Ultra Wideband Interference on Third-Generation Wireless Networks

Abstract

As a license-exempt technology, Ultra Wideband (UWB) can be used for numerous commercial and military applications, including ranging, sensing, low-range networking and multimedia consumer products. In the networking and consumer fields, the technology is envisioned to reach the mass market, with a very high density of UWB devices per home and office. The technology is based on the concept of transmitting a signal with very low power spectral density (PSD), while occupying a very wide bandwidth. In principle, the low emissions mask protects incumbent systems operating in the same spectrum from being interfered with, while the wide bandwidth offers the possibility of high data rates, in excess of 250 Mbps.

UWB has been regulated to operate in the 3.1 to 10.6 GHz portion of the spectrum, with an emissions mask for the lower and upper bands outside this range. The commercial wireless mobile services based on third generation (3G) networks occupy a portion of the spectrum in the 2 GHz band, falling under the UWB emissions mask. UWB and UMTS (Universal Mobile Telephone Systems) devices will coexist, sharing the same spectrum.

In this research, we investigate the UWB-3G coexistence problem, analyzing the impact of UWB on UMTS networks. Firstly, we review the mathematical model of the UWB signal, its temporal and spectral properties. We then analyze and model the effects of the UWB signal on a narrowband receiver. Next, we characterize the response of the UMTS receiver to UWB interference, determining its statistical behavior, and establishing a model to replicate it. We continue by proposing a link level model that offers a first order quantitative estimate of the impact of a UWB interferer on a UMTS victim receiver, demonstrating the potentially harmful effect of UWB on the UMTS link. We elaborate on that initial evidence by proposing and implementing a practical systemlevel algorithm to realistically simulate the behavior of the UMTS network in the presence of multiple sources of UWB interference.

We complete the research by performing UMTS system level simulations under various conditions of UWB interference, with the purpose of assessing its impact upon a typical UMTS network. We analyze the sensitivity of the main UWB parameters affecting UMTS performance, investigating the coverage and capacity performance aspects of the network. The proposed analysis methodology creates a framework to characterize the impact that mass-deployed UWB can have on the performance of a 3G system.

The literature on UWB-3G coexistence is inconclusive, and even contradictory, as to the impact UWB can have on the performance of third-generation wireless networks. While some studies show that UWB can be highly detrimental to 3G networks, others have concluded that both systems can gracefully coexist. Through this study, we found that at the current emissions limits regulated for UWB, a mass uptake of this technology can negatively affect the performance of third-generation (3G) wireless networks. The quality of service experienced by a 3G user in close proximity to an active UWB device can be noticeably degraded, in the form of reduced coverage range, poor voice quality (for a voice call), lower data rates (for a data session) or, in a extreme situation, complete service blockage. As the ratio of UWB devices surrounding a 3G user grows, the degradation becomes increasingly more evident. We determined that in order for UWB tocoexist with 3G networks without causing any performance degradation, a minimum power backoff of 20 dB should be applied to the current emission limits.