The paper provides a tutorial overview of ultrawideband (UWB) radio technology for high-speed wireless connectivity. Subsequent to establishing a historical and technological context, it describes the new impetus for UWB systems development and standardization resulting from the FCC's recent decision to permit unlicensed operation in the 3.1-10.6 GHz band subject to modified Part 15 rules and indicates the potential new applications that may result. Thereafter, the paper provides a system architect's perspectives on the various issues and challenges involved in the design of link layer subsystems. Specifically, we outline current developments in UWB system design concepts that are oriented to high-speed applications and describe some of the design tradeoffs involved.

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Ultrawideband radio design: the promise of high-speed, short-range wireless connectivity

Ultra-wide-band (UWB) signals are suitable for underlay communications, over a frequency band where, possibly, other systems are active. Such coexistence of UWB and other systems is possible if the mutual interference has a small impact on their respective performance. This paper aims to present recent results on the interference and coexistence among UWB systems and other conventional narrow-band (NB) systems. Specifically, we consider a point-to-point UWB (NB) under the interference generated by a finite number of NB (UWB) radio transmitters. We consider channels including additive white Gaussian noise and multipath fading both for the victim and the interfering links, and different receiver architectures. While our main focus is on UWB systems based on impulse radio, wide-band systems employing carrier-based direct-sequence spread-spectrum and orthogonal frequency-division multiplexing are also considered.

Coexistence Between UWB and Narrow-Band Wireless Communication Systems

With the increasing proliferation of different communication devices sharing the same spectrum, it is critical to understand the impact of interference in heterogeneous wireless networks. In this paper, we put forth a mathematical model for coexistence in networks composed of both narrowband (NB) and ultrawideband (UWB) wireless nodes, based on fundamental tools from stochastic geometry. Our model considers that the interferers are spatially scattered according to a Poisson field, and are operating asynchronously in a wireless environment. We first determine the statistical distribution of the aggregate interference for both cases of NB and UWB emitters. We then provide error probability expressions for two dual configurations: 1) a NB victim link subject to the aggregate UWB interference, and 2) a UWB victim link subject to the aggregate NB interference. The results show that while the impact of a single interferer on a link is often negligible due to restrictions on the transmitted power, the aggregate effect of multiple interferers may cause significant degradation. Therefore, aggregate interference must be considered to ensure coexistence in heterogeneous networks. The proposed analytical framework shows good agreement with physical-level simulations of the system.

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A stochastic geometry approach to coexistence in heterogeneous wireless networks

We consider a binary pulsed communication system, with possibly episodic transmission, i.e., the system transmits n pulses per information bit and allows for off-time separation between pulses. In the ultra-wideband (UWB) regime, such systems are motivated for overlay applications, as well as low probability of intercept and low probability of detection scenarios. Processing gain enables low-power transmission, and the UWB pulsing limits the interference effects into narrowband systems. We introduce a random ternary sequence model and use this to study multiuser system performance. We consider the issues of processing gain, jamming margin, coding gain, and multiuser interference (MUI) for a single-user matched filter receiver. The introduction of episodic transmission, with a corresponding reduction in bit rate, provides system flexibility with respect to both MUI rejection and handling multipath channels. Highly episodic transmission provides nearly orthogonal low-rate users, even with system asynchrony and no power control. Performance of a single-user RAKE receiver is evaluated via a Chernoff bound on bit error rate, in the presence of MUI. The analysis includes the impact of fading as well as pilot-aided channel estimation.

On the performance of episodic UWB and direct-sequence communication systems

We consider a binary spread spectrum system, with possibly episodic transmission; i.e., the system transmits n pulses per information bit, and allows for off time separation between pulses. Processing gain enables low power transmission, and the ultra wideband (UWB) spreading limits the interference effects into narrowband systems. We consider the issues of processing gain, jamming margin, coding gain and multiuser interference (MUI) for a single user matched filter receiver. The introduction of episodic transmission, with a corresponding reduction in bit rate, provides system flexibility with respect to both MUI rejection and handling of multipath channels. Highly episodic transmission provides nearly orthogonal users, even with system asynchrony and no power control. Performance of a single user matched filter in the presence of MUI is given via a Chernoff bound on bit error rate.

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On the performance of UWB and DS-spread spectrum communication systems

Ultra-wideband (UWB) signals will encounter many interference sources, primarily from relatively narrowband (NB) systems. In addition., UWB signals will also affect a large number of NB radios; of critical importance is the potential interference with GPS, E-911, and navigation bands, as well as cellular bands. There is a rich and growing literature on UWB radios; however, issues related to interference measurements have only been partially addressed. Here, we assess the interference caused by UWB signals via analysis and simulations. Analytical results include the aggregate effect of spatially distributed UWB radios on a receiver, and theoretical BER expressions.

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J. Turner

Papers

On the coexistence of ultra-wideband and narrowband radio systems