WO2010052620A1

WO2010052620A1 - A method for allocating resources

Info

Publication number: WO2010052620A1
Application number: PCT/IB2009/054806
Authority: WO
Inventors: Matthew P.J. Baker; Timothy J. Moulsley; Paul Bucknell; Bernard Hunt; Milos Tesanovic
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-11-07
Filing date: 2009-10-29
Publication date: 2010-05-14

Abstract

The present invention relates to a method for allocating transmission resources to a plurality of devices, wherein separate transmission resources for initial transmissions of data packets are allocated persistently to each device, and a set of transmission resources for retransmissions is allocated persistently for the plurality of devices, and wherein at each retransmission occasion at least one signalling message indicates the allocation of specific transmission resources in the set to each of the devices for which a retransmission is required.

Description

A METHOD FOR ALLOCATING RESOURCES

FIELD OF THE INVENTION

The present invention relates to methods for signalling and allocating resources to a device, and to radio stations carrying out such methods.

This invention is, for example, relevant for mobile telecommunication networks like UMTS networks or LTE networks.

BACKGROUND OF THE INVENTION In a packet based radio system, such as UMTS LTE or LTE -Advanced, the normal method of operation for a secondary station like a User Equipment (UE) wanting to send some data is to send a request for resource, then for the primary station (or eNodeB) to acknowledge the request, and grant some resource to the secondary station, then the secondary station to send its data on the granted resource. In this way, resource is allocated piecewise on a first-come first-served basis, meaning that the system carries as much data as possible. However, some resources are "wasted" in carrying the control channel signalling overheads of requesting and granting resource. In UMTS terminology, these resource grants are "dynamic grants". There is also a dynamic grant scheme for the downlink channel, where a primary station indicates to a secondary station which resources are to be listened to for the transmission of data packets.

For some types of operation, with VoIP transmissions being a good illustrative example, a secondary station will be creating data to send with a quite regular frequency and with a similar amount of data each time. In this case, rather than request a new resource for every data packet, an alternative strategy is to allocate a repeating resource to the secondary station. In this case, one request for resource is made, and the grant is for a repeating resource with some frequency of repetition, where no extra requests or grants are needed to access the subsequent resources. In UMTS terminology this is called semi-persistent scheduling (SPS).

The diagram of Figure 1 gives examples of operation of dynamic grants and SPS, with transmissions marked in black being system overheads. This description and diagram are from the point of view of uplink SPS (for transmissions from a secondary station to a primary station). It is to be noted that downlink SPS also exists, and this invention is equally applicable to both uplink and downlink.

As can be seen on Figure 1, by allocating an SPS to an individual user, those resources are no longer available for other users. If the allocated user does not use the SPS fully, this means resources which could otherwise be used by other users are not available, reducing the potential cell and system capacity.

However, not allocating SPS and relying on dynamic grants means higher overheads (also reducing cell and system capacity) for users with frequent transmission requirements, and also introduces a risk that resource is not available to be scheduled to the user, preventing transmission of data altogether.

SUMMARY OF THE INVENTION

It is an object of the invention to propose an improved method of allocating resources to a station.

It is another object of the invention to reduce the overheads for signalling the allocation of resource.

Still another object of the invention is to provide a system where the semi persistent scheduling is done so that the allocated resources are well utilised. To this end, in accordance with a first aspect of the invention, a method is proposed for allocating a set of transmission resources to a plurality of devices, comprising a primary station signalling to at least a first device of the plurality of devices an allocated transmission resource by means of a first type of signalling message capable of indicating a combination of a set of resources and a device from the set of available resources and plurality of devices respectively, the primary station further signalling to a least one device belonging to the plurality of devices an allocated transmission resource by means of a second type of signalling message, wherein the second type of signalling message is constrained to indicate a combination selected from a subset of the combinations of resources and devices which the first type of signalling message is capable of indicating. In accordance with a second aspect of the invention, a method is proposed for allocating transmission resources to a plurality of devices, wherein separate transmission resources for initial transmissions of data packets are allocated persistently to each device, and a set of transmission resources for retransmissions is allocated persistently for the plurality of devices, and wherein at each retransmission occasion at least one signalling message indicates the allocation of specific transmission resources in the set to each of the devices for which a retransmission is required.

In accordance with a third aspect of the invention, a radio station is proposed comprising means for allocating a set of transmission resources to a plurality of devices, the radio station comprising signalling means for signalling to at least a first device of the plurality of devices an allocated transmission resource by means of a first type of signalling message capable of indicating a combination of a set of resources and a device from the set of available resources and plurality of devices respectively, wherein the signalling means are arranged for signalling to a least one device belonging to the plurality of devices an allocated transmission resource by means of a second type of signalling message, wherein the second type of signalling message is constrained to indicate a combination from a subset of the combinations of resources and devices which the first type of signalling message is capable of indicating.

In accordance with a fourth aspect of the invention, a radio station is proposed comprising allocation means for allocating transmission resources to a plurality of devices, wherein the allocation means are arranged so that separate transmission resources for initial transmissions of data packets are allocated persistently to each device, and a set of transmission resources for retransmissions is allocated persistently for the plurality of devices, and wherein the allocation means are further arranged so that at each retransmission occasion at least one signalling message indicates the allocation of specific transmission resources in the set to each of the devices for which a retransmission is required.

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. 1, already described, is a time chart illustrating the difference between a dynamic allocation method and a SPS method. - Fig. 2 is a block diagram of a system in which the invention is implemented

Fig. 3 is a diagram representing the resources to be allocated in accordance with a first embodiment of the invention.

Fig. 4 is a diagram representing the resources to be allocated in accordance with another embodiment of the invention. - Fig. 5 is a diagram representing the resources to be allocated in accordance with still another embodiment of the invention.

Fig. 6 is a diagram representing the resources to be allocated in accordance with still another embodiment of the invention. Fig. 7 is a time chart representing a method of allocating the semi persistent scheduling resources in accordance with a variant of the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system of communication 300 as depicted on

Figure 2, 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. 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 or an antenna array comprising a plurality of antennas, 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 or an antenna array comprising a plurality of antennas, 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 downlink channel 160 and transmission from the secondary radio station 200 to the first radio station 100 takes place on an uplink channel 260.

In the below examples, the primary station allocates resources of the uplink channel to the secondary stations for transmission of data packets to the secondary stations. It is to be noted that the same could apply for downlink resources for receiving at the secondary stations.

As explained above, the use of SPS resources enables to reduce the signalling to be used for indication of the allocated resource. In accordance with a definition of this invention, its implementation allows a recurring resource in a packet based wireless communication system to be temporarily scheduled to a restricted group of users. This makes it available for use by these users with reduced signalling overheads, with a reduced probability of unavailability of resource, but without blocking the availability of as much system resource as if each user was individually allocated a reserved resource. The proposed solution to the problems above is for example to allow "group" SPS. In this case, a semi-persistent resource is allocated for use by a group of users, rather than an individual user. This increases the likelihood of the SPS being used efficiently, because if one user does not have data to send or receive, another one may do. But it also reduces the chance of resource not being available, as this particular resource is only available to a subset of all the users in a cell, so the contention is reduced.

A particular scenario where the invention may be applied as illustrated in some of the following embodiments is for resource allocation for retransmissions. In known systems such as LTE, resources for retransmissions are usually dynamically allocated, even if the resources for initial transmissions are allocated persistently. As it is not known in advance which secondary stations will need resources for retransmissions, dynamic allocation avoids resource wastage but at the cost of increased signalling overhead. By sharing a persistently- allocated resource for retransmissions between a group of users, the overhead of dynamic signalling can be reduced. It becomes necessary only to indicate which secondary station(s) in the group the shared resource is assigned to.

Some mechanisms to manage the sharing of the resource between users are given in the following embodiments. In order to apply SPS to groups of users, it is necessary to manage the sharing of the SPS allocated resource between the multiple users within a group. In the downlink, all transmissions originate from the primary station or eNodeB regardless of destination secondary station or UE. In this case the eNodeB can choose which UE to schedule in a particular resource, according to the availability of data to be transmitted to different UEs. However, in this case, it is also necessary for the UEs in the group to know which UE is meant to receive/decode the data.

In a typical embodiment, each UE in a group is persistently-allocated resources for initial transmissions in the same periodic set of subframes. A further periodic set of sub frames contains persistently-allocated resources for retransmissions for any of the UEs in the group. Advantageously the total amount of resource in each subframe of the further periodic set of subframes is less than the total amount of resource in each subframe persistently-allocated for initial transmissions. Typically, dynamic signalling is used to indicate which part of the resource for retransmissions is allocated to each UE. The amount of such signalling required is reduced compared to the normal dynamic scheduling messages, as the set of resource blocks from which the resource must be selected is much smaller, and the number of UEs involved is also much smaller. The dynamic signalling message may be jointly coded. In such a case it would contain information indicating which RBs are allocated to each of the UEs in the group; for example, the message could comprise a list of UE IDs, ordered according to a predetermined order of RB allocations, prior to the addition of a single CRC and application of channel coding. A typical example is shown in Figure 3. In this diagram, time/frequency resource blocks 301 are represented as a table where time is along the horizontal axis and frequency along the vertical axis. This means that the blocks of a column are all the subcarriers at a given instant. Persistently-scheduled resources 303 for each of a set of 5 UEs for initial transmissions are scheduled. Then, shared persistently- scheduled resource blocks 302 for retransmissions for any of the group of 5 UEs. This means that, should a secondary station of the set need retransmission, it can use one of the semi persistently scheduled resource for retransmission.

In the example, each UE may have a 16-bit ID, and there are 7 resource blocks (RBs) in the frequency domain, requiring 3 bits for an unconstrained resource allocation of a single RB. When 5 UEs are configured with persistently-scheduled resources for their initial transmissions, each with a 40% BLER (error rate), on average 2 RBs will be needed for retransmissions. In the example, 3 RBs are persistently-scheduled for the group of UEs according to the invention, in order to result in a low probability of being unable to transmit all the required retransmissions in any given subframe. Conventional dynamic scheduling for the retransmissions would therefore require

(16+3)x2 = 38 bits on average, while according to the invention only 3 bits are required for each UE ID and 2 bits for each resource allocation, resulting in only (3+2)x2 = 10 bits on average. In practice the number of RBs could be much larger, and different signalling schemes could be used. The saving in control channel overhead may also arise from fewer PDCCH transmissions being required.

Another exemplary embodiment is shown on Figure 4. In this diagram, time/frequency resource blocks 401 are represented as a table where time is along the horizontal axis and frequency along the vertical axis. It should be noted that the resource could be of another type, like code rather than frequency. Persistently-scheduled resources 403 for each of a set of 3 UEs for initial transmissions have been configured for instance for VoIP transmissions. Shared persistently-scheduled resources 402 for retransmissions using IRB for any of the group of 3 UEs have been scheduled.

In a variant of the invention, a similar approach may be taken for a group of secondary stations whose persistently-scheduled resources for initial transmissions are arranged successively in the time domain instead of the frequency domain. In this case, however, there may be some variation in the time delay between the initial transmission and the retransmission. This is for instance illustrated in Figure 5, where resource blocks 501 are represented. Here, the resource blocks 502 are persistently-scheduled resources for each of a set of 3 UEs for IRB initial transmissions plus some shared resource for IRB retransmissions.

In another embodiment, the shared resource for retransmissions may be defined in a different combination of time and frequency domains than the semi-persistent Iy allocated resources for the initial transmissions. A special case of this embodiment occurs when the shared resource for retransmissions is constrained to single subframe in the time domain but is spread across more than one resource block the frequency domain, even though the semi- persistent resource allocations for the corresponding initial transmissions may occur in different sub frames. With suitable timing, the resources for initial transmissions and retransmissions may be jointly allocated, as shown below for the frequency domain. This might require the UE to be capable of receiving a transmission and a retransmission at the same time (which is not currently supported by LTE specifications).

In a further embodiment the amount of resource for each UE could also be adjusted as shown on Figure 6. For example, each UE could be allocated either IRB or 2 RBs 601. This would allow some link adaptation (i.e. change of transmission rate depending on channel conditions). In this example, persistently-scheduled resources 602 are allocated for each of a set of 3 UEs for IRB or 2RBs for initial transmissions plus up to IRB for retransmissions.

In accordance with the first aspect of the invention, the primary station allocates a set of transmission resources to a secondary station, either for uplink or downlink. The allocation of the resources to each secondary station of a group of secondary stations is indicated in a single jointly-encoded signalling message, i.e. a message which is addressed to all stations; such a jointly-encoded signalling messages comprises for instance only one error checks such as a CRC or the like. The sets of resources and of secondary stations are arranged to minimize the required signalling for the allocation. For instance, the set may be constrained as follows by at least one of: - the set of transmission resources is smaller than a total set of transmission resources available; the plurality of devices is smaller than a total set of devices available; the maximum amount of resource which can be allocated from the set of transmission resources to an individual device is limited to a predetermined maximum which is smaller than the amount of transmission resource in the set; the particular transmission resources which can be allocated from the set of transmission resources to an individual device are required to correspond to a particular pattern, for example being contiguous or comprising contiguous blocks each being not smaller than a predetermined minimum size.

As seen before, this aspect may be limited to the retransmissions of packets only or to both the transmission and retransmissions, or only to the initial transmissions, the retransmission being allocated dynamically.

As explained in the above examples, the set of resource blocks may be configured or allocated "persistently" (where "persistently" could be described as being such that a parameter of the set of transmission resources is configured once for a plurality of occasions of the allocation of resources, where the parameter is at least one of the period between occasions, the set of devices in the plurality of devices, and the set of transmission resources selected from the total set of transmission resources).

In accordance with another aspect of the invention which could be combined with the preceding one, it is proposed that the primary station allocates transmission resources to a plurality of secondary stations. In this embodiment, separate transmission resources for initial transmissions of data packets are allocated persistently to each secondary station, and a set of transmission resources for retransmissions is allocated persistently for the plurality of devices. At each retransmission occasion, it is proposed that at least one signalling message indicates the allocation of specific transmission resources in the set of resource blocks dedicated to retransmission to each of the secondary stations to which a retransmission is required.

Moreover, it is possible that the set of transmission resources for retransmissions is smaller than the total amount of transmission resource allocated persistently for initial transmissions, and the signalling messages indicating the allocation of specific transmission resources to each of the devices to which a retransmission is required is a single jointly- encoded signalling message for all the devices to which a retransmission is required.

Besides, a plurality of sets of resource blocks for retransmissions may be allocated. Each of the plurality sets are configured for a different set of secondary stations. Thus, it is possible to create a plurality of groups of secondary stations, each having a set of resources semi persistently scheduled dedicated to it. For example, it is possible to assign UEs to the different sets depending on their channel quality for example. In each set of resources, the number of blocks dedicated to retransmission may vary depending of the channel quality of the dedicated group of secondary stations. By doing so, it is possible to have an amount of resource allocated for retransmission which is linked to the likelihood or the probability of needing a retransmission due to non-correct reception.

In a variant of the preceding embodiment, the indication of which resources in the shared resource apply to each secondary station can be by means of one or more dynamic signalling messages, or by other methods. Suitable other methods for the signalling of the parts of the shared resource allocation may for example include the use of a header in the data packet containing a UE identifier, or in a system with a CDMA element, through the use of UE specific scrambling codes.

Additionally, orthogonal multiple access solutions could be used to allow transmission to multiple UEs within one grant. In the uplink, transmissions can originate from multiple independent UEs. In this case, resource sharing is more difficult to manage efficiently. Requiring UEs to first request permission to transmit in a resource, followed by the eNodeB signalling the granting of permission to particular UEs, removes the benefits of SPS over dynamic scheduling.

Besides, as illustrated in Figure 7, some techniques which could be applied to allow sharing without extra signalling are: • Use of "hopping" patterns to restrict (for example by time or frequency) the choice of resources (from the overall set) which a UE is allowed to use. This guarantees that two UEs can never repeatedly choose the same resource in which to transmit - if they collide in one instance, it means they will not in a subsequent instance, (note that the diagram uses a simplistic "periodic" pattern - in practice, more complex patterns would be used, with better properties across multiple users).

• Use of orthogonal transmission techniques, such as cdma, idma or sdma which allows the eNodeB to separate overlapping transmissions from multiple UEs.

• Collision detection and random backoff techniques. In this approach, UE which do not receive acknowledgement of their transmission wait a random period before retransmitting the data. In this way, two colliding UEs will most likely choose different retransmission slots, allowing the data to get through.

With the possible exception of time hopping, these techniques in themselves are not novel, however they are techniques which can be used to make a practical embodiment of the group SPS idea. Other techniques may also exist. The invention may be applicable to mobile telecommunication systems like UMTS LTE and UMTS LTE-Advanced, but also in some variants to any communication system having allocation of resources to be done dynamically or at least semi persistently.

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.

The inclusion of reference signs in parentheses in the claims is intended to aid understanding and is not intended to be limiting.

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

Claims

1. A method for allocating a set of transmission resources to a plurality of devices, comprising a primary station signalling to at least a first device of the plurality of devices an allocated transmission resource by means of a first type of signalling message capable of indicating a combination of a set of resources and a device from the set of available resources and plurality of devices respectively, the primary station further signalling to a least one device belonging to the plurality of devices an allocated transmission resource by means of a second type of signalling message, wherein the second type of signalling message is constrained to indicate a combination selected from a subset of the combinations of resources and devices which the first type of signalling message is capable of indicating.

2. The method of claim 1 , wherein the second type of signalling message is a single jointly encoded signalling message transmitted to the subset of devices.

3. The method of claim 1 or 2 wherein the constraint comprises at least one of: the set of transmission resources is smaller than a total set of transmission resources available; the plurality of devices is smaller than a total set of devices available; the maximum amount of resource which can be allocated from the set of transmission resources to an individual device is limited to a predetermined maximum which is smaller than the amount of transmission resource in the set;

4. The method of claim 2 or 3, wherein the constraint further comprises that the particular transmission resources which can be allocated from the set of transmission resources to an individual device are required to correspond to a particular pattern.

5. The method of claim 4, wherein the pattern includes contiguous resource blocks each being not smaller than a predetermined minimum size.

6. The method of claim 1 or claim 2, wherein the allocated resource is to be used for retransmission of data messages to or from the devices previously transmitted.

7. The method of any of the preceding claims, wherein the allocated specific resources are allocated once to be used in a repeated manner over a plurality of frames.

8. A method for allocating transmission resources to a plurality of devices, wherein separate transmission resources for initial transmissions of data packets are allocated persistently to each device, and a set of transmission resources for retransmissions is allocated persistently for the plurality of devices, and wherein at each retransmission occasion at least one signalling message indicates the allocation of specific transmission resources in the set to each of the devices for which a retransmission is required.

9. A method as in claim 8, wherein the set of transmission resources for retransmissions is smaller than the total amount of transmission resource allocated persistently for initial transmissions.

10. A method as in claim 9, wherein the at least one signalling message indicating the allocation of specific transmission resources to each of the devices for which a retransmission is required is a single jointly-encoded signalling message for all the devices for which a retransmission is required.

11. The method of any of claims 8 to 10, wherein multiple sets of transmission resources for retransmission are allocated, each of the multiple sets being configured for a different set of devices.

12. A radio station comprising means for allocating a set of transmission resources to a plurality of devices, the radio station comprising signalling means for signalling to at least a first device of the plurality of devices an allocated transmission resource by means of a first type of signalling message capable of indicating a combination of a set of resources and a device from the set of available resources and plurality of devices respectively, wherein the signalling means are arranged for signalling to a least one device belonging to the plurality of devices an allocated transmission resource by means of a second type of signalling message, wherein the second type of signalling message is constrained to indicate a combination from a subset of the combinations of resources and devices which the first type of signalling message is capable of indicating.

13. A radio station comprising allocation means for allocating transmission resources to a plurality of devices, wherein the allocation means are arranged so that separate transmission resources for initial transmissions of data packets are allocated persistently to each device, and a set of transmission resources for retransmissions is allocated persistently for the plurality of devices, and wherein the allocation means are further arranged so that at each retransmission occasion at least one signalling message indicates the allocation of specific transmission resources in the set to each of the devices for which a retransmission is required.