Contributions to location in cellular networks
- Autores: Israel Martín Escalona
- Directores de la Tesis: Francisco Barceló Arroyo (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2010
- Idioma: inglés
- Tribunal Calificador de la Tesis: Jaume Riba Sagarra (presid.), Daniel Guasch Murillo (secret.), Yevgeni Koucheryavi (voc.), Boris Bellalta i Jiménez (voc.), Álvaro Marco Marco (voc.)
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- Resumen
Experts agree that in order to revitalize the wireless market, new services that represent a major addition of value must be developed. This does not mean merely translating services from the wired to the wireless context, but developing new value added services for this particular environment.
Location Based Services (LBS) are the most representative example of this set of services. This Ph.D. Thesis is aimed at providing several contributions to the field of location in cellular network, in order to improve current and future positioning systems. Specifically, four new contributions are included in this work. Firstly, the support of GSM networks for time-based tight-synchronized couplings is analyzed. Synchronization must be extremely precise in time-based couplings since the errors of synchronization are magnified in terms of the propagation speed. The main solutions for supporting time-based tight- coupled techniques in GSM networks proposed under the regulation framework set by ETSI/3GPP are analyzed to realize that it only allows coarse synchronization to be performed. Therefore a new proposal to enhance the resolution of the inter-system synchronization is proposed in this work.
Secondly, the improvement in service coverage obtained by three different ways of coupling terrestrial (E-OTD) and satellite sources (A-GPS) in multilateration techniques is studied. A simple analytical model is presented, which is used for evaluating the service coverage of each approach. Then, a field study on the availability is carried out. In particular, the availability of GSM base stations (as example of terrestrial multilateration sources) and NAVSTAR satellites (i.e. those used in the GPS-based techniques for positioning) is analyzed in certain constrained scenarios as well as regular urban scenarios.
Thirdly, a new software layer, which works as a middleware and manages several location techniques in order to maximize benefits, is presented. This middleware-like layer is based on a cost function, which aims at quantifying the resources used by each location technique at a specific time.
Implementations of this middleware in the mobile station and in the core network are studied. Three cost factors are implemented in each of them to illustrate the performance. Simulations were run to evaluate the performance of the proposed layer. UMTS and WLAN networks were considered for network-based and MS-based implementations of the middleware. Performance evaluation proves that the proposed approach improves the percentage of LBS attended successfully. Furthermore, the resources used (i.e. the cost) of providing such LBS is drastically reduced in comparison to the techniques used as standalone. Finally, a new algorithm for the positioning of nodes in ad hoc networks is presented. This algorithm works under a passive approach, i.e. it listens to the shared access medium for location messages generated by a few TOA-based nodes and computes TDOA figures from those messages in the network. Once the distance-differences are estimated, a regular TDOA algorithm is run to compute the final position for the node. The proposed algorithm operates in two different modes: assisted and autonomous. The difference between them is the position of TOA-based nodes being supplied to or estimated in the passive-TDOA nodes, respectively. Both modes boost the scalability of time-based location systems and provide good accuracy figures, with positioning errors close and often better than the RMS of the ranging error. Furthermore, the passive-TDOA algorithm performs better under NLOS and mixed NLOS/LOS conditions, which are the scenarios that more likely appear in actual ad hoc network deployments and usually degrade the location system performance.
