2017 International Conference on Computer, Electronics and Communication Engineering (CECE 2017) ISBN: 978-1-60595-476-9 Research on Hybrid Network Technologies of Power Line Carrier and Wireless MAC Layer Hao ZHANG 1, Jun-yu LIU 2, Yi-ying ZHANG 3 and Kun LIANG 3,* 1 State Grid Shandong Economic Research Institute, Shandong 250021, China 2 Beijing Guodiantong Network Technology Company, Beijing 110108, China 3 Tianjin University of Science and Technology, Tianjin 300457, China *Corresponding author Keywords: Power line carrier, Wireless, Fusion, MAC. Abstract. Through the power line carrier, wireless and other communication technologies, smart grid achieves power grid data communication. Therefore, it is a challenge to effectively integrate multi-form communication. In this paper, we analyzed the applications of power line carrier and wireless in the network of distribution system, and designed a communication method for the power line carrier and wireless MAC layer based on OFDM technology. By Turbo code, error correction coding is realized, which greatly improves the success rate of network communication. Also it effectively improved the performance of power communication network, and achieved the power line and wireless network convergence in the MAC layer communication. Finally according to different specific scenarios, we presented two different converged networking solutions. Introduction With the power grid construction is the key link in the development of smart grid. Grid communication system is bound to meet the automation, information, intelligent, interactive Compound development needs of the grid. The distribution of electrical equipment in the construction of power grid is dense and large in quantity, such as distribution station, box change, meter distribution equipment, etc. They do not need data timeliness, real-time, interactive. It is obviously that the use of high-cost fiber to complete the communication task is a huge economic waste. At present, Power Line Carrier (PLC) and wireless communication technology are used in the distribution of power network communication. However, due to the complexity of the power line itself, high-frequency signal attenuation is serious, and the noise is strong, the communication performance is difficult to meet the integrated needs of real-time, accuracy and reliability in the information transmission. There are many problems such as poor stability, blind area, data security and traffic cost in the information transmission of the public wireless network [1]. According to the different channel characteristics of PLC and wireless communication, this paper analyzes the Media Access Control (MAC) layer protocol, proposed a method of combining power line carrier and wireless physical layer based on Orthogonal Frequency Division Multiplexing (OFDM), unified scheduling power line carrier and wireless spectrum, achieved PLC and wireless network in the MAC layer of the integration of the communication network to full-duplex way to send and receive data. The scheme can effectively improve the reliability of PLC and wireless network communication mode transmission data, and become an important means of intelligent distribution network data communication. Application Analysis of PLC and Wireless in Distribution Network System PLC refers to the use of power grid with the existing power line resources as the information transmission medium communication, which usually can carry 2 ~ 20M bandwidth. The PLC mode saves the input cost of the power distribution and utilization communication project, and which 402
gradually develops into one of the preferred communication methods for the construction of the smart grid. Meanwhile, wireless communication in the smart grid construction provides a low cost, good performance, fast and convenient means of communication, including wireless terminal equipment, wireless base stations and network application management server, these three modules can meet the smart grid construction in short-range communication transmission requirement. According to the grid application of the field analysis, subject to various conditions, a single PLC or wireless communication cannot meet the complex and complex with the power grid needs. PLC communication rate is only 80% ~ 90% due to noise interference, harmonics, signal attenuation etc. The wireless communication is affected by distance, environment and interference, and the communication success rate is below 90%. Therefore, the carrier and wireless communication modes are used to integrate each other, and the heterogeneous network is constructed to realize the complementary advantages of the network resources, enhance the performance of the single network, coordinate with each other, automatically switch over and overcome the defects of the carrier and the wireless, constitute the converged communication technology solution. Power Line Carrier and Wireless Convergence Based on MAC PLC and Wireless Channel Equalization Technology PLC and wireless communication transmission channel environment is complex and changeable Because of the multipath effect caused by the inter-symbol interference problem is more prominent, the signal transmission in the band channel distortion due to ISI (Inter Symbol Interference), and then signal distortion [2]. It is necessary to use channel equalization technology to suppress this interference, to complete the appropriate measures to ISI, reduce the receiver bit error rate. Characteristics of low signal-to-noise ratio for PLC and wireless channel, Since the information transfer between the decoder and the equalizer has been subjected to multiple iterations, the channel equalization performance can be improved by using the turbo-code equalization anti-code interference scheme [3]. The Turbo equalizer uses the Single Input Single Output (SISO) decoder instead of the equalizer, recursively into the SISO decoder for MAP decoding. The equalizer receives the a priori information first, then completes the information output, maps the SISO decoder to the equalizer, So after the equalizer and decoder can handle a priori information, get posterior information Posterior information is processed by interlaced or unwrapping algorithms, and it is iterated as a priori information to complete the equalization and decoding operations and finally obtain the optimal performance. The anti-code interference scheme based on Turbo equalization principle is shown in Figure 1. Figure 1. Anti-code interference scheme based on Turbo equalization principle. In order to fully exchange information between the equalizer and the decoder, Turbo in the exchange process through multiple iterations to complete the equalization process. Assuming that the channel noise is zero mean, the mean of the sampling of the noise is zero and independent distribution, while satisfying the variance. 403
The binary data b is convoluted and mapped to the constellation of the PLC and the radio channel signal to form a data block c, n 1,2 L which is L long. After interleaving, the sequence is obtained by ISI channel z z,z,z,,z become the sequence of accepted symbols. In the Turbo equalization, the output of the equalizer is L C satisfies the formula (1): (1) In equation (1), L_e ^ E (C_n) is equalizer information, and L_a ^ E (C_n) is a priori information. Similarly, the channel decoder output L ^ D (C_n) satisfies the formula (2): (2) In equation (2), L_e ^ D (C_n) is the outer information, and L_a ^ D (C_n) is a priori information. Based on Turbo principles are: (3) Similarly Where denotes an interlace, prior information 0. (4) denotes a deinterleaving. In the initial equilibrium, the Power Line Carrier and Wireless Fusion Technology The IEEE802 series standard divides the data link layer into two sub-layers, Media Access Control (MAC) and Logical Link Control (LLC). LLC sublayer to achieve flow control, error recovery and other data link layer hardware-independent functions. The MAC sublayer provides the LLC sublayer and the physical layer interface, which controls the physical media. When the information is sent, the MAC judgment condition is allowed to be transmitted, the additional control identification information is attached to the transmission data, and the final data is sent to the physical layer in the prescribed format. When receiving data, the MAC protocol judges the accuracy of the information based on the attached information. Eventually, the control information is removed without error information and sent to the LLC layer to complete the information transfer [4]. OFDM-based power line carrier and wireless physical layer fusion communication, through the use of physical layer fusion way to fuse the PLC and wireless communication, the use of OFDM unified scheduling PLC and wireless spectrum, full-duplex way to send and receive data [5]. This can be a good solution to the problem of low reliability of electricity information communication. The communication node device fusion communication program is shown in Figure 2. 404
Figure 2. PLC and wireless physical layer integration communication program block diagram. In the physical layer of the communication node device, the carrier communication part and the wireless communication part all use the OFDM technology to share the physical layer OFDM baseband part of the way the same time, in the physical layer integration of two channels of full duplex send / receive, AD- DA conversion and baseband processing section. The shared baseband section includes: Channel coding / decoding, interleaving / deinterleaving processing, signal mapping, pilot / channel estimation, serial-to-parallel conversion, FFT / IFFT, Protection interval processing and AD / DA conversion of the entire OFDM physical layer baseband processing functions. For the MAC layer of the communication node device, the physical layer actually has only one communication channel, so the technical scheme has only a single MAC layer and MAC address. Unified MAC Layer Integration Scheme A MAC layer of power line carrier and wireless fusion method is mainly applied to low-voltage side of the power line communication and wireless communication in two ways to support the use of electricity information collection system communication network construction [6]. The power line and the wireless MAC layer using CSMA / CA, ARQ and other unified communication mechanism, which can effectively avoid the heterogeneous network MAC layer protocol conversion between the system to improve the system, Quality of Service( QoS) protection. The logical structure is shown in Figure 3. antenna Unified structure integration Power line Wireless RF PLC AFE Wireless RF PLC PHY Unified MAC Ethernet port Embedded memory MCU serial port Figure 3. PLC and Wireless Unified MAC Convergence Communication. 405
Firstly, we adopt the covariance detection and energy detection method for wireless and PLC transmission signal dynamic spectrum detection. The detection of qualified signals through the Turbo code are started the error correction coding processing, to effectively reduce the interference between the code and code. And then it integrated the PLC and wireless in MAC layer to achieve multi-node, multi-mode joint channel assessment. The establishment of a unified network is as sub-mac sub-architecture between the PLC and the wireless. After the fusion of the channel through the genetic hybrid algorithm routing relay technology, we analyzed the dual channel compatible protocol, to define the compatible data frame structure, enhance the transmission process QoS. To construct the evaluation system for PLC and wireless network, it is to achieve the unified integration of PLC and wireless network MAC layer, the logical structure shown in Figure 4. Figure 4. PLC and wireless way unified MAC layer fusion logic structure. Unified MAC Layer Communication Success Rate During the networking process, each node obtains routing information in the power line network and the wireless network. Power line carrier and wireless form a dual backup network, when a node to the target node can reach the dual channel, according to the routing algorithm to select the high value of the path. When a certain network path is interrupted, it can use another network to communicate, and truly implement a hybrid ad hoc network. Each node in the network is a peer-to-peer network, and when the data is sent, the best route is selected to avoid ring data transmission. From the concentrator to the collector using carrier + wireless dual-channel communication for fusion communication, then the success of PLC and wireless are successful, PLC success wireless failure, PLC failure wireless success, PLC and wireless are four kinds of combinations of results as shown in Table 1. Table 1. Unified MAC layer communication convergence results. No. PLC Wireless results Communication results I success success success II success fail success III fail success success IV fail fail fail Summary Low cost, high reliability, flexible access to information network is the key to the construction of intelligent distribution network, the rational use of existing power lines and wireless resources, through a unified MAC layer integration program to overcome the defects of a single data communication, this article constructs a heterogeneous network of PLC and wireless fusion, designs a unified MAC layer fusion communication scheme, realizes error correction coding processing by Turbo code, greatly improves the success rate of network communication, effectively improve the performance of power communication network, intelligent distribution network for the construction of a new means of information transmission. 406
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