Vitaliy Tykhomyrov, “Mitigating the Amount of Overhead Arising from the Control Signaling of the IEEE 802.16 OFDMa System“, Ph.D. Thesis, ISBN 978-951-39-4551-0, University of Jyväskylä, 2011.
This work focuses on mitigating the amount of overhead arising from the control signaling of the IEEE 802.16 system. It analyses existent solutions and proposes efficient methods and algorithms.
Although existent IEEE 802.16 standard proposes some techniques, it is worthwhile to point out that exact implementation is not specified and left open for alternative implementations. The first part of this work addresses the main aspects of MAC layer overhead. The second part of this work introduces efficient techniques to improve the performance of ARQ mechanism.
It is shown that the ARQ mechanism can improve significantly the performance of TCP based applications and confirms that a correct configuration plays an important role in transmitting data over wireless channels in the IEEE 802.16 OFDMa system.
It is also of the view that the proposed solutions in this work must be verified by means of extensive simulations, and therefore each proposed method and algorithm is implemented and tested within the WINSE simulator in the NS-2 framework.
I. Repo, “Performance Analysis of Voice over Internet Protocol Mobility in High Speed Downlink Packet Access Networks”, Master’s Thesis, University of Jyväskylä, 2011.
Olli Alanen, Henrik Martikainen, Vitaliy Tykhomyrov, Alexander Sayenko, Oleksandr Puchko, Vesa Hytönen and Timo Hämäläinen, “WINSE: WiMAX NS-2 Extension“, in SIMULATION Volume 87 Issue 1-2, January 2011.
The IEEE 802.16 standard defines a wireless broadband technology called WiMAX. When compared with other wireless technologies, it introduces many interesting advantages at PHY, MAC, and QoS layers.
Heavy simulations are needed to study the performance of IEEE 802.16 and propose further enhancements to this standard. Link-level simulations are not always sufficient, while system-level simulators are not always accurate enough to capture MAC and transport protocol details.
We implemented an 802.16 extension for the NS-2 network simulator. It includes upper PHY modeling, almost all of the features of the 802.16 MAC layer, as well as the QoS framework.
This article describes the implemented features and simulation methodology, while sharing our experience that can be used with other NS-2 modules. There is also an overview of the past and ongoing research.
S. Hämäläinen (Editor), H. Sanneck (Editor), C. Sartori (Editor), “LTE Self-Organizing Networks (SON): Network Management Automation for Operational Efficiency“, ISBN: 978-1-1199-7067-5, John Wiley & Sons Ltd, 2011.
Covering the key functional areas of LTE Self-Organising Networks (SON), this book introduces the topic at an advanced level before examining the state-of-the-art concepts.
The required background on LTE network scenarios, technologies and general SON concepts is first given to allow readers with basic knowledge of mobile networks to understand the detailed discussion of key SON functional areas (self-configuration, -optimisation, -healing). Later, the book provides details and references for advanced readers familiar with LTE and SON, including the latest status of 3GPP standardisation.
Based on the defined next generation mobile networks (NGMN) and 3GPP SON use cases, the book elaborates to give the full picture of a SON-enabled system including its enabling technologies, architecture and operation. ”Heterogeneous networks” including different cell hierarchy levels and multiple radio access technologies as a new driver for SON are also discussed.
H. Martikainen, I. Viering, B. Wegmann, A. Lobinger and A. Awada, “Mobility Robustness Optimization beyond Doppler Effect and WSS Assumption“, Proceedings of the eighth International Symposium on Wireless Communication Systems (ISWCS’11), Aachen, Germany, 6th – 9th November, 2011.
Mobility robustness is often understood as making the radio link Doppler-resistent. However, guaranteeing proper cell changes, e.g. handovers, is another, as important and at least as challenging aspect beyond Doppler and wide sense stationarity (WSS) assumption.
This paper tries to describe the complex optimization problem with scientific methods, in order to catalyze future academic work in the interesting field of minimizing handover problems.
Simulation results will be presented for intra-frequency mobility robustness optimization (MRO) distinguishing network-wide, cell-specific and cell-pair specific optimization.
Olli Alanen, Zheng Chang, Toni Huovinen, Timo Nihtilä, Eng Hwee Ong and Jarkko Kneckt, “IEEE 802.11ac: Enhancements for Very High Throughput WLANs“, Proceedings of 22nd IEEE Symposium on Personal, Indoor, Mobile and Radio Communications (PIMRC), Toronto, Canada, September 11-14, 2011
The IEEE 802.11ac is an emerging very high throughput (VHT) WLAN standard that could achieve PHY data rates of close to 7 Gbps for the 5 GHz band.
In this paper, we introduce the key mandatory and optional PHY features, as well as the MAC enhancements of 802.11ac over the existing 802.11n standard in the evolution towards higher data rates.
Through numerical analysis and simulations, we compare the MAC performance between 802.11ac and 802.11n over three different frame aggregation mechanisms, viz., aggregate MAC service data unit (A-MSDU), aggregate MAC protocol data unit (A-MPDU), and hybrid A-MSDU/A-MPDU aggregation.
Our results indicate that 802.11ac with a configuration of 80MHz and single (two) spatial stream(s) outperforms 802.11n with a configuration of 40 MHz and two spatial streams in terms of maximum throughput by 28% (84%).
In addition, we demonstrate that hybrid A-MSDU/A-MPDU aggregation yields the best performance for both 802.11n and 802.11ac devices, and its improvement is a function of the maximum A-MSDU size.
T. Hiltunen, F. Laakso, P. Eskelinen, K. Aho, I. Repo, and A. Lehti, “Introducing Dual Pilot Closed Loop Transmit Diversity for High Speed Uplink Packet Access“, Proceedings of IEEE 74th Vehicular Technology Conference (VTC), San Francisco, USA, September 5-8, 2011.
The alternatives for HSUPA uplink transmit diversity are being currently investigated in 3GPP.
This paper addresses the uplink transmit diversity from the perspective of closed loop beamforming where NodeB determines transmit antenna weights, and additional feedback is used for signaling the optimal weights to the user equipment.
More precisely, this paper introduces a novel transmit diversity technique which involves transmitting two non-beamformed DPCCH (pilot) signals from two antennas whereas the actual data part of the signal is beamformed. Additionally, the dual pilot transmit diversity technique is benchmarked on system level in various conditions against the baseline system performance without transmit diversity.
The studies show cell level throughput gains up to 53 % in Pedestrian A channel and up to 26 % in Vehicular A channel comparing to the baseline system. The highest relative gains are achieved in highly loaded cells with long inter-site distances.
F. Laakso, K. Aho, I. Repo, P. Eskelinen, and M. Lampinen, “Beamforming Transmit Diversity using power control commands for High Speed Uplink Packet Access“, Proceedings of IEEE 74th Vehicular Technology Conference (VTC), San Francisco, USA, September 5-8, 2011.
3GPP is investigating uplink transmit diversity alternatives for High Speed Uplink Packet Access (HSUPA).
This paper studies beamforming transmit diversity where the UE transmitter applies a weight vector to the transmit antennas. In contrast to the traditional beamforming where transmitter is aware of the channel state through channel state feedback, a practical scheme which relies on existing power control commands to calculate the weight vector is investigated.
This approach allows autonomous determination of the weight vector by the UE. Additionally, an ideal algorithm which always selects the optimal weight vectors is presented in order to obtain upper boundary for the performance. Both algorithms are benchmarked in various conditions on system level against baseline performance without transmit diversity.
The studies show that ideally open loop beamforming is capable of providing gain in simulated conditions. However, the power control command dependent realistic algorithm is able to provide gain only when the low velocity Pedestrian A 3 kmph channel is used. With more complex and higher velocity Vehicular A 30 kmph channel the realistic algorithm is not able to provide gain and reaches only baseline level performance.
P. Eskelinen, F. Laakso, K. Aho, T. Hiltunen, I. Repo, and A. Lehti, “Impact of Practical Codebook Limitations on HSUPA Closed Loop Transmit Diversity“, Proceedings of IEEE 74th Vehicular Technology Conference (VTC), San Francisco, USA, September 5-8, 2011.
Different alternatives for uplink transmit diversity for HSUPA are being investigated in 3GPP.
This paper compares the performance of two-antenna beamforming using closed loop feedback information against the baseline single antenna transmission. With beamforming, multiple transmit antennas are utilized and the UE transmitter applies a weight vector to the transmit antennas in order to amplify the received signal.
In this paper, the impact of different codebook sizes, delays and update intervals related to antenna weights are studied utilizing a comprehensive system level simulator.
The studies show that increasing codebook size provides relatively higher performance gain over the baseline. However, increasing the number of available beamforming antenna weights will also increase signaling overhead.
In terms of weight update interval the best performance is achieved with one slot interval and if the interval is prolonged to the length of Transmission Time Interval (TTI), namely 3 slots, then the performance with higher mobile velocity can be compromised. Similarly, the results with different feedback delays show that additional delays in fast fading channel should be avoided.
K. Hämäläinen, M.Enescu, T. Roman, T. Koivisto, M. Kuusela, M. Lampinen, K. Pietikainen and J. Venäläinen, “Evolution of downlink multi-antenna techniques throughout E-UTRAN LTE Releases“, Proceedings of IEEE 74th Vehicular Technology Conference (VTC), San Francisco, USA, September 5-8, 2011.
In this paper we present the evolution of downlink multi-antenna techniques over different releases of E-UTRAN LTE specifications.
First we walk through the design of MIMO transmission schemes, reference signals and channel state information feedback from Release 8 to the latest Release 10 of the specifications.
We provide extensive system simulation results for downlink single- and multi-user MIMO, demonstrating the clear performance benefits of the advanced spatial processing techniques developed throughout the evolution of LTE, and confirming the state-of-the-art design of LTE multi-antenna techniques.
Finally, we provide a glimpse to the future multi-antenna topics currently being studied in 3GPP, presenting also simulation results on the most promising candidate feature.
J. Turkka, and J. Puttonen, “Using LTE Power Headroom Report For Coverage Optimization“, Proceedings of IEEE 74th Vehicular Technology Conference (VTC), San Francisco, USA, September 5-8, 2011.
This paper describes how LTE Rel’ 8 power headroom report (PHR) can be used to detect outage problems in LTE networks. It outlines the proposed minimization of drive tests use case for PH triggered measurements, alleviates the problems in this proposal, and describes improvements which can help operators to gather more coverage and outage related information from their networks.
The article points out, that the earlier proposal can lead to unnecessary signaling, it does not work always as supposed, and the existing measurements can be used to gather the same information.
The study is conducted by simulating two different outage problem scenarios with a fully dynamic LTE system simulator.
J. Turkka, T. Ristaniemi, G. David and A. Averbuch, “Anomaly Detection Framework for Tracing Problems in Radio Networks”, Proc. of the IARIA Tenth International Conference on Networks (ICN), St. Maarten, Netherlands Antilles, January 23-28, 2011.
This paper shows a novel concept of using diffusion maps for dimensionality reduction when tracing problems in 3G radio networks.
The main goal of the study is to identify abnormally behaving base station from a large set of data and find out reasons why the identified base stations behave differently.
The paper describes an algorithm consisting of pre-processing, detection and analysis phases which were applied for RRC (Radio Resource Control) connection data gathered from the live radio networks.
The results show that the proposed approach of using dimensionality reduction and anomaly detection techniques can be used to detect irregularly behaving base stations from a large set of data in a more self-organized manner.
In modern wireless networks, the signal quality in wireless channel is estimated based on the channel quality measurements. The measurement results are used to select appropriate modulation and coding scheme for each transmission.
The target of the link adaptation is to reach the desired block error rate operation point. Operation point and system performance could potentially be compromised by non-consistent / biased channel quality indicator reporting caused by, e.g., differently calibrated user equipments or hardware inaccuracies.
This paper evaluates the extent of that phenomenon through different combinations of traffic types, bias settings and system loads by the means of fully dynamic system simulations.
The in-depth results verified that on the system level the performance is not significantly impacted by reporting imperfections. Long term evolution is used as an example technology in this study, but the same concepts are applicable to other wireless technologies also.
K. Aho, I. Repo, P. Eskelinen, and F. Laakso, “Introducing Switched Antenna Transmit Diversity for High Speed Uplink Packet Access“, Proc. of the IEEE 18th International Conference on Telecommunications (ICT), Ayia Napa, Cyprus, May 8-11, 2011.
3GPP is investigating uplink transmit diversity alternatives for HSUPA. This paper addresses uplink transmit diversity from the perspective of open loop where additional feedback information is not available.
Furthermore, the focus will be on switched antenna transmit diversity where only one antenna is active at the time even though UE is equipped with multiple transmit antennas. Five different algorithms are presented and benchmarked in system level in various conditions against baseline performance without Tx diversity.
The studies show achievable gains when the UE velocity is low but practical algorithms get only fraction of the possible gain and improper algorithms can lead to even performance loss.
I. Repo, K. Aho, P. Eskelinen, and F. Laakso, “Switched Antenna Transmit Diversity Imperfections and Their Implications to HSUPA Performance“, Proc. of the IEEE 18th International Conference on Telecommunications (ICT), Ayia Napa, Cyprus, May 8-11, 2011.
3GPP is investigating uplink transmit diversity alternatives for HSUPA. This paper focuses on a transmit diversity scheme using switching between two transmit antennas without additional feedback information.
The special focus of this paper is on various non-ideal conditions that occur in real implementations, such as antenna imbalance, correlation and the existence of multiple different SATD algorithms in the network simultaneously.
The studies show that transmit antenna correlation somewhat decreases performance but still keeps gains over the baseline, antenna imbalance reduces situations where the switching is feasible and that using a mixture of algorithms can bring down the gains.
Fedor Chernogorov, Jussi Turkka, Tapani Ristaniemi, Amir Averbuch, “Detection of Sleeping Cells in LTE Networks Using Diffusion Maps“, Proc. of the IEEE International Workshop on Self-Organizing Networks (IWSON), in conjunctiuon with VTC 2011 Spring, Budapest, Hungary, May 15-18, 2011.
In mobile networks, emergence of failures is caused by various breakdowns of hardware and software elements.
One of the serious failures in radio networks is a Sleeping Cell. In our work, one of the possible root causes for appearance of this network failure is simulated in a dynamic network simulator.
The main aim of the research is to detect the presence of a Sleeping Cell in the network and to define its location. For this purpose Diffusion Maps data mining technique is employed.
The developed fault identification framework is using the performance characteristics of the network, collected during its regular operation, and for that reason it can be implemented in real Long Term Evolution (LTE) networks within the Self-Organizing Networks (SON) concept.
J. Puttonen, J. Kurjenniemi, O. Alanen, T. Henttonen, “On Improving the Radio Resource Control Signaling Reliability in LTE Uplink“, Proc of the IEEE 73rd Vehicular Technology Conference (VTC) Spring, Budapest, Hungary, May 15-18, 2011.
In this article, we study and analyze the problems related to power limitation in Long Term Evolution (LTE) uplink (UL).
Power control (PC) has been specified for LTE UL to account for pathloss and slow fading variations and minimize the interference. The maximum transmission power has been limited to 23 dBm. Especially in sparse networks, this can lead to so called power limitation, where the terminals at the cell edge are forced to use less power per Physical Resource Block (PRB) than needed.
Power limitation could clearly increase the packet error probability and transmission delay due to increased number of retransmissions. This may be especially problematic for Radio Resource Control (RRC) messages, e.g. handover signaling, since their reliability affects evidently on user Quality of Service (QoS).
In this article we have concentrated on power boosting to improve the RRC message reliability and the performance is evaluated by means of dynamic system level simulations. It may be concluded that power boosting notably reduces the power limitation probability and thus also improves the RRC signaling reliability.
N. Kolehmainen, O. Alanen, T. Henttonen, “Mobility Performance in Heterogeneous LTE Networks with Indoor Base Stations“, Proc of the IEEE 73rd Vehicular Technology Conference (VTC) Spring, Budapest, Hungary, May 15-18, 2011.
In this paper mobility performance is studied in heterogeneous networks with both macro and indoor base stations.
Due to abrupt changes in received signal and interference level as User Equipment (UE) enters and leaves a building with indoor Home eNodeB (HeNB), there may be additional challenges for handover compared to more homogeneous network layout.
The purpose of this paper is, with a dynamic system simulation tool, to evaluate the magnitude of the handover challenges and how would the system need to be configured to optimize the mobility performance.
The results indicate that while general handover parameterization can be effectively utilized to avoid the most of mobility problems, cell-specific parameterization can further improve the mobility performance between eNB and HeNB.
Additionally, attention should be paid to both inbound and outbound HeNB mobility due to possibly very different interference conditions in handover situations inside the building with HeNB and outdoor environment.
T. Nihtilä, J. Turkka, I. Viering, “Performance of LTE Self-Optimizing Networks Uplink Load Balancing“, Proc of the IEEE 73rd Vehicular Technology Conference (VTC) Spring, Budapest, Hungary, May 15-18, 2011.
This paper presents a performance evaluation of an uplink load balancing algorithm for 3GPP Long-Term Evolution (LTE) Self-Optimizing/Organizing Networks (SON).
The algorithm handles local overload situations in uplink by two different strategies: firstly passing load from overloaded cells to under loaded cells and secondly by controlling UL interference through UL power control (PC) parameter adjustment. The algorithm is distributed so it works independently in each eNodeB (eNB).
Every eNB includes a specific SON module which takes various measurements from its own and the neighboring eNBs as an input and gives handover orders and parameter change commands to its designated eNB as an output.
In the paper we present a description of the algorithm and evaluate its performance in a locally overloaded LTE network.
The performance evaluation is done by the means of fully dynamic LTE system simulation tool comprising a detailed modeling of user equipment (UE) measurements, user mobility and handovers, traffic and radio resource management algorithms.
F. Laakso, K. Aho, I. Repo, T. Chapman, “Streamlining HSUPA TTI Lengths without Compromising HSUPA Capacity“, Proc of the IEEE 73rd Vehicular Technology Conference (VTC) Spring, Budapest, Hungary, May 15-18, 2011.
This paper proposes a s.c. 2 ms range extension scheme for High Speed Uplink Packet Access (HSUPA) networks to avoid potential coverage problems and usage of multiple TTI lengths.
With range extension UEs in poor radio conditions are configured to send bundles of 2 ms TTI transmissions without HARQ feedback to improve their coverage.
This paper analyzes the performance of range extension in comparison with normal 2 ms TTI performance with multiple inter-site distances. The analysis is conducted considering VoIP performance due to its high sensitivity to additional delays and packet loss.
The results acquired by using system level simulation tool indicate that using 2 ms range extension can improve system capacity in larger cells where normal 2 ms TTI can result into coverage problems. Moreover, utilizing repeated 2 ms TTIs instead 10 ms TTIs enables increased battery saving opportunities when UL DTX is applied.
P. Eskelinen, I. Repo, K. Aho, F. Laakso, “On HSUPA Open Loop Switched Antenna Transmit Diversity Performance in Varying Load Conditions“, Proc of the IEEE 73rd Vehicular Technology Conference (VTC) Spring, Budapest, Hungary, May 15-18, 2011.
The Switched Antenna Transmit Diversity (SATD) scheme is a promising transmit diversity technique to improve the performance in High Speed Uplink Packet Access (HSUPA) systems.
Antenna switching rests on a technique where only one antenna is active at a time even if the UE is equipped with multiple transmit antennas.
Switching and antenna selection can be based on different methods and criteria and this paper provides simulative analysis of three different open loop antenna switching algorithms for the HSUPA systems. Furthermore, the focus will be on evaluating corresponding system level performance compared to the single Tx antenna performance when bursty traffic is assumed.
The studies show that there are achievable gains and thus system performance may be enhanced by applying the antenna switching scheme, especially when the mobile velocity is low.
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