CN103458523A - Vehicle-mounted communication system wireless resource scheduling method - Google Patents

Abstract

The invention provides a vehicle-mounted communication system wireless resource scheduling method, and aims at providing the scheduling method which allows the overall performance of a vehicle-mounted communication system to be improved, allows the fairness of users to be guaranteed and allows the requirements of the users for different services to be met so that the fairness of communication between OBUs at different speeds and an RSU in the vehicle-mounted communication system can be better improved and the time delay requirements of various vehicle-mounted communication services can be met. The method includes the steps that the RSU judges state information of a vehicle, obtains location formation and movement information of the vehicle in the activated state and obtains a speed priority factor of the OBUs, service priority factors of the OBUs are obtained according to the requirements for the service types and the service quality of the OBUs, the channel quality between each OBU and the RSU is obtained according to the location information of the vehicle, the real-time transmission rates of the OBUs are calculated, fairness priority factors are obtained through calculation of the real-time transmission rates of the OBUs, the user priorities of the OBUs are obtained through a scheduling algorithm according to the speed priority factors, the service priority factors and the fairness priority factors, data are transmitted and the average transmission rate is updated and recorded according to the priority sequence, vehicle information and channel information are updated, and the scheduling process is not stopped until the circulation stops.

Description

A kind of Vehicular communication system scheduling method for wireless resource

Technical field

The present invention relates to a kind of scheduling method for wireless resource that is applied to Vehicular communication system, purpose is to introduce time-varying characteristics and the kinetic characteristic of vehicle and the quality of service requirement of distinguishing different business of channel, thereby improve the entire throughput of system, and guarantee fairness; Be applicable in Vehicular communication system.

Background technology

Traditional packet scheduling is applicable to Packet data service, arrive the random distribution characteristics of the time interval and block length for grouping, thereby the business to packet data user manages and dispatches, and come the order and spendable bit rate of concrete decision transmitted in packets by dispatching algorithm.Simultaneously, because there is the wireless channel decline situation constantly changed, needs to consider the time-varying characteristics of wireless channel, thereby improve the efficiency of system, comprise system frequency diversity gain, time diversity gain and multi-user diversity gain.This technology has become the core technology of current various types of communication system.No matter be which kind of mobile communication system, the design of dispatching algorithm should take into full account user's condition, and takes into account the fairness of different user, and the quality of service requirement of the discrimination of business is required to QoS, such as packet delay and transmission rate etc.

In existing Vehicular communication system, what it adopted is the DCF distributed coordination function based on competition in IEEE 802.11 standards, it is the mode that CSMA/CA is avoided in carrier sense/collision, the purpose at design initial stage is than the circlet border for mobility such as WLAN (wireless local area network), specifically comprise carrier detect mechanism, interFrameGap and random back flow process, use the distribution Access Algorithm of CSMA mechanism on each node, and allow each station obtain transmission route by the competition to channel, and for fear of collision, after all stations complete transmission, must continue to monitor and the interval of waiting for a period of time after just can send next frame, the type decided of the frame that wherein length of interFrameGap is sent by this station, the stand-by period of high priority is very short, can comparatively fast obtain transmission route, and the meeting of low priority is postponed transmission, when channel transfers the free time to from doing, each website just need to enter contention window and calculate random back and access channel busy channel resource after the time, wherein, IEEE 802.11 is used binary exponential backoff algorithm.When the vehicle-carrying communication business for different, employing arranges the size of different competition window parameter contention window minimum CWmin and competition window maximum CWmax and is distinguished, existing most improvement for scheduling of resource pattern in Vehicular communication system, mainly, all based on the CSMA/CA mode, the priority relevant with the Competition adjustment window has arranged.

But the decline for the vehicle-carrying communication wireless channel of continuous variation, the instant wireless channel become is the scheduling mode based on traditional 802.11 still, do not take into full account the concrete condition of channel, caused the weakening of overall system performance, and do not taken into full account for fairness factor between the vehicle of the different speeds of service yet, the factors such as the relative position of needs consideration vehicle and the speed of service, and only by being set, the long minimum value of different contention window and maximum carry out the differentiated service grade, the QoS requirement of the assurance business that such setting can not be desirable.

Summary of the invention

The object of the present invention is to provide a kind of dispatching method of Vehicular communication system, not only can increase the entire system performance, can guarantee the QoS requirement of different business again, guarantee the delay requirement of all kinds of vehicle-carrying communication business, the fairness of better communicating by letter between the mobile unit OBU of different travel speeds and roadside equipment RSU in elevator system.

For achieving the above object, the invention provides a kind of scheduling method for wireless resource of Vehicular communication system, it is characterized in that comprising following steps:

1) roadside equipment judges the state information of vehicle, obtains positional information and the movable information of vehicle under state of activation, obtains the speed priority factors of mobile unit;

2) state of activation by vehicle generates its type of service, obtains the service priority factor of mobile unit according to the quality of service requirement of business;

3) positional information and the movable information by vehicle obtains the channel quality between each mobile unit and roadside equipment, tries to achieve the real-time Transmission speed of mobile unit, and draws the fairness priority factors by the real-time Transmission rate calculations of mobile unit;

4) according to dispatching algorithm, drawn the User Priority of mobile unit by speed priority factors, the service priority factor, fairness priority factors, sequential delivery data according to priority, upgrade and record average transmission rate;

5) upgrade information of vehicles and channel information, the continuous dispatching process is to loop termination.

Method of the present invention also comprises a step: when the mobile unit of access vehicle-carrying communication network is that the user is while leaving the coverage of roadside equipment, nullifying this User Status is 0, cancel the channel condition under this wireless link of feedback, without the priority of calculating this user, reduce operand, if judgement is still in this coverage, this user is still state of activation 1.

After reading by reference to the accompanying drawings the detailed description of embodiment of the present invention, it is clearer that the other features and advantages of the invention will become.

The accompanying drawing explanation

Fig. 1 is Vehicular communication system dispatching method overall flow figure of the present invention;

Fig. 2 is different speed of a motor vehicle vehicle operating fairness schematic diagrames;

Fig. 3 is onboard system dispatching algorithm and CSMA/CA performance comparison diagram;

Fig. 4 is the performance map of each business under the vehicle dispatching algorithm;

Fig. 5 is fairness performance comparison diagram;

Embodiment

Below will be elaborated to embodiments of the present invention.Fig. 1 is Vehicular communication system dispatching method overall flow workflow graph of the present invention.This flow process starts from step S101, by the position of RSU, transmitted power P, highly, position, coverage etc. set, and generate OBU number K, set the total timeslot number of emulation simultaneously and be loop iteration total degree N, noise power σ, channel width W.

Then, at step S102, according to the mobile unit initial number, K generates motion model at random, specifically be included in the position in the roadside unit coverage, comprise two components of x axle and y axle, two directions of motion of mobile unit: forward is with reverse, and the movement velocity v of mobile unit, and the initialization mobile unit is state of activation; The relative distance D that draws and store mobile unit and roadside unit according to positional information carries out the estimation of wireless channel large scale decline path loss for S104, user in order to ensure the different speed of a motor vehicle obtains relatively consistent volume of services in the same area, has introduced speed priority factors V _i, excessive for fear of speed priority factors proportion, set V _i=log (v), calculate and preserve the calculating of the speed priority factors V=log (v) of mobile unit for dispatching algorithm S106 medium priority.

At step S103, obtained the service priority factor of mobile unit by the requirement of type of service and service quality thereof.At first whether generate at random different types of service according to the state of activation of mobile unit, in conjunction with actual vehicle-carrying communication business demand the vehicle-mounted service application Voice of three classes, Video are set respectively, the patient maximum delay τ of Best effort is 80ms, 280ms and 5000ms, it is 0.01 that the tolerable max-timeout grouping of three class service application ratio δ is set, 0.01,0.01, calculate respectively the service priority factor of whole mobile units according to quality of service requirement, wherein the service priority factor of k mobile unit is a _k=-log (δ _k)/τ _k; For each mobile unit user, the business datum buffer area is set simultaneously, records each user's a business datum buffer memory sector time delay, remove its buffer area array head of the queue after a certain user is scheduled, the data forward direction assignment of back buffer area queue.

After completing above-mentioned steps, start step S104, the roadside equipment obtained in conjunction with S102 and the relative distance D of mobile unit RSU-OBU, the path loss model of calculating the large scale decline is 2 power attenuation channel H1, the random small scale Rayleigh fading that generates channel is H2, and the signal power that can obtain the roadside equipment that each mobile unit receives is PH1 _k| H2 _k| ², show that substitution channel capacity formula after signal to noise ratio snr gets final product to obtain the instantaneous transmission speed of the user k in the S105 step, i.e. r _k=Wlog ₂(1+SNR _k), SNR wherein _k=PH1 _k| H2 _k| ²/ σ, σ is noise power, W is channel width, the average transmission rate R of whole mobile units during initialization _kbe 1, the fairness priority factors of calculating user k is

calculating for the subsequent process dispatching algorithm.

At step S106, the priority that completes most critical is calculated and compares, according to dispatching algorithm, bring speed priority factors, the service priority factor, fairness priority factors into following formula for n scheduling unit, obtaining the priority of user i in n scheduling unit is Q _{i, n}=a _{i, n}f _{i, n}v _{i, n}, the regulation goal of this channel is J=arg max{Q _{i, n}.

While carrying out step S107, according to the priority orders in S106, distribute time slot according to tdma TDMA mode successively, complete the data transmission.Then according to new formula more, average transmission rate is upgraded

wherein and if only if, and t just averages the transmission rate renewal according to above formula at t+1 when k user is scheduled for constantly constantly, otherwise

t is window parameter update time, and T is larger, and throughput is larger, but the required stand-by period is longer.

Due to the introducing of speed priority factors, the fairness of A car and the service of B car in raising Fig. 2 scene that can be fabulous, ensure that leaving regional vehicle B also can obtain the service quality same with A.

Finally, while carrying out step S108, in iterative process, after the circulation of scheduling unit, return to the relative position that step S202 calculates each mobile unit and roadside unit at every turn, judge whether still in the coverage of roadside unit, if in coverage, not putting this mobile unit is exit state, if mobile unit is state of activation in coverage, upgrades movement position and the channel information of vehicle, and continue it is completed to scheduling process; During the dispatching algorithm iteration, judge whether to arrive iterations N, arrive end loop; Arrive when iterations or rolling stock are exit state and finish scheduling process.Pass through the time delay array of recorded average transmission rate and storage, the throughput that the system that calculates is total and time delay distribution curve and the fair index of each business, its calculating formula is the fair index of Raj Jain usually adopted:

$F\left(K\right)=\frac{{\left({\mathrm{\Σ}}_{i=1}^K{R}_i\right)}^2}{K{\mathrm{\Σ}}_{i=1}^K{R}_i^2}$

Wherein K is number of users, R _ifor the average transmission rate of user i, when fair index F is larger, the fairness of system is better, F=1 when user's normalizing rate equates.

Although more than described the specific embodiment of the present invention and accompanying drawing, but those of skill in the art in the art are to be understood that, these only illustrate, and can make various changes or modifications to these execution modes, and not deviate from principle of the present invention and essence.Scope of the present invention is only limited by appended claims.

Following table 1 is simulation system parameters.

Table 1 system parameters

The RSU height	1.5m
		The RSU coverage	200m
The RSU transmitted power	44.8dBm
		Noise power	9dB
Slot length	13μs
		Update time window	20ms
Vehicle speed range	5-50m/s
		Channel width	10MHz

Fig. 3 is for adopting throughput of system performance comparison diagram under two kinds of different source scheduling modes, along with the increase that sends packet, the dispatching algorithm proposed due to this paper has better adopted the channel time-varying characteristics, has selected higher being used for of channel quality to transmit, and has therefore obtained the lifting of overall performance.

Fig. 4 shows the performance map of distinguishing each business under the vehicle dispatching algorithm, Voice business, Video business and Best effort business all are guaranteed for the requirement of time delay as shown in the figure, be less than respectively 100ms, 300ms and 500ms, obtained satisfied QoS requirement.

Shown in Fig. 5, give expression to after considering system average transmission rate and motion model fairness, the lifting of total system fairness index, be better than the mode of CSMA/CA.

Claims (6)

1. the scheduling method for wireless resource of a Vehicular communication system is characterized in that comprising following steps:

1) roadside equipment judges the state information of vehicle, obtains positional information and the movable information of vehicle under state of activation, obtains the speed priority factors of mobile unit;

2) obtained the service priority factor of mobile unit by the requirement of type of service and service quality thereof;

3) positional information by vehicle obtains the channel quality between each mobile unit and roadside equipment, tries to achieve the real-time Transmission speed of mobile unit, and draws the fairness priority factors by the real-time Transmission rate calculations of mobile unit;

4) according to dispatching algorithm, drawn the User Priority of mobile unit by speed priority factors, the service priority factor, fairness priority factors, sequential delivery data according to priority, upgrade and record average transmission rate;

5) upgrade information of vehicles and channel information, the continuous dispatching process is to loop termination.

2. according to the method for claim 1, it is characterized in that the state information of roadside equipment judgement vehicle, obtain positional information and the movable information of vehicle under state of activation, the step that obtains the speed priority factors of mobile unit comprises the following steps:

1) generate at random motion model according to mobile unit initial number K, specifically be included in the position in the roadside equipment coverage: comprise two components of x axle and y axle, two directions of motion of mobile unit: forward is with reverse, and the movement velocity v of mobile unit, the initialization mobile unit is state of activation;

2) according to 2) positional information calculation that draws store mobile unit and the relative distance D of roadside equipment, for carrying out the decline of wireless channel large scale, estimate, the speed priority factors V=log (v) that calculates simultaneously and preserve mobile unit is applied to dispatching algorithm.

3. method according to claim 1 is characterized in that requirement by type of service and service quality thereof obtains the step of the service priority factor of mobile unit as follows:

1) according to the different type of service of the random generation of the state of activation of mobile unit, in conjunction with actual vehicle-carrying communication business demand the vehicle-mounted service application Voice of three classes, Video are set respectively, the patient maximum delay τ of Best effort is 80ms, 280ms and 5000ms, it is 0.01 that the tolerable max-timeout grouping of three class service application ratio δ is set, 0.01,0.01, calculate respectively the service priority factor of whole mobile units according to quality of service requirement for dispatching algorithm calculating priority level order, the service priority factor that k mobile unit arranged is a _k=-log (δ _k)/τ _k;

2) for each mobile unit user, the business datum buffer area is set, records each user's a business datum buffer memory sector time delay, remove its number of buffer head that forms a team after a certain user is scheduled, the data forward direction assignment of back buffer area queue.

4. method according to claim 1, it is characterized in that obtaining the channel quality between each mobile unit and roadside equipment by the positional information of vehicle, try to achieve the real-time Transmission speed of mobile unit, and show that by the real-time Transmission rate calculations of mobile unit the step of fairness priority factors is as follows:

1), in conjunction with the roadside equipment obtained and the relative distance D of mobile unit, the path loss model of calculating the large scale decline is 2 power attenuation channel H1,

2) the small scale Rayleigh fading that generates at random channel is H2, and the signal power that can obtain the roadside equipment that each mobile unit receives is PH1 _k| H2 _k| ², show that substitution channel capacity formula after signal to noise ratio snr gets final product to obtain the instantaneous transmission speed of user k, i.e. r _k=Wlog ₂(1+SNR _k); SNR wherein _k=PH1 _k| H2 _k| ²/ σ, σ is noise power, W is channel width, the average transmission rate R of whole mobile units during initialization _kbe 1, the fairness priority factors of calculating user k is

calculating for dispatching algorithm.

5. method according to claim 1, it is characterized in that according to dispatching algorithm, drawn the User Priority of mobile unit by speed priority factors, the service priority factor, fairness priority factors, sequential delivery data according to priority, upgrade and to record the step of average transmission rate as follows:

1) according to dispatching algorithm, bring speed priority factors, the service priority factor, fairness priority factors into following formula for n scheduling unit, obtaining the priority of user i in n scheduling unit is Q _{i, n}=a _{i, n}f _{i, n}v _{i, n}, the regulation goal of channel is J=argmax{Q _{i, n}, after obtaining user's priority orders, then distribute time slot according to the mode of time division multiple access TDMA successively, complete the data transmission;

2) then according to new formula more, average transmission rate is upgraded

wherein and if only if, and t just averages the transmission rate renewal according to above formula at t+1 when k user is scheduled for constantly constantly, and T is window parameter update time, and T is larger, and throughput is larger, but the required stand-by period is longer.

6. method according to claim 1, is characterized in that upgrading information of vehicles and channel information, and the continuous dispatching process is as follows to the step of loop termination:

1) in iterative process, each after the circulation of scheduling unit, recalculate the relative position of each mobile unit and roadside equipment, judge that mobile unit is whether still in the coverage of roadside equipment, if in coverage, not putting this mobile unit is exit state, without the business to this vehicle, dispatched, if be still state of activation in coverage, proceed scheduling, and upgrade information of vehicles and channel information;

2) during the dispatching algorithm iteration, judge whether to arrive iterations N, arrive when iterations or rolling stock are exit state and finish end loop of scheduling process; Pass through the time delay array of recorded average transmission rate and storage, the throughput that the system that calculates is total and time delay distribution curve and the fair index of each business, its calculating formula is the fair index of Raj Jain usually adopted:

$F\left(K\right)=\frac{{\left({\mathrm{\Σ}}_{i=1}^K{R}_i\right)}^2}{K{\mathrm{\Σ}}_{i=1}^K{R}_i^2}$

Wherein K is number of users, R _ifor the average transmission rate of user i, when fair index F is larger, the fairness of system is better, F=1 when user's normalizing rate equates.

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