WO2008092745A1

WO2008092745A1 - A method of communication

Info

Publication number: WO2008092745A1
Application number: PCT/EP2008/050444
Authority: WO
Inventors: Simon Paul Davis; David Philip Hole; Eswar Vutukuri
Original assignee: Nokia Siemens Networks Gmbh & Co. Kg
Priority date: 2007-01-30
Filing date: 2008-01-16
Publication date: 2008-08-07

Abstract

A method of operating a mobile device, wher ein the mobile device is adapted for operation in downlink dual carrier, DLDC, m ode or mobile stati on receive diversity, MSRD, mode either simultaneously, or serially; the method comprising switching MSRD mode on or off in response to one of radio conditions or dynamic network indications.

Description

A METHOD OF COMMUNICATION

This invention relates to a method of communication between a mobile device and a network, in particular for mobile devices capable of operating in both mobile station receive diversity (MSRD) mode and downlink dual carrier (DLDC) mode, whether at the same time, or at different times.

These modes of operation are illustrated in Figs. 1 and 2. MSRD is a technique which combines two received versions of the same transmit signal, fc 18, 19, sent from transmitter 17 and in this example, received on two antennas at a mobile 20, to improve the performance of the MSRD mobile 20, specifically, by reducing the probability that a block of data is received with errors after decoding. This is a new feature in general packet radio service (GPRS)/enhanced data rates for global system for mobile communication (GSM) evolution (EDGE) radio access networks (RAN) which has only recently been standardised. A means of signalling to the network that the mobile is capable of MSRD has been standardised, and the required performance of a mobile operating with MSRD active has also been agreed, but other aspects of its operation are still under discussion. DLDC mobiles 23, can receive data on two carriers fcl 21 and fc2 23 from a transmitter 17, simultaneously and this has also been standardised recently as part of Rel-7 enhancements for GERAN. Compared to a mobile which is not capable of either MSRD or DLDC, a mobile which supports either of these features requires some additional functionality. However, the additional capabilities required (relative to a mobile which supports neither) are similar for both of these functions, since both features require the mobile to receive two separate signals (two versions of the same signal, in the case of MSRD, or two separate signals - one on each carrier - in the case of DLDC). To support MSRD and DLDC simultaneously, four separate signals must be received (two versions of each of the signals on each carrier). As the number of signals which are to be simultaneously received increases, the functionality (and therefore the size and cost) of the mobile increases. It is likely that most implementations of mobile stations will not allow use of DLDC and MSRD at the same time although, as stated above, it is theoretically not impossible to do so. In many cases, downlink resources are allocated dynamically. This means that currently, the mobile station must receive the signal on both downlink carriers simultaneously (and therefore may not be able to use MSRD), even if data for the mobile is sent on one, or none, of the carriers.

Furthermore, a benefit for the mobile in not activating MSRD, if it is not necessary, e.g. if the current receiver performance is acceptable, is that battery consumption in the mobile is reduced.

However, there is no mechanism for the network to signal to the mobile that it should use MSRD at any particular time, nor is there is an indication from the mobile to the network that it is using MSRD.

In accordance with a first aspect of the present invention, a method of operating a mobile device, wherein the mobile device is adapted for operation in downlink dual carrier , DLDC, mode or mobile station receive diversity, MSRD, mode either simultaneously, or serially comprises switching MSRD mode on or off in response to one of radio conditions or dynamic network indications.

Preferably, the mobile operates MSRD on a single specified carrier. In accordance with a second aspect of the present invention, a method of communicating between a network and a mobile device, wherein the mobile device is adapted for operation in downlink dual carrier, DLDC, mode or mobile station receive diversity, MSRD, mode either simultaneously, or serially comprises sending a notification from the network to the mobile device that certain information will be sent on only a single specified carrier.

Preferably, the certain information comprises at least one of control information and data retransmissions.

Preferably, an identity of the single specified carrier is notified to the mobile device in advance. Preferably, the identity of the specified carrier is notified in an assignment message.

Preferably, the mobile device operates MSRD using the single specified carrier. Preferably, the mobile device indicates to the network that MSRD is enabled. Preferably, the mobile device further provides an indication that DLDC and MSRD mode are in use simultaneously.

Preferably, whilst operating in DLDC mode, the network ceases to send on one carrier. Preferably, the network advises the mobile device to switch to MSRD mode. Preferably, the network indicates to the mobile device in one radio block period that it should operate DLDC mode in a subsequent radio block period.

Preferably, the network indicates to the mobile device in one radio block period that it should operate MSRD mode for a subsequent N radio block periods.

In accordance with a third aspect of the present invention, a method of communication between a mobile device and a network, wherein the mobile device is adapted for operation in downlink dual carrier mode, DLDC, or mobile station receive diversity mode, MSRD, either simultaneously, or serially comprises sending from the mobile device to the network, an indication that the mobile device is using MSRD mode.

Preferably, the indication is included in a packet acknowledgement message. Preferably, the mobile device further provides an indication that DLDC and MSRD mode are in use simultaneously. An example of a method of communication between a mobile device and a network according to the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows the operation of a mobile device in MSRD mode; Figure 2 shows the operation of the mobile device in DLDC mode; Figure 3 is a block diagram of a typical system in which the method of the present invention is applied;

Figure 4 illustrates a change from DLDC to MSRD in accordance with the present invention;

Figure 5 illustrates notification of the use of MSRD in accordance with the present invention;

Figure 6 illustrates simultaneous use of DLDC and MSRD in accordance with the method of the present invention;

Figure 7 illustrates dynamic indication of MSRD in accordance with the method of the present invention; and, Figure 8 shows a typical burst of data sent on the air interface in a GSM/EDGE network. The performance of the downlink is enhanced if the mobile which is not capable of supporting DLDC and MSRD simultaneously is able to know when it must enable DLDC, and when it can enable MSRD (i.e. when data is being sent to the mobile on one carrier only). In particular, it is beneficial if the use of MSRD can be ensured to maximise the probability of receiving important control information, such as handover commands, or assignment messages.

The lack of indication that the mobile device is using MSRD is a problem because then the network is not sure whether, or not, the receive performance of a mobile device is, or is not, based on the mobile using MSRD. In particular, this makes it impossible for the network to estimate the receive performance of a mobile, if it were not using MSRD, particularly, but not limited to, the case where this is because the mobile is using DLDC. An example of the consequences of this limitation is that if the mobile device reports good reception quality (i.e. has a low probability of decoding frames unsuccessfully) and is using MSRD, then if the network makes a resource assignment which requires the mobile to use DLDC and so probably not use MSRD, then the reception quality at the MS may deteriorate significantly, in the worst case leading to a dropped call.

If the network is aware of both the received quality and the mode of operation of the mobile device, i.e. whether it is MSRD enabled or MSRD disabled, then the network can make better decisions about link adaptation, handover and further resource assignments Without the present invention, the network would have to base decisions such as link adaptation, i.e. choosing the correct modulation and coding scheme; handover, i.e. handing the mobile over to another cell; and resource allocation etc., on just the signal quality reported by the mobile device and these decisions may turnout to be sub-optimal if the state of operation of the mobile (MSRD enabled/ MSRD disabled) changes. Although the MS capability is known to the network, it is not clear whether MSRD is switched on, or not, at that particular instance.

Similarly, even for non DLDC operations, the network may find it hard to perform link adaptation on the downlink and/or determine whether a handover should occur, if the MS can autonomously enable, or disable the MSRD function without informing the network. If the network is aware of whether, or not MSRD is being used, then it can take this into account. The problems addressed by the present invention arise from the recent, partial, standardisation of MSRD and DLDC. Fig.3 illustrates a typical system in which a base station 1 of a network communicates with a number of mobile devices, or mobile stations, Ml, M2, M3, M4 in different states of operation. The different forms of communication are illustrated in Figs. 4 to 7. Fig. 4 illustrates changing from dual carrier to use of a single carrier for important control information, such as handover commands and/or retransmissions. The single carrier can be pre-determined, or determined dynamically.

The mobile device Ml is receiving on the downlink 2 an assignment 3 which requires the mobile to use DLDC. If the channel quality between the base station 1 of the network and the mobile Ml degrades rapidly, then the mobile may not be able to enable MSRD, because the assignment requires the mobile to use DLDC. This prevents the mobile improving its likelihood of receiving important control information correctly. In this situation, if the mobile Ml has a DLDC assignment, the network always sends 4 important control information, such as handover commands, or new assignment messages, etc., on a specified carrier, which is one of the two carriers in the DLDC mode. The mobile, on determining that its channel quality is degrading may, without necessarily informing the network, cease receiving on the non-specified carrier, and activate MSRD, using only the specified carrier. In this way, it is guaranteed that any control information sent by the network will be received with a high probability by the mobile. The specified carrier can be pre-specified in the standard, statically e.g. on the

'first carrier'; on one carrier as defined in the various assignment messages, or when using dual transfer mode (DTM), the carrier can be specified as the one on which the CS timeslot is located. Alternatively, the carrier may be specified semi-statically, in the assignment message. Furthermore, the mobile may subsequently inform the network of the change to

MSRD, e.g. by sending a message 5, such as an ACK/NACK message, on the uplink 6, indicating that the mobile Ml has enabled MSRD on the single specified carrier. Another improvement when the network has the knowledge of such a rearrangement is that the network can optimise the performance of an acknowledged mode temporary block flow (TBF) which spans across two carriers by sending 6 re-transmissions of data blocks on the nominated carrier, as this makes it possible for the mobile to receive these blocks, with higher probability, if it has switched to using MSRD. In order to help the network perform link adaptation better, the present invention provides for the mobile device to inform the network when it is using MSRD, on a dynamic basis. In Fig. 5, a mobile device M2 indicates 7 to the base station 1 that it is operating MSRD. As an example, the indication may be included in packet acknowledgement messages, such as enhanced GPRS (EGPRS) Packet Downlink Ack/Nack messages. The benefit of this is that it gives the network a better understanding of the quality of the radio channel between itself and the mobile. This allows the network to make improved decisions regarding the appropriate modulation and coding scheme (MCS) to be used, and whether or not a handover should be initiated towards another cell. For example, if the block error rate is quite high, but

MSRD is not being used, the network knows that the mobile could continue to operate in this cell by activating MSRD. In this case the network may choose to send an indication 8 from the base station 1 to the mobile M2 to switch to MSRD. Alternatively, if the block error rate is quite high and MSRD is being used, the network may choose to initiate a handover towards another cell.

Since MSRD and DLDC are likely to be mutually exclusive for most mobile station implementations, because of the component duplication and corresponding size and power constraints, such an indication of whether, or not MSRD is active gives the network information as to how well the mobile is likely to perform if it were to make an assignment which did require the mobile to use DLDC (and therefore would not allow MSRD to be used).

Alternatively, in the case where MSRD and DLDC are not exclusive, as shown in Fig. 6 due to the implementation of the mobile, this can be indicated to the network. If a dual carrier assignment 9 is ongoing, the mobile M2 can indicate 10 to the base station of the network that it is receiving blocks on both carriers and using MSRD. This also removes the need to add an extra bit in the mobile capability indications, which are already quite crowded, with little free space. The mobile needs to indicate explicitly that it is still using DLDC and MSRD, and had not, for example, abandoned one carrier. The network is unlikely to track which blocks are sent on which carrier, so the indication from the mobile indicates DLDC yes/no, plus MSRD yes/no.

Another feature is that the network signals dynamically to the mobile device, in advance, indicating when the network will send data on one carrier only. In Fig.7, the mobile device M4 receives an indication 11 from the base station 1 that the network is sending data on one carrier only. If there is a change in the preferred single specified carrier, then the base station sends further update indications 12, 13. The identity of the one specified carrier on which data will be sent can be signalled dynamically, so that it can change during the course of a connection, or it can be 'semi-statically' indicated to the mobile, e.g. within a resource assignment message. Alternatively, the identity may be implicitly indicated, e.g. as the carrier described first in an assignment message, or the carrier on which the CS timeslot is present in case of DTM.

Therefore, it is not necessary that both the fact that only one carrier will be used and the identity of the carrier to be used is signalled; only the former need be dynamically indicated.

There are many possible ways to dynamically signal that the MS need only receive on one carrier. When downlink dual carrier assignment is made, by default and unless indicated otherwise by the network, or autonomously determined as described above, the mobile continues to be in downlink dual carrier mode of operation. This guarantees that the whole process of switching between MSRD and downlink dual carrier is fail safe, since if the mobile does not detect the indication that a single carrier is to be used, then the mobile continues receiving on both carriers.

The network may indicate in the previous block period whether or not reception on the two downlink carriers is necessary in the subsequent radio block period. This indication can be done using physical layer signalling, as illustrated with respect to the example data burst shown in Fig. 8. This comprises encrypted data bits 14, stealing flags 15 and training sequence bits 16. The indication may be provided for instance using the stealing flags 15, or a new bit in the header can be used for this purpose. An alternative is that the network explicitly signals the total number of downlink blocks on which the MS may skip reception on a given downlink carrier. To do this, more than one bit is needed for signalling. Bits in the header of the previous block can be used for this purpose, or a setting of the stealing flags is used to indicate a given number of time division multiple access (TDMA) frames in which the MS can skip reception on one of the carriers. Another option is to provide an indication to skip reception on one carrier, such that nothing is transmitted on that carrier for not just one, but for 'N' radio block periods where 'N' has been negotiated previously, for example during the assignment.

The present invention maximises the possibility for the mobile to use MSRD, even when it has a DLDC assignment, thereby maximising the probability of receiving the data correctly. The invention also allows the mobile to move to using MSRD on a single carrier, even when it has a DLDC assignment, knowing that important control information (handovers, etc.) and/or retransmissions of data will be sent on that carrier. A further advantage is that the invention improves the link adaptation used by the network when the mobile is MSRD-capable, by indicating to the network when MSRD is being used.

Claims

1. A method of operating a mobile device, wherein the mobile device is adapted for operation in downlink dual carrier , DLDC, mode or mobile station receive diversity, MSRD, mode either simultaneously, or serially; the method comprising switching MSRD mode on or off in response to one of radio conditions or dynamic network indications.

2. A method according to claim 1, wherein the mobile operates MSRD on a single specified carrier.

3. A method of communicating between a network and a mobile device, wherein the mobile device is adapted for operation in downlink dual carrier, DLDC, mode or mobile station receive diversity, MSRD, mode either simultaneously, or serially; the method comprising sending a notification from the network to the mobile device that certain information will be sent on only a single specified carrier.

4. A method according to claim 3, wherein the certain information comprises at least one of control information and data retransmissions.

5. A method according to any of claims 2 to 4, wherein an identity of the single specified carrier is notified to the mobile device in advance.

6. A method according to any of claims 2 to 5, wherein the identity of the specified carrier is notified in an assignment message.

7. A method according to any of claims 3 to 6, wherein the mobile device operates MSRD using the single specified carrier.

8. A method according to any preceding claim, wherein the mobile device indicates to the network that MSRD is enabled.

9. A method according to claim 8, wherein the mobile device further provides an indication that DLDC and MSRD mode are in use simultaneously.

10. A method according to any of claims 3 to 9, wherein, whilst operating in DLDC mode, the network ceases to send on one carrier.

11. A method according to any of claims 3 to 10, wherein the network advises the mobile device to switch to MSRD mode.

12. A method according to any of claims 3 to 9, wherein the network indicates to the mobile device in one radio block period that it should operate DLDC mode in a subsequent radio block period.

13. A method according to any of claims 3 to 9, wherein the network indicates to the mobile device in one radio block period that it should operate MSRD mode for a subsequent N radio block periods.

14. A method of communication between a mobile device and a network, wherein the mobile device is adapted for operation in downlink dual carrier mode, DLDC, or mobile station receive diversity mode, MSRD, either simultaneously, or serially; the method comprising sending from the mobile device to the network, an indication that the mobile device is using MSRD mode.

15. A method according to claim 14, wherein the indication is included in a packet acknowledgement message.

16. A method according to claim 14 or claim 15, wherein the mobile device further provides an indication that DLDC and MSRD mode are in use simultaneously.