Carlos F. M. e Silva

What happens with a proportional fair cellular scheduling when D2D communications underlay a cellular network

Device-to-Device (D2D) communications are seen as promising technology for future wireless systems. However, while underlying cellular networks they can negatively affect the performance of cellular communications when intra-cell spectrum sharing is enabled. The impact of D2D communications is not only seen on the cellular throughput, but also on the decision-making of the cellular scheduling policy. In this paper, we provide an impact assessment of D2D communications on the performance of Proportional Fair (PF) scheduling for a Long Term Evolution (LTE) multi-cell scenario through system-level simulations. Results show that due to excessive interference generated by D2D communications and depending on the accuracy of the link quality measure used to estimate the instantaneous data rate, a PF cellular scheduling policy may get stuck in an infinite loop and continuously selects the same User Equipments (UEs), which reduces the cellular throughput, or even approaches the performance of a Maximum Rate (MR)-based policy, thus affecting service coverage and fairness.

Power control schemes for energy efficiency of cellular and device-and-device communications

Device-to-Device (D2D) communications underlying cellular networks are a way to increase the network capacity and potentially save the battery lifetime of closely located physical devices. However, D2D communications can generate significant interference to the cellular network when the same resources are shared by both systems. Therefore, the design of Power Control (PC) schemes is required to keep the interference under control, get energy-efficient transmissions and protect cellular devices. In this work, we investigated operating points of the Soft Dropping Power Control (SDPC) and Open-Loop Power Control (OLPC) schemes for energy efficiency of cellular and D2D communications in uplink OFDMA systems. Results indicate that the SDPC performs better for cellular links and OLPC provides higher gains for D2D links in terms of energy efficiency. While high values of pathloss compensation factor α have been widely used in OLPC studies for the LTE standard, α ϵ {0.4, 0.5} has provided high energy efficiency gains for D2D links. Also, by properly setting the parameters of the OLPC applied to D2D links in uplink and considering the most favorable scenario for sharing resources in all cells, the minimum cost for having spectral efficiency gains for D2D communications represents an impact of 11 % on the system spectral efficiency of cellular communications.

Uplink Power Control with Variable Target SINR for D2D Communications Underlying Cellular Networks

Researches in Power Control (PC) schemes are fundamental to provide efficient algorithms and understand their behavior in Device-to-Device (D2D) scenario. The aim of the current study is to investigate Open Loop Power Control (OLPC), Closed Loop Power Control (CLPC) and indicate Soft Dropping Power Control (SDPC) like an alternative PC scheme to D2D communications underlaying a cellular network. We briefly review PC schemes, suggest a new point of dynamic offset compensation factor σ setting the issue in CLPC and evaluate its performance in terms of spectral and power efficiency. Results demonstrate that SDPC keeps a reasonable spectral efficiency and provides a gain of 70% in power efficiency in relation Long Term Evolution (LTE) PC schemes for cellular communications, and the factor σ = 0.8 can modify the behavior of CLPC because increases the Signal to Interference-plus-Noise Ratio (SINR) of the worst users.

UE grouping and mode selection for D2D communications underlaying a multicellular wireless system

Network-assisted Device-to-Device (D2D) communication is a promising technology for next generation wireless systems being seen as a means to improve spectrum utilization and reduce energy consumption. However, D2D communications can generate significant interference to cellular communications when resources are shared by both types of communication. Aiming at the reduction of the intracell interference and spectral efficiency improvement, we formulate and analyze methods to group conventional and D2D-capable User Equipments (UEs) for shared resource usage and to decide if D2D-capable UEs should communicate directly or via the Evolved Node B (eNB). The results show that D2D communications can improve the spectral efficiency of the system and that most of this improvement can be achieved by suitably grouping the UEs for sharing resources.

Interference Mitigation Using Band Selection for Network-Assisted D2D Communications

For systems with reuse factor less than one, the co- channel interference can drastically reduce the gain of primary networks, which limits the whole system performance. This paper exploits the selection of Downlink (DL) or Uplink (UL) band to be reused by a Device-to-Device (D2D) link. The band selected by the method is based on a radio distance metric, such as received power. Despite being a simple concept, results have shown that band selection can effectively mitigate the interference caused by D2D communications in a Long Term Evolution (LTE) network. Therefore, the coexistence of cellular and D2D communication modes becomes possible in time, frequency, and space.

Network-Assisted Neighbor Discovery Based on Power Vectors for D2D Communications

Device-to-Device (D2D) communication is seen as a promising technology to increase the capacity of current wireless systems without extra electromagnetic spectrum bands. However, before starting a D2D communication, Mobile Stations (MSs) must be aware of their neighbors, through a discovery process. While operating in cellular networks, such process may benefit from the network-assistance. In this paper, we propose a method based on the available network power measures to improve the discovery process. Results show that our proposal is less complex but still outperforms traditional methods when considering the time to detect all neighbors.

SWOT analysis for TV white spaces

The digital dividend will occur when the transition from analogue to digital television TV becomes effective. The freed and interleaved spectrum, known as TV white spaces TVWS, may be a good opportunity for business related with new wireless services based on software-defined radio SDR and cognitive radio CR technologies. In this scope, the strengths, weaknesses, opportunities and threats SWOT analysis-which is a tool to help in the identification of inner internal origin and outer external origin factors of a company, service or product, which characterise its position in the market-is considered a useful tool to evaluate the chances of success for this new spectrum usage paradigm. In this work, we present a suitable SWOT analysis for the use of TV white spaces considering three different reference scenarios in the European context: spectrum of commons, secondary spectrum market and prioritised services public safety.Copyright

Radio Resource Management for Device-to-Device Communications in Long Term Evolution Networks

Device-to-Device (D2D) communications enables direct and low-power communication among devices, leading to an increased and intelligent spatial reuse of radio resources and allowing to offload traffic from the primary data network. Furthermore, the proximity between devices allows data transfer with low delays and high rates without requiring extra power from devices’ batteries. Other benefits of D2D communication when underlying a conventional cellular network are the reuse gain and hop gain. However, in order to realize the potential gains of D2D communications as a secondary network, some key issues must be controlled. First, at each transmission request for a D2D-capable device, it is necessary to determine the neighbors, i.e., other D2D-capable devices that are in the vicinity of the latter and therefore may establish a D2D communication. Then, once neighbors are discovered and the target device is determined to be in the neighbors’ poll, the actual link (channel) conditions must be evaluated. Radio Resource Management (RRM) techniques are employed so that the co-channel interference caused in cellular devices is mitigated. Such techniques may be summarized as: band selection, grouping, mode selection, and power control. In this chapter, we focus our attention in the RRM for D2D communications underlying a LTE-like network, and the main RRM techniques to mitigate the co-channel interference. Namely, we draw the basis for grouping, mode selection, and power control techniques, and present some results that show their benefits.

Impact of fog and cloud computing on an IoT service running over an optical/wireless network testbed

With the advance of the Internet of Things (IoT), the interaction between humans and smart objects is already a reality. New applications that are expected to operate in dynamic environments must support different modes of human/machine interaction (e.g., voice and sign language), exhibit same or better performance in heterogeneous wireless and optical networks, and be able to react in real time. In particular, dispersed computing has arisen as an approach to deal with latency issues in this context. In the work described herein, we design a smart lighting IoT system that allows control of light bulbs (turn on/off, color and brightness change) through voice and sign language. This work addresses the idea of dispersed computing, which is implemented through fog computing, and combines it with virtualized resources to mitigate latency in the convergence point between wireless and optical networks. The proof-of-concept implementation of our design demonstrates the viability of the approach.

Demo abstract: Assessing the impact of fog and cloud computing on an IoT service running over an optical/wireless network-An experimental approach

In this demonstration, we explore the impact of optical-wireless network infrastructure when we vary the locus of computing for Internet of Things (IoT) services. Those services could involve devices ranging from low complexity sensors and actuators (e.g., smart light bulbs) to more advanced ones (e.g., multimedia sensors and smart glasses); in our experiment, we focus on the former. We design a smart light system that allows the control of light bulbs (on/off, color, brightness) through voice and sign language. We vary the location at which the command processing (voice or sign recognition) takes place — locally or in the cloud — and assess its impact on the latency in the response to the command.