Zdenek Becvar

In-Band Device-to-Device Communication in OFDMA Cellular Networks: A Survey and Challenges

Direct communication between two or more devices without the intervention of a base station, known as device-to-device (D2D) communication, is a promising way to improve performance of cellular networks in terms of spectral and energy efficiency. The D2D communication paradigm has been largely exploited in non-cellular technologies such as Bluetooth or Wi-Fi but it has not yet been fully incorporated into existing cellular networks. In this regard, a new proposal focusing on the integration of D2D communication into LTE-A has been recently approved by the 3GPP standardization community as discussed in this paper. In cellular networks, D2D communication introduces several critical issues, such as interference management and decisions on whether devices should communicate directly or not. In this survey, we provide a thorough overview of the state of the art focusing on D2D communication, especially within 3GPP LTE/LTE-A. First, we provide in-depth classification of papers looking at D2D from several perspectives. Then, papers addressing all major problems and areas related to D2D are presented and approaches proposed in the papers are compared according to selected criteria. On the basis of the surveyed papers, we highlight areas not satisfactorily addressed so far and outline major challenges for future work regarding efficient integration of D2D in cellular networks.

Mobile Edge Computing: A Survey on Architecture and Computation Offloading

Technological evolution of mobile user equipment (UEs), such as smartphones or laptops, goes hand-in-hand with evolution of new mobile applications. However, running computationally demanding applications at the UEs is constrained by limited battery capacity and energy consumption of the UEs. A suitable solution extending the battery life-time of the UEs is to offload the applications demanding huge processing to a conventional centralized cloud. Nevertheless, this option introduces significant execution delay consisting of delivery of the offloaded applications to the cloud and back plus time of the computation at the cloud. Such a delay is inconvenient and makes the offloading unsuitable for real-time applications. To cope with the delay problem, a new emerging concept, known as mobile edge computing (MEC), has been introduced. The MEC brings computation and storage resources to the edge of mobile network enabling it to run the highly demanding applications at the UE while meeting strict delay requirements. The MEC computing resources can be exploited also by operators and third parties for specific purposes. In this paper, we first describe major use cases and reference scenarios where the MEC is applicable. After that we survey existing concepts integrating MEC functionalities to the mobile networks and discuss current advancement in standardization of the MEC. The core of this survey is, then, focused on user-oriented use case in the MEC, i.e., computation offloading. In this regard, we divide the research on computation offloading to three key areas: 1) decision on computation offloading; 2) allocation of computing resource within the MEC; and 3) mobility management. Finally, we highlight lessons learned in area of the MEC and we discuss open research challenges yet to be addressed in order to fully enjoy potentials offered by the MEC.

Adaptive Hysteresis Margin for Handover in Femtocell Networks

The challenge of elimination of redundant handovers is getting more significant while femtocells with small radius are deployed in networks. The utilization of the femtocells results to more frequent initiation of a handover procedure. This paper focuses on an adaptation of actual level of hysteresis margin according to the position of the user in a cell. The hysteresis margin is commonly used parameter for elimination of redundant handovers. The purpose of this paper is to propose mechanism with minimum requirements on conventional network and user’s equipment and with a simple implementation. Evaluations of proposal in term of efficiency of the redundant handovers reduction as well as an impact on the user’s throughput in 4G wireless networks are carried out. The results show significant reduction of the amount of handovers while reducing the impact on the throughput.

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.

Dynamic Power Control Mechanism for Femtocells Based on the Frame Utilization

The femtocells are very promising concept for wireless networks to significantly enhance system capacity. Nevertheless, a lot of challenges must be still addressed. The paper focuses on a power control mechanism and proposes a novel approach for dynamic adaptation of transmitting power of femtocell access points. The basic idea is to adapt the transmitting power of femtocells according to current traffic load and signal quality between mobile stations and femtocell in order to fully utilize data frame. The advantage of this approach is its potential to decrease interference to users of macro cell or adjacent femtocells at light traffic load. Performed analytical evaluations of our proposed scheme in comparison to the existing power control mechanisms show that femtocell’s transmitting power can be significantly reduced while the same Quality of Service level is still guaranteed to the femtocell users.

A Seamless Integration of Computationally-Enhanced Base Stations into Mobile Networks towards 5G

Following Mobile Cloud Computing, Mobile Edge Computing and Network Functions Virtualisation tendencies, we envisage the utilization of computationally-enhanced base stations as computing nodes in which Virtual Machines can be deployed to perform computing tasks, leveraging the closeness of computing resources to end-users. This paper presents a seamless approach for the deployment of computationally-enhanced Small- Cells, also applicable to macro base stations, with no impact on the LTE-A architecture. To that end, the conventional mobile traffic and the traffic generated and consumed by the new computing resources are segregated and handled independently at the access point, with the latter being transmitted through the radio channel making use of the pre-established Data Radio Bearers. Assuming a general-purpose hardware configuration for the Small-Cells, we describe the functionality of the different physical and logical components along with the new protocol stacks and interfaces. Finally, we evaluate the additional delay and amount of signaling overhead introduced by the system to benchmark the proposed solution.

Offloading Multiple Mobile Data Contents Through Opportunistic Device-to-Device Communications

Opportunistic device-to-device (D2D) communication is the approach proposed to offload mobile data traffic for cellular networks. In opportunistic D2D communication, the network has to appoint relaying users to distribute content(s) to normal subscribers under a given delay-tolerance threshold. In general, the total number of relaying users is fixed. Identifying proper number of relaying users is one of the key challenges in opportunistic D2D communication. The network has to select proper number of relaying users for each content to minimize the amount of mobile data traffic. This paper presents a popularity-based relaying user selection algorithm to determine the number of relaying users for distributing multiple contents with different popularity. An analytical model is then presented to estimate the amount of reduced mobile data traffic under single-hop and multi-hop opportunistic forwarding scenarios. Results obtained by simulations as well as by our proposed analytical model show that the proposed popularity-based algorithm can find the total number of relaying users to the amount of reduced mobile data traffic. For services which have longer delay-tolerance threshold, the proposed popularity-based algorithm requires less relaying users and can achieve similar amount of reduced mobile data traffic as the state-of-the-art random fully-allocation algorithm does. For services which have shorter delay-tolerance threshold, the proposed popularity-based algorithm provide significant gain comparing with the random fully-allocation algorithm.

Impact of Handover on VoIP Speech Quality in WiMAX Networks

VoIP is one of the most emerging technologies in the area of speech communications. VoIP is widely deployed in fixed line access networks. However, user’s requirements on the mobility within communication and on the quality of the speech communications are increasing. Therefore, VoIP technology is more and more integrated into broadband wireless networks with QoS support such as WiMAX. The latest version of WiMAX standard, based on IEEE 802.16e, has implemented a full mobility support. The mobility is allowed due to a handover procedure. IEEE 802.16e specifies only one mandatory handover procedure: hard handover. This handover type is easy to implement, but it increases end-to-end packet delay that is critical for delay sensitive services such as VoIP. This paper evaluates an impact of the handover on the speech quality in VoIP networks.

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.