Radio-over-fiber systems for wireless communications
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In recent years, considerable attention has been devoted to the merging of Radio over Fiber (RoF) technologies with millimeter-wave-band signal distribution. This sort of systems have great potential to support secure, cost-effective, and high-capacity vehicular/mobile/wireless access for the future provisioning of broadband, interactive, and multimedia services over wireless media. Current trends in cellular networks are (1) reduction of the cell size to accommodate more users and (2) operation in the microwave/millimeter-wave (mm-wave, 26-100 GHz) frequency bands to avoid spectral congestion in lower frequency bands (2.4 or 5 GHz). The larger radio frequency (RF) propagation losses at mm-wave bands reduce the cell size covered by a single base station (BS) and allow an increased frequency reuse factor to improve the spectrum utilization efficiency. On the other hand, this type of network demands a large number of BSs to cover a service area, and cost effective BSs are the key to success in the market place. Thus, a stable and cost effective BSs should be designed with simple and effective architecture. In general, there are three possible techniques to transport the mmwave wireless signals over the optical fiber 1) RF-over-fiber, 2) Intermediate Frequency (IF)-over-fiber, and 3) Base band-over-fiber. Amongst the schemes, the RF-over-fiber transport scheme has the potential to simplify BS design. However, one of its major drawbacks is the requirement for high-speed optical components and modulation and detection techniques. This requirement has led to the development of system architectures where functions such as signal routing/processing, handover, and frequency allocation are carried out at a centralized station (CS), rather than at the BS. This paper reviews extensively recent patents related to RoF communication systems for wireless communications. It is expected that with this exhaustive review, many researchers and developers will be encouraged to investigate even further and develop newer topologies and systems for the use of RoF for broadband radio, expanding this knowledge in the advent of newer services and applications likely to be deployed in the near future. © 2011 Bentham Science Publishers.