System Level Modeling and Optimization of the LTE Downlink

3. Physical Layer Modeling and LTE System Level SimulationIn Figure 3.19, the pathloss L dB from the attached eNodeB is shown green, while thepahtloss from the three interferers are marked red (L + X dB pathloss). Thermalnoise is considered negligible compared to the received interferer power and setaccordingly in the link level simulator.Figure 3.20 shows the throughput results for the described scenarios, both for systemlevel (blue), and link level (red). With the addition of a power offset between thetarget eNodeB and the interferers, and the consideration of negligible thermal noise,the employed simulation parameters are analogous to those in Section 3.2.1. Relativethroughput difference results compared to link level throughput results are listed inTable 3.6, for both the with 15 dB and 20 dB offset cases.Table 3.6.: Relative throughput difference (compared to link level results).SISO 2×2 TxD 2×2 OLSM 2×2 CLSM 4×4 CLSM15 dB offset 12.15% 10.20% 5.28% 15.41% 4.54%20 dB offset 8.75% 7.28% 2.96% 2.81% 4.18%3.2.3. Comparison with other MIMO LTE Link-to-system Model ResultsPublished throughput results of LTE MIMO L2S models such as those presentedin this work, employed in a well-defined scenario and with a well-described set ofsimulation parameters are not easy to find.While some comparisons of resultsfrom different 3GPP member companies for simple 1×2 scenarios can be foundin [105, 106], no analogous MIMO results could be found. Open source simulatorssuch as [93, 95] could not be used because of their lack of detailed MIMO modeling.Unfortunately, the only similar results found, to the author’s knowledge, are thosein [107], with which a throughput results comparison in shown in Figure 3.21.F(x)10.90.80.70.60.50.40.30.20.10DOCOMOVienna UT0 1 2 3 4 5 6UE throughput [Mbit/s]Figure 3.21: Throughput ecdf results on the scenario defined in [107]. Red line: resultsfrom [107]. Black line: results from the Vienna system level simulator.49