Hossein Izadpanah

High-availability free space optical and RF hybrid wireless networks

We introduce hybrid free-space optical and RF wireless links as potential technology for designing next-generation broadband wireless networks. We present various design challenges and potential solutions for real-time link performance characterization and adaptation for enhanced performance during adverse weather conditions. First, we introduce the hybrid wireless architecture and emphasize its significant role in achieving ubiquitous carrier-grade wireless connectivity. Second, we propose a link monitoring scheme that accurately reflects the performance of optical wireless links under various weather conditions. In addition, we examine the role of known link performance restoration schemes - power and data rate control. Third, we propose two novel link restoration schemes that efficiently utilize the hybrid architecture: dynamic load switching and multihop routing. Finally, the article describes an elaborate field testbed based on the hybrid architecture and various link restoration techniques. The dynamic load switching scheme is shown to have a profound impact on the overall hybrid link availability. The results, recorded from the experiments during extreme weather conditions, validate the impact of the hybrid architecture concept and conclusively prove the availability and reliability of the architecture in achieving sustained highspeed wireless connectivity.

MM-wave wireless access technology for the wideband wireless local loop applications

We describe and demonstrate a wideband wireless local loop (W-WLL) testbed concept based on local multipoint distribution services (LMDS) millimeter wireless technology but with a modified access and backbone architecture. The testbed is intended as a demonstration platform for broadband wireless services particularly for high speed internet and shared multimedia applications. The investigation is focused on the radio link design, network architecture, system integration, and compatible interface to the existing ATM fiber and satellite core networks.

Design aspects of hybrid RF/free space optical wireless networks

We investigate various design challenges that arise in emerging optical wireless networks. Due to the high sensitivity of optical wireless links to severe weather conditions, several methods have been introduced in the literature to improve their availability figures. We investigate the merits of two potential technologies for enhancing link and network availability, namely hybrid link protection and multi-hop routing. We introduce a novel dynamic load switching algorithm that utilizes hybrid links efficiently and improves link availability. In addition, we provide some insights about the multi-hop routing approach for enhancing link and network availability.

An integrated fiber optics/broadband wireless access demonstrator for the next generation Internet (NGI) network extension

We report on the implementation and integration of gigabit fiber networks and a multi-Mbit wireless access NGI network demonstrator. The focus is to merge photonic technology and networking with the broadband wireless access system.

Reconfigurable low power, light weight wireless system based on the RF MEM switches

We present novel wireless transceiver architecture based on microelectromechanical (MEM) microwave switches. The measurements and calculated results of a reconfigurable module with a switched antenna, tunable filter, and shared components for a low weight, low power compact wireless transceiver are discussed.

High-speed optical wireless connectivity: design challenges and performance evaluation

The paper proposes free-space optics (FSO) as one of the potential solutions for the design and development of next generation, high-capacity, high-speed wireless networks. The hybrid wireless architecture is introduced and the role of FSO in the proposed architecture is highlighted. The significance of the hybrid architecture in achieving ubiquitous, carrier-grade wireless connectivity is also explained. The paper presents various FSO network design challenges and potential solutions for real-time FSO link performance characterization as well as dynamic FSO link adaptability for enhanced performance during adverse operating conditions. Dynamic power control and dynamic data rate control schemes are evaluated for FSO link adaptability. Dynamic load switching (DLS) scheme for hybrid architecture functionality during extreme conditions is also evaluated. Finally, the paper describes an elaborate field test-bed based on hybrid architecture, and various dynamic FSO link adaptation techniques implemented in to the test-bed. The performance of these dynamic link adaptation schemes and DLS functionality is presented to quantify the improvement in overall hybrid architecture performance. The results, recorded from the experiments during extreme weather conditions, validate the hybrid architecture concept and conclusively prove the reliability of the architecture in achieving sustained high-speed connectivity.

Access network technology for all-wireless WDM communications system

In this paper, we report design and implementation scenarios for a gigabit-capacity and high-data-rate fixed wireless access technology research demonstrator. The all weather survivable system is based on broadband wireless access concept and implementation techniques utilizing RF/microwave/millimeter-wave as well as free-space optical wireless high speed links. The demonstration platform provides broadband last mile access and networking solutions to Internet users in densely populated areas with homes and businesses (e.g., downtown building-centric and inner city- environment) in need of high bandwidth not served with fiber infrastructure. The focus of this investigation is radio link design, access network architecture, and system integration. Hybrid fiber radio and WDM optical wireless solutions are implemented to interface and complement the existing ATM fiber and satellite core networks in support of all wireless infrastructure for Next Generation Internet (NGI).

System architecture for proactively adapting lasercom systems

High susceptibility to adverse atmospheric conditions can severely limit the use of free-space optical systems for critical applications. This paper proposes a new architecture for lasercom systems for proactive adaptability during adverse atmospheric conditions. The hardware and software components of the proposed architecture are described in detail. We also present an in-field lasercom test-bed setup, the wireless channel propagation measurements recorded using the test-bed, and the results to validate the recommended design.

Low power transmitter experimental prototype and simulation for personal access communications system (PACS)

In this paper, we look at the benefit of using InP semiconductor technology for RF power amplifiers to improve their overall linearity and efficiency. Experimental prototype and simulation results for a PACS subscriber unit (SU) transmitter RF power amplifier are presented. The role of power amplifier nonlinearity on the emission spectral spreading and the adjacent channel interfered power ratio (ACPR) variations is demonstrated for GaAs FET, GaAs HBT, and InP HBT technologies. A technique to improve the amplifier power added efficiency (PAE) and simultaneously reduce the battery consumption current is suggested and verified by simulation.