1. Interference Minimization and Uplink Relaying For a 3G/WLAN Network Ju Wang Virginia Commonwealth University May, 2005

2. Motivation Traditional cellular network could not fulfill the massive bandwidth requirement of the mobile multimedia applications. –Asynchronized uplink access –Subject to intra-cell and inter-cell interference WLAN has the range limitations. Solution: hybrid 3G/WLAN architecture.

4. Basic Idea Cluster mobiles in the same cell to several clusters. Each cluster is served by a cluster head, which functions as a relayed points. Communications inside a cluster is through WLAN interfaces. Only cluster heads are allowed to transmit in the 3G band. Advantages : –Reduced transmission activities and interferences –Reduce uplink connections, making it easy for scheduling

5. Challenges How to select cluster heads Centralized or discrete manner Constraints Optimization goals: number of cluster, maximum cluster size… Uplink scheduling algorithms –Fair access for all mobiles –Maximizing throughput Deal with mobile movement

6. Clustering with Interference Minimization We try to minimize the possible interference to other cells Assume a 3-way sectorization Two neighbor sectors are affected most by local transmission

7. Problem Formulation

8. Problem Nature Equivalent to an instance of weighted set- cover problem, which is NP-complete. –General set cover problem does have polynomial approximation algorithm that deliver a constant upper bound. Looking for an optimum vertex cover instead –Have good heuristic –Good chance of find a backup cluster head In our case, the weight distribution is closely related to the physical location of mobile nodes, which might be helpful in heuristic.

9. Cost function characterization optimum vertex cover has as its objective to minimize the out-of-cell interference, Minimum vertex cover is the smallest vertex cover in the non-weighted graph case. An interesting observation: with the interference weight function, the above two set is very close to each other under the cell geometry.

10. Case analysis with 3 nodes

11. Pilot-assisted RMT selection measure all PLi from mobile stations. collect the WLAN connectivity information from all mobile stations to form the graph G(V;E). calculate a edge path loss : ELPj = PLj1+PLj2 where j1 and j2 are the two end nodes of edge j. sort the remaining edges according to their ELP value, and select the edge of the lowest path loss, placing it into the matching set. add the two end nodes of the selected edge to the RMT set

12. Results

13. Simulation results: Interference

14. Future works Performance evaluation considering mobile movement –Inter-cluster handoff –Inter-cell handoff –Distributed heuristics QoS guarantee –Traffic Scheduling –Admission control Questions…