DiFuse: distributed frequency domain user selection for multi-user MIMO networks

Optimal user selection is important in increasing the capacity of Multi-User Multi-Input Multi-Output Wi-Fi networks, yet it faces a significant challenge; the multi-user diversity gain can be overwhelmed by the formidable Channel State Information (CSI) acquisition overhead. To lessen the overhead, existing schemes adopt the greedy user selection which generally takes the projected norm as the user selection metric, since it considers both the channel power gain and the orthogonality. However, the projected norm suffers from occasional poor user selection, since it does not take the optimal sum capacity gain into account. This paper proposes a new distributed user selection protocol called DiFuse. To employ the sum capacity gain as the user selection metric in DiFuse, each user cleverly computes its own estimated capacity gain by overhearing the CSI feedback from others. The users then simultaneously transmit their feedbacks at the frequency domain via the distributed feedback contention, which effectively reduces the feedback overhead. Then the AP collectively utilizes them for user selection that achieves the maximum positive increment to the sum capacity gain. We implemented the prototype of DiFuse on the USRP N210, and evaluated its performance via both testbed experiments and trace-driven emulations. The results showed that DiFuse outperforms the throughput of the existing scheme called OPUS by 1.8x on average, while maintaining better fairness.OAIID:RECH_ACHV_DSTSH_NO:T201620351RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A001118CITE_RATE:1.006FILENAME:Difuse- distributed frequency domain user selection for multi-user MIMO Networks.pdfDEPT_NM:컴퓨터공학부EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/458535f3-401c-40b1-abae-d2a01534178d/linkCONFIRM:

Throughput Maximization in Unmanned Aerial Vehicle Networks

The use of Unmanned Aerial Vehicles (UAVs) swarms in civilian applications such as surveillance, agriculture, search and rescue, and border patrol is becoming popular. UAVs have also found use as mobile or portable base stations. In these applications, communication requirements for UAVs are generally stricter as compared to conventional aircrafts. Hence, there needs to be an efficient Medium Access Control (MAC) protocol that ensures UAVs experience low channel access delays and high throughput. Some challenges when designing UAVs MAC protocols include interference and rapidly changing channel states, which require a UAV to adapt its data rate to ensure data transmission success. Other challenges include Quality of Service (QoS) requirements and multiple contending UAVs that result in collisions and channel access delays. To this end, this thesis aims to utilize Multi-Packet Reception (MPR) technology. In particular, it considers nodes that are equipped with a Successive Interference Cancellation (SIC) radio, and thereby, allowing them to receive multiple transmissions simultaneously. A key problem is to identify a suitable a Time Division Multiple Access (TDMA) transmission schedule that allows UAVs to transmit successfully and frequently. Moreover, in order for SIC to operate, there must be a sufficient difference in received power. However, in practice, due to the location and orientation of nodes, the received power of simultaneously transmitting nodes may cause SIC decoding to fail at a receiver. Consequently, a key problem concerns the placement and orientation of UAVs to ensure there is diversity in received signal strength at a receiving node. Lastly, interference between UAVs serving as base station is a critical issue. In particular, their respective location may have excessive interference or cause interference to other UAVs; all of which have an impact on the schedule used by these UAVs to serve their respective users

Energy efficient offloading techniques for heterogeneous networks

Mobile data offloading has been proposed as a solution for the network congestion problem that is continuously aggravating due to the increase in mobile data demand. The concept of offloading refers to the exploitation of network heterogeneity with the objective to mitigate the load of the cellular network infrastructure. In this thesis a multicast protocol for short range networks that exploits the characteristics of physical layer network coding is presented. In the proposed protocol, named CooPNC, a novel cooperative approach is provided that allows collision resolutions with the use of an indirect inter-network cooperation scheme. Through this scheme, a reliable multicast protocol for partially overlapping short range networks with low control overhead is provided. It is shown that with CooPNC, higher throughput and energy efficiency are achieved, while it presents lower delay compared to state-of-the-art multicast protocols. A detailed description of the proposed protocol is provided, with a simple scenario of overlapping networks and also for a generalised scalable scenario. Through mathematical analysis and simulations it is proved that CooPNC presents significant performance gains compared to other state-of-the-art multicast protocols for short range networks. In order to reveal the performance bounds of Physical Layer Network Coding, the so-called Cross Network is investigated under diverse Network Coding (NC) techniques. The impact of Medium Access Control (MAC) layer fairness on the throughput performance of the network is provided, for the cases of pure relaying, digital NC with and without overhearing and physical layer NC with and without overhearing. A comparison among these techniques is presented and the throughput bounds, caused by MAC layer limitations, are discussed. Furthermore, it is shown that significant coding gains are achieved with digital and physical layer NC and the energy efficiency performance of each NC case is presented, when applied on the Cross Network.In the second part of this thesis, the uplink offloading using IP Flow Mobility (IFOM) is also investigated. IFOM allows a LTE mobile User Equipment (UE) to maintain two concurrent data streams, one through LTE and the other through WiFi access technology, that presents uplink limitations due to the inherent fairness design of IEEE 802.11 DCF. To overcome these limitations, a weighted proportionally fair bandwidth allocation algorithm is proposed, regarding the data volume that is being offloaded through WiFi, in conjunction with a pricing-based rate allocation algorithm for the rest of the data volume needs of the UEs that are transmitted through the LTE uplink. With the proposed approach, the energy efficiency of the UEs is improved, and the offloaded data volume is increased under the concurrent use of access technologies that IFOM allows. In the weighted proportionally fair WiFi bandwidth allocation, both the different upload data needs of the UEs, along with their LTE spectrum efficiency are considered, and an access mechanism is proposed that improves the use of WiFi access in uplink offloading. In the LTE part, a two-stage pricing-based rate allocation is proposed, under both linear and exponential pricing approaches, with the objective to satisfy all offloading UEs regarding their LTE uplink access. The existence of a malicious UE is also considered that aims to exploit the WiFi bandwidth against its peers in order to upload less data through the energy demanding LTE uplink and a reputation based method is proposed to combat its selfish operation. This approach is theoretically analysed and its performance is evaluated, regarding the malicious and the truthful UEs in terms of energy efficiency. It is shown that while the malicious UE presents better energy efficiency before being detected, its performance is significantly degraded with the proposed reaction method.La derivación del tráfico de datos móviles (en inglés data offloading) ha sido propuesta como una solución al problema de la congestión de la red, un problema que empeora continuamente debido al incremento de la demanda de datos móviles. El concepto de offloading se entiende como la explotación de la heterogeneidad de la red con el objetivo de mitigar la carga de la infraestructura de las redes celulares. En esta tesis se presenta un protocolo multicast para redes de corto alcance (short range networks) que explota las características de la codificación de red en la capa física (physical layer network coding). En el protocolo propuesto, llamado CooPMC, se implementa una solución cooperativa que permite la resolución de colisiones mediante la utilización de un esquema indirecto de cooperación entre redes. Gracias a este esquema, se consigue un protocolo multicast fiable i con poco overhead de control para redes de corto alcance parcialmente solapadas. Se demuestra que el protocolo CooPNC consigue una mayor tasa de transmisión neta (throughput) y una mejor eficiencia energética, a la vez que el retardo se mantiene por debajo del obtenido con los protocolos multicast del estado del arte. La tesis ofrece una descripción detallada del protocolo propuesto, tanto para un escenario simple de redes solapadas como también para un escenario general escalable. Se demuestra mediante análisis matemático y simulaciones que CooPNC ofrece mejoras significativas en comparación con los protocolos multicast para redes de corto alcance del estado del arte. Con el objetivo de encontrar los límites de la codificación de red en la capa física (physical layer network coding), se estudia el llamado Cross Network bajo distintas técnicas de Network Coding (NC). Se proporciona el impacto de la equidad (fairness) de la capa de control de acceso al medio (Medium Access Control, MAC), para los casos de repetidor puro (pure relaying), NC digital con y sin escucha del medio, y NC en la capa física con y sin escucha del medio. En la segunda parte de la tesis se investiga el offloading en el enlace ascendente mediante IP Flow Mobility (IFOM). El IFOM permite a los usuarios móviles de LTE mantener dos flujos de datos concurrentes, uno a través de LTE y el otro a través de la tecnología de acceso WiFi, que presenta limitaciones en el enlace ascendente debido a la equidad (fairness) inherente del diseño de IEEE 802.11 DCF. Para superar estas limitaciones, se propone un algoritmo proporcional ponderado de asignación de banda para el volumen de datos derivado a través de WiFi, junto con un algoritmo de asignación de tasa de transmisión basado en pricing para el volumen de datos del enlace ascendente de LTE. Con la solución propuesta, se mejora la eficiencia energética de los usuarios móviles, y se incrementa el volumen de datos que se pueden derivar gracias a la utilización concurrente de tecnologías de acceso que permite IFOM. En el algoritmo proporcional ponderado de asignación de banda de WiFi, se toman en consideración tanto las distintas necesidades de los usuarios en el enlace ascendente como su eficiencia espectral en LTE, y se propone un mecanismo de acceso que mejora el uso de WiFi para el tráfico derivado en el enlace ascendente. En cuanto a la parte de LTE, se propone un algoritmo en dos etapas de asignación de tasa de transmisión basada en pricing (con propuestas de pricing exponencial y lineal) con el objetivo de satisfacer el enlace ascendente de los usuarios en LTE. También se contempla la existencia de usuarios maliciosos, que pretenden utilizar el ancho de banda WiFi contra sus iguales para transmitir menos datos a través del enlace ascendente de LTE (menos eficiente energéticamente). Para ello se propone un método basado en la reputación que combate el funcionamiento egoísta (selfish).Postprint (published version

Scalable and rate adaptive wireless multimedia multicast

The methods that are described in this work enable highly efficient audio-visual streaming over wireless digital communication systems to an arbitrary number of receivers. In the focus of this thesis is thus point-to-multipoint transmission at constrained end-to-end delay. A fundamental difference as compared to point-to-point connections between exactly two communicating sending and receiving stations is in conveying information about successful or unsuccessful packet reception at the receiver side. The information to be transmitted is available at the sender, whereas the information about successful reception is only available to the receiver. Therefore, feedback about reception from the receiver to the sender is necessary. This information may be used for simple packet repetition in case of error, or adaptation of the bit rate of transmission to the momentary bit rate capacity of the channel, or both. This work focuses on the single transmission (including retransmissions) of data from one source to multiple destinations at the same time. A comparison with multi-receiver sequentially redundant transmission systems (simulcast MIMO) is made. With respect to feedback, this work considers time division multiple access systems, in which a single channel is used for data transmission and feedback. Therefore, the amount of time that can be spent for transmitting feedback is limited. An increase in time used for feedback transmissions from potentially many receivers results in a decrease in residual time which is usable for data transmission. This has direct impact on data throughput and hence, the quality of service. In the literature, an approach to reduce feedback overhead which is based on simultaneous feedback exists. In the scope of this work, simultaneous feedback implies equal carrier frequency, bandwidth and signal shape, in this case orthogonal frequency-division multiplex signals, during the event of the herein termed feedback aggregation in time. For this scheme, a constant amount of time is spent for feedback, independent of the number of receivers giving feedback about reception. Therefore, also data throughput remains independent of the number of receivers. This property of audio-visual digital transmission is taken for granted for statically configured, single purpose systems, such as terrestrial television. In the scope of this work are, however, multi-user and multi-purpose digital communication networks. Wireless LANs are a well-known example and are covered in detail herein. In suchlike systems, it is of great importance to remain independent of the number of receivers, as otherwise the service of ubiquitous digital connectivity is at the risk of being degraded. In this regard, the thesis at hand elaborates at what bit rates audio-visual transmission to multiple receivers may take place in conjunction with feedback aggregation. It is shown that the scheme achieves a multi-user throughput gain when used in conjunction with adaptivity of the bit rate to the channel. An assumption is the use of an ideal overlay packet erasure correcting code in this case. Furthermore, for delay constrained transmission, such as in so-called live television, throughput bit rates are examined. Applications have to be tolerant to a certain level of residual error in case of delay constrained transmission. Improvement of the rate adaptation algorithm is shown to increase throughput while residual error rates are decreased. Finally, with a consumer hardware prototype for digital live-TV re-distribution in the local wireless network, most of the mechanisms as described herein can be demonstrated.Die in vorliegender Arbeit aufgezeigten Methoden der paketbasierten drahtlosen digitalen Kommunikation ermöglichen es, Fernsehinhalte, aber auch audio-visuelle Datenströme im Allgemeinen, bei hoher Effizienz an beliebig große Gruppen von Empfängern zu verteilen. Im Fokus dieser Arbeit steht damit die Punkt- zu Mehrpunktübertragung bei begrenzter Ende-zu-Ende Verzögerung. Ein grundlegender Unterschied zur Punkt-zu-Punkt Verbindung zwischen genau zwei miteinander kommunizierenden Sender- und Empfängerstationen liegt in der Übermittlung der Information über erfolgreichen oder nicht erfolgreichen Paketempfang auf Seite der Empfänger. Da die zu übertragende Information am Sender vorliegt, die Information über den Erfolg der Übertragung jedoch ausschließlich beim jeweiligen Empfänger, muss eine Erfolgsmeldung auf dem Rückweg von Empfänger zu Sender erfolgen. Diese Information wird dann zum Beispiel zur einfachen Paketwiederholung im nicht erfolgreichen Fall genutzt, oder aber um die Übertragungsrate an die Kapazität des Kanals anzupassen, oder beides. Grundsätzlich beschäftigt sich diese Arbeit mit der einmaligen, gleichzeitigen Übertragung von Information (einschließlich Wiederholungen) an mehrere Empfänger, wobei ein Vergleich zu an mehrere Empfänger sequentiell redundant übertragenden Systemen (Simulcast MIMO) angestellt wird. In dieser Arbeit ist die Betrachtung bezüglich eines Rückkanals auf Zeitduplexsysteme beschränkt. In diesen Systemen wird der Kanal für Hin- und Rückweg zeitlich orthogonalisiert. Damit steht für die Übermittlung der Erfolgsmeldung eine beschränkte Zeitdauer zur Verfügung. Je mehr an Kanalzugriffszeit für die Erfolgsmeldungen der potentiell vielen Empfänger verbraucht wird, desto geringer wird die Restzeit, in der dann entsprechend weniger audio-visuelle Nutzdaten übertragbar sind, was sich direkt auf die Dienstqualität auswirkt. Ein in der Literatur weniger ausführlich betrachteter Ansatz ist die gleichzeitige Übertragung von Rückmeldungen mehrerer Teilnehmer auf gleicher Frequenz und bei identischer Bandbreite, sowie unter Nutzung gleichartiger Signale (hier: orthogonale Frequenzmultiplexsignalformung). Das Schema wird in dieser Arbeit daher als zeitliche Aggregation von Rückmeldungen, engl. feedback aggregation, bezeichnet. Dabei wird, unabhängig von der Anzahl der Empfänger, eine konstante Zeitdauer für Rückmeldungen genutzt, womit auch der Datendurchsatz durch zusätzliche Empfänger nicht notwendigerweise sinkt. Diese Eigenschaft ist aus statisch konfigurierten und für einen einzigen Zweck konzipierten Systemen, wie z. B. der terrestrischen Fernsehübertragung, bekannt. In dieser Arbeit werden im Gegensatz dazu jedoch am Beispiel von WLAN Mehrzweck- und Mehrbenutzersysteme betrachtet. Es handelt sich in derartigen Systemen zur digitalen Datenübertragung dabei um einen entscheidenden Vorteil, unabhängig von der Empfängeranzahl zu bleiben, da es sonst unweigerlich zu Einschränkungen in der Güte der angebotenen Dienstleistung der allgegenwärtigen digitalen Vernetzung kommen muss. Vorliegende Arbeit zeigt in diesem Zusammenhang auf, welche Datenraten unter Benutzung von feedback aggregation in der Verteilung an mehrere Empfänger und in verschiedenen Szenarien zu erreichen sind. Hierbei zeigt sich, dass das Schema im Zusammenspiel mit einer Adaption der Datenrate an den Übertragungskanal inhärent einen Datenratengewinn durch Mehrbenutzerempfang zu erzielen vermag, wenn ein überlagerter idealer Paketauslöschungsschutz-Code angenommen wird. Des weiteren wird bei der Übertragung mit zeitlich begrenzter Ausführungsdauer, z. B. dem sogenannten Live-Fernsehen, aufgezeigt, wie sich die erreichbare Datenrate reduziert und welche Restfehlertoleranz an die Übertragung gestellt werden muss. Hierbei wird ebenso aufgezeigt, wie sich durch Verbesserung der Ratenadaption erstere erhöhen und zweitere verringern lässt. An einem auf handelsüblichen Computer-Systemen realisiertem Prototypen zur Live-Fernsehübertragung können die hierin beschriebenen Mechanismen zu großen Teilen gezeigt werden

Towards Massive Connectivity Support for Scalable mMTC Communications in 5G networks

The fifth generation of cellular communication systems is foreseen to enable a multitude of new applications and use cases with very different requirements. A new 5G multiservice air interface needs to enhance broadband performance as well as provide new levels of reliability, latency and supported number of users. In this paper we focus on the massive Machine Type Communications (mMTC) service within a multi-service air interface. Specifically, we present an overview of different physical and medium access techniques to address the problem of a massive number of access attempts in mMTC and discuss the protocol performance of these solutions in a common evaluation framework

Game Theory for Multi-Access Edge Computing:Survey, Use Cases, and Future Trends

Game theory (GT) has been used with significant success to formulate, and either design or optimize, the operation of many representative communications and networking scenarios. The games in these scenarios involve, as usual, diverse players with conflicting goals. This paper primarily surveys the literature that has applied theoretical games to wireless networks, emphasizing use cases of upcoming multiaccess edge computing (MEC). MEC is relatively new and offers cloud services at the network periphery, aiming to reduce service latency backhaul load, and enhance relevant operational aspects such as quality of experience or security. Our presentation of GT is focused on the major challenges imposed by MEC services over the wireless resources. The survey is divided into classical and evolutionary games. Then, our discussion proceeds to more specific aspects which have a considerable impact on the game's usefulness, namely, rational versus evolving strategies, cooperation among players, available game information, the way the game is played (single turn, repeated), the game's model evaluation, and how the model results can be applied for both optimizing resource-constrained resources and balancing diverse tradeoffs in real edge networking scenarios. Finally, we reflect on lessons learned, highlighting future trends and research directions for applying theoretical model games in upcoming MEC services, considering both network design issues and usage scenarios