EP1864460A1

EP1864460A1 - Method for allocating subbands to streams of a multichannel link in a multicarrier modulation communication system

Info

Publication number: EP1864460A1
Application number: EP06726264A
Authority: EP
Inventors: Fabienne Moulin; Mohamed Tlich; Bastien Lamer; Eric Debeau
Original assignee: France Telecom SA
Current assignee: Orange SA
Priority date: 2005-03-23
Filing date: 2006-03-21
Publication date: 2007-12-12
Also published as: FR2883681A1; US7864728B2; US20090052383A1; CN101180847A; CN101180847B; WO2006100408A1

Abstract

The invention concerns a method for allocating a plurality of subbands (SBi) to a plurality of streams (FLj) of a multichannel link in a multicarrier modulation communication system, each stream (FLj) being successively defined in a communication frame of said multichannel link by a number Mj of bits to be transmitted and a noise margin Gj. The invention is characterized in that said method includes the following steps: a) associating with each subband (SBi) a normalized signal to noise ratio (SNR0)i on the multichannel link; b) classifying the subbands (SBi) in a specific sequence of the normalized signal to noise ratios (SNR0)i; c) determining by means of a binary allocation algorithm an energy Ei per subband (SBi); d) allocating for each stream (FLj) taken in the sequence of said frame, a number Nj of consecutive subbands (SBi) taken in the sequence of normalized signal to noise ratios, so that the sum of the numbers nij of bits in each subband (SBi) allocated to each stream (FLj), the number of bits nij being defined by: nij = log2(1+Ei,(SNR0)i/Gj), is equal to formula (I). The invention is applicable to multicarrier modulation multichannel links.

Description

METHOD FOR ALLOCATING SUBBANDS TO STREAMS OF A

MULTICHANNEL CONNECTION IN A COMMUNICATION SYSTEM

MULTI-CARRIER MODULATION

The present invention relates to a method of allocating a plurality of sub-bands to a plurality of streams of a multichannel link in a multi-carrier modulation communication system.

The invention finds a particularly advantageous application in the field of multi-channel multicarrier links, such as xDSL, PLT or Wireless links, in particular to selectively increase the quality of service (QoS) of certain streams relative to others.

It is recalled that in multi-carrier modulation communication systems, in particular DMT discrete multi-carrier modulation ("Discrete MultiTone"), the bandwidth used is divided into a plurality of sub-bands SBj, each sub-band being subject to an independent carrier modulation. The number of bits and the transmission power allocated to a subband depend on the constraints imposed on the transmission line in terms of attenuation, stationary noise, etc., and therefore vary from one subband to another .

On the other hand, it is known that a multichannel link can carry a certain number of streams FL _j , each stream being associated with a channel of the link. For example, an ADSL link is provided to transmit seven streams distributed in seven different channels, namely four high-speed unidirectional channels, denoted ASO, AS1, AS2, AS3, and three bidirectional low-rate channels, denoted LSO, LS1, LS2. . The transport channels of the link must therefore be chosen according to the service corresponding to the flow to be transported. Thus, the downstream flows of Internet or digital television services will be transmitted over unidirectional channels of the AS type, while voice over IP (VoIP) or tele-conferencing services, as well as its streams Internet services or digital television, will be transmitted on bidirectional channels type LS.

It is thus understood that, in multichannel link transmission systems like I ¹ ADSL, several services can be offered simultaneously with the constraint that the sum of bits M _j to be transmitted in streams FL _j does not exceed the total bit rate configured for the link.

After synchronization and multiplexing, and before distribution of the bits in the SB sub-bands, the flows are organized in frames so that the bits to be transmitted from each stream are grouped together and succeed one another in the frame. We can thus find in a frame the following order: Mi bits of the stream

FLi of an Internet service in the ASO channel, then M ₂ bits of the FL ₂ stream of a digital television service in the AS1 channel, then M ₃ bits of the FL ₃ stream of a VoIP service in the LSO channel, then M ₄ bits of stream FL ₄ of a videoconferencing service in channel LS1, and so on. In a conventional manner, the distribution of the bits M _j of the streams FL _j in the sub-bands SBj is done in two steps.

In a first step, each sub-band SBj is assigned, by means of binary allocation algorithms of RA type ("Rate Adaptive") known per se, a number of bits that can be transmitted in this subband, taking into account the signal-to-noise ratio of the transmission line for the sub-band and also taking into account a noise margin l ^~ . The greater this noise margin, the more robust the transmission is to the various disturbances on the line, impulsive disturbances in particular, and the better the QoS quality of service. A second step of the dispatching procedure consists in allocating the successive bits of the flows of the frame in the sub-bands SBi in the increasing order of their number and of bits. This method of bit allocation is known as "Tone Ordering".

The very principle of the currently used bit allocation algorithms has the consequence that the different flows of an ADSL link, for example, can only be transmitted with an identical noise margin l ^~ , that is to say with the same QoS quality of service. Now, some services, such as Vo! P or videoconferencing among the examples mentioned above, a priori require a better quality of service than a simple Internet connection or digital television.

Also, the technical problem to be solved by the object of the present invention is to propose a method for allocating a plurality of sub-bands to a plurality of streams of a multichannel link in a multicarrier modulation communication system. each stream being successively defined in a communication frame of said multichannel link by a number M _j of bits to be transmitted and a noise margin Tj, which would make it possible to give priority to the QoS quality of service of certain streams with respect to others.

The solution to the technical problem posed, according to the present invention, in that said method comprises the steps of: a) associating with each subband a standard signal-to-noise ratio on the multichannel link, b) classifying the sub-bands in a given order of normalized signal-to-noise ratios, c) determining, by a binary allocation algorithm, an energy Ej per subband, d) allocating for each stream taken in the order in said frame, a number Nj of sub-bands. consecutive bands taken in the order of normalized signal-to-noise ratios, so that the sum of the numbers ny bits in each sub-band allocated to each stream, the number of bits ny being defined by:

nij = log ₂ (1 + E _L (SNR ₀ VrJ),

be equal to Mj: Mj = Σny. i = 1 Thus, the invention makes it possible to attribute a quality of service QoS greater than certain flows, called privileged streams, by acting on the noise margin at the level of the binary allocation, the idea being to associate with these privileged flows of noise margins greater than those associated with other flows, called non-privileged flows. Note that it would be possible to increase the QoS service quality of the preferred streams by uniformly increasing the noise margin on all subbands. However, this method would unnecessarily increase the quality of QoS service of the non-privileged flows and especially reduce the flow over the entire link. On the other hand, the method according to the invention makes it possible to allocate larger noise margins than to the privileged streams alone, which limits the performance losses in terms of flow compared to a uniform increase in the noise margin. In order to comply with the allocation procedure "Tone

Ordering ", said determined order is the increasing order of normalized signal-to-noise ratios.

The invention also provides provisions for defining subband allocation rules that would not have been allocated after the application of the method according to the invention. The remaining capacity will be referred to as all of these additional subbands.

According to a first embodiment of the invention, if the number of sub-bands allocated is less than the total number of sub-bands, step d) is performed again by increasing, in successive increments, the number M _k of bits to transmitted in the frame by constant noise margin at given flow an amount ΔMk = (M _k / Σ _k M _k) .Δ, where Δ is a given increment, to allocate all of the subbands.

FL _k given stream in question here are unprivileged flow direction defined above. In this first arrangement, the remaining capacity after application of the method, which is the subject of the invention, is therefore shared by the non-privileged streams in proportion to the number M _k of bits that they must initially transmit.

A variant of this first arrangement consists in that, if the number of sub-bands allocated is smaller than the total number of sub-bands, step d) is performed again by successive dichotomies starting from an initial interval [Mi _nf , M _sup ] where M _inf is equal to the total number of bits to be transmitted ΣjMj by all the streams and M _sup equal to the total number of bits to be transmitted in the frame by given streams with a margin of less than the minimum margin of said given flows, increasing with each dichotomy the number M _k of bits to be transmitted in the frame by the given streams with a constant noise margin of a quantity ΔM _k = (M _k / Σ _k M _k ) (M _c -Mi _n f) where M _c is the midpoint of the previous dichotomy interval, until allocate all the subbands.

According to a second provision concerning the allocation of the remaining capacity of the subbands, if the number of allocated subbands is less than the total number of subbands, step d) is carried out again by increasing, in successive increments. , the flow noise margin given an increment, up to allocate all the subbands.

The FLi flows given here are the privileged flows in the sense defined above. In this second arrangement, the remaining capacity after application of the method, which is the subject of the invention, is therefore shared between the privileged streams by increasing their noise margin H by a constant quantity Δf until reaching the maximum capacity of the assembly. subbands.

A variant of this second arrangement is that, if the number of sub-bands allocated is less than the total number of subbands, step d) is performed again by increasing the noise margin of given flows of a sub-band. quantity calculated by successive dichotomies from an initial quantity Δf _c = (Δrj _nf + Δr _SU p) / 2 with Δr _in f = 0 and Δr _sup equal to a sufficiently large value, until allocate all the sub- bands.

The invention also relates to a computer program product comprising program code instructions for executing the steps of the method according to the invention when said program is executed on a computer, as well as a support for said computer program product. .

A distribution module in the subbands of a transmitter of a multichannel link is, according to the invention, particularly remarkable in that it comprises means for implementing the method according to the invention.

Similarly, a transmitter of a multichannel link is remarkable in that it comprises the distribution module according to the invention.

The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it could be done. FIG. 1 is a diagram of a transmitter of a multichannel link of the ADSL type in a multicarrier modulation communication system.

FIG. 2 is a frame diagram to be transmitted in the multichannel link of FIG. 1. FIG. 3 is a diagram giving the normal signal-to-noise ratio of sub-bands classified in the order of increasing frequencies.

Fig. 4 is a diagram showing the normalized signal-to-noise ratio of the subbands of Fig. 3 ranked in order of increasing normal signal-to-noise ratios. FIG. 5 is a diagram giving the energy attributed to the subbands of FIG. 4.

FIG. 6 is a diagram illustrating the allocation of the flows of the frame of FIG. 1 in the subbands of FIG. 5.

In Figure 1 is schematized a transmitter of an ADSL link in a multicarrier modulation communication system. As already mentioned above, this link comprises seven channels, namely four unidirectional high-speed channels ASO to AS3, and three bidirectional low-speed channels LSO to LS2. In the example shown in Figures 1 and 2, only four streams are to be transmitted on the connection: the LiF flux and FL ₂ channels on the ASO and AS1 and FL ₃ and ₄ flows Fl on ALO and AL1 channels. As shown in Figure 2, these flows are respectively associated with Internet services (downstream), VoIP, upstream digital TV and Internet streams, downstream digital TV streams, and video conferencing.

These streams are processed by a first unit 10 where they are synchronized and multiplexed in one or the other of two different buffers known under the names of "fast buffer" and "buffer".

"Interleaved buffer". The "interleaved buffer" is distinguished from its "fast buffer" by the possibility of correcting the transmission errors, this possibility being obtained, however, to the detriment of a delay.

At the output of the synchronization and multiplexing unit 10, frames formed in fact of two parts are obtained: one contains the data of the fast buffer and the other those of the interleaved buffer memory. Inasmuch as the invention makes no distinction between the source of the data, FIGS. 1 and 2 show a single frame T, of which it should be remembered that it successively groups the data of each stream. Here, the flow order is FL ₁ , FL ₂ , FL ₃ and FL ₄ . M1, M2, M3, M4 are the bits to be transmitted respectively by each of these flows in the frame T.

Each stream FL _j is transmitted with a margin F _j noise that depends on the quality that is desired for the associated service. In the example proposed, the margins F ₂ and F ₄ may be larger than the margins Fi and F ₃ , digital television and videoconferencing requiring a quality of service better than an Internet connection or voice over IP.

As shown in FIG. 1, the frame T is then processed by a unit responsible for distributing the bits of the frame flows in the sub-bands of the multicarrier modulation communication system. The invention specifically relates to the method for allocating said subbands to the different flows FL _j considered.

The first step of the allocation method according to the invention consists in associating with each sub-band SBj a signal-to-noise ratio rationalized (SNR ₀ ) i. FIG. 3 shows an example of subband spectrum SB ₁ on which the associated signal-to-noise ratio (SNR ₀ ) i has been plotted on the ordinate. Then, in a second step, the subbands SB are classified in the order of increasing SNRs. The result of this classification is illustrated in FIG. 4. By convention, the indexation of the subbands SB i according to the index i is performed according to this classification. The normal signal-to-noise ratio (SNR ₀ ) j therefore increases along with the index i.

In a third step shown in FIG. 5, a binary allocation algorithm of the RA type ("Rate Adaptive") is applied to the distribution of FIG. 4 so as to determine the energy Ej for each subband SBj. This determination is made by taking the same noise margin value, for example the smallest of all those associated with the different flows.

Finally, FIG. 6 shows how the fourth step of allocating the SB subbands to the FL flows is performed. The streams FL _j are taken in the order in which they appear in the frame T, and each of them is assigned a number N _j of consecutive sub-bands taken in the order of the normalized signal-to-noise ratios of FIG. The number Nj is determined by the number Mj of bits that must be transmitted by the stream FLj in the frame. More precisely, the sum of the numbers ny of bits in each of the Nj sub-bands allocated to the stream FL _j , taking into account the margin Tj desired for this fiux, must be equal to M _j . ny is given by the formula: ny = 1Og ₂ (UEi- (SNR ₀ VrJ),

i = 1

In the example of FIG. 6, we have chosen Γ ₁ = Γ ₃ <Γ ₂ = Γ ₄ . That is to say that we decided to treat the same way in terms of quality of service, on the one hand, the Internet and digital television services, and, on the other hand, the services of VoIP and videoconferencing. . On the other hand, it was also decided to improve the quality of service of the latter in relation to the former.

For each subband SBj, we can therefore compute two values of ny: one, the largest, obtained for F _j = Fi = F ₃ , the other, the weakest, obtained for F _j = F ₂ = F ₄ . These two values are shown in Figure 6.

For LiF flux, the number of subbands is allocated to N1 = 2 and M = ₁ nn + n ₂ i. Similarly, we obtain for FL ₂ , FL ₃ and FL ₄ fluxes:

N ₂ = 4 and M ₂ = n ₃₂ + n ₄₂ + n ₅₂ + n ₆₂ , N ₃ = 2 and M ₃ = n ₇₃ + n ₈₃ ,

N ₄ = 4 and M ₄ = n ₉₄ + ni ₀₄ + nii ₄ + ni ₂₄

Once all streams are processed, it may happen that the number of allocated sub-bands ΣjNj is less than the total number of existing subbands. In this case, it may decide to allocate the capacity of remaining subbands to individual flows, for example the non-privileged flow of the first allocation, namely those, LiF and FL _3, the noise margin is less than that of the other flows, FL ₂ and FL ₄ , called privileged flows. To do this, we first increase ie M _k number of bits to transmit unprivileged flow, denoted FL _k, a quantity ΔMk = (M _k / _k Σ M _k) .Δ, where Δ is a given increment. Then, the fourth allocation step as defined above is carried out again. If, after this operation, all subbands are allocated, the process is stopped. On the other hand, if there are still unallocated subbands, we carry out a new incrementation taking as increment 2Δ. And so on until total allocation of the subbands.

An alternative to this remaining capacity allocation method is to proceed by dichotomy. We first fix a lower bound M _inf and an upper bound M _SU p for the total number of bits to be transmitted by taking for Mi _nf the total number of bits to be transmitted Σ _j M _j by all the streams FL _j and for M _su p the total number of bits to be transmitted in the frame by non-privileged FL _k streams with a noise margin lower than the minimum margin of said non-privileged streams.

At the first dichotomy, the number of bits to be transmitted by each unprivileged stream is increased by a quantity ΔM _k = (Mk / ΣkMk) (Mc-M _in f) where M _c

The fourth step of allocation of the method described above is carried out again, replacing M _k by M _k + ΔM _k for the non-privileged flows FL _k . If, after this operation, all subbands are allocated, the process stops. If the number of allocated sub-bands remains smaller than the total number of sub-bands to a fixed integer number, the process is restarted by taking the new lower bound M _inf the current point M _c preceding. If, on the other hand, the number of necessary allocations exceeds the total number of sub-bands, the process continues taking the new upper bound M _sup the current point M _c preceding. Successive dichotomies stop when all the subbands are allocated to the nearest integer. Another method of allocating the remaining capacity of subbands is to first define privileged flows FLi which are those for which it was initially decided to increase the QoS quality of service by giving them a higher noise margin. large than that of other non privileged. It is recalled that, in the examples taken previously, the preferred streams are the streams Fb and FL ₄ .

According to this other allocation method, a first incrementation of the same quantity Δl ^~ of the margin H of each privileged stream FLi is carried out. Then, again the general step of allocating the subbands described above. If all subbands are allocated, the process stops. If, on the contrary, there are still subbands to be allocated, the process continues by incrementing the noise margin of the privileged flows of 2Δf. And so on until complete allocation of the subbands. An alternative to this alternative method of allocating the remaining capacity is to proceed by successive dichotomies. For this, a lower bound Δfjnf and an upper bound Δr _sup are fixed for the noise margin to be added to the noise margins of the privileged flows. We shall take Δr _inf = 0 and Δr _sup equal to a sufficiently large value in the sense that it is known in advance that the number of sub-bands obtained with this value is greater than the total number of sub-bands available. We start by increasing the noise margins of all the privileged flows of the quantity Δl ^~ _c = (Δr _inf + Δr _su p) / 2, and the step of subband allocation is performed again. If, after this operation, all subbands are allocated, the process stops. If the number of allocated sub-bands remains smaller than the total number of sub-bands to a fixed integer number, the process is restarted by taking the new lower bound Δr _{inf as} the current point Δf _{c above} . If, on the other hand, the number of necessary allocations exceeds the total number of sub-bands, the process continues taking the new upper bound Δr _sup the current point Δi ^~ _{c above} . Successive dichotomies stop when all the subbands are allocated to the nearest integer.

Claims

A method of aliocating a plurality of subbands (SB ₁ ) to a plurality of streams (FL _j ) of a multichannel link in a multi-carrier modulation communication system, each stream (FL _j ) being successively defined in a communication frame of said multichannel link by a number Mj of bits to be transmitted and a margin T _j of noise, characterized in that said method comprises the steps of: a) associating with each subband (SBj) a report standard noise signal (SNRo) i on the multichannel link, b) classifying the subbands (SBj) in a determined order of normalized signal-to-noise ratios (SNR ₀ ) j, c) determining by a bit allocation algorithm a Ej energy per subband (SBj), d) allocate for each stream (FL _j ) taken in the order in said frame, a number N _j of consecutive subbands (SBj) taken in the order of the signal ratios to noise standardized, so that the sum of the numbers ny of bits s each sub-band (SB ₁ ) allocated to each stream (FL _j ), the number of bits ny being defined by:

n, j = log ₂ (1 + E- (SNR ₀ Vn),

be equal to Mj: Mj = Σny. i = 1

2. Method according to claim 1, characterized in that said determined order is the increasing order of normalized signal-to-noise ratios (SNR ₀ ) ι.

3. Method according to one of claims 1 or 2, characterized in that, if the number of allocated subbands is less than the total number of subbands, step d) is performed again by increasing, by successive incrementations, the number M _k of bits to be transmitted in the frame by flows (FL _k) given at constant noise margin (l ^~ _k ) of a quantity ΔM _k = (M _k / Σ _k M _k ) .Δ , where Δ is a given increment, until allocate all the subbands.

4. Method according to one of claims 1 or 2, characterized in that, if the number of allocated subbands is less than the total number of subbands, step d) is performed again by successive dichotomies from of an initial interval [M _in f, Msup] where M _in f is equal to the total number of bits to be transmitted ΣjMj by all the streams (FLj) and M _sup equal to the total number of bits to be transmitted in the frame by given flows (FL _k ) with a noise margin smaller than the minimum margin of said given streams, increasing at each dichotomy the number M _k of bits to be transmitted in the frame by the flows (FL _k ) given at margin (r _k ) constant noise of a quantity ΔM _k = (M _k / Σ _k M _k ). (M _c -Minf) where M _c is the midpoint of the preceding dichotomy interval, until allocating all the sub -bands.

5. Method according to one of claims 1 or 2, characterized in that, if the number of allocated subbands is less than the total number of subbands, step d) is performed again by increasing, in increments successive, the flow noise margin (H) (FLi) given an increment (Δl ^~ ), until allocate all the sub-bands.

6. Method according to one of claims 1 or 2, characterized in that, if the number of allocated subbands is less than the total number of subbands, step d) is performed again by increasing the margin ( H) flow noise (FLi) given by an amount calculated by successive dichotomies from an initial quantity Δf _c = (Δr _inf + Δr _SU p) / 2 with Δr _inf = 0 and Δr _sup equal to a value large enough to allocate all the subbands.

A computer program product comprising program code instructions for performing the steps of the method according to any one of claims 1 to 6 when said program is executed on a computer.

8. Computer program product support according to claim 7.

9. Module for distribution in the subbands of a transmitter of a multichannel link, characterized in that it comprises means for implementing the method according to any one of claims 1 to 6.

10. Transmitter of a multichannel link, characterized in that it comprises the distribution module according to claim 9.