CN111600648B - Mobile relay position control method of mobile edge computing system - Google Patents
Mobile relay position control method of mobile edge computing system Download PDFInfo
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Abstract
A mobile relay position control method of a mobile edge computing system is suitable for a wireless mobile network. The mobile relay equipment provides data relay service for the user equipment and the base station and provides data calculation service within calculation capability for the user equipment; when the calculation force requirement of the task exceeds the calculation capability of the mobile relay equipment, the mobile relay equipment sends the current task to a server of a base station for processing, and then the current task is sent to the user equipment through the mobile relay equipment in a relay mode. The method optimizes the position of the mobile relay by using the size of the task data volume, and finds the best compromise scheme of the distance of the mobile relay and the condition of a communication channel, thereby achieving the aim of minimizing the task completion time of an application program in user equipment.
Description
Technical Field
The invention relates to a mobile relay position control method of a mobile edge computing system, in particular to a mobile relay position control method of a mobile edge computing system, which is suitable for a wireless mobile network.
Background
With the rapid development of wireless mobile networks and mobile applications, UE applications are more and more computationally scaled and are more sensitive to computational delay. Due to the limited computing resources of the UE, it is difficult to execute large mobile applications on the premise of satisfying the computation delay. The emerging MEC technology becomes an effective way for relieving the shortage of UE computing resources, and the traditional wireless access network has the conditions of service localization and close-range deployment, so that computing, storage and communication services can be more conveniently provided for the UE, thereby reducing network operation, reducing time delay and improving user experience. However, in some application scenarios, such as a mountain area, a post-disaster environment, etc., a direct communication link between the UE and the BS is blocked by an obstacle or the UE is not in the coverage of the BS at all, so that the UE cannot use the MEC service provided by the BS. The UAV has the characteristics of strong maneuverability, high flexibility and the like, and the multi-rotor UAV can vertically take off, land or hover in the air. The UAV is used for carrying the micro base station and the MEC equipment to fly or hover over the coverage area of the UE, so that the UE can be assisted to complete tasks such as data collection, real-time calculation and the like. The UAV can also be used as a relay node to forward the task input data of the UE to the BS for execution, so that the task execution speed is increased, and the task completion time is shortened.
However, in existing UAV assisted MEC systems, most of the research is focused on minimizing the energy consumption of the UAV and the UE by optimizing the resource allocation strategy in the system, and not on how to minimize the task completion time of the application in the UE by optimizing the hover position of the UAV to obtain the best communication channel conditions in the system. Since most of the currently computationally intensive applications are delay sensitive, minimizing the task completion time by finding the best UAV hover position is an effective means to reduce system latency, improving the user experience.
At present, there are a lot of studies in the direction of UAV assisted MEC systems by many domestic and foreign scholars, and the following solutions are proposed:
document 1: zhou, Y.Wu, H.Sun, Z.Chu, "UAV-enabled mobile edge computing: Offloading optimization and project design", Proc.IEEE ICC, pp.1-6, Feb.2018.
Document 2: hu, M.Jiang, Q.Zhang, Q.Li, and Jianyin Qin, "Joint optimization of UAV position, time slot allocation, and computation task partition in multiple user biological-edge computing systems," IEEE Transactions on vehicle Technology, vol.68, pp.7231-7235, July.2019.
Document 3: du, K.Yang, K.Wang, G.Zhang, Y.Zhao, and D.Chen, "Joint resources and work flow scheduling in UAV-enabled wireless-powered MEC for IOT systems," IEEE Transactions on vehicle Technology, pp.1-14, Oct.2019.
Document 4: royal resole, chinese dream, marteng, schopper, yan standing super, shaochuan, zhao fei, zhuang wei, niu bronze, unmanned aerial vehicle assistant mobile edge computing system and information bit distribution method thereof, invented patent 201810755471.
However, the above document only considers that the UAV serves as an MEC server to provide MEC service for the UE, minimizes system energy consumption by optimizing task scheduling, computing resource allocation, and the like, and does not consider optimizing a UAV hovering position and optimizing a communication channel condition between the UAV and the UE, so as to accelerate execution of a UE computing task and reduce task time. Furthermore, the above document does not consider the effect of task partitioning and possibly the priority order of large applications on the computation latency.
Disclosure of Invention
Aiming at the technical problems, the mobile relay position control method of the mobile edge computing system is simple in step, good in using effect and capable of finishing the comprehensive task of program computation and wireless transmission at the fastest speed.
In order to achieve the technical purpose, the mobile relay position control method of the mobile edge computing system comprises User Equipment (UE), a mobile relay device (UAV) and a Base Station (BS) with a high-performance edge computing server, wherein the mobile relay device (UAV) has light computing capability and provides light-weight edge computing service for the User Equipment (UE), the high-performance edge computing server of the BS has strong computing capability, and the mobile relay device (UAV) and the BS are combined to solve the problem of insufficient computing resources of the User Equipment (UE);
the user equipment UE cannot be directly in wireless connection with the base station BS, the user equipment UE can be in wireless data connection with the base station BS only through the relay of the mobile relay equipment UAV, and the mobile relay equipment UAV provides data relay service for the user equipment UE and the base station BS and provides data calculation service within computing power for the user equipment UE; when User Equipment (UE) sends a calculation request, a current task is divided into a plurality of subtasks, the plurality of subtasks are sequentially sent to a mobile relay device (UAV) and calculation capacity support required by task calculation is judged in the mobile relay device (UAV), when the calculation capacity requirement of the subtasks is smaller than the calculation capacity of the mobile relay device (UAV), the corresponding subtasks are directly processed in the mobile relay device (UAV), the final calculation result is fed back to the User Equipment (UE), when the calculation capacity requirement of the subtasks exceeds the calculation capacity of the mobile relay device (UAV), the mobile relay device (UAV) sends the current subtasks to a server of a Base Station (BS) for processing, and when the processing is completed, the calculation results of the subtasks are sent to the User Equipment (UE) through the mobile relay device (UAV), so that three calculation task scheduling modes exist: calculating a task scheduling mode I: the former sub-task is executed at the mobile relay device UAV, and the latter sub-task is calculated at the base station BS; and a calculation task scheduling mode II: both the previous subtask and the next subtask perform calculations at the mobile relay device UAV; and calculating a task scheduling mode III: the former subtask and the latter subtask are both calculated in the base station BS; for two subtasks in any kth task group, respectively searching the position of the optimal wireless relay UAV of each subtask by using a basic PSO algorithm for the three calculation task scheduling modes, then selecting the task scheduling mode with the least time spent in the three calculation task scheduling modes as an execution scheme of the two subtasks, and repeatedly comparing the three calculation task scheduling modes for every two subtasks until all subtasks are completed.
Based on three calculation task scheduling modes, the mobile position of the mobile relay device UAV is optimized according to the size of the task data volume unloaded by the user equipment UE, the best compromise of the mobile distance and the communication channel condition of the mobile relay device UAV is found, and the completion of the calculation task of the user equipment UE is accelerated through the parallel execution of the mobile relay device UAV and the base station BS, so that the purpose of minimizing the completion time of all tasks of the UE is achieved, the system delay is reduced, and the user experience is improved;
specifically, the mobile relay UAV collects task data of the user equipment UE when performing a task, and relays the task data to the base station BS, and by controlling the position of the mobile relay UAV, the task completion time is minimized, and the closer the mobile relay UAV is to the user equipment UE and the base station BS, the better the wireless channel condition is, the better the bubble individual decreases the data transmission time, but the moving time of the mobile relay UAV may also be increased.
When User Equipment (UE) executes an application program, the application program is divided into K task groups with priority orders, namely the current task group can not be executed continuously until the execution result of the direct previous task group returns; in K task groups, each task group comprises n independent subtasks, and in order to facilitate parallel calculation of the mobile relay UAV and the base station BS, the subtasks in each task group are divided into two parts according to the data size, wherein the first part is a task 1, and the second part is a task 2;
first of all input into the user terminal UE and the base station BSCoordinates, setting the initial position coordinates of the wireless relay UAV toBefore K task groups do not finish operation, the formula is used: respectively calculating the time required by the three calculation task scheduling modes, whereinThe relay position is determined according to the position coordinate u of the mobile relay UAV, the formula is determined, the optimal relay position is obtained by utilizing a basic particle swarm algorithm, the required time is further determined, and then the time is compared with the time of other two schemes;
in the formula:the time used for the task scheduling scheme I,for the time used by the task scheduling scheme II,the time used for the task scheduling scheme III,for the time required for the mobile relay UAV to move from the initial position when processing the kth task set to the position when receiving task 1 data,relaying UAVs for movement while processing kth task groupTime required for the initial position to move to the position when the task 2 data is received;the time required for the mobile relay UAV to receive the data for task 1 in the kth task group,the time required for the mobile relay UAV to receive data for task 2 in the kth task group;the time required for the mobile relay UAV to perform task 1 in the k-th task group,the time required for the mobile relay UAV to perform task 2 in the kth task group;the time required for the mobile relay UAV to move from a location receiving mission 1 data to relay this data location to the base station BS;the time required for the mobile relay UAV to relay the received data for task 1 in the kth task group to the base station BS,for the mobile relay UAV to relay the received data for task 2 in the kth task group to the base station BS,express getAndthe larger of the two values is the one,express getAndthe larger of the two values;
selectingAndthe minimum value among the three is obtained, and the data collection position of the mobile relay UAV corresponding to the minimum value among the three is obtained simultaneouslyAnd relay locationu represents a position coordinate representation symbol of the mobile relay UAV, including actual coordinate information, and the most basic particle swarm algorithm is utilized to find the optimal u;
updating location parameters of the mobile relay UAV: if the task scheduling scheme I is used for the shortest time, thenIf the task scheduling scheme III is used for the shortest time, thenThen orderOtherwise, the time for the task scheduling scheme II is shortest, soThat is to say: per executionAfter completing a task group of user terminal UE, the initial position of wireless relay UAV needs to be updated, if yesOrAt this time, the wireless relay UAV needs to relay at least one task to the base station BS for execution, so the initial position of the next task group (k +1 th task group) is the relay hovering position when relaying the data of task 2, that is, the wireless relay UAV is capable of relaying the data of task 2If it isIt is stated that task 1 and task 2 of the kth task group are both performed by the UAV in the shortest amount of time, so the initial position of the next task group is the data collection position of task 2, i.e., the position
According to the formulaCalculated, where | · | | | represents the mobile relay UAV relay locationAndthe euclidean distance between;according to the formulaComputingObtaining;according to the formulaIs obtained by calculation, whereinDenotes bk,1Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,2And c) represents bk,2Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;
wherein b isk,1Amount of data of task 1 in the kth task group, b, for a user Equipment UEk,2The data volume of task 2 in the kth task group of the user equipment UE, c is the number of CPU cycles needed by the mobile relay UAV to calculate 1-bit data, and f is the calculation capacity of the mobile relay UAV; v denotes the moving speed of the mobile relay UAV, B is the spectral bandwidth occupied by the MEC system,to handle the wireless channel gain of the user terminal UE to the mobile relay UAV at the kth task set,wireless channel gain for moving the relay UAV to the base station BS to process the kth task set;represents the data transmission rate of the system from the UE to the UAV when processing the k-th task groupIndicating the data transmission rate of the UAV to the BS when the system is processing the kth task set.
The beneficial effects are that:
the mobile relay of the invention not only can provide light-weight operation service for the user equipment, but also can be used as a relay node between the user equipment and the base station to carry out data forwarding relay by utilizing the advantages of being mobile and capable of providing calculation power. According to the task computing power request of the user equipment, under three selectable task computing power scheduling schemes, the position of the mobile relay is optimized according to the size of the task data unloaded by the user equipment, and the best compromise between the distance of the mobile relay and the communication channel condition is searched, so that the aim of minimizing the task completion time of an application program in the user equipment is fulfilled. The method has the advantages of simple steps, good using effect and wide practicability.
Drawings
FIG. 1 is a flow chart of a mobile relay location control method according to the present invention;
FIG. 2 is a schematic diagram of the components of a UAV-supported MEC system of the present invention;
FIG. 3 is a schematic diagram of the sliding trajectory and hover position selection of a UAV with an application data size of 140 MB;
FIG. 4 is a schematic diagram of the sliding trajectory and hover position selection of a UAV with an application data size of 300 MB;
FIG. 5 is a schematic diagram comparing the time required for completing an application program with different data sizes by using the hovering position control method of an unmanned aerial vehicle proposed by the present invention compared with other methods;
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
As shown in fig. 1, the mobile relay location control method of the mobile edge computing system of the present invention includes a user equipment UE, a mobile relay device UAV and a base station BS with a high performance edge computing server, where the mobile relay device UAV has a light computing capability and provides a light edge computing service for the user equipment UE, and the high performance edge computing server of the base station BS has a powerful computing capability, and the mobile relay device UAV and the base station BS are combined to solve the problem of insufficient computing resources of the user equipment UE;
the user equipment UE cannot be directly in wireless connection with the base station BS, the user equipment UE can be in wireless data connection with the base station BS only through the relay of the mobile relay equipment UAV, and the mobile relay equipment UAV provides data relay service for the user equipment UE and the base station BS and provides data calculation service within computing power for the user equipment UE; when User Equipment (UE) sends a calculation request, a current task is divided into a plurality of subtasks, the plurality of subtasks are sequentially sent to a mobile relay device (UAV) and calculation capacity support required by task calculation is judged in the mobile relay device (UAV), when the calculation capacity requirement of the subtasks is smaller than the calculation capacity of the mobile relay device (UAV), the corresponding subtasks are directly processed in the mobile relay device (UAV), the final calculation result is fed back to the User Equipment (UE), when the calculation capacity requirement of the subtasks exceeds the calculation capacity of the mobile relay device (UAV), the mobile relay device (UAV) sends the current subtasks to a server of a Base Station (BS) for processing, and when the processing is completed, the calculation results of the subtasks are sent to the User Equipment (UE) through the mobile relay device (UAV), so that three calculation task scheduling modes exist: calculating a task scheduling mode I: the former sub-task is executed at the mobile relay device UAV, and the latter sub-task is calculated at the base station BS; and a calculation task scheduling mode II: both the previous subtask and the next subtask perform calculations at the mobile relay device UAV; and calculating a task scheduling mode III: the former subtask and the latter subtask are both calculated in the base station BS; for two subtasks in any kth task group, respectively searching the position of the optimal wireless relay UAV of each subtask by using a basic PSO algorithm for the three calculation task scheduling modes, then selecting the task scheduling mode with the least time spent in the three calculation task scheduling modes as an execution scheme of the two subtasks, and repeatedly comparing the three calculation task scheduling modes for every two subtasks until all subtasks are completed.
Based on three calculation task scheduling modes, the mobile position of the mobile relay device UAV is optimized according to the size of the task data volume unloaded by the user equipment UE, the best compromise of the mobile distance and the communication channel condition of the mobile relay device UAV is found, and the completion of the calculation task of the user equipment UE is accelerated through the parallel execution of the mobile relay device UAV and the base station BS, so that the purpose of minimizing the completion time of all tasks of the UE is achieved, the system delay is reduced, and the user experience is improved;
specifically, the mobile relay UAV collects task data of the user equipment UE when performing a task, and relays the task data to the base station BS, and by controlling the position of the mobile relay UAV, the task completion time is minimized, and the closer the mobile relay UAV is to the user equipment UE and the base station BS, the better wireless channel conditions can be obtained, so that the data transmission time can be reduced, but the movement time of the mobile relay UAV can be increased, when the UAV is used as a relay, calculation is performed while relaying the data, or calculation is performed in the process of finding the optimal relay position in a moving manner, and the physical position of the relay is obtained by using a particle swarm algorithm.
When User Equipment (UE) executes an application program, the application program is divided into K task groups with priority orders, namely the current task group can not be executed continuously until the execution result of the direct previous task group returns; in K task groups, each task group comprises n independent subtasks, and in order to facilitate parallel calculation of the mobile relay UAV and the base station BS, the subtasks in each task group are divided into two parts according to the data size, wherein the first part is a task 1, and the second part is a task 2;
firstly, inputting coordinates of a user terminal UE and a base station BS, and setting initial position coordinates of a wireless relay UAV asBefore K task groups do not finish operation, the formula is used: respectively calculating the time required by the three calculation task scheduling modes, whereinIs determined according to the position coordinates u of the mobile relay UAV, the formula is determined, and the basic particle swarm algorithm is utilized to obtainObtaining the optimal relay position, further determining the required time, and then comparing the time with the time of other two schemes;
in the formula:the time used for the task scheduling scheme I,for the time used by the task scheduling scheme II,the time used for the task scheduling scheme III,for the time required for the mobile relay UAV to move from the initial position when processing the kth task set to the position when receiving task 1 data,time required for the mobile relay UAV to move from the initial position when processing the kth task group to the position when receiving task 2 data;the time required for the mobile relay UAV to receive the data for task 1 in the kth task group,the time required for the mobile relay UAV to receive data for task 2 in the kth task group;the time required for the mobile relay UAV to perform task 1 in the k-th task group,the time required for the mobile relay UAV to perform task 2 in the kth task group;the time required for the mobile relay UAV to move from a location receiving mission 1 data to relay this data location to the base station BS;the time required for the mobile relay UAV to relay the received data for task 1 in the kth task group to the base station BS,for the mobile relay UAV to relay the received data for task 2 in the kth task group to the base station BS,express getAndthe larger of the two values is the one,express getAndthe larger of the two values;
selectingAndthe minimum value among the three is obtained, and the data collection position of the mobile relay UAV corresponding to the minimum value among the three is obtained simultaneouslyAnd relay locationu represents a position coordinate representation symbol of the mobile relay UAV, including actual coordinate information, and the most basic particle swarm algorithm is utilized to find the optimal u;
updating location parameters of the mobile relay UAV: if the task scheduling scheme I is used for the shortest time, thenIf the task scheduling scheme III is used for the shortest time, thenThen orderOtherwise, the task scheduling scheme II uses the shortest orderThat is to say: updating the initial position of the wireless relay UAV after each task group of the user terminal UE is executed, if so, updating the initial position of the wireless relay UAVOrAt this time, the wireless relay UAV needs to relay at least one task to the base station BS for execution, so the initial position of the next task group (k +1 th task group) is the relay hovering position when relaying the data of task 2, that is, the wireless relay UAV is capable of relaying the data of task 2If it isIt is explained that task 1 and task 2 of the kth task group are the shortest time required for the UAV to execute, so the initial position of the next task group is the data of task 2At the location of collection, i.e.
According to the formulaCalculated, where | · | | | represents the mobile relay UAV relay locationAndthe euclidean distance between;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,1And c) represents bk,1Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,2And c) represents bk,2Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;
wherein b isk,1Amount of data of task 1 in the kth task group, b, for a user Equipment UEk,2The data volume of task 2 in the kth task group of the user equipment UE, c is the number of CPU cycles needed by the mobile relay UAV to calculate 1-bit data, and f is the calculation capacity of the mobile relay UAV; v denotes the moving speed of the mobile relay UAV, B is the spectral bandwidth occupied by the MEC system,to handle the wireless channel gain of the user terminal UE to the mobile relay UAV at the kth task set,wireless channel gain for moving the relay UAV to the base station BS to process the kth task set;represents the data transmission rate of the system from the UE to the UAV when processing the k-th task groupIndicating the data transmission rate of the UAV to the BS when the system is processing the kth task set.
Example one
In the MEC system of the mobile edge computing system provided by the invention, user terminal UE is a mobile phone, mobile relay UAV is an unmanned aerial vehicle with the computing capability of relay function, and the application scene of the UAV hovering position control method is as follows: in order to solve the problems that the UE cannot meet the time delay requirement of a user due to insufficient computing resources and the MEC service cannot be carried out when a direct communication link does not exist between the UE and the BS, the UE and the BS are assisted by the UAV to realize the MEC service, and the UAV can not only provide the light-weight MEC service for the UE, but also be used as a relay node between the UE and the BS to carry out data forwarding. The hovering position of the Unmanned Aerial Vehicle (UAV) is optimized according to the size of the task data volume unloaded by the UE, the best compromise between the UAV flight distance and the communication channel condition is found, and the aim of minimizing the task completion time of an application program in the UE is achieved. The method is characterized in that: the scheme comprises the following operation steps:
as shown in FIG. 2, the system is composed of 1 base station BS, 1 user equipment UE and 1 UAV (unmanned aerial vehicle) UAV, wherein the BS is embedded with AMAX (advanced metering and tracking) high-performance edge computing server ServMaxTMPT-1 provides a mobile edge computing MEC service for UE; user Equipment (UE) is configured with 1 antenna for receiving and sending data; an Unmanned Aerial Vehicle (UAV) is used as a data relay node between User Equipment (UE) and a Base Station (BS) and is provided with 1 antenna for receiving and sending data; unmanned aerial vehicle UAV is still configured with quad-core ARM Cortex-A57 as a lightweight meterThe computing server can provide mobile edge computing MEC service for User Equipment (UE); the BS, UE, and UAV constitute all devices of the system.
The user equipment UE has one and only one application, which when executed is divided into K prioritized computing task groups. The priority order means that the current task group must wait until the execution result of the task group immediately before the current task group returns to continue execution. In the K task groups, each task group includes n independent subtasks. In order to support parallel calculation of an Unmanned Aerial Vehicle (UAV) and a Base Station (BS), n subtasks in any k-th task group are divided into two parts according to the size of data volume to be represented, the first part is represented as a task 1, the second part is represented as a task 2, and the ratio of the size of the data volume of the task 1 to the size of the data volume of the task 2 is 1:3 (preset ratio); by bk,1(unit: bit) represents the amount of data to complete task 1 in the kth task group of the user equipment UE, denoted by bk,2(unit: bit) represents the amount of data to complete task 2 in the kth task group of the user equipment UE; c represents the number of CPU cycles required by the UAV (unmanned aerial vehicle) to calculate 1-bit data, and f (unit: Hz) represents the calculation capacity of the UAV carrying a lightweight calculation server; the flight speed of the unmanned aerial vehicle UAV is denoted by v.
The spectral bandwidth occupied by the MEC system is expressed by B (unit: Hz)Represents the wireless channel gain of the system from UE to UAV when processing the k-th task groupRepresents the wireless channel gain of the UAV to the BS when the system processes the k-th task group; by usingRepresents the data transmission rate of the system from the UE to the UAV when processing the k-th task groupIndicating the data transmission rate of the UAV to the BS when the system is processing the kth task set.
By uIRepresenting the initial hover position of the UAV after system initialization, set coordinates as uI(500, 0, 40), (this coordinate means that the drone initially hovers at an x-axis coordinate of 500m, a y-axis coordinate of 0m, and a height coordinate of 40 m). The coordinates of the UE location are (0, 0, 0), the coordinates of the BS location are (1000,0, 0), the x-axis in fig. 2 is taken as the flight orbit of the UAV, and the orbit length is 1000 m. By usingRepresenting the initial hover position when the UAV is ready to process the kth task group, note: for each task group, the unmanned aerial vehicle UAV processes task 1 and then task 2. By usingIndicating the hover position when the UE transmits data for task 1 in the kth task group to the UAVIndicating the hover position when the UE transmits data for task 2 in the kth task group to the UAVIndicating the hover position when UAV relays data for task 1 in the kth task group to BSIndicating the hover position when the UAV relays data for task 2 in the kth task group to the BS.
By usingRepresenting the time required for the UAV to fly from an initial position while processing the kth task group to a hover position while receiving task 1 data, usingIndicating a UAVTime required to fly from the initial position to the time hover position receiving task 2 data while processing the kth task group; by usingRepresents the time required for the UAV to receive data for task 1 in the kth task groupRepresents the time required for the UAV to receive data for task 2 in the kth task group; by usingRepresents the time required for UAV to perform task 1 in the kth task groupRepresents the time required for the UAV to perform task 2 in the kth task group; by usingRepresents the time required for the UAV to fly from a location receiving mission 1 data to relay this data location to the BS; by usingRepresents the time required for UAV to relay the received data of task 1 in the k-th task group to BSRepresents the time required for the UAV to relay the received data for task 2 in the kth task group to the BS.
for task 1 and task 2 in any kth task group, the three mentioned task scheduling schemes all use a basic PSO algorithm to find the respective optimal hovering position of the unmanned aerial vehicle UAV, and then the minimum value of the three is selected as the final selection scheme until each task group determines the calculation task scheduling scheme and the optimal hovering position of the UAV. For convenience of calculation, the position coordinates of the mobile relay UAV only consider x-axis coordinates, and y-axis and z-axis are fixed values, y is 0, and z is 40.
The UAV assists the UE and the BS to realize the calculation task scheduling of the MEC and the optimization method of the UAV hovering position as follows:
1 initialization parameter T: t is 0; first the coordinates of the user terminal UE and the base station BS are entered,
2, initializing parameter k: k is equal to 1, and k is equal to 1,(meaning the initial position of the first task group is equal to the initial position of the drone system);
3, when K is less than or equal to K, executing the step 3.1 to the step 3.6;
using the formula: respectively calculating the time required by the three data processing scheduling modes, whereinExpress getAndthe larger of the two values is the one,express getAndthe larger of the two values;
: data processing is carried out on an independent mobile relay device UAV, data processing is carried out on a high-performance edge computing server connected with an independent base station BS, and data processing is carried out on a mobile relay device UAV and a high-performance edge computing service connected with the base station BS at the same time; according to the formula
Operating PSO algorithm, and obtaining by calculationAnda value of (1), whereinExpress getAndthe larger of the two values is the one,express getAndthe larger of the two values;
order toWhereinExpress getAndthe minimum value among the three is obtained, and the UAV data collection hovering position corresponding to the minimum value among the three is obtained simultaneouslyAnd data relay location
Updating the hover position parameter for the UAV as follows:
Let T be T + Tk;
Let k be k + 1;
returning to the step 3;
4, if K is equal to K +1, the algorithm has executed all task groups of the UE, and outputs T;
otherwise, if K is less than or equal to K, returning to the step 3 for execution;
in the above-mentioned step 3.1,according to the formulaIs obtained by calculation, wherein | | · | | represents the hovering positionAndthe euclidean distance between;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,1And c) represents bk,1Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,2And c) represents bk,2Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;
in step 3.3, the initial position of the UAV needs to be updated after each UE has executed one task group, and if the UE has executed one task group, the initial position of the UAV needs to be updatedOrAt this time, the UAV needs to relay at least one task to the BS for execution, so the initial position of the next task group is the hovering position when relaying the data of task 2, that isIf it isIt is stated that task 1 and task 2 of the kth task group are both performed by the UAV in the shortest amount of time, so the initial position of the next task group is the data collection position of task 2, i.e., the position
Multiple simulation experiments were performed, and specific examples and performance analyses thereof are described below. Referring to the MEC system supported by UAV shown in fig. 2, the following parameters are set: the frequency spectrum bandwidth B is 10MHz, the UAV flight speed v is 30m/s, the computation capability f of the UAV carrying a lightweight computing server is 2GHz, and the CPU periodicity c required by the UAV for computing each bit of data is 300cycles/bit.
Referring to fig. 3, a schematic diagram of the sliding trajectory and hovering position selection of the UAV when the data size of the application is 140MB is shown, and how the UAV assists the UE in executing the application is intuitively explained.
The solid line in fig. 3 represents the sliding trajectory and hover position coordinates along the x-axis of the UAV performing tasks 1 and 2 in the same task group, the dashed line represents the sliding trajectory of the UAV between two consecutive task groups, and the arrow direction represents the flight direction of the UAV. As can be seen from fig. 3, scheduling scheme I is selected for all task groups except scheduling scheme II for task group 1.
Referring to fig. 4, in contrast to fig. 3, a schematic diagram of the sliding trajectory and the hovering position selection of the UAV when the data size of the application is 300MB is shown, illustrating the effect of different data sizes of the application on the sliding trajectory and the hovering position selection of the UAV.
As can be seen from fig. 4, task group 1 and task group 3 select scheduling scheme I, task group 2 selects scheduling scheme II, and task group 4 selects scheduling scheme III. As can be seen by comparison with fig. 3, when the amount of application data is larger, the task is more likely to be performed using the selection scheduling scheme III, and the data collection hover position of the UAV is closer to the UE, the data relay position is closer to the BS. It can thus be concluded that: by using the unmanned aerial vehicle hovering position control method provided by the invention, compromise between UAV flight distance and communication channel conditions can be always found, and the optimal UAV hovering position in each task group is determined.
Referring to fig. 5, a schematic diagram of the total time required for completing all tasks by using the unmanned aerial vehicle hovering position control method provided by the present invention along with the continuous increase of the data volume of the UE application program task in the system is described.
As can be seen from fig. 5: with the increasing of the data volume of the UE application program task in the system, the total time required for completing all tasks is increased continuously, but the increasing trend is gradually gentle. In order to show the superiority of the unmanned aerial vehicle hovering position control method provided by the invention, compared with other three unmanned aerial vehicle hovering position control methods, the invention can be seen that the task completion time required by the method for controlling the hovering position of the unmanned aerial vehicle is less than that of other three schemes for any task data size.
Claims (2)
1. A mobile relay position control method of a mobile edge computing system, characterized by: the mobile edge computing system comprises User Equipment (UE), a mobile relay device (UAV) and a Base Station (BS) with a high-performance edge computing server, wherein the mobile relay device (UAV) has light computing capability and provides light-weight edge computing service for the User Equipment (UE), the high-performance edge computing server of the BS has strong computing capability, and the mobile relay device (UAV) and the BS are combined to solve the problem of insufficient computing resources of the User Equipment (UE);
the user equipment UE cannot be directly in wireless connection with the base station BS, the user equipment UE can be in wireless data connection with the base station BS only through the relay of the mobile relay equipment UAV, and the mobile relay equipment UAV provides data relay service for the user equipment UE and the base station BS and provides data calculation service within computing power for the user equipment UE; when User Equipment (UE) sends a calculation request, a current task is divided into a plurality of subtasks, the plurality of subtasks are sequentially sent to a mobile relay device (UAV) and calculation capacity support required by task calculation is judged in the mobile relay device (UAV), when the calculation capacity requirement of the subtasks is smaller than the calculation capacity of the mobile relay device (UAV), the corresponding subtasks are directly processed in the mobile relay device (UAV), the final calculation result is fed back to the User Equipment (UE), when the calculation capacity requirement of the subtasks exceeds the calculation capacity of the mobile relay device (UAV), the mobile relay device (UAV) sends the current subtasks to a server of a Base Station (BS) for processing, and when the processing is finished, the calculation results of the subtasks are sent to the User Equipment (UE) through the mobile relay device (UAV), so that three calculation task scheduling modes exist: calculating a task scheduling mode I: the former sub-task is executed at the mobile relay device UAV, and the latter sub-task is calculated at the base station BS; and a calculation task scheduling mode II: both the previous subtask and the next subtask perform calculations at the mobile relay device UAV; and calculating a task scheduling mode III: the former subtask and the latter subtask are both calculated in the base station BS; for two subtasks in any kth task group, respectively searching the positions of respective optimal wireless relay UAVs by using a basic PSO algorithm for the three calculation task scheduling modes, then selecting the task scheduling mode with the least time spent in the three calculation task scheduling modes as an execution scheme of the two subtasks, and repeatedly comparing the three calculation task scheduling modes for every two subtasks until all subtasks are completed;
based on three calculation task scheduling modes, the mobile position of the mobile relay device UAV is optimized according to the size of the task data volume unloaded by the user equipment UE, the best compromise of the mobile distance and the communication channel condition of the mobile relay device UAV is found, and the completion of the calculation task of the user equipment UE is accelerated through the parallel execution of the mobile relay device UAV and the base station BS, so that the purpose of minimizing the completion time of all tasks of the UE is achieved, the system delay is reduced, and the user experience is improved;
when User Equipment (UE) executes an application program, the application program is divided into K task groups with priority orders, namely the current task group can not be executed continuously until the execution result of the direct previous task group returns; in K task groups, each task group comprises n independent subtasks, and in order to facilitate parallel calculation of the mobile relay device UAV and the base station BS, the subtasks in each task group are divided into two parts according to the data size, wherein the first part is a task 1, and the second part is a task 2;
firstly, inputting coordinates of a user terminal UE and a base station BS, and setting initial position coordinates of a wireless relay UAV asBefore K task groups do not finish operation, the formula is used:
respectively calculating the time required by the three calculation task scheduling modes, wherein The method is characterized in that the method is determined according to position coordinates u of a mobile relay device UAV, a formula is determined, the optimal relay position is obtained by utilizing a basic particle swarm algorithm, the required time is further determined, and then the time is compared with the time of other two schemes;
in the formula:the time used for the task scheduling scheme I,for the time used by the task scheduling scheme II,the time used for the task scheduling scheme III,for the time required for the mobile relay device UAV to move from the initial position when processing the kth task set to the position when receiving task 1 data,time required for the mobile relay device UAV to move from the initial position when processing the kth task group to the position when receiving task 2 data;the time required for the mobile relay device UAV to receive the data for task 1 in the k-th task group,the time required for the mobile relay device UAV to receive data for task 2 in the kth task group;the time required for the mobile relay device UAV to perform task 1 in the k-th task group,the time required for the mobile relay device UAV to perform task 2 in the kth task group;the time required for the mobile relay device UAV to move from a location where task 1 data is received to relay this data location to the base station BS;for the time required for the mobile relay device UAV to relay the received data for task 1 in the kth task group to the base station BS,for the time required for the mobile relay device UAV to relay the received data for task 2 in the kth task group to the base station BS,express getAndthe larger of the two values is the one,express getAndthe numerical value of the two is largerOne of (a); selectingAndthe minimum value among the three is obtained, and the data collection position of the mobile relay device UAV corresponding to the minimum value among the three is obtained simultaneouslyAnd relay locationu represents a position coordinate representation symbol of the mobile relay device UAV, including actual coordinate information, and the optimal u is searched by using the most basic particle swarm algorithm;
updating location parameters of the mobile relay device UAV: if the task scheduling scheme I is used for the shortest time, thenIf the task scheduling scheme III is used for the shortest time, thenThen orderOtherwise, the time for the task scheduling scheme II is shortest, soThat is to say: updating the initial position of the wireless relay UAV after each task group of the user terminal UE is executed, if so, updating the initial position of the wireless relay UAVOrAt this time, the wireless relay UAV needs to relay at least one task to the base station BS for execution, so the initial position of the K +1 th task group is the relay hovering position when relaying the data of task 2, that is, the wireless relay UAV is configured to relay the data of task 2If it isIt is stated that task 1 and task 2 of the kth task group are both performed by the UAV in the shortest amount of time, so the initial position of the next task group is the data collection position of task 2, i.e., the position
2. The mobile relay location control method of a mobile edge computing system of claim 1, wherein:according to the formulaCalculating to obtain, wherein | · | | | represents a mobile relay, and i ═ 1 or 2; device UAV relay locationAndthe euclidean distance between;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,1And c) represents bk,1Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;according to the formulaIs obtained by calculation, wherein (b)k,2And c) represents bk,2Performing a multiplication operation with c;according to the formulaCalculating to obtain;according to the formulaCalculating to obtain;
wherein b isk,1Amount of data of task 1 in the kth task group, b, for a user Equipment UEk,2The data volume of task 2 in the kth task group of the user equipment UE, C is the number of CPU cycles needed by the mobile relay device UAV to calculate 1-bit data, and f is the calculation capacity of the mobile relay device UAV; the moving speed of the mobile relay device UAV is denoted by v.
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