- Energy Transfer in Sustainable Mobile Networks
Ángel Fernández Gambín
Abstract: The design of energy efficient and possibly self-sustainable deployments is key to reduce their impact on the environment, and diminish their operating expense. As a solution to this, we advocate base stations featuring energy harvesting and storage capabilities, as well as energy transfer among network elements. Here, we first discuss about to wirelessly recharge mobile terminals as they get sufficiently close to the Base Stations (BSs) through Wireless Power Transfer (WPT) technology, accounting for different mobility models, speeds, frequency range and inter-BS distance. Our numerical results reveal that: i) mobility matters: group mobility leads to higher efficiencies and an increasing speed is also beneficial, and ii) WPT can substantially reduce the number of dead nodes in the network, although transfer efficiencies are very low under any scenario. Then, energy transfer between BSs utilizing a power packet grid will be addressed, compensating for imbalance in the harvested energy or in the load. We formulate the optimal energy allocation and routing as a convex optimization problem. An optimal assignment based on the Hungarian method is also presented. Our numerical results reveal that the proposed convex policy: (i) substantially improves the energy self-sustainability of the system, (ii) decreases its outage probability to nearly zero, and (iii) the amount of energy purchased from the electrical grid can be significantly reduced.
- Optimal renewable energy conservation policies for self-sustainable Small Cells
Abstract: Current trends anticipate that 5G mobile networks will be composed of ultra-dense deployments of heterogeneous Base Stations (BSs), where BSs using different transmission powers coexist to provide the 1000x network capacity increase that is required by 2020. Accordingly, the traditional macro cell layer will be complemented or replaced with multiple overlapping tiers of smaller cells, which extend the system capacity, thanks to a higher spatial reuse and to a better spectral efficiency. We introduce a two-tier cellular network architecture, where self-sustainable small cells, solely relying on energy harvesting and storage, can offload the grid-connected macro base station. The available energy at the SC must be allocated in an optimal way, in order to jointly minimize the consumption of grid energy and maximize the system performance. The proposed offline optimal algorithm, based on the label correcting algorithm, finds the optimal energy allocation policy, after transforming the problem into a shortest-path problem.
- Energy harvesting wireless sensor devices: battery processes analysis, battery management, 2-devices study case
Abstract: Energy harvesting is an important feature that can be implemented in mobile devices to provide them with extended autonomy, yet it poses several challenges in terms of optimal battery usage. In this paper, we highlight that some non-ideal effects, especially the so-called “charge recovery,” can have a dramatic impact on the operation policy of autonomous devices. To do so, we construct a Markov model, where we introduce a bi-dimensional battery value, including the apparent energy level, which is what available at the electrodes to power the device, and the actual energy level stored in the battery. When power is not drained by the device, these levels tend to equalize due to charge recovery, but, in the case of intense battery usage, they can be significantly different. We show that this non-ideality leads to considerably different estimates of undesirable events such as battery outages, and may cause a general underutilization of the devices if not properly accounted for. We propose a simplified self-control management of a battery expressed by restrictions, which could be used for an efficient operational strategy of the device. To achieve this, we rely on the double-queue model which includes the imperfections of the battery operation and bi-dimensional battery value. We performed some simulation and we observed that we can diminish the number of variables of the model to predict possible unwanted events such as apparent discharge events and data losses. This observation helps to achieve a self-control management by knowing and managing just few parameters, and therefore offers valuable directions for the development of autonomic and self-sustainable operation. Further, we focus on asymmetries in the nodes energetic capabilities, and how do they impact on the resulting performance. We frame the problem as a repeated Bayesian game with asymmetric players and incomplete information, where also the private information available at each node is asymmetric. We find out that instead of proportionally fair resource utilization, such a situation ends up in an even more unbalanced situation, which leads to an inefficient management where certain nodes are overutilized.
- Challenges and limitations of low power wireless duty-cycled networks
Abstract: As part of the 5GPPP vision of the next generation communication networks, an important role will be played by the industrial-IoT, with applications ranging from infrastructure monitoring to applications that require very strict timing and guarantees for industrial control. The current technologies market is fragmented with divergent solutions and standards for short range or long range communications. Lately, the LPWANs, the solutions for long range communication, is taking control of the industrial IoT market, to which we focus this work (and soon, NB-IoT will do the same in the licensed spectrum). Due to the constrained nature of the devices (power and cost), most of the current technologies on the market have been using very simple approaches, in order to make their customization, deployment and installation as simple and fast as possible. The performance of these networks is poor, as they mainly use Aloha medium access, and the deployment in the ISM bands raises many challenges in trying to improve their performances in order to match the 5G requirements. Specifically, the expected massive connectivity is incompatible with the Aloha approach. Synchronization and resource allocation is one possible solution to this problem.
This talk will go through the challenges that the introducing of synchronization into such restricted network brings, focusing on the specific problems in the way of improving the performance of the LPWAN technologies in context of the 5G demands.
- Flexible Functional Split in Energy Harvesting Virtual Small Cells
Abstract: RAN is rapidly embracing softwarization paradigm. One of these technologies that is being applied to RAN is virtualization. Virtualization enables Baseband (BB) processing in a centralized pool of BB units. The resulting architecture is called CRAN. However, CRAN has limitations due to high capacity and very low-latency front haul requirement, which becomes especially challenging with the trend of densification. To partially alleviate this problem, some literatures suggest flexible baseband functional split between local base station nodes and remote processing clouds. Hence part of the baseband processing is done locally and the remaining is done by the central cloud. This greatly reduces the capacity requirement of the fronthaul. However, power consumption due to baseband processing has a huge share in the total power consumption breakdown of smaller base stations. Given that such base stations are powered by EH, in addition to QoS constraints, energy availability can also condition which baseband processes are to be placed where in the system. This work focuses on determining optimal baseband functional split configuration in virtualized small cells that are solely powered by EH. The work will apply reinforcement learning as a tool to determine the optimal configuration decisions.
- Core network management procedures for self-organized and sustainable 5G cellular networks
Abstract: The basic idea behind green cellular operation is to alleviate the inefficiencies resulting from the fact that todays base stations (BSs) are typically deployed and operated continuously based on peak traffic estimates. Intuitively, it saves energy to carefully turn-off unutilized and under-utilized BSs during off-peak times, while maintaining coverage. From the mobile operator perspective, using mobile datasets in developing network solutions is a strategy that needs to be investigated. Therefore, network solutions should leverage the information obtained from the network logs as the datasets carry promising potential for a variety of fields. The main reason for that, is because it tracks individual and aggregate human activities overtime and space at unprecedented scales and at relatively no cost. In our research work we are developing core network management procedures for energy management in BSs using network function virtualization taking into account the available traffic load information.
Energy Minimization for Strict Delay Constrained Wireless communications
Abstract: The design of efficient transmission policies for resource scheduling and computation offloading under energy harvesting constraints is the key to minimize the energy consumption of the terminal and improve its computing capabilities. In this work, we consider only a scheduling problem using traditional power source. We propose a new scheme that takes into account a strict delay constraint for each queued packet in the system rather than an average delay constraint as in the literature, in addition to a buffer overflow constraint. We model this optimization problem as Constrained Markov Decision Problem where the actions are the number of packets sent on the known channel at each slot. The optimal random policy is exhibited through the resolution of standard linear programming. We show the gain in energy is substantial compared to naive policy.
- Network survival with energy harvesting: secure cooperation and device assisted networking
Abstract: 5G Network sustainability is a key objective in Scavenge project. Mobile devices and Internet of things objects have more energy constrains in terms of energy than other elements in the network. This motivates the deployment of device assisted features that are controlled by the infrastructure. Among these features, direct communication between devices (D2D) and devices aided back-hauling raise significant interest. We are studying cooperation schemes taking into account the security constrains, focusing on cooperation involving mobile terminals and Internet of Things objects, guaranteeing the security of these cooperation schemes.
- Analysis and Modeling of Mobile Traffic Using Real Traces
Hoang Duy Trinh
Abstract: The analysis of real mobile traffic traces is helpful to understand usage patterns of cellular networks. In particular, mobile data processing may be used for network optimization and management in terms of radio resources, network planning, energy saving, for instance. However, real network data is often difficult to be accessed from the operators’ network, due to legal and privacy issues. In our work, we overcome the lack of network information using a LTE sniffer capable of decoding the unencrypted LTE PDCCH and we present a temporal and spatial analysis of the recorded traces. Moreover, we derive a traffic a model for the daily-varying LTE traffic using a DTMC that can be useful in simulative scenarios. We compare our results to the traffic model proposed in the FP7 EARTH project and we show that, with a limited number of states, our model presents a high level of accuracy. Furthermore, we talk about our current works and future research directions.
- Implementation of a Wideband Transceiver System with Per-Band Equalisation and Synchronisation
Abstract: To emit in the TV white space (TVWS) spectrum, the regulator has requested very strict spectral masks, which can be fulfilled using a FFT-modulated filter-bank multi-carrier system (FBMC) to extract one or several TVWS channels in the 470-790MHz range. Such a system reduces the channel dispersion, but even with near-perfectly reconstructing filter bank, the need for equalisation and synchronisation remains. In this work, we propose a per-band equalisation and synchronisation approach, performed by a constant modulus algorithms (CMA) running concurrently with a direction-directed (DD) adaptation process for faster convergence and reduced phase ambiguity. We compare symbol- and fractionally-spaced versions, and investigate their fixed-point implementation on an FPGA. We compare the performance of the different systems in terms of mean squared error, computational cost, and robustness towards noise.
- Utilizing local memories to improve network communication efficiency: Caching and Distributed storage
Abstract: There has been a lot of recent interest in coded caching techniques because of the broadcast nature of wireless communications. The amount of information required to be transmitted on the network can be greatly reduced by multicasting coded messages to serve multiple users simultaneously. This finds application in broadcast satellites, wireless sensor networks and multiple terminal communications. This presentation will cover a popular coded caching strategy for a relevant model. Also with the trend moving towards smaller cells and a high density of low power base stations/access points, ensuring the integrity of data and reliability of access becomes an important issue. For this purpose, content is coded and distributed among a set of multiple nodes to provide robustness against individual node failures, and facilitate efficient repair. However, this also results in reduced gains from coded caching as compared to when a single server serving all the users simultaneously. A novel scheme combining the distributed storage strategy and the coded caching strategy, from a recently submitted paper by me, will be presented.
- Mobility and popularity aware small-cell caching policies
Mehmet Emre Ozfatura
Abstract: Due to densification process of the small-cell base stations (SBS), current methods are not sufficient to analyse the performance of the cache enabled small-cell stations. In heterogeneous cellular networks, due to mobility of users and storage constraints of SBSs, users may not be able to download all of their requested content from the SBSs within the delay deadline of the content and are directed to the macro-cell base station (MBS) in order to satisfy the service quality. In this work, we first introduce a threshold value for the delay deadline according to data rate of the SBSs. Then, we provide an optimal and near optimal distributed caching policies for the cases where the delay deadline is below and over the given threshold respectively.