**Spectrum Sharing in Cognitive Radio NetworksNeil** Tang3/23/2009 CS541 Advanced Networking

**Outline** • References • A Cognitive Radio Network • System Model • Problem Definition • Proposed Algorithms • Simulation Results • Conclusions CS541 Advanced Networking

**References** • J. Tang, S. Misra and G. Xue, Joint spectrum allocation and scheduling for fair spectrum sharing in cognitive radio wireless networks, Computer Networks, Vol. 52, No. 11, 2008, pp. 2148-2158. CS541 Advanced Networking

**A Cognitive Radio Network** CS541 Advanced Networking

**Assumptions** • A user refers to a transmitter-receiver pair. • The channels available to each user are known in advance. • A user can dynamically access a channel to deliver its packets, but can only work on one of the available channels at one time. • Half-duplex, unicast communications and no collisions. • A scheduling-based MAC layer. • A spectrum server controlling the spectrum allocation and scheduling. CS541 Advanced Networking

**Interference Model** • Primary Interference A B C A B C A B C CS541 Advanced Networking

**Interference Model** • Protocol Model: C(a) = C(b) and (d(A,D) RI or d(C,B) RI) a A B b C D CS541 Advanced Networking

**Interference Model** • Physical Model CS541 Advanced Networking

**Problem Definition** • A user-channel pair (i, j) A iff channel j is available to user i. The total number of user-channel pairs is bounded by N*C. • A traffic demand vector d = [d1, d2, … , dN], specifying the traffic demand of each user. • A transmission mode is composed of a subset of user-channel pairs which can be active concurrently. Whether concurrent transmissions are allowed or not can be determined based on the interference models. CS541 Advanced Networking

**Problem Definition** • A transmission mode can be used in one timeslot. We wish to find a transmission schedule vector p=[p1,p2, …, pT], where pt is the fraction of time that transmission mode t is activated. • Suppose that all possible transmission modes are given. The scheduling problem is to determine the frame length L and the number of active time slots pt*L of each transmission mode in one frame. • A rate allocation vectorr = [r1, r2, … , rN] and a corresponding DSF vector = [1, 2, …, N] = [r1/d1, r2/d2, … , rN/dN]. CS541 Advanced Networking

**Problem Definition** • All problems seeks a feasible rate allocation vector r, all transmission modes along with a feasible transmission schedule vector • The objective of the MAximum throughput Spectrum allocation and Scheduling (MASS) problem is maximizing the network throughput • The objective of theMax-min MAximum throughput Spectrum allocation and Scheduling (MMASS) problem is maximizing the network throughput under the condition min DSF is maximum among all feasible rate allocation vectors. • The objective of theProportional fAir Spectrum allocation and Scheduling (PASS) problem is maximizing the utility function ∑log(i) CS541 Advanced Networking

**Multi-Channel Contention Graph (MCCG)** A transmission mode based on protocol interference model corresponds to a Maximal Independent Set (MIS) in MCCG. CS541 Advanced Networking

**Proposed Algorithms** • Find all transmission modes (optimal) based on MCCG or a good subset of transmission modes (heuristic). • Formulate LPs or CP to solve the defined problems. CS541 Advanced Networking

**Compute Transmission Modes for Protocol Model** • Compute all MISs in MCCG: existing algorithms • Compute a subset of MISs: - Start from a node, keep adding other nodes until no more can be added. Then we obtain one MIS. - Go through every node. - Repeat such procedure q times. - Adding criteria in each step: w(v) = (dπ(v)cv)/(X[v] + 1)) CS541 Advanced Networking

**LP for MASS** CS541 Advanced Networking

**LPs for MMASS** CS541 Advanced Networking

**CP for PASS** CS541 Advanced Networking

**Compute Transmission Modes for Physical Model** CS541 Advanced Networking

**Simulation Results – Protocol Model ** CS541 Advanced Networking

**Simulation Results – Physical Model** CS541 Advanced Networking

**Simulation Results ** CS541 Advanced Networking

**Conclusions** • Our numerical results have shown that the performance given by our heuristic algorithms is very close to that of the optimal solutions. • A good tradeoff between throughput and fairness can be achieved by our PASS algorithms. CS541 Advanced Networking