A method for signalling allocation resource and a device therefor

FIELD OF THE INVENTION

The present invention relates to a method for signalling an allocation resource to a radio station, and a device being able to carry out such a method.

This invention is, for example, relevant for telecommunication system, like UMTS (Universal Mobile Telecommunication System) for example, or for any network systems comprising a plurality of stations sharing a limited set of telecommunication resources.

BACKGROUND OF THE INVENTION

A conventional telecommunication system, like a UMTS network, comprises at least one primary station (also noted base station, or Node B) communicating with a plurality of secondary stations (or mobile stations or User Equipment) on a plurality of channels. On an uplink channel, i.e. from the secondary stations to the primary, the physical resources are limited and shared between the secondary stations, for instance depending on the needs of every station, and/or the priority of data to be transmitted. A physical resource block can be for example one or more of time slots for Time

Division systems, frequency sub-domains for frequency domain systems, codes for code division systems, or different directions for systems that enable beam steering.

The primary station needs to signal to each secondary station which set of physical resource blocks is allocated to it. Consequently, in a conventional system, if the number of available physical resource blocks N is high, it needs to signal a bit map of N bits to every station. This leads to a huge overhead. Some solutions have been proposed to reduce this overhead. It is known to allocate the physical resources with a coarser granularity, i.e. only allocate resource blocks by groups of P blocks, P being a divider of N. For instance, in some systems with a granularity of 2, resources are allocated only by 2, 4, 6, 8, 10, etc.

However, this reduces the flexibility of the allocation, since if a secondary station needs only one resource to transmit its data, two resources will be allocated to it and the one of the two resources will not be used.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a method permitting to signal the allocation of the physical resources in an efficient manner.

Another object of the invention is to propose a method for signalling the resource allocation generating an acceptable overhead.

Still another object of the invention is to reduce the number of bits required to signal the allocation and keeping the flexibility of the allocation of resources.

Still another object of the invention is to adapt the method to the amount of physical resources allocated to the radio station, the total amount of physical resource available for allocation, and the size of the signalling message.

To this end, according to the invention, it is proposed a method for signalling to a radio station an allocation of at least one physical resource, comprising selecting an allocation scheme out of an allocation scheme set comprising a plurality of allocation schemes in dependence upon least one of: - the amount of physical resources allocated to the radio station, or the total amount of physical resource available for allocation, or the size of the signalling message; signalling the allocated physical resources to the radio station with help of the selected allocation scheme. By choosing a different allocation scheme depending on the amount of resource blocks to signal, it is possible to keep a good flexibility for low amount of allocated resources, thus avoiding wasting a high proportion of resources. Moreover, it is also possible to choose to code the resource allocation messages with different message sizes, depending on the amount of resource blocks allocated to a station. Thus, if a large number of blocks are allocated to a secondary station, using a large number of bits to code the allocation message will not create a huge overhead in proportion with the resource blocks.

In an embodiment of the invention, the method further comprises: al) computing the sum of the numbers of possible combinations of physical resources that can be allocated according to a first scheme of physical resource allocation, this summation being carried out for each amount of physical resources until a first criterion is met; a2) computing the sum of the numbers of possible combinations of physical resources that can be allocated according to a second scheme of physical resource allocation , this

summation being carried out over the amounts of physical resources which are greater than the amount of physical resources reached when the first criterion is met; a3) selecting the scheme of physical resource allocation according to whether the amount of physical resources to be allocated is greater or less than the amount of physical resources at which the first criterion is first met.

For instance, the method may further comprises, prior to step al), determining a first signalling message size (Ml) which enables the coding of a first amount of datagrams (2 ^λ M1); and wherein the first criterion is met when an amount of physical resources in each combination is reached such that the amount of possible combinations of physical resources computed at step al) is greater than a predetermined proportion of the first amount of datagrams.

In the ideal case the number of bits needed for the message format to signal a resource would be proportional to the resource size. However, in practice it may be sufficient that the message size can usually be made smaller for a small resource allocation than a large one. It would be possible to define all the necessary formats in advance, although a large number of formats could be needed to cover the possible sizes of total resource and number of bits in the message. Therefore a method is of interest for general design of sets of message formats, given the number of bits for signalling and the total available resources.

According to a second aspect of the invention, it is proposed a device comprising means for signalling allocation of physical resources according to the method of the invention.

These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein: - Fig.l is a block diagram of a system comprising a primary station and a secondary in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be implemented in a system of communication 300 as depicted in Fig.l, comprising a primary station 100, like a base station, and at least one secondary station 200 like a mobile station. The radio system 300 may comprise a plurality of the primary stations 100 and/or a plurality of secondary stations 200 (also noted UE for User Equipment). The primary station 100 comprises a transmitter means 110 and a receiving means 120. An output of the transmitter means 110 and an input of the receiving means 120 are coupled to an antenna 130 by a coupling means 140, which may be for example a circulator or a changeover switch. Coupled to the transmitter means 110 and receiving means 120 is a control means 150, which may be for example a processor. The secondary station 200 comprises a transmitter means 210 and a receiving means 220. An output of the transmitter means 210 and an input of the receiving means 220 are coupled to an antenna 230 by a coupling means 240, which may be for example a circulator or a changeover switch. Coupled to the transmitter means 210 and receiving means 220 is a control means 250, which may be for example a processor. Transmission from the primary radio station 100 to the secondary station 200 takes place on a first channel 160 and transmission from the secondary radio station 200 to the first radio station 100 takes place on a second channel 260.

The present invention relates to a method for signalling the allocation of physical resources and a device for allocating said resources. This device may be integrated within each primary station, or could be as well provided in a network controller entity.

The present invention is more especially dedicated to mobile telecommunication systems like UMTS or likewise.

It is however to be noted that the present invention is not limited to such mobile systems and could be applied to any communication systems having physical resources being allocated dynamically.

In UMTS LTE downlink signalling for indicating allocation of transmission resources to mobile terminals is under discussion. In this case the resource is number of resource blocks to be used for transmitting data from a base station to a mobile terminal, and which are identified mainly by their location in the frequency domain. Current

proposals assume that the number of bits used to signal a resource allocation would be the same, regardless of the size (i.e. in resource blocks) of the resource allocation. For example in LTE a downlink resource block is composed of a number of OFDM sub carriers in the frequency domain and a number of symbols in the time domain. In the uplink the frequency domain is represented by the bandwidth occupied by a single carrier.

Full flexibility can be achieved by using a bit map. For example, the allocation of each resource block is indicated by a separate bit. So for 50 potentially available resource blocks, signalling an allocation would require a map of 50bits. The number of bits can be reduced by changing the granularity, such that each bit in the map indicates allocation of a group of resource blocks. So for a granularity of 2 blocks, an allocation within a 50 block resource could be indicated with a map of 25 bits. However, some flexibility would be lost. For example, resource allocations might be restricted to even numbers of blocks. Another possibility would be the signalling specific resource allocations among a set of allowed combinations. One example of such a proposal is in Rl -072997. In order to reduce the number of bits, some restrictions are placed on which resources can be allocated.

We note that restricting the granularity of numbers of resource blocks that can be allocated (e.g. to even numbers of blocks), does not save many signalling bits (only one bit in this example).

One proposed scheme is in the next table 0 which shows the number of bits needed to signal the various possibilities, for the case of 50 available resource blocks. According to this proposal, the signalling message would need 26 bits to indicate an allocation.

Table 0

However, it is not obvious how such a scheme should be adapted for different amounts of available resource and different numbers of bits allowed to indicate the resource allocation.

According to the prior art, the number of bits used for the signalling message would increase if the total available resource size was increased.

A possible solution would be to use different message formats to signal different resource allocations. In the ideal case the number of bits needed for the message format to signal a resource would be proportional to the resource size. However, in practice it may be sufficient that the message size can usually be made smaller for a small resource allocation than a large one. It would be possible to define all the necessary formats in advance, although a large number of formats could be needed to cover the possible sizes of total resource and number of bits in the message. Therefore a method is of interest for general design of sets of message formats, given the number of bits for signalling and the total available resources.

The invention provides a method of designing a set of message formats for signalling a transmission resource allocation, given the different message lengths, the size of the total resource, and some guidelines for priorities of being able to signal different types of resource allocations.

The procedure is defined as follows:

1. Given that the total resource is AMAX, list the possible combinations of resource allocation for each amount of allocation A according to a predetermined Method l(e.g. The number of combinations from choosing

A from AMAX for A=0,l,2, AMAX). The number of combinations for each amount of allocation for this method would be N(A,Methodl).

2. For the smallest message size Ml bits, find the size of allocation Alsuch that a first criterion is satisfied, for example

(in the example given N(A, Methodϊ) = Choose(A, AMAX) )

3. If further combinations could be signalled within the specified number of bits, use another pre-determined allocation Method for allocations larger than Al, such that the number of combinations using this method satisfies a second criterion, such as f A=Al A=Al λ

Ml ≥ Logλ ∑N(A,Method\) + ∑N(A,Method2) \

V A=O A=A1+1 J

As an example, Method 2 could be similar to Method 1 , but with a resolution of 2 resource blocks so N(A, Method!) = Choose(A 12, AMAX 12)

4. If further combinations could be signalled with the remaining bits, then the procedure may be repeated for further allocation schemes. As a further example, the allocation scheme could signal any contiguous resource allocation in which case we would have N(A,Method3) = AMAX - A + 1

5. For additional message sizes, exactly the same procedure may be applied, with a possible variation that the list of resource allocation combinations that could be signalled with a given message size would not necessarily need to include combinations that could signalled with a smaller message size.

A further variation would be to define a method that included a set of combinations for each amount of allocation, except those that could be signalled by another method for the same amount of allocation. In a further variation some sizes of resource allocation may not be allowed.

The variations may be applied in a pre-determined way to given message sizes. The set of message formats may comprise one or more of: a. a set of formats for a message of a given size, each format being applicable to a different size of total resource, or b. a set of message formats of different sizes, all being applicable to a given size of total resource.

The size of a message is defined by the number of combinations which can be signalled thereby. This may correspond to an integer number of information bits in the case when the number of combinations is given by 2 ^N where N is the number of combinations which can be signalled by the message.

The criteria illustrated above for switching from one method to the next comprise determining when the current method cannot signal resource allocations of a larger size (due to the maximum number of signallable combinations being exceeded if the method is applied to a larger resource allocation). Other criteria could alternatively be used. Examples of other criteria might include:

• taking into account a number of reserved combinations when determining the largest resource allocation that can be signalled by the current method

(for example, comparing against a reduced maximum number of signallable combinations, where the reduction comprises a number of combinations reserved for signalling specific combinations or specific types of combination, such as large allocations, small allocations, contiguous allocations or specific patterns of allocation);

• changing method when a predetermined number of sizes of resource allocation have been identified for signalling using the current method;

• changing method when a predetermined proportion of the possible sizes of resource allocation have been identified for signalling using the current method;

• changing method when a predetermined proportion of the total number of signallable combinations have been identified for signalling using the current method;

• changing method when a predetermined number of signallable combinations have been identified for signalling using the current method;

• changing method when the resource allocation size exceeds a predetermined threshold, or a predetermined proportion of the maximum resource allocation size.

The invention is distinguished from the prior art in that a given message size may be flexibly applied to signal resources for any given size of total resource.

In one embodiment applicable to LTE, we take as example the total size of resource as 25 resource blocks (RBs). The maximum flexibility can be achieved with 25 bits (as in Table 1). Some other allocation arrangements according to the invention are shown in Tables 3 and 4.

Table 1: Resource allocation of 25 RBs with 25 bits to signal all possible combinations

(for reference)

Table 2: Resource allocation of 25 RBs with contiguous allocations only, requiring 9 bits to signal all possible combinations (For reference)

In Tables 3 and 4 the column "Select Contiguous" indicates whether all allocation combinations are signalled ("0") or only contiguous allocations ("1"). The column "Granularity" indicates the granularity of the resource allocation, except where a value of "0" is present, which indicates that an allocation of that size is not signalled. It can be seen that in some cases the size of the allocation is not an exact multiple of the granularity. This can be viewed as equivalent to an allocation size which is rounded up to the nearest multiple of the granularity, but with one or more resource blocks not allocated. The particular unallocated resources could be predetermined (e.g. "the last block is not used").

Table 3: Resource allocation of 25 RBs with 7 bits message, supporting all combinations with a single RB and allocation of 2 or 3 RB's with granularity of 2 RBs.

Table 4: Resource allocation of 25 RBs with a 13 bits message, supporting all combinations with 1, 2 or 3 RBs and some allocation sizes with 2 or 3 RB granularity, some allocation sizes with only contiguous allocation, and some allocation sizes are not supported.

According to a variant of the invention, at least one of the allocation scheme set comprises an allocation granularity being greater than an allocation granularity of another allocation scheme of the allocation scheme set.

In variants of the invention the physical resources may be one of, or a combination of the following:

- sub-carriers, such as in an OFDMA (Orthogonal Frequency Division Multiple Access) system

- or codes such as in a CDMA (Code Division Multiple Access) system - or timeslots such as in a TDMA (Time Division Multiple Access) system.

According to another variant of the invention the step of selecting an allocation scheme comprises selecting a considered allocation scheme of the allocation scheme set if the amount of physical resources allocated to the radio station belongs to a corresponding range. In this case the signalling message size corresponding to the considered allocation scheme may be predetermined, and the corresponding range chosen so that the number of possible combinations of resource allocation according to the considered allocation scheme is below a predetermined proportion of the number of datagrams (resource allocations) that can be coded with the corresponding signalling message size. The following steps may also be used: al) computing the number of possible combinations of physical resources that can be allocated according to a first scheme of physical resource allocation (schemel), this step being carried out for each amount of physical resources between a first amount and a second amount, wherein the second amount is selected to meet a first criterion; a2) selecting the first scheme of physical resource allocation (scheme 1) if the amount of resource is between the first amount and the second amount. The first criterion may be based on the total number of possible combinations of physical resources summed over the amounts of physical resources between the first and second amounts of physical resources. Additionally the first criterion may be that the total number of possible combinations of physical resources summed over the amounts of physical resources between the first and second amounts of physical resources is less than a predetermined amount. The first criterion may further include the condition that the total number of possible combinations of physical resources summed over the amounts of physical

resources between the first and second amounts of physical resources is as large as possible.

As a further variant of the invention, prior to step al) a first signalling message size (Ml) may be determined which enables the coding of a first number of datagrams (2 ^λ M1), and the first criterion may be determined such that it is met when an amount of physical resources is reached such that the number of possible combinations of physical resources computed at step al) is one of either:

- equal to a predetermined proportion of the first number of datagrams, - or greater than, a predetermined proportion of the first number of datagrams.

As a particular case the predetermined proportion may be 100%.

Further variants of the invention may include: The first criterion being met when a number of different amounts of physical resources is greater than a predetermined threshold. prior to step al) determining a first signalling message size (Ml) which enables the coding of a first number of datagrams (2 ^λ M1) and where first criterion is determined such that it is met when a number of different amounts of physical resources is greater than a predetermined proportion of the maximal number of different amounts of physical resources that can be allocated according to the first scheme of physical resource allocation and coded with the first signalling message size, prior to step al) determining a first signalling message size (Ml) which enables the coding of a first number of datagrams (2 ^λ M1), this message size being the same for messages signalling allocation of physical resources using the first allocation scheme or a second allocation scheme. the predetermined proportion of the first number taking into account a number of reserved combinations for resource allocation according to another allocation scheme.

In the present specification and claims the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, the word

"comprising" does not exclude the presence of other elements or steps than those listed.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art of radio communication and the art of transmitter power control and which may be used instead of or in addition to features already described herein.