Optical-Wireless Network with Multi-Layer Reconfigurability - CiteSeerX

OSA / ANIC 2010 a369_1.pdf AWC2.pdf

Optical-Wireless etwork with Multi-Layer Reconfigurability §

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B. Huiszoon , J. Aracil , H.D. Jung , A.M.J. Koonen , E. Tangdiongga , I. Tomkos , and C.P. Tsekrekos

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§: High Performance Computing and etworking (HPC) group, Universidad Autónoma de Madrid, 28049 Madrid, Spain. ¥: COBRA Institute, Eindhoven University of Technology, PO BOX 513, 5600MB Eindhoven, The etherlands. ξ: High-speed etworks and Optical Communication group, Athens Information Technology Center - AIT, 19002 Peania, Greece. {bas.huiszoon, javier.aracil}@uam.es, {h.d.jung, e.tangdiongga, a.m.j.koonen}@tue.nl, {itom, tsek}@ait.edu.gr

Abstract: Current telecom access architectures do not support broadband networking in a converged way on fixed/mobile networks. Here, a highly-configurable optical-wireless network is presented capable of handling dynamics inferred by user mobility and varying service demands. © 2010 Optical Society of America OCIS codes: (060.4252) Networks, broadcast; (060.5625) Radio frequency photonics

1. Introduction Society increasingly demands ubiquitous broadband connections to the Internet. Large investments are made to improve the capabilities and convergence of the fixed and wireless networks as reflected by strong growth figures in [1]. This work presents a hybrid optical-wireless network architecture featuring multi-layer reconfigurability, digital signal processing, integration potential, and intelligence centralization. Mobile networking dynamics are handled centrally across different networks and transport technologies. Additionally, the radio access points (RAPs) are remotely-seeded for a colorless operation and deployment. This work is organized as follows: Section 2 presents the network architecture from a functional and technological point of view. Section 3 addresses the design of the central office (CO), remote node (RN) and RAP after which concluding comments are given in section 4. 2. Scenario, Description and Requirements A broadband fixed/mobile converged networking environment is considered, consisting of a landscape of densely distributed RAPs, buildings, mobile users and vehicles. Broadband services are delivered to (mobile) devices at any time and at any location, while the network configuration, status, and service demands of the subscribers are continuously monitored. This also includes femtocells which are used for high-rate in-building wireless network coverage to offload existing base stations and, consequently, to lower their power consumption [2]. In a typical mobility scenario, a user initiates a service at work and then travels home by public transportation while the service, e.g. personal computer virtualization [3], is continuously delivered by the metro/core tier. Thus it involves not only horizontal and vertical handovers but also handovers between internet service providers (ISPs). Introducing optical technologies in the access network solves issues on connectivity and mobility management because it becomes a single broadcast domain [4]. Different kind of fiber topologies are considered to connect the CO with the RNs. In this light, the presented network is hybrid (wired and wireless) and heterogeneous (multiple topologies). Multiusage scenarios are envisioned to enable open access where several ISPs or vendors share the architecture. Reconfigurability is a key requirement because user mobility, in terms of location and wireless signal quality, and varying mobile network or service requests have a direct influence on the resulting traffic streams and on the capacity provisioning in the optical-wireless network. Three techniques are considered in order to quickly adapt the status of the network to such varying conditions. Firstly, optical routing and reconfigurability is enabled at the RN such that optical data flows can be easily switched from one RAP to another. A reconfigurable RN also allows for the dynamic provisioning of capacity because wavelengths can be dropped at any RAP in a flexible manner. To that respect, optical burst switching techniques are employed. Secondly, the network reconfigurability and capacity allocation should be managed by using cross-layer techniques. Finally, an advanced technique such as optical multicasting may be used to enable cooperative multiple-input multiple-output (Cooperative MIMO) or Network MIMO which exploits the spatial diversity in a high-density RAP configuration [5]. It should be noted that the complexity shift from the RAP to the CO is in line with work done by the CPRI and OBSAI consortia, where fiber-optic transmission is used to transport the data of the wireless networks while the RF mixing is done close to the antenna. In this work, the CPRI/OBSAI approach is taken a step further by using the digitized radio frequency over fiber (dRFoF) technique [6]. The dRFoF offers potential advantages on handling the mobile network dynamics. It consists in bandpass sampling the analogue RF signals with an analog-to-digital converter (ADC) and transmitting the digitized RF data to the RAP through the optical link. A digital-to-analog (DAC) converter is then used to recover the wireless signals. In other words, the RAP does not house any analogue sources. With respect to handovers, these are fully managed at the CO by adapting the RF and/or transmitting the data to other RAPs. The assembly of bursts at nodes accommodate an overlay with existing packet-based access networks and, for example, fixed users may also be connected to an RAP. Previous work demonstrated that dRFoF obtains a comparable quality, in terms of error-vector magnitude, using low-end ADC/DAC technology with

OSA / ANIC 2010 a369_1.pdf AWC2.pdf

respect to conventional wireless systems [6]. However, Ref. [7] indicated that the technique has strong ADC/DAC requirements when digitizing wireless networks operating at high central RF frequencies. It is therefore proposed to separately broadcast the central RF frequencies such that the analogue signals may be digitized at their sub-carrier frequency. In that case, low-end technology may be used for many broadband wireless networks. A suitable radioover-fiber technique is then selected out of the many that are available in order to remotely generate RF carriers at the RAPs. Regarding the optical data link, remote seeding of the RAPs is considered to enable mass-production of colorless units and a dynamic handling of wavelengths in the network. Remote provisioning of wireless and optical carriers with dRFoF at the sub-carrier introduces the required network flexibility, as well as central reconfigurability and control to handle the envisioned mobile dynamics. 3. etwork Design The network architecture is schematically shown in Fig. 1 for a point-to-multipoint topology. Data arrives from the ISPs at the CO’s transmitter (TX) inbound packet processor which determines if the data is intended for a fixed or mobile user. Here, the CO is connected to the metro/access tier and it is assumed to be protocol-agnostic at the ISPside. The packet is then forwarded to the TX outbound packet processor or to one of the RF-TX blocks based on user-location information in a look-up table. A standard usage of common wireless chips is envisioned although the up-conversion to the central RF frequency should not be done. Multiple RF-TX blocks may be present at the CO depending on the wireless network deployment scenario. An ADC digitizes the analogue output and the resulting stream is sent to the CO’s TX outbound packet processor which assembles and schedules a burst. It is clear that the control layer should be adapted to configure the RNs accordingly. The three optical signals (data, RF-generating, and remote-seed) are wavelength-multiplexed and transmitted downstream. Data received from the RAPs is handled by the CO’s receiver (RX) inbound packet processor in a similar fashion. The RX outbound packet processor sends packets either to the metro/access tier or back into the CO’s sub-net. The latter loopback ensures local connectivity because measurements showed that over 70% of voice calls are between people in the same geographical area [8]. Clearly, the RN should house a very fast optical switch to accommodate optical burst switching [9]. On the RAPside, the received packets are processed and the ones intended for a wireless network are sent to the DAC of the corresponding antenna unit. The carrier frequencies are recovered at the photo diode and selectively mixed with the analogue signals from the DAC. The wireless signals are amplified by a power amplifier (PA) and radiated by the antenna. The reader should note that the central RF frequencies are also used as local oscillator to down-convert the received wireless signals. Similar to the CO, the wireless signals are digitized by an ADC at their sub-carrier. A reflective electro-optical conversion block is then used to transmit the burst on a selected optical carrier [10]. Control and Management O/E

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Fig. 1. A hybrid optical-wireless network architecture with multi-layer reconfigurability showing two optical bursts on the same wavelength

4. Conclusion An optical-wireless network architecture is proposed with a strong focus on multi-layer reconfigurability and in which intelligence is centralized. It is expected that the proposed solutions can contribute to a long-term reduction in expenses because of an increased sharing of functionality and the adoption of optical transmission technologies. References [1] OECD report, Communications Outlook 2009, pp. 1-352, Aug. 2009. [6] P.A. Gamage, et al., J. Lightw. Technol., 27(12), pp. 2052, Jul. 2009 [2] D. Calin, et al., IEEE Commun. Mag., 48(1), pp. 26-32, Jan. 2010. [7] C. Lim, et al., J. Lightw. Technol., 2010 (forthcoming issue). [3] FP7 STREP IST-MAINS web site (Feb. 2010): www.ist-mains.eu/. [8] Ericsson White Paper, How efficient mobile backhaul..., Feb. 2009. [4] B. Huiszoon, et al., J. Lightw. Technol., 26(13), pp. 1752, Jul. 2008. [9] G.I. Papadimitriou, et al., J. Lightw. Technol., 21(2), pp. 384, 2003. [5] R.A. Valenzuela, Proc. WCG 2005 Texas Wirel. Symp., Oct. 2005. [10] I. Papagiannakis, et al., Phot. Technol. Lett., 20(24), pp. 2168, 2008 Acknowledgements: This work was carried out as a Joint Activity of Work Package 23 in the BONE project (``Building the Future Optical Network in Europe''), a Network of Excellence funded by the European Commission through the 7th ICT-Framework Programme. The Spanish Ministry of Science and Innovation (MICINN) is acknowledged for funding the post-doctoral subprogram “Juan de la Cierva”.