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Interference Minimization and Uplink Relaying for Enhanced 3G/WLAN Network Performance

This paper addresses the limitations of traditional cellular networks in supporting high bandwidth demands of mobile multimedia applications and the resulting interferences. Proposed is a hybrid architecture utilizing clustered mobile nodes with designated cluster heads acting as relays within a WLAN interface while minimizing uplink connections to the 3G band. The study formulates problems related to selecting optimal cluster heads, minimizing interference, and maximizing throughput, employing heuristic and optimization strategies. Simulation results highlight performance implications and suggest future research directions in enhancing mobility and QoS in network traffic management.

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Interference Minimization and Uplink Relaying for Enhanced 3G/WLAN Network Performance

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  1. Interference Minimization and Uplink Relaying Fora 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.

  3. 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

  4. 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

  5. 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

  6. Problem Formulation

  7. 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.

  8. 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.

  9. Case analysis with 3 nodes

  10. 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

  11. Results

  12. Simulation results: Interference

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

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