Martin Hellebrandt

Location tracking of mobiles in cellular radio networks

Some useful services in cellular radio networks and also a class of handover algorithms require knowledge of the present position and velocity of mobiles. This paper deals with a method to track mobiles by on-line monitoring of field strength data of surrounding base stations at successive time points. Such data is available in present global system for mobile communication (GSM) systems each 0.48 s and also in code-division multiple-access (CDMA) systems for transmission control. Because of strong random fluctuations of the signals, appropriate smoothing is the key point of the procedure. We develop a locally linear prediction model of successive positions as a basis for Kalman filtering. This approach turns out to be extremely successful, achieving average mislocations of 70 m in simulated test runs. Further improvement is possible by using external geographical information.

Estimating position and velocity of mobiles in a cellular radio network

Determining the position and velocity of mobiles is an important issue for hierarchical cellular networks since the efficient allocation of mobiles to large or microcells depends on its present velocity. We suggest a method of tracing a mobile by evaluating subsequent signal-strength measurements to different base stations. The required data are available in the Global System for Mobile (GSM) system. The basic idea resembles multidimensional scaling (MDS), a well-recognized method in statistical data analysis. Furthermore, the raw data are smoothed by a linear regression setup that simultaneously yields an elegant, smoothed estimator of the mobiles speed. The method is extensively tested for data generated by the simulation tool GOOSE.

Location tracking of mobiles: a smart filtering method and its use in practice

Accurate location tracking of mobile stations in cellular radio networks is of tremendous interest for many applications. In this work, we analyze the performance of a speed and location tracking algorithm using data from a field trial. The algorithm fits received signal strengths of surrounding base stations to corresponding predictions. These raw location estimates, in GSM available each 0.48 s, are subsequently smoothed by a model-based Kalman filter. An essential ingredient of our method is to find suitable initial parameters. The method is tested with measurement data from a field trial by Siemens. Although the field strength prediction method is rather simple, the location algorithm itself yields promising results. Typical average deviations from the true positions were 173.5 m for indoor, 117.7 m for walking, and 104.9 m for driving scenarios. This shows that the method is robust against moderate errors in the prediction model and leads to good results in a real GSM network.

Cumulated interference power and bit-error-rates in mobile packet radio

In this paper we determine the probability distribution function of cumulated instantaneous interference power in a mobile radio network, when the positions of interfering stations are distributed according to a one‐ or two‐dimensional Poisson point process, truncated at a finite horizon. The influences of Rice and Rayleigh fading, lognormal shadowing, near far effect and capture are taken into account. From the resulting distribution the probability of successful transmission and corresponding bit‐error‐rates are derived.

Frequency allocation and linear programming

The present paper deals with optimal fixed channel assignment for large real-world cellular radio networks. Examples are taken from data of the D2-network, operated by Mannesmann Mobilfunk (MMO) in Germany. Because of the huge size of the problems an exact optimal solution is presently out of reach. We present a heuristic iterative approach which performs extremely well, and significantly outperforms channel designs presently used by network operators. The basic ingredients of our approach are: (1) fast and well established simple heuristics as initial assignments; (2) splitting the whole problem into smaller subproblems which can be optimized efficiently by solving a binary linear program (BLP), and repeating this process iteratively; (3) past-processing the resulting near-optimal design to avoid undesirable properties. A lot of detailed problems must be solved, such as a powerful preprocessing of constraints for the BLPs, and a careful selection of the subproblems in (2). In summary, a very flexible tool is derived, also capable of taking into account external constraints from practical requirements.

Fast and efficient automatic channel allocation in cellular radio networks

In this paper, a fully automated frequency planning tool is described, using integer linear programming as a basic building block. The algorithm itself is very versatile, and able to cope with a variety of demands. It aims at satisfying all requirements as well as minimizing the total sum of interference probabilities, regarding compatibility, coherence bandwidth and non-supplied cells. Traffic and broadcast control channels are treated under different quality requirements. Practical experience shows that channel designs of highest quality are achieved which clearly outperform those generated by standard planning tools.

Optimum Mirror-HLR Locations to Reduce Signalling Load in Cellular Radio Networks

As a new policy, Mirror Home Location Registers (MHLR) are introduced to avoid expensive signalling traffic of roaming users to a far distant HLR in mobile communication networks. We investigate the question what the optimum location strategy will be. Three basic ingredients are necessary to tackle this problem: a realistic, but tractable, mobility model, a precise description of signalling costs, and an optimization method to solve the complicated minimization problems.

MOBILITY MODELING IN CELLULAR RADIO NETWORKS, PRODUCT FORM SOLUTIONS AND BLOCKING

In this paper, we introduce a Markovian traffic model for cellular radio networks. The mobility of users is characterized by six parameters per cell which can be estimated from data available in the mobile switching centers. It is shown that the model is equivalent to a Jackson network with accordingly chosen parameters. The product form solution of the corresponding steady state distribution is explicitly determined. Taking advantage of the block structure of the routing matrix, the throughput of the network can be calculated by inverting a (in general sparsly occupied) matrix of order equal to the number of cells. As an important issue, blocking under fixed channel assignment is considered. Necessary and sufficient conditions on the parameters of the network are given ensure reversibility and hence product form of the equilibrium distribution. Furthermore, product form solutions are characterized without assuming reversibilty.