Pavel Mach

Improvement of handover prediction in mobile WiMAX by using two thresholds

One of the most important challenges in mobile wireless networks is to provide full mobility together with minimum degradation of quality of service. This can be ensured by handover prediction. Handover prediction means a determination of the next station that will serve a mobile station. This paper proposes a prediction technique based on monitoring the signal quality between the mobile station and all base stations in its neighborhood. The proposed technique utilizes two different thresholds for selection of the most likely target base station. Further, the potential improvement of the prediction efficiency via techniques originally proposed for minimizing the number of redundant handovers is analyzed. The efficiency of the proposed prediction technique is evaluated and compared with other prediction techniques based on channel characteristics in scenarios according to IEEE 802.16m. The proposed technique achieves a prediction hit rate of up to 93%.

An architecture for mobile computation offloading on cloud-enabled LTE small cells

Small cell networks are currently seen as a new way to satisfy the increasing wireless traffic demand. The proximity of base stations to subscribers brings many possibilities for the development of new applications, including new offerings based on cloud computing. Smartphones can directly offload applications to close base stations, provided that these are equipped with additional computational and storage resources. The cloud concept applied in the framework of small cells can also combine radio and computation aspects in order to optimise the service delivery. This paper introduces a new element called the Small Cell Manager (SCM), which optimises the overall operation of a cluster of cloud-enabled small cells. The SCM, aware of the cluster situation in terms of both radio and cloud aspects, interacts not only with the cloud-enabled base stations, but also with LTE core network components. To that end, different possibilities for the general architecture of a small-cell-cloud are analysed. Furthermore, the paper describes different evaluation criteria an LTE operator has to consider before adopting this approach in order to optimise the required investment and maximise benefits.

QoS-Guaranteed Power Control Mechanism Based on the Frame Utilization for Femtocells

The paper focuses on a power control mechanism and proposes a novel approach for dynamic adaptation of femtocells transmitting power. The basic idea is to adapt the transmitting power of femtocells according to current traffic load and signal quality between user equipments and the femtocell in order to fully utilize radio resources allocated to the femtocell. The advantage of the proposed scheme is in provisioning of high quality of service level to the femtocell users, while interference to users attached to macrobase station is minimized. The paper proposes the power adaptation algorithm and evaluates its performance in terms of mobility events, achieved throughput, and FAPs transmitting power. Performed simulations show that the proposed scheme can significantly reduce the number of mobility events caused by passerby users and thus to minimize signaling overhead generated in the network. In addition, our proposal enhances overall throughput for most of the investigated scenarios in comparison to other power control schemes.

Path selection using handover in mobile networks with cloud-enabled small cells

To overcome latency constrain of common mobile cloud computing, computing capabilities can be integrated into a base station in mobile networks. This exploitation of convergence of mobile networks and cloud computing enables to take advantage of proximity between a user equipment (UE) and its serving station to lower latency and to avoid backhaul overloading due to cloud computing services. This concept of cloud-enabled small cells is known as small cell cloud (SCC). In this paper, we propose algorithm for selection of path between the UE and the cell, which performs computing for this particular UE. As a path selection metrics we consider transmission delay and energy consumed for transmission of offloaded data. The path selection considering both metrics is formulated as Markov Decision Process. Comparing to a conventional delivery of data to the computing small cells, the proposed algorithm enables to reduce the delay by 9% and to increase users satisfaction with experienced delay by 6.5%.

On enhancement of handover decision in femtocells

Deployment of femtocells with open or hybrid access into mobile networks leads to problems with handling handover of mobile users. In this paper we discuss two important aspects that can be considered and exploited in a design of innovative handover procedure for scenario with femtocells. The first aspect is related to varying quality and limited capacity of femtocells backbone. Further, an accuracy of determination of a time spent by users in a femtocell is analyzed in this paper with purpose to exploit it for elimination of redundant handovers. The implementation aspects of proposed enhancements in handover decision algorithm are discussed as well.

Thermomechanical analysis of electrically conductive adhesives

Mechanical properties of isotropic electrically conductive adhesives (ICAs) are mainly influenced by their formulation and thermal processing. Thermomechanical analysis of ICAs was used with the goal to find influence of addition of two types of nanoparticles, silver nanoballs and carbon nanotubes, and two types of curing processes, on air and in vacuum, on the glass transition temperature and storage modulus of bisphenol epoxy adhesives filled with silver flakes (70 to 80 % by weight). Specimens were formed as blocks. Three groups of specimens were fabricated: specimens of adhesives used as received and cured according to the recommendation of a supplier in air; specimens of adhesives used as received and cured according to the recommendation of a supplier in vacuum, specimens of the same adhesives added with low fraction (0,3 to 10 % by weight) of silver nanoballs, colloidal dispersion of silver, or carbon nanotubes. There were found differences in the glass transition temperatures and storage and loss moduli in dependence on the type of particles added into adhesive. It was also found that the adhesive cured in vacuum had lower thermal expansion coefficient and higher the storage and loss modulus in comparison with adhesive cured in air.

Cloud-aware power control for cloud-enabled small cells

Requirements of current services and applications on computational power are still increasing. Hence, the utilization of these by the mobile user equipment (UE) having limited battery lifetime is quite a challenge. To cope with this problem, the mobile cloud computing can be exploited to offload high complex applications to the cloud. Nevertheless, the conventional mobile cloud solution introduces high delay and limits the use of delay sensitive services and applications. One feasible solution is to enhance small cells (SCeNBs) with computing capabilities and, thus, perform computing closer to the users accomplishing low delay. However, the high density deployment of the SCeNBs and UEs mobility can result in often outage situation or handover when low delay tolerant data cannot be delivered from the cloud on time and become irrelevant. In this paper we propose power control algorithm, which purpose is to guarantee that the requests processed by the small cell cloud are received by the UE within required delay. This is done by coarse and dynamic fine setting of the SCeNBs transmitting power level. The simulations demonstrate the amount of undelivered requests from the small cell cloud can be significantly minimized when compared to competitive schemes. At the same time, QoS of non-cloud users is only slightly impaired when compared to the scheme giving solely preferences to non-cloud users. We also show that the overhead introduced by our power control mechanism is negligible.

Optimization of association procedure in WiMAX networks with relay stations

When a MS enters to the WiMAX network, a network entry procedure has to be performed. The aim of procedure is twofold. Firstly, several connections between the MS and BS are created, i.e. basic, primary and secondary management connections to control data transmissions. Secondly, the MS is admitted into the network. According to the IEEE 802.16 standard, a MS always tries to associate to BS with the highest received signal quality. This method is suitable as long as the MS is directly connected to the network via BS. However by introducing relay stations to the WiMAX architecture, the MS entry procedure needs to be modified. Mainly, the point of attachment influences the network performance. This paper proposes an optimized association procedure which takes into account the use of relays stations in the network. The obtained results show improvement of system performance.

Cloud-aware power control for real-time application offloading in mobile edge computing

Running computationally demanding real-time applications at the mobile user equipment (UE) is complicated because of limited battery life time of the UEs. One solution is to offload demanding computing tasks to a centralized cloud. Nevertheless, this option introduces significant delay consisting in delivery of the offloaded tasks to the cloud and back. Such delay is inconvenient for real-time applications. To cope with high delay, a concept of mobile edge computing has been introduced. The feasible way enabling mobile edge computing is to enhance the small cell base stations (SCeNBs) with computing capabilities. However, a high density of the SCeNBs together with even low mobility of users can result in often outage situation or handover when delay sensitive data cannot be delivered from the computing SCeNBs in time and become irrelevant. In this paper, we propose distributed cloud-aware power control algorithm, which targets to increase the ratio of delivery of computation results to the UE within required delay. Then, we enhance cloud-aware power control by adaptive algorithm. This algorithm exploits iterative process to find appropriate time when the power control is triggered in order to further improve the performance of the cloud-aware power control. The simulations demonstrate notable increase in the ratio of delivered offloaded tasks from the computing SCeNBs comparing with competitive schemes. At the same time, the amount of served data to the users exploiting common, non-cloud, services is increased. As the proposed solution is distributed, related signaling overhead is negligible. Copyright

Mitigation of redundant handovers to femtocells by estimation of throughput gain

A deployment of femtocells to mobile wireless networks can increase a throughput of indoor as well as outdoor users. On the other hand, it introduces several problems such as serious interference or high number of performed handovers. This paper is focused on mitigation of redundant handovers to femtocells with open or hybrid access. The redundant handovers decrease users throughput due to a management overhead and due to introduced interruption. We design a novel handover decision algorithm based on an estimation of throughput gain reached by a handover to a femtocell. In the proposal, the handover is initiated only if the estimated gain in users throughput exceeds a predefined threshold. As the results indicate, high ratio of eliminated redundant handovers is achieved by the designed procedure. Moreover, a drop in users throughput due to the handover procedure is reduced by the proposed algorithm and thus the users throughput is increased.