On the computation of the maximum capacity of TDMA-CDMA/TDD systems

International audienceThe combination of the TDD mode and the TDMA technique in WCDMA systems engenders a new degree of flexibility that can increase system capacity and QoS levels of active channels if efficient slot allocation techniques are used. These techniques allow the system to control the allocation of slots to users, and thus lead to relevant reduction in interference levels. In order to study slot allocation performance, it is important to define a reference performance that gives adequate approximation of system maximum capacity. In this paper, we propose a novel formulation to the computation of system maximum capacity using a set of combinatorial optimization problems. Furthermore, we propose meta-heuristic algorithms that give satisfactory approximations for each combinatorial proble

Multicast vs multiple-unicast scheduling in high-speed cellular networks

International audiencePacket scheduling is one of the key features in data-oriented radio interfaces of cellular networks like HSDPA (High Speed Downlink Packet Access). It has been primarily designed for unicast applications. Nevertheless, unicast may not optimise the resource usage when the same content has to be transmitted to several users in the same cell. In this paper, we compare the performance of multicast and unicast scheduling considering both a theoretical generic system and an HSDPA system. We prove the benefit of deploying multicast which is found to have merits when the average channel quality is good enough. Results show that the better the average channel quality is, the more users are allowed to receive the service simultaneously

Analytical evaluation of multicast packet delivery and user clustering schemes in high-speed cellular networks

International audienceTransmission on data-oriented radio interfaces of cellular networks has been primarily designed for unicast applications. Nevertheless, unicast may not optimize the resource usage when the same content has to be transmitted to several users in the same cell. In this context, multicast seems to be an efficient means to convey data. In this paper, we develop an analytical model that allows the computation of the mean bitrate for both multicast and multiple-unicast transmission schemes. Furthermore, we propose a multicast transmission scheme called the equal-bitrate (EB) algorithm that allocates bandwidth to mobiles according to their instantaneous channel quality. We compare it to adaptations of the well-known Max-SNR and Round Robin (RR) to multicast. We propose to group users into clusters. The clustering method combines multicast and unicast transmission schemes according to the user’s average channel conditions.We use the analytical model to evaluate the proposed solutions. We compare the resulting performance against pure multicast and multiple-unicast approaches. We show that EB algorithm offers a good trade-off between throughput and fairness. Also, we show that mixed clustering achieves good performance compared to conventional clustering methods

Biased Random Walk Model to estimate Routing Performance in Wireless Sensor Networks

International audienceLes réseaux de capteurs sans fils sont constitués d'un grand nombre de noeuds assujettis `à de sévères contraintes en terme d'énergie, de capacité de traitement et de communication. Dans ce contexte, afin de réduire la complexité, un des défis majeurs rencontrés dans ce type de réseau est le calcul des routes et la mise en oeuvre de schémas de routage efficaces tout en minimisant la quantité d'information utilisée sur l' état du système. De nombreux travaux ont ́etudié ce compromis de façon qualitative ou grâce à des simulations. Nous proposons un modèle basé sur la théorie de la marche aléatoire pour estimer analytiquement ce compromis en considérant plus particulièrement l'influence du degré de connaissance de l'état du système que posséde un noeud sur le temps moyen de collecte dans un réseau de capteurs sans fils

Random Walk Based Routing Protocol for Wireless Sensor Networks

International audienceIn recent years, design of wireless sensor networks using methodologies and mechanisms from other disciplines has gained popularity for addressing many networking aspects and providing more flexible and robust algorithms. We address in this paper the problem of random walk to model routing for data gathering in wireless sensor networks. While at first glance, this approach may seem to be overly simplistic and highly inefficient, many encouraging results that prove its comparability with other approaches have been obtained over the years. In this approach, a packet generated from a given sensor node performs a random motion until reaching a sink node where it is collected. The objective of this paper is to give an analytical model to evaluate the performance of the envisioned routing scheme with special attention to two metrics: the mean system data gathering delay and the induced spatial distribution of energy consumption. The main result shows that this approach achieves acceptable performance for applications without too stringent QoS requirements provided that the ratio of sink nodes over the total number of sensor nodes is carefully tuned

On the data delivery delay taken by random walks in wireless sensor networks

International audienceIn recent years, the use of random walk techniques in wireless sensor networks has attracted considerable interest among numerous research efforts. The popularity of this approach is attributed to the natural properties of random walks such as locality, simplicity, low-overhead and inherent robustness. However, throughout the variety of research works that assess the effectiveness of random walk techniques, most results are derived from a qualitative view or by means of simulations. Furthermore, when analytical tools are used, the obtained results often provide bounds on various performance metrics of interest, which may have little consequences for practical applications. Instead, our goal in this paper is to quantify the effectiveness of such techniques based on the derivation of closed-form expressions. In particular, we focus on the data delivery delay taken for the random walk to deliver messages from sensor to sink nodes and study its statistics through closed-form derivations

Overview of evolved Multimedia Broadcast Multicast Services (eMBMS)

MBMS was introduced as a service to optimize the dissemination of common interest multimedia content. Recently, it evolved to eMBMS based on LTE-centered flexibilities. However, launch of eMBMS over LTE may support new services e.g. pushed content for M2M services and delivery of premium content to the users enjoying secured QoS. This document primarily focusses on the rules, procedures and architecture supporting MBMS based data exchanges, which have not seen any major changes since Release 9

Optimization of link adaptation and HARQ schemes for multicast in high speed cellular networks

International audienceThis paper targets multicast transmission where the same data is destined to many users simultaneously. Although multicast allows bandwidth saving, it prevents a precise link adaptation over radio links. Indeed, users are subject to the same bitrate despite their different and variable radio conditions. Neither operators nor 3GPP standard offer solutions to support link adaptation in a multicast scenario. In this context, we propose different solutions. We compare conservative and aggressive schemes by computing the resulting throughput performance. For this purpose, we propose a model to compute the average number of retransmissions. We also study the mapping between the reported SNR and the packet sizes in HSDPA systems. We show that the existing mapping offers the best performance for unicast but cuts down the throughput in a multicast scenario. Then, we propose a convenient mapping for multicast, namely shifted mapping. Despite the better precision of this solution, the resulting gain remains marginal

A Cross-Layer Medium Access Control and Routing Protocol for Wireless Sensor Networks

National audienceMany contention-based routing protocols in Wireless Sensor Networks (WSN) proposed so far require that the sensor node knows the location or position of all neighbors in its transmission range in order to forward packets in the geographic direction of the destination. Location awareness, gained by localization techniques such as observing beacon messages each node sends out periodically or with the help of Global Positioning System (GPS), is not practical for reasons of cost (in volume, money and power consumption). Therefore, a novel cross-layer integrated medium access control/routing protocol called RSSI-based Forwarding (RBF), based on a Received Signal Strength Indicator (RSSI) as a routing parameter, is proposed for multi-hop WSN. Without using prior knowledge of nodes' geographical locations and without maintaining neighborhood routing tables, the next-hop node for data-forwarding task is determined at the same time as the contention process among the possible forwarding nodes is solved. For an arriving beacon signal transmitted by the sink, received power levels are computed for each sensor node in the network and these levels are then used as a decision parameter for the nodes to contend for the forwarding task of the data packets. Simulation results are presented to evaluate the sensor nodes' end-to-end delay in transmitting the data packets towards the sink