The Application of 5G Wireless Communication in Maritime Environment

Recently, 5G wireless communication have been rapidly adopted for maritime applications. As a result, significant progress has been made in the ocean digitalization. 5G features with low latency, high reliability, and a large bandwidth, which satisfies the requirements of maritime applications. Due to significant differences between land and marine radio propagation environments, the maritime communication encounters a large challenge for providing maritime users with reliable data communication service. In order to solve the abovementioned challenge, we designed a maritime 5G terminal and tested it on an unmanned surface vehicle (USV) in the Lanyue Lake of Zhejiang Ocean University. The test data were collected, and the corresponding data analysis are presented, which includes signal strength, signal reception quality, upload and download data rate. The received signal level (RSL) and transmission data rate obtained by the maritime 5G terminals demonstrate great potential of meeting the communication requirements of the maritime users. It is also can be found that the RSL and the data transmission rate of the maritime 5G can be used for the remote control of the unmanned ships, with the signal strength at sea up to -89.45 dBm, and maximum rate up to 226 Mbps.


Introduction
Reliable and high-throughput maritime communications are considered an essential and vital technology of maritime activities which involve various types of ships, autonomous ships, nearshore facilities, unattended buoy platforms, autonomous underwater facilities, coastal and onshore observatories, etc. Unmanned surface vehicle (USV) and the digitization of numerous marine activities, such as oil extraction, marine transportation, fish farming, and environmental monitoring, involve data transmission, environmental sensing, data security, and business flow routing, which require high-speed and reliable communication solutions to support.To obtain efficient information transmission and costeffective operation, maritime activities need reliable communication solutions with low latency, wide coverage, high throughput and low cost.Therefore, the maritime activity field and the marine communication industry are continuously promoting technological innovation of maritime connectivity, such as the improvement of latency optimization capability, the development of coverage technology [1], and the development of energy-efficient technology [2], which can meet the communication services required by unmanned boats' maritime activities.
In 2020, China begins deployment and testing of 5G base stations with massive multi-input and multi-output capabilities [3].At present, communication for offshore applications through 5G is being carried out gradually.The paper [4] analyzes the propagation characteristics of 5G wireless signals in the marine environment, in which the antenna design was improved at the base station side and the transmit power was enhanced at the terminal side.As a result, the adaptability problem of 5G communication in marine environment is solved, and the performance and coverage capability of offshore communication is improved.In paper [5] utilizes an automated barge control system based on 5G networks and validates it in a real port environment.The results of the study show that the 5G system performs well in terms of latency while successfully addressing the safety and reliability of ship operations.The paper [6] by integrating maritime search and rescue operations with 5G networks and related technological components, significantly improves the collaborative task performance of maritime search and rescue operations, strengthens the operational framework of first responders, and effectively enhances the efficiency and success rate of the missions.To address the existing issue of inadequate communication capabilities of 5G at sea, we developed a dedicated maritime 5G terminal and deployed it on an Unmanned Surface Vehicle (USV).It needs to be mentioned that the terminal was tested for its performance in Lanyue Lake at Zhejiang Ocean University, as depicted in figure 1. Lanyue Lake, which is connected to the sea, and accurately represents realistic maritime conditions to ensure the testing environment close to the actual sea scenarios.Therefore, the results obtained from the tests conducted in Lanyue Lake can be considered representative of the terminal's performance in typical sea conditions.This paper researches the performance of the maritime 5G system for autonomous ship applications, which provides important information for the application of maritime 5G technology on unmanned ships.The abbreviations and definitions used in this paper are shown in Table 1.
The article is organized as follows: in Section 2, the entire test scenario description is presented.In Section 3, the results of the offshore environmental terminal measurements are shown.In Section 4, the results are analyzed.In Section 5, the paper is concluded, and future research plan is given.

Measurement campaign description
The CPU chipset stm32mp157c [7] is used in the self-developed marine 5G terminal for the main control, which is integrated with 5G module, temperature and humidity sensor, wifi module.All the model control and data acquisition are through the embedded system.In order to test and evaluate the performance of the maritime 5G terminal on the USV, we carried out the performance test of the maritime 5G terminal based on the USV in the marine test site of Zhejiang Ocean University, Lake Lanyue.The unmanned boat started from the center of the pontoon and sailed around the lake clockwise for 1 hour, covering about 2.6 km.The test route is shown in figure 2.
During the measurement campaign, a mobile 5G IoT sim-card was used to verify the network performance and to remotely view the operation of the terminal through the 5G Internet.At the same time, the marine 5G terminal will also automatically collect various kinds of sensor data from the environment during the trip to better evaluate the performance of the terminal in the maritime environment in terms of data rate, signal strength, system reliability, stability, etc.The parameters are listed in Table 2.

Result RSRP and RSRQ
RSRP is the signal strength of the received power of the reference signal transmitted by the transmitter, reflecting the current channel path loss strength.Its value range are -44 ~ -140 dBm.It needs to be pointed out that larger value represents better signal strength.RSRQ is used to measure the quality of the reference signal received by the receiver, which reflects the strength and reliability of the signal received by the user equipment.RSRQ is obtained from the ratio of the average power of the received reference signal and the associated interference power.The higher value of RSRQ indicates that the quality of the received signal is better.The range of RSRQ is [-3, -20] dB, which means if the value of RSRQ is less than -20 dB, it is not possible to establish a network.Figure 3 shows the base station location information used in this test, and the 5G terminal mounted on the USV is used to receive the base station signals.The test analyzed the RSRP and RSRQ acquired by the 5G terminal.The RSRP and RSRQ were obtained and analyzed as shown in figure 4 and figure 5, respectively, from which it can be found that the RSRP and RSRQ data received in the band n41 are less fluctuating and relatively stable.The mean value of RSRP is -89.45 dBm, maximum value -71 dBm, minimum value -120 dBm, and variance 7.74 dBm.The mean value of RSRQ is -12.54 dB, maximum value -11 dB, minimum value -31 dB, and variance 1.95 dB.At 15:45, the unmanned ship began to enter an area with very poor 5G signal coverage, but RSRP could still be obtained.It indicates that the maritime 5G terminal can provide good signal reception capability and shows good reliability and stability in this band.When the USV is about 5 km away from the base station7, the RSRP and RSRQ slightly fluctuate, but the RSRQ is still larger than -20 dB.The terminal was remotely controlled by a panel PC via the 5G network, and the system control was very smooth with a latency of 0.6 milliseconds as tested by Iperf, which proves that the terminal can provide high reliability and high data rate to support remote control of the USV.It needs to be mentioned that the network handover occurred during the whole route and the connected base stations are shown in the figure 3.

Throughput
System throughput (Mbit/sec) is one of the most important indicators of maritime communication solutions.In our measurement campaign, a widely used open-source software Iperf [8] is used for the throughput test, which can measure the uplink and downlink throughput of terminals using either TCP or UDP protocols.We measured the uplink rate and downlink rate of the whole communication link during the measurement process, and the results are shown in figure 6 and figure 7, respectively.From figure 6, it can be seen that the upload data rate is within the range of [0.113, 74.5] Mbps when the USV was sailing in Lanyue Lake, while the download data rate is within the range of [0, 226] Mbps.The downlink rate delay is shown in figure 8, and the delay is in the range of [0.134, 1.988] ms/sec.
Figures 9 and 10 show the Iperf upload and download data rates as a function of TX-RX distance, as well as the distribution of network rates during the test period.The exact locations of the connected base stations during the test period are shown in figure 3. When the USV with 5G terminal head 1 km away from the base station, the Iperf upload data rate reaches the highest value and the download data rate also remains relatively stable.As the distance of the USV from the base station increases, the Iperf upload rate decreases slightly, and when the distance from the base station is 4 km, the uplink rate can still be maintained at a rate of 53.8 Mbits and the downlink rate at a rate of 226 Mbits.At a distance of 5 kilometers from the base station, the downlink rate can be maintained at more than 200 Mbits.In addition, between 15:45 and 16:00, the USV drives into the area of Lanyue Lake where the 5G signal coverage is particularly weak.Corresponding to 15:45 to 16:00 in figures 4 and 5 above, our terminal can still receive signals, but the signal strength and quality are not high, resulting in low throughput, which indicates that the terminal can also provide a stable wireless link in this environment.

Conclusion
In this paper, the system performance of our developed marine 5G terminal was tested in the 5G band n41 ([2.496,2.690]GHz).By comparing the RSRP and RSRQ obtained by unmanned ships equipped with 5G terminals in this frequency band, it can be found that the average signal strength and model quality obtained by the terminal in areas with poor 5G signal coverage are -89.45dBm and -12.54 dB, respectively.This indicates that the 5G terminal can provide a stable and reliable signal acquisition capability for ships.Based on the upload and download data rates obtained by Iperf and the fact that the terminal was then able to provide a network even in areas with poor 5G signal coverage, it proved that the offshore 5G terminal has good data transmission capabilities and stability at sea.It has the potential of meeting the requirements of unmanned ships in terms of wide coverage, high data rate, and low latency, and providing good support for applications such as automatic navigation of ships and ports, remote management of autonomous ships, and real-time wireless monitoring of marine pollution.

Figure 1．The
Figure 1．TheUSV used in the test.

Figure 9 .
Figure 9. Upload data rate during the test route.

Figure 10 .
Figure 10.Download data rate during the test route.