54 research outputs found
Joint Design and Separation Principle for Opportunistic Spectrum Access in the Presence of Sensing Errors
We address the design of opportunistic spectrum access (OSA) strategies that
allow secondary users to independently search for and exploit instantaneous
spectrum availability. Integrated in the joint design are three basic
components: a spectrum sensor that identifies spectrum opportunities, a sensing
strategy that determines which channels in the spectrum to sense, and an access
strategy that decides whether to access based on imperfect sensing outcomes.
We formulate the joint PHY-MAC design of OSA as a constrained partially
observable Markov decision process (POMDP). Constrained POMDPs generally
require randomized policies to achieve optimality, which are often intractable.
By exploiting the rich structure of the underlying problem, we establish a
separation principle for the joint design of OSA. This separation principle
reveals the optimality of myopic policies for the design of the spectrum sensor
and the access strategy, leading to closed-form optimal solutions. Furthermore,
decoupling the design of the sensing strategy from that of the spectrum sensor
and the access strategy, the separation principle reduces the constrained POMDP
to an unconstrained one, which admits deterministic optimal policies. Numerical
examples are provided to study the design tradeoffs, the interaction between
the spectrum sensor and the sensing and access strategies, and the robustness
of the ensuing design to model mismatch.Comment: 43 pages, 10 figures, submitted to IEEE Transactions on Information
Theory in Feb. 200
Packet Relaying Control in Sensing-based Spectrum Sharing Systems
Cognitive relaying has been introduced for opportunistic spectrum access
systems by which a secondary node forwards primary packets whenever the primary
link faces an outage condition. For spectrum sharing systems, cognitive
relaying is parametrized by an interference power constraint level imposed on
the transmit power of the secondary user. For sensing-based spectrum sharing,
the probability of detection is also involved in packet relaying control. This
paper considers the choice of these two parameters so as to maximize the
secondary nodes' throughput under certain constraints. The analysis leads to a
Markov decision process using dynamic programming approach. The problem is
solved using value iteration. Finally, the structural properties of the
resulting optimal control are highlighted
Joint Spectrum Sensing and Resource Scheduling for Cognitive Radio Networks Via Duality Optimization
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