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Wireless high-definition services over optical fiber access networks

We experimentally demonstrate key technologies to further explore the converged benefits of the optical and wireless systems to offer wireless high-definition (HD) services for both fixed and mobile users. These technologies include spectrum-efficient multi-band generation and dispersion-tolerant transmission, and transport feasibility study for flexible optical routing using multiple reconfigurable optical add/drop multiplexers (ROADMs). Using the developed system, we successfully implement the testbed trial on the delivery of uncompressed 270-Mb/s SDTV and 1.485-Gb/s HDTV video signals over optical fiber and air links.

SECTION I.

Introduction

High-speed broadband penetration and the ongoing growth of Internet traffic among residential and business customers have placed a huge bandwidth demand on the underlying telecommunications infrastructure. According to the study [1], global IP traffic in 2007 stands at more than 6 exabytes per month, more than quadrupling to reach 29 exabytes per month in 2011. Meanwhile, traffic patterns have been propelled from voice-and text-based services to user-generated interactive video services [2]. Peer-to-peer (P2P) traffic is the largest share of internet traffic today, but approximately 70 percent of P2P traffic is due to the exchange of video files. YouTube is just the beginning: real-time video communications and dynamic video content will ultimately test the network more than pre-recorded video content. In response to this remarkable development, the metro and core networks of the telecommunication infrastructure have experienced tremendous growth in bandwidth and capacity with the wide deployment of fiberoptic technology in the past decade [3]. As shown in Fig. 1, data speeds in metro and long-haul systems are evolving from 10-Gbps to 40-Gbps transmission; 100 Gbps per wavelength channel system is taking shape as next step for core and metro networks [4]. Access bandwidth requirements for delivering multi-channel high-definition television (HDTV) signals and online gaming services are expected to grow to gigabits/second in the near future. However, the current subscriber access networks have not been scaled up commensurately. To avoid being the bottleneck in the last miles and last meters, and to exploit the benefits of both wired and wireless technologies, carriers and service providers are actively seeking a convergent network architecture to deliver multiple services to serve both fixed and mobile users [5]. In this regard, optical-wireless access technologies have been considered the most promising solution to increase the capacity, coverage, bandwidth, and mobility in environments such as conference centers, airports, hotels, shopping malls - and ultimately to homes and small offices [6]. In this paper, we demonstrate key technologies for more bands generation, longer transmission distance, and more flexibility of system configurations. The testbed trial is successfully demonstrated for the delivery of uncompressed 270-Mb/s standard-definition television (SDTV) and 1.485-Gb/s HDTV video signals over fiber and air links.

Fig. 1. Emerging broadband applications and future network requirements.

SECTION II.

Multi-band Signal Generation And Transmission

Simultaneous generation of baseband, microwave, and millimeter-wave has been reported for flexible configuration in hybrid fiber-fed wireless systems [7] [8] [9] [10]. However, little effort is made to extend the fiber transmission distance based on a dispersion-tolerant scheme. An efficient photonic frequency tripling (PFT) technology for 60-GHz optical-wireless systems is experimentally demonstrated to simultaneously realize millimeter-wave, microwave, and baseband signal generation and dispersion-tolerant transmission. A novel scheme over both fiber and air links is also developed to provide Wi-Fi services at 2.4 GHz, WiMAX services at 5.8 GHz, and WiMedia services at 60-GHz millimeter-wave carrier on a single wavelength.

A. Photonic frequency tripling technology

The schematic diagram is shown in Fig. 2 for multi-band signal generation and dispersion-tolerant transmission based on PFT technology. Wireless baseband signals initially modulate an RF signal at 20 GHz (one third of the LO frequency). The resulting signal is then subcarrier multiplexed (SCM) onto the optical carrier using an intensity modulator, thus forming dual sidebands. An optical filter with a sharp passband window is used for vestigial sideband (VSB) filtering. The filtered signals are then injected into a dual-arm Mach-Zehnder modulator (MZM) to perform the optical carrier suppression (OCS) using the same clock. After OCS, the optical carrier and the remaining sideband have been suppressed, leaving four longitudinal subcarriers, equally-spaced by 20 GHz, two of which carry the signal. After transmission, another interleaver is used to separate different frequency bands that are needed for wired and wireless connections.

Fig. 2. Schematic diagram of PFT scheme, OF: optical filter, OCS: optical carrier suppression.
Fig. 3. Experimental setup (TL: tunable laser, TD: time delay, FD: frequency doubler, IL: optical interleaver).

Figure 3 depicts the experimental setup of the simultaneous multi-band generation and dispersion-tolerant transmission based on PFT technology. At the central office (CO), the 21-GHz electrical wave is generated using a frequency doubler (FD). This is then mixed with 2.1-Gb/s pseudo-random binary sequence (PRBS) data to drive the modulator. The VSB filtering is achieved by cascading a 25/50- and a 50/100- GHz optical interleaver with 100-GHz periodicity. After transmission over 50-km of SMF-28, the other 50/100-GHz optical de-interleaver is then used to separate the four subcarriers. Direct heterodyne detection of the 63-GHz wireless is achieved by a 60-GHz bandwidth PIN photodiode. The bit-error rate (BER) as a function of the received optical power at back-to-back (B-t-B) and after transmission over 50-km SMF-28 is shown in Fig. 4. The power penalty after 50-km fiber transmission for both signals is less than 1.0 dB at the given BER of 10?9. The insets in Fig. 4 show the electrical eye diagrams after 50-km SMF-28 transmission. No eye penalty from the chromatic dispersion is observed for both situations. This technology has unique advantages in terms of low-bandwidth requirements for both optical and electrical components to realize dispersion-tolerant transmission for 60-GHz optical-wireless systems.

Fig. 4. BER curves and error-free electrical eye diagrams.

B 2.4-GHz/5.8-GHz/60-GHz millimeter-wave on a single wavelength

To integrate the 60-GHz optical-wireless system with the existing Wi-Fi (2.4-GHz) and pre-certified WiMAX (5.8-GHz) systems for long-reach delivery and ultra-high bandwidth provision with a cost-and spectrum-efficient scheme, we show the first demonstration for simultaneously feeding three independent wireless signals on a single wavelength for converged optical-wireless access networks in this section. The panel, dish, and horn antenna with different gains are used to receive wireless signals to evaluate the BER performance.

Fig. 5. Experimental setup of three independent signals over fiber and air links. (resolution: 0.01nm).

Figure 5 illustrates the experimental setup for the multiband generation and transmission system. At the central office, a CW lightwave is generated by a tunable laser at 1554.336 nm and modulated by a phase modulator (PM) driven by a 30-GHz electrical wave. The optical 60-GHz millimeter-wave is generated using an optical coupler to combine the two first-order sidebands. The generated optical 60-GHz millimeterwave signals are then modulated by 2.5-Gb/s data. At the base station, three different signals are separated by cascading two optical ILs with 25/50- and 50/200-GHz channel spacing. One pair of rectangular horn antennas with a gain of 25-dBi at range of 50-GHz to 75-GHz are utilized to broadcast and receive the 60-GHz signal at certain air distance. The other two signals for WiFi and WiMAX transmissions are divided by the optical filter and then electrically up-converted to 2.4-GHz and 5.8-GHz band to emulate the function of WiFi and WiMAX transmitters. The signals are broadcasted by a 2.4-GHz panel antenna with a gain of 10 dBi and a 5.8-GHz parabolic dish antenna with a gain of 29 dBi. After transmitting over 25-km SSMF, the power penalties at the given BER of 10?9 for different air distance are less than 1.5 dB. The wireless transmission distance in the experiment is limited by our lab environment.

SECTION III.

ROADM Networking

Wavelength selective switch (WSS)-based ROADM with a low-cost configuration is expected to be compatible with DWDM optical-wireless networks to support flexible optical routing in optical-wireless networks. Using the flexibility offered by ROADMs, the number of base stations sharing a wavelength channel can be adapted, and thus the available capacity per BS can be tuned to match its traffic demands. For example, when a hot spot with high traffic load emerges, the respective BS can provide extra millimeter-wave carrier as soon as another wavelength channel is directed to this hot spot via remote software control in ROADMs [11] [12] [13].

Fig. 6. Experimental setup for 60-GHz optical-wireless signals over 3-cascaded ROADMs.

Figure 6 depicts the experimental setup for super-broadband wireless signals over a ring access system with 3 cascaded ROADM nodes. At the data source center, an optical transmitter at 1553.9 nm is modulated 2.5-Gb/s or 5-Gb/s data signals. The lightwave is then modulated by a LiNbO3 phase modulator driven by a 30-GHz sinusoidal clock, which is generated by using 1:4 frequency multiplexer and a 7.5-GHz microwave source. The optical signal is then amplified by an EDFA to 6 dBm before transmission over 3-cascaded ROADM links. The optical spectrum of modulated signals after amplification is shown in Fig. 6 inset (a). Then, the modulated signals pass through the linear cascaded ROADMs (the structure includes 1�9 WSS as shown as inset (i)). Transmission is performed through 3 ROADM nodes and total 100-km SSMF with the dispersion coefficient of 16.7 ps/nm/km. The dispersion compensation fiber with total dispersion of 1650 ps and 15-dB loss is used to compensate fiber chromatic dispersion. The insertion loss of each WSS is around 5.5 dB for the transmission channel. The cumulative filtering shape of WSSs is shown in Fig. 6 inset (ii).

Fig. 7. Eye diagrams evolution along the transmission link.

Figure 7 shows the optical and electrical eye diagrams of 2.5- and 5-Gb/s data signals. It is seen that the eyes are wide open despite 100-km SMF transmission. The power penalty for 2.5-Gb/s signals after 100-km SSMF transmission is less than 1.5 dB. The penalty mainly arises from the residual dispersion accumulation and ASE noise from EDFA along optical links. The power penalty after 100-km SSMF transmission is less than 1.5dB. The penalty mainly arises from the residual dispersion accumulation and ASE noise from EDFA along optical links. The receiver sensitivity is high for both situations because of the use of optical pre-amplifier.

SECTION IV.

Testbed Demo

Video applications are implemented based on our developed technologies for optical millimeter-wave signal generation, transmission and processing in optical-wireless access systems. The designed testbed for uncompressed SD/HD signals transmission over optical-wireless networks is shown in Fig. 8. The uplink transmission based on wavelength reuse of downlink carrier is similar to our former work [14].

Fig. 8. Testbed demonstration of SD/HDTV signals over optical-wireless systems.

At the CO, an analog-to-digital (A/D) converter is used to convert the analog video signal from a DVD player into the 270-Mb/s (SMPTE 259-M SDTV signal) or 1.485-Gb/s (SMPTE-292 HDTV signal) SDI signals to drive the MZM modulator for the baseband modulation. Then, the modulated baseband signal is up-converted to millimeter-wave band using the developed all-optical millimeter-wave generation methods. The millimeter-wave carriers at 35 GHz, 40 GHz, and 60 GHz are demonstrated based on the OCS scheme or the external phase modulation with subsequent optical filtering scheme. After transmission over 25-km SMF, the up-converted signal is sent to the BS. The O/E conversion is performed via a high-frequency photodetector. The converted electrical signal is then boosted by an RF low-noise electrical amplifier before it is broadcasted through a double ridge guide horn antenna. The received wireless signal from the other identical antenna is down-converted through a mixer and a LO signal. The downconverted signal is converted to analog video signal by the D/A converter and then displayed on a TV. We also show the display for the wired signals (baseband) using a low-frequency optical receiver. Photographs of the testbed and implementation environment are shown in Fig. 9. The received videos on two Tvs are clear, noise-free, and stable.

Fig. 9. Testbed setup, measurement environment (laboratory hallway), and received videos.

SECTION V.

Conclusions

The hybrid optical-wireless networks can explore the converged benefits of the optical and wireless technology to offer wireless HD services for both fixed and mobile end users. We have developed new systems for multi-band generation and transmission. Based on PFT technology, 60-GHz optical millimeter-wave signals are successfully transmitted over 50-km SSMF without dispersion compensation. We also show the first demonstration of independent generation of multiple wireless services on WiFi (2.4 GHz), WiMAX (5.8 GHz), and 60-GHz carrier, and simultaneous transmission over fiber and air links. We also investigate transport feasibility of super-broadband wireless signals over flexible WSS-based ROADM nodes. Using the technologies that we developed, we successfully implement the testbed trial on the delivery of uncompressed 270-Mb/s SDTV and 1.485-Gb/s HDTV video signals over optical fiber and air links. All the experimental results show that these technologies are highly practical to be deployed in the convergence of optical-wireless networks for wireless HD service delivery.

ACKNOWLEDGMENT

The author would like to express sincere gratitude to Prof. Gee-Kung Chang and Dr. Jianjun Yu for their valuable help on the research work.

Footnotes

"No Data Available"

References

1. Cisco Systems , "Global IP Traffic Forecast and Methodology, 2006C2011," (2008).

2. A. M. Odlyzko, " Internet traffic growth: Sources and implications," in Proc. SPIE: Optical Transmission systems and Equipment WDM Networking II, vol, 5427 (2003).

3. J. Mcdonough, "Moving standards to 100 GbE and beyond," IEEE Commun. Mag., 45, 6-9 (2007) .

4. G.-K. Chang, A. Chowdhury, J. Yu, Z. Jia, R. Younce, "Next generation 100Gbit/s Ethernet Technologies," Asia-Pacific Optical Communications 2007, Wuhan China (2007).

5. T. Koonen, "Fiber to the home/fiber to the premise: what, where, and when?" Proc. of the IEEE 94, 911-934 (2006).

6. G.-K. Chang, Z. Jia, J. Yu, A. Chowdhury, "Super broadband optical wireless access technologies," Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference 2008, OSA Technical Digest (CD) (Optical Society of America, 2008), paper OThD1.

7. Z. Jia, J. Yu, G. Ellinas , G.-K. Chang, "Key enabling technologies for optical-wireless networks : optical millimeter-wave generation, wavelength reuse and architecture," IEEE/OSA J. of Lightw. Technol, 25,3452-3471 (2007).

8. K. Ikeda, T. Kuri, K. Kitayama, "Simultaneous three-band modulation and fiber-optic transmission of 2.5-Gb/s baseband, microwave-, and 60-GHz-band signals on a single wavelength," IEEE/OSA J. Lightw. Technol, 21, 3194-3202 (2003).

9. C.-T. Lin, J. Chen, P.-C. Peng, C.-F. Peng, W.-R. Peng, B.-S. Chiou, S. Chi, "Hybrid optical access network integrating fiber-to-the-home and radio-over-fiber systems," IEEE Photon. Technol, Lett. 19, 610-612 (2007).

10. M. Bakaul, A. Nirmalathas, C. Lim, D. Novak , R. Waterhouse, "Hybrid multiplexing of multiband optical access technologies towards an integrated DWDM network," IEEE Photon. Technol. Lett. 18, 2311-2313 (2006).

11. J. J. V. Olmos , T. Kuri, and K. Kitayama, "Dynamic reconfigurable WDM 60-GHz millimeter-wav eband radio-over-fiber access network: architectural considerations and experiment," IEEE/OSA J. Lightw . Technol. 25, 3374-3380 (2007).

12. C. Lim, A. Nirmalathas, D. Novak, R. Waterhouse, "Capacity analysis for WDM fiber-radio backbones with star-tree and ring architecture incorporating wavelength interleaving," IEEE/OSA J. Lightwave Technol. 21, 3308-3314 (2003).

13. J. C. Attard, J. E. Mitchell, "Optical network architectures for dynamic reconfiguration of full-duplex, multiwavelength, radio over fiber," J. Opt. Netw. 5, 435-444 (2006).

14. Z. Jia, J. Yu and G.-K. Chang, "A full-duplex radio-over-fiber system based on optical carrier suppressing and reuse, " IEEE Photon. Technol. Lett. 18, 1726-1728 (2006).

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Zhensheng Jia

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