4 Introduction Broadcasting Tree and Coloring System Model and Problem Definition Broadcast Scheduling Simulation 6 Conclusion and Future Work

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4  Cognitive Radio Networks (CRNs)  The utilization of spectrum assigned to licensed users varies from 15% to 85% temporally and geographically (FCC report)  Unlicensed users (Secondary Users, SUs) can sense and learn the communication environment, and opportunistically access the spectrum without causing any unacceptable interference to licensed users (Primary Users, PUs)

 Broadcast Scheduling in CRNs  Task and goal  Broadcast a data packet from the source to all the other nodes  Minimum-latency and minimum-redundancy  Motivation  NP-hard even in traditional wireless networks under the simple UDG model  It is not straightforward to move traditional broadcast algorithms to CRNs  Existing solutions are either heuristic solutions without performance guarantee or with performance far from the optimal solution  Our contributions  A Mixed Broadcast Scheduling (MBS) algorithm for CRNs under both the Unit Disk Graph (UDG) model and the Protocol Interference Model (PrIM)  Comprehensive latency and redundancy analysis 5

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 Primary Network  N Primary Users (PUs):  Transmission/interference radius:  Network time is slotted:  Primary transmitters are Poisson distributed with density  Secondary Network  A source and n randomly distributed Secondary Users (SUs)  Transmission/interference radius:  Topology graph: 7

 Interference Model  Unit Disk Graph (Model):  Protocol Interference Model (PrIM):  Problem definition  To seek a broadcast scheduling strategy of minimum latency  Low broadcast redundancy  the maximum possible transmission times of the broadcast packet by a SU during the scheduling 8

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 Connected Dominating Set (CDS)  Dominators (black), Connectors (blue), and Dominatees (white)  CDS-based broadcasting tree 10

 Tesselation  A tessellation of a plane is to cover this plane with a pattern of flat shapes so that there are no overlaps or gaps  A regular tessellation is a pattern made by repeating a regular polygon, e.g. hexagon 11

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 MBS-UDG: Idea  Phase I: broadcast to all the dominators  by Unicast  Phase II: broadcast to all the dominatees  by mixed Unicast and Broadcast  Depending on how many dominatee children are waiting for receiving the broadcast packet 13

 Latency and redundancy performance analysis  The expected time consumption of MBS-UDG is upper bounded by and (Theorem 3).  The broadcast redundancy of MBS-UDG is at most and (Theorem 4). 14

 MBS-PrIM  No significant difference with MBS-UDG  Performance analysis  Let. The expected number of time slots consumed by MBS-PrIM is upper bounded by if and if (Theorem 7).  The broadcast redundancy of MBS-PrIM is upper bounded by if, and if (Theorem 8). 15

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 Latency performance 17

 Redundancy performance 18

 A Mixed Broadcast Scheduling (MBS) algorithm is proposed  Comprehensive latency and redundancy performance analysis  Simulations are conducted  Future Research Directions  Considering more accurate dynamic spectrum model and access model  Distributed broadcasting algorithm with performance guarantee 19