Delay-Optimal User Scheduling and Inter-Cell Interference Management in Cellular Network via Distributive Stochastic Learning

In this paper, we propose a distributive queueaware intra-cell user scheduling and inter-cell interference (ICI) management control design for a delay-optimal celluar downlink system with M base stations (BSs), and K users in each cell. Each BS has K downlink queues for K users respectively with heterogeneous arrivals and delay requirements. The ICI management control is adaptive to joint queue state information (QSI) over a slow time scale, while the user scheduling control is adaptive to both the joint QSI and the joint channel state information (CSI) over a faster time scale. We show that the problem can be modeled as an infinite horizon average cost Partially Observed Markov Decision Problem (POMDP), which is NP-hard in general. By exploiting the special structure of the problem, we shall derive an equivalent Bellman equation to solve the POMDP problem. To address the distributive requirement and the issue of dimensionality and computation complexity, we derive a distributive online stochastic learning algorithm, which only requires local QSI and local CSI at each of the M BSs. We show that the proposed learning algorithm converges almost surely (with probability 1) and has significant gain compared with various baselines. The proposed solution only has linear complexity order O(MK)

Scheduling y control de flujo en HSDPA

En los próximos años, se espera que los servicios de datos se conviertan en la principal fuente de tráfico en redes móviles celulares 3G. Esta evolución del mercado de las comunicaciones móviles supondrá la demanda de sistemas de mayor capacidad y de mayores tasas de transferencia. Dentro de este contexto, el 3GPP ha introducido una nueva funcionalidad dentro de las especificaciones de Release 5 que se conoce como High Speed Downlink Packet Access (HSDPA) y que representa una evolución de la interfaz radio WCDMA. Los principales objetivos de HSDPA son incrementar la tasa de transferencia por usuario, mejorar la calidad de servicio percibida por el usuario y conseguir reducir el coste por bit de datos entregado. El logro de estos objetivos está fuertemente condicionado por la elección e interacción de dos mecanismos clave dentro del funcionamiento de HSDPA: el scheduling realizado en el Nodo B y el control de flujo entre Nodo B y RNC. En este artículo se pretende recoger y resumir los distintos tipos de uno y otro mecanismo aparecidos en la literatura científica hasta la fecha, identificando sus bondades e inconvenientes

Contribución a la mejora del control de flujo en redes de acceso inalámbrico

[SPA] Esta tesis se enmarca en el estudio de la red de transporte de las redes de acceso radio (Radio Access Networks, RANs), también denominado Backhaul. En particular esta tesis aborda los problemas asociados a la congestión en el Backhaul mediante una aproximación basada en teoría de control y la optimización matemática. Los problemas causados por la congestión en el Backhaul son de distinta naturaleza dependiendo de la tecnología RAN a la que da soporte. En esta tesis elaboramos un recorrido histórico por la evolución de las tecnologías RAN durante las dos últimas décadas, en el que nos centramos en las funcionalidades que dependen del Backhaul, y en las diferentes y en general, más exigentes, demandas que éstas imponen en la infraestructura de Backhaul. Iniciamos nuestro recorrido en las redes 3G (Universal Mobile Telecommunication System, UMTS), proseguimos con 3.5G (High Speed Data Access, HSDA) y finalizamos con 4G (Long Term Evolution, LTE). Describimos el impacto que la congestión del Backhaul tiene en cada una de ellas y se proponen mecanismos de control para contrarrestar sus efectos negativos. Los objetivos de esta tesis son los siguientes: 1. Proponer y evaluar mecanismos de control que mejoren el rendimiento de la sincronización de canal de transporte en FP en situaciones de congestión del backhaul. El marco tecnológico de este objetivo son las redes 3G (UMTS). 2. Proponer y evaluar mecanismos de control de flujo que consideren conjuntamente el interfaz radio y en el backhaul. El marco tecnológico de este objetivo es 3.5G (HSPA). 3. Proponer y evaluar un scheduling radio que considere conjuntamente los recursos del interfaz radio y del backhaul. El marco tecnológico de este objetivo es 4G (LTE). 4. Proponer y evaluar mecanismos de asignación coordinada de recursos en el interfaz radio y el backhaul. El marco tecnológico de este objetivo es 4G (LTE). 5. Abordar los objetivos anteriores dentro de la compatibilidad con las especificaciones técnicas de los protocolos implicados. Con respecto al último objetivo, consideramos que no resulta realista plantear algoritmos que impliquen un cambio en sistemas ya estandarizados y de amplio despliegue. Sin embargo, las especificaciones del 3GPP no tienen vocación de definir el funcionamiento de todos los algoritmos involucrados ya que su objetivo último es determinar claramente las interfaces para facilitar la interconexión entre dispositivos y equipos de distintos fabricantes y operadores. Los mecanismos que internamente emplean muchos protocolos para realizar ciertas tareas, en particular algoritmos de gestión de recursos o scheduling, se dejan abiertos a la implementación de los fabricantes, de forma que estos pueden diferenciarse tecnológicamente unos de otros en un entorno de competencia. Esto permite que nuevos mecanismos como los propuestos en este trabajo tengan cabida en los sistemas considerados. El objetivo principal de la Sincronización de Canal de Transporte en redes UMTS es que las tramas enviadas por la RNC lleguen a tiempo a los Nodos B para su transmisión a través del interfaz radio. Para ello, el 3GPP especifica un algoritmo conocido como Timing Adjustment que se encarga de controlar el retraso que experimentan las tramas en el interfaz Iub sumando o restando una cantidad constante. Este algoritmo reacciona con demasiada lentitud ante variaciones abruptas del retardo del interfaz Iub y, además, se puede volver inestable en escenarios de alta demora. Son situaciones que pueden estar propiciadas, entre otros motivos, por la congestión en el backhaul. Aplicando teoría de control en tiempo discreto, proponemos un nuevo mecanismo que garantiza la estabilidad en cualquier situación y mejora el rendimiento del algoritmo clásico. Las medidas de rendimiento se realizan mediante un simulador de la red UTRAN (UMTS RAN) teniendo en cuenta condiciones reales de tráfico en el interfaz Iub. Con la incorporación de HSPA en las redes UMTS la función de scheduling se ha desplazado desde la RNC hasta el Nodo B, generando la necesidad de unos buffers en el Nodo B. A su vez, esta nueva distribución de la capacidad de almacenamiento entre la RNC y el Nodo B requiere de un mecanismo de control de flujo que regule la transferencia de datos entre ambos. En esta tesis realizamos un detallado estudio analítico de este control de flujo abordándolo como un problema de optimización cuadrática. Partiendo de este análisis desarramos un nuevo algoritmo de control de flujo que consigue minimizar el retardo extremo a extremo gracias a que incorpora como parámetro la ocupación de los buffers de la RNC (además de la ocupación en el backhaul en el algoritmo de gestión de recursos radio, o scheduling. Para ello consideramos un escenario sencillo compuesto por una sola celda y una infraestructura backhaul consistente en un enlace punto-a-punto de capacidad C. Mostramos que cuando el backhaul es el cuello de botella, el rendimiento del scheduler radio con consideraciones de backhaul es claramente superior al scheduler convencional. Haciendo uso de técnicas de optimización de la utilidad de la red (NUM), abordamos de forma conjunta la gestión de recursos radio y del backhaul. Empleando descomposición dual, proponemos un mecanismo distribuido y de baja carga computacional que permite generar decisiones de asignación de recursos en el backhaul y en el interfaz radio, de forma coordinada y subtrama a subtrama. Finalmente, incorporamos en nuestro algoritmo el control _optimo de colas tandem, mejorando aun más el rendimiento respecto a los schedulers no coordinados. el Nodo B), algo que no se había considerado en algoritmos anteriores. Se trata, por tanto, de un control de flujo consciente del backhaul (backhaul-aware). Desde la implantación de LTE (4G), las tasas máximas de transmisión alcanzables en el interfaz radio se han disparado con respecto a las anteriores generaciones de sistemas móviles. Por primera vez operadores, fabricantes y comunidad académica coinciden en la necesidad de optimizar el uso los recursos del backhaul además de los recursos radio. En esta tesis estudiamos el impacto que tiene el backhaul en el algoritmo de gestión de recursos radio, o scheduling. Para ello consideramos un escenario sencillo compuesto por una sola celda y una infreastructura backhaul consistente en un enlace punto-a-punto de capacidad C. Mostramos que cuando el backhaul es el cuello de botella, el rendimiento del scheduler radio con consideraciones de backhaul es claramente superior al scheduler convencional. Haciendo uso de t_ecnicas de optimización de la utilidad de la red (NUM), abordamos de forma conjunta la gestión de recursos radio y del backhaul. Empleando descomposición dual, proponemos un mecanismo distribuido y de baja carga computacional que permite generar decisiones de asignación de recursos en el backhaul y en el interfaz radio, de forma coordinada y subtrama a subtrama. Finalmente, incorporamos en nuestro algoritmo el control _optimo de colas tandem, mejorando aun más el rendimiento respecto a los schedulers no coordinados.[ENG] The framework of this thesis is the backhaul of radio access networks (RANs). We refer to backhaul as the infrastructure connecting the base stations of a cellular networks to either the radio network controller (RNCs) nodes or the core network nodes. In particular, this thesis addresses the issues associated to the congestion of the backhaul and the control algorithms that manage the resources of this infrastructure. The potential problems caused in the RAN by the backhaul congestion are of different nature depending on the RAN technology. We will provide a historical overview of the evolution of the RAN technologies over the last two decades, focusing on the functionalities relying on the backhaul, and how each generation imposes different and somewhat more stringent demands on the backhaul infrastructure. Along this work we focus chronologically on a specific RAN generation, starting with 3G, in particular Universal Mobile Telecommunication System (UMTS), then 3.5, High Speed Data Access (HSPA) and 4G Long Term Evolution (LTE). On each one, we study the impact of backhaul congestion on the RAN performance and propose a strategy to optimally control and manage the resources of the system. The objectives of this thesis can be formulated as follows: 1. To develop and evaluate effective control schemes to improve the performance of the transport channel synchronization functionality under backhaul congestion. The technological framework of this first objective is 3G (UMTS). 2. To develop and evaluate own control mechanisms that jointly consider the radio interface and the backhaul. The technological framework of this second objective is 3.5G (HSPA). 3. To study the impact of backhaul congestion on downlink scheduling over the radio interface. The technological framework of this second objective is 3.5G (HSPA). 4. To develop and evaluate mechanisms for coordinate resource allocation at both the radio interface and the backhaul. 5. To address previous objective with proposals that are compliant with the technical specifications of the involved protocols. With regard to this last objective, we consider that it is not fully realistic to come up with algorithms implying changes in systems that are already standardized and widely deployed. However, 3GPP standards do not pretend to define every algorithm involved, since the 3GPP's main objective is to clearly specify the interfaces to allow the interoperability between operators and deferent vendors' devices. The internal mechanisms contained in deferent layers of the protocol stack to accomplish each task are generally left open to operator or vendor choice. Especially resource management functions (such as scheduling or congestion control). This approach leverages innovation and research within the industry and the academia, and allows that mechanisms as the ones presented in this thesis be feasible within existing standardized cellular networks. The main objective of transport channel synchronization in UMTS is to make sure that the frames sent by the RNC arrive on time to the Nodes B (NBs) to be transmitted over the radio interface. For this task, the 3GPP specifies an algorithm known as timing adjustment (TA) that controls the delay suffered by the frames over the interface (Iub) connecting each NB with its corresponding RNC. The TA can add or subtract a certain quantity to the transmission delay. We show that the typical mechanism reacts too slowly in situations where the Iub delay increases abruptly, e.g. under transient congestion of the Iub. Besides, this classic algorithm shows potential instability issues in scenarios of very high delay. We address this problem using the tools of discrete-time control theory, which allows us to propose a new scheme that assures stability under any circumstances and improves the classical mechanism. The performance evaluation is carried out by means of simulation and considering realistic traffic scenarios for the Iub. With the introduction of HSPA (3.5G) in UMTS, the scheduling function was moved from the RNC to the Node B, imposing the inclusion of new data buffers at the NBs. Additionally, this redistribution of the data storage function between the RNCs and the NBs created the need of a flow control mechanism regulating the data transfers on the Iub. We model and analyze this mechanism as a quadratic optimization problem, and exploit this approach to propose a new flow control scheme that minimizes the end-to-end delay over the RAN by considering no only the situation of the NB buffer, but also of the RNC buffers. Our approach is a backhaul-aware optimal flow control system for RAN. Finally, in LTE (4G) systems, the peak transmission rates achievable by a user over the radio interface have boosted compared to previous generations. For the first time operators, vendors and the academic community agree on the need to optimize the backhaul resources, not only the radio resources. In fact, our point is that backhaul congestion impacts the performance of radio resource allocation and this function should be redesigned taking into consideration the capacity limitation of the backhaul. We use network utility maximization (NUM) techniques to address the problem of joint radio-backhaul scheduling. We use a dual decomposition approach to propose a low-complexity, distributed mechanism, that can make resource allocation decisions in a subframe basis. Finally, we incorporate the optimal control policy for tande queues in our mechanism, improving even more the performance compared to non-coordinated schedulers.Universidad Politécnica de Cartagen

A study of mobile VoIP performance in wireless broadband networks

Voice service is to date still the killer mobile service and the main source for operator revenue for years to come. Additionally, voice service will evolve from circuit switched technologies towards packet based Voice over IP (VoIP). However, using VoIP over wireless networks different from 3GPP cellular technologies makes it also a disruptive technology in the traditional telecommunication sector. The focus of this dissertation is on determining mobile VoIP performance in different wireless broadband systems with current state of the art networks, as well as the potential disruption to cellular operators when mobile VoIP is deployed over different access networks. The research method is based on an empirical model. The model and experiments are well documented and based on industry standards for voice quality evaluation. The evaluation provides results from both experiments in a controlled laboratory setup as well as from live scenarios. The research scope is first, evaluate each network technology independently; second, investigate vertical handover mobility cases; third, determine other aspects directly affecting end user experience (e.g., call setup delay and battery lifetime). The main contribution of this work is a systematic examination of mobile VoIP performance and end user experience. The research results point out the main challenges for achieving call toll quality, and how derive the required changes and technological performance roadmap for improved VoIP service. That is, investigate how the performance and usability of mobile VoIP can eventually be improved to be a suitable substitute for circuit switched voice. In addition, we evaluate the potential disruption to cellular operators that mobile VoIP brings when deployed over other access networks. This research extends the available knowledge from simulations and provides an insight into actual end user experience, as well as the challenges of using embedded clients in handheld devices. In addition, we find several issues that are not visible or accounted for in simulations in regard to network parameters, required retransmissions and decreased battery lifetime. The conclusion is that although the network performance of several wireless networks is good enough for near toll quality voice in static scenarios, there are still a number of problems which make it currently unfeasible to use as a primary voice service. Moreover, under mobility scenarios performance is degraded. Finally, there are other issues apart from network performance such as energy consumption, hardware limitations and lack of supporting business models (e.g., for WiFi mesh) that further limit the possibility of rolling out mobile VoIP services

Dynamic control of wireless networks with confidential communications

Future wireless communication systems are rapidly transforming to satisfy everincreasing and varying mobile user demands. Cross-layer networking protocols have the potential to play a crucial role in this transformation by jointly addressing the requirements of user applications together with the time-varying nature of wireless networking. As wireless communications becoming an integral and crucial part of our daily lives with many of our personal data is being shared via wireless transmissions, the issue of keeping personal transactions confidential is at the forefront of any network design. Wireless communications is especially prone to attacks due to its broadcast nature. The conventional cryptographical methods can only guarantee secrecy with the assumption that it is computationally prohibitive for the eavesdroppers to decode the messages. On the other hand, information-theoretical secrecy as defined by Shannon in his seminal work has the potential to provide perfect secrecy regardless of the computational power of the eavesdropper. Recent studies has shown that information-theoretical secrecy is possible over noisy wireless channels. In this thesis, we aim to design simple yet provably optimal cross-layer algorithms taking into account information-theoretical secrecy as a Quality of Service (QoS) requirement. Our work has the potential to improve our understanding the interplay between the secrecy and networking protocols. In most of this thesis, we consider a wireless cellular architecture, where all nodes participate in communication with a base station. When a node is transmitting a confidential messages, other legitimate nodes are considered as eavesdroppers, i.e., all eavesdroppers are internal. We characterize the region of achievable open and confidential data rate pairs for a single and then a multi-node scenario. We define the notion of confidential opportunistic scheduler, which schedules a node that has the largest instantaneous confidential information rate, with respect to the best eavesdropper node, which has the largest mean cross-channel rate. Having defined the operational limits of the system, we then develop dynamic joint scheduling and flow control algorithms when perfect and imperfect channel state information (CSI) is available. The developed algorithms are simple index policies, in which scheduling and flow control decisions are given in each time instant independently. In real networks, instantaneous CSI is usually unavailable due to computational and communication overheads associated with obtaining this information. Hence, we generalize our model for the case where only the distributions of direct- and crosschannel CSI are available at the transmitter. In order to provide end-to-end reliability, Hybrid Automatic Retransmission reQuest (HARQ) is employed. The challenge of using HARQ is that the dynamic control policies proposed in the preceding chapter are no longer optimal, since the decisions at each time instant are no longer independent. This is mainly due to the potential of re-transmitting a variant of the same message successively until it is decoded at the base station. We solve this critical issue by proposing a novel queuing model, in which the messages transmitted the same number of times previously are stored in the same queue with scheduler selecting a head-of-line message from these queues. We prove that with this novel queuing model, the dynamic control algorithms can still be optimal. We then shift our attention to providing confidentiality in multi-hop wireless networks, where there are multiple source-destination pairs communicating confidential messages, to be kept confidential from the intermediate nodes. For this case, we propose a novel end-to-end encoding scheme, where the confidential information is encoded into one very long message. The encoded message is then divided into multiple packets, to be combined at the ultimate destination for recovery, and being sent over different paths so that each intermediate node only has partial view of the whole message. Based on the proposed end-to-end encoding scheme, we develop two different dynamic policies when the encoded message is finite and asymptotically large, respectively. When the encoded message has finite length, our proposed policy chooses the encoding rates for each message, based on the instantaneous channel state information, queue states and secrecy requirements. Also, the nodes keep account of the information leaked to intermediate nodes as well the information reaching the destination in order to provide confidentiality and reliability. We demonstrate via simulations that our policy has a performance asymptotically approaching that of the optimal policy with increasing length of the encoded message. All preceding work assumes that the nodes are altruistic and/or well-behaved, i.e., they cooperatively participate into the communication of the confidential messages. In the final chapter of the thesis, we investigate the case with non-altruistic nodes, where non-altruistic nodes provide a jamming service to nodes with confidential communication needs and receiving in turn the right to access to the channel. We develop optimal resource allocation and power control algorithms maximizing the aggregate utility of both nodes with confidential communication needs as well as the nodes providing jamming service

Prediction-based techniques for the optimization of mobile networks

Mención Internacional en el título de doctorMobile cellular networks are complex system whose behavior is characterized by the superposition of several random phenomena, most of which, related to human activities, such as mobility, communications and network usage. However, when observed in their totality, the many individual components merge into more deterministic patterns and trends start to be identifiable and predictable. In this thesis we analyze a recent branch of network optimization that is commonly referred to as anticipatory networking and that entails the combination of prediction solutions and network optimization schemes. The main intuition behind anticipatory networking is that knowing in advance what is going on in the network can help understanding potentially severe problems and mitigate their impact by applying solution when they are still in their initial states. Conversely, network forecast might also indicate a future improvement in the overall network condition (i.e. load reduction or better signal quality reported from users). In such a case, resources can be assigned more sparingly requiring users to rely on buffered information while waiting for the better condition when it will be more convenient to grant more resources. In the beginning of this thesis we will survey the current anticipatory networking panorama and the many prediction and optimization solutions proposed so far. In the main body of the work, we will propose our novel solutions to the problem, the tools and methodologies we designed to evaluate them and to perform a real world evaluation of our schemes. By the end of this work it will be clear that not only is anticipatory networking a very promising theoretical framework, but also that it is feasible and it can deliver substantial benefit to current and next generation mobile networks. In fact, with both our theoretical and practical results we show evidences that more than one third of the resources can be saved and even larger gain can be achieved for data rate enhancements.Programa Oficial de Doctorado en Ingeniería TelemáticaPresidente: Albert Banchs Roca.- Presidente: Pablo Serrano Yañez-Mingot.- Secretario: Jorge Ortín Gracia.- Vocal: Guevara Noubi

Intelligent Circuits and Systems

ICICS-2020 is the third conference initiated by the School of Electronics and Electrical Engineering at Lovely Professional University that explored recent innovations of researchers working for the development of smart and green technologies in the fields of Energy, Electronics, Communications, Computers, and Control. ICICS provides innovators to identify new opportunities for the social and economic benefits of society.　 This conference bridges the gap between academics and R&D institutions, social visionaries, and experts from all strata of society to present their ongoing research activities and foster research relations between them. It provides opportunities for the exchange of new ideas, applications, and experiences in the field of smart technologies and finding global partners for future collaboration. The ICICS-2020 was conducted in two broad categories, Intelligent Circuits & Intelligent Systems and Emerging Technologies in Electrical Engineering