With the increasing of the business carried by the power wireless private network and the continuous development of the new network technology, the problems in the traditional mode of power wireless private network are becoming more and more obvious. In order to solve the problems such as poor business service quality, low system throughput, and fairness problems in the uplink resource scheduling process of power wireless private network, a dynamic uplink resource scheduling algorithm is proposed on the basis of Software Defined Optical Network (SDON). By studying the business characteristics of the uplink transmission of power wireless network, the priority of the service is evaluated before the resource scheduling is carried out. According to the characteristics of OFDM resource allocation and the numerical control separation and programmable feature of SDON, different scheduling methods are designed for different services. Simulation analysis shows that this algorithm can effectively improve the system throughput, guarantee QoS, and improve the transmission performance of different services.
With the development of smart distribution grid, the application of new generation wireless broadband technology in distribution network has become the research hotspot in current power communication system [
Time Division Long Term Evolution (TD-LTE) is the mainstream of wireless broadband access technology. In smart grid, TD-LTE is used to build power wireless broadband network, which will be an important way of distribution network communications [
However, as an optical fiber communication, OFDM-PON is difficult to break the Shannon limit by enhancing fiber capacity. And expanding the scale will bring the cost and energy consumption of the sharp rise, so its development needs to find a new breakthrough point. SDON networking can solve the above problems fundamentally. By introducing a software defined intelligent network in the optical layer, the PON network can be made more active, thus further releasing its bandwidth potential and promoting the deep integration of network and business [
In both OFDM-PON and the LTE network carried by it, multicarrier technology is utilized in the uplink and downlink transmission schemes and the uplink is SC-FDMA, while the downlink is OFDMA. Multicarrier means that the channel is divided into a number of orthogonal subcarriers, and different carrier frequency modulation methods are used in each subcarrier; thus the signal with high bit rate is able to be converted to several low bit rate signals for transmission. High frequency is used in power broadband wireless private network; specifically the same frequency networking technology is used in the 1.8 GHz band. However, only 5 M bandwidth can be applied in the construction of power wireless private network. So it is more necessary to focus on the improvement of spectrum utilization and optimization of uplink and downlink resource reuse [
There are many traditional resource scheduling schemes. At present, the uplink scheduling algorithm is based on the Proportional Fair (PF) algorithm. The main problem of this algorithm applied for smart gird network is that they do not consider the actual power grid business situation and cannot guarantee business quality of service (QoS) [
Playing a supporting role, the power communication private network is required to be able to cover all aspects of the power system, including power generation, transmission, distribution, utilization, and scheduling process. For the guarantee of the power communication, businesses such as metering, online monitoring, video management, and distribution automation need to be better carried out. The coverage and communication requirements of various types of services in power distribution communication network are different. It is necessary to focus on the analysis of these requirements, so as to provide the basis for technology and solution selection in the power distribution communication network construction.
The typical business in power distribution network includes traditional business such as distribution automation (remote measure, remote control, and remote communication), electricity information collection, transmission line monitoring, and infrastructure video monitoring and new business like distributed power supply (10 kV) and electric vehicle charging pile [
The QoS requirement of business.
Business class | Typical business | Delay requirement | Bandwidth requirement of an access node |
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Power distribution | Distribution automation | ≤1000 ms | 20 kbps |
Distributed power (10 kV) | ≤1000 ms | 2 kbps | |
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Distribution network operation monitoring | Transmission line monitoring (video) | ≤1 s | 2 Mbps |
Mobile inspection (video) | ≤10 s | 384 kbps | |
Infrastructure video monitoring | ≤1 s | 2 Mbps | |
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Power utilization | Electricity information collection | ≤10 s | 10 kbps |
Electric vehicle charging pile | ≤1 s | 0.3 kbps |
According to the QoS requirements and the importance of the business, the priority of key business transmitting in the power wireless private network is divided into three categories:
Based on the QoS requirements of uplink business in the power distribution network, this paper designs a dynamic resource scheduling algorithm based on SDON for the purpose of optimal transmission and resource allocation.
SDON technology arranging and abstracting the network resources through the controllers breaks the way of traditional networking and makes the realization of customer-centric application possible [ SDON is able to virtualize the management of optical network resources. Through a unified and open resource management platform into the network infrastructure management, make full use of the advantages of various types of resources to achieve optimal resource utilization. Optical network resources can be programmed on demand. Optical network resources can be programmed on demand control and offer the fastest and most flexible way to provide users with customized service functions and enhance customer satisfaction. Multilevel multivendor network can be achieved between the more convenient interoperability. Through the expansion of OpenFlow and other related protocols and the development of the object-oriented interactive control interface, it can achieve heterogeneous network cross-level interconnection. Thus in the data network and optical network, core network and access network, wireless network, and cable network establish a unified control of the cross-domain interoperability network architecture.
In the architecture shown in Figure
SDON based network architecture.
LTE technology has advantages of high bandwidth and low latency. Business data transmission system based on TD-LTE technology can adapt to the complex structure and wide demand characteristics of power grid: Due to its high data throughput and high spectrum utilization, TD-LTE can provide a higher transmission rate for power grid data transmission in the case of limited bandwidth resources. TDD duplex mode is used in TD-LTE technology. This makes it flexible to change the ratio of uplink and downlink resources. So TD-LTE can meet the special requirement in power system that the uplink demand rate is higher than the downlink. Thus it can be better applied to the power communication network construction [
As shown in Table
Uplink and downlink ratio.
Frame | Subframe number | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |
5 ms | D | S | U | U | U | D | S | U | U | U |
The basic idea of OFDM divides a high-speed serial data stream into a plurality of low-speed data streams and transmits the plurality of low-speed data streams through subcarriers orthogonal to each other in several frequencies, thereby effectively improving the bandwidth utilization efficiency of the system.
Since RoF is used in OFDM-PON to transmit radio frequency signal according to the proposed architecture shown in Figure
For TDD, the uplink and downlink are separated in time, while the carrier frequency is the same. That is, in every 10 ms cycle, there are totally 10 subframes using for uplink and downlink, and each subframe is either uplink or downlink.
In TD-LTE communication system, the minimum resource allocation unit is defined as 12 consecutive subcarriers in the frequency domain and 7 OFDM symbols in the time domain (in the conventional CP case). That is the resource block (RB). For each user, one or more RBs can be used for business bearing. Figure
Schematic of RB in OFDM.
The traditional packet scheduling algorithms include Maximum Carrier to Interference (MAX C/I) algorithm, Round Robin (RR) algorithm, and Proportional Fair (PF) algorithm. The goal of the MAX C/I algorithm is to obtain the maximum throughput of the system, so it does not take into account the fairness of the user transmission. The Round Robin algorithm takes into account the fairness of the users and transmits the user data in turn but sacrifices the throughput of the system. The Proportional Fair algorithm is between those two algorithms, taking into account both fairness and system throughput. So many resource scheduling systems choose the PF algorithm [
However, due to the lack of business QoS requirements and the need for uplink resource allocation fairness considerations, the above three algorithms are not applicable to the power wireless network resource scheduling system. Based on the business characteristics of power grid, this paper designs an algorithm of uplink dynamic scheduling based on PF algorithm, which taking into account the power grid business QoS requirements, the terminal channel quality, and a series of key factors. At the same time, SDN technology is introduced to manage OFDM-PON resources. The tasks are managed according to the priority of the software, and the resources are allocated based on the different priorities of the tasks, which makes the uplink resource scheduling more fast, flexible, and intelligent.
As show in Figure
Structure of uplink dynamic scheduling algorithm.
Different scheduling methods for each type of business are as follows.
Select the business packet
(2) For the second type of distribution network operation monitoring business
Then update
(3) For the third type of the electricity business
In order to simulate the business data in the power grid, the simulation will randomly generate different kinds of business data packets in each TTI and record the simulation data in the process of execution. As the algorithm is based on the business priority to dynamically schedule the packet, in order to evaluate the advantages and disadvantages of the proposed algorithm, we compare the overall throughput and the throughput of different service packets with the traditional PF algorithm and the RR algorithm.
The simulation compared the throughput of the system under the new algorithm proposed by us and the traditional algorithm. The data include the throughput of the three different algorithms when dealing with different data requests. By setting the number of data requests initiated by the system unit time, record the amount of business data successfully transmitted under different algorithms per unit time. The minimum allocation unit of the data in the simulation is the resource block RB defined in TD-LTE. RB is composed of 12 consecutive subcarriers and 7 OFDM symbols in the time domain. The results are shown in Figure
System throughput under different algorithm.
Compared with the traditional PF and RR algorithms, the throughput of the new algorithm will be higher. Particularly when the number of packets is close to the maximum load of the LTE unit frame, the gap between the proposed algorithm and the traditional algorithms is the largest. As the frame transmission capacity tends to saturate, the gap between them eventually decreases. It can be seen from the figure that the new algorithm proposed by us has better performance in data transmission capability.
We use a measure of scheduling fairness of the indicators Jain Fairness to a variety of algorithms which were compared; the Jain Fairness calculation method is as follows:
System fairness under different algorithm.
As can be seen from the figure, when the simulation has just begun, because the system is in the initialization state, send buffer and receive buffer data are not saturated, so the data has not yet arrived at the receiver. At this time, the PF algorithm and the RR algorithm increase the total data of the denominator when measuring the fairness, but the user’s acceptance of the data has not been increased, so the value is reduced, but as the simulation progresses, the experiment tends to be stable and the result shows that the RR algorithm has the highest fairness because it is round robin scheduling. It is shown that the fairness coefficient of the new algorithm is between the traditional PF and RR algorithms. This is because the new algorithm proposed in this paper takes the priority factors of various services such as RLT into account, while the traditional PF and RR algorithms are based on the overall system fairness and do not take the priority of the business on a particular packet into account, so the fairness coefficient is lower.
As the algorithm focuses on the transmission of different priorities of the business, we compare the business data throughput of it with the traditional scheduling algorithm with different priorities. This algorithm divides the service type into three priorities. By counting the amount of different business data for 40 TTIs and comparing them to traditional algorithms. Due to the different bandwidth requirements of each service, in order to visualize the transmission capability of the algorithm for different priority services, we limit the number of packets sent by various services when performing traffic simulation. As shown in Figure
The throughput of different business under different algorithm.
In order to verify the guarantee of real-time requirement of the first and second class services, the system simulates the time of various types of packets from generation to the scheduled time under different algorithm as shown in Figure
The delay of different business under different algorithm.
In this paper, a dynamic uplink resource scheduling algorithm based on SDON is proposed for power wireless private network, which is improved on the basis of the traditional PF algorithm. Considering the business characteristics of the power wireless private network, the QoS requirement of business is ensured by the SDON resource management platform allocation resource based on service priority. Simulation results show that the proposed algorithm is more suitable for the communication in power wireless private network. Under the constraints of uplink resource allocation in TD-LTE system, the algorithm proposed in this paper can guarantee the best uplink transmission rate of terminals, improve the system throughput, and meet the complex QoS requirements of business in power wireless private network.
The author declares that he has no conflicts of interest.
This work was supported by State Grid Science and Technology Project 52018E15000G.