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In opportunistic networks, mobile nodes such as mobile phones and PDAs use the mobility of devices in addition to wireless forwarding between intermediate nodes to facilitate communication without requiring a simultaneous path between source and destination.Without guaranteed connectivity, the strategy for forwarding messages has a significant effect on system performance. Most of the existing research...
Overlay network architectures that use orthogonal channels have been known to provide effective additional resources to underlying networks in high demand. Overlays are composed of relay nodes provided with rich computational resources and multiple wireless interfaces that make them capable of establishing several non-interfering networks. These networks can be used to move traffic around in a non-interfering...
In this paper we examine opportunistic content distribution. We design and evaluate a caching strategy where a node will fetch and share contents on behalf of other nodes, although the contents are not of its own interest. We propose three caching options for improving the use of network resources: relay request on demand, hop-limit, and greedy relay request. The proposed strategies are implemented...
We propose in this paper, a distributed optimal relay selection scheme for cooperative wireless networks to improve the performance of multimedia transmissions, while taking into account application layer quality of service (QoS), i.e., multimedia distortion. We formulate the cooperative relaying network as a stochastic bandit system. Moreover, the adaptive modulation and coding (AMC) strategy at...
In recent years, multicast over wireless access networks has become a popular research topic and application. However, if relay nodes are supported, forming an efficient multicast topology is a challenging issue. In this paper, we propose a multi- hop multicast recipient maximization scheme for wireless relay networks. First, we formulate an important problem called Multi-Hop Recipient Maximization...
In this paper, we introduce an adaptive cooperative system that selects the best relay among the available relay nodes to cooperate with a source node for transmitting the information signal to a destination node if the spectral efficiency can be maximized. This maximization is achieved as long as the average bit error rate is below a target level. The channels are modeled as independent and identically...
With the ever-growing demands of wireless communications, traffic load sharing is essentially important to provide consistent high quality of service (QoS). It is known that the QoS of mobile users is affected by the limited bandwidth in both wireless link and wired backhaul link beyond a base station (BS). Femtocell is a promising technology to bear part of the traffic load from the BS. Nonetheless,...
There is substantial and growing motivation to deploy wireless relays in 3G+ and 4G networks both in residential and commercial contexts to achieve significant coverage extension and capacity increases at potentially relatively low cost. However, relays operating in shared spectrum may introduce interference thus potentially counterbalancing gains, and conversely, relays requiring a dedicated resource...
We investigate the impact of cooperative relaying on uplink multi-user (MU) wireless video transmission. We formulate the problem as an MU Markov decision process (MDP) that explicitly considers the cooperation at the physical layer and the medium access control sublayer, the video users' heterogeneous traffic characteristics, and the dynamically varying network conditions. Although MDPs notoriously...
We study the sum capacity of multiple unicasts in wireless multihop networks. With 2 source nodes and 2 sink nodes, there are a total of 4 independent unicast sessions (messages), one from each source to each sink node (this setting is also known as an X network). We explore the degrees of freedom (DoF) of wireless multihop X networks with a layered structure, allowing arbitrary number of hops and...
In this paper, we consider a wireless cellular network capable of supporting Machine-to-Machine (M2M) applications. According to the recent IEEE 802.16p proposals, a wireless M2M device may act as an aggregation point and communicate data packets on behalf of the other M2M devices, which may lack a cellular interface or have a poor communication link to the network. We propose a client relay scheme...
In this paper, we investigate joint relay and jammer selection in a two-way relay network with secrecy constraints, in which there are two sources, a cluster of intermediate nodes, and one eavesdropper. Under a decode-and-forward (DF) protocol, the considered two-way relay network implements a complete transmission in three phases. An intermediate node is selected as conventional relay and another...
In this paper, we investigate the impact of relay cooperation for maintaining coverage area against aggregate interference from incumbent underlaid interferers. We employ a guard zone for uplink so that non-urgent interferers are inhibited and urgent ones are admitted with a controlled access probability as long as the primary receiver can tolerate. Numerical results show the outage probability of...
Aiming at improving the QoS performance over fading channels, this paper presents an analysis of the effective capacity for a relay-assisted communication system which utilizes a cooperative packet retransmission protocol at the link-layer in conjunction with AMC-based multi-rate transmission at the physical layer. In the considered model, a source (S) node employs AMC to transmit delay-constrained...
Time asynchronism is a practical issue needs to be addressed for a general distributed two-way relay network, where two terminal nodes exchange information through multiple spatial-separated relay nodes. In this paper, we propose an analog network coding (ANC) scheme for a time asynchronous two-way relay network. In the proposed scheme, each relay node linearly transforms the received mixed asynchronous...
Recent studies have shown that network coding (NC) directly applied at the physical layer -physical layer network coding (PLNC)- is a promising technique for two-way relay channels (TWRC). Unfortunately, to date, most existing PLNC works have mainly addressed cases of time-invariant channels rather than more realistic multipath time-varying wireless channels. To make further progress in understanding...
Cooperative communication can significantly enhance transmission reliability and bandwidth efficiency in wireless networks. Most existing works are focused on physical layer issues of cooperative communications. Many upper layer aspects of cooperative communications merit further research. In this paper, we investigate its impacts on network topology and capacity. Specifically, we present a novel...
In cognitive radio (CR) networks, cooperative relaying is emerging as a key technology to improve the performance of secondary users (SUs), while ensuring the quality of service of primary transmissions. Most previous work considers maximizing physical layer throughput as a design criterion. However, the end-to-end Transmission Control Protocol (TCP) performance perceived by SUs is largely ignored...
We investigate the capacity bounds for a wireless multicast relay network where two sources simultaneously multicast to two destinations through Gaussian channels with the help of a full-duplex relay node. All the individual channel gains are assumed to be time-invariant and known to every nodes in the network. The transmissions from two sources and from the relay use the same channel resource (i...
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