Radio-over-Fiber based architecture for seamless wireless indoor communication in the 60 GHz band☆,☆☆
Introduction
In the last few years, broadband access has experienced an explosive boom with the demand for higher data rates to accommodate a great diversity of new services and the growing number of end users. On one hand, we have witnessed a massive penetration of x-DSL and cable internet access in business and household environments. Fiber-to-the-home (FTTH) deployments are nowadays also becoming very popular as a future-proof infrastructure to provide high speed and triple play support, comprising both switched Ethernet-based and passive optical network (PON)-based architectures [2]. On the other hand, wireless LAN systems like IEEE 802.11a/b/g have made broadband wireless access a reality, with the proliferation of cheap and easy-to-deploy Access Points (AP) in households, buildings, airports, shopping malls, etc. Emerging broadband fixed wireless access systems like IEEE 802.16 aim to enhance these broadband capabilities with innovative approaches in the sub-11 GHz band and in the millimeter wave region [3]. In the quest for more available bandwidth, much attention has also been paid to the 60 GHz band, where as much as 5 GHz of spectrum has been allocated worldwide. This unprecedented amount of available spectrum holds the potential for much higher data rate ever compared to other bandwidth-limited channels that are currently used. It is predicted that the wireless data rate in the range of 1 Gbps will be the order of the day [4].
However, the migration to such an aspiring radio band imposes some challenges for the design of a reliable access network infrastructure:
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Due to the huge propagation losses at 60 GHz, this band has been proposed for short-range broadband communications and wireless access in the indoor environment. In this environment, a radio cell is typically confined to a room, where walls and floors can be automatically defined as reliable boundaries [4], [7]. Thus, at least one radio access point (AP) is required in a confined indoor area, such as a room, a hall, a corridor, etc. Consequently, a large number of APs is required to provide a certain geographical area with wireless access coverage [5], which augments enormously the infrastructure cost and the network management complexity. Therefore, a flexible and cost-effective network architecture is necessary to make the radio access in this band economically viable, and to provide a smooth convergence of the (wireless) last mile access with the growing fiber-based broadband access networks.
- (2)
Since the propagation of millimeter radio wave is strongly hindered by attenuation, in an indoor environment, a radio cells typically spans only a room. As a result, an overlap area between two adjacent cells exist only around open areas such as doors or windows. Moreover, these overlap areas are often narrow and directional. In a multi-channel communication system, where handovers (HO) are required when a Mobile Station (MS) roams from one cell to another, these overlap areas might be too small to allow an MS sufficient time to trigger and complete a handover. It is therefore crucial to design new mobility strategies that enlarge the overlap areas in order to enable a seamless communication environment.
To satisfy the above requirements, we propose a network architecture based on the deployment of a flexible and cost-effective Radio-over-Fiber (RoF) distribution antenna system. RoF distribution antenna systems have been identified as a flexible, bandwidth-efficient, and cost-effective option for fiber-based wireless access infrastructure, especially in in-building and business environments [6]. They enable the consolidation of the radio access control and signal processing at a centralized processing point (the Central Station (CS) in Fig. 1) and the delivery of the radio signals transparently to the simplified antenna stations (AT) via optical fiber . The main goal of these RoF systems is to reduce the infrastructure cost and to overcome the capacity bottleneck in wireless access networks and at the same time allowing a flexible merge with the conventional optical access networks.
The RoF link lies within the physical layer of the wireless system to be supported, and thus, it becomes an extension of the radio access domain. This enables the possibility of allocating dynamically radio resources from the remote central station (CS) and thus optimizing the spectrum utilization. Additionally, mobility management strategies can be efficiently performed from the CS in combination with a proper radio resource management in order to guarantee optimum overlapping areas for a seamless roaming environment. In the proposed architecture, to achieve sufficient overlap areas between cells, we propose to group several adjacent radio cells into one Extended Cell (EC). In other words, multiple adjacent antennas are allowed to transmit the same content over the same frequency channel. Each EC is designated to cover a number of adjacent rooms and a part of a transitional area, such as a corridor or a hallway. By doing so, overlap areas are created along transitional areas where mobile users move from one cell to another. To illustrate the effectiveness of the proposed architecture, we have simulated the proposed architecture in an office building. We discuss that the system has large enough overlap areas to perform handover and the number of drop calls is therefore minimized.
Despite the benefits derived from this centralized and transparent architecture, the fact of inserting a fiber link between an AT and the CS introduces an additional propagation round trip delay in the radio access which might outrun the timing boundaries of the Medium Access Control (MAC) protocols of some wireless standards. In this paper, we present a study of the two protocols, namely IEEE 802.11 and IEEE 802.16, to find the effect of the additional delay on the MAC performance.
This paper is organized as follows. Section 2 reviews the contributions and drawbacks of some prominent solutions for indoor networking at millimeter wave bands that are not based on RoF infrastructure. Section 3 introduces Optical Frequency Multiplication (OFM) – the RoF technique on which our architecture is based – and describes the characteristics of a physical layer design for broadband wireless access employing this technique. Section 4 presents the characteristics of the indoor environment at the 60 GHz band, proposes a network architecture based on Extended Cells (EC) to guarantee seamless mobility and analyzes its system performance with a simulation study. Section 5 addresses the impacts of a RoF-based infrastructure on some of the state-of-the-art Medium Access Control (MAC) protocol standards. Finally, the main benefits of the proposed architecture are discussed in Section 6.
Section snippets
Related work
Extensive studies have been carried out on the physical aspects of the radio propagation channel in the millimeter band by Smulders [4] and Giannetti [7]. Nevertheless, the issues of designing an infrastructure supporting seamless pico-cellular communication at the millimeter band have not yet been thoroughly considered. To the best of our knowledge, there is no reported work in the literature that attempts to solve the problem of signal coverage for a multi-room indoor environment at the 60 GHz
Radio-over-Fiber physical layer design
In order to design a reliable RoF-based access infrastructure, RoF techniques must (a) be capable of generating the wireless radio signals and (b) allow a reliable radio signal transmission over the optical link. Among many other RoF techniques, the Optical Frequency Multiplication (OFM) method [11] satisfies these two main requirements by generating the microwave signals with a single laser source and low frequency electronics and presenting high tolerance to dispersion impairments in
Wireless indoor broadband network at 60 GHz
In this section, we propose an architecture that is able to provide a seamless environment for networking at millimeter wave bands. A simulation study including the effect of radio propagation is also presented. We consider quality of connections for MSs vis-a-vis the effect of propagation at 60 GHz.
Impact of a RoF-based architecture on the state-of-the-art MAC protocol standards
The major effect when an optical distribution system is inserted in a traditional wireless network is the additional propagation delay introduced by the fiber links. This additional propagation delay can exceed the timing boundary of the network’s MAC protocol and eventually stop the network from working. For centralized MAC schemes, such as IEEE 802.16 and ETSI HiperLAN/2, the effect of the additional propagation delay is less severe since the timing between different phases are allowed to be
Summary and conclusions
We have presented a system-level architecture for broadband indoor networks at the 60 GHz band. The RoF physical layer design is based on the Optical Frequency Multiplication (OFM) technique, which allows to generate and distribute microwave signals to remote simplified antenna stations by using one single laser source and low frequency electronics at the central station. The proposed RoF physical layer offers bidirectional RF transmission, increased cell capacity allocation, multiple standard
Bao Linh Dang received a B.Sc. degree in Electronics and Telecommunications from Hanoi University of Technology, Vietnam, in May 2001, and an M.S. degree in Computer Engineering from Delft University of Technology, Netherlands, in August 2003. Currently, he is working toward his Ph.D. degree in Wireless and Mobile Communications (WMC) group, Delft University of Technology. His research interests include performance analysis of various wireless technologies, e.g. IEEE 802.11 and 802.16; mobility
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Bao Linh Dang received a B.Sc. degree in Electronics and Telecommunications from Hanoi University of Technology, Vietnam, in May 2001, and an M.S. degree in Computer Engineering from Delft University of Technology, Netherlands, in August 2003. Currently, he is working toward his Ph.D. degree in Wireless and Mobile Communications (WMC) group, Delft University of Technology. His research interests include performance analysis of various wireless technologies, e.g. IEEE 802.11 and 802.16; mobility and home networking. Currently, he is also involving in designing short-range networks at millimeter wave band.
Maria Garcia Larrode was born in Zaragoza, Spain, in 1977. She received an M.Sc. degree in telecommunications engineering from the Centro Politecnico Superior, University of Zaragoza, Spain, in 2001. Currently, she is working toward the Ph.D. degree in the area of broadband wireless access networks employing radio over fiber techniques at the COBRA Research Institute, Eindhoven University of Technology, Netherlands. From 2000 to 2004, she was with Siemens AG, Germany, as a Systems Engineer in mobile radio access networks, focusing on radio resource management, signaling, and performance evaluation of GSM/GPRS/EDGE and UMTS networks.
R. Venkatesha Prasad received a B.E and an M.Tech. degree from University of Mysore, India and Ph.D. in 2003 from Indian Institute of Science, Bangalore, India. During 1994 and 1996 he was working as a consultant and project associate at ERNET lab of ECE Department in Indian Institute of Science. While pursuing Ph.D., from 1999 to 2003, he was working as a consultant for CEDT, Indian Institute of Science, as part of Nortel Networks sponsored project. From 2003 to 2005 he was heading a team of engineers at Esqube Communication Solutions Pvt. Ltd., Bangalore, India. From 2005 until date he is with WMC, TU Delft. He is part of the TPC of many IEEE/ACM conferences and a regular reviewer for many IEEE transactions and other journals. He has one patent and another four under process. He is also a member of IEEE∼1900, IEEE TCCC, TCCN and AHSNTC. Currently he is also a consultant for Esqube working on innovative voice enabling applications.
Prof. Dr. Ir. Ignas Niemegeers received bachelor degree in Electrical Engineering from the University of Gent, Belgium, in 1970. In 1972 he received an M.Sc.E. degree in Computer Engineering and in 1978 a Ph.D. degree from Purdue University in West Lafayette, Indiana, USA. From 1978 to 1981 he was a designer of packet switching networks at Bell Telephone, Antwerp, Belgium. From 1981 to 2002 he was a professor at the Computer Science and the Electrical Engineering Faculties of the University of Twente, Netherlands. From 1995 to 2001 he was Scientific Director of the Centre for Telematics and Information Technology (CTIT) of the University of Twente, a multi-disciplinary research institute on ICT and applications. Since May 2002 he holds the chair Wireless and Mobile Networks at Delft University of Technology, where he is heading the Center for Wireless and Personal Communication (CWPC). He is an active member of the Wireless World Research Forum (WWRF) and IFIP TC-6 Working Group on Personal Wireless Communication. He was involved in many European research projects, in particular ACTS TOBASCO, ACTS PRISMA, ACTS HARMONICS, RACE MONET, RACE INSIGNIA and RACE MAGIC. He is one of the originators of the concept of Personal Networks. He is one of the initiators of the FP6 IP project MAGNET and MAGNET Beyond on Personal Networks, where he is an executive committee member.
Ton Koonen is since 2001 a full professor at the COBRA Institute at Eindhoven University of Technology in the Netherlands, and since 2004 chairman of the Electro-Optical Communication Systems group. Prior to that, he spent more than 20 years at Bell Labs in Lucent Technologies as a technical manager of applied research. Next to his industrial position, he has been a part-time professor at Twente University from 1991 to 2000. He is a Bell Labs Fellow since 1999, and an IEEE Fellow since 2007. His main interests are currently in broadband fiber access and in-building networks. He has initiated and led several European and national R&D projects in the access area, a.o. in dynamically reconfigurable fiber access networks for fiber-to-the-curb and fiber-to-the-home. He has also led the European FP5 IST project STOLAS on label-controlled optical packet routing. Presently, he is involved in a number of access/in-home projects in the Dutch Freeband program, in the Dutch IOP Generieke Communicatie program, and in the European FP6 IST Broadband for all programs (MUSE, e-Photon/ONe+, POF-ALL).
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This research was carried out in the Broadband In-home Networks employing Radio-over-Fiber project within IOP GenCom program funded by the Dutch Ministry of Economics Affairs.