CN101026577A - Scheduling method for ensuring time delay stability of non-real-time business data packet for OFDMA system - Google Patents

Abstract

Improving jitter performance of time delay of C-MCPFS proportion fairness algorithm in multicarrier system, the disclosed method accomplishes allocation of frequency resources. The method includes following five operation steps: (1) preparative step for partitioning resources, and setting up initialization parameters; (2) step for feeding back information of channel state; (3) step for allocating RB resources; (4) data transmission step; (5) step for estimating time delay of data packet. Considering channel state of user and practical transfer rate of traffic in scheduling process, the method keeps good proportion fairness performance. Two points of innovation are: introducing time delay control mechanism, and estimating time delay of data packet. The method provides smooth data rate for transmission layer, and keeps efficiency and fairness of C-MCPFS algorithm.

Description

The dispatching method that in the OFDMA system, ensures time delay stability of non-real-time business data packet

Technical field

The present invention relates to the dispatching method that a kind of OFDMA of being used for system ensures time delay stability of non-real-time business data packet, belong to the scheduling of resource technical field in the radio communication.

Background technology

Along with the continuous development of wireless communication technology, the fusion of wireless network and Internet becomes the main flow trend of Communication Development from now on, and traditional Cellular Networks based on circuit-switched service has begun constantly to develop along the network configuration of all-IP.In such network configuration, all business all will be based on packet switching, and all packets all need be dispatched by systematic unity.

Scheduling of resource plays critical effect for the performance that ensures wireless communication system.On the one hand,, consider the difference of the residing geographical environment of different user, resource allocation is given channel conditions user preferably as far as possible, realize effective utilization Radio Resource from throughput of system; On the other hand, guarantee the different service quality QoS of all types of user (Quality-of-Service) requirement, realize the resource justice, reasonably distribute.

In packet network, one of topmost qos requirement is embodied in the degrees of tolerance of business data packet to time delay, according to this principle, usually general Packet data service is divided into real time business and non-real-time service.Real time business is relatively more responsive to the time delay of packet, and as business such as VOIP (Voice over IP), video flowings, but this type of business does not have strict requirement to packet loss, and transport layer generally adopts UDP (User DatagramProtocol) agreement; Non-real-time service is lower to delay requirement, and as business such as FTP, HTTP, for the business of this type, the reliability that needs the strict guarantee data to transmit is so transport layer generally adopts TCP (Transfer Control Protocol) agreement.The present invention mainly considers the scheduling of non-real-time service.

Owing to have good anti-frequency selective characteristic, OFDM (OFDM) technology has become one of mainstream technology that solves WiMAX access of future generation, and has been adopted as the physical layer key technology by each big standards such as 3GPP LTE (Long termevolution), IEEE 802.16.OFDM OFDMA technology based on OFDM can realize the orthogonality between each user in the sub-district, thereby has avoided inter-user interference effectively.In OFDM OFDMA system, whole frequency band is divided into the subband of some near flat declines, in same Transmission Time Interval TTI (Transmission time interval), can choose a plurality of users simultaneously and utilize different frequency bands to carry out transfer of data.Compare with single-carrier system, from system perspective, in scheduling process, except the time domain specification that can utilize the subscriber channel situation obtains certain multi-user diversity gain, the multichannel parallel transmission characteristic of OFDMA system has also further been expanded the space of multi-user diversity gain at frequency domain.From user perspective, owing to utilize different frequency ranges to carry out transfer of data, can obtain certain frequency diversity gain, in conjunction with certain frequency-domain-interleaving and error correction coding, can improve reliability of data transmission greatly.

Resource scheduling at wireless network, especially single-carrier system, a large amount of achievements in research has been arranged, and three kinds of wherein the most representative algorithms are max carrier to interference (Max C/I) algorithms, poll (Roundrobin) algorithm and equitable proportion (Proportional fair) algorithm.In the max carrier to interference algorithm, in each scheduling constantly, system all chooses the best user of current channel conditions and carries out transfer of data, and this scheduling mechanism can greatly improve the throughput of system, has good validity; But there is great unjustness, because most of user far away from the base station can not get the chance of transfer of data basically because the carrier/interface ratio of received signal is lower.The polling algorithm user in the dispatching patcher successively carries out transfer of data, strict guarantee the fairness of resource allocation, but owing to do not consider user's channel conditions, probably resource allocation is given the user of channel conditions very severe, can not realize effective utilization Radio Resource.

So, in the scheduling process of reality, take into account system and user's requirement, must be to the processing of compromising of the validity of resource allocation and fairness.For realizing this goal, IS-95/CDMA2000 1x HDR (High data rate) system at first introduces equitable proportion algorithm (" CDMA/HDR:A bandwidthefficient high speed data service for nomadic users ", IEEE Comm.Magazine, July, 2000.).About equitable proportion, on economics, provided strict definition.For the dispatching algorithm S of any wireless network resource, when algorithm P satisfies $\mathrm{\Σ}(R_i^{\left(S\right)}-R_i^{\left(P\right)})/R_i^{\left(P\right)}\≤0,i\∈U$ The time, promptly having reached the target of equitable proportion, the raising of any one user performance must cause the decline of entire system performance in this moment system.Wherein U represents the user's set in the system, R _i ^(S), R _i ^(P)Dispatching algorithm S is adopted in expression respectively, during P, and the data rate of user i.In addition, the elementary object of equitable proportion is to make target function ∑ log (R _i ^(S)), it is maximum that i ∈ U reaches, and wherein utility function log () is used to reflect the satisfaction of user to message transmission rate; Above-mentioned target function is exactly to make the effectiveness sum of all users in the system reach maximum.For single-carrier system, reach above-mentioned target, in each scheduling constantly, need according to $j=\arg \mathrm{ma}{x}_i{r}_i/\stackrel{\‾}{R_i},$ I ∈ U chooses user j and carries out transfer of data, wherein r _iThe maximum data rate of the current support of expression user i,

The mean data rate that expression user i reaches.The equitable proportion algorithm is when utilizing the subscriber channel state information, considered the message transmission rate of each user's reality, guarantee to transmit data under the situation relatively preferably in the subscriber channel situation as far as possible, both embody the fairness between the user, realized effective utilization of Radio Resource again to a certain extent.

Generally speaking, single-carrier system HDR has only a user to carry out transfer of data in same scheduling constantly.And in the OFDMA system, the subband owing to whole frequency band being divided into a plurality of parallel transmissions can have a plurality of users to transmit data at synchronization.So in scheduling process, not only will consider the time domain specification of channel conditions, also need to embody the frequency selectivity of channel.Equitable proportion under the multicarrier condition passes through $P=\arg {\max }_S\underset{i\∈U}{\mathrm{\Π}}(1+\underset{k\∈C_i}{\mathrm{\Σ}}{r}_{i,k}/(T-1)\stackrel{\‾}{R_i}),$ I ∈ U realize optimal solution (referring to " A proportional fairscheduling for multicarrier transmission systems ", publish in IEEE Commun.Lett., vol.9, no.3, pp.210-212, Mar.2005.), r wherein _{I, k}The maximum data rate that expression current time user i supports at subband k,

Expression user's mean data rate, T represents the update cycle of user's mean data rate, has reflected the sensitivity of algorithm to channel state variations to a certain extent, if T is less, relatively more responsive to the variation of channel, vice versa.Can find out that from following formula the optimal solution problem of equitable proportion is a combinatorial optimization problem under the multicarrier condition, because the combined expanded characteristic of this problem, the complexity of realization is higher, is difficult to realize in engineering.

A kind of fairly simple C-MC-PFS (Conventional multi-carrier proportional fairscheduling) algorithm is (referring to " System level performance of OFDMA forward link withproportional fair scheduling ", publish in Proc.IEEEPIMRC, vol.2, Sept.2004, pp.1384-1388.) realize in real system than being easier to that this algorithm is the simple extension of equitable proportion algorithm in multicarrier system in the HDR system.In each scheduling constantly, be followed successively by each frequency band according to k (n)=arg max _kr _{K, n}(t)/R _k' (t) select the user, promptly at subscriber channel situation transmission data, wherein r preferably the time _{K, n}(t) represent the data rate that user k supports, R on frequency band n _k' (t) expression is by the t mean data rate of user k constantly.This algorithm has realized the equitable proportion of multicarrier system for the present invention bigger reference value being arranged by simple and practical expansion.

Because the equitable proportion algorithm is not considered concrete qos requirement, generally is applicable to non-real-time service, as FTP, HTTP etc.This type of business does not have strict requirement to the time delay of packet, but need use Transmission Control Protocol to guarantee the reliability of transmitting in transport layer.TCP reduces professional packet loss by overtime re-transmission or quick the re-transmission, in predefined retransmission time out time RTO (Retransmission Timeout), do not receive the correct answer signal of the packet that is sent when transmitting terminal, just think that this packet loses in network, need retransmit at transmitting terminal.RTO obtains according to RTT return interval of data packets for transmission (Round trip time) estimation, reflected current network bandwidth to a certain extent, so if the variation of the RTT between the packet is more violent, just be difficult to the RTO of estimation follow-up data bag.If estimated value is too small, will cause unnecessary retransmission continually, the waste system bandwidth; Otherwise, then can cause the long wait of transmitting terminal, greatly influenced user's data speed.

In Cellular Networks, the time delay of packet mainly comprises two parts: Access Network time delay and core net time delay.The Access Network time delay depends mainly on the RRM strategy that system adopts, and the core net time delay depends mainly on the queuing policy that router adopts and the load state of network.The present invention mainly considers the influence of the dispatching algorithm of Access Network part to data packet delay characteristic.Traditional C-MC-PFS has guaranteed the coordination between the user throughput when considering the subscriber channel situation, the validity and the fairness of the utilization of resources have been carried out good compromise processing.But because the dynamic change of subscriber channel situation very likely causes the instability of user resources distribution, thereby cause the instability of packet time delay, cause the deterioration of transport layer performance.

Summary of the invention

In view of this, the purpose of this invention is to provide the dispatching method that a kind of OFDMA of being used for system guarantees the packet delay stability of time of non-real-time service, this method can provide smoother data rate for transport layer, and can keep the validity and the fairness of C-MCPFS algorithm preferably.

In order to achieve the above object, the invention provides a kind of dispatching method that orthogonal frequency division multiplexing multiple access OFDMA system ensures time delay stability of non-real-time business data packet that is used for, it is characterized in that: this method is improved by the delay variation performance to traditional multicarrier Proportional Fair C-MC-PFS (conventionalmulti-carrier proportional fairness scheduling) algorithm of using in the multicarrier system, finishes the distribution to frequency resource; Described method comprises the following steps:

(1) preparatory stage: divide frequency domain and time-domain resource, and the least unit of scheduling of resource, determine dispatching cycle, and establish the principle of power resource allocation and the Adaptive Modulation and Coding scheme that is adopted;

(2) channel condition information feedback stage: for know the user current on each Resource Block RB supported data rate, utilize the uplink feedback channel transmitting channel state information of travelling carriage, promptly the carrier/interface ratio on each RB is carried out multi bit quantization, and quantitative information fed back, and in feedback procedure, take into account the precision and the efficient of feedback;

(3) the RB resource allocation stage: constantly in each scheduling, according to user's channel condition information, the data rate that has transmitted, pass the RB number that the user has been assigned in the time delay information of packet and the current transmission time interval TTI, respectively each RB is calculated user's priority, then RB is distributed to the highest user of priority; Promptly on C-MC-PFS algorithm basis, introduce data packet delay information, so that, control delay variation better according to the user's time delay that time delay and current data packet experienced of data packets for transmission priority of regulating the user;

(4) data transfer phase: in each TTI, after all RB were distributed, the channel conditions on each RB that is assigned to according to the user calculated equivalent signal-to-noise ratio, selects suitable modulation coding mode thus; Be mapped on the corresponding RB then according to transmissible data volume in efficiency calculation user's current TTI of selected modulation coding mode, and with user data, upgrade user's average data transfer rate again;

(5) packet time delay estimation stages: under the constraint of equitable proportion, the time delay information of the packet that has transmitted according to the user, under current channel condition, the estimation user transmits the needed time of next packet, is used for the time delay at follow-up scheduling process control data bag; This time delay has reflected the actual transmissions ability that the user is current, can be in the time delay that keeps equitable proportion performance basis upper domination number according to bag.

Described step (1) further comprises following content of operation: OFDMA system plurality of adjacent subcarrier is divided into a subband, quantity is set on time domain constitutes a subframe, then subband on the frequency domain and N least unit-Resource Block RB (Resource block) that mark space formation first resource is dispatched on the time domain for natural number N OFDM symbol greater than 1; Carry out the scheduling of delay stability of time energy at each Transmission Time Interval TTI, promptly in each subframe, carry out once scheduling; In same scheduling constantly, a RB only distributes to a user, and each RB that each user is assigned to adopts identical code modulation mode, carries out power division and does not consider retransmission data packet may with equalitarian distribution method on each subband.

Described step (2) further comprises following content of operation: in each Transmission Time Interval TTI, average carrier/interface ratio SINR on each RB of moving table measuring (Signal to interference and noise ratio), and adopt many bits to quantize, wherein the number N of many bits is a natural number, can choose flexibly according to the distribution situation of SINR, feedback frequency depends on the speed degree of channel variation, to reduce the power consumption of up signaling consumption and travelling carriage as far as possible, and between precision of feeding back and efficient, choose compromise preferably.

The number of bits N of described multi bit quantization is 4, and promptly the SINR on each RB adopts 4 bit quantizations, is used to represent 16 kinds of states of channel, and is fed back by travelling carriage.

Described step (3) further comprises following content of operation:

(31) data rate of on each RB, supporting according to user's current time and the mean data rate that has transmitted, and the current time delay that packet experienced that is about to transmission, come the delay variation between the control data bag, for this to the priority that unappropriated RB still calculates the user, again these RB are distributed to the highest user of priority; The computing formula of User Priority wherein, promptly j the user's that the priority on m RB is the highest selection criterion is: $j=\arg {\max }_i\frac{{\left(\exp \left(\frac{D_{H,i}-D_{E,i}}{D_{E,i}}\right)\right)}^a}{{\left(\max (1,O{P}_i)\right)}^b}\×\frac{r_{i,m}\left(t\right)}{R_i^{\′}\left(t\right)},$ In the formula, D _{H, i}Be the time delay of i the current packet that is transmitting of user, D _{E, i}Be the next needed time of packet of transmission that the time delay according to the packet that transmitted estimates, OP _iBe the number of the RB that i user taken in current TTI, a, b are respectively the weight coefficient of shake controlling elements and resource occupation controlling elements, and natural number i, j are respectively user's sequence numbers, r _{I, m}(t) be i the data rate that the user supports on m RB, R _i' (t) be the average transmission rate of i user in a period of time of setting, its computing formula is: $R_i^{\′}\left(t\right)=(1-\frac{1}{T_c})\×R_i^{\′}(t-1)+\frac{1}{T_c}\×r_i,$ In the formula, r _iIn current TTI, after all RB assigned, the user carried out the transmission rate that calculates behind the Adaptive Modulation and Coding AMC (Adaptivemodulation and coding) according to the channel conditions on all RB that distributed; T _cBe to be used to reflect that user's mean data rate upgrades the parameter of speed, this parameter should embody the variation of channel status, guarantees resource distributional equity in the setting-up time again, is set to 1000 (TTI) usually;

(32) the resource allocation fairness in the same TTI of control: in a TTI, too much take the RB resource for preventing the user, introducing resource occupation controlling elements (max (1, OP _i)) ^b,, then in process, reduce this user's priority to follow-up RB calculating priority level whenever the user is assigned to a RB; Even the priority of i user on m RB is the highest, then upgrades OP _i, OP _i=OP _i+ 1, make this i user who is assigned to a RB when distributing next RB, this user's priority decreases; If all RB distribute in the current TTI, then change next step (4) over to, otherwise return step (31), continue to distribute remaining RB resource.

Shake controlling elements JCF in the described priority computing formula (Jitter Control Factor) is (exp ((D _{H, i}-D _{E, i})/D _{E, i})) ^a, be used for the delay variation between the control data bag; If the time delay of the current packet that will just transmit then reduces user's priority less than the time delay of estimation, otherwise, its priority then improved.

Described shake controlling elements JCF paired domination number plays an important role according to the delay variation between the bag, in the computing formula of User Priority $j=\arg {\max }_i\frac{{\left(\exp \left(\frac{D_{H,i}-D_{E,i}}{D_{E,i}}\right)\right)}^a}{{\left(\max (1,O{P}_i)\right)}^b}\×\frac{r_{i,m}\left(t\right)}{R_i^{\′}\left(t\right)}$ In, the numerical values recited of weight coefficient a of shake controlling elements directly determines the quality of delay variation performance, the numerical value of a is to be set to according to actual needs: and 0.01,0.03,0.05 or other numerical value, if strict to delay variation, need to increase the value of a; Otherwise, reduce the value of a.

Described step (4) further comprises following content of operation:

(41) carry out Adaptive Modulation and Coding for each user who is assigned to RB according to channel conditions: in engineering practice, for realizing easily and reducing signaling consumption, to each user's the identical modulation coding mode of all RB employings; Because the SINR difference on each RB will be calculated equivalent signal-to-noise ratio for each user according to channel capacity formula earlier: ${\mathrm{SNR}}_{\mathrm{Ei}}=2^{\frac{1}{K_i}\underset{j=1}{\overset{K_i}{\mathrm{\Σ}}}{\log }_2(1+\mathrm{SIN}{R}_{i,j})}-1,$ In the formula, SNR _EiBe i user's equivalent signal-to-noise ratio, SINR _{I, j}Be the carrier/interface ratio of i user on j RB, K _iIt is the number of the RB that is assigned to of i user; Select corresponding modulation coding mode according to above-mentioned equivalent signal-to-noise ratio then;

(42) calculate current TTI user's data transmission rate: r according to selected code modulation mode _i=η * K _i* M * N/TTI, wherein, η is the efficient of modulating-coding, i.e. institute's loaded information bit number on each carrier wave, K _iBe the number of the RB that is assigned to of i user, M is the number that each RB goes up subcarrier, and N is OFDM symbolic number that each TTI comprised; Utilize this current user's data transmission rate r again _iAnd the computing formula of above-mentioned steps (31) is to the average data transfer rate R of this user in the setting-up time _i' (t) upgrade.

Described step (5) further comprises following content of operation: establishing the bit number that user i current data packet transmitted is Bits _Ri, the quantity of complete data packet is Bits _p, upgrade Bits according to the following equation _r: Bits _Ri=mod (Bits _Ri+ η * K _i* M * N, Bits _p), in the formula, mod represents modulo operation; If Bits _RiSatisfy following formula: (Bits _Ri+ η * K _i* M * N)/Bits _p〉=1, the expression current data packet has transmitted and has finished, and enters the transmission of next packet; Estimate according to following formula again and transmit the needed time delay of next packet: $D_{E,i}=(1-\frac{1}{S_u})\×D_{E,i}^{\′}+\frac{1}{S_u}\×D_{H,i}^{\′},$ In the formula, D _{E, i}Be the propagation delay time of the next packet that estimates, D _{E, i}' for having transmitted the time delay that a packet estimates, D _{H, i}' be the intact time delay that packet experienced of current transmission, S _uUndated parameter for the time delay of reflection time delay renewal speed.

Described estimation transmits the undated parameter S of the time delay in the computing formula of the needed time delay of next packet _uNumerical value unsuitable too small, follow the tracks of difficulty with the time delay of avoiding the follow-up data bag, but numerical value is also unsuitable excessive, to embody the variation of subscriber channel situation, S usually _uValue be 2000 (TTI).

Comprehensively above-mentioned, the present invention is a kind of basic thought by C-MC-PFS, at non-real-time service, and the dispatching method of the guarantee message transmission rate stability that provides for the OFDMA system.Dispatching method of the present invention has been considered user's channel conditions and professional actual transfer rate in the process of scheduling, kept the good proportion fair characteristic.The innovation part of this method mainly contains 2 points: the one, introduce certain time delay controlling mechanism, if the time delay of the current packet that will just transmit just reduces user's priority less than the time delay of estimation; Otherwise, just improve priority, well the scope of the delay variation between the control data bag.Another innovative point is the estimation of introducing the data packet delay, under the constraint of equitable proportion principle, utilize the time delay information of data packets for transmission, estimate and transmit the needed time delay of next packet, be used to reflect the transmittability of user at current channel, just utilize the time delay estimate to control the delay variation of follow-up data bag, thereby can keep the characteristic of traditional equitable proportion algorithm well.Simulation results by the embodiment of the invention as can be seen, dispatching method of the present invention not only makes the delay variation performance of packet that significantly improvement has been arranged, and compare with traditional equitable proportion algorithm, the performance of validity and fairness aspect does not all have significantly to descend.Therefore, the present invention has good popularization and application prospect.

Description of drawings

Fig. 1 is the realization flow block diagram that the present invention is used for the dispatching method that the OFDMA system ensures time delay stability of non-real-time business data packet.

Fig. 2 is the throughput performance schematic diagram relatively that the present invention is used for the dispatching method that the OFDMA system ensures time delay stability of non-real-time business data packet

Fig. 3 is the delay variation performance schematic diagram relatively that the present invention is used for the dispatching method that the OFDMA system ensures time delay stability of non-real-time business data packet

Fig. 4～Fig. 6 is respectively the distribution situation schematic diagram of representative apart from the user data packet delay of the three kinds of diverse geographic locations in base station

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in further detail below in conjunction with the drawings and Examples simulation scenarios.

Referring to Fig. 1, introduce five operating procedures or stage that the present invention is used for dispatching method that the OFDMA system ensures time delay stability of non-real-time business data packet:

(1) preparatory stage of resource division, parameter initialization: divide frequency domain and time-domain resource, and the least unit of scheduling of resource, determine dispatching cycle, and establish the basic principle of power resource allocation and the Adaptive Modulation and Coding scheme implementation that is adopted;

Particular content is that OFDMA system plurality of adjacent subcarrier is divided into a subband, quantity is set on time domain constitutes a subframe, then subband on the frequency domain and N least unit-Resource Block RB that mark space formation first resource is dispatched on the time domain for natural number N OFDM symbol greater than 1; Carry out the scheduling of delay stability of time energy at each Transmission Time Interval TTI, promptly in each subframe, carry out once scheduling; In same scheduling constantly, a RB only distributes to a user, and each RB that each user is assigned to adopts identical code modulation mode, carries out power division and does not consider retransmission data packet may with equalitarian distribution method on each subband.

(2) channel condition information feedback stage: utilize the uplink feedback channel transmitting channel state information of travelling carriage, know the user current on each Resource Block RB supported data rate, again the carrier/interface ratio on each RB is carried out multi bit quantization and feedback; And in feedback procedure, take into account the precision and the efficient of feedback;

Particular content is: in each Transmission Time Interval TTI, each travelling carriage is measured SINR on each subcarrier according to descending pilot frequency, calculate the average carrier/interface ratio SINR on each RB, and SINR adopted 4 bit quantizations, represent 16 kinds of channel statuss of RB, then travelling carriage according to actual needs with terminal capability feedback all or part RB on SINR and the sign ID of corresponding RB.Feedback frequency depends on the speed degree of channel, reduce the power consumption of up signaling consumption and travelling carriage as far as possible, and chooses compromise preferably between precision of feeding back and efficient.

(3) the RB resource allocation stage: constantly in each scheduling, according to user's channel condition information, the data rate that has transmitted, pass the RB number that the user has been assigned in the time delay information of packet and the current transmission time interval TTI, respectively each RB is calculated user's priority, then RB is distributed to the highest user of priority (or RB distributed to different user according to the height of User Priority); Promptly on C-MC-PFS algorithm basis, introduce data packet delay information, so that, control delay variation better according to the user's time delay of data packets for transmission priority of regulating the user;

Information as scheduling need be converted into the SINR of user on each RB maximum supported message transmission rate, and the present invention advises adopting the computational methods of more accurate information theory channel capacity.Being followed successively by each RB then selects the user of priority maximum to carry out transfer of data.Shake controlling elements JCF (exp ((D in the priority computing formula _{H, i}-D _{E, i})/D _{E, i})) ^aPaired domination number plays critical effect according to the delay variation between the bag.If the time delay of the current packet that will just transmit suitably reduces user's priority less than the time delay of estimating; Otherwise, just improve priority.The size of the weight parameter a of the shake controlling elements during priority is calculated has directly determined the quality of delay variation performance.A can be provided with according to the actual needs, and for example 0.01,0.03,0.05 etc.; If the requirement to delay variation is relatively stricter, need to increase the value of a.Certainly, the stable data packet delay is that loss with certain throughput is a cost.Resource occupation controlling elements weight parameter b during priority is calculated is set to 1.It is to dispatch constantly too much band occupancy resource for fear of a certain user at one, and is each user upper limit that assignable band resource is provided with in a TTI.Way of the present invention be in the calculating of priority, introduce the resource occupation controlling elements (max (and 1, OP _i)) ^b, promptly whenever user i is assigned to a frequency range, OP _iWill increase by 1, when distributing next RB, the priority of user i will decrease, and has guaranteed so to a certain extent in same scheduling moment frequency domain resource distributional equity.

(4) data transfer phase: in each TTI, after all RB are distributed, user data is mapped on the corresponding RB; Channel conditions on each RB that is assigned to according to the user calculates equivalent signal-to-noise ratio again, choose suitable modulation coding mode thus, and, upgrade user's average data transfer rate then according to transmissible data volume in efficiency calculation user's current TTI of selected modulation coding mode;

If all RB have assigned in current TTI, need calculate the data volume that can transmit according to the channel conditions of each RB for each user who is scheduled, at first will select modulation coding mode this moment.In practical communication system, consider the complexity of Project Realization and avoid too much signaling consumption, generally all RB to same user adopt identical modulation coding mode, so need calculate equivalent signal-to-noise ratio (can be obtained by the computing formula in the operating procedure (41)) according to the carrier/interface ratio on all RB of unique user.Again according to the equivalent signal-to-noise ratio that calculates, table 1 below the inquiry, select corresponding suitable Modulation and Coding Scheme, calculate the data volume and the instantaneous data rates that can transmit in the current TTI, and upgrade user's mean data rate according to the computing formula of the mean data rate in the operating procedure (31).Wherein parameter Tc has reflected the speed that user data rate is upgraded, and should embody the variation of channel status, guarantees resource distributional equity in the certain hour again, parameter T _cBe traditionally arranged to be 1000 (TTI).

Table 1 Modulation and Coding Scheme:

The AMC rank	Signal to noise ratio (dB)	Code rate	Modulation type	Efficient (η)
					1	-3.4	1/4	BPSK	0.25
2	-0.4	1/2	BPSK	0.5
					3	2.2	1/2	QPSK	1
4	5.2	3/4	QPSK	1.5
					5	7.6	2/3	8PSK	2
6	10.9	3/4	16QAM	3
					7	14.5	2/3	64QAM	4

(5) packet time delay estimation stages: under the constraint of equitable proportion, the time delay information of the packet that has transmitted according to the user and under current channel condition, the estimation user transmits the needed time of next packet, is used for the time delay at follow-up scheduling process control data bag; This time delay has reflected the actual transmissions ability that the user is current, can be in the time delay that keeps equitable proportion performance basis upper domination number according to bag.

Calculate the data volume that the user can transmit under selected modulation coding mode according to operating procedure (42) in current TTI, calculate in this step again and upgrade the bit number that current data packet has been transmitted.If the judgement current data packet has transmitted finish, then enter the transmission of next packet, and according to formula $D_{E,i}=(1-\frac{1}{S_u})\×D_{E,i}^{\′}+\frac{1}{S_u}\×D_{H,i}^{\′}$ Estimation transmits the needed time of next packet.The estimation of packet time delay and measuring and calculating play a very important role to characteristic and the control delay variation that keeps equitable proportion.Under the constraint of equitable proportion principle, estimate and transmit the needed time delay of next packet, reflected the transmittability of user, for the control of the propagation delay time of follow-up data bag provides of great value information at current channel.S in the above-mentioned formula _uBe the undated parameter of time delay, reflected the speed that time delay is upgraded.S _uRenewal unsuitable too fast because can cause the time delay of follow-up data bag to follow the tracks of difficulty, on the other hand, embody the variation of subscriber channel situation again, S _uValue be generally 2000 (TTI).

Referring to Fig. 2 and Fig. 3, introduce the embodiment situation of a test of the present invention, and the packet that proposes among the present invention stablized the dispatching method of time delay equitable proportion (SD-PF, stable rate-proportional fair) and the performance of C-MC-PFS algorithm compares.Suppose that available data are 600 from the carrier number order in the OFDMA system of a 10M bandwidth, be divided into 24 subbands, each subband has 25 subcarriers, and each TTI is made up of 7 OFDM symbols, and parameter b chooses 1, T _cSelect 1000, S _uSelect 2000, a chooses 0.01,0.03,0.05 successively and comes performance is compared.

Each travelling carriage sends downlink channel condition information to the base station.At first, in each TTI, travelling carriage is measured average carrier/interface ratio on each RB by descending pilot frequency, feed back information on each RB according to the ability of speed, real business demand and the travelling carriage self of channel state variations then, if channel variation is very fast, can reduce feedback cycle as far as possible; If traffic carrying capacity is bigger, can feed back more RB information.

Table 1 has provided the threshold value that various Modulation and Coding Scheme are chosen, in each TTI, after the priority of having calculated according to above-mentioned criterion on each RB, the travelling carriage that obtains RB calculates equivalent signal-to-noise ratio according to the carrier/interface ratio on each RB that is distributed, and chooses suitable modulation coding mode according to the threshold value of table 1 defined again.

After choosing transmission plan, the data volume that can transmit in the efficiency calculation current TTI of transmitting terminal according to selected modulation coding mode, and the renewal mean data rate, the user who is not scheduled need upgrade this parameter equally, and just instantaneous data rates is set to 0 in the renewal process.When judging that the user has transmitted a packet in current TTI, need the estimation time delay of update package, be used for delay variation at follow-up scheduling process control data bag.

Comparison schematic diagram referring to traditional equitable proportion mode with the inventive method delay variation performance under the situation of different weight parameter a shown in Figure 3, estimate for delay variation being made intuitively, defined the computing formula of delay variation indication DVI (delay variation indicator): ${\mathrm{DVI}}_{i,j}=(D_{i,j}-\stackrel{\‾}{D_i})/\stackrel{\‾}{D_i},$ Wherein, DVI _{I, j}Represent the delay variation indication of j packet of i user, D _{I, j}The time delay of representing j packet of i user, The average delay of representing i all packets of user.According to the embodiment simulation result of testing as can be seen, if adopt traditional equitable proportion algorithm (performance curve is represented with intensive fine dotted line), the time delay fluctuation ratio between the packet is more violent; If adopt dispatching method of the present invention, along with the value of a constantly increases, the time delay of packet is smooth-out.This TCP control for transport layer has crucial effects.If delay variation is too violent, TCP is difficult to estimate the transmission time-out time RTO of follow-up data bag, if estimate too smallly, will cause unnecessary retransmission continually, the waste system bandwidth; Otherwise, then can cause the long wait of transmitting terminal, greatly influence user's data speed, thereby brought the decline of systematic function.

Referring to Fig. 4～Fig. 6, the packet time delay distribution that these three figure have provided three different users of geographical position respectively when adopting different dispatching method.Wherein Fig. 4 represents the user closer from the base station, and Fig. 6 represents the edge customer of sub-district, and the user of Fig. 5 representative is between between the two above-mentioned.As can be seen, adopt traditional equitable proportion algorithm, the time delay distribution scope is bigger, adopts dispatching method of the present invention, and along with the numerical value increase of weight parameter a, it is concentrated that time delay distribution is tending towards.Since to the control of delay variation, the throughput of having lost user and system to a certain extent, and this point can be as seen from Figure 2.So along with the increase of a, because the reduction of user's Mean Speed, the average delay of packet can increase to some extent, time delay distribution can correspondingly be offset to the right.From following table 2 as can be seen, the loss of throughput of system is not remarkable, compare with traditional equitable proportion algorithm, when a is 0.05, the loss of throughput is less than 18%, and this moment, the delay variation performance had improvement significantly, this assurance for TCP layer data speed has very important meaning, because the frequent re-transmission that violent delay variation brings can cause the serious reduction of upper-layer service packet throughput, to exchange metastable packet time delay for be highly significant so sacrifice the throughput of certain link layer.

Table 2 throughput of system compares:

Algorithm	C-MC-PFS	SD-PF(a＝0.01)	SD-PF(a＝0.03)	SD-PF(a＝0.05)
					Throughput (Mbps)	33.04	32.08	29.94	27.21

In a word, dispatching method of the present invention is on the basis of remaining valid property and fairness, by in implementation step, introducing certain delay variation controlling mechanism, reduced the dynamic range that time delay changes to a great extent, can provide smoother data rate for transport layer, and realize simply having higher engineering using value.

Claims (10)

1, a kind ofly is used for the dispatching method that orthogonal frequency division multiplexing multiple access OFDMA system ensures time delay stability of non-real-time business data packet, it is characterized in that: this method is improved by the delay variation performance to traditional multicarrier Proportional Fair C-MC-PFS algorithm of using in the multicarrier system, finishes the distribution to frequency resource; Described method comprises the following steps:

(1) preparatory stage: divide frequency domain and time-domain resource, and the least unit of scheduling of resource, determine dispatching cycle, and establish the principle of power resource allocation and the Adaptive Modulation and Coding scheme that is adopted;

(2) channel condition information feedback stage: for know the user current on each Resource Block RB supported data rate, utilize the uplink feedback channel transmitting channel state information of travelling carriage, promptly the carrier/interface ratio on each RB is carried out multi bit quantization, and quantitative information fed back, and in feedback procedure, take into account the precision and the efficient of feedback;

(3) the RB resource allocation stage: constantly in each scheduling, according to user's channel condition information, the data rate that has transmitted, pass the RB number that the user has been assigned in the time delay information of packet and the current transmission time interval TTI, respectively each RB is calculated user's priority, then RB is distributed to the highest user of priority; Promptly on C-MC-PFS algorithm basis, introduce data packet delay information, so that, control delay variation better according to the user's time delay that time delay and current data packet experienced of data packets for transmission priority of regulating the user;

(4) data transfer phase: in each TTI, after all RB were distributed, the channel conditions on each RB that is assigned to according to the user calculated equivalent signal-to-noise ratio, selects suitable modulation coding mode thus; Be mapped on the corresponding RB then according to transmissible data volume in efficiency calculation user's current TTI of selected modulation coding mode, and with user data, upgrade user's average data transfer rate again;

(5) packet time delay estimation stages: under the constraint of equitable proportion, the time delay information of the packet that has transmitted according to the user, under current channel condition, the estimation user transmits the needed time of next packet, is used for the time delay at follow-up scheduling process control data bag; This time delay has reflected the actual transmissions ability that the user is current, can be in the time delay that keeps equitable proportion performance basis upper domination number according to bag.

2, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 1, it is characterized in that: described step (1) further comprises following content of operation: OFDMA system plurality of adjacent subcarrier is divided into a subband, quantity is set on time domain constitutes a subframe, then subband on the frequency domain and N least unit-Resource Block RB that mark space formation first resource is dispatched on the time domain for natural number N OFDM symbol greater than 1; Carry out the scheduling of delay stability of time energy at each Transmission Time Interval TTI, promptly in each subframe, carry out once scheduling; In same scheduling constantly, a RB only distributes to a user, and each RB that each user is assigned to adopts identical code modulation mode, carries out power division and does not consider retransmission data packet may with equalitarian distribution method on each subband.

3, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 1, it is characterized in that: described step (2) further comprises following content of operation: in each Transmission Time Interval TTI, average carrier/interface ratio SINR on each RB of moving table measuring, and adopt many bits to quantize, wherein the number N of many bits is a natural number, can choose flexibly according to the distribution situation of SINR, feedback frequency depends on the speed degree of channel variation, to reduce the power consumption of up signaling consumption and travelling carriage as far as possible, and between precision of feeding back and efficient, choose compromise preferably.

4, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 3, it is characterized in that: the number of bits N of described multi bit quantization is 4, be that SINR on each RB adopts 4 bit quantizations, be used to represent 16 kinds of states of channel, and feed back by travelling carriage.

5, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 1 is characterized in that: described step (3) further comprises following content of operation:

(31) data rate of on each RB, supporting according to user's current time and the mean data rate that has transmitted, and the current time delay that packet experienced that is about to transmission, come the delay variation between the control data bag, for this to the priority that unappropriated RB still calculates the user, again these RB are distributed to the highest user of priority; The computing formula of User Priority wherein, promptly j the user's that the priority on m RB is the highest selection criterion is: $j=\arg {\max }_i\frac{{\left(\exp \left(\frac{D_{H,i}-D_{E,i}}{D_{E,i}}\right)\right)}^a}{{\left(\max (1,{\mathrm{OP}}_i)\right)}^b}\×\frac{r_{i,m}\left(t\right)}{R_i^{\′}\left(t\right)},$ In the formula, D _{H, i}Be the time delay of i the current packet that is transmitting of user, D _{E, i}Be the next needed time of packet of transmission that the time delay according to the packet that transmitted estimates, OP _iBe the number of the RB that i user taken in current TTI, a, b are respectively the weight coefficient of shake controlling elements and resource occupation controlling elements, and natural number i, j are respectively user's sequence numbers, r _{I, m}(t) be i the data rate that the user supports on m RB, R _i' (t) be the average transmission rate of i user in a period of time of setting, its computing formula is: $R_i^{\′}\left(t\right)=(1-\frac{1}{T_c})\×R_i^{\′}(t-1)+\frac{1}{T_c}\×r_i,$ In the formula, r _iIn current TTI, after all RB assigned, the user carried out the transmission rate that calculates behind the Adaptive Modulation and Coding AMC according to the channel conditions on all RB that distributed; T _cBe to be used to reflect that user's mean data rate upgrades the parameter of speed, this parameter should embody the variation of channel status, guarantees resource distributional equity in the setting-up time again, is set to 1000 (TTI) usually;

(32) the resource allocation fairness in the same TTI of control: in a TTI, too much take the RB resource for preventing the user, introducing resource occupation controlling elements (max (1, OP _i)) ^b,, then in process, reduce this user's priority to follow-up RB calculating priority level whenever the user is assigned to a RB; Even the priority of i user on m RB is the highest, then upgrades OP _i, OP _i=OP _i+ 1, make this i user who is assigned to a RB when distributing next RB, this user's priority decreases; If all RB distribute in the current TTI, then change next step (4) over to, otherwise return step (31), continue to distribute remaining RB resource.

6, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 5 is characterized in that: the shake controlling elements JCF in the described priority computing formula is (exp ((D _{H, i}-D _{E, i})/D _{E, i})) ^a, be used for the delay variation between the control data bag; If the time delay of the current packet that will just transmit then reduces user's priority less than the time delay of estimation, otherwise, its priority then improved.

7, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 6 is characterized in that: described shake controlling elements JCF paired domination number plays an important role according to the delay variation between the bag, in the computing formula of User Priority $j=\arg {\max }_i\frac{{\left(\exp \left(\frac{D_{H,i}-D_{E,i}}{D_{E,i}}\right)\right)}^a}{{\left(\max (1,{\mathrm{OP}}_i)\right)}^b}\×\frac{r_{i,m}\left(t\right)}{R_i^{\′}\left(t\right)},$ In, the numerical values recited of weight coefficient a of shake controlling elements directly determines the quality of delay variation performance, the numerical value of a is to be set to according to actual needs: and 0.01,0.03,0.05 or other numerical value, if strict to delay variation, need to increase the value of a; Otherwise, reduce the value of a.

8, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 1 is characterized in that: described step (4) further comprises following content of operation:

(41) carry out Adaptive Modulation and Coding for each user who is assigned to RB according to channel conditions: in engineering practice, for realizing easily and reducing signaling consumption, to each user's the identical modulation coding mode of all RB employings; Because the SINR difference on each RB will be calculated equivalent signal-to-noise ratio for each user according to channel capacity formula earlier: ${\mathrm{SNR}}_{\mathrm{Ei}}={\text{2}}^{\frac{1}{K_i}\underset{j=1}{\overset{K_i}{\mathrm{\Σ}}}{\log }_2(1+{\mathrm{SINR}}_{i,j})}-1,$ In the formula, SNR _EiBe i user's equivalent signal-to-noise ratio, SINR _{I, j}Be the carrier/interface ratio of i user on j RB, K _iIt is the number of the RB that is assigned to of i user; Select corresponding modulation coding mode according to above-mentioned equivalent signal-to-noise ratio then;

(42) calculate current TTI user's data transmission rate: r according to selected code modulation mode _i=η * K _i* M * N/TTI, wherein, η is the efficient of modulating-coding, i.e. institute's loaded information bit number on each carrier wave, K _iBe the number of the RB that is assigned to of i user, M is the number that each RB goes up subcarrier, and N is OFDM symbolic number that each TTI comprised; Utilize this current user's data transmission rate r again _iAnd the computing formula of above-mentioned steps (31) is to the average data transfer rate R of this user in the setting-up time _i' (t) upgrade.

9, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 1 is characterized in that: described step (5) further comprises following content of operation: establishing the bit number that user i current data packet transmitted is Bits _Ri, the quantity of complete data packet is Bits _p, upgrade Bits according to the following equation _Ri: Bits _Ri=mod (Bits _Ri+ η * K _i* M * N, Bits _p), in the formula, mod represents modulo operation; If Bits _RiSatisfy following formula: (Bits _Ri+ η * K _i* M * N)/Bits _p〉=1, the expression current data packet has transmitted and has finished, and enters the transmission of next packet; Estimate according to following formula again and transmit the needed time delay of next packet: $D_{E,i}=(1-\frac{1}{S_u})\×D_{E,i}^{\′}+\frac{1}{S_u}\×D_{H,i}^{\′},$ In the formula, D _{E, i}Be the propagation delay time of the next packet that estimates, D _{E, i}' for having transmitted the time delay that a packet estimates, D _{H, i}' be the intact time delay that packet experienced of current transmission, S _uUndated parameter for the time delay of reflection time delay renewal speed.

10, the dispatching method that ensures time delay stability of non-real-time business data packet according to claim 9 is characterized in that: described estimation transmits the undated parameter S of the time delay in the computing formula of the needed time delay of next packet _uNumerical value unsuitable too small, follow the tracks of difficulty with the time delay of avoiding the follow-up data bag; But numerical value is also unsuitable excessive, to embody the variation of subscriber channel situation, common S _uValue be 2000 (TTI).

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