GB2420054A

GB2420054A - A method of controlling transmission rate in a mobile terminal in soft handover

Info

Publication number: GB2420054A
Application number: GB0424527A
Authority: GB
Inventors: Philip Booker; Thomas Malcolm Chapman; Anthony Peter Hulbert; Joern Krause
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2004-11-05
Filing date: 2004-11-05
Publication date: 2006-05-10
Also published as: GB0424527D0

Abstract

A method of controlling transmission rate in a mobile terminal (T1-T7) in soft handover comprises receiving one or more overload indicators at the mobile terminal. A priority level of data being transmitted by the mobile terminal is determined and the transmission rate at the mobile terminal is adapted in accordance with the received overload indicator and the priority of the data being transmitted.

Description

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A METHOD OF CONTROLLING TRANSMISSION RATE IN A MOBILE

TERMINAL IN SOFT FIANDOVER

Enhanced Uplink is a new package of features introduced into 3GPP Release 6 that aims to improve radio resource management in the uplink and hence to improve uplink throughput and reducc delay.

One of the key features introduced in Enhanced Uplink is node B scheduling. In this feature, the node B is given autonomy to restrict, using layer I signalling, the data rate at which enhanced uplink dedicated channel (E-DCH) enabled terminals may transmit in order to manage at least a portion of its wideband code division multiple access (WCDMA) interference. To facilitate node B scheduling, information is required to be sent by the user equipment (UE) to the node B. This information may be sent using separate physical layer signalling, or as a header included with E-DCI-I data packets.

1 5 Some terminals will be in inter node B soft handover, which means that the uplink transmission is received by a number of node Bs. As soon as one of the node Bs indicates that it has correctly received a data block, the terminal may start to transmit a new block, even though the remaining node Bs never received the block correctly. In such a soft handover (SHO) situation, at least one node B may be designated as a primary node B responsible for scheduling, and this node B needs to receive the scheduling information.

It is likely that only one node B will be responsible for scheduling a UE in soft handover, even though the UE will cause interference and processing requirements in neighbouring cells. To avoid potentially damaging overload situations, it is envisaged that the neighbouring cells will be given the ability to send "overload" indicators to the UE, which indicate that the UE must reduce its transmit rate. The overload indicators may be common to all LIEs in SF10 with a node B, or dedicated.

The problem is that the node Bs that set overload indicators do not necessarily know whether the UE needs to transmit high priority data. Also, common overload indicators will apply to all UEs, regardless of whether they have high or low priority data. Hence the overload indicator mechanism may affect the ability of the network to provide the required quality of service (QoS).

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a a a,*. * I. I I a a g S I * I in accordance with the present invention, a method of controlling transmission rate in a mobile terminal in soft handover comprises receiving one or more overload indicators at the mobile terminal; determining a priority level of data being transmitted by the mobile terminal; and adapting the transmission rate at the mobile terminal in accordance with the received overload indicator and the priority of the data being transmitted.

Node B scheduling of UE data rates is new to the Enhanced Uplink feature and hence this feature has not arise before now in the 3GPP standards. The present invention enables the terminal behaviour to change in response to an overload indicator, dependent upon the priority of the data being transmitted at the time.

In one embodiment, high and low priority overload indicators are received; the indicator related to the determined priority level of the data being transmitted is applied; and the transmission rate adapted accordingly.

Alternatively, a single indicator is received; and the mobile terminal adapts its transmission rate by an amount related to the determined priority level of the data.

In another embodiment, an overload indicator bit level is set in the terminal, whereby the transmission rate is only adapted if the number of received overload indicators exceeds the set level.

Preferably, the predetermined level is related to the priority level of the data being transmitted by the mobile terminal.

In some cases, the transmission rate does not change, but preferably, the transmission rate is reduced.

The present invention modifies the UE behaviour such that each logical flow in the UE is linked to a priority setting that determines how many consecutive overload (OL) bits, or OL bits from multiple node Bs, the UE must receive before it is required to reduce its rate. This number could be set lower for low priority classes compared to higher priority classes. Alternatively, each logical flow in the UE is linked to a priority setting that determines the amount by which the UE must reduce its data rate, or its transmit power. Lower priority data is required to be reduced by a larger factor than higher priority data. In another embodiment, each logical flow in the UE is linked to a different "overload indicator" sent by the network dependent upon its priority. In this solution, the network has to send overload bits relating to each priority class. a fa.

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In this invention there is a UE behaviour in which the response to overload bits is dependent on the priority of the data. A number of examples are described below.

Example I:

Two UEs, UEI and UE2 are in soft handover between two node Bs, NB1 and NB2.

Both of the UEs are scheduled by NBI. UEI has high priority data, whereas UE2 has lower priority data. The following sequence of events takes place: * The interference at NB2 rises above an acceptable threshold and NB2 sets a common overload bit * The overload bit is received by LJEI and UE2. The priority setting for UEI is such that UEI must respond when it receives 1 overload bit, whereas UE2 must only respond when it receives 2 overload bits.

* UE 1 reduces its data rate. However the interference at NB2 is still too high, so the overload bit is set again * UEI again reduces its data rate, and this time UE2 reduces its data rate

Example 2:

Two UEs, IJEl and UE2 are in soft handover between three node Bs, NBI and NB2 and NB3. Both of the UEs are scheduled byNBI. UEI has high priority data, whereas UE2 has lower priority data. The following sequence of events takes place: * The interference at NB2 and at NB3 rises above an acceptable threshold and NB2 sets a common overload bit * The overload bits are received by UEI and UE2. The priority setting for [JE! is such that UEI must respond when it receives I overload bit, whereas the other UE must only respond when it receives 2 overload bits.

* UEI reduces its data rate. UE2 counts two overload bits, one from NB2 and one from NB3 and also reduces its data rate

Example 3:

Two UEs, UEI and UE2 are in soft handover between two node Bs, NB! and NB2.

Both of the UEs are scheduled by NBI. UEI has high priority data, whereas UE2 has lower priority data. The following sequence of events takes place: 8 I * 4 8 * 8 4 * 4 4 8 8 8 I 8 8 I r I 144 4 8*4 4 4 I * S J I Ii* * The interference at NB2 rises above an acceptable threshold and NB2 sets a common overload bit * The overload bit is received by UEI and UE2. UEI reduces its transmit power (and data rate) by a factor P1. UE2 reduces its transmit power (and data rate) by a factor P2. Pl>P2.

Figures 1, 3,4 and 6 illustrate example 1. Figures 2 and 7 illustrate example 2 and Figures I and 8 illustrate example 3. Figure 5 shows what the conventional effect of applying the control shown in Figure 4 would be.

In Figure 1, a number of terminals TI, T3 and T6 are scheduled by a first node B, NB I. The other terminals T2, T4, T5 and T7 are scheduled by NB2. Since all the terminals in soft handover may be communicating via NBI or NB2, problems can arise if there is a conflict in the instructions from one or other node B. For example 1 above, as shown by Fig. 3, NB2 increases the data rate for T5 and T7, but Fig. 4 shows that this causes an overload at NBI which sends a down signal to all the terminals TI, T3, T5, T6 and T7, within its area Al, including both T5 and T7.

Conventionally, the effect of this overload down indication is for all the terminals to reduce their data rate by the same amount, as shown in Fig. 5 for T5 and T7.

However, Fig. 6a illustrates the effect described in example 1, where T5 has high priority and T7 has low priority. In this case, T5 keeps transmitting at the same data rate and T7 goes down, but if NB I sends another overload indicator, then the combined effect, shown in Fig. 6b is to exceed the limit, even for the high priority data, so T5 and T7 both go down this time.

Figs. 2 and 7 illustrate example 2, where there are 3 node Bs, NBI, NB2 and NB3 and the effect of an overload indicator from 2 out of the 3 is to put both the low and high priority terminals T7 and T5 down.

Figs. I and 8 illustrate another situation with two node Bs. Here the overload indicator causes each terminal to go down by a factor P1 for the low priority terminal and P2 for the high priority terminal.

Claims

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1. A method of controlling transmission rate in a mobile terminal in soft handover, the method coniprising receiving one or more overload indicators at the mobile terminal; determining a priority level of data being transmitted by the mobile terminal; and adapting the transmission rate at the mobile terminal in accordance with the received overload indicator and the priority of the data being transmitted.

2. A method according to claim 1, wherein high and low priority overload indicators are received; the indicator related to the determined priority level of the data being transmitted is applied; and the transmission rate adapted accordingly.

3. A method according to claim 1, wherein a single indicator is received; and the mobile terminal adapts its transmission rate by an amount related to the determined priority level of the data.

4. A method according to claim 1, wherein an overload indicator bit level is set in the terminal, whereby the transmission rate is only adapted if the number of received overload indicators exceeds the set level.

5. A method according to claim 4, wherein the set level is related to the priority level of the data being transmitted by the mobile terminal.

6. A method according to any preceding claim, wherein the transmission rate is reduced.