CN105792310B - Relay selection method based on LTE Internet of vehicles - Google Patents

Relay selection method based on LTE Internet of vehicles Download PDF

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CN105792310B
CN105792310B CN201610124133.9A CN201610124133A CN105792310B CN 105792310 B CN105792310 B CN 105792310B CN 201610124133 A CN201610124133 A CN 201610124133A CN 105792310 B CN105792310 B CN 105792310B
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base station
relay
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CN105792310A (en
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杨志华
李国治
赵尚春
陈守凤
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Shenzhen Graduate School Harbin Institute of Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L67/00—Network arrangements or protocols for supporting network services or applications
    • H04L67/01—Protocols
    • H04L67/12—Protocols specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/12—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality
    • H04W40/16—Communication route or path selection, e.g. power-based or shortest path routing based on transmission quality or channel quality based on interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/22—Communication route or path selection, e.g. power-based or shortest path routing using selective relaying for reaching a BTS [Base Transceiver Station] or an access point
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention relates to the technical field of vehicle networking communication, in particular to a relay selection method based on LTE (Long term evolution) vehicle networking. The invention provides a D2D-assisted communication relay selection algorithm based on location partition, which aims to solve the problem of optimization selection of relay communication nodes on the basis of building a vehicle internet communication network based on LTE. Compared with the traditional search algorithm based on the signal-to-interference-and-noise ratio maximization exhaustion, the algorithm of the invention has the advantages that although the system capacity is reduced, the reduction degree is not large; the performance of the algorithm is greatly improved in the aspects of reducing the load of the base station and reducing the signaling overhead of the system, and the simulation result shows that the number of channels needing to be fed back is greatly reduced and the running time of the whole algorithm is greatly reduced during the running of the algorithm. Due to the improvement of the performance in the aspects, the algorithm provided by the invention can better adapt to the vehicle internet environment with variable channel environments.

Description

relay selection method based on LTE Internet of vehicles
Technical Field
the invention relates to the technical field of vehicle networking communication, in particular to a relay selection method based on LTE (Long term evolution) vehicle networking.
background
1. internet of vehicles communication technology
the internet of vehicles mainly refers to the technology of sensing road information and traffic information in all directions by using advanced sensor technology, network technology and computing technology, and realizes data information interaction and sharing among a plurality of systems or a plurality of users, thereby solving the problem of cooperative interaction among people, vehicles, roads and the like, and providing networks and applications which mainly aim at traffic efficiency and traffic safety. From the foregoing, it can be seen that wireless communication technology is the basis for vehicle networking applications and implementations. At present, main technologies applied to vehicle networking communication are VANET and LTE, wherein VANET is a mobile Ad-hoc network technology (Ad-hoc) which is mainly used for interconnection communication by allocating a dedicated frequency band, each vehicle supporting the technology can perform vehicle-to-vehicle communication (V2V) and vehicle-to-roadside unit communication (V2I) on the dedicated frequency band through a vehicle-mounted unit, and the roadside unit is connected with a backbone network, so that all-around sensing information obtained by each vehicle node can be transmitted to vehicle nodes or users in a wider range through the roadside unit; the LTE is a long term evolution of a universal mobile telecommunications system technology standard established by a 3GPP organization, and the LTE system introduces key technologies such as OFDM, which significantly improves the spectrum efficiency and the data transmission rate, and significantly improves the system capacity and coverage. In addition, compared with the prior mobile communication system, the network architecture of the LTE system is more flat and simplified, and the complexity of network nodes and the system is reduced, so that the system delay is reduced, and the deployment and maintenance cost of the network is also reduced.
D2D communication technology
In a conventional cellular network communication system, any two users need to communicate through the relay of a base station even when the two users are close to each other. As the number of users in a cell increases and communication services increase, the load of a base station increases, spectrum resources are insufficient, and the capacity of cellular users decreases. If two users at a short distance can not pass through the relay of the base station, the direct communication may bring the advantages of reducing the load of the base station, and the like, and based on the direct communication, the idea of introducing the D2D communication technology in the cellular network communication is generated. D2D communication is not a new technology, but is only a communication mode, such as bluetooth technology, which has been widely used earlier. The D2D communication technology is introduced into the cellular network, and under the control of the system, the devices are allowed to directly communicate by multiplexing cell resources without the need of transfer through a base station, so that the load of the base station can be reduced to a certain extent, and beneficial effects can be brought on the aspects of improving the spectrum efficiency, the system capacity and the like of the system. There are three modes of D2D communication: firstly, a cellular mode: D2D users are out of a certain threshold distance or communication mode that must be relayed through the base station. ② an orthogonal mode: the communication resources of the D2D user and the communication resources of the cellular user are orthogonal to each other, i.e., no co-channel interference exists in the communications between them. And thirdly, multiplexing mode: D2D users communicate by multiplexing cellular user resources, where co-channel interference exists for communications between them.
3.D2D communication relay technology
D2D communication can multiplex uplink or downlink resources of cellular users, and due to different multiplexing of uplink or downlink resources, interference situation in the whole network will be different, and considering that the base station has stronger interference control capability, and the uplink load may be lower compared to the downlink, most studies assume that the D2D user multiplexes uplink resources of cellular users. When the distance between the D2D users exceeds the maximum range allowed by the D2D communication, if the D2D mode is still used for communication, the relay user node must be selected to assist the D2D communication, and the whole D2D communication link is divided into two segments due to the addition of the relay node, the multiplexing of cellular user resources by each segment can be performed in many cases, and in each case, the communication performance of the whole D2D link is different due to the difference of the multiplexing resources. Existing D2D relay selection algorithms are generally designed based on the largest signal to interference plus noise ratio or the smallest interference, and they need to calculate the signal to interference plus noise ratio or the interference of each idle user when relay selection is performed, and under the assumption that each cellular user resource allowed to be multiplexed is multiplexed, respectively calculate the signal to interference plus noise ratio or the interference of each idle user, select the cellular user resource with the largest signal to interference plus noise ratio or the smallest interference, and allocate the communication resource to the corresponding D2D communication user pair, so that the communication is assisted by D2D.
at present, the communication technologies applied to vehicle interconnection mainly comprise VANET and LTE, and the VANET and the LTE have advantages and disadvantages respectively.
The VANET has the advantages of easy deployment, mature technology, capability of directly supporting V2V and the like, but meanwhile, the technology also has the defects of poor expandability, uncontrollable time delay, incapability of guaranteeing quality of service (QoS) and the like. VANET can only provide short or intermittent V2I communication due to limited radio coverage of the roadside units.
due to the wide deployment of cellular mobile communication networks, the generally large coverage area of a base station (eNB), and the like, LTE has the advantages of wide coverage area, high transmission rate, low time delay, and the like compared with VANET, but application of LTE to vehicle networking may face some problems: firstly, the spectrum resources in the LTE system are very precious, if the LTE is directly applied to the internet of vehicles, a large number of vehicle nodes need to be accessed into the system, the existing resources in the LTE system are already very tense, and if more vehicle node users are added, the problem of insufficient spectrum resources is certainly more serious. Secondly, in order to realize interaction and sharing of information between vehicles as real as possible, the vehicles must constantly transmit own information to the base station for other vehicles to obtain, and with the increase of the number of the vehicles, signaling overhead of the base station is inevitably increased rapidly, so that load of the base station is overlarge. In addition, the application in the aspects of traffic efficiency, traffic safety and the like may be paid more attention to the car networking, and the application has higher requirements on reliability and time delay performance, and the car interconnection communication is realized in a transfer mode based on the LTE system base station, so that some transfer processing time is inevitably needed, and the time delay performance requirement of the car networking may not be well met.
According to the analysis, the VANET and the LTE are applied to the car networking and have various defects, and the D2D communication mode is introduced on the basis of the LTE-A, so that the cars can directly communicate by multiplexing cellular user resources under the control of the base station without passing through the transfer of the base station. In the car networking environment, the communication distance of the D2D pair is likely to exceed the maximum value allowed by the D2D communication, and at this time, the D2D communication needs to be realized by means of relay assistance.
disclosure of Invention
Aiming at the defects or shortcomings in the prior art, the invention researches on the aspect of D2D relay assistance, and provides a D2D assisted communication relay selection algorithm based on location partition on the basis of building a vehicle interconnection communication network based on LTE (Long term evolution), so as to mainly solve the problem of optimal selection of relay communication nodes, such as the defects of overlarge load of a base station, high system signaling overhead and the like.
in order to achieve the above object, the present invention adopts a technical solution to provide a relay selection method for establishing a D2D communication relay model and then performing location-based zoning, the method comprising the following steps: (1) initializing system parameters, acquiring speed and position information of all cellular users and idle users, initializing a cellular user set M, wherein the total number of the idle users N is N, i is 0, in is 0, max is 0, and min is PI;
(2) Judging whether i is true or not, if so, carrying out the step (3), and if so, carrying out the step (7);
(3) And judging: if the Ris are not all true, adding Ri into the set B, and performing the step (4), and if the Ris are not true, directly performing the step (6);
wherein beta is the ratio of PD to PC, PD is the transmission power of cellular user D, PC is the transmission power of cellular user C, dSRi is the distance from node S to node Ri, dCR is the distance from node C to base station and base station to node Ri, dRiD is the distance from node Ri to node D, gamma D is the signal-to-drying ratio of cellular user D, gamma C is the signal-to-drying ratio of cellular user C, delta D is the interrupt probability threshold value of cellular user D, delta is the interrupt probability threshold value, r is the radius of cellular user,
(4) the distance of the section with longer distance in the two links is called as effective distance and is marked as dRi, the formula is used for representing that dRi is max (dSRi, dRiD), whether min > dRi is true or not is judged, if yes, the step (6) is carried out, and if yes, the step (5) is carried out;
(5) And min is dRi, in is i, and the step (6) is carried out;
(6) and i is i +1, and the step (2) is carried out;
(7) setting i to 0, calculating dA ═ din + a, and setting in to 0; dA is the shortest effective distance, a is the compensation distance, and din is the effective distance between the alternative optimal relay node and the transmitting node;
(8) Judging whether i is true or not, if so, jumping to the step (15), and if not, performing the step (9);
(9) judging whether dRi < dA is true, if so, carrying out the step (10), and if not, carrying out the step (14);
(10) respectively calculating interference values ISB and IRiB of the two sections of communication links to the base station, and performing the step (11), wherein c is a constant coefficient, alpha is a path loss coefficient, dSB and dRiB are respectively distance values between a sending end and a relay node to the base station, PSB and PRIB are respectively the sending power of the sending end and the relay node, and hSB and hRiB are respectively small-scale fading between the sending end and the relay node to the base station;
(11) and judging: ISB < IT, wherein IT is a base station interference threshold, if true, the step (12) is carried out, and if false, the step (14) is carried out;
(12) Calculating and judging max < gamma Ri, if true, performing the step (13), and if not, jumping to the step (14); in the formula: gamma Ri is a signal-to-dryness ratio of a node Ri, Ps, PCm and PRI are respectively the transmitting power of a node S, a node m and a node Ri, hSRi, hCMRi, hRID and hCMD are respectively the small-scale fading of the node S to the node Ri, the node m to the node Ri, the node Ri to the node D and the node m to the node D, N0 is the Gaussian white noise power, dCmRi is the distance from a cellular user m to a relay node Ri, and dCmD is the distance from the cellular user m to a target node D;
(13) If in is equal to i and max is equal to gamma Ri, carrying out the step (14);
(14) and i is i +1, and the step (8) is carried out;
(15) If yes, setting i as 0, and in as 0, executing step (16), if not, i is the selected relay, and ending;
(16) and searching the optimal relay in the set B according to the method for searching the optimal relay in the set A.
b is the frequency bandwidth of the occupied resource block, N0 is the Gaussian white noise power,
as a further improvement of the present invention, the establishing D2D communication relay model includes the following steps:
1) assuming that the D2D user communicates by multiplexing the uplink resources of the cellular user, assuming that the channel model only considers the effects of path loss and small-scale fading, the channel gain can be expressed as follows:
the hC, hD, hDC and hCD are small-scale fading from a cellular user to a base station, between D2D users, between D2D users to a base station and between a cellular user to a D2D user respectively; the PLC, PLD, PLDC, PLCD are the path loss from the cellular user to the base station, between D2D users, from D2D users to the base station, from the cellular user to D2D user; gC. The gD, gDC and gCD are the channel gains from the cellular user to the base station, from the D2D user to the base station, from the D2D user to the base station and from the cellular user to the D2D user respectively;
2) D2D relay-assisted communication is divided into two links, and assuming that the two links both multiplex uplink resources of the cellular user m, the signal received by the node Ri can be obtained as follows:
The signal received by the destination node D is:
wherein xs, xRi, xCm1 and xCm2 are respectively the emission signals of the node S, the node Ri, the first stage of the node m and the second stage of the node m; dSRi, dCmRi, dRiD, dCmD are distances from node S to node Ri, from node m to node Ri, from node Ri to node D, and from node m to node D, respectively; hSRi, hCMRi, hRID and hCMD are small-scale fading from a node S to a node Ri, from a node m to a node Ri, from a node Ri to a node D and from a node m to a node D respectively; ps, PCm and PRI are respectively the transmitting power of the node S, the node m and the node Ri, and n0 is a noise signal;
3) In the process of D2D relay assisted communication, the signals acquired by the base station in the first phase and the second phase are:
In the formula, dCm, dSCm and dRiCm are distances from a cellular user to a base station, from a source node S to the base station and from a relay node Ri to the base station respectively; hCm, hSCm and hRiCm are small-scale fading from a cellular user to a base station, from a source node S to the base station and from a relay node Ri to the base station respectively;
4) according to the receiving end signal in the step 3), the signal to interference plus noise ratios of the first-hop communication link and the second-hop communication link of the D2D are respectively obtained as follows:
And then, the channel capacities of the first hop link and the second hop link are respectively as follows according to the shannon formula:
B is the frequency bandwidth of the occupied resource block, and N0 is the Gaussian white noise power;
then for the entire D2D communication link, its channel capacity is:
C＝min(C,C)；
5) If the target is selected by the relay with the largest signal-to-interference-and-noise ratio or the largest channel capacity, the optimization objective function of the whole system can be shown by the following formula:
wherein, aacmri is a multiplexing coefficient, and if the value is 1, it means that the relay node Ri and the cellular user Cm multiplex the same communication resource; if the value is 0, the communication resources between the two are orthogonal, and the same frequency interference does not exist;
6) in order to ensure the reliability of D2D communication, the reliability of communication in the internet of vehicles will be described by introducing an interruption probability, and the calculation formula of the interruption probability corresponding to the cellular user and the D2D user can be obtained as follows:
wherein δ is an interruption probability threshold, β is a ratio of PD to PC, D is a corresponding distance value, PrC is an interruption probability of the cellular user i, dCi is an interruption probability of D2D user j, dDjCi is a distance from D2D user j to the cellular user i, dDj is a distance from the base station to D2D user j, and dCiDj is a distance from the cellular user i to D2D user j.
the invention has the beneficial effects that: the invention reduces the number of channels to be fed back and the running time of the algorithm to a great extent, thereby enabling the load of the base station to become smaller and reducing the signaling overhead of the whole system. For the improvement of the performances, the relay selection algorithm provided by the invention can be better applied to vehicle interconnection communication based on LTE.
drawings
Fig. 1 is a diagram of multiplexed uplink resource relay selection interference of the present invention;
FIG. 2 is a diagram of a D2D communication relay system model of the present invention;
fig. 3 is a schematic diagram of location-based sectorization relay selection of the present invention;
FIG. 4 is a block flow diagram of a location-based sectorized relay selection method of the present invention;
FIG. 5 is a diagram of a simulation scenario of the present invention;
fig. 6 is the number of relay nodes versus the D2D capacity of the present invention;
FIG. 7 is a plot of D2D distance versus D2D capacity for the present invention;
FIG. 8 is a diagram of a simulation of the relationship between the number of relay nodes and the number of channels to be fed back according to the present invention;
FIG. 9 is a diagram of simulation of the relationship between the number of cellular users and the number of channels requiring feedback according to the present invention;
FIG. 10 is a graph of simulation of the relationship between D2D distance and the number of channels requiring feedback in accordance with the present invention;
FIG. 11 is a graph of a simulation of the number of idle nodes and the algorithm run time of the relay node of the present invention;
FIG. 12 is a graph showing a simulation of the relationship between the number of cellular users and the running time of the algorithm in accordance with the present invention;
fig. 13 is a graph of a simulation of the D2D distance versus algorithm operation of the present invention.
Detailed Description
The invention is further described with reference to the following description and embodiments in conjunction with the accompanying drawings.
the following analyzes some problems of the conventional D2D communication relay selection algorithm applied to the internet of vehicles:
the conventional relay selection algorithm is an exhaustive search algorithm based on the largest signal to interference plus noise ratio or the smallest interference, that is, when the D2D communication distance is greater than the allowed maximum value, for all idle nodes that can be used as relays, under the condition of multiplexing all cellular user resources that can be multiplexed, the signal to interference plus noise ratio values or interference values of two links are respectively calculated, and finally, the idle node corresponding to the largest signal to interference plus noise ratio value or the smallest interference value of the whole D2D link is selected as the relay node, and the corresponding cellular user resource is allocated to the D2D communication link for use. As shown in fig. 1, HS, HR, HC, GS, GR, GCR, GCD are the channel gains of node S to node R, node R to node D, cellular user to base station, node S to base station, node R to base station, cellular user to node R, cellular user to node D, respectively. The HC, GS and GR base stations can be directly obtained, and the rest of the base stations need the user nodes to measure and report the results to the base stations. As can be seen from the above brief analysis, as the number of reusable cellular users, the number of idle users, and the number of D2D pairs needed to assist relay communication increase, the total number of channels to be measured increases rapidly, which inevitably causes the signaling overhead of the base station to become large, and at the same time, wastes the power of idle user nodes. In the car networking environment, due to the influence of factors such as continuous movement of cars, variable channel environments and the like, the relay selection situation is bound to become worse.
1. Algorithm design
From the above brief introduction and analysis, when there are a large number of cellular user nodes and D2D pairs of user nodes in the car networking environment, there are two main problems with using the conventional D2D relay to assist communication: the traditional D2D relay selection algorithm is an exhaustive search algorithm, and needs the base station to acquire Channel State Information (CSI) by itself or the user to detect and acquire the CSI and feed the CSI back to the base station, so that the signaling overhead and the load of the base station will be greatly increased as the number of user nodes increases. Secondly, even if all related Channel State Information (CSI) is obtained at the cost of large signaling overhead, relay selection is carried out by aiming at the minimum total interference or the maximum total signal-to-interference-and-noise ratio value of the system, the time complexity of the algorithm is high, the number of times of iterative operation of the algorithm is large, and therefore long time delay is caused. In order to better adapt to the application environment of the internet of vehicles, the patent aims to reduce the complexity of the algorithm and reduce the signaling overhead of a base station, and designs a new D2D relay selection algorithm.
first, a D2D communication relay model is established, and assuming that D2D users communicate by multiplexing uplink resources of cellular users, a schematic system diagram thereof can be used as shown in fig. 2 below. And assuming that the channel model only considers the effects of path loss and small-scale fading, the channel gain can be represented as follows:
The hC, hD, hDC and hCD are small-scale fading from a cellular user to a base station, between D2D users, between D2D users to a base station and between a cellular user to a D2D user respectively; the PLC, PLD, PLDC, PLCD are the path loss from the cellular user to the base station, between D2D users, from D2D users to the base station, from the cellular user to D2D user; gC. gD, gDC, gCD are channel gains for cellular user to base station, D2D user to base station, D2D user to base station, cellular user to D2D user, respectively.
suppose there are four categories of users in the system, namely cellular users, D2D users, idle users who can act as relays, D2D users who need relay assistance for communication, and we mainly study those D2D communication users who need relay assistance when the D2D communication distance exceeds the maximum D2D allowed distance. As shown in fig. 2, the D2D relay-assisted communication is divided into two segments, and it can be obtained if the two segments both multiplex uplink resources of cellular user m
the signals received by the relay node Ri are:
the signal received by the destination node D is:
wherein xs, xRi, xCm1 and xCm2 are respectively the emission signals of the node S, the node Ri, the first stage of the node m and the second stage of the node m; dSRi, dCmRi, dRiD, dCmD are distances from node S to node Ri, from node m to node Ri, from node Ri to node D, and from node m to node D, respectively; hSRi, hCMRi, hRID and hCMD are small-scale fading from a node S to a node Ri, from a node m to a node Ri, from a node Ri to a node D and from a node m to a node D respectively; ps, PCm, PRi are the transmission powers of the node S, the node m, and the node Ri, respectively.
In the process of D2D relay assisted communication, the signals acquired by the base station in the first phase and the second phase are:
in the formula, dCm, dSCm and dRiCm are distances from a cellular user to a base station, from a source node S to the base station and from a relay node Ri to the base station respectively; hCm, hSCm, hRiCm are small-scale fading from a cellular user to a base station, from a source node S to the base station, and from a relay node Ri to the base station, respectively.
according to the receiving end signal, the signal to interference plus noise ratios of the D2D first-hop communication link and the second-hop communication link are respectively:
and then, the channel capacities of the first hop link and the second hop link are respectively as follows according to the shannon formula:
wherein, B is the frequency bandwidth of the occupied resource block, and N0 is the gaussian white noise power.
then for the entire D2D communication link, its channel capacity is: crel min (CSRi, CRiD). Based on the above description and description, if the target is selected in terms of maximum sir or maximum channel capacity, the optimization objective function of the whole system can be shown by the following equation:
wherein aCmRi is a multiplexing coefficient. If the value is 1, the relay node Ri and the cellular user Cm multiplex the same communication resource; if the value is 0, it means that the communication resources between them are orthogonal, and there is no co-channel interference. The limiting condition is to ensure the communication of the multiplexed cellular user and the communication of the two relay links in the relay selection process, and the optimization problem of relay selection can be considered only on the premise that the requirements are met.
The conventional D2D relay assistance algorithm is based on all cellular users that can be multiplexed and idle users that can act as relay nodes to perform relay selection according to the objective function given above. Assuming that the number of cellular users that can be multiplexed in the network under consideration is M, the number of D2D communications that require relay assistance is N pairs, and the number of idle users that can act as relays is K. As shown in fig. 2, for a given relay-assisted D2D communication pair, GCD is only relevant to multiplexed cellular users, the number of times GCD detection is required is M × N; the GCR is related to both the multiplexing cellular user and the relay node user, and the number of times of detecting the GCR is M multiplied by K; the number of times HS and HR detection is N × K. And the total number of channel sounding times is M × (N + K) +2N × K.
from the above calculation results, as the number of cellular users, the number of idle users, and the number of pairs of relay assistance D2D are increased, the total number of channels to be detected is increased very fast. This will lead to the load of base station to increase rapidly, have the participation of the relay node at every channel detection at the same time, idle node waste electric quantity, etc. shortcoming exist. The number of vehicle nodes and mobile phone terminals is large in the vehicle network environment, so that the disadvantage of the method is more obvious in the vehicle network environment. Based on the above, the patent provides a relay selection algorithm based on location partition, and the basic starting points are that the load of a base station is reduced, the signaling overhead of a system is reduced, and the operation complexity of the algorithm is correspondingly reduced, so as to better adapt to the vehicle networking environment.
From the above analysis, it can be known that the channel capacity for the D2D relay-assisted communication depends on the smaller capacity of the two links. Since the communication distance is dominant to the channel capacity when the small-scale fading is less affected, the channel capacity of the D2D relay-assisted communication depends on the link that is farther away, considering only the geographical location information. For convenience of expression, the distance with a longer distance between two links is called as an effective distance, and in the environment of the car networking, the fast movement of car nodes causes fast change of channels, small-scale fading of the channels is difficult to accurately and timely obtain, and factors such as shadow fading exist. First, go through all idle users that can be used as relays, find out the shortest effective distance, and assume the shortest distance value as d, plus the offset distance a, assuming dA as d + a. Therefore, the source node S and the destination node D are respectively used as circle centers, dA is used as a radius to draw circles, all idle nodes in the obtained overlapping area are probably used as optimal relay nodes, and the area is set as an area A; all idle nodes in the area a are likely to be users for final relay assistance, and certainly, there is no user that can be used for relay assistance in the area a due to the fact that the number of idle users in the area a is small or the factors such as reliability requirements cannot be met, and at this time, a larger area B is obtained according to the above location partitioning method with dB ═ dD2D (max) as a radius; in addition, the idle node in the a area may not meet the signal to interference plus noise ratio requirement, and at this time, the selection area needs to be enlarged, and at this time, a new overlapping area is obtained with the maximum allowable communication distance of D2D as a radius, the relay node selection is performed in the area, the area is set as the B area, then the selection of the relay assisting user is performed in the area, if the relay assisting user is not found, the relay selection fails, and the next D2D assisting communication request is processed. The location partition of the relay selection algorithm of this patent can be illustrated by the following fig. 3:
To ensure the reliability of D2D communication, we will introduce an interruption probability to describe the reliability of communication in the internet of vehicles. Through the application of the known knowledge and the derivation of the formula, we can obtain the outage probability calculation formula corresponding to the cellular user and the D2D user as follows:
wherein δ is the interrupt probability threshold, β is the ratio of PD to PC, and d is the corresponding distance value, and the specific derivation process can be seen in the appendix. Based on the above analysis, the detailed steps of the relay selection method based on location partition proposed in this patent are listed as follows: (1) initializing system parameters, acquiring speed and position information of all cellular users and idle users, initializing a cellular user set M, wherein the total number of the idle users N is N, i is 0, in is 0, max is 0, and min is PI;
(2) judging whether i is true or not, if so, carrying out the step (3), and if so, carrying out the step (7);
(3) and judging: if the Ris are not all true, adding Ri into the set B, and performing the step (4), and if the Ris are not true, directly performing the step (6);
(4) The distance of the section with longer distance in the two links is called as effective distance and is marked as dRi, the formula is used for judging whether min > dRi is true or not, if so, the step (6) is carried out, and if so, the step (5) is carried out;
(5) and min is dRi, in is i, and the step (6) is carried out;
(6) and i is i +1, and the step (2) is carried out;
(7) setting i to 0, calculating dA ═ din + a, and setting in to 0;
(8) Judging whether i is true or not, if so, jumping to the step (15), and if not, performing the step (9);
(9) judging whether dRi < dA is true, if so, carrying out the step (10), and if not, carrying out the step (14);
(10) respectively calculating interference values ISB and IRiB of the two sections of communication links to the base station, and performing the step (11), wherein c is a constant coefficient, alpha is a path loss coefficient, dSB and dRiB are respectively distance values between a sending end and a relay node to the base station, PSB and PRIB are respectively the sending power of the sending end and the relay node, and hSB and hRiB are respectively small-scale fading between the sending end and the relay node to the base station;
(11) and judging: ISB < IT, wherein IT is a base station interference threshold, if true, the step (12) is carried out, and if false, the step (14) is carried out;
(12) calculating and judging max < gamma Ri, if true, performing the step (13), and if not, jumping to the step (14);
(13) If in is equal to i and max is equal to gamma Ri, carrying out the step (14);
(14) and i is i +1, and the step (8) is carried out;
(15) and (3) judging that max is 0, if yes, setting i to 0, and in to 0, executing the step (16), if not, determining that i is the selected relay, and ending.
(16) and searching the optimal relay in the set B according to the method for searching the optimal relay in the set A.
appendix: outage probability formula derivation
in order to ensure the reliability in the communication process, an interruption probability mathematical model is introduced:
Pr＝Pr[γ<γ]＝δ (1)
wherein, the threshold value of the interruption probability is delta, gamma e is the signal-to-interference-and-noise ratio of the cellular user, and r is the radius of the cellular user.
Since hC obeys rayleigh distribution, | hC |2 obeys exponential distribution [48], the following equation can be obtained:
For simplicity, assuming that PD ═ β PC, then the received snrs for cellular user i and D2D user j can be derived as follows:
According to the relevant literature, the following theorem can be derived: h1 and h2 are rayleigh distributed, so | h1|2 and | h2|2 are independent exponential distributions, x is m | h1|2, y is n | h2|2+1/θ, and CDF of z is x/y is:
therefore, the outage probabilities for cellular user i and D2D user j obtained from equations (4), (5) and (6) are:
second, performance evaluation
the section carries out simulation evaluation on the performance indexes of the relay selection algorithm based on the position partition, and compares the performance indexes with the traditional exhaustive search algorithm based on the signal-to-interference-and-noise ratio maximization. Four roads are around the network under consideration, each road being a dual lane, with nodes of vehicles on the roads randomly distributed and traveling at uniform speeds, assuming that cellular users that can be reused are also randomly distributed on the roads, without loss of generality, assuming that there is a pair of D2D users that need relay-assisted communication. In addition, some idle users which can be used as relay nodes exist on the road in a random distribution mode. The specific simulation scene diagram is shown in fig. 5:
fig. 6 is a simulation diagram of the relationship between the number of relay nodes and the capacity of D2D, in which the distance between D2D is 80m and the number of cellular users is 50. It can be seen from the figure that for a certain number of relay nodes, the relay selection algorithm based on location partition and the relay selection algorithm based on signal-to-noise ratio perform similarly in the capacity of D2D. When the number of the relay nodes is 20, the capacity difference between the algorithm and the relay selection algorithm based on the signal-to-noise ratio is about 0.02 Mbps. This difference remains almost constant as the number of available relay nodes increases. But the capacity of both algorithms increases. The reason is that the number of idle nodes which can be used as relay nodes is increased due to the random distribution of the idle nodes, the number of nodes falling between D2D is increased, and the number of users with good channels at the transmitting end and the receiving end of the distance D2D is also increased.
fig. 7 is a graph of a simulation of the relationship between the distance D2D and the capacity D2D, in which the number of idle users that can act as relays is 30 and the number of cellular users is 50. It can be seen that for a certain distance D2D, the location-based and snr-based relay selection algorithms herein perform similarly on the capacity of D2D. When the distance D2D is 75m, the capacity of the relay selection algorithm based on the signal-to-noise ratio differs by about 0.02 Mbps. This difference remains almost constant as the D2D distance increases. But the capacity of both algorithms is reduced. The reason is that the distance between D2D increases, and the distance between two subsequent links increases under the condition that the number of available users as relays does not change, and the link loss value increases, thereby reducing the capacity.
fig. 8 is a simulation diagram of the relationship between the number of relay nodes and the number of channels that need to be fed back. The distance between D2D is 80m and the number of cellular users is 50. As can be seen from the figure, for a certain number of relay nodes, the number of channels required to be fed back by the location-based-partition relay selection algorithm is significantly less than that of the relay selection algorithm based on the signal-to-noise ratio. When the number of the relay nodes is 20, the feedback channel number is about 1600 difference between the algorithm and the relay selection algorithm based on the signal-to-noise ratio. As the number of available relay nodes increases, the algorithm herein requires the number of feedback channels to grow slower, while the signal-to-noise ratio based algorithm requires the number of feedback channels to increase faster. The reason for this large difference is that the number of channel feedbacks and the number of relays that can be selected are linear based on the relay selection algorithm with the largest signal-to-noise ratio, while the algorithm based on location zoning is linear only with the number of nodes in the a-zone. The number of the relay nodes is increased, and the number of the nodes in the area A is less increased.
Fig. 9 is a simulation diagram of the relationship between the number of cellular users and the number of channels requiring feedback. The distance between D2D in the figure is 80m, and the number of idle nodes which can be used as relay users is 30. It can be seen that for a certain number of cellular users, the number of channels to be fed back by the location-based relay selection algorithm is less than that of the relay selection algorithm based on the snr. When the number of cells is 30, the feedback channel number is required to be close to 1500 by the algorithm and the relay selection algorithm based on the signal-to-noise ratio. However, as the number of cellular users increases, the algorithm herein requires the number of feedback channels to grow slower, while the signal-to-noise ratio based algorithm requires the number of feedback channels to increase faster. When the number of cellular users is 60, the two algorithms require that the number of feedback channels differ by approximately 3600. The reason for this large difference is that the number of channel feedbacks is linearly related to the number of cellular users based on the relay selection algorithm with the largest signal-to-noise ratio, whereas the location-based algorithm is only linearly related to the number of cellular users in the area D3 of the relay node and the number of cellular users in the area D3 of the destination node. The number of cellular users increases and the number of nodes in the D3 area of the relay node and the destination node increases less.
fig. 10 is a simulation diagram of the relationship between the D2D distance and the number of channels requiring feedback. The number of cellular users in the figure is 50, and the number of idle nodes which can be used as relay users is 30. It can be seen that for a certain distance D2D, the number of channels required to be fed back by the location-based relay selection algorithm is less than that of the relay selection algorithm based on the snr. As can be seen from the figure, the two curves are almost horizontal. The number of feedback channels needed is almost independent of the D2D distance.
fig. 11 is a diagram of a relationship simulation of the number of idle nodes that can be used as relay nodes and the running time of an algorithm. The distance between D2D is 80m and the number of cellular users is 50. It can be seen from the figure that for a certain number of relay nodes, the time of the relay selection algorithm based on the location partition is significantly shorter than that of the relay selection algorithm based on the signal-to-noise ratio. As the number of available relay nodes increases, the algorithm runtime herein increases very slowly, while the signal-to-noise ratio based relay selection algorithm runtime increases very rapidly.
fig. 12 is a diagram showing a simulation of the relationship between the number of cellular subscribers and the running time of the algorithm. The distance between D2D in the figure is 80m, and the number of idle nodes which can be used as relay users is 30. It can be seen that for a certain number of cellular users, the location-based sectorization relay selection algorithm herein runs significantly less time than the signal-to-noise ratio based relay selection algorithm. However, as the number of cellular users increases, the algorithm herein runs slower in time and the signal-to-noise ratio based algorithm requires a faster increase in the number of feedback channels.
fig. 13 is a graph of simulation of the relationship between D2D distance and algorithm operation. The number of cellular users in the figure is 50, and the number of idle nodes which can be used as relay users is 30. It can be seen that for a certain distance D2D, the relay selection algorithm based on location partition has less running time than the relay selection algorithm based on signal-to-noise ratio. As can be seen from the figure, the two curves are almost horizontal. The two algorithms run time is almost independent of the D2D distance.
through comparison of simulation results, the position-based zoning relay selection algorithm provided by the patent has little difference in system capacity compared with the traditional maximum exhaustive search algorithm based on the signal-to-interference-and-noise ratio, but the number of channels needing to be fed back and the operation time of the algorithm are greatly reduced, so that the load of a base station becomes smaller and the signaling overhead of the whole system is reduced. For the improvement of the performances, the relay selection algorithm provided by the patent can be better applied to vehicle interconnection communication based on LTE.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (2)

1. a relay selection method based on LTE Internet of vehicles is characterized in that:
establishing a D2D communication relay model, and then performing a relay selection method based on location partition, wherein the method comprises the following steps:
(1) initializing system parameters, acquiring speed and position information of all cellular users and idle users, initializing a cellular user set M, wherein the total number of the idle users N is N, i is 0, in is 0, max is 0, and min is PI;
(2) Judging whether i is true or not, if so, carrying out the step (3), and if so, carrying out the step (7);
(3) and judging: if the node Ri is not in the set B, the step (4) is carried out, and if the node Ri is not in the set B, the step (6) is directly carried out;
Wherein beta is the ratio of PD to PC, PD is the transmission power of cellular user D, PC is the transmission power of cellular user C, dSRi is the distance from node S to node Ri, dCR is the distance from node C to base station and base station to node Ri, dRiD is the distance from node Ri to node D, gamma D is the signal-to-drying ratio of cellular user D, gamma C is the signal-to-drying ratio of cellular user C, delta D is the interrupt probability threshold value of cellular user D, delta is the interrupt probability threshold value, r is the radius of cellular user,
(4) The distance of the section with longer distance in the two links is called as effective distance and is marked as dRi, the formula is used for representing that dRi is max (dSRi, dRiD), whether min is greater than dRi is judged, if yes, the step (6) is carried out, and if yes, the step (5) is carried out;
(5) And min is dRi, in is i, and the step (6) is carried out;
(6) and i is i +1, and the step (2) is carried out;
(7) Setting i to 0, calculating dA ═ din + a, and setting in to 0; dA is the shortest effective distance, a is the compensation distance, and din is the effective distance between the alternative optimal relay node and the transmitting node;
(8) Judging whether i is true or not, if so, jumping to the step (15), and if not, performing the step (9);
(9) judging whether dRi < dA is true, if so, carrying out the step (10), and if not, carrying out the step (14);
(10) respectively calculating interference values ISB and IRiB of the two sections of communication links to the base station, and performing the step (11), wherein c is a constant coefficient, alpha is a path loss coefficient, dSB and dRiB are respectively distance values between a sending end and a relay node to the base station, PSB and PRIB are respectively the sending power of the sending end and the relay node, and hSB and hRiB are respectively small-scale fading between the sending end and the relay node to the base station;
(11) And judging: ISB is less than IT, IRiB is less than IT, wherein IT is a base station interference threshold, if true, the step (12) is carried out, and if false, the step (14) is carried out;
(12) calculating and judging that max is less than gamma Ri, if true, performing the step (13), and if not, jumping to the step (14); in the formula: gamma Ri is a signal-to-dryness ratio of a node Ri, Ps, PCm and PRI are respectively the transmitting power of a node S, a node m and a node Ri, hSRi, hCMRi, hRID and hCMD are respectively the small-scale fading of the node S to the node Ri, the node m to the node Ri, the node Ri to the node D and the node m to the node D, N0 is the Gaussian white noise power, dCmRi is the distance from a cellular user m to a relay node Ri, and dCmD is the distance from the cellular user m to a target node D;
(13) If in is equal to i and max is equal to gamma Ri, carrying out the step (14);
(14) And i is i +1, and the step (8) is carried out;
(15) if yes, setting i as 0, and in as 0, executing step (16), if not, i is the selected relay, and ending;
(16) And searching the optimal relay in the set B according to the method for searching the optimal relay in the set A.
2. The relay selection method based on the LTE Internet of vehicles according to claim 1, wherein the establishing D2D communication relay model comprises the following steps:
1) assuming that the D2D user communicates by multiplexing the uplink resources of the cellular user, assuming that the channel model only considers the effects of path loss and small-scale fading, the channel gain can be expressed as follows:
the hC, hD, hDC and hCD are small-scale fading from a cellular user to a base station, between D2D users, between D2D users to a base station and between a cellular user to a D2D user respectively; the PLC, PLD, PLDC, PLCD are the path loss from the cellular user to the base station, between D2D users, from D2D users to the base station, from the cellular user to D2D user; gC. The gD, gDC and gCD are the channel gains from the cellular user to the base station, from the D2D user to the base station, from the D2D user to the base station and from the cellular user to the D2D user respectively;
2) D2D relay-assisted communication is divided into two links, and assuming that the two links both multiplex uplink resources of the cellular user m, the signal received by the node Ri can be obtained as follows:
The signal received by the destination node D is:
wherein xs, xRi, xCm1 and xCm2 are respectively the emission signals of the node S, the node Ri, the first stage of the node m and the second stage of the node m; dSRi, dCmRi, dRiD, dCmD are distances from node S to node Ri, from node m to node Ri, from node Ri to node D, and from node m to node D, respectively; hSRi, hCMRi, hRID and hCMD are small-scale fading from a node S to a node Ri, from a node m to a node Ri, from a node Ri to a node D and from a node m to a node D respectively; ps, PCm and PRI are respectively the transmitting power of the node S, the node m and the node Ri, and n0 is a noise signal;
3) in the process of D2D relay assisted communication, the signals acquired by the base station in the first phase and the second phase are:
in the formula, dCm, dSCm and dRiCm are distances from a cellular user to a base station, from a source node S to the base station and from a node Ri to the base station respectively; hCm, hSCm and hRiCm are small-scale fading from a cellular user to a base station, from a source node S to the base station and from a node Ri to the base station respectively;
4) according to the receiving end signal in the step 3), the signal to interference plus noise ratios of the first-hop communication link and the second-hop communication link of the D2D are respectively obtained as follows:
and then, the channel capacities of the first hop link and the second hop link are respectively as follows according to the shannon formula:
b is the frequency bandwidth of the occupied resource block, and N0 is the Gaussian white noise power;
then for the entire D2D communication link, its channel capacity is:
C＝min(C,C)；
5) if the target is selected by the relay with the largest signal-to-interference-and-noise ratio or the largest channel capacity, the optimization objective function of the whole system can be shown by the following formula:
Wherein, aacmri is a multiplexing coefficient, and if the value is 1, it means that the node Ri and the cell user Cm multiplex the same communication resource; if the value is 0, the communication resources between the two are orthogonal, and the same frequency interference does not exist;
6) in order to ensure the reliability of D2D communication, the reliability of communication in the internet of vehicles will be described by introducing an interruption probability, and the calculation formula of the interruption probability corresponding to the cellular user and the D2D user can be obtained as follows:
wherein δ is an interruption probability threshold, β is a ratio of PD to PC, D is a corresponding distance value, PrC is an interruption probability of a cellular user i, dCi is an interruption probability of D2D user j, dDjCi is a distance from D2D user j to cellular user i, dDj is a distance from a base station to D2D user j, and dCiDj is a distance from the cellular user i to D2D user j; PrD is the outage probability for user j, D2D.
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