1,720,963 research outputs found
Considerations on the multiplexing and diversity tradeoff in IEEE 802.11 networks
No full textMultiple-input multiple-output (MIMO) techniques have received a considerable attention from the research community for their promising performance in faded environments, and particular interest has been given to the physical (PHY) layer implications of the tradeoff between multiplexing and diversity. This study discusses this tradeoff extending the analysis to the medium access control (MAC) layer. To this purpose, a theoretical model for assessing the performance of an 802.11 network that relies on a MIMO-enabled PHY layer is presented. The proposed model characterises the different MIMO systems in terms of their multiplexing gain and bit error rate performance, considering both the diversity gain of the specific MIMO scheme and the impact of the spatial distribution of the nodes. The results compare, from a MAC layer perspective, the benefits of multiplexing and diversity, providing some analytic insights on the tradeoff between increasing the system’s reliability and enhancing the data rate of the single link
Incremental and Complementary Coding Techniques for Cooperative Medium Access Control Protocols
No full textCooperative Coding Schemes: Design and Performance Evaluation
No full textCooperation has been recently introduced to mitigate
the impairments imposed by fading on a communication
channel. A cooperative transmission, in which the destination
may overhear all transmission attempts, benefits from incremental
redundancy techniques, achieving a higher throughput
and reducing the packet delay and the outage probability. This
paper presents a theoretical framework to assess the limiting performance
of efficient coding techniques in Decode-and-Forward
cooperative scenarios. In this paper it is shown that suitable
designed codes, such as punctured turbo codes, approach the
limiting performance in all the studied scenarios. The paper also
addresses the design of punctured turbo code schemes capable
of performing close to the presented limiting bound. A novel
Genetic Algorithm (GA) is introduced for designing incremental
puncturing schemes suited to cooperative transmissions. The
algorithm uses a recently proposed tri-dimensional (3D) EXtrinsic
Information Transfer (EXIT) chart technique to model the
decoding behavior of parallel concatenations of non-systematic
periodically punctured convolutional codes. It is shown that the
design algorithm allows contriving capacity approaching codes
for the source and the relay. The paper further shows that the
GA aided designed codes closely approach the theoretical results,
outperforming previously proposed systematic incremental and
complementary schemes
Design criteria and genetic algorithm aided optimization of three-stage-concatenated space-time shift keying systems
No full textThe Space-Time Shift Keying (STSK) framework subsumes diverse Multiple-Input Multiple-Output (MIMO) schemes, offering a near-capacity performance at a reduced complexity. The STSK system’s performance crucially depends on the dispersion matrix (DM) set used for encoding the transmitted symbols. We introduce a novel criterion, based on EXtrinsic Information Transfer (EXIT) chart analysis, for selecting capacity-approaching sets from candidate DMs, and a novel Genetic Algorithm (GA) for efficiently exploring the search space formed by the candidate DM sets. Our proposed GA allows obtaining DM sets that enhance the system’s performance compared to a random selection, while simultaneously reducing the search algorithm’s complexity.<br/
On the Design of MAC Protocols for Multi-Packet Communication in IEEE 802.11 Heterogeneous Networks Using Adaptive Antenna Arrays
Full text linkThis paper discusses the design requirements for enabling multiple simultaneous peer-to-peer communications in IEEE 802.11 asynchronous networks in the presence of adaptive antenna arrays, and proposes two novel access schemes to realize multipacket communication (MPC). Both presented solutions, which rely on the information acquired by each node during the monitoring of the network activity, are suitable for distributed and heterogeneous scenarios, where nodes equipped with different antenna systems can coexist. The first designed scheme, called threshold access MPC (TAMPC), is based on a threshold on the load sustainable by the single-node, while the second protocol, called signal-to-interference ratio (SIR) access MPC (SAMPC), is based on an accurate estimation of the SIR and on the adoption of low density parity check codes. Both protocols, which are designed to be backward compatible with the 802.11 standard, are numerically tested in realistic scenarios. Furthermore, the performance of the two schemes is compared to the theoretical one and to that of the 802.11n extension in a mobile environment
Multi-Packet Communication in 802.11 Networks by Spatial Reuse: from Theory to Protocol
No full textThis paper analyzes the problem of modeling the collisions in a distributed and heterogeneous fixed wireless network supporting multi-packet communication (MPC) by spatial reuse. In an MPC scenario, where multiple node pairs can be simultaneously active, the result of a transmission attempt is typically established using two main approaches: one, more idealized but suitable for theoretical analyses, based on a threshold on the number of sustainable communications, and another one, more realistic, relying on the signal-to-interference ratio (SIR) experienced by the receiving node. The two approaches may lead to considerably different results, since the number of allowed communications is often estimated neglecting many physical aspects. This study investigates this issue by presenting a mathematical model, validated by independent simulations, which relates the capture probability to the statistic of the SIR. The developed framework, which accounts in detail for the network topology and the antenna system characteristics of each node, is applied to an 802.11-based multi-packet scenario to evaluate the saturation throughput of an MPC network
Relay selection schemes relying on adaptive modulation and imperfect channel knowledge for cooperative networks
No full textCooperative MAC protocols have been shown to increase the attainable network throughput and to reduce the outage probability when perfect Channel State Information (CSI) is available either at the source station or at candidate relays. This paper investigates the realistically achievable network performance of relay selection schemes under imperfect CSI knowledge. Novel relay selection algorithms, based on a Markov Decision Process (MDP) framework, are proposed for mitigating the performance degradation introduced by imperfect channel knowledge. We demonstrate that the performance of cooperative MAC schemes crucially depends on the accuracy of the CSI knowledge. Furthermore, it is shown that the Markov framework allows the source station to predict the channel quality and hence to reduce the number of transmission errors, ultimately resulting in an improved network performance
Cross-Layer Solutions for Cooperative Medium Access Control Protocols
Full text linkAbstract— Recent studies have shown that designing a Medium Access Control (MAC) protocol combined with a cooperative approach may improve the attainable network throughput, despite reducing the mean packet delay. In this paper we design a MAC scheme adopting cooperative physical layer aided cross-layer techniques. We consider a popular cooperative MAC protocol, namely the CoopMAC technique of Liu et al., which is improved by facilitating cooperative signal combining at the destination and employing two relays in the context of a successive relaying technique. The performance of the proposed scheme is evaluated by Monte-Carlo simulations. We demonstrate that a cross-layer design further improves the performance gain provided by the CoopMAC protocol over that of the legacy 802.11 Distributed Coordination Function (DCF), enhancing both the achievable network throughput and the outage probability
EXIT Chart Aided Design of Periodically Punctured Turbo Codes
Full text linkEXtrinsic Information Transfer (EXIT) charts have proved to be an effective tool for studying the convergence behaviour of iterative decoders. However, classical EXIT chart analysis fails to assess the performance of turbo codes in which the systematic bits are punctured periodically. In this letter, a novel 3-Dimensional (3D) EXIT chart technique is proposed for accurately modeling the convergence behaviour of turbo codes that are punctured following a periodic pattern. Finally, the novel 3D EXIT chart technique is validated for a particular periodic turbo code, which is shown to outperform the equivalent randomly punctured code
- …
