ABSTRACT We present a system for real‐time traffic support in infrastructure andad hocIEEE 802.11 networks. The proposed elastic MAC (E‐MAC) protocol provides a distributed transmission schedule for stations with real‐time traffic requirements, while allowing a seamless coexistence with standard IEEE 802.11 clients, protecting best‐effort 802.11 traffic from starvation by means of admission control policies. Our scheduling decisions are based on an ‘elastic’ transmission opportunity (TXOP) assignment which allows for efficient wireless resource usage: whenever a real‐time station does not use the assigned TXOP, the other real‐time stations can take over the unused access opportunity, thus preventing the well‐known inefficiencies of static time division multiple access (TDMA) schemes. Unlike other TDMA‐based solutions for 802.11, E‐MAC does not require a tight synchronization among the participating clients, thus allowing its implementation on commodity WLAN hardwareviaminor software changes at the client side, and no changes at the access points (APs). We studied the performance of our mechanismvians‐2 simulations and a mathematical model, showing that it outperforms IEEE 802.11e in terms of throughput, delay, and jitter. We finally provide a proof of concept through the results obtained in a real testbed where we implemented the E‐MAC protocol. Copyright © 2011 John Wiley & Sons, Ltd.

This paper presents a recommender system for contextual targeted advertisement in Video-on-demand scenarios. The proposal arises from a real case of a Japanese company planning to add advertisement to its On-Demand IPTV services. The advertisements consist of icon or text-based links that may be shown before, during or after the playing of the film the customer has selected to watch. The goal of the company is to maximize the number of times customers follow the links to advertised sites because its revenues depends on this. Since only a small portion of the advertising links can be included in a movie, these must be selected carefully. This work proposes a recommender system for selecting the most appropriate advertisement for a certain customer based on the success the advertisement has had in the past among other customers having similar preferences. The paper describes the proposed method, shows the implementation work done so far and describes the remaining work in order to test it in the real scenario.

The current Internet architecture does not properly handle multi-homed hosts, since each interface of a multi-connected end-host terminal generally appears as a completely different node. The lack of transparency about the multi-homing degree of end-hosts brings even more problems when those hosts are mobile. On the one hand, in our view the combined use of local hierarchical locators and global flat identifiers for both end hosts and networks is important to reach an efficient control of multi-homing and mobility. On the other hand, when planning to use flat global identifiers for networks we must consider an increased number of access autonomous systems. To target that scenario, this paper presents a novel addressing scheme and a global lookup system based on multi-level flat identifiers, which operate between the Internet domain naming service and its routing system. The proposed mechanism allows Internet access providers to deploy networks that may not be physically adjacent to each other, without having to reveal their topological location. This is done by grouping access networks of the same organization in the same virtual organizational zone. Virtual zones aim to hide the control of multi- homing and mobility from the Internet core. The second major goal of employing virtual zones is to bring closer to the end-host the decision about the most suitable access network and terminal interface to be used. This allows the exploitation of end-hosts interface diversity and local path diversity in a more efficient way.

Cooperative relaying has been shown to provide diversity gains which can significantly improve the packet error rate (PER) in wireless transmissions. In ad hoc wireless routing where packets may travel over a number of hops before reaching the destination, hop-wise cooperative relaying may severely reduce network capacity. This approach was mainly addressed in literature so far. In this paper, we efficiently apply cooperative relaying along a complete path and over multiple hops at the same time. We use information from the routing layer to improve the medium access control (MAC) layer's performance. Simulations and testbed implementation show appealing gains through diversity resulting in up to 66% better PER performance and up to 148% goodput increase compared to conventional approaches.

Opportunistic Relaying (OR) and Selection Decode-and-Forward (SDF) cooperation protocols can both substantially improve the performance of wireless networks but fundamentally differ in utilized redundancy, relays, and channel knowledge. To analyze when SDF or OR improves error and data rate, we (1) derive their general outage probability and capacity for arbitrary relay configurations, (2) systematically benchmark both approaches in two-hop configurations, (3) study how often beneficial configurations occur in large networks, and, finally, condition our capacity results by this occurrence probability. Our results clearly show that OR maximizes the outage capacity at high acceptable error rate while SDF succeeds if a low error rate is required. SDF performs best if even the relays can cooperate among themselves, supported frequently in networks with more than three neighbors. Consequently, cooperating relays, adapting between OR and SDF, and joining these two approaches should be the focus of future protocol design. To this end, our paper provides a theoretical basis, adaptation rules, and design guidelines.

In this paper a cooperative retransmission scheme for 802.11 WLANs is proposed. The mechanism allows stations with good channel to the access point to retransmit packets on behalf of other stations with worse channel. The cooperative partner selection is carried out in a completely opportunistic and distributed way that is compatible with 802.11. Simulations performed in a realistic WLAN scenario with adaptive modulation show that the system provides considerable gains in terms of goodput and packet error rate in comparison with legacy 802.11.

To overcome the lack of strict QoS guarantees in existing hotspots, in this paper we present a system for realtime traffic support in 802.11 networks that works in either infrastructure or ad-hoc mode. The proposed mechanism, called elastic MAC (E-MAC) protocol, helps stations with real-time traffic to organize and establish a transmission schedule in a distributed manner, while coexisting with standard 802.11 stations. This distributed scheduling guarantees very short delays and a minimum reserved data rate for real-time stations, while protecting best-effort 802.11 traffic from starvation. Another feature of our mechanism is time-slot reuse, which improves the network efficiency by allowing other real-time stations to take over unused slots (e.g., in case of using voice codecs with silence suppression). We evaluate the performance of our system using a testbed implementation, ns-2 simulations and a mathematical model, and show how it outperforms other QoS schemes (e.g., 802.11e) in terms of throughput, delay, and jitter.

Future mobile services are expected to have different levels of QoS requirements, raising the need to enhance networks with the capacity to differentiate among different classes of traffic, which may use different QoS models. To support and shelter different QoS models, future mobile networks should make use of an inter-network mechanism allowing the establishment of bi-lateral service level specifications (SLSs), without making any assumption about the signalling supported by internal network devices. Hence, this paper aims to explore the best way to use bi-lateral signalling to build end-to-end chains of SLSs. Two methods are evaluated. In the first one, control messages are only propagated after the establishment of an SLS between a pair of networks; in the second one control messages flow from the provider of the SLS to each of its customers, passing a chain of transit-networks.

The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single-AP (access point) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to be solved. Some proposed solutions to build such mesh architectures are based on single-channel ad-hoc oriented schemes in which IEEE 802.11 protocol has been modified. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself. The task group S of IEEE 802.11 is currently working out standards for IEEE 802.11-compliant mesh architectures in a number of usage scenarios including residential, office and campus/community/public access network but a lot of work remains to be done since the group was established just on last year. In this paper we propose a new multi-radio multi-channel mesh architecture for hot zones which works using a distributed coordination function (DCF)-based technique for interconnecting APs and a simple but effective radio routing mechanism. A major advantage of our proposed scheme is that, putting routing issues aside, it introduces no change into the MAC protocol of IEEE 802.11. Our simulations results obtained in OPNET show the great effectiveness of radio routing for balancing the traffic load within the network as well as interesting results related with the size of packets and the mesh architecture itself that could lead to further research in the future. Moreover, the results show the proposed architecture yields a very good performance in terms of total throughput and transmission delay

In this paper, we propose a new transmission and resource allocation technique on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers the scheme reduces the inter-carrier interference generated by high-speed users while keeping the inter-symbol interference at a low level due to the multicarrier transmission. The analysis and results show that a substantial mitigation of both the intercarrier interference and bit error ratio, without reducing the system bandwidth efficiency, can be achieved. That makes our proposed method a god candidate for future broadband highly-mobile networks.

The proposed medium access protocol deals especially with the timely-transmission of real-time packets in wireless multimedia networks where users of various types of traffic are present. It works based on the time division multiple access (TDMA) with time division duplex (TDD) technique as well as fixed-length packet switching incorporating two policies, which work differently during non-congestion and congestion states. The simulation results show good performance of the proposed method, even under high-load conditions, and a good trade-off characteristic between real-time access delay and non-real time buffer occupancy, during periods of congestion.