# Evolution and Testing of NB-IoT Solutions
## 5 End-to-End NB-IoT Testing
### NB-IoT Performance Results  
In this paper, we have quantified the impact that the network configuration has on power consumption and round trip time. Two different scenarios have been defined, following the same approach as in [1]. Scenario 1 called \"normal\" provides a configuration that corresponds to a situation with good propagation conditions; the second scenario is called \"robust\" and represents an adverse network scenario which requires configuring a higher number of repetitions. The maximum number of NPDCCH Repetitions has been configured to 8 in both scenarios. This parameter delimits the number of DCI subframe repetitions to 1, 2, 4, or 8. The \"normal\" scenario has been configured with one DCI subframe and the \"robust\" scenario has been configured with eight repetitions. Regarding the coding  
Figure 8: Control messages between the UE and the eNodeB emulator. Figure 9: Spectrum, signal strength, and quality measurements. rate, in the normal scenario, we have chosen an Index of Modulation and Coding Scheme (IMCS) of 10 that provides a Transport Block Size (TBS) of 680 and a coding rate of 0.6769 with limited redundancy. In the robust scenario, the coding rate is reduced significantly to enable detection under more impaired conditions. Using a IMCS of 1, a smaller amount of TBS of 256 is used, and an overall coding rate of 0.1346 is obtained with additional redundancy as targeted. eDRX and PSM have not been configured in these initial experiments and will be the focus of future experiments. Figure 10 shows the power consumption pattern and the round trip time (RTT) for a series of periodic PING messages that are sent from the UE to the network. In this case, a normal coverage scenario is reproduced by using a moderate redundancy in both time and frequency resource allocations, and a limited number of retransmissions. It can be observed that an average delay of hundreds of ms is obtained for the round trip time because of the repetitions, and that power consumption peaks below 1 W are detected. In this test, the UE is a NB-IoT modem (Hologram Nova, U-Blox SARA-R410) connected to a Next, Unit of Computing (NUC) and the traffic generated is higher than that expected from a sensor. In addition, background traffic is present, which explains the peaks detected. Large delays are expected in NB-IoT as the downlink control information (DCI) transmitted in the control channel (NPDCCH) and the actual data transmission in the data channel (NPDSCH) are repeated over a number of subframes and not transmitted simultaneously unlike in LTE technologies. For each ping repetition, two bursts of power consumption can be observed, one initial narrow pulse, where the NB-IoT device transmits the ping request to the network, and a second burst where the ping reply is received by the UE and feedback is provided back to the network. In Figure 11, it is shown the equivalent power and RTT patterns for a \"robust\" configuration designed to address scenarios with worse propagation conditions. For that purpose, a higher number of retransmissions and more redundant resource allocations are used. Both the duration of the power burst and the average power during each burst increase in the robust scenario as shown in the figure. The reason is that the NB-IoT device needs to repeat the uplink transmission during a larger number of subframes. It can also be observed that the delays in the round trip back have increased because of the larger NPDCCH periods and the additional repetitions both for NPDCCH, NPDSCH, and NPUSCH. In Figure 12, both patterns are superposed for easier comparison. The differences in the power, reaching up to 1.5 W peaks, can be appreciated, as well as the noticeable wider initial transmission and the duration of the power gap to receive the downlink data that matches the measured values on the order of 1 s.  
Figure 10: Power and round trip time in normal scenarios. Table 1 provides a comparative of power consumption for different radio technologies during continuous transmission.