Impulse Wavelet versus Chaotic Carrier: Selection of Optimum Carrier for Uwb Radio

Data communications is going to wireless everywhere, from computer keyboard to Internet, from sensor networks to embedded systems. The spread of wireless communications is blocked by the fact that the radio channels have been already assigned to conventional communication systems and except a very few and crowded ISM bands there are no empty channels. Radio communications via channels already occupied by conventional narrowband systems can be achieved by using ultra-wideband (UWB) radio [1], where extremely wideband wavelets are used as carriers in order to reduce the power spectral density (psd) of transmitted signal and, consequently, to keep the interference caused in the narrowband systems low enough. The minimum and typical bandwidths of the transmitted UWB signals are 500 MHz and 2 GHz, respectively, the frequency band assigned for UWB radio goes from 3.1 GHz to 10.6 GHz. In UWB radio, only the psd of radiated signal is limited, the FCC regulation does specify neither the type of carrier nor the modulation scheme. The UWB radio is a low-data rate system working in the Personal Operating Space (POS, max. 100 m coverage). The UWB devices should operate in an ad-hoch network established without infrastructure and providing self-healing capability. These networking devices will be used in sensor networks, embedded systems, etc., where the average data rate is low. Operation without maintenance is a must and nobody is going to repair the failed devices. The UWB devices should be equipped with location capability. Operation for years is expected using the same battery and the price of one UWB device has to be less than USD10.00. These requirements cannot be satisfied by simply improving the performance of conventional radio systems, instead, a brand new approach is required where new carriers, modulation schemes and transceiver architectures are used. To keep the cost low, the UWB networking devices are built with CMOS technology using the System-on-a-Chip (SoC) concept. Both the carrier generation and modulation scheme must support the implementation with CMOS technology. Chaos-communications has been proposed as an alternative solution to conventional communications. Since in chaoscommunications there is an inevitable loss in exploitable a priori information [2], its noise performance lags behind that of the conventional coherent systems. The recovery of UWB carriers is not feasible, consequently, coherent UWB receivers cannot be built. The advantage of conventional communications over the chaotic one is lost in UWB applications. The duration of UWB impulses is very short, the typical value is about 0.5 ns. The generation and reception of such UWB impulses with CMOS circuitry is a very hard task, especially if low price and low power consumption have to be achieved. Chaotic carriers can be generated by simply circuitry, the transmitted reference modulation scheme offers a very simple and robust transceiver configuration. The simple transceiver architecture offers a low price and results in a low power consumption. This article shows that the noise performance of chaotic UWB systems are competitive with that of the UWB impulse radio, while the chaos-based systems offer a simpler and cheaper system configuration.