Page 187 - Kaleidoscope Academic Conference Proceedings 2020
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Industry-driven digital transformation




               10×10 input data. The best handover decision generated  the value of w 2 is set to be 0, 0.5, 1, 2, 5. When w 2 = 0, the
               in the previous step is regarded as the corresponding  UE will always connect to the strongest beam. As shown in
               label.                                         Figure 6 and Figure 7, with the increase of w 2 , the handover
                                                              number and average RSRP will both decrease.
            4. The input data and the corresponding labels from
               different UEs are used to train the CNN in Figure 5.
               After some epochs, the testing accuracy will converge.

           The trained CNN can be used to make suboptimal handover
           decision for a new UE. In each time slot, the UE extracts
           the historical RSRP values of the 10 strongest beams as the
           input of the trained CNN. The output contains 10 values and
           the index of the largest value is regarded as the serving beam
           in the next time slot. It is worth noting that the handover
           decision is actually a prediction for the next time slot, so the
           time lag in the handover procedure can be compensated.


                           4.  SIMULATION
           The proposed methods are numerically evaluated in this
           section. The simulation parameters are mainly referred to
           the parameter Set-1 in [11]. Some important parameters are
           shown in Table 1.                                  Figure 6 – The cumulative distribution function of handover

                      Table 1 – Simulation parameters         number for different w 2

              Parameter                      Value
              orbit altitude                 600 km
              simulation scenario            rural
              carrier frequency              2GHz
              antenna type                   Bessel antenna
              antenna aperture               2m
              effective isotropic radiated power (EIRP)  34dBW/MHz


           As described in Subsection 2.1, the LEO network in
           simulation consists of three orbits. Each satellite has 37
           beams which forms a hexagon. Some points are randomly
           generated within one hexagon in the UV plane.  The
           projections of the points on the earth are calculated as the
           positions of the UEs.

           4.1 The optimal handover strategy based on directed
               graph model                                    Figure 7 – Average RSRP during simulation for different w 2
           With the constructed LEO network, the RSRP values for each
           UE are calculated in each time slot. The length of a one time
           slot is set to be 0.5s, and about 140 time slots are considered  4.2 Performance of CNN in handover optimization
           in the whole simulation. The optimal handover strategy for
           each UE is generated by using the directed graph based model  Three methods for handover optimization are compared in
           in Subsection 3.1.2.                               this subsection. The first method assumes the UE can predict
                                                              its RSRP and make handover decision based on the directed
           In the graph based model, the two parameters w 1 and w 2 form  graph model. The second method means that the UE using the
           a trade-off between RSRP strength and handover number and  trained CNN to make handover decision. The CNN is trained
           need to be predetermined. In this subsection, the w 1 is fixed  by the results of the directed graph model with w 2 = 1. In the
           and different w 2 are evaluated to show the change of handover  third method, the UE is always served by the strongest beam.
           number and average RSRP strength. Because of the large path
           loss, the received power of the strongest beam in one resource  Comparing with the “strongest beam” method, the CNN can
           element is near 10 −17 W. Therefore, the w 1 in Equation (1)  largely reduce the number of handovers without a requirement
           is set to be 10 , which means that the benefit of accessing  for UE capability. The Figure 8 and Figure 9 show that the
                      17
           the strongest beam in one time slot is around 1. Meanwhile,  handover number of more than 70% of the UEs are reduced




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