Marco Caretti

Energy Efficiency in LTE-Advanced Networks with Relay Nodes

this document analyses the energy efficiency of two relaying schemes that represent a possible way to deploy a relay enhanced network: the two hop scheme and the multicast cooperative scheme. Results exist in literature that provide a model for the theoretical evaluation of the capacity improvement that these solutions can yield, however no analysis is available at present on the energy efficiency of these schemes. This work enhances the existing theoretical models for capacity evaluations, providing a first analysis from an energy efficiency point of view of these two approaches, considering a fully loaded network and the total emitted RF power of the transmitting nodes. Results are provided in terms of the Energy Consumption Index (ECI) of these schemes, a metric proposed in the EARTH project for the assessment of the energy consumption of network solutions. The ECI distribution is obtained and compared with the case of a network deployed without relay nodes, showing that besides the possible improvements in capacity, relays are also candidates as a valuable tool to reduce the energy consumption of a telecommunication network.

An E 3 F based assessment of energy efficiency of relay nodes in LTE-advanced networks

this document analyses the energy efficiency of two possible schemes that have been discussed as a possible way to deploy a relay enhanced network. In the first part the main results obtained in a previous work [1] are summarized, showing the energy efficiency of a relay enhanced network obtained considering small scale simulations, in a full load scenario and measuring only the radiated power. These results provided a first indication of the potentiality of relay nodes as a tool to reduce energy consumption. In the second part a deeper analysis is provided, showing how the energy efficiency of the network can be obtained also considering the whole power consumed by all the components of the transmitting nodes, and considering scenarios where the network is not fully loaded. This kind of result has been used as input to the E3F framework proposed by the EARTH project, that allows to take into account long-term traffic variations and the mix of deployments that are typical of a modern telecommunication network, providing in that way a global assessment of energy efficiency in relay enhanced network.

Resource allocation for network-controlled device-to-device communications in LTE-Advanced

Network-controlled device-to-device (D2D) communication allows cellular users to communicate directly, i.e., without passing through the eNodeB, while the latter retains control over resource allocation. This allows the same time–frequency resources to be allocated to spatially separated D2D flows simultaneously, thus increasing the cell throughput. This paper presents a framework for: (1) selecting which communications should use the D2D mode, and when, and (2) allocating resources to D2D and non-D2D users, exploiting reuse for the former. We show that the two problems, although apparently similar, should be kept separate and solved at different timescales in order to avoid problems, such as excessive packet loss. We model both as optimization problems, and propose a heuristic solution to the second, which must be solved at millisecond timescales. Simulation results show that our framework is practically viable, it avoids the problem of packet losses, increases throughput and reduces delays.

Practical large-scale coordinated scheduling in LTE-Advanced networks

In LTE-Advanced, the same spectrum can be re-used in neighboring cells, hence coordinated scheduling is employed to improve the overall network performance (cell throughput, fairness, and energy efficiency) by reducing inter-cell interference. In this paper, we advocate that large-scale coordination can be obtained through a layered solution: a cluster of few (i.e., three) cells is coordinated at the first level, and clusters of coordinated cells are then coordinated at a larger scale (e.g., tens of cells). We model both small-scale coordination and large-scale coordination as optimization problems, show that solving them at optimality is prohibitive, and propose two efficient heuristics that achieve good results, and yet are simple enough to be run at every transmission time interval. Detailed packet-level simulations show that our layered approach outperforms the existing ones, both static and dynamic.

FANTASTIC-5G: flexible air interface for scalable service delivery within wireless communication networks of the 5th generation

5th generation mobile networks will have to cope with a high degree of heterogeneity in terms of services, mobility, number of devices and so on. Thus, diverse and often contradicting key performance indicators need to be supported, but having multiple radio access technologies for multi-service support below 6i¾źGHz will be too costly. FANTASTIC-5G will develop a new multi-service air interface through a modular design. To allow the system to adapt to the anticipated heterogeneity, some properties need to be pursued, like simplicity, flexibility, scalability, versatility, efficiency and future proofness. Based on these properties, a selected set of use cases and link and network design will be presented. The paper will also comprise validation and system level simulations through some indicative results and will conclude with the overall impact to 5G standardisation. Copyright

Power-Aware Allocation of MBSFN Subframes Using Discontinuous Cell Transmission in LTE Systems

In LTE and its evolutions, energy efficiency is a critical aspect, also in view of the dramatic traffic growth foreseen for the next years. Cell Discontinuous Transmission (DTX) techniques can be important tools to achieve the needed efficiency in the networks, and one possibility is to implement the DTX by switching off the eNB at some subframes (MBSFN subframes) and not in others (where reference signals are also transmitted). Switching schedules in LTE are made for larger periods (e.g., 40/80ms or even more). We present an algorithm that i) estimates how many resources will be needed in a period, and ii) decides how many resource blocks to activate in each subframe so as to maximize the power efficiency. We show that the power saving is significant, close to the theoretical minimum at low loads. This comes with no reduction in cell throughput and without impacting the QoS (a tolerable extra delay is added only at low loads).

Flexible dynamic coordinated scheduling in virtual-RAN deployments

Using Coordinated Scheduling (CS), eNodeBs in a cellular network dynamically agree on which Resource Blocks (not) to use, so as to reduce the interference, especially for cell-edge users. This paper describes a software framework that allows dynamic CS to occur among a relatively large number of nodes, as part of a more general framework of network management devised within the Flex5Gware project. The benefits of dynamic CS, in terms of spectrum efficiency and resource saving, are illustrated by means of simulation and with live measurements on a prototype implementation using virtualized eNodeBs.

Fast and Agile Lossless Mode Switching for D2D Communications in LTE-Advanced Networks

Direct (or D2D) communications allow two UEs to communicate without passing through the eNodeB. However, the two UEs may still need to relay their communication through the eNB from time to time, hence should be able to switch from the direct to the re-layed mode seamlessly, without this affecting the QoS. In this paper we show that in conventional systems a mode switching may cause relevant losses, and propose two architectures to miti-gate or solve this problem. Our proposals do not require extra signaling or additional functionalities to be added to the network, hence are scalable and inexpensive. We assess their effectiveness through detailed system-level simulations.

Broadcasting in LTE-Advanced networks using multihop D2D communications

In an LTE-Advanced network, network-controlled Device-to-Device (D2D) communications can be combined in a multihop fashion to distribute broadcasts over user-defined (and possibly large) areas, with small latencies and occupying few resources. Such a service may be exploited for several purposes, (e.g. Internet of Things, Vehicular communications). Engineering a multihop D2D-based broadcast service requires working at both the application level on the User Equipment (UE) and at the resource-allocation level within the eNodeBs. This paper describes the necessary modifications at both the UE and the eNodeB, what the main issues are, and how to solve them efficiently. We evaluate the performance of the above service using system-level simulations, and demonstrate its advantages over standard broadcasting techniques.

Improving network performance via optimization-based centralized coordination of LTE-A Cells

This paper shows how to improve the overall network performance (cell throughput, fairness, and energy efficiency) via centralized coordination of LTE-A cells. We first present optimization models for small-scale coordination (i.e., three cells). Then, we show that extending the same solution to a higher number of cells is generally unfeasible, due to both an unfeasible amount of reporting on the UE side, and too high computational requirements. To overcome this limitation we then propose a layered solution which i) relies on small-scale coordination at the first level (e.g., three cells at the same site), and ii) coordinates groups of coordinated cells at a higher scale (i.e., tens of cells), using optimization models, reaping the benefits of a centralized architecture. We show through packet-level simulations that our scheme brings significant benefits, in terms of fairness, throughput, and energy efficiency.