IST-4-027756 WINNER II D6.13.12 v1.0 Final CG “local area ...

WINNER II D6.13.12 v1.0Average Throughput (Mbps)191715131197SINR_Target=28dBSINR_Target=18.5dBSINR_Target=14dBNo Handover50.1 1 10Targer BS and current BS Load RatioFigure 11.9: Average throughput of the user terminal S0 as a function of the load on the targetchannel for different SINR valuesFinally we show the performance gain that can be achieved performing handovers triggered by theresidual throughput in different load conditions. Consider as an example the topology presented in Figure11.8. The user terminal S0 is under the coverage of both BSla BS1 and BS2 and it is initially connected toBS1. Assume that, due to its placement, the SINR of the radio channel to BS1 perceived by S0 is 18.5dB.Then we vary the position of BS2 to achieve SINR in the second cell equal, lower and higher than that inthe first cell. Moreover, we assume the other nodes connected to BS1 generate a load of 5 Mbps, whilethe load of BS2 is varying.Figure 11.9 reports the layer 2 throughput achieved by station S0, as a function of the load ratio betweenthe two cells, for different values of the SINR on the target channel (to BS2). The throughput achievedtransmitting towards BS1, that is, if no handover is performed, is reported as a reference.First of all, note that all the handovers result in a throughput gain. The estimation of the residualthroughput indeed let the user correctly judge if advantages in performance can be achieved handing over.Moreover, we can gather that when the SINR on the target cell is higher than that one the current cell, thehandover is performed until high values of load of the target cells. Otherwise, if there if no gain in thesignal strength and thus in the used data rate, the handover is performed only when the load on the targetcell is lower than that on the current cell.As a conclusion, the handover strategy implemented in the WINNER system offer several advantages:• The time necessary to scan the other channels is reduced by the use of the neighbouring cell lists andperformed periodically, offering an up-to-date evaluation of available cells.• The use of Mobile IP and the layer-3 handover cases are dramatically reduced by the introduction ofthe pool of gateways sharing resources, offering a reduction of the latency of 2–3 sec.• The handover is not triggered only by the loss of connectivity, but also by the availability of betterresources, resulting in a higher achieved throughput.Page 74 (86)