Opportunistic Spectrum Access in Cognitive Radio Networks (Well known) Motivations as long as Cognitive Radio Networks Opportunistic Spectrum Access Three basic access schemes Problem Formulation

Opportunistic Spectrum Access in Cognitive Radio Networks (Well known) Motivations as long as Cognitive Radio Networks Opportunistic Spectrum Access Three basic access schemes Problem Formulation www.phwiki.com

Opportunistic Spectrum Access in Cognitive Radio Networks (Well known) Motivations as long as Cognitive Radio Networks Opportunistic Spectrum Access Three basic access schemes Problem Formulation

Bowman, Rebecca, Managing Editor has reference to this Academic Journal, PHwiki organized this Journal Opportunistic Spectrum Access in Cognitive Radio Networks Project Team: Z. Ding in addition to X. Liu (co-PIs) S. Huang in addition to E. Jung (GSR) University of Cali as long as nia, Davis (Well known) Motivations as long as Cognitive Radio Networks Spectrum scarcity. More wireless services. Inefficient static spectrum allocation. Existence of a large amount of under-utilized spectrum. Advantage of flexible in addition to cognitive spectrum access scheme needed: cognitive radio. Opportunistic Spectrum Access Design Objectives: Non-intrusiveness Spectral efficiency Cost efficiency Decentralized

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Three basic access schemes PU – primary user (licensee of the channel) SU – secondary user (cognitive ratio) Problem Formulation Assumptions: Exponentially distributed idle period General primary busy period distribution Perfect sensing Knowledge of average idle time/busy time Constraint Metrics: Bounded collision probability Bounded overlapping time Optimization problem: Fundamental limits of opportunistic spectrum access Primary channel with exponentially distributed idle period Bounded collision probability constraints Maximum achievable throughput of a secondary user — collision probability bound — percentage of idle time (by primary users)

Comparison of VX in addition to VAC Comparison of VX in addition to KS Observations VX, VAC in addition to KS schemes have indistinguishable throughput per as long as mance, under collision probability constraint; The smaller the packet length, the larger the throughput. The result can be extended to systems with multiple primary users in addition to multiple secondary users (treat all secondary users as a “super” secondary user)

Fixed length packet wins Under the collision probability constraint, the secondary user achieves the maximum throughput when it transmits fixed length packets Overhead Consideration Optimal packet length achieves trade-off between overhead in addition to collision probability Relation between two constraint metrics

Multi-b in addition to multiple secondary systems No synchronization between secondary users in addition to primary users No control channel as long as secondary users Collision probability constraint Perfect sensing Two sensing strategies Simulation result as long as Multi-b in addition to competitive systems

Smart Antenna Technique Applied in Cognitive Radio Networks Design Objective: Maximize the QoS of SUs while protecting PUs Design MAC Protocols to take advantages of smart antenna technologies System Setup: One primary Tx (PT), one primary Rx (PR) One cognitive Tx (CT) , one cognitive Rx (CR) PT in addition to CT transmit simultaneously to PR in addition to CR, respectively Per as long as mance metric: talk-able zone of CR System Model Optimal Beam as long as ming Problem with Constraints Can be solved efficiently by convex optimization method

A Typical Beam as long as ming pattern of a Secondary TX Simulation Results (1) PT uses omni-directional antenna PRs are evenly distributed over the area centered at PT Interference to PR is less than 0.1 of the received signal power Spectrum efficiency increased at least by: Simulation Results (2) PT uses Transmit beam as long as ming PRs are evenly distributed over the area centered at PT Interference to PR is less than 0.1 of the received signal power Spectrum efficiency increased at least:

Integration of MAC/PHY design in Cognitive Radio Networks Design Objective: Under the collision probability constraint, increase the capacity of secondary users A cross-layer approach Channel models Rich scattering environment: Rayleigh fading MISO channel from CT to CR in addition to PR Rayleigh SISO fading channel from PT to PR in addition to CR Received signal model Idea: when overlapping happens, primary user can decode its signal as long as the interference power from secondary user is very small. Transmit beam as long as ming helps in this scenario, since it can mitigate the interference to primary users; Collision probability: Simulation Result

Bowman, Rebecca Journal of Endovascular Therapy Managing Editor www.phwiki.com

Conclusions Opportunistic spectrum access of secondary users can increase the spectrum efficiency of system Smart antenna technique enables concurrent transmission of primary users in addition to secondary users, in addition to reduces interference to primary user Integration of PHY/MAC layer can improve system’s spectrum efficiency

Bowman, Rebecca Managing Editor

Bowman, Rebecca is from United States and they belong to Journal of Endovascular Therapy and they are from  Phoenix, United States got related to this Particular Journal. and Bowman, Rebecca deal with the subjects like Science

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