CN116939711A - -based predictive multi-user joint relay selection strategy in cooperative communication - Google Patents
-based predictive multi-user joint relay selection strategy in cooperative communication Download PDFInfo
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Abstract
The invention belongs to the technical field of Internet of vehicles communication, and particularly relates to a predictive multi-user joint relay selection strategy based on in cooperative communication; predicting the channel gain of a transmission link by utilizing a channel prediction technology, and in the bandwidth demand estimation, estimating the bandwidth demand on the premise of guaranteeing the QoS requirement based on a bandwidth demand estimation method; in relay selection, based on bandwidth demand estimation, in each prediction time slot in a prediction window, relay joint pre-selection of a plurality of mobile terminals is realized with the aim of minimizing total bandwidth demand; taking the relay pre-selection in the first step as input, and combining the current relay selection information to adjust the relay selection of the next time slot so as to achieve the purpose of relieving frequent switching of links; aiming at the relay selection problem of cooperative transmission in a vehicle network, the cooperative transmission scheme based on the method has the characteristics of low bandwidth requirement and high link stability in the high-mobility vehicle network.
Description
Technical Field
The invention belongs to the technical field of Internet of vehicles communication, and particularly relates to a predictive multi-user joint relay selection strategy based on in cooperative communication.
Background
As one of the most important enabling technologies in intelligent transportation systems, vehicle networks are introduced as transmission media for driving assistance, safety monitoring, multimedia services, etc., where V2I (vehicle to infrastructure, vehicle-to-infrastructure communication) and V2V (vehicle to vehicle, vehicle-to-vehicle communication) enable vehicles to communicate with roadside units and inter-vehicles to communicate with each other. In a scene where the deployment of the roadside units is sparse, when the terminal automobile drives to an area covered by the edge of the roadside units, the communication quality between the roadside units and the terminal automobile is poor, so that the direct communication between the roadside units and the terminal automobile can cause the need of larger resource consumption so as to ensure the service quality requirement of a user. In the cooperative communication technology, by configuring a mobile relay with good communication quality with a roadside unit for a terminal car driving in a roadside unit edge coverage area, auxiliary forwarding of information flows is realized, and QoS (quality of service ) can be improved and resources can be saved.
Currently, most relay options for cooperative communication are aimed at minimizing resource utilization. In relay selection with the aim of minimizing bandwidth consumption, the accuracy of the bandwidth demand estimation directly affects the benefits of the relay selection strategy. However, the bandwidth required to transmit data is not only related to data traffic but also QoS. It is difficult to estimate the bandwidth requirements of a data stream, especially for data streams with random burstiness, while guaranteeing QoS requirements. Compared with an effective bandwidth and effective capacity method, the method better reserves the random characteristic of the captain when analyzing the queue delay characteristic, so that the method can analyze the system delay performance more accurately, and the bandwidth estimation based on the technology is more accurate. In addition, in the relay forwarding link, the information transmission performance of the entire forwarding link is affected by a change of any one node on the link, and it is necessary to reduce the number of relays on the forwarding link as much as possible. Meanwhile, considering the buffer pressure of the relay car, the number of terminals served by one relay car at the same time is limited, so that relay selection among users is no longer independent. Therefore, how to implement multi-user joint relay selection and reduce the bandwidth requirement of the transmission data stream is a considerable problem.
In a vehicle network with high mobility, this way of determining a relay scheme by minimizing the single objective of resource requirements often results in frequent handovers of links. Frequent switching of links not only increases signaling bandwidth cost, but also causes delay jitter and other problems. Therefore, how to alleviate the pressure of frequent link switching while reducing bandwidth usage is a concern.
Disclosure of Invention
In order to overcome the above problems, the present invention proposes a predictive multi-user joint relay selection strategy based on , in which each mobile relay is limited to assist only one terminal at the same time and one terminal is assisted by one relay at the same time. Aiming at the bandwidth estimation problem, the joint relay selection problem and the link switching problem in cooperative communication, the method provides a predictive multi-user joint relay selection strategy based on , and achieves the aims of reducing bandwidth requirements and improving link stability.
In order to achieve the above object, the present invention provides the following technical strategies:
a -based predictive multi-user joint relay selection strategy comprising the steps of:
step one, channel prediction:
historical information about vehicle travel speed and road traffic is stored in an MEC server deployed on the wireless access network; k PTSs are arranged in one PW, a MEC server predicts a vehicle track corresponding to each PTS in the PW through a big data analysis technology, a vehicle with forwarding qualification in a communication coverage area of a terminal vehicle in each PTS is recorded as a mobile alternative relay of the terminal vehicle in the corresponding PTS, and channel gains between the terminal vehicle and the mobile alternative relay, between the terminal vehicle and an RSU in a prediction window and between the mobile alternative relay and the RSU are estimated through mapping the predicted track by a radio environment map;
step two, based on bandwidth demand estimation:
estimating the bandwidth requirement of the transmission information stream of all the alternative transmission links in each PTS of the PW by the MEC server through the shannon theorem according to the predicted channel gain, wherein the bandwidth requirement is represented by the number of consumed PRBs; for a single-hop transmission link, the bandwidth requirement at PTS t is the bandwidth resource required for transmitting data between the roadside unit and the terminal automobile iFor a two-hop transmission link, bandwidth requirement at PTS t +.>Bandwidth resource +.>And the bandwidth resources required for transmitting data between the mobile alternative relay j to the terminal car i +.>Sum total
Step three, relay selection:
analyzing bandwidth requirements in PW, and determining transmission links of the next time slot for all terminal automobiles by the MEC server through a sliding window two-step relay selection scheme; the specific contents are as follows:
3.1, relay preselection:
in each PTS t of PW, a transmission link is preselected for all terminal automobiles with the minimum overall bandwidth requirement as a target, and the specific steps are as follows:
3.2, relay adjustment:
according to the preconfigured relay information in all PTSs obtained in the step 3.1, combining the relay information of the current time slot, and determining the transmission link of each terminal automobile in the next time slot;
step four, information release:
the MEC server forwards the transmission instruction to the roadside unit, the mobile relay and the terminal automobile to finish the release of the link information; and in the next time slot, carrying out information data transmission according to the link configuration instruction.
The specific steps of estimating the bandwidth requirement in the second step are as follows:
2.1, modeling an arrival stream as an MMBP video stream, and constructing an arrival of the MMBP arrival; uniformly modeling a service process as a poisson process, and constructing a service for each poisson service;
each PTS has L TTIs; a (m) is the number of arriving packets at the mth TTI,for the total number of data packets arriving cumulatively from TTI 0 to TTI n, n=1, 2,3, … … L, m=1, 2,3, … … n; s (m) is the number of packets served in the mth TTI,/for the number of packets served in the mth TTI>Indicating the total number of data packets to be accumulated for service from TTI 0 to TTI n;
reaching :
for the followingThe arrival of the build MMBP arrival procedure is:
M a (n)＝ha(a(n))e θ(A(0,n)-nKa) (1)
where θ is the decay index, ka and ha (a (n)) are parameters that depend on θ; t (T) θ An exponential transformation matrix representing MMBP process, sp (T θ ) Representing T θ Is the maximum eigenvalue of (2); arrival parameter for MMBP arrival satisfiesha (a (n)) is T θ Right feature vector of (2);
service :
for the followingThe services that construct the poisson service procedure are:
M s (n)＝hs(s(n))e θ(nKs-S(0,n)) (2)
wherein Ks and hs (s (n)) are parameters that are θ -dependent; e []Service parameters representing the expected poisson service satisfy ks= -lnE [ e ] -θs(n) ]/θ，hs(s(n))＝1；
2.2, according to QoS index, combining data flow, utilizing analysis frame to determine the needed service rate of roadside unit in single-hop transmission link when forwarding data flow;
w (n) represents the end-to-end delay of the single-hop transmission link in the nth TTI, and P { } represents the probability; the delay violation probability inequality in a single-hop transmission link is:
wherein W is max As a time delay threshold value, epsilon is the upper bound of the time delay violation probability;
H＝min{ha(a(n))hs(s(n)):a(n)-s(n)＞0,n≥0}，θ * ＝sup{θ＞0:Ka≤Ks}
according to the inequality of the delay violation probability of , determining the service data packet rate lambda packets/TTI meeting the QoS requirement by a dichotomy, and specifically calculating according to the following formula:
2.3, respectively determining the service rate required by the roadside units in the two-hop transmission link when forwarding the data stream and the service rate required by the alternative relay when forwarding the link by utilizing analysis frames according to QoS indexes and combining with the data flow;
the delay violation probability inequality in a two-hop transmission link is as follows: :
wherein Ks 1 And Ks 2 The service parameters corresponding to the first and second hops respectively,H＝min{ha(a(n)):a(n)＞0,n≥0}，θ * ＝sup{θ＞0:Ka≤Ks 1 ＝Ks 2 }；
according to the inequality of the delay violation probability of , the V2I channel service data packet rate lambda meeting the QoS requirement is determined by a dichotomy 1 packet/TTI and V2V channel service packet rate lambda 2 packets/TTI；
2.4, estimating the bandwidth requirement of all the alternative transmission links in each PTS when transmitting information streams by combining the predicted channel gain in the transmission links and the required service rate of each node on the links;
the size of the data packet is fixed as psi bits, and the PRB transmission quantity on each link is calculated according to the channel gain by means of shannon theorem;
in a single-hop transmission link, the PRB transmission quantity of a V2I channel is d bits, the required service data packet rate is lambda packets/TTI, and the bandwidth requirement of the link at PTS t is as follows:
in the two-hop transmission link, the PRB transmission quantity of the V2I channel is d 1 bits, the required service data packet rate is lambda 1 The PRB transmission quantity of the packet/TTI and the V2V channel is d 2 bits, the required service data packet rate is lambda 2 The bandwidth requirements of this link at PTS t are:
the specific content of the step 3.1 in the step three is as follows:
3.1.1, for each terminal car, sequencing the alternative transmission links of the current time slot according to the order of the time slot bandwidth requirement from small to large; here, a single-hop unrepeatered transmission link is represented by relay 0; for the terminal automobile i, the relay vector f is obtained after sequencing i And the bandwidth demand vector Φ of the corresponding link i The method comprises the steps of carrying out a first treatment on the surface of the The transmission link where the relay with the minimum bandwidth requirement is located is preselected for each terminal automobile, and the preselected relay of the terminal automobile i is f at the moment i,1 ；
3.1.2, for the terminal car i, determining whether its transmission link is a two-hop transmission link; if not, directly entering step 3.1.3; if the transmission link is a two-hop transmission link, determining the relay f of the forwarding link i,1 Whether to be simultaneously preconfigured to other terminal automobiles; if not, directly entering step 3.1.3; if so, then find that this preconfigured identical relay f i,1 Selecting a terminal car from the terminal cars i and i, and replacing a preselected transmission link;
the specific selection and replacement rules are as follows: calculating bandwidth requirement corresponding to current transmission link of terminal automobile i and replacing relay as relay f i,2 Bandwidth requirement phi corresponding to transmission link at the time i,2 Bandwidth demand difference phi between i,2 -Φ i,1 Similarly, the same operation is carried out on the i, and the bandwidth requirement difference before and after the i is replaced is obtained; comparing the bandwidth requirements before and after replacement with i, selecting a terminal automobile with smaller bandwidth requirements, and replacing a transmission link with bandwidth requirements inferior to the current bandwidth requirements; updating a corresponding relay vector and a bandwidth demand vector of a terminal automobile for replacing a link;
3.1.3 repeating step 3.1.2 for each terminal car until there are no more terminal cars pre-configured with the same relay at the same PTS.
In the third step, the relay adjustment in the step 3.2 is specifically as follows:
according to the preconfigured relay information in all PTSs obtained in the step 3.1, and combining the relay information of the current time slot, determining the transmission link of each terminal automobile in the next time slot, wherein the steps are as follows:
3.2.1, the alternative transmission link of the terminal automobile refers to the transmission link where the alternative relay or no relay alternative is located, and the alternative relay of the terminal automobile i in the next time slot comprises the relay of the terminal automobile i configured in the current time slot and the relay preconfigured in the PW; at the current time slot t 0 For each terminal car, refer to the relay information preconfigured per PTS within PW in step 3.1, as t 0 Alternative transmission link statistics for +1 slot at current slot t 0 And the number of times configured in K PTSs of PW, and sorting t according to the order of the configured times from big to small 0 For the transmission links with the same configuration times, the alternative transmission links with the time slots +1 determine the sequence according to the bandwidth requirement of the corresponding link of the next time slot, and the bandwidth requirement is small and the priority is high; for the terminal automobile i, the relay vector f is obtained after sequencing i And a configuration frequency vector fs i ；
3.2.2, pre-selecting a transmission link with the most configuration times of the relay for each terminal automobile as a transmission link of the next time slot;
3.2.3, for the terminal automobile i, determining whether the transmission link of the terminal automobile i is a two-hop relay forwarding link; if not, directly entering step 3.2.4; if the relay is a two-hop relay forwarding link, determining whether the relay of the forwarding link is simultaneously preconfigured to other terminal automobiles, if not, directly entering a step 3.2.4, if so, finding a terminal automobile i with the same preconfigured relay, selecting one terminal automobile from the i and the i, and replacing a preselected transmission link; the specific selection and replacement rules are as follows:
calculating the current transmission link, namely relay f, of terminal automobile i i,1 Corresponding to the linkThe number of times of allocation and the replacement relay is relay f i,2 The difference fs between the corresponding configuration times of the transmission links at the time i,1 -fs i,2 The same operation is carried out on the i, and the link configuration frequency difference before and after the i is replaced is obtained; comparing the difference of the link configuration times before and after the replacement of the i and the i, if the difference of the link configuration times is not equal, selecting a terminal automobile with smaller difference of the link configuration times, wherein the replacement configuration times is only inferior to the transmission link of the current link; if the configuration times are equal, calculating the sum lambda of the link bandwidth requirements corresponding to the terminal automobiles i and i when i is replaced by i is not replaced by i 1 And adding the sum lambda of the link bandwidth requirements corresponding to the terminal automobiles i and i when i is replaced by i and not replaced by i 2 The method comprises the steps of carrying out a first treatment on the surface of the Comparing the added bandwidth requirements under the two replacement modes, adopting a smaller replacement mode, and configuring the transmission link with the frequency inferior to that of the current link for the corresponding terminal automobile replacement; updating corresponding relay vectors and configuration times vectors of terminal automobiles for replacing links;
3.2.4, repeating the step of 3.2.3 for each terminal car until there are no more terminal cars configured with the same relay in the next time slot.
The invention has the beneficial effects that:
the invention provides a predictive multi-user joint relay selection strategy based on ; in MEC, the automobile track is predicted by a big data analysis technology, and is mapped into a radio environment map, so that the channel gain is predicted. In the bandwidth demand estimation, a -based bandwidth demand estimation method is proposed to accurately estimate the required bandwidth to meet specified QoS requirements. In the multi-user joint relay selection, a sliding window two-step relay selection scheme under the assistance of channel prediction is provided, and in the scheme, the bandwidth utilization rate is effectively improved, and the problem of frequent link switching caused by the vehicle network cooperative transmission technology is relieved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following description will briefly explain the drawings to be used in the description of the embodiments of the present invention, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the contents of the embodiments of the present invention and these drawings without inventive effort for those skilled in the art.
FIG. 1 is a scene graph of the present invention;
FIG. 2 is a flow chart of the general scheme of the present invention;
FIG. 3 is a sliding window two-step relay selection-relay pre-selection flow chart of the present invention;
FIG. 4 is a flow chart of a two-step relay selection-relay adjustment with sliding window according to the present invention;
fig. 5 is a schematic diagram showing the comparison of the total bandwidth consumption of each mobile terminal according to the present invention under different schemes;
fig. 6 is a schematic diagram illustrating comparison of link switching times of each mobile terminal under different relay selection schemes according to the present invention;
fig. 7 is a schematic diagram showing average user bandwidth consumption comparison of the sliding window two-step relay selection scheme of the present invention under different PWs;
fig. 8 is a schematic diagram showing average link switching times under different PWs according to the sliding window two-step relay selection scheme of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.
As shown in fig. 1, in the vehicle network, there is one RSU (road side unit), one MEC (Mobile Edge Computing ) server and a plurality of vehicles with forwarding capability; the number of the automobiles with forwarding capability is N, and M automobiles are mobile terminals for requesting data; in the unrepeatered transmission link, the requested data flow arrives at the RSU from the core network, and the data packet which cannot be immediately forwarded in the RSU is stored in the RSU to wait for transmission; in the relay forwarding link, the data flow arrives at the RSU from the core network, and the data packet which cannot be immediately forwarded in the RSU is stored in the RSU to wait for transmission; among the packets arriving at the mobile relay from the RSU, packets that can be immediately forwarded arrive at the mobile terminal from the mobile relay, and the remaining packets are buffered by the mobile relay and await transmission.
A predictive multi-user joint relay selection strategy based on in cooperative communication, comprising:
step one, channel prediction:
historical information about vehicle travel speed and road traffic is stored in an MEC server deployed on the wireless access network; k PTSs (prediction time slot, predicted transmission time slots) are arranged in one PW (prediction window, a prediction window), a MEC server predicts a vehicle track corresponding to each PTS in the PW through a big data analysis technology, records an automobile with forwarding qualification in a communication coverage area of a terminal automobile in each PTS as a mobile alternative relay of the terminal automobile in the corresponding PTS, and estimates channel gains between the terminal automobile and the mobile alternative relay, between the terminal automobile and an RSU and between the mobile alternative relay and the RSU in the prediction window through mapping the predicted track of a radio environment map;
step two, based on bandwidth demand estimation:
considering the stability of the link, we consider only a single-hop (no relay auxiliary forwarding) link and a two-hop (single relay auxiliary forwarding) link; according to the predicted channel gain, estimating, by the MEC server, in each PTS of the PW by shannon theorem, the bandwidth requirements of all alternative transmission links (including two-hop transmission links where alternative mobile relays are located and single-hop transmission links where no relay is located) transmission information flows, expressed by the number of consumed PRBs (physical resource block, physical resource blocks); for a single-hop transmission link, the bandwidth requirement at PTS t is the bandwidth resource required for transmitting data between the roadside unit and the terminal automobile iFor a two-hop transmission link, bandwidth requirement at PTS t +.>Bandwidth resource +.>And the bandwidth resources required for transmitting data between the mobile alternative relay j to the terminal car i +.>Sum->
The specific steps for estimating bandwidth requirements are as follows:
2.1, modeling an arrival stream as an MMBP video stream, and constructing an arrival of the MMBP arrival; uniformly modeling a service process as a poisson process, and constructing a service for each poisson service;
each PTS has L TTIs (transmission time interval ); a (m) is the number of arriving packets at the mth TTI,for the total number of data packets arriving cumulatively from TTI 0 to TTI n, n=1, 2,3, … … L, m=1, 2,3, … … n; s (m) is the number of packets served in the mth TTI,/for the number of packets served in the mth TTI>Indicating the total number of data packets to be accumulated for service from TTI 0 to TTI n;
reaching :
for the followingThe arrival of the build MMBP arrival procedure is:
M a (n)＝ha(a(n))e θ(A(0,n)-nKa) (1)
where θ is the decay index, ka and ha (a (n)) are parameters that depend on θ;
T θ representing MMBP procedureAn exponential transformation matrix, sp (T θ ) Representing T θ Is the maximum eigenvalue of (2); arrival parameter for MMBP arrival satisfiesha (a (n)) is T θ Right feature vector of (2);
service :
for the followingThe services that construct the poisson service procedure are:
M s (n)＝hs(s(n))e θ(nKs-S(0,n)) (2)
where θ is the decay index, ks and hs (s (n)) are parameters that depend on θ; e []Service parameters representing the expected poisson service satisfy ks= -lnE [ e ] -θs(n) ]/θ，hs(s(n))＝1；
2.2 according to QoS index (delay threshold W max The upper bound epsilon of the time delay violation probability) is combined with the data traffic (reaching the known value), and a analysis framework is utilized to determine the required service rate of the roadside units in the single-hop transmission link when forwarding the data stream;
w (n) represents the end-to-end delay of the single-hop transmission link in the nth TTI, and P { } represents the probability; the delay violation probability inequality in a single-hop transmission link is:
wherein W is max As a time delay threshold value, epsilon is the upper bound of the time delay violation probability;
H＝min{ha(a(n))hs(s(n)):a(n)-s(n)＞0,n≥0}，θ * ＝sup{θ＞0:Ka≤K s }
according to the inequality of the delay violation probability of , determining the service data packet rate lambda packets/TTI meeting the QoS requirement by a dichotomy, and specifically calculating according to the following formula:
2.3, respectively determining the service rate required by the roadside units in the two-hop transmission link when forwarding the data stream and the service rate required by the alternative relay when forwarding the link by utilizing analysis frames according to QoS indexes and combining with the data flow;
the delay violation probability inequality in a two-hop transmission link is as follows: :
wherein Ks 1 And Ks 2 The service parameters corresponding to the first and second hops respectively,H＝min{ha(a(n)):a(n)＞0,n≥0}，θ * ＝sup{θ＞0:Ka≤Ks 1 ＝Ks 2 }；
according to the inequality of the delay violation probability of , the V2I channel service data packet rate lambda meeting the QoS requirement is determined by a dichotomy 1 packet/TTI and V2V channel service packet rate lambda 2 packets/TTI；
2.4, estimating the bandwidth requirement of all the alternative transmission links in each PTS when transmitting information streams by combining the predicted channel gain in the transmission links and the required service rate of each node on the links;
the size of the data packet is fixed as psi bits, and the PRB transmission quantity on each link is calculated according to the channel gain by means of shannon theorem;
in a single-hop transmission link, the PRB transmission quantity of a V2I channel is d bits, the required service data packet rate is lambda packets/TTI, and the bandwidth requirement of the link at PTS t is as follows:
in the two-hop transmission link, the PRB transmission quantity of the V2I channel is d 1 bits, the required service data packet rate is lambda 1 The PRB transmission quantity of the packet/TTI and the V2V channel is d 2 bits, the required service data packet rate is lambda 2 The bandwidth requirements of this link at PTS t are:
step three, relay selection:
analyzing bandwidth demand in PW, determining transmission link of next time slot for all mobile terminals by MEC server through sliding window two-step relay selection scheme; fig. 2 is a flowchart of a sliding window two-step relay selection scheme, and the details are as follows:
3.1, relay preselection (fig. 3):
in each PTS t of PW, a transmission link is pre-selected for all mobile terminals with the minimum overall bandwidth requirement as a target, and the specific steps are as follows:
3.1.1, for each terminal car, sequencing the alternative transmission links of the current time slot according to the order of the time slot bandwidth requirement from small to large; here, a single-hop unrepeatered transmission link is represented by relay 0; for the terminal automobile i, the relay vector f is obtained after sequencing i And the bandwidth demand vector Φ of the corresponding link i The method comprises the steps of carrying out a first treatment on the surface of the The transmission link where the relay with the minimum bandwidth requirement is located is preselected for each terminal automobile, and the preselected relay of the terminal automobile i is f at the moment i,1 ；
3.1.2, for the terminal car i, determining whether its transmission link is a two-hop transmission link; if not, directly entering step 3.1.3; if the transmission link is a two-hop transmission link, determining the relay f of the forwarding link i,1 Whether to be simultaneously preconfigured to other terminal automobiles; if not, directly entering step 3.1.3; if so, then find that this preconfigured identical relay f i,1 I and selecting one of i and iA terminal car, replacing a preselected transmission link;
the specific selection and replacement rules are as follows: calculating the current transmission link (relay f) of terminal automobile i i,1 Located link) corresponding bandwidth requirements and replacement relay to relay f i,2 Bandwidth requirement phi corresponding to transmission link at the time i,2 Bandwidth demand difference phi between i,2 -Φ i,1 Similarly, the same operation is carried out on the i, and the bandwidth requirement difference before and after the i is replaced is obtained; selecting a terminal car with smaller bandwidth requirement difference compared with the bandwidth requirement difference before and after replacement of i and i, and replacing the transmission link with the bandwidth requirement which is inferior to the current bandwidth requirement (if phi i,2 -Φ i,1 <Φ i*,2 -Φ i*,1 Changing the transmission link of i to relay f i,2 A transmission link in which the transmission link is located); for the terminal car of the replacement link, updating the corresponding relay vector and the bandwidth demand vector (the first element in the reject vector) thereof;
3.1.3 repeating step 3.1.2 for each terminal car until there are no more terminal cars pre-configured with the same relay in the same PTS;
in the first step the goal of reducing the overall bandwidth requirements while meeting relay selection constraints is achieved.
3.2, relay adjustment (fig. 4):
link related information such as channel status, car position, etc. has a correlation in time, which means that for a certain mobile terminal, modifying the current relay selection with reference to future time slots does not lead to significant bandwidth demand changes. Therefore, we propose to determine the next slot relay selection by jointly analyzing the future relay selection and the current relay information, so as to improve the correlation of the relay selection in time, and further achieve the purpose of alleviating the problem of frequent switching of links. The specific mode is that the transmission link of each terminal car in the next time slot is determined according to the preconfigured relay information in all PTSs obtained in the step 3.1 and by combining the relay information of the current time slot, the steps are as follows:
3.2.1, the alternative transmission link of the terminal automobile refers to the transmission link where the alternative relay or no relay alternative is located, and the terminal automobile in the next time slotThe alternative relays of i comprise relays of the terminal automobile i configured in the current time slot and relays preconfigured in PW; at the current time slot t 0 For each terminal car, refer to the relay information preconfigured per PTS within PW in step 3.1, as t 0 Alternative transmission links of +1 time slot (including two-hop transmission links where alternative mobile relay is located and single-hop transmission links without relay) are counted at the current time slot t 0 And the number of times configured in K PTSs of PW, e.g., at t 0 +1PTS, for alternative relay x of mobile terminal i, if at current slot t 0 When the mobile terminal i is configured with the mobile relay x and a number of PTSs of the mobile relay x are preset for the mobile terminal i in PW, the configuration times corresponding to the alternative transmission links where the alternative relay x is positioned for the mobile terminal i are a+1; here we use relay 0 to represent a single hop unrepeatered transmission link, ordering t in order of configuration times from big to small 0 For the transmission links with the same configuration times, the alternative transmission links with the time slots +1 determine the sequence according to the bandwidth requirement of the corresponding link of the next time slot, and the bandwidth requirement is small and the priority is high; for the terminal automobile i, the relay vector f is obtained after sequencing i And a configuration frequency vector fs i ；
3.2.2 preselecting the transmission link of the relay with the highest allocation times for each terminal car as the transmission link of the next time slot (the preselecting relay of the terminal car i is f at the moment) i,1 )；
3.2.3, for terminal car i, determining if its transmission link is a two-hop relay forwarding link, (wherein if the preselected relay is relay 0 then the transmission link is a single-hop link, otherwise, a two-hop forwarding link); if not, directly entering step 3.2.4; if the relay is a two-hop relay forwarding link, determining whether the relay of the forwarding link is simultaneously preconfigured to other terminal automobiles, if not, directly entering a step 3.2.4, if so, finding a terminal automobile i with the same preconfigured relay, selecting one terminal automobile from the i and the i, and replacing a preselected transmission link; the specific selection and replacement rules are as follows:
computing terminal automobile iCurrent transmission link, i.e. relay f i,1 The corresponding configuration times of the link and the replacement relay are the relay f i,2 The difference fs between the corresponding configuration times of the transmission links at the time i,1 -fs i,2 The same operation is carried out on the i, and the link configuration frequency difference before and after the i is replaced is obtained; comparing the difference of the link configuration times before and after the replacement of the i and the i, if the difference of the link configuration times is not equal, selecting a terminal automobile with smaller difference of the link configuration times, wherein the replacement configuration times are only inferior to the transmission link of the current link (if fs i,1 -fs i,2 <fs i*,1 -fs i*,2 Changing the transmission link of i to relay f i,2 A transmission link in which the transmission link is located); if the configuration times are equal, calculating the sum lambda of the link bandwidth requirements corresponding to the terminal automobiles i and i when i is replaced by i is not replaced by i 1 And adding the sum lambda of the link bandwidth requirements corresponding to the terminal automobiles i and i when i is replaced by i and not replaced by i 2 The method comprises the steps of carrying out a first treatment on the surface of the Comparing the sum of the bandwidth requirements under the two replacement modes, adopting the replacement mode with smaller sum, and configuring the transmission link (if lambda) with the number of times being only inferior to that of the current link for the corresponding terminal automobile replacement 1 ＜Λ 2 Changing the transmission link of terminal i to relay f i,2 A transmission link in which the transmission link is located); updating a corresponding relay vector and a configuration times vector (discarding the first element in the vector) of the terminal automobile for replacing the link;
3.2.4 repeating the steps of 3.2.3 for each terminal car until there are no more terminal cars configured with the same relay in the next time slot;
in the second step, the frequent switching problem of the links in the first step is alleviated at the expense of part of the bandwidth benefit in the first step. Finally, under the limitation of relay selection, the joint relay selection of multiple users is realized, and the purposes of reducing bandwidth requirements and reducing link switching are achieved.
Step four, information release:
the MEC server forwards the transmission instruction to the roadside unit, the mobile relay and the terminal automobile to finish the release of the link information; and in the next time slot, carrying out information data transmission according to the link configuration instruction.
In order to verify the effectiveness of the predictive multi-user joint relay selection method provided by the embodiment, the effect of the method is verified through simulation. The simulation test examples are as follows:
1. simulation conditions:
referring to table 1, various parameters in the vehicle network are shown.
Table 1: parameter setting
| Simulation parameters | Simulation parameter values |
| Base station transmit power | 43dBm |
| Automobile emission power | 27dBm |
| Noise power | -55dBm |
| Prediction Window (PW) | 1,2,3,6,9s |
| Prediction Time Slot (PTS) | 0.5s |
| Data stream rate | 5.7Mbps |
| Time delay threshold W max | 40ms |
| Upper bound epsilon of delay violation probability | 10 -4 |
The embodiment of the invention simulates MATLAB. Assuming a coverage area of 600m for RSUs, a communication coverage area of 300m for cars. Modeling V2I channel we use a free space propagation model, and V2V channel we use a dual slope channel model. The frequency and time domains of the PRB are designed to be 180kHz and 0.5ms, respectively.
2. The simulation content:
in the vehicle network we assume a total of 20 vehicles with forwarding capability, including 6 mobile terminals requesting data. The experimental observation time of each group was set to 60s (120 slots).
We performed multiple sets of experiments. In the experiment 1, the duration of PW is 3s, we randomly generate initial track positions of 20 automobiles between-600 m and 0m, and randomly generate driving speeds of 20 automobiles between 30km/h and 40km/h, and we test the advantages of the method in the aspect of bandwidth utilization rate and link stability in the experimental observation time, and the experimental result is shown in fig. 5 and 6. In the remaining 10 groups of experiments, we randomly generated initial track positions of 20 automobiles and driving speeds thereof again according to the criteria of the first group of experiments, and tested pw=1, 2,3,6,9s in each group of experiments, respectively, the performance of the proposed method in terms of bandwidth utilization and link stability was shown in fig. 7 and 8.
3. Simulation result analysis:
fig. 5 shows a comparison of the total PRB consumption of each terminal vehicle in a no-relay transmission scheme (V2I only), a coordinated transmission scheme based on a single target relay selection (considering only bandwidth requirements), and a coordinated transmission scheme based on a sliding window two-step relay selection. As can be seen from fig. 5, the overall bandwidth consumption of the scheme based on the single target relay selection is lower than the overall bandwidth consumption of the scheme based on the method herein, because the relay selection method presented herein considers not only the bandwidth requirements but also the link switching. The total bandwidth consumption of the two cooperative transmission schemes is significantly lower than that of the unrepeatered transmission scheme, which indicates that the cooperative transmission scheme has an advantage in terms of bandwidth utilization performance.
Here, we evaluate the link stability using two indicators, the number of link switches and the link switch time interval. The link switch time interval is the time interval between adjacent switches. Fig. 6 shows the link switching related situation in the cooperative transmission scheme based on the single target relay selection and the cooperative transmission scheme based on the sliding window two-step relay selection, and each sub-graph in fig. 6 corresponds to the number of link switching times of each mobile terminal in the two cooperative transmission schemes under the specified switching time interval constraint. In combination with four sub-graphs with different switching time interval constraints, the cooperative transmission scheme based on the method herein is significantly lower in the number of link switches than the cooperative transmission scheme based on single target relay selection, which demonstrates our improvement in link stability.
Fig. 7 shows a ratio between the bandwidth consumption of the cooperative transmission scheme and the bandwidth consumption of the unrepeatered transmission scheme. Fig. 8 shows information related to link switching in a cooperative transmission scheme. In fig. 7 and 8, we statistically averaged the results of 10 sets of experiments. Fig. 7 records the statistical average bandwidth consumption ratio of the cooperative transmission scheme based on single target relay selection (pw=0 s) and the cooperative transmission scheme based on sliding window two-step relay selection (pw=1, 2,3,6,9 s) to the unrepeatered transmission scheme. It can be seen that as PW becomes larger, the bandwidth consumption ratio is large because the correlation of link-related information such as channel state, car position, etc. over time becomes weaker as the time interval is lengthened, and at the same time, the influence of the link state of the same slot on the relay selection becomes weaker as the number of slots of the prediction window increases. Fig. 8 records the number of link switches under different switch time interval constraints in two coordinated transmission schemes. It can be seen that as PW becomes larger, the number of link switching times becomes smaller, because the time correlation of relay selection becomes stronger as PW becomes larger.
The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the scope of the present invention is not limited to the specific details of the above embodiments, and within the scope of the technical concept of the present invention, any person skilled in the art may apply equivalent substitutions or alterations to the technical solution according to the present invention and the inventive concept thereof within the scope of the technical concept of the present invention, and these simple modifications are all within the scope of the present invention.
In addition, the specific features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various possible combinations are not described further.
Moreover, any combination of the various embodiments of the invention can be made without departing from the spirit of the invention, which should also be considered as disclosed herein.
Claims (4)
1. A predictive multi-user joint relay selection strategy based on , comprising the steps of:
step one, channel prediction:
historical information about vehicle travel speed and road traffic is stored in an MEC server deployed on the wireless access network; k PTSs are arranged in one PW, a MEC server predicts a vehicle track corresponding to each PTS in the PW through a big data analysis technology, a vehicle with forwarding qualification in a communication coverage area of a terminal vehicle in each PTS is recorded as a mobile alternative relay of the terminal vehicle in the corresponding PTS, and channel gains between the terminal vehicle and the mobile alternative relay, between the terminal vehicle and an RSU in a prediction window and between the mobile alternative relay and the RSU are estimated through mapping the predicted track by a radio environment map;
step two, based on bandwidth demand estimation:
estimating the bandwidth requirement of the transmission information stream of all the alternative transmission links in each PTS of the PW by the MEC server through the shannon theorem according to the predicted channel gain, wherein the bandwidth requirement is represented by the number of consumed PRBs; for a single hop transmission link, the bandwidth requirement at PTS t is roadside unit-to-roadsideBandwidth resource required by data transmission between terminal automobiles iFor a two-hop transmission link, bandwidth requirement at PTS t +.>Bandwidth resource +.>And the bandwidth resources required for transmitting data between the mobile alternative relay j to the terminal car i +.>Sum total
Step three, relay selection:
analyzing bandwidth requirements in PW, and determining transmission links of the next time slot for all terminal automobiles by the MEC server through a sliding window two-step relay selection scheme; the specific contents are as follows:
3.1, relay preselection:
in each PTS t of PW, a transmission link is preselected for all terminal automobiles with the minimum overall bandwidth requirement as a target, and the specific steps are as follows:
3.2, relay adjustment:
according to the preconfigured relay information in all PTSs obtained in the step 3.1, combining the relay information of the current time slot, and determining the transmission link of each terminal automobile in the next time slot;
step four, information release:
the MEC server forwards the transmission instruction to the roadside unit, the mobile relay and the terminal automobile to finish the release of the link information; and in the next time slot, carrying out information data transmission according to the link configuration instruction.
2. The predictive multi-user joint relay selection strategy based on of claim 1, wherein the estimating bandwidth requirements in step two comprises the following specific steps:
2.1, modeling an arrival stream as an MMBP video stream, and constructing an arrival of the MMBP arrival; uniformly modeling a service process as a poisson process, and constructing a service for each poisson service;
each PTS has L TTIs; a (m) is the number of arriving packets at the mth TTI,for the total number of data packets arriving cumulatively from TTI 0 to TTI n, n=1, 2,3, … … L, m=1, 2,3, … … n; s (m) is the number of packets served in the mth TTI,/for the number of packets served in the mth TTI>Indicating the total number of data packets to be accumulated for service from TTI 0 to TTI n;
reaching :
for the followingThe arrival of the build MMBP arrival procedure is:
M a (n)＝ha(a(n))e θ(A(0,n)-nKa)
where θ is the decay index, ka and ha (a (n)) are parameters that depend on θ; t (T) θ An exponential transformation matrix representing MMBP process, sp (T θ ) Representing T θ Is the maximum eigenvalue of (2); arrival parameter for MMBP arrival satisfiesha (a (n)) is T θ Right feature vector of (2);
service :
for the followingThe services that construct the poisson service procedure are:
M s (n)＝hs(s(n))e θ(nKs-S(0,n))
wherein Ks and hs (s (n)) are parameters that are θ -dependent; e []Service parameters representing the expected poisson service satisfy ks= -lnE [ e ] -θs(n) ]/θ，hs(s(n))＝1；
2.2, according to QoS index, combining data flow, utilizing analysis frame to determine the needed service rate of roadside unit in single-hop transmission link when forwarding data flow;
w (n) represents the end-to-end delay of the single-hop transmission link in the nth TTI, and P { } represents the probability; the delay violation probability inequality in a single-hop transmission link is:
wherein W is max As a time delay threshold value, epsilon is the upper bound of the time delay violation probability;
H＝min{ha(a(n))hs(s(n)):a(n)-s(n)＞0,n≥0}，
θ * ＝sup{θ＞0:Ka≤Ks}
according to the inequality of the delay violation probability of , determining the service data packet rate lambda packets/TTI meeting the QoS requirement by a dichotomy, and specifically calculating according to the following formula:
2.3, respectively determining the service rate required by the roadside units in the two-hop transmission link when forwarding the data stream and the service rate required by the alternative relay when forwarding the link by utilizing analysis frames according to QoS indexes and combining with the data flow;
the delay violation probability inequality in a two-hop transmission link is as follows: :
wherein Ks 1 And Ks 2 The service parameters corresponding to the first and second hops respectively,H＝min{ha(a(n)):a(n)＞0,n≥0}，
θ * ＝sup{θ＞0:Ka≤Ks 1 ＝Ks 2 }；
according to the inequality of the delay violation probability of , the V2I channel service data packet rate lambda meeting the QoS requirement is determined by a dichotomy 1 packet/TTI and V2V channel service packet rate lambda 2 packets/TTI；
2.4, estimating the bandwidth requirement of all the alternative transmission links in each PTS when transmitting information streams by combining the predicted channel gain in the transmission links and the required service rate of each node on the links;
the size of the data packet is fixed as psi bits, and the PRB transmission quantity on each link is calculated according to the channel gain by means of shannon theorem;
in a single-hop transmission link, the PRB transmission quantity of a V2I channel is d bits, the required service data packet rate is lambda packets/TTI, and the bandwidth requirement of the link at PTS t is as follows:
in the two-hop transmission link, the PRB transmission quantity of the V2I channel is d 1 bits, the required service data packet rate is lambda 1 The PRB transmission quantity of the packet/TTI and the V2V channel is d 2 bits, the required service data packet rate is lambda 2 The bandwidth requirements of this link at PTS t are:
3. the predictive multi-user joint relay selection strategy based on of claim 2, wherein the specific content of step 3.1 in the third step is as follows:
3.1.1, for each terminal car, sequencing the alternative transmission links of the current time slot according to the order of the time slot bandwidth requirement from small to large; here, a single-hop unrepeatered transmission link is represented by relay 0; for the terminal automobile i, the relay vector f is obtained after sequencing i And the bandwidth demand vector Φ of the corresponding link i The method comprises the steps of carrying out a first treatment on the surface of the The transmission link where the relay with the minimum bandwidth requirement is located is preselected for each terminal automobile, and the preselected relay of the terminal automobile i is f at the moment i,1 ；
3.1.2, for the terminal car i, determining whether its transmission link is a two-hop transmission link; if not, directly entering step 3.1.3; if the transmission link is a two-hop transmission link, determining the relay f of the forwarding link i,1 Whether to be simultaneously preconfigured to other terminal automobiles; if not, directly entering step 3.1.3; if so, then find that this preconfigured identical relay f i,1 Selecting a terminal car from the terminal cars i and i, and replacing a preselected transmission link;
the specific selection and replacement rules are as follows: calculating bandwidth requirement corresponding to current transmission link of terminal automobile i and replacing relay as relay f i,2 Bandwidth requirement phi corresponding to transmission link at the time i,2 Bandwidth demand difference phi between i,2 -Φ i,1 Similarly, the same operation is carried out on the i, and the bandwidth requirement difference before and after the i is replaced is obtained; comparing the bandwidth requirements before and after replacement with i, selecting a terminal automobile with smaller bandwidth requirements, and replacing a transmission link with bandwidth requirements inferior to the current bandwidth requirements; updating a corresponding relay vector and a bandwidth demand vector of a terminal automobile for replacing a link;
3.1.3 repeating step 3.1.2 for each terminal car until there are no more terminal cars pre-configured with the same relay at the same PTS.
4. The predictive multi-user joint relay selection strategy based on of claim 3, wherein the relay adjustment in step 3.2 in step three is specifically as follows:
according to the preconfigured relay information in all PTSs obtained in the step 3.1, and combining the relay information of the current time slot, determining the transmission link of each terminal automobile in the next time slot, wherein the steps are as follows:
3.2.1, the alternative transmission link of the terminal automobile refers to the transmission link where the alternative relay or no relay alternative is located, and the alternative relay of the terminal automobile i in the next time slot comprises the relay of the terminal automobile i configured in the current time slot and the relay preconfigured in the PW; at the current time slot t 0 For each terminal car, refer to the relay information preconfigured per PTS within PW in step 3.1, as t 0 Alternative transmission link statistics for +1 slot at current slot t 0 And the number of times configured in K PTSs of PW, and sorting t according to the order of the configured times from big to small 0 For the transmission links with the same configuration times, the alternative transmission links with the time slots +1 determine the sequence according to the bandwidth requirement of the corresponding link of the next time slot, and the bandwidth requirement is small and the priority is high; for the terminal automobile i, the relay vector f is obtained after sequencing i And a configuration frequency vector fs i ；
3.2.2, pre-selecting a transmission link with the most configuration times of the relay for each terminal automobile as a transmission link of the next time slot;
3.2.3, for the terminal automobile i, determining whether the transmission link of the terminal automobile i is a two-hop relay forwarding link; if not, directly entering step 3.2.4; if the relay is a two-hop relay forwarding link, determining whether the relay of the forwarding link is simultaneously preconfigured to other terminal automobiles, if not, directly entering a step 3.2.4, if so, finding a terminal automobile i with the same preconfigured relay, selecting one terminal automobile from the i and the i, and replacing a preselected transmission link; the specific selection and replacement rules are as follows:
calculating the current transmission link, namely relay f, of terminal automobile i i,1 The corresponding configuration times of the link and the replacement relay are the relay f i,2 The difference fs between the corresponding configuration times of the transmission links at the time i,1 -fs i,2 The same operation is carried out on the i, and the link configuration frequency difference before and after the i is replaced is obtained; comparing the difference of the link configuration times before and after the replacement of the i and the i, if the difference of the link configuration times is not equal, selecting a terminal automobile with smaller difference of the link configuration times, wherein the replacement configuration times is only inferior to the transmission link of the current link; if the configuration times are equal, calculating the sum lambda of the link bandwidth requirements corresponding to the terminal automobiles i and i when i is replaced by i is not replaced by i 1 And adding the sum lambda of the link bandwidth requirements corresponding to the terminal automobiles i and i when i is replaced by i and not replaced by i 2 The method comprises the steps of carrying out a first treatment on the surface of the Comparing the added bandwidth requirements under the two replacement modes, adopting a smaller replacement mode, and configuring the transmission link with the frequency inferior to that of the current link for the corresponding terminal automobile replacement; updating corresponding relay vectors and configuration times vectors of terminal automobiles for replacing links;
3.2.4, repeating the step of 3.2.3 for each terminal car until there are no more terminal cars configured with the same relay in the next time slot.
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