Design of a Multiband OFDM System for Realistic UWB Channel Environments

Abstract

In February 2002, the Federal Communications Commission allocated 7500 MHz of spectrum for unlicensed use of commercial ultra-wideband (UWB) communication devices. This spectral allocation has initiated an extremely productive activity for industry and academia. Wireless communications experts now consider UWB as available spectrum to be utilized with a variety of techniques, and not specifically related to the generation and detection of short RF pulses as in the past. There are many differences between real-world behavior of narrow-band and UWB systems. All wireless systems must be able to deal with the challenges of operating over a multipath propagation channel, where objects in the environment can cause multiple reflections to arrive at the receiver (RX). For narrow-band systems, these reflections will not be resolvable by the RX when the narrow-band system bandwidth is less than the coherence bandwidth of the channel. The large bandwidth of UWB waveforms, instead, significantly increases the ability of the RX to resolve the different reflections in the channel. The UWB channel model developed by the IEEE 802.15.3a standard body is described in this paper. For highly dispersive channels, an orthogonal frequency-division multiplexing (OFDM) RX is more efficient at capturing multipath energy than an equivalent single-carrier system using the same total bandwidth. OFDM systems possess additional desirable properties, such as high spectral efficiency, inherent resilience to narrow-band RF interference, and spectral flexibility, which is important because the regulatory rules for UWB devices have not been finalized throughout the entire world. This paper describes the design of a UWB system optimized for very high bit-rate, low-cost, and low-power wireless networks for personal computing (PC), consumer electronics (CE), and mobile applications. The system combines OFDM modulation technique with a multibanding approach, which divides the spectrum into several sub-bands, whose bandwidth is approximately 500 MHz. The system described in this paper has been selected by several key industry organizations [Mulitband OFDM Alliance, WiMedia, Wireless Universal Serial Bus (USB)] because of its very good technical characteristics for the diverse set of high performance short-range applications that are eagerly anticipated for CE, PC, and mobile applications.