H. Martikainen, “PHY and MAC Layer Performance Optimization of the IEEE 802.16 System“, Ph.D. Theses, ISBN 978-951-39-4829-0, University of Jyväskylä, 2012.
This thesis concentrates on how to improve the performance of the IEEE 802.16 system in three main areas. The first problem area is system throughput optimization by selecting the optimal MAC PDU size when ARQ is used. A method for selecting the optimal size is proposed and evaluated.
In the second part, various ARQ features are evaluated and also the performance of the ARQ and HARQ error correction methods are evaluated. Finally, the two different frame optimization problems are investigated.
First the three duplexing modes of IEEE 802.16 are compared, namely Time Division Duplexing, Full Frequency Division Duplexing and Half Frequency Division Duplexing. A novel group division algorithm is proposed for H-FDD. Second, the relay mechanism of IEEE 802.16 is presented and its performance evaluated.
The performance evaluation of all presented problems is done by simulations with the WINSE extension which is build on top of the NS-2 network simulator
D. Petrov, “Synthesis and Application of Orthogonal Signal Bases Possessing Enhanced Time-Frequency Localization for Mobile Wireless Networks“, Ph.D. Thesis, ISBN 978-951-39-4000-2, University of Jyväskylä, 2012.
This thesis concentrates on the development and theoretical validation of a framework which can be used on the physical layer of modern and future wireless multi-carrier, in particular OFDM-based, systems. From a practical perspective, mobile networks set a very strict environment for different services, which should be reliably provided even in harsh channel conditions.
Thus, the study addresses several main problems of OFDM technology, such as poor localization of signal basis in the frequency domain and reduced efficiency due to the cyclic prefix utilization. These problems cannot be efficiently solved because of theoretical limitations of the classical WH basis.
The main approach developed in this thesis is the utilization of modified orthogonal signal bases possessing enhanced time-frequency localization. Their practical application requires overcoming several challenges, which are considered and solved in the dissertation.
Z. Chang, and T. Ristaniemi, “Asymmetric Radio Resource Allocation Scheme for OFDMA Wireless Networks with Collaborative Relays,” Springer Wireless Networks, DOI: 10.1007/s11276-012-0490-8, 2012.
This work addresses the radio resource allocation problem for cooperative relay assisted OFDMA wireless network. The relays adopt the decode-and-forward protocol and can cooperatively assist the transmission from source to destination.
Recent works on the subject have mainly considered symmetric source-to-relay and relay-to-destination resource allocations, which limits the achievable gains through relaying.
In this paper we consider the problem of asymmetric radio resource allocation, where the objective is to maximize the system throughput of the source-to-destination link under various constraints.
In particular, we consider optimization of the set of cooperative relays and link asymmetries together with subcarrier and power allocation. We derive theoretical expressions for the solutions and illustrate them through simulations.
The results show clear additional performance gains through asymmetric cooperative scheme compared to the other recently proposed resource allocation schemes.
Z. Chang, and T. Ristaniemi, “Resource Allocation for Cooperative Relay-assisted OFDMA Networks with Imperfect CSI,” Proceedings of the IEEE Military Communication Conference (MILCOM’12), October 29- November 1, 2012, Orlando, FL, USA.
This work addresses the radio resource allocation (RRA) problem for cooperative relay assisted OFDMA wireless networks.
The relays adopt the decode-and-forward protocol and can cooperatively assist the transmission from source to destination. The RRA scheme addresses practical implementation issues of resource allocation in OFDMA networks: the inaccuracy of channel-state information (CSI) available to the source. Instead, the source only knows estimated channel status and distributions of related estimation errors.
The objective is to maximize the system throughput of the source-to-destination link under various constraints. Since the optimization problem is known as NP-hard, we divide the original problem to three subproblems including relay selection, subcarrier and power allocations.
We derive theoretical expressions for the solutions and illustrate them through simulations. Results validate clearly that our proposed RRA algorithm can enhance the performance of system with imperfect CSI compared to the other newly proposed resource allocation schemes.
M.Z. Asghar, S. Hamalainen, and N. Meinke, “Experimental System for Self-Optimization of LTE Networks“, Proceedings of The 15th ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWIM’12), October 21-25, 2012, Paphos, Cyprus.
The aim of this paper is to present an experimental platform developed for 3GPP Long Term Evolution (LTE) networks where the effectiveness of self-optimization algorithms can be tested in a realistic environment. Several Self-organizing networks (SON) use cases are implemented in realistic scenarios.
The system is developed to provide self-optimization functionalities in the framework of Self organizing networks (SON). The experimental system shown is built on top of radio network simulators and commercial network management products.
In this work, different commercial network management products like Radio Network Optimizer, Radio Network Simulator and Operational Subsystem (OSS) Middleware are integrated to provide automatic and efficient SON solutions, thus reducing human effort on the one hand and improving network performance in terms of coverage, capacity and service quality on the other.
The network performance impacts of remote electrical antenna tilt (RET) optimization and transmission power optimization could be shown with the tool. Average cell throughput and per physical resource block (PRB) throughput are shown for constant bit rate (CBR) service before and after optimization. Coverage improvements are seen in improvements in handover (HO) failure statistics. Robustness and convergence time of optimization algorithms are studied.
Mitigation of inter-carrier (ICI) and inter-symbol interference (ISI) in the systems based on Orthogonal Frequency Division Multiplexing (OFDM) has been a popular research topic already for several decades.
Utilisation of signal bases with ameliorated time-frequency (TF) localisation is one of the methods to increase interference robustness. However, this approach results in more complicated signal processing.
In this paper, we theoretically derive and formulate computationally efficient algorithms for modulation of discrete finite-dimensional signals constructed from well-localised bases. These results can be used directly for software implementation. In addition, we present the comparison of computing load for straightforward matrix multiplication, for developed algorithm and for Fast Fourier Transform (FFT) used in OFDM.
This study shows that the number of operations can be significantly reduced allowing signal processing with a great number of sub-carriers and time shifts in a reasonable time.
Fault management is an important part of the operations and maintenance subsystem (OSS) of cellular mobile networks. Perhaps the most important reason is to reduce the number of outages and duration of outages in the network in order to meet the operator’s requirements such as network availability, robustness, coverage and capacity etc.
Increasing complexity of the cellular networks has significant impact on the operations and maintenance of the network. Automation is necessary to protect the operational as well as capital expenses of the cellular network.
The aim of this paper is to present a self-healing framework developed for 3GPP Long Term Evolution (LTE) networks and to provide a platform where the detection and compensation of cell outages are evaluated in realistic environment.
The impact of early fault detection and timely execution of compensation tasks are shown in terms of radio link failures and number of connected users.
Z. Chang, and T Ristaniemi, “Reducing Energy Consumption via Cooperative OFDMA Mobile Clusters,” Proceedings of the 17th IEEE Workshop on Computer-Aided Modeling Analysis and Design of Communication Links and Networks (CAMAD’12), September 17-19, 2012, Barcelona, Spain.
Aggressive techniques induce high energy consumption for the circuits of MTs, which drain the batteries fast and consequently limit mobility. In order to solve such a problem, a scheme called distributed mobile cloud (DMC) is foreseen as one of the potential solutions to reduce energy consumption per node in a network.
In this paper we provide a detailed analysis of the energy consumption of a terminal joining the DMC and also analyze the conditions for energy savings opportunities.
Numerical results are also provided to illustrate the analysis and show the potential of significant reduction of the per-node energy consumption in the mobile cloud concept.
J. Puttonen, E. Virtej, I. Keskitalo, E. Malkamäki, “On LTE Performance Trade-off Between Connected and Idle States with Always-on Type Applications“, Proceedings of 23rd IEEE International Symposium on Personal, Indoor and and Mobile Radio Communications (PIMRC), 9-12 September 2012, Sydney, Australia.
In cellular networks it is envisioned an explosion of diverse data applications running in smart phones, which could increase significantly not only user plane but also control plane load in the network.
Smart phones and their always-on applications introduce several challenges: From the network perspective, an increased amount of UEs/applications can increase the signaling load due to frequent state transitions and handover signaling. From the UE perspective, challenges of power consumption are evident, since UE would increasingly be in connected state.
In this article we study the trade-off between releasing the UE into idle state vs. keeping the UE in connected state, in a LTE system. The results indicate that optimum performance can be achieved using UE specific RRC release timer and DRX configurations by taking advantage of traffic characteristics and UE mobility.
F. Laakso, P. Eskelinen, M. Lampinen, “Uplink Weight Signaling for HSUPA Closed Loop Transmit Diversity“, Proceedings of 23rd IEEE International Symposium on Personal, Indoor and and Mobile Radio Communications (PIMRC), 9-12 September 2012, Sydney, Australia.
3GPP is investigating uplink transmit diversity alternatives for High Speed Uplink Packet Access. This paper studies closed loop beamforming transmit diversity where NodeB determines transmit antenna weight vectors and additional feedback is used for signaling the optimal weights to the user equipment.
The used transmit antenna weights are signaled back to the NodeB in order to ensure correct decoding. This approach is benchmarked against the results where the used weights are not signaled back to the NodeB. Performance is analyzed in various conditions on system level against the performance without uplink weight signaling.
The results show that signaling the used weights increases the performance over the case without uplink signaling especially with higher bit error rates. However, uplink weight signaling requires additional signaling bits which may not be justified if weight feedback bit error rates are expected to be low.
Additionally when uplink weight signaling is used, even if the weight signaled in downlink were correctly received, signaling errors can happen in uplink which also will result in incorrect decoding at the NodeB.
F. Laakso, P. Eskelinen, M. Lampinen, “Performance of Absolute and Recursive Feedback Methods with HSUPA Closed Loop Transmit Diversity“, Proceedings of 23rd IEEE International Symposium on Personal, Indoor and and Mobile Radio Communications (PIMRC), 9-12 September 2012, Sydney, Australia.
3GPP is investigating uplink transmit diversity alternatives for High Speed Uplink Packet Access. This paper presents a closed loop beamforming transmit diversity scheme where NodeB determines the transmit antenna weight vectors and feedback is used for signaling the optimal weights to the user equipment.
Two promising feedback method candidates are presented and benchmarked in various conditions on system level against the baseline performance without transmit diversity. In each time slot the absolute feedback method signals the whole weight vector information, while the recursive feedback method signals only a single bit and the weight vector is recursively calculated from multiple bits sent over consecutive time slots.
The results show that both feedback methods are capable of providing gain over the baseline in simulated conditions. However, while the recursive feedback method requires less signaling bits per slot, it is more vulnerable to the effects of weight signaling errors due to the signaling error propagation.
D. Petrov, I. Repo and M. Lampinen, “Performance of Multiflow Aggregation Scheme for HSDPA with Joint Intra-Site Scheduling and in Presence of CQI Imperfections“, Proceedings of the 12th International Conference on Next Generation Wired/Wireless Networking (NEW2AN 2012), August 27 – 29, 2012, St. Petersburg, Russia.
Lately several Single Frequency Dual Cell (SF-DC) techniques for High Speed Downlink Packet Access (HSDPA) were considered in the Third Generation Partnership Project (3GPP), which were aimed to enhance network performance for users at the cell edges.
In this paper we are concentrating on intra-site multiflow aggregation scheme, where User Equipment (UE) can receive two independent transmissions from separate sectors.
Furthermore, this paper focuses on the impact of Channel Quality Indicator (CQI) reporting interval and measurement imperfections on the system performance. Moreover, we present a joint scheduling algorithm, which selects users site-wide instead of independently in each sector.
Simulation results for scenarios mentioned above are presented and analysed in the paper. This study shows that joint scheduling gives some extra gain compared to independent scheduling. In addition, impact of CQI errors and CQI update period are studied.
Z. Chang, O. Alanen, E. H. Ong, J. Kneckt and T. Ristaniemi, “Enhanced Channel Scanning Schemes for Next Generation WLAN system”, Proceedings of the IEEE International Conference on Communication in China (ICCC’12), August 15-17, 2012, Beijing, China.
The IEEE 802.11 standard based Wireless Local Area Networks (WLANs) are widely deployed and have gained greater popularity.
It is anticipated that WLAN will play an important rule in the future wireless communication systems in order to provide several gigabits data rate. However, it has been a challenging problem to support the IEEE 802.11 WLAN devices to fully exploit the high throughput gains offered by the IEEE 802.11 standard whenever possible since the current channel scanning mechanisms in standard may result in unacceptable delay for network discovery.
In this work, we review the behavior of passive and active channel scanning schemes of the current IEEE 802.11 specification, and also propose two enhancements for the active scanning mechanism based on the draft of IEEE 802.11ai standard.
The proposed schemes can reduce the overhead of transmitted management messages while improving the channel scanning performance. In addition, it can also increase the speed of discovery of APs before associating with one and enable more precise discovery operations. Through simulation study, it is shown that simulation results can explicitly verify our expectations on the superorities of the proposed schemes.
Z. Chang, O. Alanen, T. Huovinen, T. Nihtilä, Eng Hwee Ong, Jarkko Kneckt and T. Ristaniemi, “Performance Analysis of 802.11ac DCF with Hidden Nodes“, Proceedings of 75th IEEE Vehicular Technology Conference (VTC), 6-9 May 2012, Yokohama, Japan.
Recently, the IEEE 802.11 standard based Wireless Local Area Networks (WLAN) have become more popular and are widely deployed.
It is anticipated that WLAN will play an important rule in the future wireless communication systems in order to provide several gigabits data rate. IEEE 802.11ac is one of the ongoing WLAN standard aiming to support very high throughput (VHT) with data rate of up to 6 Gbps below the 6 GHz band.
In the development of IEEE 802.11ac standard, several new physical layer (PHY) and medium access control layer (MAC) features are taken into consideration, such as employing wider bandwidth in PHY and incrementing the limits of frame aggregation in MAC. However, due to the newly introduced features, some traditional techniques used in previous standards could face some problems.
This paper presents a performance analysis of 802.11ac Distributed Coordination Function (DCF) in presence of hidden nodes in overlapping BSS (OBSS) environment. The effectiveness of DCF in IEEE 802.11ac WLAN when using different primary channels and different frequency bandwidth has also been discussed.
Our results indicate that the traditional RTS/CTS handshake mechanism faces shortcomings and needs to be modified in order to support the newly defined 802.11ac amendment.
F. Chernogorov, and T. Nihtilä, “QoS verification for Minimization of Drive Tests in LTE networks“, Proceedings of 75th IEEE Vehicular Technology Conference (VTC), 6-9 May 2012, Yokohama, Japan.
Nowadays, operational quality and robustness of cellular networks are among the hottest topics wireless communications research.
As a response to a growing need in reduction of expenses for mobile operators, 3rd Generation Partnership Project (3GPP) initiated work on Minimization of Drive Tests (MDT). There are several major areas of standardization related to MDT, such as coverage, capacity, mobility optimization and verification of end user quality.
This paper presents results of the research devoted to Quality of Service (QoS) verification for MDT. The main idea is to jointly observe the user experienced QoS in terms of throughput, and corresponding radio conditions. Also the necessity to supplement the existing MDT metrics with the new reporting types is elaborated.
P. Eskelinen, F. Laakso, and M. Lampinen, “Impact of Amplitude Component on HSUPA Closed Loop Transmit Diversity Performance“, Proceedings of 75th IEEE Vehicular Technology Conference (VTC), 6-9 May 2012, Yokohama, Japan.
3GPP is investigating uplink transmit diversity alternatives for High Speed Uplink Packet Access (HSUPA).
This paper addresses uplink transmit diversity from the perspective of Closed Loop Beamforming (CLBF) when amplitude component is included in the beamforming codebook. This allows transmitter to divide the total transmit power unequally to transmit antennas based on the feedback from the NodeB.
This study includes the investigation of the potential benefits of antenna selection and amplitude adaptation as part of the feedback. Furthermore, the focus will be on evaluating corresponding system level performance when long term antenna imbalance is assumed.
The studies show that there are achievable gains and thus system performance may be enhanced by applying the amplitude component, especially when the antenna imbalance is high. However, the trends indicate that gains are mainly seen by the cell edge users, thus introducing amplitude component in the codebook increases coverage and fairness.
D. Petrov, I. Repo, and M. Lampinen, “Overview of Single Frequency Multipoint Transmission Concepts for HSDPA and Performance Evaluation of Intra-site Multiflow Aggregation Scheme“, Proceedings of 75th IEEE Vehicular Technology Conference (VTC), 6-9 May 2012, Yokohama, Japan.
WCDMA based third generation networks are widely deployed and 3GPP is constantly seeking to evolve their performance.
It is a well-known problem that reception quality degrades at cell edges. Multipoint transmission from two separate cells can be used to overcome this problem in single frequency deployments.
In this paper we make an overview of several techniques for single frequency multipoint transmission, which are under consideration in 3GPP.
This study presents the simulation results of Intra-site Multiflow Aggregation scheme where UEs can receive two independent transmissions from separate sectors. The performance of Type 3 and Type 3i receivers is also benchmarked in such scenario. Considerable improvement of radio network performance is demonstrated for users with Type 3i receivers on the borders of the cells without any sensible negative effect for all other users.
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