On the Benefits of Edge Caching for MIMO Interference Alignment

In this contribution, we jointly investigate the benefits of caching and interference alignment (IA) in multiple-input multiple-output (MIMO) interference channel under limited backhaul capacity. In particular, total average transmission rate is derived as a function of various system parameters such as backhaul link capacity, cache size, number of active transmitter-receiver pairs as well as the quantization bits for channel state information (CSI). Given the fact that base stations are equipped both with caching and IA capabilities and have knowledge of content popularity profile, we then characterize an operational regime where the caching is beneficial. Subsequently, we find the optimal number of transmitter-receiver pairs that maximizes the total average transmission rate. When the popularity profile of requested contents falls into the operational regime, it turns out that caching substantially improves the throughput as it mitigates the backhaul usage and allows IA methods to take benefit of such limited backhaul.Comment: 20 pages, 5 figures. A shorter version is to be presented at 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC'2015), Stockholm, Swede

Traffic-aware scheduling and feedback reporting in wireless networks

Demand of wireless communication systems for high throughputs continues to increase, and there are no signs this trend is slowing down. Three of the most prominent techniques that have emerged to meet such demands are OFDMA, cooperative relaying and MIMO. To fully utilize the capabilities of systems applying such techniques, it is essential to develop eficient scheduling algorithms and, more generally, eficient resource allocation algorithms. Classical studies on this subject investigate in much detail settings where the data requests of the users are not taken into consideration or where the perfect and full CSI is assumed to be available for the scheduling mechanism. In practice, however, diferent limitations may result in not having perfect or full CSI knowledge, such as limited feedback resources, probing cost and delay in the feedback process. Accordingly, in this thesis we examine the problems of scheduling and feedback allocations under realistic considerations concerning the CSI knowledge. Analysis is performed at the packet level and considers the queueing dynamics in the systems with arbitrary arrival processes, where the main performance metric we adopt is the stability of the queues. The first part of the thesis considers a multi-point to multi-point MIMO system with TDD mode under limited backhaul capacity and taking into account the feedback probing cost. Regarding the interference management technique, we apply interference alignment (IA) if more than one pair are active and SVD if only one pair is active. The second part of the thesis considers a multiuser multichannel OFDMA-like system where delayed and limited feedback is accounted for. Two scenarios are investigated, namely the system without relaying and the system with relaying. For the latter one, an additional imperfection we account for is that the users have incomplete knowledge of the fading coeficients between the base-station and the relay.La demande des systèmes de communication sans fil pour des débits élevés continue d'augmenter, et il n'y a pas de signes que cette tendance va se ralentir. Trois des techniques les plus importantes qui ont émergé pour répondre à de telles demandes sont l'OFDMA, le relais coopératif et le MIMO. Afin d'utiliser pleinement les capacités des systèmes appliquant de telles techniques, il est essentiel de développer des algorithmes efficaces d'ordonnancement et, plus généralement, des algorithmes efficaces d'allocation de ressources. Les études classiques sur ce sujet examinent des systèmes où les demandes de données des utilisateurs ne sont pas prises en considération et/ou un CSI parfait et complet est supposée être disponible pour le mécanisme d'ordonnancement. Cependant, dans la pratique, différentes limitations peuvent entraîner l'absence d'une connaissance parfaite et/ou complète du CSI, telles que les ressources limitées pour le feedback, le co^ut de sondage et le retard dans le processus de feedback.Par conséquent, dans cette thèse nous examinons les problèmes d'ordonnancement et de feedback sous des considérations réalistes concernant la connaissance du CSI. L'analyse est effectuée au niveau des paquets et considère la dynamique des files d'attente avec des processus d'arrivée arbitraires, et où la mesure de performance principale que nous adoptons est la stabilité des files d'attente. La première partie de la thèse considère un système MIMO multipoint à multipoint utilisant le mode TDD, tout en supposant un backhaul à capacité limitée et en tenant compte du coût du feedback. En ce qui concerne la technique de gestion de l'interférence, nous appliquons l'alignement d'interférence (IA) si plus d'une paire sont actives et SVD si une seule paire est active. La deuxième partie de la thèse considère un système OFDMA avec plusieurs utilisateurs et canaux, où un feedback retardé et limité est pris en compte. Deux scénarios sont étudiés, à savoir le système sans relais et le système avec relais. Pour ce dernier, nous considérons une imperfection supplémentaire supposant que les utilisateurs ont une connaissance incomplète des coefficients du fading entre la station de base et le relais

Ordonnancement et feedback dans les réseaux sans fil avec prise en compte du trafic

La demande des systèmes de communication sans fil pour des débits élevés continue d'augmenter, et il n'y a pas de signes que cette tendance va se ralentir. Trois des techniques les plus importantes qui ont émergé pour répondre à de telles demandes sont l'OFDMA, le relais coopératif et le MIMO. Afin d'utiliser pleinement les capacités des systèmes appliquant de telles techniques, il est essentiel de développer des algorithmes efficaces d'ordonnancement et, plus généralement, des algorithmes efficaces d'allocation de ressources. Les études classiques sur ce sujet examinent des systèmes où les demandes de données des utilisateurs ne sont pas prises en considération et/ou un CSI parfait et complet est supposée être disponible pour le mécanisme d'ordonnancement. Cependant, dans la pratique, différentes limitations peuvent entraîner l'absence d'une connaissance parfaite et/ou complète du CSI, telles que les ressources limitées pour le feedback, le co^ut de sondage et le retard dans le processus de feedback.Par conséquent, dans cette thèse nous examinons les problèmes d'ordonnancement et de feedback sous des considérations réalistes concernant la connaissance du CSI. L'analyse est effectuée au niveau des paquets et considère la dynamique des files d'attente avec des processus d'arrivée arbitraires, et où la mesure de performance principale que nous adoptons est la stabilité des files d'attente. La première partie de la thèse considère un système MIMO multipoint à multipoint utilisant le mode TDD, tout en supposant un backhaul à capacité limitée et en tenant compte du coût du feedback. En ce qui concerne la technique de gestion de l'interférence, nous appliquons l'alignement d'interférence (IA) si plus d'une paire sont actives et SVD si une seule paire est active. La deuxième partie de la thèse considère un système OFDMA avec plusieurs utilisateurs et canaux, où un feedback retardé et limité est pris en compte. Deux scénarios sont étudiés, à savoir le système sans relais et le système avec relais. Pour ce dernier, nous considérons une imperfection supplémentaire supposant que les utilisateurs ont une connaissance incomplète des coefficients du fading entre la station de base et le relais.Demand of wireless communication systems for high throughputs continues to increase, and there are no signs this trend is slowing down. Three of the most prominent techniques that have emerged to meet such demands are OFDMA, cooperative relaying and MIMO. To fully utilize the capabilities of systems applying such techniques, it is essential to develop eficient scheduling algorithms and, more generally, eficient resource allocation algorithms. Classical studies on this subject investigate in much detail settings where the data requests of the users are not taken into consideration or where the perfect and full CSI is assumed to be available for the scheduling mechanism. In practice, however, diferent limitations may result in not having perfect or full CSI knowledge, such as limited feedback resources, probing cost and delay in the feedback process. Accordingly, in this thesis we examine the problems of scheduling and feedback allocations under realistic considerations concerning the CSI knowledge. Analysis is performed at the packet level and considers the queueing dynamics in the systems with arbitrary arrival processes, where the main performance metric we adopt is the stability of the queues. The first part of the thesis considers a multi-point to multi-point MIMO system with TDD mode under limited backhaul capacity and taking into account the feedback probing cost. Regarding the interference management technique, we apply interference alignment (IA) if more than one pair are active and SVD if only one pair is active. The second part of the thesis considers a multiuser multichannel OFDMA-like system where delayed and limited feedback is accounted for. Two scenarios are investigated, namely the system without relaying and the system with relaying. For the latter one, an additional imperfection we account for is that the users have incomplete knowledge of the fading coeficients between the base-station and the relay

Extended Version of the Work on Opportunistic Feedback for Multichannel Wireless Networks

International audienceThis work studies the problems of feedback allocation and scheduling for a multichannel downlink cellular network under limited and delayed feedback. We consider a realistic scenario where a fixed and small numberF of link states can be reported to the base-station (BS) per time-slot. We study the trade-off between knowing at the BS a small number of accurate link states (i.e. that can be reported within one time-slot) and a larger but outdated number of link states (i.e. number of link states >F that requires more than one slot to be reported). We propose an efficient algorithm that selects the link states that should be reported to the base-station. A novelty here is that this feedback allocation algorithm is performed at the users side. We show that this algorithm combined with the Max-Weight scheduling achieves at least a fraction η of the stability region achieved under the ideal system (i.e. with full and perfect feedback at no cost). We then provide numerical results that show the best aforementioned trade-off under various system setups

Opportunistic Feedback Reporting and Scheduling Scheme for Multichannel Wireless Networks

International audienceThis work studies the problems of feedback allocation and scheduling for a multichannel downlink cellular network under limited and delayed feedback. We consider a realistic scenario where a fixed and small number ¯ F of link states can be reported to the base-station (BS) per time-slot. We study the trade-off between knowing at the BS a small number of accurate link states (i.e. that can be reported within one time-slot) and a larger but outdated number of link states (i.e. number of link states > ¯ F that requires more than one slot to be reported). We propose an efficient algorithm that selects the link states that should be reported to the base-station. A novelty here is that this feedback allocation algorithm is performed at the users side. We show that this algorithm combined with the Max-Weight scheduling achieves at least a fraction η of the stability region achieved under the ideal system (i.e. with full and perfect feedback at no cost). We then provide numerical results that show the best aforementioned trade-off under various system setups

Queueing stability and CSI probing of a TDD wireless network with interference alignment

International audienceThis paper characterizes the performance of IA technique taking into account the dynamic traffic pattern and the probing/feedback cost. We consider a TDD system where transmitters acquire their CSI (Channel State Information) by decoding the pilot sequences sent by the receivers. Since global CSI knowledge is required for IA, the transmitters have also to exchange their estimated CSIs over a backhaul of limited capacity. Under this setting, we characterize in this paper the stability region of the system and provide a probing algorithm that achieves the max stability region. In addition, we compare the stability region of IA to the one achieved by a TDMA system where each transmitter applies a simple ZF (Zero Forcing technique)

System performance of interference alignment under TDD mode with limited backhaul capacity

International audienc