System Level Considerations for Ultra-Low Power Transmitter-only Wireless Networks in the Indoor Environment

Indoor networking applications requiring only low duty cycles and low data rates offer unique opportunities for drastic reductions in power consumption, leading to extended battery lifetimes and at the same time delivering robustness. In order to reach those goals, careful investigation of multiple system level parameters is necessary. A main distinction can be made between applications requiring both a transmitter and a receiver in the wireless devices, and applications in which a transmitter that communicates with a residential gateway suffices. This paper concentrates on the last class of applications, discussing parameters as the data rate, the use of spread spectrum and the modulation scheme. It is shown that a data rate of a few kilobits per second delivers excellent performance in terms of power efficiency. Furthermore, a system test bench is constructed using Simulink, in order to verify theory in the comparison between direct sequence spread spectrum (DSSS), for example used in Zigbee, and frequency hopping spread spectrum (FHSS). Regarding robustness, the results show that FHSS outperforms DSSS in the indoor environment and for low data rates. This situation can be changed by increasing the complexity of the DSSS system, for instance by using equalization techniques. However, doing this may lead to more power consumption. Finally, reference values for the hopping rate and hopping set are also given.