Keywords

1 Introduction

Energy Internet is a new type of power network node composed of distributed energy acquisition device, distributed energy storage device and various types of load, which combines advanced power electronics technology, information technology and intelligent management technology to realize energy peer-to-peer exchange and sharing network with two-way energy flow [1,2,3,4,5].

Wireless communication has the advantages of ubiquitous access, flexible deployment, fast construction and so on, it has unique advantages in meeting the information and communication needs of the global energy Internet [6,7,8,9]. It makes up for the problem that optical fiber communication can not cover all the business scope of power system because of the limitation of terrain, cost and so on [9,10,11,12].

VoLTE opens the way to mobile broadband voice, which brings two aspects of value to operators, one is to improve the efficiency of wireless spectrum and reduce the network cost, and the other is to enhance user experience [13,14,15]. In this paper, the deployment and networking scheme of VoLTE service in power wireless private network are studied, and a pilot verification project is established.

In this paper, the deployment and networking scheme of VoLTE service in power wireless private network are studied, and a pilot verification project is established. According to the mobile characteristics and network coverage characteristics of the mobile terminal of the power wireless private network, the application model of the VoLTE in the power wireless special network is proposed, and the optimization direction is pointed out through analysis.

2 System Architecture of VoLTE

There are three solutions for LTE voice in the industry, which are VoLTE, CSFB and SGLTE, respectively [16]. The VOLTE and the CSFB are standardization scheme in 3GPP, and the SGLTE is the terminal implementation scheme, wherein the VoLTE is the ultimate scheme of the mobile 4G voice solution. SGLTE does not need to change the network, and both VOLTE and CSFB need to modify the network [16, 17].

In the VoLTE, it uses IMS as the business control layer system, and EPC only as the bearing layer [18]. The switching of SRVCC solves the problem of voice continuity, and the delay of call time is short. The network frame diagram of VoLTE is as follows (Fig. 1).

Fig. 1.
figure 1

Framework diagram of VoTLE network

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The protocol architecture of VoLTE is as follows. As can be seen from the Fig. 2, the sip protocol only supports both the terminal and the IMS, and it’s just a transmission function for wireless access networks.

Fig. 2.
figure 2

Protocol architecture of VoLTE

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3 Analysis of User Requirements in Power Network

The wireless special network can support the construction of smart grid, support distribution automation, marketing load control, power collection, smart home, new energy grid-connected communication, operation inspection and repair monitoring and other smart grid services, to meet the requirement of reliability, security, real-time (Tables 1 and 2).

Table 1. Demand analysis of power distribution automation services
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Table 2. Demand analysis of Smart grid extension service
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4 Test Environment of VoLTE

The system is composed of wireless private network, IMS special network, administrative mobile background service and mobile soft terminal [19]. In which the IMS private network and the administrative mobile background service are deployed in the machine room, the wireless private network is deployed at the power company headquarters building, and the base station of wireless private network is in the substation. The deployed wireless private network is connected with the IMS private network and the administrative mobile background service through the SDH channel. The composition architecture of the system is as shown in the figure [20] (Fig. 3).

Fig. 3.
figure 3

Architecture of wireless private network system

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The power wireless private network provides three voice solutions, the first is UC client;2, the second is administration client; the third is VoLTE. Scenarios 1 and 2 belong to the VoIP pattern, in this mode, the client software needs to be deployed on the mobile phone. The service platform is deployed on the IMS core network, and the terminal is accessed via wireless private network and registered to the service platform. Solution 3 does not need to deploy client software on power private network mobile phones. The performance indicators of voice and video under the three voice solutions are tested in this test.

Performance index refers to the quality of voice and video calls under different wireless signal intensities. The specific performance indicators are shown in the following table. The test car runs at medium speed depending on the actual road traffic conditions, and the vehicle speed is about 30 km/hour (Table 3).

Table 3. Alternative condition
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5 Test Result

5.1 Test of Voice Quality

The test topology diagram shows that a pair of test terminals are attached to the power wireless private network and registered to the UC background and the administrative background respectively (Fig. 4).

Fig. 4.
figure 4

Fixed-point voice test topology

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Two test terminals are connected to the voice tester, and one test terminal acts as the caller and calls the other terminal. After dialing, sending the voice through the voice tester to the called terminal through the calling terminal, and returning the voice to the voice tester after being accepted by the called terminal. The test results are as follows.

  1. (1)

    Voice test under good conditions

RSRP = −67 dBm and SINR = 28 dB, and the test site is 1 km from the base station by the side of the road (Tables 4 and 5)

Table 4. MOS value of speech quality (a good place)
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Table 5. End-to-end call delay (a good place)
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  1. (2)

    Voice test under medium conditions

RSRP = −98 dBm and SINR = 16 dB, and the test site is 3 km from the base station by the side of the road (Tables 6 and 7)

Table 6. MOS value of speech quality (a general place)
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Table 7. End-to-end call delay (a general place)
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  1. (3)

    Voice test under poor conditions

RSRP = −108 dBm and SINR = 11 dB, and the test site is 5.5 km from the base station by the side of the road (Tables 8 and 9)

Table 8. MOS value of speech quality (a bad place)
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Table 9. End-to-end call delay (a bad place)
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  1. (4)

    Voice test under very poor conditions

RSRP = −120 dBm and SINR = 0 dB, and the test site is 7 km from the base station by the side of the road (Tables 10 and 11)

Table 10. MOS value of speech quality (a very poor place)
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Table 11. End-to-end call delay (a very poor place)
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6 Test of Video Quality

The test topology diagram shows that a pair of test terminals are attached to the power wireless private network and registered to the UC background and the administrative background respectively (Fig. 5).

Fig. 5.
figure 5

Fixed-point voice test topology

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Two test terminals are connected to a voice tester, and one test terminal acts as a caller and calls the other terminal. After dialing, the video stream is sent to the called terminal through the calling terminal through the video quality tester, and the called terminal receives it and returns it to the video quality tester.

  1. (1)

    Video test under good conditions

    RSRP = −67 dBm and SINR = 28 dB, and the test site is 1 km from the base station by the side of the road (Table 12)

    Table 12. Test results of video quality index (a good place)
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  2. (2)

    Video test under medium conditions

    RSRP = −98 dBm and SINR = 16 dB, and the test site is 3 km from the base station by the side of the road (Table 13)

    Table 13. Test results of video quality index (a general place)
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  3. (3)

    Video test under poor conditions

    RSRP = −108 dBm and SINR = 11 dB, and the test site is 5.5 km from the base station by the side of the road (Table 14)

    Table 14. Test results of video quality index (a bad place)
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  4. (4)

    Video test under very poor conditions

    RSRP = −120 dBm and SINR = 0 dB, and the test site is 7 km from the base station by the side of the road (Table 15)

    Table 15. Test results of video quality index (a bad place)
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7 Road Test

  1. (1)

    Test terminal is terminal 1, and the call mode is administrative communication. The road test results are shown in the figure below (Fig. 6).

    Fig. 6.
    figure 6

    Road test results

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  2. (2)

    Test terminal is terminal 2, and the call mode is administrative communication. The road test results are shown in the figure below (Fig. 7).

    Fig. 7.
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    Road test results

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  3. (3)

    Test terminal is terminal 1, and the call mode is UC Client. The road test results are shown in the figure below (Fig. 8).

    Fig. 8.
    figure 8

    Road test results

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  4. (4)

    Test terminal is terminal 2, and the call mode is UC Client. The road test results are shown in the figure below (Fig. 9).

    Fig. 9.
    figure 9

    Road test results

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The green marker in the above test results indicates that the MOS value of voice is more than 4, the yellow marker indicates that the MOS value of voice is more than 3, and the red marker indicates that the MOS value of voice is less than 3. From the above test results, it can be seen that in the same call mode, the call performance of terminal 2 is better than that of terminal 1 at the edge far from the base station. In the UC mode, the MOS value of voice is mostly > 4, while in the administrative mode, the MOS value of voice is between 3 and 4.

8 Conclusion

In this paper, based on the wireless private network, the application of VoLTE technology in power wireless private network is studied, and the performance index of power wireless private network in three voice solutions based on multiple terminals and VOLTE is tested. The performance indexes include the voice, the video call quality under different wireless signal strengths, and the call quality in the course of road motion. The analysis of Volte research in power wireless private network supports the application of power wireless private network in the future, provides technical support, and lays a solid foundation for the popularization and application of power wireless private network.