Heiko Schmitz

A new method for positioning of mobile users by comparing a time series of measured reception power levels with predictions

Many modern applications for mobile phones are based on information about the exact position of the user. There are several methods, which fulfill this task. Some require extensions of the network or the terminals; others do not, but provide little accuracy. The method presented here uses exclusively standard measurements, network parameters, and data from the network planning process. The power level measurements of the mobile reports to the network for handover and other radio resource management tasks are compared with the field strength values predicted by network planning tools. Using a single report is a well-known positioning method, which is not very accurate, because it is very sensitive to fading and other random variations of the signal levels. In the new method, a series of several reports is used. This series corresponds to a path, on which the user moves. An efficient algorithm calculates the probability of the most probable path leading to each point in the search area. The estimated position is the weighted average of all these points. Since searching the whole area of a network is not feasible in practice, the calculation effort is drastically reduced by a preprocessing step, which allows the preselection of the search area based on information about the current service cell of the user. Extensive field trials in existing GSM networks have shown that the method works well and gives substantial improvement compared to other positioning methods, such as CI/TA. An average accuracy of 130m was observed in an urban environment and about 300m in rural areas. An UTRAN provides some measurements, which are very similar to those of GSM, it is possible to apply this method in UMTS networks as well.

Improved method for positioning mobile phones based on series of measured reception power levels

Finding the position of a mobile user has become important for many wireless applications. There are many methods, which fulfill this task but require extensions of the network or the terminals. The technique presented here is based on the received signal powers obtained from standard measurements. It uses a restricted search area and a time series of measurements. The search area is determined by the intersection of the maximum area covered by the serving cell and a ring determined from round-trip time measurements. A Viterbi-like algorithm is used to compare the time series of reception power levels measured by the handset with predicted values from the network planning process. It returns a weighted average of possible positions. Since only standard measurements are used, no changes of the network or the handsets are required, making the method inexpensive. Furthermore, the method can be used for traffic localization. The method has actually been implemented by Siemens for GSM. Extensive field trials in an operating network in Germany showed an accuracy of 130 meters in urban environments and about 300 meters in suburban and rural areas. Since similar measurements exist in UMTS networks, the method is applicable in UTRAN as well.

Real-Time Demonstration of Mobile Broadcasting Services via MBMS

MBMS (Multimedia Broadcast/Multicast Service) is a unidirectional point-to-multipoint (p-t-m) service which allows to transmit data from a single source entity to a group of mobile users in a certain coverage region. In order to investigate the performance of this IP datacast (IPDC) type of services over packet-switched cellular networks like UMTS or GPRS, a real-time MBMS system demonstrator has been developed jointly by Nomor Research, Siemens Networks GmbH, and Siemens AG. The unique setup covers most of the functionalities specified for the various MBMS network elements, as well as realistic channel models for the specified MBMS bearers. In addition, several advanced features are supported, including Application Layer Forward Error Correction (AL-FEC), system-internal switching between p-t-p and p-t-m radio bearers, and user-defined selection of different media services during operation. The whole setup is complemented by a streaming server and multiple PDA clients connected via IP to the simulator. Hence, realistic multimedia content can be broadcasted via the simulator in real-time, and the received quality at different mobile terminals can be visualized immediately for different system parameter settings and media contents. Besides its live demonstration capabilities, the presented platform can also be used as a valuable tool in research and development.