Abstract
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.
Highlights
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
What does this imply for the link budget of a typical UWB frequency modulation (UWBFM) communications system operating at 4 GHz with a bandwidth of 1 GHz, and data rate R, subcarrier modulation index βsub = 1, at an error probability Pb of 1E-6?
The UWBFM signal is centered at 4 GHz and has a deviation ∆ f = 600 MHz and a sinusoidal subcarrier signal m(t) of frequency fm = 1 MHz
Summary
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. The spectrum of such a pulse sequence (usually Gaussian) has a single broad main lobe with slow spectral roll-off These pulsed systems were originally intended for radar applications where short pulse duration translates into a high resolution. The proposed solution is a constant-envelope frequencydomain approach called UWB frequency modulation (UWBFM) [5] This double FM scheme uses lowmodulation index FSK followed by high-modulation index analog FM to achieve the wide bandwidth. It addresses the closely related issue of the robustness of UWBFM to narrowband interference.
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