and degradation with minimal disturbance to the signal on the fiber. The WDM channels in next generation dynamic optical networks will traverse multiple complex paths, and, will have different transport history including path and network elements. These dynamic changes of the transported channels demands adaptive techniques for gain equalization compensation, chromatic dispersion compensation and polarization mode dispersion (PMD) compensation etc. over conventional bit error rate (BER), loss of signal (LOS), and  signal-to-noise (SNR) degradation monitoring in line terminating elements (LTEs). In OPM, the monitoring technique is applied on a channel that has traversed the optical path having the data superimposed onto it. Therefore, monitoring has to be done in such a way that the disturbance to the data carrying channel is minimal. In NICTA’s Networked Systems Group, currently we are exploring the development of low cost, in-band OSNR monitors as well as a multi-impairment monitor (MIM) that can diagnose and measure simultaneous multiple impairments in next generation DWDM optical networks. Our next plan is to develop and implement low-cost dispersion and PMD monitors as well as path monitor for passive optical network. Selected recent publications in this area can be seen via the following links.

1. M. Bakaul, K. Clarke, T. Anderson, D. Hewitt, and S. D Dods, “Low-cost in-band optical signal-to-noise ratio monitoring using an optical interferometer,” Proc. IEEE LEOS’2006, Montreal, Canada, October, 2006.
2. T. Anderson, K. Clarke, S. D Dods, and M. Bakaul, “Robust, low cost, in-band optical signal to noise monitoring using polarization diversity,” Proc. Optical Fiber Communication Conference (OFC/NFOEC’2007), Anaheim, USA, Mar. 25-29, 2007.
3. S. D Dods, T. Anderson, K. Clarke, M. Bakaul, and Adam Kowalczyk, “Asynchronous sampling for optical performance monitoring,” Proc. Optical Fiber Communication Conference (OFC/NFOEC’2007), Anaheim, USA, Mar. 25-29, 2007 [Invited]
4. M. Bakaul, “Low-cost, PMD Insensitive and Dispersion Tolerant In-band OSNR Monitor Based on Uncorrelated Beat Noise Measurement,” submitted for publication in IEEE Photonics Technology Letters.

I will engage in active research in these areas in the near future.