Introduction

In UROOF it is addressed the challenging problem of low-cost and high performance conversion of high data rates modulated communication signals from optical domain (over single mode and multimode fibre) to radio frequency domain and vice-versa. UROOF focus on photonic components and device concepts that apply for transmission of Ultra-wideband (UWB) radio signal over hybrid wireless/fiber networks.

UWB signals occupy huge bandwidths (0.5 to 7.5 GHz) and with extremely low spectral power density, at the level of parasitic emissions in a typical indoor environment (FCC part 15: -41.3 dBm/MHz). UWB is considered a complementary communication solution within the future integrated networks beyond 3G. The ultimate target of UWB systems is to utilize broadband unlicensed spectrum (FCC: part 15: 3.1-10.6 GHz) by emitting noise-like signals. The major UWB advantages are potentially low complexity and low power consumption that implies that UWB technology is suitable for broadband services in the mass markets of wireless personal area networks (WPAN). Inherently, the high data rates of say 480 Mbps are available over short-range of less than 10m. This is simply derived from the constraints on allowed emissions and fundamental limits of thermal noise and Shannon limits. In many cases the 10m range is too short for many residential applications.

UROOF bring UWB benefits to large coverage areas enabling high data rate UWB to say 10 – 10000 meters distances as depicted in Figure 1.

Figure 1 Figure 1: Range extension UWB application

UROOF address the coverage area extention keeping in mind the low-cost requirements. UROOF develops innovative photonics components that address low-cost conversion from the optical-to-UWB domain and vice-versa. Existing approaches to extend the fundamentally limited short-range nature of the high data rate UWB are either practically not available from link budget considerations or too expensive for the WPAN market (by example, free space optical link suffers 41 dB losses over 10km, roughly the same as 0.375 inch Coax cable of 10km length operating at 10 GHz ) [C. H. Cox, Analog optical links theory and Practice, Cambridge University press 2004] .
UROOF fibre-distribution approach is convenient as free-space RF signal link losses at say 4GHz centre frequency would be at least 125dB. This can be compared to the incredible clarity of optical fibers with less thank 3dB attenuation at 1.55 micro-meter wavelength). Other potential solutions using ad-hoc and multi-hop network topology to deliver the high data rate between the nodes of WPAN would impose major delay constraints that will prevent the sending of most target WPAN services and applications.
UROOF develops novel modulation devices to distribute UWB over fibre in a economic way. Legacy approach to demodulate the UWB signal and transmit it digitally as 1Gbit/s Ethernet data over single mode fiber is too expensive for WPAN applications. Furthermore, this solution would be tailored to the specific UWB technology being employed. UROOF employs generic (e.g. agnostic to the specific modulation technology at the access point) and scalable solutions that can be easily applied to other less demanding cases (e.g. range extension of wireless local area networks, WLAN.


UROOF innovations

The ultra-wide band (UWB) radio over fiber technology (UROOF) is a novel technology for the transmission of UWB signals by using an optical carrier propagating through optical fiber. In the UROOF system, the UWB RF signal itself is superimposed on the optical CW carrier. This strategy makes the conversion process transparent to the UWB's modulation method and allows avoiding the high costs of additional electronic components required for synchronization. Another advantage of this strategy is that the optically controlled microwave converter used for O/UWB conversion needs no microwaves carrier. Besides the required transparency to the UWB modulation method, the overall combination of these features allow for low cost photonic converting devices at both directions.

The UROOF project presents innovations in three areas:

The core activities of the UROOF project are devoted to development of three novel photonic components. Namely, Optically Controlled Microwaves Converter (OCMC), Photonic mixer and enhanced EAT. The OCMC will be further investigated to allow working prototypes. The second approach in UROOF is addressing optimised EAT transceiver for UWB operation. Additionally, innovative VCSEL technologies will be explored for low cost UROOF applications.

These components are used to develop new devices which, in turn, are utilized to develop new systems and applications. These areas are arranged in the circles schematically illustrated in Figure 2.

Figure 2 Figure 2: UROOF circles of innovation