1,721,228 research outputs found
Link adaptation in retransmission-based cognitive radio systems
No full textIn this paper we consider cognitive radio systems with automatic repeat request (ARQ)-based error control and propose a throughput-maximizing transmission strategy at the cognitive transmitter which takes advantage of opportunities that arise during ARQ retransmissions. In particular, we present a cross-layer approach to link adaptation design which integrates adaptive modulation and coding (AMC) at the physical layer with packet retransmission at the data-link layer. In this formulation, the cognitive throughput performance is maximized subject to (i) a packet-loss-rate (PLR) constraint at the cognitive link, and (ii) a minimum required throughput and a PLR constraint at the primary link. The results indicate that the maximum cognitive throughput is determined based on a tradeoff between the primary PLR and delay requirements
Transmission Strategy Design in Cognitive Radio Systems With Primary ARQ Control and QoS Provisioning
No full textIn this paper, we consider an underlay cognitive radio paradigm with a primary packet system which implements automatic repeat request (ARQ)-based error control. We propose cognitive transmission strategies which provision for minimum primary quality of service (QoS) requirements. The proposed strategies take advantage of opportunities that arise during ARQ retransmissions of the primary system at the link layer, and adapt channel fading variations by employing adaptive modulation and coding (AMC) and power control at the physical layer. In this cross-layer formulation, the cognitive throughput is optimized subject to 1) a packet-loss-rate (PLR) constraint on the cognitive link, and 2) a minimum required throughput and a PLR constraint on the primary link. We first derive analytical expressions for the link-layer throughput of the cognitive link defined in terms of the data rate successfully received at the receiver side. Next, we present optimized AMC and power control schemes for the cognitive transmitter. Numerical results show significant improvement in terms of the cognitive throughput and PLR performance. Namely, when the cognitive transmitter employs both power and rate control the throughput-maximizing strategy is determined based on a tradeoff between the primary PLR and delay (in terms of the number of retransmission rounds) QoS metrics
Effective Capacity for Multi-Rate Relay Channels with Delay Constraint Exploiting Adaptive Cooperative Diversity
No full textThe effective capacity (EC) for a wireless system expresses the maximum arrival source rate that the system can transmit over the wireless channel by fulfilling certain probabilistic delay constraints. This paper presents an EC analysis for a relay-assisted cooperative protocol exploiting adaptive transmission at physical and data-link layers. In the considered model, a source employs adaptive modulation and coding (AMC) in conjunction with a cooperative ARQ protocol, to transmit delay-constrained traffic to the destination node. To achieve adaptive cooperative diversity, a relay node, also equipped with AMC, performs cooperation when it decodes the source packet correctly and the destination requested a packet retransmission. We derive a tight closed-form upper-bound expression for the EC of the queue service process at the source node when wireless links are subject to time-correlated fading. To this end, a Markov model for the relay channel is used. We also present a cross-layer approach to delay-aware AMC design for the relay channel which provides the maximum system throughput subject to a probabilistic delay constraint. The numerical and simulation results show that the proposed adaptive cooperative protocol can dramatically improve the EC and the system throughput over time-correlated fading channels when compared to a direct transmission system
Effective Capacity Analysis for Multi-Rate Relay Channels Exploiting Adaptive Cooperative Diversity
No full textAiming 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 packet traffic to the destination (D) node. To achieve adaptive cooperative diversity, a relay node, also equipped with AMC, forwards the packet received from node S to node D if it was able to decode the source packet correctly and node D requested a packet retransmission. For this protocol we derive a closed-form expression for the effective capacity of the queue service process at node S. Numerical results reveal that the proposed cooperative protocol can dramatically increase the effective capacity with respect to a direct transmission system with AMC
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A Type II Hybrid ARQ Protocol with Adaptive Modulation and Coding for Time-Correlated Fading Channels: Analysis and Design
No full textThis paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocol in wireless networks which employ adaptive modulation and coding (AMC) at the physical layer and are subject to time-correlated fading channels. Utilizing a Markov channel model which accounts for the temporal correlation in successive parity transmissions by the adaptive rate HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional (RCPC) code family. As an application, we then present a cross-layer AMC design which takes into account the performance gain of the HARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocol leads to a substantial throughput gain, but the channel correlation strongly diminishes the performance of the HARQ protocol in terms of throughput and packet loss rate
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Analysis of Non-Cooperative and Cooperative Type II Hybrid ARQ Protocols with AMC over Correlated Fading Channels
No full textThis paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocols in wireless networks, which employ adaptive modulation and coding (AMC) in conjunction with adaptive cooperative diversity and are subject to time-correlated fading channels. We first consider a point-to-point scenario, i.e., non-cooperative HARQ with AMC. Utilizing a Markov channel model which accounts for the temporal correlation in the successive transmission of incremental redundancy by the HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional code family. Next, we consider a cooperative HARQ (CHARQ) scheme in which a relay node, also equipped with AMC, retransmits redundancy packets when it is able to decode the source information packet correctly. For this scenario, we also derive the throughput and packet loss performance. Finally, we present a cross-layer AMC design approach which takes into account the hybrid ARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocols leads to a substantial throughput gain. While the performance of the AMC with HARQ protocol is strongly affected by the channel correlation, the CHARQ protocol provides noticeable performance gains over correlated fading channels as well
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