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WiFi transceivers are available in most hand-held devices and thus are well suited for indoor localisation. However, their critical high-power consumption is challenging acceptable battery runtimes for frequent localisation (such as tracking). Alternative transceivers that operate at frequencies of 868 MHz can be expected to be included in upcoming smartphones and achieve similar transmission ranges but have significant lower power-consumption. Thus, this article analyses if these alternative transceivers — so-called Sub GHz transceivers — are better suited for frequent indoor localisation, than WiFi transceivers. Therefore, localisation accuracies and battery runtimes have been analysed via trace-driven empirical studies and battery runtime tests. The results indicate that Sub GHz transceivers are better suited than WiFi transceivers in both considered terms and are especially more robust regarding the influence of obstacles and peoples. Sub GHz transceivers achieve significant lower RSS errors and are less influenced by wall attenuations. Consequently, their localisation achieved ca. 1 m more accurate median error distances than the corresponding versions that utilise WiFi transceivers. In addition, the battery runtimes are extended by 48% when using Sub GHz transceivers instead of WiFi transceivers.

Since Wi-Fi transceivers are available in most handheld devices, they are well suited for indoor localisation. This article analyses the relevance of thirteen factors of modelbased received signal strength indoor-localisation algorithms on localisation accuracies and identifies for each of these factors algorithms or parameter-settings that achieve high position accuracy. In order to assure the results' meaningfulness and comparability, these factors' optima have been identified via trace-driven empirical studies. By comparing position accuracies of the optimised optLoc localisation algorithm and of the Radar algorithm, a significant increase of accuracy was shown. In case of the optLoc algorithm, error distances dropped by ca. 1m and localisation-error rates decreased also significantly. In addition, the article studies energy efficiency of Wi-Fi based indoor localisation and identifies the most energy efficient approach.

Common problems of many elderly include falling accidents and getting lost while leaving their common surroundings unattended. We developed a mobile device that includes indoor localization based on the energy-efficiency Sub 1GHz wireless communication via radio signal strength (RSS) measurements and fall detection functionality. Power management is a critical part for the success of such a device. The authors suggest the use of Sub 1GHz transceivers (using the 433, 868 or 915 MHz frequency bands) with their optimized energy characteristics and increased transmission ranges for localization and emergency calls in case of a fall. Therefore, we present a hardware design of an energy efficient mobile device, the so-called EMU, that includes Sub 1GHz and Wi-Fi transceivers. An optimization of the Wi-Fi localization increased the uptime from 7 h to 9:25 hours. Further, the utilization of Sub 1GHz for localization has more than doubled the uptime to 21 hours, as shown in two benchmarks (measuring perchip power-consumption and system uptime while performing network communication), while achieving a comparable location accuracy.

This work presents a dependable SIP overlay network for the usage in mobile ad hoc wireless networks focusing the availability of registrar and location services in combination with a reduced message transmission overhead regarding amount and size. In addition we enable a SIP presentity service which offers subscriber presentity state information to others. We show the performance of our approach through measurements with a prototype in a testbed.