Convergence of Optical and Wireless Access Networks: Technologies and Applications
Prof. GK-Chang, Arshad Chowdhury
Background and Context: The ever-increasing bandwidth requirements for delivering high-speed data, multichannel HDTV signals, online gaming and user-driven interactive video services will grow toward multigigabits/second in the near future. This explosive growth in bandwidth-rich applications, the limitations on present
infrastructure, the desire for mobility and the emergence of new wireless standards is driving the need for faster and
simpler integrated broadband access infrastructure. A passive optical network (PON)-based access such as WDMand TDM-PON can increase both capacity and coverage of the next-generation optical access; however, opticalwireless access technologies, mainly radio-over-fiber (RoF), have been considered the most practical and efficient
solution to increase the capacity, coverage and mobility to the end user terminals. The following paragraphs
summarize recent research accomplishments on convergence of optical and wireless access networks.
Multi-service Multi-band 60-GHz Wireless-over-Fiber Network: Optical-wireless access operating at 60-GHz mmwave is gaining much attention for its huge bandwidth over 7-9 GHz unlicensed mm-wave band. The 60-GHz mmwave is specially the choice of wireless carrier for next generation very high throughput (VHT) wireless personal
area networks (WPAN). The 60-GHz un-licensed band is divided into four frequency sub-bands with frequency
separation of 2.160 GHz and the symbol rate of 1.728 GS/s. A future wireless-over-fiber network should be able to
transmit multiband multi-service radio signals at 60-GHz mm-wave band to facilitate the seamless convergence
with future-proof VHT-WPAN with optical wireless access. We created an all-optical simultaneous up-conversion
technique to provide separate Gigabit/s services at 60GHz and 64GHz mm-wave carried by one single lightwave for
in-building optical wireless access system (Fig. 1).
Very-High-Throughput Millimeter-Wave Optical-Wireless System: The 60-GHz radio is more line-of-sight (LOS)
oriented with extremely high atmospheric loss. However, such short-reach LOS nature may in turn open the
possibility of directly leveraging wireline modulation formats in the potential convergence of optical and wireless
communications. Duobinary, a correlative line coding/modulation technique in broadband fiber-optic
communication, has shown the robustness in its spectral compression capability and high tolerance to inter-symbol
interference that achieves a data rate twice the channel bandwidth and features direct detection using traditional nonreturn-to-zero receivers. We have a spectral-efficient 60-GHz optical-wireless converged system that delivers 10Gbps Duobinary coded bit streams from end to end last-meter VHT wireless access (Fig. 2). No complicated
demodulators are needed in the direct down-conversion 60-GHz receivers.
Converged Optical-Wireless Field demonstration: The development of single-chip low-cost IC solutions at 60-GHz
mm-wave with integrated RF front-end functionalities, baseband processing capabilities and low-power multigigabit modulation/demodulation techniques makes mobile high-speed wireless access a reality in the near future.
We have demonstrated a field-trial testbed of multi-service in-building wireless-over-fiber access system that
supports bi-directional 60-GHz mm-wave optical wireless providing 1.485Gbps uncompressed high-definition video
connectivity and uncompressed 270Mbs SD video broadcast using 2.4GHz RF to connect two research labs at
Georgia Tech campus (Fig. 3). At the mobile receiver terminal, the integrated mm-wave multi-gigabit CMOS
wireless transceiver is used for HD video service. Fig. 4 shows the inter-operability between the 60-GHz CMOS
radio receiver and optical wireless system and Fig. 5 shows the 3-screen video receiver at the Aware Home.
WDM-PON Protection and restoration: As per channel data rate in the future WDM-PON access networks are
envisioned to 10Gbps or more, the network reliability and survivability of such high-speed networks need to be
addressed. We demonstrate a novel centrally controlled self-protected, bi-directional, color-less WDM-PON
architecture using optical carrier suppression (OCS) technique. The self-survivable scheme can simultaneously
protect and restore multiple network failures at feeder fiber, distribution fiber, remote node and laser failure at
central office.
Future work:
The emergence of multiple input multiple output (MIMO) in wireless communications has greatly facilitate to
achieve higher data rate, longer transmission range and better link reliability. MIMO is already incorporated in the
next-generation wireless access networks (WLAN) such as WiFi 802.11n, WiMAX 802.16e and the future-proof
4G/LTE (Long Term Evolution) based cellular systems adopted by many worldwide carriers. In future, we would
like to implement a MIMO based multi-carrier multi-service integrated optical wireless system.