ECG of small cell RANs with DTX enabled

We investigate the ECG of SISO and MIMO RANs when 100 m radius picocells are deployed homogeneously instead of macrocells. The remaining simulation parameters do not vary from those used in the macro cells’ case. Picocell base station power consumption is used to estimated 𝑃𝑂𝑁 and 𝑃𝑂𝐻 for the pico cell base station. The reference scheme for calculating the ECG is a pico cell SISO RAN with DTX disabled. The ECG vs. cell average offered traffic is plotted in Figure 5-18 for the cases of DTX disabled and enabled. The results show that a value of 𝛿𝐷𝑇𝑋 > 8 is needed to have the ECG of pico cell 2x2 MIMO RAN close to that of SISO at high values of offered traffic . while the ECG of the 4x4 MIMO schemes is always below unity. Also, all MIMO RAN schemes without DTX consume more energy that the SISO RAN. Additionally, the 4x4 MIMO RAN with DTX achieves almost the same ECG as the 2x2 MIMO scheme without DTX. The results are attributed to the different power consumption characteristics in pico cells compared to macro cells, whereby the larger proportion of overhead power consumption in pico cells makes their power consumption less depending on the cell average load (see Figure 5-5). Therefore, in pico cell MIMO RANs the reduction in energy consumption attributed to lower cell averge load values is very small and readily offset by the increase in the energy consumption caused by the adding additional RF chains. In DTX mode, switching off more components in the base station is required during the no traffic load periods

8 10 12 14 16 18 20 22 24 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

Cell average offered traffic (Mbit/s)

ECG SISO Macro RBS _DTX=4 MIMO 2x2 Macro RBS  DTX=4 MIMO 4x4 Macro RBS _DTX=4 SISO Macro RBS _DTX=8 MIMO 2x2 Macro RBS  DTX=8 MIMO 4x4 Macro RBS _DTX=8

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to achieve substantial effective energy savings which illustrated by the value of 𝛿𝐷𝑇𝑋 = 8 in Figure 5-18 in order to have the ECG of 2x2 MIMO RAN approach the ECG level of SISO RAN at high offered traffic load values.

Figure 5-18: ECG of small cell SISO and MIMO RANs

5.7 Summary

An evaluation of the energy consumption of an LTE-based MIMO RANs has been presented in this chapter. The MIMO RAN ECG is evaluated with reference to a SISO RAN under the same capacity requirements. Two cases are evaluated: the first case evaluates the MIMO RAN ECG in new RAN deployment when the operator has the choice to deploy SISO or MIMO base stations. The results obtained for this case results have conclusively shown that dimensioning the RAN using MIMO base stations is more energy efficient than using SISO base stations when the same requirements of area capacity are assumed. This is due to fewer MIMO cells being required to deliver the same offered traffic. The second case evaluates MIMO macrocell RAN ECG when upgrading an existing SISO RAN to MIMO, i.e. the number of base stations is the same for SISO and MIMO deployments. Two MIMO schemes were considered in the second case: 2x2 and 4x4 MIMO. A non-full buffer traffic model was used to model the variation in cell average traffic load in order to observe the impact of the average load variation on the RAN energy consumption. Moreover, the analysis is extended by modeling of the power consumption in radio base stations when DTX is enabled.

8 10 12 14 16 18 20 22 24 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Cell average offered traffic (Mbit/s)

ECG SISO Pico RBS _DTX=8 MIMO 2x2 Pico RBS No DTX MIMO 4x4 Pico RBS No DTX MIMO 2x2 Pico RBS  DTX=8 MIMO 4x4 Pico RBS _DTX=8

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The key findings for the second case are that for macro cells, the 2x2 MIMO RAN achieves higher ECG than SISO RAN for the same offered traffic irrespective of DTX is enabled or not. When DTX is enabled, the 4x4 MIMO RANs also become more energy efficient than SISO RAN. For pico cell RANs, the SISO RAN with DTX enabled is the most energy-efficient option. Furthermore, these results indicate that adaptive antenna muting technique should be implemented with caution in macrocell RANs, as it may lead to more energy consumption if applied on 2x2 MIMO RAN.

Finally, the main outcome of this chapter can be summarized into two points: 1) it is always more energy efficient to upgrade the existing SISO base stations to MIMO to meet the increase in demand for high area capacity requirements. 2) Even if there is no increase in the traffic demand, upgrading the existing SISO macro RANs to 2x2 MIMO improves the per users data rates, and in same time reduces the overall RAN energy consumption. On the other hand, the MIMO picocell RAN can be more energy efficient than the SISO picocell RAN only when high MIMO capacity gain is achievable.

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Chapter 6