Juha-Pekka Mäkelä

Indoor geolocation science and technology

This article presents an overview of the technical aspects of the existing technologies for wireless indoor location systems. The two major challenges for accurate location finding in indoor areas are the complexity of radio propagation and the ad hoc nature of the deployed infrastructure in these areas. Because of these difficulties a variety of signaling techniques, overall system architectures, and location finding algorithms are emerging for this application. This article provides a fundamental understanding of the issues related to indoor geolocation science that are needed for design and performance evaluation of emerging indoor geolocation systems.

Handoff in hybrid mobile data networks

With the emergence of a variety of mobile data services with variable coverage, bandwidth, and handoff strategies, and the need for mobile terminals to roam among these networks, handoff in hybrid data networks has attracted tremendous attention. This article presents an overview of issues related to handoff with particular emphasis on hybrid mobile data networks. Issues are logically divided into architectural and handoff decision time algorithms. The handoff architectures in high-speed local coverage IEEE 802.11 wireless LANs, and low-speed wide area coverage CDPD and GPRS mobile data networks are described and compared. A survey of traditional algorithms and an example of an advanced algorithm using neural networks for PTO decision time in homogeneous networks are presented. The HO architectural issues related to hybrid networks are discussed through an example of a hybrid network that employs GPRS and IEEE 802.11. Five architectures for the example hybrid network, based on emulation of GPRS entities within the WLAN, mobile IP, a virtual access point, and a mobility gateway (proxy), are described and compared. The mobility gateway and mobile IP approaches are selected for more detailed discussion. The differences in applying a complex algorithm for HO decision time in a homogeneous and a hybrid network are shown through an example.

Optimization scheme for mobile users performing vertical handoffs between IEEE 802.11 and GPRS/EDGE networks

The next generation wireless networks are characterised by anywhere, anytime connectivity, enhanced data services and higher data rates to enduser. New technologies such as IEEE 802.11 WLAN, Bluetooth, HIPERLAN/2, GPRS/EDGE, cdma2000 and WCDMA aim to achieve this. To facilitate new services, and make them flexible and bandwidth efficient, vertical roaming of mobile nodes is a tempting possibility for operators. Benchmarks and metrics are needed to assess these issues. The need for qualitative and quantitative results for these parameters in a real time situation is critical. One such scenario is the effect on the network performance by means of effective throughput and handoff latency perceived by the mobile user, with increasing number of active users or network load. This paper presents simulation results for mean throughput and handoff delay obtained in vertical handoff and horizontal handoff in IEEE 802.11 and GPRS/EDGE networks. An optimization scheme for mobile users performing vertical handoffs is presented with analysis.

Analysis of handoff in a location-aware vertical multi-access network

Integration of WLAN hotspots into next generation cellular networks requires considerations on location management, resource allocation, handoff algorithms and their sensitivity to mobility related features such as velocity of the mobile and the handoff delay. This article presents architecture for seamless location-aware integration of WLAN hotspots into cellular networks and provides an analysis for an optimal handoff decision in moving in and out of a hotspot. For a mobile station, it may be beneficial to know the whereabouts of the hotspots in order to facilitate optimal handoff between the two access networks. In an integrated cellular-WLAN environment, one has to consider location management as part of mobility management due to differences in the cell sizes of the two overlapping technologies. Location information acquired through GPS may be helpful in some cases for advanced location management. In this paper we propose a location-aware architecture to support vertical roaming among heterogeneous wireless access networks. The article includes a description of a preliminary system architecture and the procedures and algorithms needed to implement mobility and location management. In conclusion, a comparison is given of two handoff algorithms (power and dwell-timer based) for moving-in and moving-out transitions, and their sensitivity to mobile velocity and handoff delay.

Handoff procedure for heterogeneous wireless networks

Handoff is an important issue when considering mobility in heterogeneous telecommunication networks. During the past ten years, telecommunication networks have emerged as a central strategic component in various fields. Today, added flexibility of the heterogeneous wireless networks in the form of robust inter-technology mobility management schemes and sophisticated algorithms is becoming more important. Also data applications and IP protocols have become more important players when designing future architechtures. This paper gives a novel approach to procedures, algorithms and metrics involved in handoff in heterogeneous wireless networks. A network layer Mobile IP based handoff procedure between WLAN and GPRS is presented as a case study example.

Handoff decision in multi-service networks

The fourth generation of telecommunication networks will be a mix of existing and emerging wireless and wired networks. They will provide a framework for multi-service usage cases, such as Internet access, geolocation and real-time applications (such as voice and video). In this paper we refer this collection of interoperating networks as multi-service networks and elaborate the aspects of system architecture and mobility management in this heterogeneous environment. First, requirements for system architecture are outlined. A novel multi-service architecture is defined based on fully integration of location based services and IP mobility approach. Handoff decision policies for multi-service network scenarios are then considered and simulation results for the handoff algorithm are presented. The suitability of the fuzzy logic algorithm is discussed in this context.

Supporting resource allocation with vertical handoffs in multiple radio network environment

Vertical handoff means mobility between heterogeneous wireless access network technologies. Hierarchical radio access networks with overlapping cells gives an opportunity to handoff between local area high bandwidth networks and wide coverage cellular data. Vertical mobility combines the capacity of local area networks and the coverage of wide area cellular networks. Resource allocation in this kind of environment has not been yet fully addressed in the current research work. Clearly, additional bandwidth offered by wide-band local area wireless networks opens a new area for network performance optimization. For that, it is needed to understand the processes that have an effect on the system performance. In particular, vertical mobility is usually characterized by handoffs between systems having different data rates. The most critical area for system performance is at the very edge of the cell, where the received signal strength (RSS) varies around the sensitivity threshold of the receiver. Simulation results show the estimates of the delay and general performance in a multiple radio network environment. Generalization of handoff performance between multiple radio networks with different data rates is given with analysis.

Data downloading on the sparse coverage-based wireless networks

Infostation, hotspot, and drive-thru internet are examples of sparse coverage-based wireless networks. These wireless communication networks provide low-cost, delay insensitive high data rate services intermittently with discontinuous coverage. Radio propagation parameters, velocity of the user, distance between the user, and access point are the key factors that affect the throughput and the amount of information downloaded from such sparse coverage-based wireless networks. To evaluate the performance of such wireless communication networks analytically the impact of above mentioned factors can be modeled with simplified relationship model such as received signal strength versus distance or signal to noise ratio versus throughput. In the paper, we exploit the relationship between throughput and distance and develop two throughput distance relationship models to evaluate the performance of multirate wireless networks. These two throughput distance relationship models are used in calculation of average throughput as well as downloaded file size. Numerical values are presented for the IEEE 802.11n standard. The numerical results verify that the new proposed technique can be used as an alternative to the simulations to evaluate the performance of sparse coverage-based wireless networks.

Ultra-Wideband Signal Impact on the Performances of IEEE 802.11b and Bluetooth Networks

This paper presents the results of a coexistence study investigating the impact of ultra-wideband (UWB) interference on IEEE 802.11b and Bluetooth networks. The results are based on the experimental test measurements made at the University of Oulu, Finland. Simple high-power UWB transmitters are used to interfere with victim networks. Preliminary results show that only under extreme interference conditions with thousands of equivalent Federal Communications Commission– (FCC)-compliant devices in close proximity, will the IEEE 802.11b and Bluetooth networks experience significant performance degradation. The impact of the UWB interference on the IEEE 802.11b network was insignificant if the distance to UWB transmitters was greater than 40 cm. The impact on Bluetooth was even less noticeable. In our study, several high-power UWB transmitters that greatly exceed the FCC radiation regulations have been used, and the measurement settings presents the worst case scenario because of the very short distance between the interferers and the victim system. Effectively our study approximates the use of thousands of FCC-complaint UWB devices in the same space.

Geolocation information and inter-technology handoff

Mobility between dissimilar networks is one of the future trends in network design towards fourth generation of telecommunication systems. A cellular network can be overlaid with a spottish high data-rate WLAN network in areas such as business centers, hotels and airports. To avoid unnecessary search of WLAN beacon the terminal must be aware of the whereabouts of the overlay system to be visited. We suggest the usage of geolocation information in mobility management via distributed location databases to enable a moving host to prepare for handoff. Three scenarios and the related problems are presented, and the requirements for the system architecture and terminal are outlined. Considerations on the algorithm are given and preliminary simulation results of a fuzzy logic handoff algorithm are presented.