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 ={pr 1, pr 2, …, pr. N} 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. d 0 is a reference distance. PL(d 0) 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. 4 Km x 5. 6 Km, 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).
Results of scenario a 1/2
Results of scenario a 2/2
Results of scenario b 1/2
Results of scenario b 2/2
Скачать презентацию Research on cognitive radios Presented by George Fortetsanakis
10b6f30aa19a34abc6becad93a95b0c5.ppt