Patent Application
20080069045
The invention concerns the field of communication networks with allocation of shared resources, and more precisely the allocation of shared resources on the return link between user terminals and communication management stations of such networks.
Networks with allocation of shared resources, also called two-way broadband or two-way narrowband networks, such as multifrequency-time division multiple access (MF-TDMA) networks, for example, use what the man skilled in the art calls time/frequency plans for the allocation of shared resources on the return links.
A time/frequency plan is an arrangement of one or more types of carrier “transporting” time slots intended to be allocated to the various user terminals for the transport of data or of signals. Here “carrier type” means carriers having different frequencies and/or different symbol rates and/or different coding rates and/or using different modulations.
The time/frequency plans are generally established in advance on the basis of a model of predicted traffic matrices and of expected user distribution, in order to obtain during operation an optimum configuration of the return link. A plurality of configurations may be (pre)defined in order to respond to variations in users' requirements.
The change from one configuration to the other necessitates a certain time and generally corresponds to predefined time slots of known user profiles. Because of this, any difference relative to the initial model or the initial profiles may lead to degraded use of resources, since no configuration will then have been provided. This deterioration is particularly harmful in the case of satellite networks for reasons of cost. Moreover, any change of configuration, and thus of time/frequency plan, must be signaled to each user terminal by means of dedicated signaling messages transmitted over the air interface, which induces additional delays and necessitates the use of additional resources.
In the presence of a slow, and substantially continuous evolution, it is possible to define new sets of configurations better adapted to the situation. On the other hand, in the presence of more dynamic load variations (such as an event consuming a great deal of capacity, for example) and/or an unpredictable and/or sudden event (such as rain, for example) impacting on the capacity available on the return link, the predefined time/frequency plans may prove unsuitable or even amplify the disturbing phenomenon. In this case, bottlenecks appear, thus reducing the usable capacity of the network and its efficacy. A correlated deterioration in the quality of service of each user terminal occurs, in particular in the case of low-cost terminals that are often more sensitive to signal attenuation since their transmit power is limited.
Moreover, the distribution between carriers of different types imposes a breakdown into as many aggregates as there are types, which limits the possibilities of statistical multiplexing by aggregates.
Furthermore, the number of time/frequency plans to be predefined may be very high, without necessarily covering all situations, and difficult to configure and to manage.
To facilitate the configuration of the return link with different carrier types, in MF-TDMA type networks a standard known as DVB-RCS has been proposed. Such a standard is described in particular in the document “Digital Video Broadcast (DVB); Interaction channel for satellite distribution systems”, ETSI EN 301 790 V1.3.1 (2003-03).
According to this standard, the return link is divided into superframes, themselves divided into frames which are themselves divided into time slots. A superframe is a selected portion of times and of frequencies made up of frames, the simultaneous number of which cannot exceed 32 and each consisting of time slots the simultaneous number of which cannot exceed 2048. To define a given time/frequency plan, the frames and the time slots are classified (numbered) from the lowest frequency and from the first time to the highest frequency and the last time, relative to the center frequency and the time origin of the superframe. As a result, each frame of a superframe defines a usable time/frequency plan portion. Each user terminal is advised of the time slot that it must use within a frame of a superframe by means of dedicated messages transmitted by the communication management station of its network, known as burst time plans.
Because of the classification (or numbering) of the frames, the time/frequency plans may be regarded as similar to two-dimensional (2D) puzzles in which each piece is defined in the standard by a frame. Consequently, at a given time and for a given time/frequency plan, only one combination of frames (only one puzzle) is potentially accessible to a user terminal. This combination of accessible frames and the respective arrangements of those frames within the superframe are therefore predefined and can be modified only by means of dedicated commands, which does not correspond to real time and/or adaptive processing.
This scheme of puzzles (or plans) induces a partitioning of the global capacity of the return link that significantly limits the effect of statistical multiplexing. Moreover, each piece of the puzzle must be preconfigured in order for the complete puzzle to be compatible with the predicted traffic matrix model. The DVB-RCS standard undoubtedly enables the predefined puzzle to be modified by changing its pieces (or frames) and/or their arrangement in the superframe to obtain a new time/frequency plan, but each modification (or updating) of the contents of the superframes and of the frames must be signaled to each user terminal by means of a dedicated signaling message, which takes time and consumes bandwidth. Furthermore, the problem of the configuration of the new puzzle best adapted to a new situation remains intact.
No known solution being entirely satisfactory, an object of the invention is therefore to improve on the situation.
To this end it proposes a shared resource allocation device comprising processing means adapted:
The device according to the invention may have other features and in particular, separately or in combination:
The invention also proposes a resource allocation controller for a return link subsystem of the communication management equipment of a communication network, equipped with a resource allocation device of the type described hereinabove.
The invention further proposes a return link subsystem for a communication management equipment of a communication network, equipped with a resource allocation controller of the type described hereinabove or a resource allocation device of the type described hereinabove.
The invention further proposes communication management equipment for a communication network with allocation of shared resources, equipped with a return link subsystem of the type described hereinabove or a resource allocation device of the type described hereinabove.
The invention is particularly well adapted, although not exclusively so, to MF-TDMA type networks, and more particularly to those of satellite type (the communication management equipment then being a satellite station (or gateway)).
Other features and advantages of the invention will become apparent on examining the following detailed description and the appended drawings, in which:
The appended drawings constitute part of the description of the invention as well as contributing to the definition of the invention, if necessary.
An object of the invention is to enable optimized and adaptive management of shared resources of the return link of a communication network with allocation of shared resources.
It is considered hereinafter, by way of nonlimiting example, that the network with allocation of shared resources is a multifrequency time division multiple access (MF-TDMA) satellite network. The invention is not limited to satellite type networks or to MF-TDMA type networks, however. In fact it concerns all terrestrial or satellite networks including two-way broadband or two-way narrowband channels and using time/frequency plans for the allocation of shared resources to their return links (i.e. between the user terminals and the communication management equipments).
Moreover, it is considered hereinafter, by way of illustrative example, that the communication network is a broadband type network, but it could equally well be a narrowband network, such as a 3G network, for example, such as an IS-95 network.
As shown in
The satellite access network includes firstly at least one communication management equipment, represented here in the form of a satellite station or gateway GW connected to the core network CR by a radio network controller CRR, and at least one telecommunication satellite SAT enabling exchange of data by radio between the gateway SG and user terminals UE equipped with a satellite transceiver.
Here “user terminal” means any network equipment capable of exchanging data in the form of signals either with another equipment, via their parent network(s), or with its own parent network. For example, it may be a fixed or portable computer, a fixed or mobile telephone, a personal digital assistant (PDA) or a server.
It is considered hereinafter, by way of illustrative example, that the user terminals UE are satellite mobile telephones.
The satellite link constitutes an air type satellite interface. Moreover, the radio network controller CRR provides the service and control functions at the same time, for example.
The gateway SG is in particular responsible for processing of the signal and for management of requests for access to the satellite network. The satellite SAT is additionally associated with one or more radio cells situated in each of its coverage areas ZC. In the example shown, the satellite SAT covers only one cell, which corresponds to a single beam.
The gateway SG includes in particular a return link subsystem SSC including a resource allocation controller CAR responsible in particular for controlling the modem MOD. The return link subsystem SSC also provides return link monitoring and control functions (from user terminals UE to the satellite stations GW) and generates some or all of the signaling necessary for the operation of this return link. The resource allocation controller CAR also provides return link shared resource access control functions.
For efficient and adaptive management of the resources of the network on the return link, the invention proposes a shared resource allocation device D.
As shown in
The device D includes primarily a processing module MT responsible firstly for determining, on command or periodically, a set of time/frequency plans as a function, on the one hand, of at least one symbol rate capacity that has been requested for a set of user terminals, for example by their network access provider, and, on the other hand, on the designation of a chosen set of frames Ti (i is an integer greater than 2 and generally less than or equal to 32), each defined by a chosen set of time slots ITi of the same type.
Here “time slots of the same type” means time slots of a frame Ti associated with a given carrier type and therefore all associated with the same symbol rate.
According to the invention, each time/frequency plan of a set of plans determined by the processing module MT consists of a single chosen frame Ti. In other words, the frames Ti of the same set cover substantially the same band of frequencies and the same time portion, ignoring any offset, as explained hereinafter with reference to
Each set of time/frequency plans can therefore be seen as a stack of frames Ti along an axis AE, or as a three-dimensional (3D) time/frequency plan, as opposed to a standard two-dimensional (2D) time/frequency plan.
A nonlimiting overall example including three time/frequency plans and thus three frames T1 to T3 (i=1 to 3) is shown in
As shown in
This variant with shifts is particularly well adapted to the DVB-RCS return link configuration standard described hereinabove. In fact, it enables the frames Ti to be distinguished from each other by means of their respective time and frequency origins without having to assign each of them an identifier or number.
The amplitude of each offset is then chosen to conform to the DVB-RCS standard, which authorizes a maximum frequency offset of 100 Hz and a maximum time offset of 1/27 MHz (i.e. 17 ns).
This enables use of the signaling defined by the DVB-RCS standard to transmit to each of the user terminals concerned the definition of the set of frames (or time/frequency plans) that concern them. This is advantageous because it avoids defining new signaling messages that would necessitate an adaptation of the user terminals UE.
However, a variant may be envisaged in which the frames Ti of each set are distinguished from each other by identifiers or numbers assigned by the processing module MT.
Whatever the mode of distinguishing between them employed, once the processing module MT has defined a set of frames (or time/frequency plans) dedicated to a set of user terminals UE, as a function at least of a symbol rate capacity, the definition of that set is transmitted by the gateway GW to said user terminals UE, here via the satellite SAT. The other parameters that can be taken into account for the definition of the set of frames include in particular the center frequency of the set (or superframe).
The processing module MT is also responsible, each time that a user terminal UE requests at least one capacity, for determining an optimum time slot from the time/frequency plans of the set corresponding to said terminal user UE, which it has previously determined.
The word “optimum” must be understood as relative to the time of determination, i.e. the time at which the request is processed by the processing module MT. In other words, a time slot may be the optimum for one user terminal at a given time, given the state of the network and where appropriate the quality of service (QoS) associated with the user terminal UE concerned, and no longer be so at another time because said network is in another state.
This optimum slot determination is effected as a function at least of the capacity requested by the requesting user terminal. It preferably takes into account the quality of service (QoS) associated with the user terminal UE concerned. However, it may equally well be effected as a function of at least one complementary parameter such as a state (at the time of the processing of the request by the processing module MT) of the transmission channel of the requesting user terminal UE, for example, such as the measured level of the signal transmitted in the channel associated with the time slot used by the user terminal UE, or a load state of the network at the time of processing of the request by the processing module MT (representative of its congestion or its non-congestion, for example). Remember that the load state of the network impacts on the capacity that can be allocated to a user terminal.
If the processing module MT receives from different user terminals UE requests to obtain respective capacities, at least, it determines among the frames Ti of the current set those that are the most appropriate for each of the time slots IT to be assigned to said requesting user terminals. In other words, the processing module MT determines for each requesting user terminal UE the symbol rate that is the best adapted to the capacity that it has requested, given the state of the network. Each symbol rate determined in this way is then the optimum, relative to the time of determination, for the user terminal concerned.
Each frame Ti of a particular set corresponding to a given symbol rate, to each optimum rate there therefore corresponds a time slot IT for a given user terminal UE. Each of the time slots IT, corresponding to an optimum symbol rate and coming from one or the other of the frames Ti of the set previously determined, is referred to as the optimum relative to the time of determination.
The processing module MT can, for example, determine the time slots that are the optimum at a given time by means of a capacity distribution algorithm such as the weighted fair queuing algorithm used in many networks. Remember that an algorithm of this type distributes capacity as a function or attributes linked, for example, to the quality of service (QoS) and/or the contract of each user.
Determining optimum time slots enables optimization, and preferably maximization, of the allocation of the shared resources of the network.
When the processing module MT has determined the optimum time slots for the requesting user terminals UE, given the above parameter or parameters, the gateway GW transmits to each of them, here via the satellite SAT, a dedicated message designating the optimum time slot that it must use in order for the corresponding shared resources to be allocated to them. If the DVB-RCS standard is used, the dedicated message is the terminal burst time plan (TBTP).
On receipt of this dedicated message, the user terminal UE is capable of determining in the last definition of the set of valid time/frequency plans, which it has previously received, the definition of the time slot that it must use.
Also, the processing module MT transmits to the modem MOD, in an interpretable format, the optimum time slots that it has determined. In fact, they together constitute an optimum time/frequency plan for configuring the demodulator portion of modem MOD.
For example, the processing module MT may determine dynamically the set of optimum time slots that constitute an optimum time/frequency plan by means of an available resource filling algorithm such as the carrier load algorithm developed by Alcatel.
This optimum time/frequency plan PO, which results from this dynamic determination of the optimum time slots, is of 2D type, and not of 3D type.
Two examples of optimum time/frequency plans are shown diagrammatically in
More precisely, in the example shown in
In the example shown in
It will be noted that in certain situations the symbol rate requested by a user terminal UE (by means of its capacity request) may be less than at least one of the symbol rates of the time slots of different types that at a given time constitute an optimum time/frequency plan.
It is important to note that the optimum time slots may be determined either substantially in real time, i.e. following the reception of requests coming from the user terminals UE, or with a slight delay, i.e. a few moments after the reception of said requests. In the latter case, each determination time may be predefined, for example to comply with a chosen periodicity.
The shared resource allocation device D according to the invention, and in particular its processing module MT, may be produced in the form of electronic circuits, software (or electronic data processing) modules, or a combination of circuits and software.
Thanks to the invention, it is no longer necessary to configure a multitude of time/frequency plans in advance. There is virtually no limit on the number of possibilities offered by the invention. Moreover, it is no longer necessary to transmit signaling messages over the air interface each time that a new time/frequency plan is applied. Furthermore, the invention can reduce very significantly the number of bottlenecks induced by the predefined frames of the prior art. Also, the invention maintains statistical multiplexing and can be used in the context of the DVB-RCS standard. Finally, the invention allocates to each user terminal at all times the time slot of the type best adapted to his requirements at that time given the state of the network at the time concerned, which optimizes the use of the shared resources of the network.
The invention is not limited to the shared resource allocation device, resource allocation controller, return link subsystem and communication management equipment embodiments described hereinabove by way of example only, but encompasses all variants that the man skilled in the art might envisage that fall within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0408655 | Aug 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR05/50486 | 6/23/2005 | WO | 10/18/2007 |
