CN111246437B - A method for selecting the number of D2D relay time slots - Google Patents

A method for selecting the number of D2D relay time slots Download PDF

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CN111246437B
CN111246437B CN202010021520.6A CN202010021520A CN111246437B CN 111246437 B CN111246437 B CN 111246437B CN 202010021520 A CN202010021520 A CN 202010021520A CN 111246437 B CN111246437 B CN 111246437B
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裴二荣
易鑫
刘珊
鹿逊
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Shenzhen Hongyue Information Technology Co ltd
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Abstract

The invention relates to a D2D relay time slot number selection method, and belongs to the field of narrowband Internet of things. The invention comprises the following steps: s1: setting the number of reserved time slots of DRE to be NtsSorting the candidate relays, and taking the UE with the maximum relay intention as an actual DRE; s2: calculating to obtain a working time table of the DRE; s3: establishing a transmission success rate model of the DRE; s4: establishing an energy consumption model of the DRE; s5: constructing utility function f (N)ts) And obtain an optimization problem Maxf (N)ts) (ii) a S6: find f (N)ts) Maximized NtsThe value is obtained. The method can find the N of the maximized utility function value under different delta values according to different preference requirements of userstsAnd obtaining the optimal compromise between energy consumption and transmission success rate.

Description

一种D2D中继时隙数量选择方法A method for selecting the number of D2D relay time slots

技术领域technical field

本发明属于窄带物联网领域，涉及一种D2D中继时隙数量选择方法。The invention belongs to the field of narrowband Internet of Things, and relates to a method for selecting the number of D2D relay time slots.

背景技术Background technique

窄带物联网作为一种新兴的LPWAN技术，十分适合在很远的范围内传输少量信息的物联网应用。由于NB-IoT中大多数用户设备(User Equipment,UE)都是采用电池供电并且大规模部署，所以更换电池的成本很高。因此，将能耗保持在最低水平至关重要。为解决这一问题，有研究人员提出将D2D通信用于辅助NB-IoT系统的数据传输。在D2D辅助的NB-IoT系统中，D2D短距离通信的节能特性完美地弥补了NB-IoT设备靠电池驱动所造成的能量短缺。As an emerging LPWAN technology, NB-IoT is very suitable for IoT applications that transmit a small amount of information over a long distance. Since most User Equipment (UE) in NB-IoT are powered by batteries and deployed on a large scale, the cost of replacing batteries is high. Therefore, it is crucial to keep energy consumption to a minimum. To solve this problem, some researchers proposed to use D2D communication to assist the data transmission of NB-IoT systems. In the D2D-assisted NB-IoT system, the energy-saving features of D2D short-range communication perfectly compensate for the energy shortage caused by battery-driven NB-IoT devices.

在D2D辅助的NB-IoT中，D2D中继/接收设备(D2D Relay/Receiver Equipment,DRE)需要为D2D通信和数据转发预留时隙。在最理想的情况下，至少应该预留两个时隙，一个时隙用于D2D通信，一个时隙用于中继转发数据至基站(Base Station,BS)。然而，在实际中，D2D通信和中继转发阶段都可能存在传输失败，进而导致重传。为了提升传输成功率，DRE需要为D2D通信与中继转发预留更多的时隙以便可以允许更多次的重传。然而，太多的重传次数(特别是在信道质量较差的情况下)将显著地增加UE的能耗，进而降低UE的生命周期。因此，D2D数据传输算法是NB-IoT系统中重要的研究问题之一。In D2D-assisted NB-IoT, D2D relay/receiver equipment (D2D Relay/Receiver Equipment, DRE) needs to reserve time slots for D2D communication and data forwarding. In the most ideal situation, at least two time slots should be reserved, one time slot is used for D2D communication, and one time slot is used for relaying and forwarding data to a base station (Base Station, BS). However, in practice, there may be transmission failures in both the D2D communication and relay forwarding stages, resulting in retransmissions. In order to improve the transmission success rate, the DRE needs to reserve more time slots for D2D communication and relaying to allow more retransmissions. However, too many retransmission times (especially in the case of poor channel quality) will significantly increase the energy consumption of the UE, thereby reducing the life cycle of the UE. Therefore, D2D data transmission algorithm is one of the important research issues in NB-IoT systems.

现有NB-IoT中基于D2D通信的数据传输算法没有考虑DRE最优通信时隙数量的配置问题。需要为DRE确定一个预留时隙数，一方面能够尽可能地提升传输成功率，另一方面尽可能将能耗控制在一个可以容忍的水平。因此，设计一种NB-IoT中基于D2D通信的中继时隙数量选择方法，具有现实意义。The existing data transmission algorithms based on D2D communication in NB-IoT do not consider the configuration of the optimal number of communication time slots for DRE. It is necessary to determine a reserved time slot number for the DRE. On the one hand, the transmission success rate can be improved as much as possible, and on the other hand, the energy consumption can be controlled to a tolerable level as much as possible. Therefore, it is of practical significance to design a method for selecting the number of relay time slots based on D2D communication in NB-IoT.

发明内容SUMMARY OF THE INVENTION

有鉴于此，本发明提供了一种NB-IoT中基于D2D通信的中继时隙数量选择方法，为DRE确定一个最优的通信时隙数，用来平衡传输成功率和能量消耗。In view of this, the present invention provides a method for selecting the number of relay time slots based on D2D communication in NB-IoT, to determine an optimal number of communication time slots for DRE to balance transmission success rate and energy consumption.

为了达到上述目的，本发明提供如下技术方案：In order to achieve the above object, the present invention provides the following technical solutions:

一种D2D中继时隙数量选择方法，包括以下步骤：A method for selecting the number of D2D relay time slots, comprising the following steps:

S1：设置DRE的预留时隙数量为Nts，对候选中继进行排序，将中继意愿最大的UE作为实际DRE；S1: Set the number of reserved time slots for the DRE to N ts , sort the candidate relays, and take the UE with the greatest relay intention as the actual DRE;

S2：计算得到DRE的工作时间表；S2: Calculate the work schedule of DRE;

S3：建立DRE的传输成功率模型；S3: establish the transmission success rate model of DRE;

S4：建立DRE的能量消耗模型；S4: Establish the energy consumption model of DRE;

S5：构造效用函数f(Nts)，并得到优化问题Maxf(Nts)；S5: Construct the utility function f(N ts ), and obtain the optimization problem Maxf(N ts );

S6：求得使f(Nts)最大化的Nts值；S6: Find the value of N ts that maximizes f(N ts );

进一步，在步骤S1中，将DRE预留的通信时隙数量设置为Nts；用

Figure BDA0002360971660000021
表示NB-IoT终端u的候选中继集，它是终端u到BS的路径中点附近的D2D通信范围内的K个UEs，用于帮助终端u将分组上传至BS。候选中继按照中继意愿函数
Figure BDA0002360971660000022
进行排序，将中继意愿最大的设备rk作为实际DRE ropt，其中Ek为DRE剩余能量，
Figure BDA0002360971660000023
为该DRE到BS的传输成功率的历史平均值，
Figure BDA0002360971660000024
为DRE到BS的距离。Further, in step S1, the number of communication time slots reserved by DRE is set to N ts ;
Figure BDA0002360971660000021
Represents the candidate relay set of NB-IoT terminal u, which is K UEs within the D2D communication range near the midpoint of the path from terminal u to the BS, and is used to help terminal u upload packets to the BS. Candidate relays follow the relay willingness function
Figure BDA0002360971660000022
Sort the device r k with the largest relay willingness as the actual DRE r opt , where E k is the remaining energy of the DRE,
Figure BDA0002360971660000023
is the historical average of the transmission success rate from the DRE to the BS,
Figure BDA0002360971660000024
is the distance from DRE to BS.

进一步，在步骤S2中，用一个(N-1)×1的向量

Figure BDA0002360971660000025
表示终端u的工作时间表，如果候选DRE
Figure BDA0002360971660000026
的第i个时隙是为D2D通信预留的，则判决变量
Figure BDA0002360971660000027
为1，否则为0。Further, in step S2, a (N-1)×1 vector is used
Figure BDA0002360971660000025
represents the work schedule of terminal u, if the candidate DRE
Figure BDA0002360971660000026
The i-th time slot of is reserved for D2D communication, then the decision variable
Figure BDA0002360971660000027
1, otherwise 0.

进一步，在步骤S3中，用

Figure BDA0002360971660000028
表示具有给定
Figure BDA0002360971660000029
的终端u的分组传输率，表示终端u到BS在两跳上的预期分组传输率。Further, in step S3, use
Figure BDA0002360971660000028
means that the given
Figure BDA0002360971660000029
The packet transmission rate of terminal u represents the expected packet transmission rate of terminal u to BS in two hops.

用P表示终端u的传输成功率。基于平均SINR，加性高斯白噪声中二进制信号检测的平均比特错误率为：

Figure BDA00023609716600000210
Let P represent the transmission success rate of terminal u. Based on the average SINR, the average bit error rate for binary signal detection in additive white Gaussian noise is:
Figure BDA00023609716600000210

其中Q(·)表示标准高斯误差函数，

Figure BDA00023609716600000211
where Q( ) represents the standard Gaussian error function,
Figure BDA00023609716600000211

假设比特错误彼此独立发生，对于L比特分组，可以通过考虑正确接收所有单独比特的概率来计算P。由于假设瑞利衰落，SINR可能会在分组传输时间内发生变化。为了简化分析，我们假设干扰在l比特的传输时间内缓慢变化，假定l个连续比特的SINR是相同的。在这种情况下，L比特分组的P可以表示为：Assuming that bit errors occur independently of each other, for an L-bit packet, P can be calculated by considering the probability of correctly receiving all individual bits. Due to the assumption of Rayleigh fading, the SINR may vary within the packet transmission time. To simplify the analysis, we assume that the interference varies slowly over the transmission time of 1 bits, and that the SINR of 1 consecutive bits is the same. In this case, the P of the L-bit packet can be expressed as:

Figure BDA00023609716600000212
Figure BDA00023609716600000212

其中，pb(j)是分组的第j个l比特长片段的比特错误率。则包含W个分组的传输成功率为：where p b (j) is the bit error rate of the jth l-bit long segment of the packet. Then the transmission success rate containing W packets is:

Figure BDA0002360971660000031
Figure BDA0002360971660000031

对于给定的工作时间表

Figure BDA0002360971660000032
终端u的EDR为：for a given work schedule
Figure BDA0002360971660000032
The EDR of terminal u is:

Figure BDA0002360971660000033
Figure BDA0002360971660000033

其中，

Figure BDA0002360971660000034
是分组在第i个时隙被DRE
Figure BDA0002360971660000035
成功接收的概率，具体为：in,
Figure BDA0002360971660000034
is the DRE of the packet in the ith slot
Figure BDA0002360971660000035
The probability of successful reception, specifically:

Figure BDA0002360971660000036
Figure BDA0002360971660000036

其中，PtoR是终端u和DRE之间链路的分组传输率估计值。前式的

Figure BDA0002360971660000037
是DRE
Figure BDA0002360971660000038
与BS之间链路的分组传输率估计值，最大为N-i次传输。其值为：Among them, P toR is the estimated value of the packet transmission rate of the link between terminal u and DRE. anterior
Figure BDA0002360971660000037
is DRE
Figure BDA0002360971660000038
The estimated value of the packet transmission rate of the link with the BS, up to Ni times of transmission. Its value is:

Figure BDA0002360971660000039
Figure BDA0002360971660000039

因为数据发送的最后期限为Ntsτ，总的传输计数不能超过Nts。若D2D通信占用i个时隙，则第二跳的最大传输计数最多为Nts-i次。Since the deadline for data transmission is N ts τ, the total transmission count cannot exceed N ts . If the D2D communication occupies i time slots, the maximum transmission count of the second hop is at most N ts -i times.

进一步，在步骤S4中，用

Figure BDA00023609716600000310
表示具有给定
Figure BDA00023609716600000311
的终端u的能量消耗，表示终端u通过两跳链路发送一个分组到BS的期望能量消耗。Further, in step S4, use
Figure BDA00023609716600000310
means that the given
Figure BDA00023609716600000311
The energy consumption of terminal u represents the expected energy consumption of terminal u sending a packet to the BS through the two-hop link.

对于给定的工作时间表Δ(u)，终端u的EEC(Δ(u))为：For a given work schedule Δ (u) , the EEC(Δ (u) ) for terminal u is:

Figure BDA00023609716600000312
Figure BDA00023609716600000312

其中，

Figure BDA00023609716600000313
是
Figure BDA00023609716600000314
将分组传输到BS的预期能量消耗，且最多传输Nts-i次，即in,
Figure BDA00023609716600000313
Yes
Figure BDA00023609716600000314
The expected energy consumption of transmitting the packet to the BS up to N ts -i times, i.e.

Figure BDA00023609716600000315
Figure BDA00023609716600000315

其中，

Figure BDA00023609716600000316
和
Figure BDA00023609716600000317
是根据能耗模型计算的第一跳及第二跳的能量消耗。
Figure BDA00023609716600000318
为前i-1个时隙传输失败及在时隙i传输成功产生的能耗。
Figure BDA00023609716600000319
为l次传输所消耗的能量，前l-1次未成功传输，第l次成功传输。具体如下：in,
Figure BDA00023609716600000316
and
Figure BDA00023609716600000317
is the energy consumption of the first hop and the second hop calculated according to the energy consumption model.
Figure BDA00023609716600000318
is the energy consumption for the first i-1 time slot transmission failure and the successful transmission in time slot i.
Figure BDA00023609716600000319
is the energy consumed by l transmissions, the first l-1 unsuccessful transmissions, and the lth successful transmission. details as follows:

Figure BDA00023609716600000320
Figure BDA00023609716600000320

Figure BDA00023609716600000321
Figure BDA00023609716600000321

其中，

Figure BDA0002360971660000041
分别为蜂窝UE和D2D UE的传输功率。in,
Figure BDA0002360971660000041
are the transmission powers of cellular UEs and D2D UEs, respectively.

进一步，在步骤S5中，为了求得能耗和传输成功率的最优折中，构造一个效用函数：Further, in step S5, in order to obtain the optimal compromise between energy consumption and transmission success rate, a utility function is constructed:

Figure BDA0002360971660000042
Figure BDA0002360971660000042

其中，E和P为所求能耗和传输成功率，Pmin表示NB-IoT边缘UE能够接受的最低传输成功率，而Emax表示NB-IoT边缘UE进行一次数据上传所消耗的最大能量。由Emax/E和P/Pmin可知，E越小或P越大，效用函数值就越大。Nts表示DRE的预留D2D通信时隙的数量，由于完成第一跳和第二跳传输至少需要两个时隙，故其值为等于或者大于2的整数。δ为能耗和传输成功率的权重因子。较大的δ值倾向于更加节能，但导致过低的传输成功率；较小的δ值倾向于提高传输成功率，但是导致过高的能耗。当δ＝0时，效用函数表示最大化传输成功率，但是同时带来最大的能耗；当δ＝1时，表示最小化能耗，同时获得最小的传输成功率。Among them, E and P are the required energy consumption and transmission success rate, P min represents the minimum transmission success rate that the NB-IoT edge UE can accept, and E max represents the maximum energy consumed by the NB-IoT edge UE for one data upload. It can be known from E max /E and P/P min that the smaller E or the larger P is, the larger the utility function value is. N ts represents the number of reserved D2D communication time slots of the DRE. Since at least two time slots are required to complete the first hop and the second hop transmission, its value is an integer equal to or greater than 2. δ is the weighting factor of energy consumption and transmission success rate. Larger values of δ tend to be more energy efficient, but result in too low transmission success rates; smaller values of δ tend to increase transmission success rates, but result in too high energy consumption. When δ=0, the utility function indicates that the transmission success rate is maximized, but at the same time brings the maximum energy consumption; when δ=1, it indicates that the energy consumption is minimized and the minimum transmission success rate is obtained at the same time.

进一步，在步骤S6中，考虑到场景中的一些限定条件，将这个效用函数作为目标函数能够得到如下优化问题：Further, in step S6, considering some limited conditions in the scene, the following optimization problem can be obtained by using this utility function as the objective function:

Max f(Nts)Max f(N ts )

Figure BDA0002360971660000043
Figure BDA0002360971660000043

其中，θi,k为判决变量，当DRE的时隙是为D2D通信和转发数据所预留时，其值为1，否则为0。考虑到目标函数是一个具有极大值的函数，采用二分法对DRE最优值进行搜索，即根据用户的不同偏好需求，在不同的δ取值下，找到最大化效用函数值的Nts值，获得能耗和传输成功率的最优折中。Among them, θ i,k is a decision variable, when the time slot of DRE is reserved for D2D communication and forwarding data, its value is 1, otherwise it is 0. Considering that the objective function is a function with a maximum value, the optimal value of DRE is searched by the dichotomy method, that is, according to the different preferences of users, under different values of δ, find the N ts value that maximizes the value of the utility function. , to obtain the optimal compromise between energy consumption and transmission success rate.

本发明的有效效果在于：在D2D辅助NB-IoT中，提出一个单中继选择方案，该方案可以保证一定的传输成功率，并不需要其他中继设备的等待，有利于节省能量。如果数据提前传输完毕，中继设备提前进入休眠，有利于进一步节省能量。同时研究了D2D辅助NB-IoT中DRE最优通信时隙数量的配置问题，为了求得传输成功率和能耗的最优折中，构造了一个基于加权的传输成功率和能耗的效用函数，并且基于这个效用函数，构造了一个DRE通信时隙配置的优化问题，最终通过配置最优的Nts来获得最好的能耗以及几乎最好的传输成功率。The effective effect of the present invention is: in D2D-assisted NB-IoT, a single relay selection scheme is proposed, which can ensure a certain transmission success rate, does not require waiting of other relay equipment, and is beneficial to saving energy. If the data transmission is completed in advance, the relay device goes to sleep in advance, which is conducive to further saving energy. At the same time, the configuration problem of the optimal number of communication time slots for DRE in D2D-assisted NB-IoT is studied. In order to obtain the optimal compromise between transmission success rate and energy consumption, a utility function based on weighted transmission success rate and energy consumption is constructed. , and based on this utility function, an optimization problem of DRE communication time slot configuration is constructed, and finally the best energy consumption and almost the best transmission success rate can be obtained by configuring the optimal N ts .

附图说明Description of drawings

为了使本发明的目的、技术方案和有益效果更佳清楚，本发明提供如下附图进行说明：In order to make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for description:

图1为本发明实施例的流程示意图；1 is a schematic flowchart of an embodiment of the present invention;

图2为基于D2D通信的窄带物联网网络模型图；Fig. 2 is the network model diagram of narrowband Internet of Things based on D2D communication;

图3为本发明实施例的DRE工作时间表示意图；3 is a schematic diagram of a DRE work schedule according to an embodiment of the present invention;

图4为本发明实施例的网络场景示意图。FIG. 4 is a schematic diagram of a network scenario according to an embodiment of the present invention.

具体实施方式Detailed ways

下面结合附图，对本发明的优选实施例进行详细的描述。The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

本发明针对窄带物联网中上行链路数据传输问题，提出一种D2D中继时隙数量选择方法。为了求得传输成功率和能耗的最优折中，本文构造了一个基于加权的传输成功率和能耗的效用函数，并且基于这个效用函数，构造了一个DRE通信时隙配置的优化问题，一方面能够尽可能地提升传输成功率，另一方面尽可能将能耗控制在一个可以容忍的水平。为DRE确定一个预留时隙数，保证一定的传输成功率，不需要其他中继设备的等待，有利于节省能量。并且，如果数据提前传输完毕，中继设备提前进入休眠，有利于进一步节省能量。NB-IoT中基于D2D通信的D2D中继时隙数量选择方法的流程图如图1所示。Aiming at the problem of uplink data transmission in the narrowband Internet of Things, the present invention proposes a method for selecting the number of D2D relay time slots. In order to find the optimal compromise between transmission success rate and energy consumption, this paper constructs a utility function based on weighted transmission success rate and energy consumption, and based on this utility function, constructs an optimization problem of DRE communication time slot configuration, On the one hand, the transmission success rate can be improved as much as possible, and on the other hand, the energy consumption can be controlled to a tolerable level as much as possible. Determining a reserved time slot number for the DRE ensures a certain transmission success rate, does not require the waiting of other relay devices, and is conducive to saving energy. Moreover, if the data transmission is completed in advance, the relay device goes to sleep in advance, which is conducive to further saving energy. The flowchart of the method for selecting the number of D2D relay time slots based on D2D communication in NB-IoT is shown in Figure 1.

基于D2D通信的NB-IoT网络模型图如图2所示。处于小区边缘的UE先与邻近且信道条件较好的UE即DRE建立D2D链路，再由其将接收到的数据上传至基站，每个UE通过最多两跳将数据上传到基站。首先设置DRE预留时隙数量为Nts，按中继意愿大小将候选中继进行排序，将中继意愿最大的设备rk作为实际DRE ropt。根据候选中继和传输时间得到DRE的工作时间表。建立DRE的传输成功率模型，然后建立DRE的能量消耗模型。再根据传输成功率和能量消耗模型构造效用函数，并建立一个优化问题。采用二分法对DRE Nts最优值进行搜索，找到最大化效用函数值的Nts值，获得能耗和传输成功率的最优折中。The NB-IoT network model diagram based on D2D communication is shown in Figure 2. The UE at the cell edge first establishes a D2D link with a nearby UE with better channel conditions, namely the DRE, which then uploads the received data to the base station. Each UE uploads data to the base station through at most two hops. First, set the number of time slots reserved by the DRE as N ts , sort the candidate relays according to the relay willingness, and take the device rk with the largest relay willingness as the actual DRE r opt . The working schedule of the DRE is obtained according to the candidate relay and transmission time. The transmission success rate model of DRE is established, and then the energy consumption model of DRE is established. Then, the utility function is constructed according to the transmission success rate and energy consumption model, and an optimization problem is established. The optimal value of DRE N ts is searched by the dichotomy method, and the N ts value that maximizes the utility function value is found to obtain the optimal compromise between energy consumption and transmission success rate.

如图1所示，NB-IoT中基于D2D通信的能耗和传输成功率的最优折中方法，该方法包括以下步骤：As shown in Figure 1, the optimal compromise method of energy consumption and transmission success rate based on D2D communication in NB-IoT, the method includes the following steps:

S1：设置DRE的预留时隙数量为Nts，对候选中继进行排序，将中继意愿最大的UE作为实际DRE；S1: Set the number of reserved time slots of the DRE to N ts , sort the candidate relays, and take the UE with the greatest relay willingness as the actual DRE;

S2：计算得到DRE的工作时间表；S2: Calculate the work schedule of DRE;

S3：建立DRE的传输成功率模型；S3: establish the transmission success rate model of DRE;

S4：建立DRE的能量消耗模型；S4: Establish the energy consumption model of DRE;

S5：构造效用函数f(Nts)，并得到优化问题Maxf(Nts)；S5: Construct the utility function f(N ts ), and obtain the optimization problem Maxf(N ts );

S6：求得使f(Nts)最大化的Nts值；S6: Find the value of N ts that maximizes f(N ts );

为了得到候选中继集合，将DRE预留的通信时隙数量设置为Nts；用

Figure BDA0002360971660000061
表示NB-IoT终端u的候选中继集，它是终端u到BS的路径中点附近的D2D通信范围内的K个UEs，用于帮助终端u将分组上传至BS。候选中继按照中继意愿函数
Figure BDA0002360971660000062
进行排序，将中继意愿最大的设备rk作为实际DRE ropt，其中Ek为DRE剩余能量，
Figure BDA0002360971660000063
为该DRE到BS的传输成功率的历史平均值，
Figure BDA0002360971660000064
为DRE到BS的距离。In order to obtain the candidate relay set, the number of communication time slots reserved by the DRE is set as N ts ;
Figure BDA0002360971660000061
Represents the candidate relay set of NB-IoT terminal u, which is K UEs within the D2D communication range near the midpoint of the path from terminal u to the BS, and is used to help terminal u upload packets to the BS. Candidate relays follow the relay willingness function
Figure BDA0002360971660000062
Sort the device r k with the largest relay willingness as the actual DRE r opt , where E k is the remaining energy of the DRE,
Figure BDA0002360971660000063
is the historical average of the transmission success rate from the DRE to the BS,
Figure BDA0002360971660000064
is the distance from DRE to BS.

用一个(N-1)×1的向量

Figure BDA0002360971660000065
表示终端u的工作时间表，如果候选DRE
Figure BDA0002360971660000066
的第i个时隙是为D2D通信预留的，则判决变量
Figure BDA0002360971660000067
为1，否则为0。DRE的工作时间表如图3所示。Use a (N-1)×1 vector
Figure BDA0002360971660000065
represents the work schedule of terminal u, if the candidate DRE
Figure BDA0002360971660000066
The i-th time slot of is reserved for D2D communication, then the decision variable
Figure BDA0002360971660000067
1, otherwise 0. The work schedule of DRE is shown in Figure 3.

根据终端u的工作时间表

Figure BDA0002360971660000068
用
Figure BDA0002360971660000069
表示终端u的分组传输率，表示终端u到BS在两跳上的预期分组传输率。According to the work schedule of terminal u
Figure BDA0002360971660000068
use
Figure BDA0002360971660000069
represents the packet transmission rate of terminal u, and represents the expected packet transmission rate from terminal u to BS in two hops.

用P表示终端u的传输成功率。基于平均SINR，加性高斯白噪声中二进制信号检测的平均比特错误率为：

Figure BDA00023609716600000610
Let P represent the transmission success rate of terminal u. Based on the average SINR, the average bit error rate for binary signal detection in additive white Gaussian noise is:
Figure BDA00023609716600000610

其中Q(·)表示标准高斯误差函数，

Figure BDA00023609716600000611
where Q( ) represents the standard Gaussian error function,
Figure BDA00023609716600000611

假设比特错误彼此独立发生，对于L比特分组，可以通过考虑正确接收所有单独比特的概率来计算P。由于假设瑞利衰落，SINR可能会在分组传输时间内发生变化。为了简化分析，我们假设干扰在l比特的传输时间内缓慢变化，假定l个连续比特的SINR是相同的。在这种情况下，L比特分组的P可以表示为：Assuming that bit errors occur independently of each other, for an L-bit packet, P can be calculated by considering the probability of correctly receiving all individual bits. Due to the assumption of Rayleigh fading, the SINR may vary within the packet transmission time. To simplify the analysis, we assume that the interference varies slowly over the transmission time of 1 bits, and that the SINR of 1 consecutive bits is the same. In this case, the P of the L-bit packet can be expressed as:

Figure BDA00023609716600000612
Figure BDA00023609716600000612

其中，pb(j)是分组的第j个l比特长片段的比特错误率。则包含W个分组的传输成功率为：where p b (j) is the bit error rate of the jth l-bit long segment of the packet. Then the transmission success rate containing W packets is:

Figure BDA0002360971660000071
Figure BDA0002360971660000071

对于给定的工作时间表

Figure BDA0002360971660000072
终端u的EDR为：for a given work schedule
Figure BDA0002360971660000072
The EDR of terminal u is:

Figure BDA0002360971660000073
Figure BDA0002360971660000073

其中，

Figure BDA0002360971660000074
是分组在第i个时隙被DRE
Figure BDA0002360971660000075
成功接收的概率，具体为：in,
Figure BDA0002360971660000074
is the DRE of the packet in the ith slot
Figure BDA0002360971660000075
The probability of successful reception, specifically:

Figure BDA0002360971660000076
Figure BDA0002360971660000076

其中，PtoR是终端u和DRE之间链路的分组传输率估计值。前式的

Figure BDA0002360971660000077
是DRE
Figure BDA0002360971660000078
与BS之间链路的分组传输率估计值，最大为N-i次传输。其值为：Among them, P toR is the estimated value of the packet transmission rate of the link between terminal u and DRE. anterior
Figure BDA0002360971660000077
is DRE
Figure BDA0002360971660000078
The estimated value of the packet transmission rate of the link with the BS, up to Ni times of transmission. Its value is:

Figure BDA0002360971660000079
Figure BDA0002360971660000079

因为数据发送的最后期限为Ntsτ，总的传输计数不能超过Nts。若D2D通信占用i个时隙，则第二跳的最大传输计数最多为Nts-i次。NB-IoT中基于D2D通信的网络场景示意图如图4所示。Since the deadline for data transmission is N ts τ, the total transmission count cannot exceed N ts . If the D2D communication occupies i time slots, the maximum transmission count of the second hop is at most N ts -i times. A schematic diagram of a network scenario based on D2D communication in NB-IoT is shown in Figure 4.

根据终端u的工作时间表

Figure BDA00023609716600000710
用
Figure BDA00023609716600000711
表示具有给定
Figure BDA00023609716600000712
的终端u的能量消耗，表示终端u通过两跳链路发送一个分组到BS的期望能量消耗。According to the work schedule of terminal u
Figure BDA00023609716600000710
use
Figure BDA00023609716600000711
means that the given
Figure BDA00023609716600000712
The energy consumption of terminal u represents the expected energy consumption of terminal u sending a packet to the BS through the two-hop link.

对于给定的工作时间表Δ(u)，终端u的EEC(Δ(u))为：For a given work schedule Δ (u) , the EEC(Δ (u) ) for terminal u is:

Figure BDA00023609716600000713
Figure BDA00023609716600000713

其中，

Figure BDA00023609716600000714
是DRE
Figure BDA00023609716600000715
将分组传输到BS的预期能量消耗，且最多传输Nts-i次，即in,
Figure BDA00023609716600000714
is DRE
Figure BDA00023609716600000715
The expected energy consumption of transmitting the packet to the BS up to N ts -i times, i.e.

Figure BDA00023609716600000716
Figure BDA00023609716600000716

其中，

Figure BDA00023609716600000717
和
Figure BDA00023609716600000718
是根据能耗模型计算的第一跳及第二跳的能量消耗。
Figure BDA00023609716600000719
为前i-1个时隙传输失败及在时隙i传输成功产生的能耗。
Figure BDA00023609716600000720
为l次传输所消耗的能量，前l-1次未成功传输，第l次成功传输。具体如下：in,
Figure BDA00023609716600000717
and
Figure BDA00023609716600000718
is the energy consumption of the first hop and the second hop calculated according to the energy consumption model.
Figure BDA00023609716600000719
is the energy consumption for the first i-1 time slot transmission failure and the successful transmission in time slot i.
Figure BDA00023609716600000720
is the energy consumed by l transmissions, the first l-1 unsuccessful transmissions, and the lth successful transmission. details as follows:

Figure BDA0002360971660000081
Figure BDA0002360971660000081

Figure BDA0002360971660000082
Figure BDA0002360971660000082

其中，

Figure BDA0002360971660000083
分别为蜂窝UE和D2D UE的传输功率。in,
Figure BDA0002360971660000083
are the transmission powers of cellular UEs and D2D UEs, respectively.

为了求得能耗和传输成功率的最优折中，构造一个效用函数：In order to find the optimal compromise between energy consumption and transmission success rate, a utility function is constructed:

Figure BDA0002360971660000084
Figure BDA0002360971660000084

其中，E和P为所求能耗和传输成功率，Pmin表示NB-IoT边缘UE能够接受的最低传输成功率，而Emax表示NB-IoT边缘UE进行一次数据上传所消耗的最大能量。由Emax/E和P/Pmin可知，E越小或P越大，效用函数值就越大。Nts表示DRE的预留D2D通信时隙的数量，由于完成第一跳和第二跳传输至少需要两个时隙，故其值为等于或者大于2的整数。δ为能耗和传输成功率的权重因子。较大的δ值倾向于更加节能，但导致过低的传输成功率；较小的δ值倾向于提高传输成功率，但是导致过高的能耗。当δ＝0时，效用函数表示最大化传输成功率，但是同时带来最大的能耗；当δ＝1时，表示最小化能耗，同时获得最小的传输成功率。Among them, E and P are the required energy consumption and transmission success rate, P min represents the minimum transmission success rate that the NB-IoT edge UE can accept, and E max represents the maximum energy consumed by the NB-IoT edge UE for one data upload. It can be known from E max /E and P/P min that the smaller E or the larger P is, the larger the utility function value is. N ts represents the number of reserved D2D communication time slots of the DRE. Since at least two time slots are required to complete the first hop and the second hop transmission, its value is an integer equal to or greater than 2. δ is the weighting factor of energy consumption and transmission success rate. Larger values of δ tend to be more energy efficient, but result in too low transmission success rates; smaller values of δ tend to increase transmission success rates, but result in too high energy consumption. When δ=0, the utility function indicates that the transmission success rate is maximized, but at the same time brings the maximum energy consumption; when δ=1, it indicates that the energy consumption is minimized and the minimum transmission success rate is obtained at the same time.

考虑到场景中的一些限定条件，将这个效用函数作为目标函数能够得到如下优化问题：Considering some constraints in the scene, using this utility function as the objective function can lead to the following optimization problem:

Max f(Nts)Max f(N ts )

Figure BDA0002360971660000085
Figure BDA0002360971660000085

其中，θi,k为判决变量，当DRE的时隙是为D2D通信和转发数据所预留时，其值为1，否则为0。考虑到目标函数是一个具有极大值的函数，采用二分法对DRE最优值进行搜索，即根据用户的不同偏好需求，在不同的δ取值下，找到最大化效用函数值的Nts值，获得能耗和传输成功率的最优折中。Among them, θ i,k is a decision variable, when the time slot of DRE is reserved for D2D communication and forwarding data, its value is 1, otherwise it is 0. Considering that the objective function is a function with a maximum value, the optimal value of DRE is searched by the dichotomy method, that is, according to the different preferences of users, under different values of δ, find the N ts value that maximizes the value of the utility function. , to obtain the optimal compromise between energy consumption and transmission success rate.

最后说明的是，以上优选实施例仅用以说明本发明的技术方案而非限制，尽管通过上述优选实施例已经对本发明进行了详细的描述，但本领域技术人员应当理解，可以在形式上和细节上对其作出各种各样的改变，而不偏离本发明权利要求书所限定的范围。Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should Various changes may be made in details without departing from the scope of the invention as defined by the claims.

Claims (4)

1.一种D2D中继时隙数量选择方法，其特征在于：该方法包括以下步骤：1. A method for selecting the number of D2D relay time slots, characterized in that: the method comprises the following steps: S1：设置D2D中继/接收设备(D2D relay/receiver equipment，DRE)的预留时隙数量为Nts，对候选中继进行排序，将中继意愿最大的UE作为实际DRE；S1: Set the number of reserved time slots of the D2D relay/receiver equipment (D2D relay/receiver equipment, DRE) to N ts , sort the candidate relays, and take the UE with the greatest relay intention as the actual DRE; S2：计算得到DRE的工作时间表；S2: Calculate the work schedule of DRE; S3：建立DRE的传输成功率模型。用
Figure FDA0003544971040000011
表示具有给定
Figure FDA0003544971040000012
的终端u的分组传输率，表示终端u到BS在两跳上的预期分组传输率。加性高斯白噪声中二进制信号检测的平均比特错误率为：
Figure FDA0003544971040000013
其中Q(·)表示标准高斯误差函数，
Figure FDA0003544971040000014
SINR为平均信扰噪比。假设比特错误彼此独立发生，对于L比特分组，可以通过考虑正确接收所有单独比特的概率来计算终端u的传输成功率P。假设干扰在l比特的传输时间内缓慢变化，因而l个连续比特的SINR是相同的。在这种情况下，l比特分组的成功传输率P可以表示为：
Figure FDA0003544971040000015
其中，pb(j)是分组的第j个l比特长片段的比特错误率。包含W个分组的传输成功率为：
Figure FDA0003544971040000016
对于给定的工作时间表
Figure FDA0003544971040000017
终端u到BS在两跳上的预期分组传输率EDR为：
Figure FDA0003544971040000018
其中，
Figure FDA0003544971040000019
是分组在第i个时隙被DRE
Figure FDA00035449710400000110
成功接收的概率，具体为：
Figure FDA00035449710400000111
其中，PtoR是终端u和DRE之间链路的分组传输率估计值，
Figure FDA00035449710400000112
为判决变量。前式的
Figure FDA00035449710400000113
是
Figure FDA00035449710400000114
与BS之间链路的分组传输率估计值，最大为N-i次传输，其值为：
Figure FDA00035449710400000115
其中PtoBS为该DRE到基站的传输成功率的历史平均值。因为数据发送的最后期限为Ntsτ，总的传输计数不能超过Nts。若D2D通信占用i个时隙，则第二跳的最大传输计数最多为Nts-i次。S3: Establish a transmission success rate model of the DRE. use
Figure FDA0003544971040000011
means that the given
Figure FDA0003544971040000012
The packet transmission rate of terminal u represents the expected packet transmission rate of terminal u to BS in two hops. The average bit error rate for binary signal detection in additive white Gaussian noise is:
Figure FDA0003544971040000013
where Q( ) represents the standard Gaussian error function,
Figure FDA0003544971040000014
SINR is the average signal-to-interference-to-noise ratio. Assuming that bit errors occur independently of each other, for an L-bit packet, the transmission success rate P of terminal u can be calculated by considering the probability of correctly receiving all individual bits. Assume that the interference varies slowly over the transmission time of 1 bits, so the SINR of 1 consecutive bits is the same. In this case, the successful transmission rate P of a 1-bit packet can be expressed as:
Figure FDA0003544971040000015
where p b (j) is the bit error rate of the jth l-bit long segment of the packet. The transmission success rate containing W packets is:
Figure FDA0003544971040000016
for a given work schedule
Figure FDA0003544971040000017
The expected packet transmission rate EDR from terminal u to BS over two hops is:
Figure FDA0003544971040000018
in,
Figure FDA0003544971040000019
is the DRE of the packet in the ith slot
Figure FDA00035449710400000110
The probability of successful reception, specifically:
Figure FDA00035449710400000111
where PtoR is the estimated packet transmission rate of the link between terminal u and DRE,
Figure FDA00035449710400000112
is the decision variable. anterior
Figure FDA00035449710400000113
Yes
Figure FDA00035449710400000114
The estimated value of the packet transmission rate of the link with the BS, the maximum is Ni times of transmission, and its value is:
Figure FDA00035449710400000115
Wherein P toBS is the historical average value of the transmission success rate of the DRE to the base station. Since the deadline for data transmission is N ts τ, the total transmission count cannot exceed N ts . If the D2D communication occupies i time slots, the maximum transmission count of the second hop is at most N ts -i times. S4：建立DRE的能量消耗模型。用
Figure FDA00035449710400000116
表示具有给定
Figure FDA00035449710400000117
的终端u的能量消耗，表示终端u通过两跳链路发送一个分组到BS的期望能量消耗。对于给定的工作时间表Δ(u)，终端u的EEC(Δ(u))为：
Figure FDA0003544971040000021
其中，
Figure FDA0003544971040000022
是
Figure FDA0003544971040000023
将分组传输到BS的预期能量消耗，且最多传输Nts-i次，即
Figure FDA0003544971040000024
其中，PtoBS表示为该DRE到基站的传输成功率的历史平均值，
Figure FDA0003544971040000025
和
Figure FDA0003544971040000026
是根据能耗模型计算的第一跳及第二跳的能量消耗。
Figure FDA0003544971040000027
为前i-1个时隙传输失败及在时隙i传输成功产生的能耗。
Figure FDA0003544971040000028
为l次传输所消耗的能量，前l-1次未成功传输，第l次成功传输。具体如下：
Figure FDA0003544971040000029
其中，
Figure FDA00035449710400000210
分别为蜂窝UE和D2D UE的传输功率，Eelec是发射或接收每比特信息所消耗的能量，τ为一个时隙的长度。S4: Establish an energy consumption model of DRE. use
Figure FDA00035449710400000116
means that the given
Figure FDA00035449710400000117
The energy consumption of terminal u represents the expected energy consumption of terminal u sending a packet to the BS through the two-hop link. For a given work schedule Δ (u) , the EEC(Δ (u) ) for terminal u is:
Figure FDA0003544971040000021
in,
Figure FDA0003544971040000022
Yes
Figure FDA0003544971040000023
The expected energy consumption of transmitting the packet to the BS up to N ts -i times, i.e.
Figure FDA0003544971040000024
Among them, P toBS is expressed as the historical average of the transmission success rate from the DRE to the base station,
Figure FDA0003544971040000025
and
Figure FDA0003544971040000026
is the energy consumption of the first hop and the second hop calculated according to the energy consumption model.
Figure FDA0003544971040000027
is the energy consumption for the first i-1 time slot transmission failure and the successful transmission in time slot i.
Figure FDA0003544971040000028
is the energy consumed by l transmissions, the first l-1 unsuccessful transmissions, and the lth successful transmission. details as follows:
Figure FDA0003544971040000029
in,
Figure FDA00035449710400000210
are the transmission powers of cellular UEs and D2D UEs, respectively, E elec is the energy consumed by transmitting or receiving each bit of information, and τ is the length of a time slot. S5：构造效用函数f(Nts)，并得到优化问题Maxf(Nts)。为了求得能耗和传输成功率的最优折中，构造一个效用函数：
Figure FDA00035449710400000211
其中，E和P为所求能耗和传输成功率，Pmin表示NB-IoT边缘UE能够接受的最低传输成功率，而Emax表示NB-IoT边缘UE进行一次数据上传所消耗的最大能量。由Emax/E和P/Pmin可知，E越小或P越大，效用函数值就越大。Nts表示DRE的预留D2D通信时隙的数量，由于完成第一跳和第二跳传输至少需要两个时隙，故其值为等于或者大于2的整数。δ为能耗和传输成功率的权重因子。较大的δ值倾向于更加节能，但导致过低的传输成功率；较小的δ值倾向于提高传输成功率，但是导致过高的能耗。当δ＝0时，效用函数表示最大化传输成功率，但是同时带来最大的能耗；当δ＝1时，表示最小化能耗，同时获得最小的传输成功率。S5: Construct the utility function f(N ts ), and obtain the optimization problem Maxf(N ts ). In order to find the optimal compromise between energy consumption and transmission success rate, a utility function is constructed:
Figure FDA00035449710400000211
Among them, E and P are the required energy consumption and transmission success rate, P min represents the minimum transmission success rate that the NB-IoT edge UE can accept, and E max represents the maximum energy consumed by the NB-IoT edge UE for one data upload. It can be known from E max /E and P/P min that the smaller E or the larger P is, the larger the utility function value is. N ts represents the number of reserved D2D communication time slots of the DRE. Since at least two time slots are required to complete the first hop and the second hop transmission, its value is an integer equal to or greater than 2. δ is the weighting factor of energy consumption and transmission success rate. Larger values of δ tend to be more energy efficient, but result in too low transmission success rates; smaller values of δ tend to increase transmission success rates, but result in too high energy consumption. When δ=0, the utility function indicates that the transmission success rate is maximized, but at the same time brings the maximum energy consumption; when δ=1, it indicates that the energy consumption is minimized and the minimum transmission success rate is obtained at the same time. S6：求得使f(Nts)最大化的Nts值。S6: Find the value of N ts that maximizes f(N ts ). 2.根据权利要求1所述的一种D2D中继时隙数量选择方法，其特征在于：在步骤S1中，将DRE预留的通信时隙数量设置为Nts；用
Figure FDA00035449710400000212
表示NB-IoT终端u的候选中继集，它是终端u到BS的路径中点附近的D2D通信范围内的K个UEs，用于帮助终端u将分组上传至BS。候选中继按照中继意愿函数
Figure FDA00035449710400000213
进行排序，将中继意愿最大的设备rk作为实际DREropt，其中Ek为DRE剩余能量，
Figure FDA0003544971040000031
为该DRE到BS的传输成功率的历史平均值，
Figure FDA0003544971040000032
为DRE到BS的距离。2. a kind of D2D relay time slot quantity selection method according to claim 1, is characterized in that: in step S1, the communication time slot quantity reserved by DRE is set to Nts ;
Figure FDA00035449710400000212
Represents the candidate relay set of NB-IoT terminal u, which is K UEs within the D2D communication range near the midpoint of the path from terminal u to the BS, and is used to help terminal u upload packets to the BS. Candidate relays follow the relay willingness function
Figure FDA00035449710400000213
Sort, take the device r k with the greatest relay willingness as the actual DREr opt , where E k is the remaining DRE energy,
Figure FDA0003544971040000031
is the historical average of the transmission success rate from the DRE to the BS,
Figure FDA0003544971040000032
is the distance from DRE to BS. 3.根据权利要求1所述的一种D2D中继时隙数量选择方法，其特征在于：在步骤S2中，用一个(N-1)×1的向量
Figure FDA0003544971040000033
表示终端u的工作时间表，如果候选DRE
Figure FDA0003544971040000034
的第i个时隙是为D2D通信预留的，则判决变量
Figure FDA0003544971040000035
为1，否则为0。3. The method for selecting the number of D2D relay time slots according to claim 1, wherein in step S2, a vector of (N-1)×1 is used
Figure FDA0003544971040000033
represents the work schedule of terminal u, if the candidate DRE
Figure FDA0003544971040000034
The i-th time slot of is reserved for D2D communication, then the decision variable
Figure FDA0003544971040000035
1, otherwise 0. 4.根据权利要求1所述的一种D2D中继时隙数量选择方法，其特征在于：在步骤S6中，考虑到场景中的一些限定条件，将这个效用函数作为目标函数能够得到如下优化问题：4. a kind of method for selecting the number of D2D relay time slots according to claim 1, is characterized in that: in step S6, taking into account some limited conditions in the scene, the following optimization problem can be obtained by using this utility function as the objective function : Max f(Nts)Max f(N ts )
Figure FDA0003544971040000036
Figure FDA0003544971040000036
 其中，θi,k为判决变量，当DRE的时隙是为D2D通信和转发数据所预留时，其值为1，否则为0。考虑到目标函数是一个具有极大值的函数，采用二分法对DRE最优值进行搜索，即根据用户的不同偏好需求，在不同的δ取值下，找到最大化效用函数值的Nts值，获得能耗和传输成功率的最优折中。Among them, θ i,k is a decision variable, when the time slot of DRE is reserved for D2D communication and forwarding data, its value is 1, otherwise it is 0. Considering that the objective function is a function with a maximum value, the optimal value of DRE is searched by the dichotomy method, that is, according to the different preferences of users, under different values of δ, find the N ts value that maximizes the value of the utility function. , to obtain the optimal compromise between energy consumption and transmission success rate.
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