Throughput Guaranteed Handoff for SDN-Based WLAN in Distinctive Signal Coverage

Abstract

In SDN-based WLAN, controller needs to collect the state info of Mobile Nodes (MNs) like received signal strength indicator (RSSI) for handoff. In such scenarios, high sampling rate facilitates handoff, but it also easily leads to system overhead thus limits access scale of MN. Besides, dynamical adjustment of transmit power of access point (AP) leads to the distinctive signal coverage. Existing handoff algorithms that directly use the uplink RSSI as handoff condition would result in significant throughput decay of MN. Also in indoor deployment RSSI may varies much, large variation of RSSI result in unstable handoff. To address the issues, we design a variable sampling rate mechanism, then filter sampling RSSI and propose a handoff algorithm for distinctive signal coverage scenarios. Our sampling mechanism uses a finite state machine (FSM) to adjust the sampling rate by MN on all nearby APs. Our handoff algorithm uses Kalman filter to achieve stable and trend-reflecting uplink RSSI estimation, then estimate downlink signal noise ratio (SNR) difference between potential and current AP. We implement our algorithm and deployed a test-bed for extensive experiments. Results show our sampling mechanism could achieve sampling quantity decrease by 60%; compared to mean filter based approach, our handoff algorithm improves throughput by 10-50% in distinctive signal coverage scenarios. Besides, handoff frequency decreased by about 60%, indicating a more stable handoff decision.