FIELD OF THE INVENTION

The invention generally relates to a method of determining a capability of a mobile station. More particularly, the invention relates to determining a frequency capability of a mobile station, as well as the number of carriers it can support.

BACKGROUND OF THE INVENTION

In order to cater for ever-increasing data rates, recent wireless broadband access communications systems have introduced a multi-band concept that allows them to run more than a single carrier across several frequency bands. Unlike simpler single-band multi-carrier systems, where all the carriers are adjacent to each other and reside in the same band, the multi- band system assumes that a mobile station or user equipment (UE) can support at least two RF chains with at least one carrier in a particular band.

The 3GPP UMTS REL-9 DB-HSDPA is an example of such a solution. It is logical to foresee that further enhancements to 3GPP will aim at increasing the number of carriers in each band or even the number of bands. The latter is especially an interesting case as a particular band always has a limited bandwidth. As an example, a wireless communications network with at least two RF chains and up to 4 carriers is being standardized in 3GPP UMTS Rel-10 framework. However, since UEs accessing the network may differ widely in capabilities, it is crucial that the network knows which bands and carriers are supported to configure the UE so that it can correctly run various radio resource management (RRM) algorithms. A flexible and efficient signalling for multi-band and multi-carrier system must support various UE configuration capabilities. As an example, consider a UE with two RF chains (for frequency bands A and B), that can each support up to 4 carriers, where each carrier takes a bandwidth of 5 MHz in the band. Depending on the RF design, the following cas- es are possible:

15+5 (A+B) MHz RF design. The UE can support 3+1 carrier combination for bands A+B, respectively, and, of course, all the lower combinations, e.g., 2+1 and 1 +1 carriers. Note that in this case the UE cannot support more than one carrier in band B.

15+5 MHz RF design where RF chains can be swapped between the bands A and B. In this case, the UE can support either 3+1 or 1+3 carriers with lower combinations. However, the 2+2 configuration is not supported because one of the receivers is only 5 MHz.

15+15 MHz RF design. The UE can support 3+1 , 2+2, 1+3 carriers and all the lower combinations. Obviously, 3+2 is not valid because the UE can only support up to 4 carriers.

10+10 MHz design. The UE can support 2+2 carriers with all the lower

combinations. Neither 3+1 nor 1+3 is supported because for both receivers the maximum bandwidth is only 10 MHz.

A few cases presented above are valid for the 3GPP Rel-10 4C-HSPDA work item to be proposed for standardization, with a maximum of two RF chains and four carriers. However, these examples can be extended for a system supporting more than four carriers, for example 4+2, where a similar problem exists. Thus, there must be a way to differentiate between the configuration capabilities of each UE in the network.

There are several different methods that have been proposed so far in 3GPP with regard to determining the band and/or carrier capabilities of a UE. One solution is to signal an ID that will encode the band combination and the number of carriers supported in each band. However, this method lacks flexibility and may require a long list of IDs, since a UE can support many different configurations. Another approach is to separate the band combination list from the number of supported carriers in each band. In turn, the latter is conveyed by means of a special bit field with all the carrier combinations. A similar idea is to use a sequence of IDs, where each ID represents a particular combination of number of carriers. Even though these solutions work for a case of two bands and maximum of four carriers, they become almost unmanageable when more carriers and/or bands are introduced due to the large number of carrier combinations required to be represented.

A flexible solution is therefore required, which allows the capabilities of a UE to be deter- mined with minimum complexity, even in the case where more than two bands and more than a maximum of four carriers become incorporated in the standard.

SUMMARY OF THE I NVENTION

Accordingly, the invention provides a method of determining a capability of a mobile station. The method includes signalling frequency bands that the mobile station can support, wherein the signalling includes an indication of a maximum number of carriers supported by the mobile station for each supported frequency band. The signaling also includes an indication of a carrier in one of the supported frequency bands in which transmission or reception of an data may take place by the mobile station. Furthermore, the method includes reporting whether data may also be transmitted or received in said carrier in another one of the supported frequency bands. In other words, the frequency bands and the maximum number of carriers a mobile station can support for a particular band combi- nation (in both uplink and downlink) is simply signaled in a new information element and, in the same information element it is reported to the network whether the maximum number of carriers can be swapped between frequency bands supported by the mobile station

In this way, the RF design of the mobile station is implicitly signaled, so that the network knows the frequency capability of the mobile station in both uplink and downlink, without requiring the introduction of a long bit field or a sequence of carrier combination I Ds. This means that the solution is not complex and is flexible for future 3GPP releases, where more than a maximum of four carriers and/or more frequency bands may be introduced. Preferably, the signaling further includes an indication of whether the mobile station can exchange the frequency band on which the data is transmitted or received in said carrier. An indication may be added to the signaling to indicate whether the mobile station can swap between the frequency bands so that it can transmit or receive carriers in the same combination but in a different supported frequency band on a different transmit- ter/receiver. This indication may be in one bit of information or in any other suitable format. The indication can be contained in the same information element containing the maximum number of frequency bands and number of carriers supported in each frequency band. This provides the advantage that more versatile mobile stations with the capability to "swap" receivers between frequency bands may be supported in future networks; i.e., the method could be applied in a network where a mobile station is able to support three or more different frequency bands.

Resources may be allocated to the mobile station based on a report of whether the mobile station can exchange the frequency band on which the data is transmitted or received in said carrier. Since this method implicitly signals the RF design of the mobile station, the network may then allocate appropriate resources to the mobile station based on the signaling information it receives regarding the number of frequency bands supported by the mobile station, the number of supported carriers in each frequency band, as well as the position in the frequency band in which the carriers are located. The indication may indicate a combination of carriers in each of the frequency bands in which transmission or reception of the data may take place by the mobile station, instead of just one carrier. When one or more of the frequency bands supported by the mobile station may support multiple carriers, the combination of carriers, and where the carriers are located in the frequency band, may also be signaled.

In this case, the signaling may further include an indication of whether the mobile station can exchange the frequency band on which the data is transmitted or received in the combination of carriers (whether the carrier combination may be swapped between frequency bands). The carrier combinations supported by the mobile station, and whether the carrier combinations may be "swapped" between frequency bands, may also be signaled. This may be achieved by adding a "swappable" indication bit to the signaling indicating whether the mobile station can exchange the transmission/reception from a particular combination of carriers in one supported frequency band to the same combination of carriers in another supported frequency band. Then resources may be allocated to the mobile station based on a report of whether the mobile station can exchange the frequency band on which the data is transmitted or received in the combination of carriers.

The invention additionally provides a transceiver unit configured to signal frequency bands that the mobile station can support and configured to signal a maximum number of carri- ers supported by the mobile station for each supported frequency band. The transceiver unit is further configured to report an indication of a carrier in one of the supported fre- quency bands in which transmission or reception of data may take place by the mobile station, as well as an indication of whether data may also be transmitted or received in the carrier in another one of the supported frequency bands. The mobile station may signal to the network the number of frequency bands that it can support, as well as the number of carriers on which it is able to transmit or receive data in each frequency band. It may also signal whether data may be transmitted/received on that same carrier or combination of carriers in another frequency band that it supports. In this way, the network can be aware of the capability of the mobile station and allocate resources to it accordingly. This provides the advantage that the mobile station can signal its capability to the network in a simplified manner, without the need for a long bit field or a complicated sequence of carrier combination IDs, and is an efficient and forward compatible signaling of mobile station capabilities concerning supported carrier combinations depending on the frequency bands (filters) implemented by the mobile station. The invention further provides a network node. The network node includes a transceiver unit configured to receive a signal containing information about a frequency band that a mobile station accessing a communications network via the network node can support, wherein the signal further includes information about a maximum number of carriers supported by the mobile station for each supported frequency band, an indication of a carrier in one of the frequency bands in which transmission or reception of data may take place by the mobile station, and wherein the transceiver unit is further configured to receive a report indicating frequency capabilities of the mobile station including whether the mobile station may transmit or receive data in the carrier (or combination of carriers) in another one of the supported frequency bands. A radio resource control unit is configured to as- sign resources to the mobile station according to its reported frequency capabilities. This provides the advantage that the network can always support future designs of mobile stations, which may be able to transmit and receive data on three or more frequency bands.

The invention will now be described, by way of example only, with reference to specific embodiments, and to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified schematic block diagram of a communications network in which a method according to an embodiment of the invention may be

implemented; - Figure 2 is a simplified schematic diagram of frequency bands and associated carriers in which a mobile station according to an embodiment of the invention may transmit or receive data; and

Figure 3 is a simplified schematic diagram of frequency bands and associated car- riers in which a mobile station according to an embodiment of the invention may transmit or receive data

DETAILED DESCRI PTION OF EXEMPLARY EMBODIMENTS Figure 1 shows a wireless communications network that can be accessed by a mobile station (or user equipment) UE for sending and receiving data via a NodeB 1. The NodeB 1 is coupled to a radio network controller (RNC) 2 and is controlled by the RNC 2 over an lub interface. The user equipment UE includes a transmit/receive unit TxRx for sending and receiving data such as voice, multimedia, etc. The transmit receive unit TxRx includes two filters F1 and F2, which allow the user equipment UE to transmit and receive data on two different frequency Bands A and B, respectively. The filters F1 and F2 may be constructed from several smaller filters so that data may be transmitted/received on different carriers within the frequency band, with each smaller filter only allowing transmission and reception of signals in the frequency range of its corresponding carrier. For the UMTS network illustrated here, as an example, the frequency band A could be operating band I , from 1920- 1980 MHz in the uplink and 21 10-2170 in the downlink, and the frequency band B could be operating band VI I I, from 880-915 MHz in the uplink to 925-960 MHz in the downlink.

The RNC 2 has a transceiver unit 3 and a radio resource control unit 4, which is configured to assign resources to the user equipment UE according the frequency capabilities it reports to the RNC 2 when a radio link RL is established between the user equipment UE and the network over the NodeB 1 and the RNC 2. During establishment of the radio link RL, the user equipment UE signals to the network the frequency bands it can support, in this case Band A and Band B. However, the user equipment UE may also be able to support three or more bands. The method can be equally well applied in cases where the user equipment UE can transmit and receive data on more than two bands.

In Figure 2, the situation is illustrated where each of the two frequency bands, Band A and Band B, supported by the user equipment UE has up to four possible carriers a, b, c and d, in which data can be transmitted and received. When the user equipment UE signals to the network the frequency bands A and B it can support, it also indicates the number of carriers in each band, where the network can configure any carrier, or number of carriers, within the band, subject to the capabilities of the user equipment UE. The user equipment UE also reports to the network in the signaling whether it can transmit and receive data on the same carrier configuration or combination in a different frequency band. The carriers in which data can be transmitted and received by the user equipment UE are represented by the shaded areas in Figure 2.

For the example illustrated in Figure 2, the maximum number of carriers supported by the user equipment UE in each band is (3, 1) - 3 carriers in Band A and 1 in band B (carrier a). One bit of information in the message signaled from the user equipment UE to the network provides a report to the network as to whether this combination may also be transmitted/received as (1 , 3) - 1 carrier in Band A (carrier a) and 3 carriers in Band B.

In other words, this one bit received by the network from the user equipment UE tells the network if the user equipment UE is able to "swap" transmitters/receivers (filters) between the bands.

The message containing the indication whether swapping between frequency bands is supported may be a message related to radio resource control, for example a handover message or UE capability message exchanged between the user equipment UE and the node responsible for radio resource control of the user equipment UE in the network, for example the RNC 2 or NodeB 1. Examples of those messages are INTER RAT

HANDOVER INFO, RRC CONNECTION SETUP COMPLETE, UE CAPABILITY

INFORMATION. Other carrier combinations supported by the user equipment UE are (3, 3) - 3 carriers in Band A and 3 in Band B (carriers a, b and c in both bands); also any carrier configuration that does not exceed the maximum of 4 carriers, as well as (2, 2) - 2 carriers in Band A and 2 carriers in Band B.

Figure 3 illustrates an example where the frequency bands A and B may each contain a maximum of 6 carriers each (a, b, c, d, e and f). This fact is signalled by the user equipment UE to the network, along with the allowed carrier combinations supported, so, for example, in the case of the carrier combination (4, 2) - 4 carriers in Band A and 2 in Band B, one bit of information is also signalled to the network when the mobile station also supports swapping of carrier configuration between the bands to (2, 4) - 2 carriers in Band A and 4 in Band B.

In this situation, the user equipment UE can also support the following carrier combina- tions:

1. (3, 3): the 15+15 MHz RF design, 3+3 and the lower combinations are allowed

2. (4, 2): In the (4, 2) carrier combination described above: in for example a 20+10 MHz RF design, 4+2 and the lower combinations are allowed.

3. (4, 2) (2, 4): in the 20+10 MHz RF design with receivers that can be tuned to any band, 4+2 and 2+4 combinations are allowed.

4. (4, 3): in a 20+15 MHz RF design, 4+2 and the lower combinations in conjunction with 3+3

5. (4, 4): in a 20+20 MHz RF design, any combination that does not exceed 6

carriers is allowed.

If the transceiver unit 3 of the RNC 2 receives a report from the user equipment UE including the one bit of information that the user equipment UE has the capability to exchange transmission/reception carrier configurations between its supported frequency bands, the radio resource control unit 4 then allocates appropriate resources to the user equipment UE based on its reported frequency capabilities.

An example of a new list that the user equipment UE will use to signal the maximum num- ber of supported carriers in each band, as well as whether carriers are swappable between bands, is shown in Table I. The number of items in this list must be the same as in the band combination list. Absence of the list means that the user equipment UE supports only a 1+1 carrier configuration. Such an interpretation allows for the backward compatibility with pre Rel-10 UEs, e.g., Rel-9 DB-HSDPA. The abbreviations OP and MP indicate the need of the information element; i.e., whether this information element is included optionally or mandatorily, respectively. The numbering 1 .. 16 indicates that at least 1 and up to 16 occurrences of the information elements may be included if they are is included.

Table I

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments, and no doubt further alternatives will occur to the skilled person, that lie within the scope of the invention as claimed. For example, the radio resource control unit 4 could also be located in the NodeB 1 , so that the Node B 1 is the network node that assigns resources to the user equipment UE, instead of the RNC 2, based on the signalling it receives from the user equipment UE indicating its frequency capabilities. The method is carried out in exactly the same way as described above.