Publications 2010

Academic theses (1)

K. Aho, “Enhancing System Level Performance of Third Generation Cellular Networks through VoIP and MBMS Services“, Ph.D. Thesis, ISBN 978-951-39-4143-7, University of Jyväskylä, 2010.

The purpose of this thesis is to address variety of performance enhancements and configurations in terms of 3G/3.5G cellular networks. Multimedia Broadcast Multicast Service (MBMS) and Voice over IP (VoIP) are used to benchmark different features as they are undeniably key concepts also in the wireless cellular networks and thus securing their performance can be considered as critical.

From a practical perspective, wireless networks set a very strict environment for different services through additional delays, packet loss, jitter, corruption and so forth. This thesis addresses those challenges by evaluating variety of diversity options, mobility performance aspects and robustness, battery saving opportunities, interference coordination and finally applicability of dual carrier.

Studies are conducted with the help of time driven cellular system simulators where, e.g., fading, propagation and radio management functionalities are explicitly taken into account.

Journal articles (1)

K. Aho, T. Henttonen, J. Puttonen, L. Dalsgaard, and T. Ristaniemi, “User Equipment Energy Efficiency versus LTE Network Performance“, International Journal on Advances in Telecommunications, vol 3, no 3&4, 2010.

The purpose of this article is to analyze the trade-off conditions between battery saving opportunities at the user terminal and Long Term Evolution network performance. To achieve the goal Voice over IP with discontinuous reception and a vast amount of different settings, including on duration, inactivity and discontinuous reception cycle timers, have been studied.

An adaptive discontinuous reception with synchronizing the on duration time with the Voice over IP packet arrival has been proposed to minimize the delays caused by discontinuous reception. In addition, a channel quality indicator preamble time has been introduced to enable channel quality indicator update prior the on duration period.

The quality of service and battery saving opportunities have been evaluated with a dynamic system simulator enabling detailed simulation of multiple users and cells with realistic assumptions. It can be concluded that high battery saving, i.e. increased talk-time opportunities, can be achieved without compromising the performance when discontinuous reception is properly adapted.

Adaptive discontinuous reception and channel quality indicator preamble can effectively mitigate the capacity loss when more stricter DRX settings enabling higher energy efficiency at the terminal are applied.

Conference articles (17)

Henrik Martikainen, Olli Alanen, Vesa Hytönen and Alexander Sayenko, “Handover performance in the IEEE 802.16 mobile networks“, SIMUTools ’10: Proceedings of the 3rd International ICST Conference on Simulation Tools and Techniques, Malaga, Spain, March 16-18, 2010.

The IEEE 802.16 standard provides a full mobility support for stations moving across cell borders. In addition, the WiMAX Forum Network Working Group defines a set of procedures to support handovers in the mobile access network.

One of the main characteristics of mobility support is fully controlled and optimized handover (HO), in which a mobile station (MS) migrates from the air interface of one base station (BS) to another one. It is vital to keep the BS transition phase as short as possible to decrease delays and data loss, which is especially crucial for real-time applications, such as VoIP.

In this paper we analyze ASN-anchored mobility performance and provide advisable handover related parameters. The obtained results show that it is reasonable to adapt the handover initiation functionality to the environment where the network is deployed.

K. Aho, T. Henttonen, J. Puttonen and T. Ristaniemi, “Trade-off Between Increased Talk-time and LTE Performance“, Proc. of The Ninth International Conference on Networks, Menuires, The Three Valleys, French Alps, France, April 11-16, 2010.

The purpose of this paper is to analyze the trade-off conditions between battery saving opportunities and long term evolution network performance.

To achieve this goal, voice over IP with discontinuous reception is studied. Analysis is conducted with vast amount of different settings, including on duration, inactivity and discontinuous reception cycle timers.

The quality of service and battery saving opportunities with discontinuous reception are evaluated with a dynamic system simulator which enables detailed simulation of multiple users and cells with realistic assumptions.

This paper indicates high battery saving, i.e., increased talk-time opportunities without compromising the performance when discontinuous reception is properly adapted.

O. Alanen, H. Martikainen and A. Sayenko, “Analysis of the Non-Transparent In-Band Relays in the IEEE 802.16 Multi-Hop System“, Proc. of Wireless Communications and Networking Conference (WCNC), Sydney, Australia, April 18-21, 2010.

This paper presents extensive dynamic simulations of the non-transparent in-band relays working in the distributed scheduling mode.

The simulation results show that in-band relays can improve noticeably the spectral efficiency without acquiring an additional radio spectrum. Also, packet transmission delays become smaller.

An important outcome of the dynamic simulations is that it is very crucial to choose a correct relay zone size where the base station and relay nodes exchange data. Otherwise, throughput fairness of the whole system declines. It indicates an importance of the relay zone size adjustment algorithm that the base station must run.

K. Aho, T. Henttonen, J. Puttonen and L. Dalsgaard, “Channel Quality Indicator Preamble for Discontinuous Reception“, Proc of the 71st IEEE Vehicular Technology Conference, Taipei, Taiwan, May 16-19, 2010.

This paper proposes a potential enhancement for Discontinuous Reception (DRX) operation in Long Term Evolution (LTE) networks. In Third Generation Partnership Project’s (3GPP’s) Release 8 it is specified that User Equipment (UE) may be configured with DRX which controls the UE’s Physical Downlink Control Channel (PDCCH) monitoring activity.

By allowing discontinuous monitoring of PDCCH the UE can switch its receiver circuitry on and off for battery saving purposes. However, if UE turns its receiver circuitry off it is not capable to neither perform nor send any Channel Quality Indicator (CQI) measurements to the network prior to ‘on-duration’ (i.e., activity) period. This means that the Evolved Node B (e- Node B) might not have accurate CQI information and the scheduling and resource allocation could be based on outdated CQI information.

To avoid reduced performance caused by the out-of-date information, this paper evaluates a scheme where a CQI preamble period is introduced prior to the actual ‘on duration’ time. During the preamble period UE measures the CQI and sends the measurement result to the e-Node B.

The performance of the scheme is evaluated together with Voice over IP (VoIP) service. Used tool is a dynamic system level simulator which enables detailed simulation of users in multiple cells with realistic call generation, propagation, fading and mobility models. In addition to VoIP performance the UE power consumption is also evaluated with a simple model.

This paper concludes that the preamble scheme can lead to improved performance in terms of VoIP capacity, and that the improvements can be achieved with acceptable trade-off in terms of battery saving opportunities.

J. Kurjenniemi, O. Alanen, T. Henttonen and J. Kaikkonen, “Inter-Frequency Re-Selection for CSG Cell Interference Avoidance in LTE Network”, Proc of the 71st IEEE Vehicular Technology Conference, Taipei, Taiwan, May 16-19, 2010.

In 3GPP Rel’8 access to a Home eNodeB may be restricted to only UEs belonging to a Closed Subscriber Group (CSG).

These cells are called CSG cells and a UE with CSG subscription would have an Allowed CSG List containing CSG Identities associated with the CSG cells on which the UE is allowed access. This however, can be problematic for the users located near the CSG cells, but who are not allowed to access them.

The interference caused by the CSG cell can be devastating if the UE is connected to a macro cell using the same frequency. Some solutions for these interference problems have been proposed in 3GPP standardization and in this study we have evaluated the performance of different options for handling the interference issues related to mixed carrier CSG deployments.

The proposals utilize different details of the LTE re-selection algorithm and suggestion on the best solution is also given.

F. Laakso, K. Aho, T. Chapman and T. Ristaniemi, “Applicability of Interference Coordination in Highly Loaded HSUPA Network”, Proc of the 71st IEEE Vehicular Technology Conference, Taipei, Taiwan, May 16-19, 2010.

This paper evaluates the performance of highly loaded High Speed Uplink Packet Access (HSUPA) network with and without network wide static Interference Coordination (IC).

IC alternates the priorities for user transmission periods throughout the network to achieve reduced interference levels and higher performance. A large variety of combinations including, e.g., different schedulers, cell center/edge user definitions (user splits) and interference targets are investigated in this paper.

Performance is analyzed using a quasi-static system level simulator which is also used to support Third Generation Partnership Project (3GPP) standardization work. The simulator contains detailed and commonly accepted models, for instance, for channel profiles, fading and propagation.

The study indicated that IC can bring gain in certain scenarios. However, the gain comes at the expense of fairness leading to users that already have high throughput benefiting from the situation. Moreover, it was shown that the major part of the gain comes from splitting users to different groups and scheduling these groups without any network wide interference coordination.

T. Nihtilä and V. Haikola, “HSDPA Performance with Dual Stream MIMO in a Combined Macro-Femto Cell Network”, Proc of the 71st IEEE Vehicular Technology Conference, Taipei, Taiwan, May 16-19, 2010.

3rd Generation Partnership Project (3GPP) responsible of the standardization of 3G systems selected dual stream Transmit Antenna Array (D-TxAA) as the Multiple Input – Multiple Output (MIMO) scheme for High Speed Downlink Packet Access (HSDPA) in 3GPP specification Release 7. MIMO doubles the theoretical peak data rate of HSDPA from 14.4 Mbps to 28.8 Mbps.

However, successful reception of dual stream MIMO transmissions requires good signal conditions. Very high signal to noise ratios can be achieved with the use of femto base stations in small isolated areas with insufficient or no macro cell coverage.

This paper studies the effect of D-TxAA concept in a combined single frequency macro and femto cell scenario with Linear Minimum Mean Squared Error (LMMSE) chip-level equalizer receivers used at user entities (UE).

The impact of receivers employing MIMO transmission mode is analyzed as a function of indoor user penetration using fully dynamic system level simulations.

J. Turkka, “A Study of G-Distribution Statistical Properties under Fractional Network Loading”, Proc of the 71st IEEE Vehicular Technology Conference, Taipei, Taiwan, May 16-19, 2010.

This paper shows how statistical properties of the downlink interference vary along a fractional network loading in case of the 3GPP Long Term Evolution (LTE) system in highly interference limited scenario, where radio resources are shared in time and frequency domain with proportional fair (PF) scheduler.

Results show at least 15 dB variations in average signal-to-interference (SINR) ratios for scheduled users under different loading conditions. Moreover, the paper shows how this knowledge can be used in network dimensioning process and link budget calculations.

The results revealed clear SINR performance degrading for system loadings between 70% and 90% which could indicate that radio resource management (RRM) parameters can be optimized even more based on the current system loading and service type.

J. Puttonen, I. Repo, K. Aho, T. Nihtilä, J. Kurjenniemi, T. Henttonen, M. Moisio and K. Chang, “Non-Regular Network Performance Comparison between HSDPA and LTE”, Proc. of the IEEE International Symposium on Wireless Pervasive Computing, Modena, Italy, May 5-7, 2010.

In this paper we study and benchmark the performance of 3rd Generation Partnership Project (3GPP) High Speed Downlink Packet Access (HSDPA) and 3GPP Long Term Evolution (LTE) Downlink with constant bit rate type traffic.

In addition a non-regular simulation scenario is considered using realistic propagation data and base station positions related to Tokyo city downtown area.

The results show that LTE Release 8 outperforms HSDPA Release 8 in terms of spectral efficiency and user throughput. With 8 UEs per cell and LTE MIMO about 90% of UEs are fully satisfied, while about 45% of the UEs are fully satisfied with HSDPA MIMO.

This results also about 30% gain in spectral efficiency even through with LTE the network is running half empty due to uneven UE distribution in non-regular network with variable cell sizes.

N. Kolehmainen, J. Puttonen, T. Henttonen and J. Kaikkonen, “Performance of Idle Mode Mobility State Detection Schemes in Evolved UTRAN”, Proc. of the IEEE International Symposium on Wireless Pervasive Computing (ISWPC), Modena, Italy, May 5-7, 2010.

In this paper we study the performance of idle mode mobility state detection schemes targeted for 3rd Generation Partnership Project (3GPP) Evolved UTRAN.

The purpose is to compare the mobility state detection scheme specified in 3GPP Release 8 and a dual trigger scheme for 3GPP Release 9 using different User Equipment (UE) velocity conditions and cell reselection triggering sensitivity levels.

A single set of cell reselection parameters may not be optimal throughout the E-UTRAN velocity range, thus both schemes provide in a way a means of using UE velocity dependent cell reselection parameters.

According to the results, both schemes provide gain over a single set of cell reselection parameters. Dual trigger provides gain over Release 8 mobility state detection scheme in terms of time spent in the best cell and downlink SINR. However, this comes with a small increase in power consumption due to increased amount of cell reselections per UE.

K. Aho, I. Repo, J. Puttonen, T. Henttonen, M. Moisio, J. Kurjenniemi and K. Chang, “Benchmarking of VoIP over HSDPA and LTE Performance with Realistic Network Data”, Proc. of the IEEE International Symposium on Wireless Pervasive Computing, Modena, Italy, May 5-7, 2010.

The purpose of this paper is benchmark the performance of voice over IP in high speed downlink packet access and in long term evolution networks.

Benchmarking is conducted in homogeneous and heterogeneous scenario layouts assuming realistic propagation data generated over Tokyo map. Tools used in this paper are two fully dynamic time driven system simulators which have been used to support 3GPP standardization work.

This benchmarking study provides insights to what e.g. different radio access technologies, scheduling mechanisms and receivers do for the performance of voice over IP. This paper indicated in various scenarios that long term evolution can offer higher performance for voice over IP than high speed packet access.

I. Repo, K. Aho, S. Hakola, T. Chapman and F. Laakso, “Enhancing HSUPA System Level Performance with Dual Carrier Capability”, Proc. of the IEEE International Symposium on Wireless Pervasive Computing, Modena, Italy, May 5-7, 2010.

The purpose of this paper is to analyze how dual carrier capability can enhance High Speed Uplink Packet Access performance in comparison to using only single carrier.

Dual carrier operation gives the User Equipment the possibility to transmit simultaneously using two 5 MHz bands, theoretically doubling the peak data rates and user throughput.

The analysis is conducted with a system level simulation tool. This paper first indicates with single carrier simulations that, especially in small cells, terminals have spare power available for dual carrier operation.

These observations are verified with dual carrier simulations by showing that the burst throughput can be practically doubled. In the larger cells only the users in good position can fully benefit from using dual carrier.

J. Puttonen, J. Turkka, O. Alanen and J. Kurjenniemi, “Coverage Optimization for Minimization of Drive Tests in LTE with Extended RLF Reporting”, Proc. of the 21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Istanbul, Turkey, September 26-29, 2010.

In this article we have studied the coverage optimization for 3G Long Term Evolution (LTE) according to Minimization of Drive Tests (MDT) work item description in Third Generation Partnership Project (3GPP).

The target for the MDT work item is to define a set of measurements and measurement reporting procedures, so that operators are able to collect measurement data from users and thereby reducing need for manual drive tests. The main focus of MDT is coverage optimization.

We propose an extended Radio Link Failure (RLF) reporting for both coverage and mobility optimization use cases for MDT. In this paper the MDT studies and especially the benefits of extended RLF reporting and classification are analyzed by means of dynamic system level simulations.

The RLFs are classified into three categories based on the content in extended RLF reports: coverage, handover parameterization and interference problem. It can be concluded that the coverage as well as other problems may be identified with quite high probability with only a minimal standardization effort.

J. Puttonen, J. Kurjenniemi and O. Alanen, “Radio Problem Detection Assisted Rescue Handover for LTE”, Proc. of the 21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Istanbul, Turkey, September 26-29, 2010.

In this paper we propose a radio problem detection based rescue handover for 3G Long Term Evolution (LTE).

The radio problem detection based handover algorithm takes advantage of already existing Radio Link Failure (RLF) detection mechanism specified in 3GPP for LTE. In coverage limited scenarios as well as challenging interference and mobility conditions, the event triggered handover measurement report may not be even sent to Evolved NodeB at the time of RLF.

In proposed algorithm UE shall monitor the downlink quality based on the cell-specific reference signal in order to detect the downlink radio link quality of the serving cell. In case of a detected radio link problem handover process is initiated to a better cell.

The proposed handover algorithm is compared to the default UE assisted hard handover process by means of fully dynamic system level simulations.

Based on the studies it can be concluded that the radio problem detection assisted handover algorithm decreases the amount of RLFs thereby improving the handover and system performance. Especially the RLFs that occur before the handover process is even started are basically non-existent.

F. Laakso, K. Aho, I. Repo and T. Chapman, “Extended HSUPA Coverage and Enhanced Battery Saving Opportunities with Multiple TTI Lengths”, Proc. of the 21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Istanbul, Turkey, September 26-29, 2010.

3GPP has specified that terminals can be configured to use either 2 or 10 ms transmission time interval in high speed uplink packet access systems.

The purpose of this paper is to evaluate the benefit of exploiting a mixture of both of the transmissions time intervals within a cell instead of only one. The study is quantified by means of studying the achievable coverage of voice over IP and possible battery saving benefits.

The analysis is conducted with a system level simulator modeling network and terminal behavior in detail. The paper indicates that utilizing a mixture of both transmission time intervals can extend coverage whilst providing enhanced battery saving opportunities.

J. Turkka and A. Lobinger, “Non-regular Layout for Cellular Network System Simulations”, Proc. of the 21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Istanbul, Turkey, September 26-29, 2010.

This paper defines a synthetic non-regular Springwald network layout which is easy to take into use in cellular network system simulations.

The performance of the non-regular layout was compared with two regular 3GPP simulation scenarios. The benefit of the non-regular layout is that it reflects better the live network deployments and therefore results in more realistic benchmarking metrics.

The results shows that the Springwald layout provides a simulation environment where the system level performance is comparable with the reference scenarios, however, with some additional features of the non-regular effects.