Extended dynamic resource allocation for packet data transfer

IS 2 255 690 T3

DESCRIPTION

Extended dynamic allocation of resources for a packet data transfer.

This invention relates to multiple access communication systems and relates in particular to dynamic resource allocation in time division multiple access systems.

In wireless multiple access systems such as GSM, several mobile stations communicate with a network. The allocation of physical communication channels for use by mobile stations is fixed. A description of the GSM system can be found in The GSM System for Mobile Communications by M. Mouly and MB Pautet, published in 1992 under the reference ISBN 2-9507190-0-7.

With the advent of packet data communications over Time Division Multiple Access (TDMA) systems, more flexibility is required in the allocation of resources and in particular in the use of physical communication channels. For packet data transmissions in General Packet Radio Systems (GPRS) a number of Packet Data Channels (PDCH) provide the physical communication links. The time division is by frames of 4.615 ms duration and each frame has eight consecutive intervals of 0.577 ms. A description of the GPRS system can be found in (3GPP TS 43.064 v5.1.1). The slots can be used for uplink or downlink communication. Uplink communication is a transmission from the mobile station for reception by the network to which it is attached. The reception by the mobile station of a transmission from the network is described as downlink.

To use the available bandwidth very effectively, channel access can be allocated in response to changes in channel conditions, traffic load, Quality of Service, and subscription class. Due to continuously changing channel conditions and traffic loads a method is available for dynamic allocation of available channels.

The amounts of time that the mobile station receives downlink or transmits uplink can be varied and the slots can be assigned accordingly. The sequences of slots allocated for reception and transmission, the so-called multi-slot configuration is generally described in the form RXTY. The reception intervals (R) being assigned the number X and the transmission intervals (T) assigned the number Y. A number of multi-slot classes, one to 45, is defined for GPRS operation and the maximum uplink (Tx) and downlink (Rx) slot assignments are specified for each class.

In a GPRS system, access to a shared channel is controlled by means of an Uplink Status Flag (USF) transmitted on the downlink to each communicating mobile station (MS). Two allocation methods are defined in GPRS methods, differing in the convention around which uplink slots are made available upon receipt of a USF. The present invention relates to a particular assignment method, in which an equal number "N" of PDCHs, a "PDCH" representing a pair of uplink and downlink slots corresponding to each other on a 1-1 basis, are assigned for potential use by MS. The uplink slots available for actual use by a particular mobile station sharing the uplink channel are indicated in the USF. The USF is a data element capable of taking 8 V0-V7 values, and allows assigning uplink resources between up to 8 mobiles where each mobile recognizes one of these 8 values ​​as "valid", that is, it confers exclusive use of resources to said mobile. A particular mobile station may recognize a different USF value in each of the slots assigned to that mobile station. In the case of the extended dynamic allocation method, for example, the receipt of a valid USF in slot 2 of the present frame will indicate the actual availability for transmission of 2 ... N transmission slots in the next TDMA frame or group of frames, where N is the number of assigned PDCHs. In general for a valid USF received in the reception slot n, the transmission takes place in the next transmission frame in the transmission slots n, n + 1 and following the number of allocated slots (N). For the extended dynamic allocation method as currently defined these allocated ranges are always consecutive.

The mobile station is not capable of instantly switching from a receiving condition to a transmitting condition or vice versa and the time allocated to these reconfigurations is called the changeover time. It is also necessary for the mobile station, while in packet transfer mode, to perform contiguous cell measurements. The mobile station has to continuously monitor all Broadcast Control Channel (BCCH) carriers as indicated by the BA (GPRS) list and THE BCCH carrier of the serving cell. A received signal level measurement sample is taken in each TDMA frame, on at least one of the BCCH carriers (3GPP TS 45.008v5 10.0). The change and measurement times guaranteed by the network for a mobile station depend on the multislot class with which the mobile claims compliance (3GPP TS 45.001v5.9.0 Annex B).

Contiguous cell measurements are taken before reconfiguration from reception to transmission or before reconfiguration from transmission to reception.

A mobile station operating in extended dynamic allocation mode currently must start uplink transmission in the time slot Tx corresponding to the time slot Rx in which the first valid USF is recognized. That is, there is a fixed relationship in the timing of the downlink assignment signaling and the next uplink transmission. Due to the physical limitations of

ES 2 255 690 T3 single transceiver mobile stations some desirable multi-slot configurations are not available for use.

These restrictions reduce the availability of slots for uplink transmissions thereby reducing data flow and flexibility in response to changing conditions. Therefore, a method must be provided by which to allow the use of the multi-range configurations currently not available for Extended Dynamic Assignment.

EP-A-1248479 describes a multiple access communication method in a network that transmits an Uplink State Flagger to a mobile station in a downlink time slot, where an Uplink State Flagger commands a mobile station that performs uplink transmission in a first uplink time slot is transmitted in a first uplink slot.

An object of this invention is to reduce the constraints that affect extended dynamic allocation with minimal effect on the existing prescription. This can be achieved by altering the fixed ratio in the timing of the downlink assignment signaling and the next uplink transmission for some classes of mobile station.

According to the invention there is a method for controlling uplink packet data transmissions and a mobile station operating according to the method set forth in the appended claims.

An embodiment of the invention will now be described with reference to the accompanying figures in which:

Figure 1 illustrates the TDMA GPRS frame structure showing the numbering convention used for uplink (UL) and downlink (DL) time slots.

Figure 2 illustrates a prior art 4-time slot R1T4 steady state assignment.

Figure 3 illustrates a prior art prohibited R1T5 5 slot steady state assignment.

FIG. 4 illustrates a 5 slot R1T5 steady state assignment enabled by the method of the present invention.

Figure 5 illustrates an offset USF applied to a Class 7 MS with 3 assigned uplink slots.

Figure 6 illustrates a Class 7 MS with 2 assigned uplink slots.

Figure 7 is a flow chart for the implementation of offset USF in a mobile station.

Figure 8 illustrates a transition from one uplink slot to five uplink slots for a class 34 MS.

Figure 9 illustrates a transition from four to five uplink slots for a class 34 MS.

In this embodiment, the invention is applied to a GPRS wireless network operating according to the standards applicable to multi-slot classes. In Figure 1 the TDMA DPRS frame structure is illustrated and shows the numbering convention used for uplink (Tx) and downlink (Rx) time slots. It should be noted that in practice Tx can be advanced relative to Rx due to timing advance (TA), although this is not depicted in the illustration. Thus, in practice, the amount of time between the first Rx and the first Tx of a frame can be reduced by a fraction of an interval from the illustrated value of 3 intervals due to timing advance.

Two successive TDMA frames are illustrated with separately identified downlink (DL) and uplink (UL) slots. The slot positions within the first frame are represented by the numbers 0 to 7 with the transmit and receive slots shifted by a margin of three slots. This is according to the convention that the first transmission frame in ONE TDMA delays the first reception frame by an offset of 3 (thus, ordinary single-slot GSM can be considered as a concrete case where only slot 1 of transmission and reception).

The remaining figures are in accordance with the illustration in Figure 1 but the interval numbering has been removed for clarity. The shaded intervals are those assigned for the particular states and the arrow inserts indicate the applicable measurement and change intervals. The dashed intervals indicate the receipt of a valid USF and the time interval in which that USF is received. As mentioned above, limitations are imposed by the need to allow measurement and change intervals and the prescription of these in 3GPP TS 45.002 Annex B limits the dynamic allocation as shown in table 1.

IS 2 255 690 T3

TABLE 1

<td>Multi-interval class</td><td colspan="3">Maximum number of intervals</td><td colspan="4">Minimum number of intervals</td>

<td></td><td>Rx</td><td>Tx</td><td>Sum</td><td>Tta</td><td>Ttb</td><td>Tra</td><td>^Trb</td>

<td> 7</td><td> 3</td><td> 3</td><td> 4</td><td> 3</td><td> 1</td><td> 31</td><td> 3</td>

<td> 4</td><td> 5</td><td> 5</td><td> 6</td><td> 2</td><td> 1</td><td> 1</td><td> 1</td>

<td> 39</td><td> 5</td><td> 5</td><td> 6</td><td> 2</td><td> 1</td><td>¹+ to</td><td> 1</td>

<td> 45</td><td> 6</td><td> 6</td><td> 7</td><td> 1</td><td> 1</td><td> 1</td><td>to</td>

T_ta is the time required for the MS to measure the adjacent cell signal level and prepare to transmit.

T_tb is the time required for the MS to prepare to transmit

T_ra is the time required for the MS to measure the adjacent cell signal level and prepare to receive.

Trb is the time required for the MS to prepare to receive.

It should be noted that in practice the times T_ta and T_tb they can be shortened a fraction of an interval due to timing advance.

T₀ is the time advance offset of 31 symbol periods.

Referring to Figure 2, a steady state single downlink and 4 uplink slot assignment is illustrated for a class 34 mobile station. The changeover and metering periods for this class are shown in Table 1 as Tra , Trb and Ttb each having one interval and Tta having two intervals. These periods can be accommodated for this assignment when a valid USF is received in time span 0.

However, when the uplink slot allocation is extended to five, a limitation arises as indicated in the figure 3 illustration which is for a class 34 mobile station with an allocation of one downlink and five link slots. upward. The limitation occurs in the position indicated with “A” because no time is allowed for the change from transmission to reception (Trb). In downlink time slot 0 a valid USF is received and the next two slots provide Tta. According to the invention, for this embodiment the mobile has uplink slots assigned in the usual way, by using USF_TN0 ... USF_TN7 Information Elements in Packet Uplink Assignment and Packet Time Slot Reconfiguration messages. The network sends the USF, however, during both the assigned first and second time slots on the downlink PDCH associated with the assigned second time slot.

Considering as an example a class 34 MS with an assignment of 5 uplink slots (TN0-TN4) as explained above where the network sends USF_TN0 in time slot 1 instead of time slot 0. This arrangement is illustrated in figure 4 where it can be seen that the intervals marked "B" and "C" provide times of change Tra and Trb, respectively.

An allocation by the network of 4 uplink slots to the MS will be signaled by sending USF_TN1 in time slot 1. The characters of the two signals USF_TN0 and USF_TN1 must differ and must be distinguishable by the mobile station.

No extra information elements need to be added to indicate when the offset USF mechanism is to be used, because it may be implicit in the time slot assignments for the particular multislot class of the mobile station. Therefore, no increased signaling load will be required.

Referring to Figure 5, another example of an offset USF implementation enabled assignment is illustrated in Figure 5. The application is a Class 7 MS with three assigned uplink slots. The USF in downlink slot 1 that allocates the 3 uplink slots indicates that the first available uplink slot is uplink slot 0 instead of the usual slot 1. This gives the periods Ttb and Tra (as required from Table 1) and as indicated in Figure 5 at D and E, respectively. The assignment would not have been previously available due to the desire of a sufficient period for Tra.

IS 2 255 690 T3

The 2 slot allocation illustrated in Figure 6 reverts to normal operation, ie the USF is not offset. There are no physical limitations to the normal assignments for this 2-slot arrangement of Figure 6 and the standard USF in time slot 1 allocates uplink slots starting with uplink slot number 1.

Alternatively it may be desirable to apply positive signaling of the uplink assignment position shift and an implementation of an offset USF in a mobile station operating extended dynamic assignment is illustrated in Figure 7. It should be noted that the indication (2) in Figure 7 can be explicit (ie extra signaling) or implicit (automatic for particular multi-slot class configuration). With reference to FIG. 7, the mobile station receives at 1 an allocation of uplink resources and USFs from the network. If an indication to use a shifted USF is detected at 2, for the first USF, the second downlink slot (3) is checked, otherwise the first downlink slot (4) is checked. In any case, when a valid USF has been received at 5, the uplink transmissions are started in the first uplink slot of the mobile station (6). When no valid USF has been received at 5, the second downlink slot is checked for a second USF at 7 and if valid (8), the uplink transmissions are started on the second uplink slot (9).

In the examples illustrated in Figures 2 to 6 the assignments are steady state such that the displayed assignments are maintained from frame to frame. The invention is not limited to regime state assignments and can also be applied to control uplink resources that change from one frame to another.

Examples of transitions are illustrated in Figures 8 and 9. These figures represent four consecutive frames but have been divided for presentation.

Figure 8 illustrates the transition from an uplink slot assignment to a five slot uplink assignment, for a Class 34 mobile. The first two (upper) frames show steady state operation with one slot and the two Subsequent (lower) frames show transition frames. For this transition the slot position of the USF is changed.

Figure 9 illustrates the transition from four uplink slots to five uplink slots, for a Class 34 mobile. The first two frames show steady state operation with four slots and the next two frames show the transition frames. For this transition the USF interval position is constant but the USF value is changed.

To implement the invention in GPRS for example a table (Table 2) for a Type 1 MS can be constructed to allow extended dynamic allocation using the following principles:

In the case of extended dynamic allocation it is desirable that the MS be able to "transmit up to its physical interval limit"; specifically, the MS should be able to transmit the maximum number of slots possible according to the limitation of its multi-slot class, while continuing to receive and decode the USF value in exactly one slot and perform measurements. If it is not possible to define a multi-slot configuration that allows the MS to “transmit up to its physical slot limit” using T_ra, but it would be possible using T_ta, T will be used_ta.

If it is not possible to define a multi-slot configuration for extended dynamic allocation that allows the MS to “transmit up to its physical slot limit”, but would be possible using the offset USF mechanism, offset USF will be used. In this case, Tra will be used as the first preference, but if this is not possible, Tta is used as the second preference.

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IS 2 255 690 T3

TABLE 2

<td>Medium access mode</td><td>Number of intervals</td><td>T will be applied_ra</td><td>T will be applied_ta</td><td>Applicable multi-interval classes</td><td>Note</td>

<td rowspan="5">Link upward, extension dynamic</td><td> 1-3</td><td>Yes</td><td> -</td><td> 1-12, 19-45</td><td></td>

<td> 4</td><td>Do not</td><td>Yes</td><td> 33-34, 38-39,43-45</td><td> 2</td>

<td> 5</td><td>Yes</td><td> -</td><td> 34, 39</td><td> 5</td>

<td> 5</td><td>Do not</td><td>Yes</td><td> 44-45</td><td> 2,4</td>

<td> 6</td><td>Do not</td><td>Yes</td><td> 45</td><td> 5</td>

<td rowspan="7">Descending + upward, extension dynamic</td><td>d + u = 2-4</td><td>Yes</td><td> -</td><td> 1-12, 19-45</td><td></td>

<td>d + u = 5&gt; d</td><td>Yes</td><td> -</td><td> 8-12, 19-45</td><td></td>

<td>d = 1, u = 4</td><td>Do not</td><td>Yes</td><td> 30-45</td><td> 2</td>

<td>d + u = 6, d&gt; 1</td><td>Yes</td><td></td><td> 30-45</td><td> 2,3</td>

<td>d = 1, u = 5</td><td>Yes</td><td></td><td> 34, 39</td><td> 5</td>

<td>d + u = 7, d&gt; 1</td><td>Do not</td><td>Yes</td><td> 40-45</td><td> 2,4</td>

<td>d = 1, u = 6</td><td>Do not</td><td>Yes</td><td> 45</td><td> 5</td>

Note 1 Normal measurements are not possible (see 3GPP TS 45.008).

Note 2 Normal BSIC decoding is not possible (see 3GPP TS 45.008).

Note 3 TA offset is required for 35-39 multi-slot classes.

Note 4 TA offset is required for 40-45 multi-slot classes.

Note 5 Offset USF operation will apply (see 3GPP TS 44.060).