Georgia Tseliou

Optimization of fractional frequency reuse in long term evolution networks

In cellular systems, Fractional Frequency Reuse (FFR) partitions each cell into two regions; inner region and outer region and allocates different frequency band to each region. Since the users at the inner region are less exposed to inter-cell interference, the frequency resources in each inner region can be universally used. Based on this frequency band allocation, FFR may reduce channel interference and offer large system capacity. This paper proposes a mechanism that selects the optimal FFR scheme based on the user throughput and user satisfaction. In detail, the mechanism selects the optimal size of the inner and outer region for each cell as well as the optimal frequency allocation between these regions that either maximizes the mean user throughput or the user satisfaction. The mechanism is evaluated through several simulation scenarios.

Selecting the Optimal Fractional Frequency Reuse Scheme in Long Term Evolution Networks

Long Term Evolution (LTE) networks offer high capacity and are specified and designed to accommodate small, high performance, power-efficient end-user devices. One limiting factor that influences LTE performance is the interference from neighbouring cells, the so called Inter-Cell Interference (ICI). The investigation of ICI mitigation techniques has become a key focus area in achieving dense spectrum reuse in next generation cellular systems. Fractional Frequency Reuse (FFR) has been proposed as a technique to overcome this problem, since it can efficiently utilize the available frequency spectrum. This manuscript proposes a dynamic mechanism that selects the optimal FFR scheme based on a custom metric, which is called user satisfaction. In detail, the proposed mechanism divides the cell into two regions, the inner and outer region, and selects the optimal size as well as the optimal frequency allocation between these regions with main target to maximize the user satisfaction metric. The proposed mechanism is evaluated through several simulation scenarios that incorporate users’ mobility and its selected FFR scheme is compared with other frequency reuse schemes in order to highlight its performance.

Fractional Frequency Reuse in Integrated Femtocell/Macrocell Environments

Femtocells have a strong potential for increasing the efficiency, cell coverage and network capacity of next-generation mobile networks. In Long Term Evolution technology, the adaptation of Fractional Frequency Reuse techniques has been proposed in order to overcome the co-channel interference and augment the total throughput of the network. In this work, we propose a Fractional Frequency Reuse method that on the one hand calculates the optimal inner region radius and frequency allocation of a macrocell and on the other hand assigns frequency resources to the femtocells in order to mitigate the co-channel interference. We apply this method in an integrated femtocell/macrocell environment and evaluate it based on the optimization of three metrics, depending on the network operator’s needs.

Policy recommendations for public administrators on free and open source software usage

Free and open source software, holding a strategic position in knowledge economy, reaffirms the critical role of governments and regional authorities in establishing strategies for integrating effective and sustainable Information Technology solutions in the public sector towards economic growth and social welfare. Moreover, public services, organisations and territorial administrations collectively represent a major software user with great impact on the software market. In this sense, software selection in the public sector is a highly political and strategic process; various collateral implications and policy aspects should be considered in order to reach the best possible decisions. Within this context, this manuscript provides policy recommendations on issues and challenges pertaining to the use of free and open source software by European public administrations. The recommended policy actions are mainly based on review of the current policy framework. The main goal of this manuscript is to contribute in providing policy orientations and proposing actions that can help governments, public administrations and European institutions fully harvest the benefits of open source.

Methodology for Public Administrators for selecting between open source and proprietary software

The public sector needs to change over to communicating digitally. This development makes great demands both on work processes in the public sector and on the Information Technology systems, on which e-government is based. From the economic perspective, the change-over poses great challenges, as huge investments will have to be made in Information Technology in the public sector. It is therefore natural, in connection with these investments, for a detailed assessment to be made of what forms of technology it is anticipated to be used, and who controls the development and ownership of this technology. The question is: to what extent Free and Open Source Software can supplement or completely replace proprietary software? This work constitutes a review of literature on pre-existing comparative studies regarding the technical, social, economic and organizational factors on Free and Open Source Software usage. Furthermore, this work includes guidelines that Public Administrations should follow for the selection between open source and proprietary software. Our goal is to help public stakeholders understand the technical/social/economic/organizational environment and therefore reach informed decisions when selecting the appropriate software. The manuscript can also be useful for Free and Open Source Software developers, users and communities who are either directly or indirectly involved in the software market.

Enhancing FEC application in LTE cellular networks

3rdGeneration Partnership Projects (3GPP) Long Term Evolution (LTE) is focused on enhancing the Universal Terrestrial Radio Access (UTRA). Evolved-Multimedia Broadcast and Multicast Service (e-MBMS) uses Multimedia Broadcast over a Single Frequency Network (MBSFN) operation in order to improve its performance. In MBSFN operation, data are transmitted simultaneously over the air from multiple tightly time-synchronized cells. Raptor codes have been standardized as the main application layer Forward Error Correction (FEC) method for e-MBMS due to the advanced error protection they offer and their overall performance. In this study, we investigate the application of FEC in MBSFN-enabled LTE cellular networks and we propose a new scheme that takes into account the properties of MBSFN in order to provide a more efficient operation of FEC during e-MBMS transmissions. The proposed scheme is compared with other file recovery methods and is evaluated against various network parameters in a realistic simulation environment.

Forward Error Correction for Reliable e-MBMS Transmissions in LTE Networks

The Long Term Evolution (LTE) project focuses on enhancing the Universal Terrestrial Radio Access (UTRA) and optimizing 3rd Generation Partnership Project (3GPP) radio access architecture. A key new feature of LTE is the possibility to exploit the Orthogonal Frequency-Division Multiplexing (OFDM) radio interface to transmit multicast or broadcast data as a multicell transmission over a synchronized Single Frequency Network (SFN): this is known as Multimedia Broadcast and Multicast Service (MBMS) over Single Frequency Network (MBSFN) operation. MBSFN transmission enables a more efficient operation of the MBMS (3GPP, 2008a), allowing over-the-air combining of multi-cell transmissions towards the User Equipments (UEs). This fact makes the MBSFN transmission appear to the UE as a transmission from a single larger cell. Transmission on a dedicated carrier for MBSFN with the possibility to use a longer Cyclic Prefix (CP) with a sub-carrier bandwidth of 7.5 kHz is supported as well as transmission of MBSFN on a carrier with both MBMS transmissions and point-to-point (PTP) transmissions using time division multiplexing. MBMS service defines two delivery methods: the download and the streaming delivery. There are many ways to provide reliability in multicast transmission. The best-known method that operates efficiently for unicast transmission is the Automatic Repeat re-Quest (ARQ). When ARQ is applied in a multicast session, receivers send requests for retransmission of lost packets over a back channel towards the sender. Although ARQ is an effective and reliable tool for point-to-multipoint (PTM) transmission, when the number of receivers increases, it reveals its limitations. One major limitation is the feedback implosion problem which occurs when too many receivers are transmitting back to the sender. A second problem of ARQ is that for a given packet loss rate and a set of receivers experiencing losses, the probability that every single data packet needs to be retransmitted quickly approaches unity as the number of receivers increases. In other words, a high average number of transmissions are needed per packet. In wireless environments, ARQ has another major disadvantage. On most wired networks the feedback channel comes for free, but on wireless networks the transmission of feedback from the receiver can be expensive, either in terms of power consumption, or due to limitations of the communication infrastructure. Thus, due to its requirement for a bidirectional communication link, the

Cost optimization of MBSFN and PTM transmissions for reliable multicasting in LTE networks

Long Term Evolution (LTE) systems have been specified and designed to accommodate small, high performance, power-efficient, end-user devices. The evolved Multimedia Broadcast/Multicast Service (e-MBMS) feature is introduced by the 3rd Generation Partnership Project (3GPP) as a complement to the existing MBMS service in order to accommodate multicast groups that are interested in receiving the same data. MBMS service is provided by MBMS over a Single Frequency Network (MBSFN) and/or Point-To-Multipoint (PTM) transmission methods. One of the challenges of MBMS is the complete error recovery of the transmitted files, a matter of great importance since the distribution of binary data must result in 100% error-free download. To fulfill this tight requirement, Forward Error Correction (FEC) mechanism has been proposed by 3GPP. In this work, we investigate the reliable multicasting by introducing a transmission method that combines the advantages of MBSFN and PTM transmission methods. We compare several FEC-based file recovery methods and evaluate them against various network parameters in a realistic simulation environment. The comparison is based on a cost-oriented analysis of MBMS service that takes into account the transmission cost over all the interfaces and nodes of the LTE architecture. The simulation results are performed with the aid of a new simulation tool and show that the performance of the file repair schemes depend on the network configuration.

Reliable multicasting over LTE: A performance study

With the booming of multimedia services, the 3rd Generation Partnership Project (3GPP) has introduced the evolved Multimedia Multicast/Broadcast Service (e-MBMS) feature for LTE systems. The main objective of MBMS is to introduce real broadcast distribution capabilities into cellular systems. This purposed 3GPP to introduce the MBMS over a Single Frequency Network (MBSFN) operation. In this work we investigate the provision of MBMS service over a combination of MBSFN and PTM transmission schemes. We focus on the file repair procedure, because the distribution of binary data via MBMS must result in 100% error-free downloaded files. In order to achieve this goal, MBMS offers a Forward Error Correction (FEC) mechanism. Our simulation results show that there are some file repair schemes that achieve better performance as far as different network configurations are concerned. Furthermore, we compare all the file recovery methods and evaluate them against various network parameters in a realistic simulation environment.

Optimizing the combination of MBSFN and PTM transmissions in LTE systems

The 3rd Generation Partnership Project (3GPP) has introduced the evolved Multimedia Broadcast/Multicast Service (e-MBMS) feature for cellular systems as an evolution to the existing MBMS service. To support e-MBMS in Long Term Evolution (LTE) systems, 3GPP recommends the use of Point-to-Multipoint (PTM) transmissions and MBMS over a Single Frequency Network (MBSFN). MBSFN is a new feature where a time-synchronized common waveform is transmitted from multiple cells. In this paper we investigate the provision of MBMS service over a combination of MBSFN and PTM transmission methods. A cost analysis of the MBMS service is presented based on the transmission cost over all the interfaces and nodes of the LTE architecture. We evaluate the performance of this transmission scheme from telecommunication cost perspective and we compare it with other transmission schemes. The performance evaluation has been performed with the aid of a new simulation tool that estimates the cost for the MBMS provision under different network topologies, MBSFN deployments and user distributions.