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Path Loss Measurements of Indoor LTE System for the Internet of Things

ABSTRACT

The Internet of Things (IoT) provides communication service for future smart manufacturing, which is capable of independently exchanging and responding to information to manage industrial production processes. For the purpose of connecting machines, devices, sensors, and people with each other in a factory, reliable and scalable communication networks used in the cellular IoT are of great importance. This paper aims at channel parameter measurements of indoor Long Term Evolution systems in order to achieve good coverage and service reliability (SR) for the IoT.

For the purpose of determining the path loss exponent and the standard deviation of the received shadow fading signal, we use software defined radio techniques to build a small cell experimental platform which contains an evolved node B and user equipment. Received power measurements were performed on this platform. Finally, based on the experimental results, the modified path loss model and the calculated fade margin (FM) for 90% SR are exploited to predict the coverage range of the small cell base station deployed in the factory. The measured path loss channel models are compared with International Telecommunication Union (ITU) path loss channel model.

PRINCIPLES

The path loss is defined as the ratio of the transmit power to the receive power. In a link budget, this refers to the largest transmit power that the transmitter can send and the smallest receive power at which the receiver can recover the original information. Then, the greatest path loss can be calculated from the measured largest transmit power and smallest receive power. A path loss model relates the path loss to the distance between the transmitter and the receiver. By combining the link budget with a suitable path loss model, we can estimate the coverage range of the base station.

EXPERIMENTAL METHODS

Figure 3. The LOS test scenario while the Tx-Rx distance is 1 m

Figure 3. The LOS test scenario while the Tx-Rx distance is 1 m

Figure 4. The LOS test scenario while the Tx-Rx distance is 4 m

Figure 4. The LOS test scenario while the Tx-Rx distance is 4 m

The output port of eNB transmitter was connected to a single transmit antenna through a cable with 14.1 dB loss and a power amplifier (ZX60-V63+) with 18 dB gain. The signal was returned to the input port of the UE receiver through a single receive antenna, as Figure 3 and 4 show.

EVALUATION RESULTS

Figure 6. Path loss versus distance for the LOS and NLOS scenarios

Figure 6. Path loss versus distance for the LOS and NLOS scenarios

Figure 6 illustrates the modified path loss model obtained from the field trail in laboratory, where the solid curve is the ITU-R indoor office path loss model; the circle dotted and solid curves are the average LOS path loss measurement and the modified LOS path loss model, respectively; and the square dotted and solid curves are the average NLOS path loss measurement and the modified NLOS path loss model respectively.

Figure 8. Coverage radius versus transmit power for the LOS and NLOS scenarios

Figure 8. Coverage radius versus transmit power for the LOS and NLOS scenarios

Figure 8 shows the coverage range of the eNB deployed in the laboratory. It is shown that the coverage range increases with the transmit power. Under the same transmit power, the coverage range of the NLOS testing is smaller than the LOS testing. At a coverage range of 10 m, the required transmit power of eNB for LOS testing, NLOS testing and ITU model are −19 dBm, −10 dBm and −1 dBm respectively.

CONCLUSIONS

In this paper, the measurement results of SDR-based small cell experimental platform were used to estimate the channel parameters, to improve the accuracy of ITU indoor path loss model, and to predict the coverage range of small cell base stations in indoor environments. The modified path loss model and the calculated fade margin (FM) for 90% SR were exploited to predict the coverage range of the deployed small cell base station of indoor LTE systems in the laboratory.

In subsequent research, the proposed experimental method will be applied to factorial environments to perform wireless channel parameter measurements. The results could improve the configuration and optimization of LTE small cell base stations in factory environments in order to meet high SR communication requirements for future IoT applications.

Source: Yuan Ze University
Authors: Guan-yi Liu | Tsung-yu Chang | Yung-chun Chiang | Po-chiang Lin | Jeich Mar

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