Subproject Goals:
One way to significantly increase the capacity of the third-generation mobile communications systems is to employ adaptive antenna array technologies together with sophisticated signal processing algorithms. Therefore, in this project work we have concentrated on the development of efficient algorithms and methods for tracking Direction-of-Arrival (DOA) information of targets. The methods for the mobile user tracking systems should provide fast tracking capability, low parameter estimation error and furthermore, its hardware realization should be of low complexity. The DOA estimation of mobile users in a stationary signal scenario can be dealt with in a more straightforward way. Therefore, the main focus is evidently on those problems that arise in non-stationary channels where efficient adaptive parameter estimation schemes are required.
Publication [1]:
In this licentiate thesis the main focus was directed towards the development of adaptive tracking algorithms for DOA estimation of mobile users especially in non-stationary signal scenarios. We concentrated on developing fast and realizable algorithms for mobile user tracking systems.
Publication [4]:
In this paper for the user tracking application we develop a step by step adaptation method for tracking the parameter vector in the noise subspace. Also, we develop the control strategy for the noise subspace roots eliminating the problems with the spurious roots. The performance comparison of the developed user tracking system will be investigated in terms of the tracking capability. As the performance criterion, the mean Direction of Arrival (DOA) error will be invoked in the stationary and non stationary signal scenarios. The simulation results confirm that the proposed noise subspace approach can achieve similar tracking performance as the signal subspace approach in terms of the convergence speed and the final misadjustment level.
Publication [5]:
In this paper, we construct the user tracking system by employing an efficient Conjugate Gradient (CG) method based on a step-by-step adaptation scheme. Furthermore, the paper investigates the tracking capability and the computational complexity issues of the proposed system. The simulation results confirm that the proposed CG method achieves better tracking performance than gradient methods both in the stationary and non-stationary signal scenario.
Publication [6]:
This paper investigates the spatial and temporal correlation by measurements of an 8-element adaptive antenna array. The channel measurement data is gathered at a 2.154 GHz range outdoor radio channel. The measurement analysis is divided into three different categories: Investigation of spatial correlation between antenna elements at the base station (BS), spatial correlation of different mobile station (MS) locations and temporal correlation of the different multipath components. Also the differences in the correlation coefficient functions by using the complex-valued taps instead of the magnitude-valued taps are studied at the BS. The measurement analysis reveals that signals strongly correlate in the nearby BS antenna elements. However, at the different MS locations uncorrelated signals can be received when the physical separation is larger than half a wavelength. The multipath components in the impulse response profile become temporally uncorrelated after the excess delay values of 50 ns. measurement results.
Publication [7]:
In this paper we propose a fast multi-user tracking system based on the spatial domain beamforming concept. The simulation results show that the proposed tracking system reacts fast and gives small tracking errors.
Publication [8]:
In future telecommunication systems, one of the most important ways to increase system capacity is to use adaptive antennas. They enable reception and transmission using narrow beams which drastically reduce interference for other users. The problem with the conventional adaptive tracking algorithms is that the adaptation performance is dictated by the choice of the convergence parameter or step size. In this paper we employ a multi-target tracking method and modify its tracking performance by adaptive step size. The simulation results show that the proposed adaptive control of convergence parameter gives fast convergence and small misadjustment errors, which cannot be combined by using fixed step size.
[9] Petri T. Karttunen, Timo I. Laakso and Jorma Lilleberg, "Adaptive Step Size Method for User Tracking in Mobile Communication System," Proceedings of the Finnish Signal Processing Symposium (FINSIG'97), pp. 6-10, Pori, May 22, 1997. (not available in the electronic format)
[10] Petri Karttunen, Comparison of Direction of Arrival and Beamforming Methods. Master thesis, Helsinki University of Technology, Finland, January 1997. (not available in the electronic format)
[11] Petri T. Karttunen, Seppo J. Ovaska, and Timo I. Laakso, "Comparison of Direction of Arrival Estimation Methods: a Case Study," Proceedings of the IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 223-227, Espoo, Finland, September 24-27, 1996. (not available in the electronic format)