Publications 2015

Academic Theses (2)

V. Hytönen, “Enhancing the Performance of HSDPA Communication with Multipoint Transmission Techniques“, Ph.D. Thesis, ISBN 978-951-39-6434-4, University of Jyväskylä, 2015.

The evolution of mobile phones, tablets and other mobile communication de vices has led to a significant increase in the amount of data delivered over mobile networks. In order to satisfy the climbing data rate demands of customers, existing mobile broadband networks are being expanded with new features that allow ubiquitous and consistent networking experience.

This research presents three multipoint transmission techniques for Wideband Code Division Multiple Access (WCDMA) based High-Speed Downlink Packet Access (HSDPA) communication protocol. Multiflow, High-Speed Single-Frequency Network (HS-SFN) and Multipoint-to-Point Single-Frequency Network (M2P-SFN) enable transmission of user-dedicated data from several cells, with the objective to improve performance, especially in cell edges where the signal quality is usually weak.

The main difference between the concepts is the way cell-specific scrambling codes are configured in the network, which eventually determines how flow control, physical layer resource allocation and signal formation and reception will be con ducted. The performance of each technique is separately evaluated with system level simulations. In addition, the dissertation discusses issues with regard to interference conditions and mobility control that may originate from multipoint transmissions.

F. Chernogorov, “Advanced Performance Monitoring for Self-Healing Cellular Mobile Networks“, Ph.D. Thesis, ISBN 978-951-39-6235-7, University of Jyväskylä, 2015.

This dissertation is devoted to development and validation of advanced performance monitoring system for existing and future cellular mobile networks. Knowledge mining techniques are employed for analysis of user speciﬁc logs, collected with Minimization of Drive Tests (MDT) functionality.

Ever increasing quality requirements, expansion of the mobile networks and their extending heterogeneity, call for effective automatic means of performance monitoring. Nowadays, network operation is mostly controlled manually through aggregated key performance indicators and statistical proﬁles. These methods are are not able to fully address the dynamism and complexity of modern mobile networks.

Self-organizing networks introduce automation to the most important network functions, but the opportunity of processing large arrays of user reported performance data is underutilized. Advanced performance monitoring system developed in the presented research considers both numerical and sequential properties of the MDT data for detection of faults. Network malfunctions analyzed in this study are sleeping cells in either physical or medium access layer.

A full data mining cycle is employed for identiﬁcation of problematic regions in the network. Pre-processing with statistical normalization and sliding window methods, both linear and non-linear transformation and dimensionality reduction algorithms, together with clustering and classiﬁcation methods are used in the discussed research. Several post-processing and detection quality evaluation methods are proposed and applied.

The developed system is capable of fast and accurate detection of non- trivial network dysfunctions and is suitable for future mobile networks, even in combination with cognitive self-healing. As a result, operation of modern mobile networks would become more robust, increasing quality of service and user experience.

Journal articles (3)

J. Turkka, P. Kela and M. Costa, “Borderless Mobility in 5G Outdoor Ultra-Dense Networks“, IEEE Access, 2015.

This paper considers borderless 5G ultra-dense networks (UDNs). In particular, a novel scheduling algorithm is proposed that achieves a more uniform distribution of user-throughput than that of the state-of-the-art maximum-throughput (MT) schedulers.

The proposed scheduling algorithm also takes the coherence time of the channel into account as well as the impact to the acquired channel state information. A novel radio frame structure that is appropriate for achieving a 1-ms round trip time latency is also proposed. Such a low latency allows one to employ multiuser as well as cooperative multiple input multiple output schemes for mobile users.

An evaluation of matched-filter and zero-forcing precoding for mobile users in UDNs is included. The performance of the proposed 5G UDN concept is assessed using a system-level simulator. Extensive numerical results show that the proposed borderless scheduling concept achieves ~77% higher median user-throughput than that of the MT scheduler at the cost of ~17% lower area-throughput. Such results are obtained for a high density of mobile users at velocities of ~50 km/h.

J. Zhang, M.Z.H. Bhuiyan and E.S. Lohan, “Analysis of Galieo E1 Receiver Performance with a Power-controlled Front-end“, European Journal of Navigation, 2015.

Power consumption is an important figure of merit for Global Navigation Satellite Systems (GNSS) receiver design. Low power consumption is essential in mass-market GNSS receivers which depend upon a battery for a power source.

To achieve the reduction in the power consumption, the front-end of the receiver can be powered down for a fraction of time, but in a continuous manner so that the baseband can still keep track of the signals. This method can reduce the average power while still continuously tracking. However, its effects on the receiver performance have not been studied much in the literature.

In this article, the authors analyze the receiver performance in terms of detection probability, code tracking error and bit error rate with different power switching time intervals. The analysis is performed both from the theoretical point of view and via signal simulations.

Our results show that the performance of a power-controlled GNSS receiver is meaningfully degraded when power-blank-ing is applied. According to the obtained results, there is a loss of around 3 dB in terms of Carrier-to-Noise-density ratio (C/N0) of the received signal in both acquisition and tracking while compared with the traditional receiver without having any power reduction.

F. Chernogorov, S. Chernov, K. Brigatti and T. Ristaniemi, “Sequence-based detection of sleeping cell failures in mobile networks“, Springer Wireless Networks, 2015.

This article presents an automatic malfunction detection framework based on data mining approach to analysis of network event sequences. The considered environment is Long Term Evolution (LTE) for Universal Mobile Telecommunication System (UMTS) with sleeping cell caused by random access channel failure.

Sleeping cell problem means unavailability of network service without triggered alarm. The proposed detection framework uses N-gram analysis for identification of abnormal behavior in sequences of network events. These events are collected with Minimization of Drive Tests (MDT) functionality standardized in LTE.

Further processing applies dimensionality reduction, anomaly detection with k-nearest neighbor, cross-validation, post-processing techniques and efficiency evaluation. Different anomaly detection approaches proposed in this paper are compared against each other with both classic data mining metrics, such as F-score and receiver operating characteristic curves, and a newly proposed heuristic approach.

Achieved results demonstrate that the suggested method can be used in modern performance monitoring systems for reliable, timely and automatic detection of random access channel sleeping cells.

Conference articles (12)

J. Puttonen, S. Rantanen, F. Laakso and J. Kurjenniemi, “Satellite Network Simulator 3“, Workshop on Simulation for European Space Programmes (SESP), Noordwijk, Netherlands, March 24-26, 2015.

In this article, Satellite Network Simulator 3 (SNS3) is presented. SNS3 focuses on geostationary multi-spot beam satellite networks and DVB-RCS2 and DVB-S2 protocol stacks.

SNS3 has been developed within ESA ARTES 5.1 project to function, e.g., as a common platform for ESA activities. It is intended to reduce consecutive simulation software development efforts. SNS3 may also run in real-time emulation mode, enabling both the usage of pure simulations and real-time emulations with the same implementation.

J. Turkka, P. Kela, M. Costa, T. Hiltunen, M. Hronec, J. Salmi, K. Leppänen, “A Novel Radio Frame Structure for 5G Dense Outdoor Radio Access Networks”, Proc. of the Vehicular Technology Conference (VTC Spring), 2015 IEEE, Glasgow, Scotland, 11–14 May, 2015.

This paper proposes a novel frame structure for the radio access interface of the next generation of mobile networks. The proposed frame structure has been designed to support multiuser spatial multiplexing, short latencies on the radio access interface, as well as mobility and small packet transmissions. The focus is on ultra dense small cell networks deployed in outdoor environments.

This paper also highlights the various prospects and constraints of the proposed dense outdoor system in comparison with alternative system designs. Numerical results are included and a comparison to the Long Term Evolution (LTE) system is provided.

Results show that the proposed radio frame structure leads to an improvement of the area spectral efficiency by a factor of ≈ 2.4 as well as a reduction of the average air interface latency by a factor of 5, thus remaining shorter than 1 millisecond.

F. Chernogorov, I. Repo, V. Räisänen, T. Nihtilä and J. Kurjenniemi, “Cognitive Self-Healing System for Future Mobile Networks“, Proc. of the International Wireless Communications & Mobile Computing Conference (IWCMC 2015), Dubrovnik, Croatia, August 24-27, 2015.

This paper introduces a framework and implementation of a cognitive self-healing system for fault detection and compensation in future mobile networks.

Performance monitoring for failure identification is based on anomaly analysis, which is a combination of the nearest neighbor anomaly scoring and statistical profiling. Case-based reasoning algorithm is used for cognitive self-healing of the detected faulty cells. Validation environment is Long Term Evolution (LTE) mobile system simulated with Network Simulator 3 (ns-3).

Results demonstrate that cognitive approach is efficient for compensation of cell outages and is capable to improve network coverage. Anomaly analysis can be used for identification of network failures, and automation of performance management.

Introduction of data mining and cognition to the future mobile networks, e.g. 5^th Generation (5G), is especially important as it allows to meet the strict requirements for robustness and enhanced performance.

N. Kolehmainen, S. Hailu, P. Lunden, E. Virtej, O. Tirkkonen, C. Wijting, “DRX-Aware Power and Delay Optimized Scheduler for Bursty Traffic Transmission“, Proc. of the Vehicular Technology Conference (VTC Spring), 2015 IEEE, Glasgow, Scotland, 11–14 May, 2015.

Discontinuous Reception (DRX) is one of the mechanisms to reduce User Equipment (UE) power consumption in Long Term Evolution (LTE) systems. In this work, a DRX-aware power and delay optimized scheduling scheme is proposed for downlink transmission of bursty packet data traffic.

The UE power consumption is minimized by reducing the time that a UE spends receiving data. This is achieved by predominantly scheduling a single UE at a time. The mean packet burst end-to-end delay is minimized by giving priority to packet bursts with relatively small transmission time requirement when compared to a weighted value of the estimated remaining transmission time of the predominantly scheduled packet burst.

The weight parameter can be adjusted according to power-delay trade off preference. The DRX timers are further taken into account to avoid wake up delays, by keeping some of the waiting UEs active before the transmission to the currently scheduled packet burst ends.

Based on LTE system level simulation results, the UE power consumption could be significantly reduced while improving the mean delay using the scheduler, comparing to conventional proportional fair scheduler.

J. Puttonen, S. Rantanen, F. Laakso, B. Herman, J. Kurjenniemi, J. Suomalainen, M. Majanen, J. Vehkaperä and J. Mäkelä, “Multicast Security Framework for Multi-spot Beam Satellite Network“, Proc. of the 21st Ka and Broadband Communications Conference, Bologna, Italy, October 12-14, 2015.

This article presents an overview of a secure multicast framework as well as a secure multicast system demonstrator used for end-to-end performance assessment of secure multicast service delivery over satellite.

The security framework relies on IP security with multicast extensions and Group Domain of Interpretation (GDOI) multicast key management.

The framework addresses challenges in the delivery of secure multicast services on top of multi-spot beam satellite networks by proposing several enhancements to overcome the bottlenecks.

T. Hiltunen, R. Mondal, J. Turkka and T. Ristaniemi, “Generic Architecture for Minimizing Drive Tests in Heterogeneous Networks“, Proc. of the Vehicular Technology Conference (VTC Fall), 2015 IEEE, Boston, September, 2015.

This paper proposes a generic measurement architecture for automating the collection of User Equipment (UE) radio measurements to minimize the need of manual drive-tests in heterogeneous small cell networks consisting of LTE (Long Term Evolution) and WLAN (Wireless Local Area Network) access nodes. The proposed architecture relies on Minimization of Drive Tests (MDT) functionality specified in Third Generation Partnership Project (3GPP) and consists of user plane solution with trace assistance.

In the proposed solution, trace assistance information, which is signaled to UE as part of MDT configuration, is provided to UE WLAN measurement unit allowing exchanging and correlating measurements later between LTE and WLAN network management systems.In addition, the prospects and the constraints of the architecture are discussed highlighting the importance in various operator use cases.

Finally, the RF fingerprint positioning performance improvement of the proposed concept is analyzed by means of field measurements.

J. Turkka, R. Mondal and T. Ristaniemi, “An Efficient Cluster-based Outdoor User positioning using LTE and WLAN Signal Strengths“, Proc. of the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), Hong Kong, August, 2015.

In this paper we propose a novel cluster-based RF fingerprinting method for outdoor user-equipment (UE) positioning using both LTE and WLAN signals. It uses a simple cost effective agglomerative hierarchical clustering with Davies-Bouldin criterion to select the optimal cluster number.

The positioning method does not require training signature formation prior to UE position estimation phase. It is capable of reducing the search space for clustering operation by using LTE cell-ID searching criteria. This enables the method to estimate UE positioning in short time with less computational expense.

To validate the cluster-based positioning real-time field measurements were collected using readily available cellular mobile handset equipped with Nemo Handy software. Output results of the proposed method were compared with a single grid-cell layout based RF fingerprinting method. Simulation results show that if a single LTE and six WLAN signal strengths are used then the proposed method can improve positioning accuracy of 35% over the grid-based RF fingerprinting.

T. Hiltunen, J.Turkka, R. Mondal and T. Ristaniemi, “Performance Evaluation of LTE Radio Fingerprint Positioning with Timing Advancing“, Accepted to the 10th International Conference on Information, Communications and Signal Processing (ICICS 2015), Singapore, December, 2015.

This paper studies the feasibility of using Timing Advancing (TA) information together with radio fingerprints for improving position estimation of Minimization of Drive Test (MDT) trace record measurements.

Performance evaluation is carried out by analyzing field measurements from commercially deployed LTE (Long Term Evolution) networks operating on 800 MHz, 1800 MHz and 2600 MHz frequency bands. Positioning performance is analyzed with grid-based fingerprints consisting of LTE radio and TA measurements.

Performance results indicate that the radio frequency fingerprint containing both LTE Reference Signal Received Power (RSRP) and TA measurements provides a higher positioning accuracy than the fingerprint containing only RSRP information. Moreover, the weighting of TA measurements was studied in order to obtain the best positioning accuracy. Weight 20 was found to be optimal in the studied scenario resulting in 20% reduction in positioning error.

T. Ristaniemi, R. Mondal and J. Turkka, “Cluster-Based RF Fingerprint Positioning Using LTE and WLAN Outdoor Signals“, Accepted to the 10th International Conference on Information, Communications and Signal Processing (ICICS 2015), Singapore, December, 2015.

In this paper we evaluate user-equipment (UE) positioning performance of three cluster-based RF fingerprinting methods using LTE and WLAN signals.

Real-life LTE and WLAN data were collected for the evaluation purpose using consumer cellular-mobile handset utilizing `Nemo Handy’ drive test software tool. Test results of cluster-based methods were compared to the conventional grid-based RF fingerprinting.

The cluster-based methods do not require grid-cell layout and training signature formation as compared to the grid-based method. They utilize LTE cell-ID searching technique to reduce the search space for clustering operation. Thus UE position estimation is done in short time with less computational cost.

Among the cluster-based methods Agglomerative Hierarchical Cluster based RF fingerprinting provided best positioning accuracy using a single LTE and six WLAN signal strengths. This method showed an improvement of 42.3 % and 39.8 % in the 68th percentile and 95th percentile of positioning error (PE) over the grid-based RF fingerprinting.

D. Petrov, B. Herman, T. Hämäläinen and S. Melnik, “On the System Level Performance of Cellular FBMC-Based Wideband PMR Network“, Proc. Twelves International Symposium on Communication Systems (ISWCS 2015), Brussels, Belgium, August 25-28, 2015.

New physical layer solutions are required for the next generation professional mobile radio (PMR) networks. Filter bank based multi-carrier (FBMC) technique is one of the promising candidates for beyond OFDM 5G wireless communication systems.

This paper presents the simulation framework and models necessary for the study of the FBMC-based networks on the system level. PMR-specific 450 MHz frequency band is considered in the study. Special attention is devoted to the implementation of link-to-system interface model, which is sensitive to FBMC intrinsic interference.

We demonstrate that even with simple one tap equalizer the performance of OFDM and FBMC systems are very close in the same baseline configuration. Moreover, implementation of advanced receivers together with more flexible and efficient spectrum utilization renders FBMC as the superior technology.

D. Petrov, S. Chernov and T. Ristaniemi, “Location Accuracy Impact on Cell Outage Detection in LTE-A Networks“, Proc. of The International Wireless Communications & Mobile Computing Conference (IWCMC 2015), Dubrovnik, Croatia, August 24-28, 2015.

Automated and timely detection of malfunctioning cells in Long-Term Evolution (LTE) networks is of high importance. Sleeping cell is a particular type of cell degradation hardly detectable by traditional network monitoring systems. The recent introduction of Minimization of Drive Test (MDT) functionality enables to collect user-level statistics from regular user devices without expensive and time-consuming drive-test and measurement campaigns.

In this study, data mining techniques are used to process MDT measurements to detect efficiently a sleeping cell. The developed earlier data mining framework is briefly overviewed in the paper. Special attention is devoted to post-processing stage as one of the key elements of the detection scheme.

In practice, location information of collected measurements might contain considerable errors. This factor impacts the precision of malfunctioning cell detection. Therefore several post-processing algorithms are proposed, where location accuracy is taken into account.

The performance of the algorithms is compared based on the results of thorough system-level LTE network simulations. Combined post-processing method shows the best reliability against location errors in terms of Root Mean Squared Error (RMSE) and percent gain.