## 4 Results and Discussion  
In Figures 3-5, results are provided regarding the mean uplink transmission power of the network nodes to the BS for three MIMO orientations: 2 \(\times\) 2, 3 \(\times\) 3, and 4 \(\times\) 4. Processing gain (\(PG\)) is equal to 128/64/32, while SNR may vary from 3 to 7 dB. In the first set of simulations, the diversity combining transmission mode has been assumed. Hence, for a WCDMA bandwidth equal to 3.84 MHz [1], the three \(PG\) values correspond to an equivalent transmission rate of 30/60/120 Kbps, respectively. Figure 4: Mean power per node for SNR = 5 dB. Figure 3: Mean power per node for SNR = 3 dB. In each graph, where mean transmission power per node is provided on a vertical axis, notation x,y,z stands for the number of transmit antennas/the number of receive antennas/_PG_. As can be observed in Figure 3, the mean transmission power is higher for the 2 \(\times\) 2 orientation compared to the other two cases. With 21 nodes per floor and a _PG_ equal to 128 in the 2 \(\times\) 2 case, the mean transmission power is 2.08 W. The corresponding values for the 3 \(\times\) 3 and 4 \(\times\) 4 cases are 1.185 W and 0.8205 W, respectively. Hence, as the order of the MIMO orientation increases (i.e., the number of transmit and receive antennas), the mean transmission power decreases as expected, while this is also the case for the power reduction rate. Moreover, as can be observed from Figure 3, the 2 \(\times\) 2 case is more vulnerable to _PG_ variations. For _PG_ = 64, the mean transmission power is 2.23 W, while the corresponding value for _PG_ = 32 is 2.614 W. Hence, in the first case, we have an increment of 7% compared with the transmission power for _PG_ = 128, and this increment further increases to almost 26% in the second case (i.e., _PG_ = 32). When more antennas are added at both ends of the MIMO link, this increment is significantly lower, especially in the 4 \(\times\) 4 orientation. In this case, for _PG_ = 32 and one node per floor mean transmission power is 0.8159 W. For 21 nodes per floor, then this value increases to 0.8944 W. The corresponding values for the 2 \(\times\) 2 case are 1.944 W/2.614 W, respectively. Hence, as the number of nodes increases, the MIMO order should be increased as well in order to calibrate transmission power increment. In Figures 4 and 5, the results corresponding to Figure 3 are presented for SNR = 5 dB and SNR = 7 dB, respectively. As can be observed in Figure 4, in the 2 \(\times\) 2 case, the power gap among transmissions with _PG_ = 128 and _PG_ = 32 increased. For 21 nodes in the network, in the first case, the mean transmission power is 2.614 W, while in the latter case, it is 5.184 W; hence, there is an increment of almost 100%. In the 4 \(\times\) 4 case, the corresponding transmission power is 0.8944 W/1.522 W for _PG_ = 128/32, respectively. Hence, power increment is now 70%. Similar conclusions can be drawn from Figure 5 as well. Note, however, that in the 2 \(\times\) 2 case there is a severe power outage for 21 nodes in the network. In all sets of simulations, no power thresholds were set, as the main goal was the performance evaluation of all MIMO orientations in extreme scenarios. In Figure 6, results are provided for the case of antenna selection (AS) at mobile nodes. In this case, it is desirable to select a subset of transmit antennas in order to reduce RF complexity, at the cost, however, of increased transmission power. In the considered simulation scenario, a 4 \(\times\) 4 MIMO  
Figure 5: Mean power per node for SNR = 7 dB. transmission scenario has been considered with three cases: No AS, two selected antennas, and three selected antennas.