Principles and Limitations of Ultra-Wideband FM Communications Systems
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Principles and Limitations of Ultra-Wideband FM Communications Systems John F. M. Gerrits Centre Suisse d’Electronique et de Microtechnique SA, Jaquet-Droz 1, CH-2007 Neuchˆatel, Switzerland Email: [email protected]
Michiel H. L. Kouwenhoven National Semiconductor BV, Amplifier Design Europe, Delftech Park 19, 2628 XJ Delft, The Netherlands Email: [email protected]
Paul R. van der Meer Electronics Research Laboratory/DIMES, Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS), Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands Email: [email protected]
John R. Farserotu Centre Suisse d’Electronique et de Microtechnique SA, Jaquet-Droz 1, CH-2007 Neuchˆatel, Switzerland Email: [email protected]
John R. Long Electronics Research Laboratory/DIMES, Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS), Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands Email: [email protected] Received 10 October 2003; Revised 7 March 2004 This paper presents a novel UWB communications system using double FM: a low-modulation index digital FSK followed by a high-modulation index analog FM to create a constant-envelope UWB signal. FDMA techniques at the subcarrier level are exploited to accommodate multiple users. The system is intended for low (1–10 kbps) and medium (100–1000 kbps) bit rate, and short-range WPAN systems. A wideband delay-line FM demodulator that is not preceded by any limiting amplifier constitutes the key component of the UWBFM receiver. This unusual approach permits multiple users to share the same RF bandwidth. Multipath, however, may limit the useful subcarrier bandwidth to one octave. This paper addresses the performance with AWGN and multipath, the resistance to narrowband interference, as well as the simultaneous detection of multiple FM signals at the same carrier frequency. SPICE and Matlab simulation results illustrate the principles and limitations of this new technology. A hardware demonstrator has been realized and has allowed the confirmation of theory with practical results. Keywords and phrases: UWB, FM, FDMA, WPAN, subcarrier, multipath.
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INTRODUCTION
Ultra-wideband (UWB) communications systems are poised to play an increasingly important role in today’s short-range communications systems, especially personal area network (PAN) applications. By definition, the −10 dB RF bandwidth This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
BRF of a UWB signal centered at a frequency fc should be at least 20% of this central frequency or at least 500 MHz for operation above 3.1 GHz [1]. Since the definition of a UWB signal does not specify a particular air interface or modulation scheme, many different techniques may be applicable to a UWB signal. Originally, UWB started as an impulse radio, using a time-domain approach
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