OFC/NFOEC 2008 OThP3.pdf Perspectives of Radio over Fiber Technologies A M.J. Koonen, M. Garcia Larrode, A Ng'oma*, K. Wang, H. Yang, Y Zheng, E. Tangdiongga Den Dolech 2, P. O. Box 513, NL 5600 MB Eindhoven, The Netherlands, e-mail: a m.i. koonen @tue. nl ( A Ng'oma is now with Corning Inc, NY, USA) Abstract: Radio-over-Fiber technologies enable efficient provisioning of broadband wireless ervices both in access and in in-building networks, in particular when combined with flexible optical routing and dispersion-robust RoF transport techniques, such as optical frequency multiplying C2008 Optical Society of America OCIS codes:(0602330)Fiber optics communications;(060.5625) Radio frequency photonics 1. Introduction Wireless services are taking a steadily increasing share of the telecommunications market. The end users not only benefit from its main virtue, mobility, but are also demanding ever larger bandwidth. Larger wireless capacity per user requires the reduction of the wireless cell size, i.e. establishing pico-cells, which is enabled by increasing the radio microwave frequency. The wireless LAN IEEE 802. 11g WiFi standard offers up to 54 Mbit/s in the 2.5 GHz range; the IEee 802. 16 WiMAX standard offers up to 100 Mbit/s in the range of 10 to 66 GHz; IEEE 802.15.3 UWB operates at frequencies up to 60 GHz, offering short-range capacity up to 480 Mbit/s. Smaller radio cells imply that ever more antennas are needed to cover a certain area. Such an area may encompass the rooms in a residential home, but may also be a hospital, an office building, an airport lounge, a conference site, etc. When needing so many antenna sites, it becomes economically attractive to locate the microwave signal generation and modulation not at every antenna, but centrally in a cabinet from where optical fibers with their inherent low losses and wide bandwidth can nicely bring the signal to the antennas. The antennas then only have to do the simple optical-to-electrical conversion, and to emit and receive the wireless signal. Centralizing the sophisticated signal handling eases maintenance and upgrading. The signal handling may include techniques for multiple-input multiple-output antenna schemes, smart beam forming antennas, mobility and connection handovers, feeding multiple radio standards to an antenna, reconfiguration of services to antennas, etc. Hence radio-over-fiber(roF) technologies can bring many advantages in operating, maintaining and upgrading wireless networks This paper addresses two major application areas of RoF: outdoor fixed wireless access via standard single- mode fiber, where the last link to the end user's premises is established wirelessly, and indoor wireless access via preferably multimode fiber (already widely installed in buildings), where flexible local networks need to be ealized 2. Radio over Fiber technologies A lot of techniques have been reported to transport radio signals over fiber to the antenna site Basically, one may directly modulate the light intensity of the optical source by the radio signal. At the antenna station, the received optical signal just needs a photodetector and bandpass amplifier, and the regained radio signal is then to be radiated by the antenna. However, the bandwidth and linearity requirements on the laser transmitter and the receiver are high. Also careful fiber dispersion compensation techniques may be needed at higher RF frequencies and longer fiber lengths. Thus the application of this intensity-modulation(IM) scheme is restricted to Alternatively, one may use various optical frequency conversion methods to generate the microwave signal at the antenna site. As a first method, two narrow-linewidth laser diodes may be deployed, of which one is intensity modulated with the data signal. When the optical frequency spacing between these two lasers is carefully kept equal to the desired microwave frequency, after traveling through the fiber link, the heterodyning of the two optical signals in the photodiode generates the modulated microwave carrier. However, the linewidth of the microwave signal is equal to the sum of the linewidths of the two laser diodes, and may exceed the requirements for adequate detection of the usually multilevel signal modulation format(such as multi-level QAM). Hence the linewidth of the laser diodes needs to be very small, which is e.g. achievable by injection locking A second optical frequency conversion method uses just a single laser followed by a Mach Zehnder Interferometer(MZI) modulator which is biased at its inflexion point(Vn) and is driven by a sinusoidal signal at half the desired microwave frequency [1] At the MzIs output, a two-tone optical signal emerges with a tone spacing equal to the microwave frequency, and with suppressed optical carrier. When modulating the laser with thePerspectives of Radio over Fiber Technologies A.M.J. Koonen, M. García Larrodé, A. Ng’oma*, K. Wang, H. Yang, Y. Zheng, E. Tangdiongga COBRA Institute, Dept. of Electrical Engineering, Eindhoven University of Technology, Den Dolech 2, P. O. Box 513, NL 5600 MB Eindhoven, The Netherlands, e-mail: a.m.j.koonen@tue.nl (* A.Ng’oma is now with Corning Inc., NY, USA) Abstract: Radio-over-Fiber technologies enable efficient provisioning of broadband wireless services both in access and in in-building networks, in particular when combined with flexible optical routing and dispersion-robust RoF transport techniques, such as optical frequency multiplying. ©2008 Optical Society of America OCIS codes: (060.2330) Fiber optics communications; (060.5625) Radio frequency photonics 1. Introduction Wireless services are taking a steadily increasing share of the telecommunications market. The end users not only benefit from its main virtue, mobility, but are also demanding ever larger bandwidth. Larger wireless capacity per user requires the reduction of the wireless cell size, i.e. establishing pico-cells, which is enabled by increasing the radio microwave frequency. The wireless LAN IEEE 802.11g WiFi standard offers up to 54 Mbit/s in the 2.5 GHz range; the IEEE 802.16 WiMAX standard offers up to 100 Mbit/s in the range of 10 to 66 GHz; IEEE 802.15.3 UWB operates at frequencies up to 60 GHz, offering short-range capacity up to 480 Mbit/s. Smaller radio cells imply that ever more antennas are needed to cover a certain area. Such an area may encompass the rooms in a residential home, but may also be a hospital, an office building, an airport lounge, a conference site, etc. When needing so many antenna sites, it becomes economically attractive to locate the microwave signal generation and modulation not at every antenna, but centrally in a cabinet from where optical fibers with their inherent low losses and wide bandwidth can nicely bring the signal to the antennas. The antennas then only have to do the simple optical-to-electrical conversion, and to emit and receive the wireless signal. Centralizing the sophisticated signal handling eases maintenance and upgrading. The signal handling may include techniques for multiple-input￾multiple-output antenna schemes, smart beam forming antennas, mobility and connection handovers, feeding multiple radio standards to an antenna, reconfiguration of services to antennas, etc. Hence radio-over-fiber (RoF) technologies can bring many advantages in operating, maintaining and upgrading wireless networks. This paper addresses two major application areas of RoF: outdoor fixed wireless access via standard single￾mode fiber, where the last link to the end user’s premises is established wirelessly, and indoor wireless access via preferably multimode fiber (already widely installed in buildings), where flexible local networks need to be realized. 2. Radio over Fiber technologies A lot of techniques have been reported to transport radio signals over fiber to the antenna site. Basically, one may directly modulate the light intensity of the optical source by the radio signal. At the antenna station, the received optical signal just needs a photodetector and bandpass amplifier, and the regained radio signal is then to be radiated by the antenna. However, the bandwidth and linearity requirements on the laser transmitter and the receiver are high. Also careful fiber dispersion compensation techniques may be needed at higher RF frequencies and longer fiber lengths. Thus the application of this intensity-modulation (IM) scheme is restricted to the low/medium RF range. Alternatively, one may use various optical frequency conversion methods to generate the microwave signal at the antenna site. As a first method, two narrow-linewidth laser diodes may be deployed, of which one is intensity￾modulated with the data signal. When the optical frequency spacing between these two lasers is carefully kept equal to the desired microwave frequency, after traveling through the fiber link, the heterodyning of the two optical signals in the photodiode generates the modulated microwave carrier. However, the linewidth of the microwave signal is equal to the sum of the linewidths of the two laser diodes, and may exceed the requirements for adequate detection of the usually multilevel signal modulation format (such as multi-level QAM). Hence the linewidth of the laser diodes needs to be very small, which is e.g. achievable by injection locking. A second optical frequency conversion method uses just a single laser followed by a Mach Zehnder Interferometer (MZI) modulator which is biased at its inflexion point (Vπ) and is driven by a sinusoidal signal at half the desired microwave frequency [1]. At the MZI’s output, a two-tone optical signal emerges with a tone spacing equal to the microwave frequency, and with suppressed optical carrier. When modulating the laser with the a828_1.pdf OThP3.pdf OFC/NFOEC 2008