CN1917492A - Allocation scheme of OFDMA dynamic sub carrier based on unified priorities - Google Patents

Abstract

The basic principle of allocating sub-carrier wave is: according to the channel state information of each user, determining a unified sub-carrier wave allocating priority; according to the priority of allocating sub-carrier wave, sequentially allocating each sub-carrier wave to its corresponding user. The invention reduces the complexity of algorithm when ensuring the near-optimality.

Description

OFDMA dynamic sub carrier allocative decision based on unified priority

Technical field

The present invention relates to wireless communication system, relate in particular to a kind of dynamic sub carrier allocative decision that is used for orthogonal frequency division multiple access system.

Background technology

OFDM (OFDM) is the multi-carrier transmission technology under a kind of wireless environment, and its subcarrier can equivalence be the flat fading channel of a plurality of quadratures, because subcarrier overlapping on frequency spectrum greatly improved the availability of frequency spectrum.OFDM (OFDMA) is based on OFDM, distributes the subcarrier of some to realize that the multi-user inserts by giving each user.OFDMA is except the advantage of inheriting OFDM, also has distribution mechanism very flexibly, can be according to the quantity of the big or small dynamic assignment subcarrier of subscriber traffic, and can on different subcarriers, use different modulation and coded system and transmitting power to reduce interference, increase power system capacity.

The OFDMA technology combined with the Dynamic Resource Allocation for Multimedia technology can significantly improve systematic function.At present, people have proposed the scheme of many OFDMA system dynamics resource allocation.Wherein more famous is subcarrier, bit and the power associating allocative decision that proposed in 1999, and its complexity is high, is not suitable for using in real system.After this, Didem has proposed a kind of sub-optimal algorithm of determining subcarrier allocation in two steps on the basis of this algorithm, and this algorithm is under the condition of the bit error rate that satisfies the expectation of user rate demand and receiving terminal, makes total transmitting power minimum.The result shows that the complexity of this algorithm is more much lower than former algorithm, but performance is approaching in the extreme.Although this algorithm is greatly reduced on complexity, still more complicated is not suitable for real system.Though some sub-optimal algorithm complexities of Ti Chuing are lower afterwards, bigger performance loss is arranged all generally.Therefore, the research of the Resource Allocation Formula that complexity is low to performance is excellent is one of focus in the present wireless communication field.

Summary of the invention

Traditional algorithm often just directly carries out subcarrier allocation according to the size of channel gain, or utilizes iterative algorithm progressively to determine the allocation order of subcarrier.Often there is certain loss in the subcarrier allocation algorithm that complexity is low on performance, and better algorithm often is difficult to realize.In order to solve traditional algorithm, the invention provides a kind of effective subcarrier distribution scheme in the problem that is difficult to get both aspect two of performance and the complexities.

The basic principle of new method is as follows: for k user, utilize its average channel gain on all carrier waves to calculate a performance number P _kReplace average transmit power as approximation, and if rough calculation go out n subcarrier allocation to the required transmitting power P of this user _{K, n}, P _{K, n}With P _kBetween difference δ _{K, n}Represent.In the process of allocation of subcarriers, distribute a subcarrier to give unique user, if divide timing all to select δ at every turn at every turn _{K, n}(k=1,2 ..., K, n=1,2 ..., N) user and the subcarrier of middle minimum value correspondence, after all subcarriers all were assigned with, total transmitting power also will be near minimum, so δ so _{K, n}Approximate the reflection n subcarrier allocation of size to the importance of k user for total transmitting power.The present invention has utilized this character with δ _{K, n}(k=1,2 ..., K, n=1,2 ..., N) according to the priority that sorts to determine subcarrier allocation from small to large.

Subcarrier distribution scheme provided by the invention comprises the steps:

Consider an OFDMA system, K user wherein arranged, N subcarrier.Before carrying out this programme, suppose that the sub-carrier number that each user should distribute determines, promptly k user sub-carrier number that should distribute is m _k, k=1 wherein, 2 ..., K.

For k user, rated output P _{K, n}=f _k(P _k/ m _k)/| h _{K, n}| ²And P _k=f _k(R _k/ m _k)/h _k, h wherein _{K, n}Represent the channel fading coefficient of k user on n subcarrier, h _kThe average channel gain of representing k user.

Calculate P _{K, n}With P _kBetween difference power δ _{K, n}, as the foundation that determines n subcarrier to k user's assignment order.

By to δ _{K, n}(k=1,2 ..., K, n=1,2 ..., N) sort from small to large and determine the priority of subcarrier allocation, give corresponding user with each subcarrier allocation successively then.

The beneficial effect of dynamic sub carrier allocative decision provided by the invention is: by a unified priority, determined the assignment order of each user on each subcarrier liberally, not only guaranteed nearly excellent systematic function, and had low-down complexity.

Description of drawings

Fig. 1 shows the OFDMA system block diagram that has dynamic sub carrier, bit and power division.

Fig. 2 shows flow chart of the present invention.

Fig. 3 shows and calculates δ _{K, n}(k=1,2 ..., K, n=1,2 ..., flow chart N).

Fig. 4 shows and upgrades A _α, #A _αAnd δ _{K, n}(k=1,2 ..., K, n=1,2 ..., flow chart N).

Table 1 shows the concrete parameter that system adopted in the emulation.

The performance that Fig. 5 shows the present invention and ACG, RCG algorithm relatively.

Embodiment

The present invention will be described in detail below by drawings and Examples.

Fig. 1 shows the OFDMA system block diagram that has dynamic sub carrier, bit and power division.Suppose that there be K user in this system, N subcarrier, known all the subscriber channel state informations in base station.h _{K, n}, P _{K, n}And R _{K, n}The bit number of representing k channel fading coefficient, transmitting power and the transmission of user on n subcarrier respectively.Wherein, 0≤R _{K, n}≤ M, M are the maximum number bits that can transmit simultaneously on a subcarrier.In the bit error rate (BER) of receiving terminal in order to guarantee to expect, the transmitting power of k user on n subcarrier should equal

P _k，n＝f _k(R _k，n)/|h _k，n| ²

Wherein, f _k(x) be illustrated in channel gain and equal at 1 o'clock, k user realizes the required transmitting power of a reliable reception x information bit on some subcarriers.Annotate: the f of different user _k(x) can be different.

The purpose of dynamic sub carrier, bit and power division is to find a kind of method of salary distribution of the best, makes total transmitting power reach minimum.That is:

$P_{\mathrm{total}}=\min \underset{k=1}{\overset{K}{\mathrm{\Σ}}}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{f}_k\left(R_{k,n}\right)/{\left|h_{k,n}\right|}^2$

For k=1,2 ..., K need meet the following conditions

$\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{R}_{k,n}=R_k,0\≤R_{k,n}\≤M$

Fig. 2 shows flow chart of the present invention, is used for dynamic sub carrier, bit and the power divider part of Fig. 1.This flow process begins to enter initialization step 203 from step 201, and its concrete steps are as follows: for k=1, and 2 ..., K defines vectorial A _k, be used for depositing the sequence number of the subcarrier of distributing to k user.Initialization makes A _k=, #A _kExpression A _kThe number of middle element.

After this, enter step 205,, calculate δ for k user _{K, n}As the foundation that determines n subcarrier to k user's assignment order, k=1 wherein, 2 ..., K, n=1,2 ..., N.

In step 207, to counting variable initialize, m=1.

In step 209, from δ _{K, n}(k=1,2 ..., K, n=1,2 ..., pick out minimum value in N), obtain corresponding user and subcarrier number (being designated as: α and β).

In step 211, give α user with β subcarrier allocation.

In step 213, to A _α, #A _αAnd δ _{K, n}Upgrade, k=1 wherein, 2 ..., K, n=1,2 ..., N.

Enter step 215, counting variable adds 1, i.e. m=m+1.

Judge in step 217, if m≤N then enters step 209, otherwise in step 219 process ends.

Fig. 3 shows and calculates δ _{K, n}(k=1,2 ..., K, n=1,2 ..., flow chart N).Begin to enter step 303 from step 301, make k=1, be used for counting.

In step 305, calculate the average channel gain of k user on all subcarriers ${\stackrel{\‾}{h}}_k={\mathrm{\Σ}}_{n=1}^N{\left|h_{k,n}\right|}^2/N,$ According to h _kCalculate P _k=f _k(R _k/ m _k)/h _k

In step 307, make n=1, be used for counting.

In step 309, calculate P _{K, n}=f _k(R _k/ m _k)/| h _{K, n}| ²

In step 311, calculate P _{K, n}And P _kBetween value of delta _{K, n}=P _{K, n}-P _k, as the foundation that determines n subcarrier to k user's assignment order.

In step 313, make n=n+1.Judge in step 315 then,, otherwise then continue execution in step 317 if n≤N then enters step 309.

In step 317, make k=k+1.Judge in step 319 then, if k≤K then enters step 305, otherwise in step 321 process ends.

Fig. 4 shows and upgrades A _α, #A _αAnd δ _{K, n}Flow process, k=1 wherein, 2 ..., K, n=1,2 ..., N.Begin to enter step 403 from step 401, to A _αAnd #A _αUpgrade, its concrete steps are as follows: when β subcarrier has been determined when distributing to α user, β puts into A with sequence number _αIn, this moment A _αThe number of middle element increases by 1, that is, and and #A _α=#A _α+ 1.

In step 405, make k=1, be used for counting.

In step 407, put δ _{K, β}=NaN, promptly β subcarrier no longer participates in the distribution of back.

Adjudicate in step 409, if k=is α, then enter step 409, otherwise enter step 415.

In step 411, calculate the sub-carrier number that α user obtained, if #A _α=m _α, then entering step 413, obtained enough subcarrier owing to α user this moment, thus just no longer participate in the subcarrier allocation of back, so make δ _{α, n}=NaN, n=1 wherein, 2 ..., N.If #A _α＜m _α, promptly α user also do not obtain enough subcarriers, then enters step 415.

Behind the completing steps 413, enter step 415, make k=k+1.Judge in step 417 then, if k≤K then enters step 407, otherwise in step 419 process ends.

Performance evaluation

Fig. 5 shows in the performance comparison result between the present invention and traditional algorithm RCG, the ACG under the channel circumstance of the COST207 in 12 footpaths.RCG is famous subcarrier allocation algorithm, and near optimum performance, and complexity is relatively low; The ACG algorithm is the improvement of RCG algorithm, and its complexity is further reduced.Because optimal algorithm be difficult to realize, so compare on performance with RCG and ACG algorithm and the present invention here.

Table 1 has provided the concrete parameter that relates in the analogue system, as number of users, sub-carrier number, modulation system of being adopted or the like.In addition, use greedy algorithm to realize the distribution of bit and power in the emulation.

The abscissa of Fig. 5 is represented number of users, and ordinate is represented total transmitting power.As can be seen from the figure, performance of the present invention obviously is better than the ACG algorithm, and slightly is better than the RCG algorithm.

Analysis of complexity

Because the performance of ACG algorithm does not possess comparativity far below the present invention and RCG algorithm, therefore only compare the complexity of the present invention and RCG algorithm here.

Below complexity of the present invention is carried out simple analysis:

Calculate δ _{K, n}(k=1,2 ..., K, n=1,2 ..., complexity N) is

Utilize sort method based on the comparison that it is sorted, complexity is

Number of users all is far smaller than sub-carrier number usually in real system, promptly K＜＜N, therefore complexity of the present invention is If adopt the higher linear ordering method of efficient, complexity of the present invention can be reduced to

The complexity of RCG algorithm mainly depends on the state of channel: under best situation, its complexity is

Under situation worst, its complexity up to That is to say that the complexity of RCG algorithm exists Between the fluctuation.

In real system, the maximum complexity of algorithm determines one of key factor of its feasibility often.The maximum complexity of RCG algorithm is So no matter the present invention adopts sort method based on the comparison still is the linear ordering method, the complexity of RCG algorithm all is far longer than complexity of the present invention.

Claims (7)

1, a kind of dynamic sub carrier allocative decision that is applicable to OFDM (OFDMA) system, this scheme is characterised in that, unified subcarrier allocation priority is determined according to each user's channel condition information in the base station, gives corresponding user with each subcarrier allocation successively then.

2, the dynamic sub carrier allocative decision based on unified priority according to claim 1 is characterized in that, determines that the step of subcarrier allocation priority is as follows:

For k user,, calculate P according to its channel condition information on n subcarrier _{K, n}

According to its average channel gain on all subcarriers, calculate P _k

P _{K, n}With P _kValue of delta _{K, n}As the foundation that determines n subcarrier to k user's assignment order.

By to δ _{K, n}(k=1,2 ..., K, n=1,2 ..., N) sort from small to large and determine the priority of subcarrier allocation.

3, the method for definite subcarrier allocation priority according to claim 2 is characterized in that, calculates P _kStep as follows:

Calculate k user's average channel gain ${\stackrel{\‾}{h}}_k={\mathrm{\Σ}}_{n=1}^N{\left|h_{k,n}\right|}^2/N;$

Calculate P _k=f _k(R _k/ m _k)/h _k

Here, h _{K, n}Represent the channel fading coefficient of k user on n subcarrier, N represents sub-carrier number, R _kRepresent the bit number that k user transmitted in each OFDM symbol, m _kRepresent the sub-carrier number that k user should distribute, f _k(x) be illustrated in channel gain and equal at 1 o'clock, k user realizes the required transmitting power of a reliable reception x information bit on some subcarriers.

4, subcarrier allocation Determination of priority method according to claim 2 is characterized in that, calculates δ _{K, n}Step as follows:

Calculate P _{K, n}=f _k(R _k/ m _k)/| h _{K, n}| ²

Calculate δ _{K, n}=P _{K, n}-P _k

5, subcarrier allocation Determination of priority method according to claim 2 is characterized in that δ _{K, n}(k=1,2 ..., K, n=1,2 ..., N) order from small to large is the assignment order of subcarrier, i.e. δ _{K, n}More little, give k user's priority just high more n subcarrier allocation.

6, the dynamic sub carrier allocative decision based on unified priority according to claim 1 is characterized in that, and is as follows to the step that subcarrier distributes according to the distribution priority of subcarrier:

At δ _{K, n}(k=1,2 ..., K, n=1,2 ..., pick out the user and the subcarrier number (being designated as respectively: α and β) of minimum value correspondence in N).

Give α user with β subcarrier allocation.

Upgrade δ _{K, n}(k=1,2 ..., K, n=1,2 ..., N), repeat above step and all be assigned with up to all subcarriers.

7, renewal δ according to claim 6 _{K, n}Method, it is characterized in that, make δ _{1, β}=δ _{2, β}=...=δ _{K, β}=NaN, promptly β subcarrier can not be used by other users again; Equal m if distribute to α user's sub-carrier number _α, then make δ _{α, 1}=δ _{α, 2}=...=δ _{α, N}=NaN, promptly α user no longer participates in the subcarrier allocation of back.

Images