GB2482316A

GB2482316A - Resource management in a multiuser network

Info

Publication number: GB2482316A
Application number: GB201012690A
Authority: GB
Inventors: Fengming Cao
Original assignee: Toshiba Research Europe Ltd
Current assignee: Toshiba Europe Ltd
Priority date: 2010-07-28
Filing date: 2010-07-28
Publication date: 2012-02-01
Anticipated expiration: 2030-07-28
Also published as: GB2482316B; GB201012690D0

Abstract

Resources in a multiuser network having a plurality of subcarriers (e.g. OFDM) are managed by allocating an initial power to each of the plurality of subcarriers. An instantaneous transmission rate for each user is determined based on the initial allocated power. The resources are then allocated to each of the users in the network by using a fairness algorithm which takes into consideration the instantaneous transmission rate and an average past throughput of each of the users. Power below a predefined threshold is allocated to each of the plurality of subcarriers. Finally, the past throughput of each of the users is updated. The method decouples resource allocation and power loading into two consecutive steps by allocating the resources using proportional fairness based on approximated instantaneous rates, and performing iterative power loading using a conventional power loading method.

Description

NETWORK RESOURCE MANAGEMENT METHODS AND APPARATUS

Field

Embodiments described herein relates generally to network resource management methods and apparatus.

Background

Multicarrier transmission techniques, including orthogonal frequency division multiplexing (OFDM), are commonly used for communicating over broadband channels in multipath fading environments. It has been known that a substantial increase in throughput or capacity can be achieved if power loading is applied across the subcarriers of an OFDM signal. The achievable transmission rate of a multicarrier system with power loading can be modelled as: C(p) = Iog(1 +ps) log(1 +p (1) where p = [p1,..., PN]' pn denotes the power allocated at the nth (1«=n«=N)subcarrier, I h2 denotes the gain of the nth subcarrier, N0 denotes the variance of additive noise, and Jh 2 Sn = -f--is the unit power signal-to-noise ratio of the nth subcarrier, which is known at N0 a transmitter and can be provided by a receiver via a feed back path.

To maximise the achievable rate, optimal power loading subject to constraints of «=Fm andp »=O can be obtained through a conventional waterfilling algorithm as follows: (2) JJsn where [A] max(A, 0) is the larger number between A and 0, and/I denotes the water level, which are selected such that the total power constraint of = is satisfied.

In some applications, the power allocated to the subcarriers has to be limited such that the resulting interference from the allocated power to other systems is at a negligible or

an acceptable level.

Multicarrier transmission techniques can also be applied to multiuser systems, where different subcarriers are allocated to different users. In a single user system the aim of optimal power loading is to maximise the throughput or capacity of the system. On the other hand, the multiuser system, in addition to the throughput (or capacity), has to consider fairness among users in the system.

One of the fairness algorithms is the proportional fairness (PF) algorithm which is commonly used in cellular systems.

In a proportional fairness algorithm, a user scheduled on the nthsubcarrier in the tth symbol can be expressed as: r (t,n) u(n,t)=argmax m (3) m Tm(t,fl) where rm(t,n) is the instantaneous transmission rate which the mth user can achieve at the nthsubcarrier in the tthsymbol, and Tm(t,fl) is the mthuser's average throughput in the past. The average throughputs are updated at each subcarrier according to the following expression: 1 1 (1--)Tm(t,n)+--rm(t,n) m=u(n,t) C C (4) (1---)Tm(t,n) m!=u(n,t)

C

where t is a time constant adjusted to maintain fairness over a pre-determined time period.

In order to apply the proportional fairness algorithm in an OFDM system, the transmitter needs to identify the exact instantaneous rate, rm(t,n), and the past throughput, Tm(t,fl). However, it is appreciated that these information are generally not known before power allocation is considered, as the instantaneous rate rm(t,n) is associated with the loaded power at the nth subcarrier.

Furthermore, it is noted that conventional optimal resource and power allocation aims to maximise the overall throughput regardless of user fairness and power constraint.

Description of the drawings

Embodiments will now be described with reference to the accompanying drawings, wherein: Figure 1 shows the subcarriers of an OFDM signal spectrum, with frequency on the x-axis, and power on the y-axis; Figure 2 is a schematic diagram of an example communication device; Figure 3 is a flow diagram illustrating a process of allocating power in a single user system; Figure 4 is a flow diagram illustrating a process of performing power loading and resource allocation in a multiuser system according to an embodiment; Figure 5 is a flow diagram illustrating an initial power loading process on subcarriers of a multiuser system according to an embodiment; Figure 6 is a flow diagram illustrating a process of allocating power in a multiuser system according to an embodiment; and Figure 7 is an example illustrating an implementation of an embodiment in a femtocell network;

Detailed Description

Embodiments will be described in further detail on the basis of the attached diagrams.

It will be appreciated that this is by way of example only, and should not be viewed as presenting any limitation on the scope of protection sought.

According to one embodiment there is provided a method of managing resources in a multiuser network having a plurality of subcarriers, the method comprising allocating an initial power to each of said plurality of subcarriers, determining an instantaneous transmission rate for each user based on said initial allocated power, allocating resource to each of said users by means of a fairness algorithm taking into account said determined instantaneous transmission rate and an average past throughput of said each of said users, allocating power to said each of said plurality of subcarriers, wherein said allocated power is below a predefined threshold value, and updating past throughput of said each of said users.

In one embodiment of the above aspect, the method may further include predefining a total power to be allocated to said plurality of subcarriers, and an initial predefined threshold value for each of the subcarriers.

The step of allocating said initial power may be an iterative process in which one subcarrier is allocated with said initial power in each iteration, said allocated initial power in said subcarrier consist of a portion of said predefined total power, and said iterative process is terminated when said total power has been allocated to said plurality of subcarriers.

The step of allocating said initial power may include identifying a lowest initial predefined threshold value among said plurality of subcarriers that have not been allocated with said initial power.

In one embodiment, the method may include determining an average remaining power of said total power over said subcarriers that have not been allocated with said initial power.

In a further embodiment, the method may further include determining whether said identified threshold value is less than said average remaining power.

in an embodiment, the method includes allocating the initial predefined threshold value of a current subcarrier in said iteration as said initial power for said current subcarrier if said identified threshold value is less than said average remaining power.

In another embodiment, the method may include allocating said average remaining power as said initial power for said subcarriers that have not been allocated with said initial power if said identified threshold value is more than said average remaining power.

The instantaneous transmission rate may be determined by means of a predefined link adaptation function that maps signal-to-noise values to said transmission rates.

The fairness algorithm may include a proportional fairness algorithm.

The step of allocating said power may be an iterative process in which at least one subcarriers are allocated with said power in each iteration, said allocated power in said subcarrier consist of a portion of said predefined total power, and said iterative process is terminated when said total power has been allocated to said plurality of subcarriers.

The step of allocating power to each of said plurality of subcarriers in each of said iteration may include performing a water filling method to determine interim powers for said subcarriers that have not been allocated with power under a condition that the summation of said interim powers is equal to the remaining total power.

The step of allocating power to each of said plurality of subcarriers in each of said iteration may further include identifying a subcarrier having an interim power above its initial predefined threshold.

In one embodiment, the method may include allocating the initial predefined threshold value of said identified subcarrier to said identified subcarrier.

In an alternative embodiment, the method may include allocating said interim power to said subcarriers that have not been allocated with said power if a subcarrier having an interim power above its initial predefined threshold is not been identified.

In one embodiment, there is provided an apparatus for managing resources in a multiuser network having a plurality of subcarriers, the apparatus comprising power allocation means for allocating an initial power to each of said plurality of subcarriers, means for determining an instantaneous transmission rate for each user based on said initial allocated power, resource allocation means for allocating resource to each of said users by means of a fairness algorithm taking into account said determined instantaneous transmission rate and an average past throughput of said each of said users, said power allocation means being further operable to allocate power to said each of said plurality of subcarriers, wherein said allocated power is below a predefined threshold value, and means for updating past throughput of said each of said users.

In one embodiment, the apparatus may further include means for predefining a total power to be allocated to said plurality of subearriers, and an initial predefined threshold value for each of the subcarriers.

The power allocation means may be operable to perform an iterative process in which one subcarrier is allocated with said initial power in each iteration, said allocated initial power in said subcarrier consist of a portion of said predefined total power, and said iterative process is terminated when said total power has been allocated to said plurality of subcarriers.

The power allocation means may be operable to identify a lowest initial predefined threshold value among said plurality of subcarriers that have not been allocated with said initial power.

In another embodiment, the apparatus may include means for determining an average remaining power of said total power over said subcarriers that have not been allocated with said initial power.

In another embodiment, the apparatus may further include means for determining whether said identified threshold value is less than said average remaining power.

The power allocation means may be operable to allocate the initial predefined threshold value of a current subcarrier in said iteration as said initial power for said current subcarrier if said identified threshold value is less than said average remaining power.

The power allocation means may be operable to allocate said average remaining power as said initial power for said subcarriers that have not been allocated with said initial power if said identified threshold value is more than said average remaining power.

The fairness algorithm may include a proportional fairness algorithm.

The power allocation means may be operable to perform a further iterative process in which at least one subcarriers are allocated with said power in each iteration, said allocated power in said subcarrier consist of a portion of said predefined total power, and said iterative process is terminated when said total power has been allocated to said plurality of subcarriers.

The power allocation means is operable to perform a water filling method to determine interim powers for said subcarriers that have not been allocated with power under a condition that the summation of said interim powers is equal to the remaining total power in each of said iteration.

In one embodiment, the apparatus may include means for identifying a subcarrier having an interim power above its initial predefined threshold.

In one embodiment, the power allocation means may be operable to allocate the initial predefined threshold value of said identified subcarrier to said identified subcarrier.

In an alternative embodiment, the power allocation means may be operable to allocate said interim power to said subcarriers that have not been allocated with said power if a subcarrier having an interim power above its initial predefined threshold is not been identified.

One embodiment provides a computer program product comprising computer executable instructions which, when executed by a computer, cause the computer to perform a method as set out above. The computer program product may be embodied in a carrier medium, which may be a storage medium or a signal medium. A storage medium may include optical storage means, or magnetic storage means, or electronic storage means.

The described embodiments can be incorporated into a specific hardware device, a general purpose device configure by suitable software, or a combination of both.

Aspects can be embodied in a software product, either as a complete software implementation, or as an add-on component for modification or enhancement of existing software (such as a plug in). Such a software product could be embodied in a carrier medium, such as a storage medium (e.g. an optical disk or a mass storage memory such as a FLASH memory) or a signal medium (such as a download).

Specific hardware devices suitable for the embodiment could include an application specific device such as an ASIC, an FPGA or a DSP, or other dedicated functional hardware means. The reader will understand that none of the foregoing discussion of embodiment in software or hardware limits future implementation of the invention on yet to be discovered or defined means of execution.

Figure 1 illustrates an example of a multicarrier signal 10, such as an OFDM signal, wherein the subcarriers 12 are spaced so that they overlap. Although the embodiments are described with reference to subcarriers, it will be appreciated that the techniques can also be applied to subchannels, wherein each of the subchannels comprises a set of subcarriers allocated to the users. In the case of subchannels, the unit power signal-to-noise ratio can be expressed as an effective signal-to-noise ratio, i.e. the average of the unit power signal-to-noise ratio over the subcarriers within a subchannel.

Figure 2 illustrates schematically a communication device 20 providing an example of background to the embodiments. The device 20 comprises a processor 22 operable to execute machine code instructions stored in a working memory 23 and/or retrievable from a mass storage device 21. By means of a general-purpose bus 25, user operable input devices 26 are in communication with the processor 22. The user operable input devices 26 comprise1 in this example, a keyboard and a touchpad, but could include a mouse or other pointing device, a contact sensitive surface on a display unit of the device, a writing tablet, speech recognition means, haptic input means, or any other means by which a user input action can be interpreted and converted into data signals.

Audio/video output devices 27 are further connected to the general-purpose bus 25, for the output of information to a user. Audio/video output devices 27 include a visual display unit, and a speaker, but can also include any other device capable of presenting information to a user.

A communications unit 200 is connected to the general-purpose bus 25, and further connected to an antenna 255. By means of the communications unit 200 and the antenna 255, the device 20 is capable of establishing wireless communication with another device. The communications unit 200 is operable to convert data passed thereto on the bus 25 to an RF signal carrier in accordance with a communications protocol previously established for use by a system in which the laptop computer 20 is appropriate for use.

In the device 20 of Figure 2, the working memory 23 stores user applications 24 which, when executed by the processor 22, cause the establishment of a user interface to enable communication of data to and from a user. The applications 24 thus establish general purpose or specific computer implemented utilities and facilities that might habitually be used by a user.

Embodiments of the techniques described herein are applicable to any rnulticarrier system including a single user system and a multiuser system.

The achievable transmission rate of a system with power oading and resource allocation at a tth symbol for M »= 2 multiple users can be expressed as: C(p) = log(1 + Pnm (t, fl))Ymn =1og(1+p Ihm(tfl)2)y (5) where = [PI...PN]I p denotes the power allocated at the nth (1 «= n «= N) subcarrier; Ikn (t, n)2 denotes the gain of the nth subcarrier for the mth (1 «= m «= M) user; N0 denotes the variance of additive noise, Ymn denotes the nthsubcarrier to which the mth (1«=m«=M) user is scheduled or assigned; and Sm(tfl) = is the unit power signal-to-noise ratio of nthsubcarrier for the mth (1«=m«=M) user, which is known at a transmitter and can be provided by a receiver via a feed back path.

In addition to the constraints of «=Pm andp »=0 applied at the nthsubcarrier, the allocated power must also not exceed a given threshold, i. Furthermore, only one user is scheduled or assigned to that subcarrier. Therefore Ymn is either 1 when the inth (1 «= in «= M) user is scheduled or assigned at the nth subcarrier or 0 otherwise, i.e. 1 or Ymn('Ymn)° respectively. Hence, the following constraints can be derived: Pnn >Pn «=P Ymn =1 Yarn (1-Ymn) = 0 »= 0 Where I is the threshold at the nth (1«=n«=N)subcarrier, in which the power allocated thereto must not exceed.

Single user example

An example of an OFDM system having multiple carriers allocated to a single user (i.e. M = 1) will be described in the following paragraphs.

For brevity, the user index, m, and the time index, t, in equation (5) are omitted, and equation (5) is simplified to equation (1) with the following constraints: pn «= In pn »= 0 Applying the Karush-Kuhn-Tucker (KKT) optimality, the solution for power loading can be expressed as 1 __L1 (6) [a+/3 Sn] where /3 is the Lagrange multiplier for the p, «= constraint and a is the Lagrange multiplier for the threshold constraint P «= I. It will be appreciated that without the threshold constraint, the power loading solution is essentially a conventional power loading solution. Nevertheless, it becomes very complex to calculate p due to the introduction of the threshold constraint, as it is particularly complex to determine the water level, a + fi.

Figure 3 illustrates the steps of allocating power over the subcarriers for a single user OFDM system.

In step 50, the process commences by an initialisation process which includes denoting a set of subcarriers that has been allocated with power as S 0, denoting the set of subcarriers in the system as N={1,...,N}, denoting the remaining unallocated subcarrier(s) as S N \ S, assigning a constant value to a total power for the subcarriers as P = P, defining the threshold power for each of the subcarrier as k* In step 52, the conventional waterfilling method is carried out to allocate the interim power p over the unallocated subcarriers, S under the condition = nS r p=!_!. fornES [/3 sj A detailed implementation of the waterfilling algorithm is described in A. Leke and JM.

Cioffi, "A maximum rate loading algorithm for discrete multi-tone modulation systems' in Proceedings of IEEE Globecom 97, vol 3, Nov 1997, pp 1514-1518.

In step 54, it is determined whether any of the allocated interim power of the remaining subcarriers, S, exceeds their respective predefined thresholds (step 54). These subcarriers can be denoted as k {kI Pk > k and k S}. Accordingly, While k!=O Pk k for k E k (for the subcarriers in set k, assign the respective predefined thresholds as the allocated powers -see step 56).

In step 58, the set of allocated subcarriers, S, the set of remaining non-allocated subcarrier S, and the remaining power are updated as: kk S=kS S =N\S End Otherwise, the allocated interim power for each subcarrier is assigned as the final allocated power of the subcarriers in set S, that is p = p for k E S, in step 60.

The above is an iterative process for allocating power across the subcarriers. In each iteration an interim power loading step is carried out for the remaining non-allocated subcarriers, S, using the remaining total power, P. Subsequently, the interim powers allocated in the subcarriers are determined whether they are within their predefined thresholds. If the allocated interim power of these subcarriers does not exceed the respective predefined thresholds, the allocated interim power for each of these subcarriers is set as the final allocated power. Otherwise, the subcarriers in which the interim power exceeds their respective predefined thresholds will be allocated with the predefined thresholds as the final power. The process is iterated until the threshold constraint for each of the subcarriers is met.

Multiple users case The following paragraphs describe an example of a multiuser OFDM system in which power loading and resource allocation are performed on a symbol.

In this example N = {i,..., N} is denoted as the set of subcarriers to be allocated, M -{1,...,M} as the set of users, S as the set of allocated subcarriers during the iterations, S =N\S as remaining non-allocated subcarriers, 0 as null set, and as the cardinality of the set S. Referring to Figure 4, the process begins with an initialisation (step 70) in which the initial throughput for each of the users (1 «= m «= M) is set as Tm = 0.

In step 72, an initial power loading process is performed on the subcarriers of the multiuser system. It is noted that during this process, the initial allocated power, p5,,, for each of the subcarriers must not exceed the respective predefined thresholds of the subcarriers. The process of performing the initial power loading will now be described detail.

Referring to figure 5, the process commences with an initialisation step which the following are defined: S = 0 denotes the set of subcarriers that has been allocated with power; N {i,..., N} denotes the set of subcarriers to be allocated with power; and S N \ S denotes the remaining unallocated subcarriers.

assigns a constant value to the total power for the unallocated subcarriers Find the subcarrier that has the lowest threshold among the remaining unallocated subcarriers, S (step 726). Accordingly, the index of that subcarrier and its respective threshold are defined as n =argminI and minI respectively. nS nS

Check whether the detected lowest threshold is less than the average power of the remaining subcarriers (step 72C). Accordingly, If minI <-then nS l lSl Allocate the initial power for the n*th subcarrier (step 72D) as the predefined threshold power of that subcarrier. Accordingly: un. In and update the set of allocated subcarriers, S, the set of remaining non-allocated subcarrier, S and the remaining power, P (step 72E) as: P=P-p-n.

S=Su{n*} S =N\S else Allocate the initial power for each of the remaining subcarriers, S, as the average power of the remaining subcarriers: -P + p,=__ for VneS Referring back to Figure 4, in step 74, the instantaneous transmission rate for each user is approximated based on the initial power allocated at each of the subcarriers.

Accordingly, the instantaneous transmission rate at the nth (1 «= n «= N) subcarrier for the mth (1«= m «= M) user can be denoted as, (t,n). It is noted that the approximated rate can be obtained by a predefined link adaptation function f: R -9 that maps signal-to-noise values to information values representing transmission rates. In an example, the Shannon bound can be applied to calculate the instantaneous rate, and is expressed as: For Vn E N and m E M rm (t,n) = log2(1 + PnSm(t,t7)) bps/Hz In step 76, resource allocation to the users is performed using the proportional fairness method based on the approximated instantaneous rates and average past throughputs of the users. Accordingly, T,,,;=Tm(t,N) VmEM Loop: n from I to N 7 (t, n) Rm(fl)= , VmM m u(n,t)=maxRm(n) mM Vme M, 4(1_h1'tc) +,;(t,n)/t ffmu(n,t) (1-1/ta)],, if m!=u(n,t) End Loop where u(n,t) is the index of the user allocated to nth (1 «= n «= N) subcarrier at the tth symbol.

In step 78, power loading is performed over the subcarriers of the multiuser system.

This is an iterative process for allocating power across the subcarriers. Essentially, the power loading process is carried out on the subcarriers S using the total power This process is described in detail, with reference to Figure 6, in the following paragraphs.

In step 78A, the process commences by an initialisation process which includes assigning a constant value to the total power for the subcarriers as P = P, and defining a threshold power for each of the subcarriers as k* In Figure 6, S =0 denotes the set of subcarriers that has been allocated with power; N = {1,...,N} denotes the set of subcarriers in the system; and S = N \ S denotes the remaining unallocated subcarriers.

In step 786, the conventional waterfilling method is used to determine the interim powers p over the subcarriers in S under the condition = P,X as nS r 1 I forneS L sU(fl,)(t,n)J Check whether any of the determined interim powers of the remaining subcarriers, S exceeds the respective predefined thresholds (step 78C). These subcarriers can be denoted as: k = {kI Pk > 1k and k S}. Accordingly, While k!=0 Pk = k for k e k (for the subcarriers in set k, assign the predetermined thresholds as the respective final allocated powers -see step 78D).

Accordingly, the set of allocated subcarriers, S, the set of remaining unallocated subcarriers, S, and the remaining power are updated as: kk S=kuS S=N\S End Otherwise, the interim powers are assigned as the final allocated powers for each of the remaining unallocated subcarriers, S, that is p, p for k E S' in step 78E.

Referring back to Figure 4, in step 80, the past average throughput of each user is updated at the tth symbol as Tm(t,N) using the instantaneous rate obtained from the power allocation in step 78. Essentially, the updated past throughput will be used for resource allocation of subsequent symbols.

(1_!)7(t_1--(t_J,l\ if m=zt) C 1 (1-)7(t-1,N) e1e

C

Loop: n from 2 to N rm(t,n) = 1og(1+ps(t,n) Vm EM (i-1)7,(t,n)4 rm(t,n) if m=z4n,t) 7(t,n+1)= C 1 (1-)7(t,n) else

C

End Loop As described in the preceding paragraphs, a proportional fairness method used in a multiuser system provides fairness in resource allocation among the users of the system. However, a problem arises when the fair resource allocation and power loading are performed simultaneously. This is because the proportional fairness method requires accurate instantaneous rate while power loading renders the instantaneous rate uncertain.

The described embodiments essentially decouple the resource allocation and power loading into two consecutive steps. As described above, this is achieved by allocating the resources using proportional fairness based on approximated instantaneous rates, and performing iterative power loading using a conventional power loading method.

The described embodiments can be applied in applications where power over the subcarriers are limited to specific values and/or the resources need to be allocated to the users fairly. One example is the resource allocation and power loading/control in a femtocell base station.

A femtocell is typically deployed on top of an existing macrocell network to improve coverage in limited locations, such as indoor environments. Therefore a femtocell base station is usually installed at locations where users are experiencing unsatisfactory radio coverage. The femtocell and the macrocell may operate on the same RF channel frequency, which inevitably could result in co-channel interference. In order to avoid interference from the femtocell to the macrocell, or to limit the interference to an acceptable level, it has to be ensured that any interference from a femtocell base station to a macrocell user does not exceed a certain threshold.

Figure 7 illustrates a femtocell been deployed on top of a macrocell network. In this example, both the femtocell and the macrocell are OFDM-based system. Power loading and resource allocation as described above are applied at the femtocell base station 100. In Figure 7, the resource allocation is illustrated by partitioning the space around the femtocell base station 100 into zones 102, 104, 106. Zone 106 divides a region over which a macrocell user 108c can use resources defined by subcarrier 0 (SubO) and the region where a femtocell user lOOb can use the same resources without causing interference to each other. The femtocell base station 100 controls the radius of this zone by adjusting its power.

In another scenario where macrocell user 108b moves towards the femtocell base station, the femtocell base station will need to reduce zone 104 by reducing power on the appropriate subcarrier. Alternativ&y, the femtocell could reallocate the subcarriers used by femtocell user lOOa. Mathematically, the radius of the zone for a specific subcarrier can be represented as a threshold, i.e. the power in this specific subcarrier cannot exceed the threshold.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and apparatus described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and apparatus described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

CLAIMS: 1. A method of managing resources in a multiuser network having a plurality of subcarriers, the method comprising: allocating an initial power to each of said plurality of subcarriers; determining an instantaneous transmission rate for each user based on said initial allocated power: allocating resource to each of said users by means of a fairness algorithm taking into account said determined instantaneous transmission rate and an average past throughput of said each of said users; allocating power to said each of said plurality of subcarriers, wherein said allocated power is below a predefined threshold value; and updating past throughput of said each of said users.
2. A method according to claim 1, further includes predefining a total power to be allocated to said plurality of subcarriers, and an initial predefined threshold value for each of the subcarriers.
3. A method according to claim 2, wherein the step of allocating said initial power is an iterative process in which one subcarrier is allocated with said initial power in each iteration, said allocated initial power in said subcarrier consist of a portion of said predefined total power, and said iterative process is terminated when said total power has been allocated to said plurality of subcarriers.
4. A method according to claim 2 or claim 3, wherein the step of allocating said initial power includes identifying a lowest initial predefined threshold value among said plurality of subcarriers that have not been allocated with said initial power.
5. A method according to any one of claims 2 to 4, includes determining an average remaining power of said total power over said subcarriers that have not been allocated with said initial power.
6. A method according to claim 5, further includes determining whether said identified threshold value is less than said average remaining power.
7. A method according to claim 6, includes allocating the initial predefined threshold value of a current subcarrier in said iteration as said initial power for said current subcarrier if said identified threshold value is less than said average remaining power.
8. A method according to claim 6, includes allocating said average remaining power as said initial power for a current subcarrier if said identified threshold value is more than said average remaining power.
9. A method according to any one of the preceding claims, wherein said instantaneous transmission rate is determined by means of a predefined link adaptation function that maps signal-to-noise values to said transmission rates.
10. A method according to any one of the preceding claims, wherein the fairness algorithm includes a proportional fairness algorithm.
11. An apparatus for managing resources in a multiuser network having a plurality of subcarriers, the apparatus comprising: power allocation means for allocating an initial power to each of said plurality of subcarriers; means for determining an instantaneous transmission rate for each user based on said initial allocated power; resource allocation means for allocating resource to each of said users by means of a fairness algorithm taking into account said determined instantaneous transmission rate and an average past throughput of said each of said users; said power allocation means being further operable to allocate power to said each of said plurality of subcarriers, wherein said allocated power is below a predefined threshold value; and means for updating past throughput of said each of said users.
12. An apparatus according to claim 11, further includes means for predefining a total power to be allocated to said plurality of subcarriers, and an initial predefined threshold value for each of the subcarriers.
13. An apparatus according to claim 12, wherein said power allocation means is operable to perform an iterative process in which one subcarrier is allocated with said initial power in each iteration, said allocated initial power in said subcarrier consist of a portion of said predefined total power, and said iterative process is terminated when said total power has been allocated to said plurality of subcarriers.
14. An apparatus according to claim 12 or claim 13, wherein said power allocation means is operable to identify a lowest initial predefined threshold value among said plurality of subcarriers.
15. An apparatus according to any one of claims 12 to 14 includes means for determining an average remaining power of said total power over said subcarriers that have not been allocated with said initial power.
16. An apparatus according to claim 15 further includes means for determining whether said identified threshold value is less than said average remaining power.
17. An apparatus according to claim 16, wherein said power allocation means is operable to allocate the initial predefined threshold value of a current subcarrier in said iteration as said initial power for said current subcarrier if said identified threshold value is less than said average remaining power.
18. An apparatus according to claim 16, wherein said power allocation means is operable to allocate said average remaining power as said initial power for a current subcarrier if said identified threshold value is more than said average remaining power.
19. An apparatus according to any one of claims 11 to 18, wherein said instantaneous transmission rate is determined by means of a predefined link adaptation function that maps signal-to-noise values to said transmission rates.
20. An apparatus according to any one claims 11 to 19, wherein the fairness algorithm includes a proportional fairness algorithm.