Experimental design and analysis of transmission properties in an indoor wireless sensor network

In this paper, we systematically investigate different factors and their effects on the wireless transmission properties using a full-factorial experimental design of a wireless sensor network in a real-world indoor environment. We quantify the impact of primary factors such as the wireless channel, physical position, transmission power, and their interactions on the received signal strength (RSS). While some of our results support conventional assumptions, this study also shows that there are many properties which are in contrast to existing findings. For example, there is no significant correlation in the measured RSS between different but equally-distant transmitters, yet the correlation coefficient between two transmitters is above 94%. In addition, changing the wireless channel even in a static network scenario results in highly unpredictable interaction with other factors and significantly influences the measured RSS. Since the analyzed network only consists of low-cost, commodity transmitters, the results of this experimental analysis can serve as valuable insights in planning and deploying wireless sensor networks in different application scenarios.

I. Introduction

One of the most crucial assumptions in wireless network research is made on the behavior of the wireless channel. Because wireless channel characteristics are in general more environment-dependent than characteristics of wired channels, those assumptions are also the most arguable ones. While many papers assume symmetric wireless links and a predictable received signal strength (RSS), others strongly disagree and characterize wireless signal behavior as highly erratic, uncorrelated, and unpredictable. For example, in the well-known paper “The Mistaken Axioms of Wireless Network Research” [1], Kotz et al. react on the simplifying assumption of the wireless signal behavior and demonstrate that such assumptions are highly unappropriated under realworld conditions. They present a set of experiments using IEEE 802.11 to justify that most of the protocols relying on symmetric links and predictable RSS are contrary to the facts. On the other hand, another well-known paper, “RSSI is Under Appreciated” [2], argues that RSS values are stable over time and that certain symmetric behavior of the signal propagation, especially in case of packet reception rate (PRR), can be observed. Yet, in [3], the authors show that RSSI (RSS Indicator) values are highly variable and that there is less correlation between RSS and packet error rate in outdoor environments. Similarly, there is a number of other papers (such as [4], [5], [6]) that report on different wireless channel behavior for various network settings.