GB2415327A

GB2415327A - Controlling data rates for a terminal in soft handover

Info

Publication number: GB2415327A
Application number: GB0413445A
Authority: GB
Inventors: Anthony Peter Hulbert
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2004-06-16
Filing date: 2004-06-16
Publication date: 2005-12-21
Also published as: GB0413445D0

Abstract

In third generation EUL (enhanced uplink) data transmission, the Node B sets data rate on a dynamic basis. In soft handover, a terminal 4 may be in contact with several Nodes B 1-3, setting different rates according to their perception of the terminal priority, at least one of which may be a low rate L. In general the lowest rate will be that which sets the actual data rate used, to avoid unplanned noise rise in the system. Alternatively, if the highest rate is chosen, terminals in soft handover will tend to dominate uplink resources. In the present invention, scheduling is carried out at a central controller, using a knowledge of the requirements of all terminals in soft handover. The controller then signals priorities to each Node B, such that the terminals are given similar priorities, increasing the likelihood of similar data rates being set.

Description

241 5327

A METHOD OF CONTROLLING DATA TRANSMISSION FOR A TERMINAL IN

SOFT HANDOVER

This invention relates to a method of controlling data transmission for a terminal in soft handover, in particular for 3r<i generation mobile phone networks.

In enhanced uplink (EUL), the data rate at which a user equipment (UK) is permitted to transmit, is set on a dynamic basis by a scheduling node B. If the UE is in soft handover, then several node Bs will send such data rate restrictions to the UK. To avoid unplanned noise rise, it is sensible for the UE to choose the lowest of these rate restrictions so that noise rise is not wasted in the node Bs that attempted to allocate a higher rate.

However if the node Bs are scheduling in a sequential fashion, such as round robin there exists a significant risk that at least one of the active set node Bs will always send a low rate restriction to the soft handover (SHO) UE in each scheduling interval, since the schedulers in the node Bs may be out of sequence. This would result in the UE always selecting a low data rate and reduced throughput and fairness for SHO users.

This situation does not only apply to node Bs using sequential type schedulers; in a SHO situation where node B schedulers are not aware of time instances in which other schedulers have allocated significant data rate to a terminal there is a significant risk of low data rates for the terminal or unplanned noise rise. Unplanned noise rise could occur if the UE signalling does not automatically select the lowest rate.

Furthermore, even if there is only one scheduling node B. other node Bs are not aware of time instances at which the UE is likely to be scheduled and hence will create unplanned noise rise.

Alternatively, although less likely is that the SHO UE may be required to select the highest transport format combination (TFC). In this case, the probability of SHO UEs transmitting at high rates and dominating the use of uplink resources, to the detriment of non-StIO UEs is high.

In accordance with a first aspect of the present invention, a method of controlling data transmission for a terminal in soft handover comprises receiving data rate restrictions at the terminal from one or more base stations; and transmitting data at a rate in accordance with the restriction set by at least one base station; wherein a # .. . . parameter is signalled from a central controller to each base station indicating a desired scheduling interval for the terminal, such that the probability of each of a series of base stations signalling a similar data rate restriction is increased; and whereby the transmission data rate is optimised.

'l'he present invention enables a central directive to be applied to the base stations, so that a particular terminal has an improved chance of getting a high priority from all the base stations and so can transmit at a higher data rate.

Preferably, the indicated scheduling interval is one which repeats periodically.

This ensures that if a certain base station is not able to give the requested priority, for example if there is a significantly larger short term demand for data than it can supply due to a large download, then another opportunity will arise automatically.

Pref rably, each of the series of base stations schedule sequentially.

Preferably, only a single base station in the series is responsible for scheduling the terminal.

Preferably, the terminal signals to each base station the data rate it will assume for its transmission.

Typically, the terminal chooses to transmit at the lowest data rate set by any base station in the series.

Preferably, the signalled parameter is set during set-up of the soft handover connection.

Preferably, the base station is one of a Node B or RNC.

In accordance with a second aspect of the present invention, a communication system comprises a terminal, a plurality of base stations and at least one data channel, wherein the system is adapted to carry out the method of the first aspect.

An example of a method of controlling data transmission for a terminal in soft handover in accordance with the present invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates priority levels for a particular terminal from different base stations in two scheduling intervals; Figure 2 illustrates the priority given to each terminal in a conventional soft handover; and, r 8 8 * C e Figure 3 illustrates priority given to each terminal using the method of the present invention.

Figure I a shows a first example of how different base stations I, 2, 3 allocate priority to a terminal 4. Base stations I and 3 give the terminal 4 a high priority in a particular scheduling interval and base station 2 gives it a low priority. In a subsequent scheduling interval, shown in Fig.lb, base stations 2 and 3 give the terminal a high priority, whilst base station 1 gives the terminal a low priority. Thus, a terminal may find itself always being allocated a low priority, and hence a low data rate, by at least one of the base stations in soft handover. Since the terminal is usually obliged to operate at the lowest data rate offered to avoid causing unexpected noise rise at any base station, then the terminal in soft handover will always be at a disadvantage.

Figure 2 shows another way of illustrating the allocation of priority by each base station for a specific terminal in a list held by each base station. Base station 1 gives highest priority to terminal 1 and lowest to terminal 6; base station 2 gives highest priority to a different terminal 2A and lowest to 6A - terminal 1 is third in the list; and base station 3 gives highest priority to terminal 2B, lowest to terminal 4B and puts terminal 1, fourth in line. In effect base station 3 determines the data rate for terminal I in this example.

It is desirable that there should be some way of coordinating the priority given at a particular scheduling interval to give a terminal a better data rate. This is done by signalling a parameter from a central controller (not shown) to each base station which indicates a desired scheduling interval for a particular terminal. Provided that the individual base stations are not engaged with traffic which prevents its compliance, such as being in the middle of transmitting a large amount of data, then the base stations will tend to allocate the requested scheduling interval and so, as shown by Fig. 3, terminal I has priority from all 3 base stations at the same time and so can use a higher data rate.

The extra parameter signalled from the central controller, may be signalled over an interface to unit B (IuB) using radio resource control (RRC) signalling. The parameter is signalled to serving node Bs 1, 2, 3 when an enhanced dedicated channel (E-DCH) radio bearer is set up. This parameter is specific to the terminal or user equipment (UK) and bearer and indicates time periods when scheduling of the 1 8 C C e . terminal/bearer should be prioritized. Since each of the active set node Bs will be aware of the parameter, the chance of all node Bs allocating a relatively high rate to the UE in the same scheduling interval can be greatly increased, thus improving fairness to the UK, or reducing unplanned noise rise variance.

Furthermore, if there is only one scheduling node B. the parameter can be signalled to other node Bs to allow for non scheduling node Bs to have a better understanding of when unplanned noise rise is likely.

Claims

r I r r r . i CLA IMS

1. A method of controlling data transmission for a terminal in soft handover; the method comprising receiving data rate restrictions at the terminal from one or more base stations; and transmitting data at a rate in accordance with the restriction set by at least one base station; wherein a parameter is signalled from a central controller to each base station indicating a desired priority level and scheduling interval for the terminal, such that the probability of each of a series of base stations signalling a similar data rate restriction is increased; and whereby the transmission data rate is optimised.

2. A method according to claim, wherein the indicated scheduling interval is one which repeats periodically.

3. A method according to claim I or claim 2, wherein each of the series of base stations schedule sequentially.

4. A method according to claim I or claim 2, wherein only a single base station in the series is responsible for scheduling the terminal.

5. A method according to any preceding claim, wherein the terminal signals to each base station the data rate it will assume for its transmission.

6. A method according to any preceding claim, wherein the terminal chooses to transmit at the lowest data rate set by any base station in the series.

7. A method according to any preceding claim, wherein the signalled parameter is set during set-up of the soft handover connection.

8. A method according to any preceding claim, wherein the base station is one of a Node B or RNC.

I I e e .' ace e e e e e

9. A communication system comprising a terminal, a plurality of base stations and at least one data channel, wherein the system is adapted to carry out the method of any preceding claim.

10. A method of controlling data transmission for a terminal in soft handover as hereinbefore described with reference to the accompanying drawings.