GB2420254A

GB2420254A - A method of controlling transmission rate in a mobile terminal in soft handover

Info

Publication number: GB2420254A
Application number: GB0522360A
Authority: GB
Inventors: Philip Booker; Thomas Malcolm Chapman; Anthony Peter Hulbert; Joern Krause
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2004-11-04
Filing date: 2005-11-02
Publication date: 2006-05-17
Anticipated expiration: 2025-11-02
Also published as: WO2006048631A1; GB0522360D0; GB2420254B

Abstract

A method of controlling transmission rate in a mobile terminal (T5, T) 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.

Description

A METHOD OF CONTROLLING TRANSMISSION RATE IN A MOBILE

TERMINAL [N SOFT HANDOVER Enhanced Uplink is a new package of features introduced into the 3 generation partnership project (3GPP) Release 6 that aims to improve radio resource management in the uplink and hence to improve uplink throughput and reduce 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 1 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 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-DCH data packets.

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 I *

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UE, which indicate that the tiE must reduce its transmit rate. The overload indicators

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**5. . may be common to all UEs in SHO 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 * 30 data. Hence the overload indicator mechanism may affect the ability of the network to * 555.

provide the required quality of service (QoS).

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. This is achieved by making adjustments at the terminal side, rather than on the network side, as has been done conventionally. This provides the advantage that the terminal receives overload indicators form multiple base stations and adapts its data rate according to the priority of data at the terminal, rather than simply being told by the network what data rate to use.

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 * I * I.. * *, 25 transmission rate is reduced. *

* III An example of a method of controlling transmission rate in a mobile terminal in * : * soft handover will now be described with reference to the accompanying drawings in * 1* II.... wnic

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Figure 1 illustrates a first arrangement in which the method of the present * 30 invention is carried out; S...

* ** a Figure 2 illustrates a second arrangement in which the method of the present invention is carried out; Figure 3 illustrates signalling for the example of Fig. I; Figure 4 illustrates further signalling for the example of Fig. 1; Figure 5 shows the conventional effect of applying the control shown in Fig. 4; Figure 6 illustrates control applied in a first example for the arrangement of Fig. 1; Figure 7 illustrates control applied for the arrangement of Fig. 2; and, Figure 8 illustrates control applied in a second example of the arrangement of Fig. I. 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. Thus, not only are instructions from neighbouring base stations taken into account when determining transmission rate, but also the priority setting of a particular logical flow. This allows the terminal to influence the outcome, rather than simply accept instructions from the network.

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. The UE behaviour is such that the response to overload bits is dependent on the priority of the data.

* ** Referring now to a first example based on the arrangement shown in Fig.!, a * S * S.. * number of terminals Ti, T3 and T6 are scheduled by a first node B, NB!. The other

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terminals T2, T4, T5 and T7 are scheduled by NB2. Since all the terminals in soft handover may be communicating via NBI orNB2, problems can arise if there is a *..: conflict in the instructions from one or other node B. Two of the UEs, T5 and T7 are in

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soft handover between the two node Bs, NBI and NB2. Both of these UEs are scheduled by NB2. T7 has high priority data, whereas T5 has lower priority data. if the interference at NB! rises above an acceptable threshold, then NB I sets a common overload bit. As shown by Fig. 3, NB2 increases the data rate for T5 and T7, but Fig. 4 shows that this causes an overload at NB I which sends a down signal to all the terminals TI, T3, T5, T6 and T7, within its area Al, including both T5 and T7, without affecting the terminals in the remainder of area A2.

The overload bit is received by 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, the priority setting for T5 is such that T5 must respond when it receives 1 overload bit, whereas T7 only needs to respond when it receives 2 overload bits. Fig. 6a illustrates the effect where T7 has high priority and T5 has low priority. When the down signal is sent, T5 reduces its data rate and T7 keeps transmitting at the same data rate. However the interference at NB2 is still too high, so the overload bit is set again. When NB 1 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 again reduces its data rate, and this time T7 reduces its data rate Figs. 2 and 7 illustrate a second example, where there are 3 node Bs, NBI, NB2 and NB3 covering areas Al, A2 and A3 respectively and the effect of an overload indicator from 2 out of the 3 base stations is to put both the low and high priority terminals down. The two UEs, T5 and T7 are in soft handover between the three node Bs, NBI and NB2 and NB3. Both of the UEs are scheduled by NB2. T7 has high priority data, whereas T5 has lower priority data. When 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 T5 and T7. The priority setting for T5 is such that T5 must respond when it receives 1 overload bit, whereas the other UE must only respond when it receives 2 overload bits. Therefore, T5 reduces its data rate and T7 counts two * overload bits, one from NB2 and one from NB3 and also reduces its data rate.

Based on the armngement of Fig. 1, Fig. 8 illustrates 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. The two UEs, T5 and T7 are in soft handover between two node Bs, NB! and NB2. Both of the UEs are

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* scheduled by NBI. T7 has high priority data, whereas T5 has lower priority data. If the interference at NB2 rises above an acceptable threshold, NB2 sets a common overload * S 5' bit and the overload bit is received by T5 and T7. T5 reduces its transmit power (and data rate) by a factor P1 and T7 reduces its transmit power (and data rate) by a factor P2 where P1 >P2 to reflect the terminals relative priorities.

Claims

I. A method of controlling transmission rate in a mobile terminal in soft handover, the method comprising 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 predetermined 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 a. a.

reduced. a * a.'. o *

* * .. . a a a a

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