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Research on cognitive radios. Presented by George Fortetsanakis. Network paradigm. We consider a geographical region Λ , in which a set of service providers P, sell Internet access.
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Research on cognitive radios Presented by George Fortetsanakis
Network paradigm • We consider a geographical region Λ, in which a set of service providers P, sell Internet access. • Each provider p∈P owns a cellular network consisting of Base station that are located on the sites of a triangular grid. • The Bandwidth of the provider p is distributed among its Base station according to a frequency reuse scheme with factor kp. • The set of all Base stations in the region of interest is denoted by B. • The medium access scheme is TDMA • All channels that are available to a Base station are divided into a number of time-frequency slots.
Secondary users • A set of secondary users U, that are scattered at various locations in the region Λ try to buy Internet access from Base stations in their vicinity. • A secondary user can connect to a base station using a unique time-frequency slot.
Game-theoretical problem formulation • We describe the system as a game in which: • The players are the service providers and the secondary users. • Each service provider can choose among a discrete set of prices Sp ={pr1, pr2, …, prN} for the services he offers. • A secondary user can choose to connect to specific base station or not to buy Internet access at all. • The set of strategies for a secondary user is denoted by Su = B∪{e} . • The strategy e corresponds to the case that a secondary device does not buy Internet access.
Channel model • The channel gain between a secondary user x∈U and a Base station y∈B is given by a path loss model. • Where • L(x) and L(y) are the locations of x and y respectively. • d0 is a reference distance. • PL(d0) is the path loss at distance do from the transmitter. • N is the path loss exponent.
Interference power • When a secondary user x∈U communicates with a Base station y∈B we take into consideration the worst case of interference from Base stations that function at the same channels as y. • x and y can communicate only if their distance is lower than the threshold • Where: • Dp: Distance between y and the closest interfering Base station. • γ:Required SINR for successful communication.
Example of a cellular network • Red spots: Interfering Base stations. • Frequency reuse factor is Kp = 7. • Dp: Distance of closest interferers. • : Cell radius.
Required transmission power • The required transmission power for a secondary user x∈U to communicate with a Base station y∈B is equal to: • Where: • Tmax: maximum allowable transmission power.
Payoff of a secondary user • The payoff function of a secondary user x∈U is defined as follows: • Where: • k: The Base station with which x chooses to connect. • σ(k): The price offered by the Base station y. • : Maximum price that x can tolerate. • τx: Significance of transmission power for x. • κx: Significance of price for x.
Payoff of a service provider • The payoff function of a service provider p ∈P when he interacts with a secondary user x ∈U is defined as follows: if BS k belongs to y • Where: • σ(p): Price that all the Base stations of the provider p offer. • k: The Base station with which x chooses to connect.
Game evolution • Each secondary user reconsiders his strategy at time instances that are produced by a Poisson process of mean lu. • At the time instances the secondary user chooses to connect to a Base station that maximizes his payoff function. • Each service provider reconsiders his price at time instances that are also produced by a Poisson process of mean lp. • At these time instances a service provider chooses a price that maximizes his payoff. • Usually lp << lu.
Simulation testbed • In a region of 5.4Km x 5.6Km, three cellular networks function that belong to different service providers. • 400 secondary users are scattered in this region with a uniform spatial distribution. • We study two scenarios: • Scenario a: All secondary users are value transmission power more than price (tx>>kx). • Scenario b: All secondary users are value price more than transmission power (tx<<kx).
