GB2413242A

GB2413242A - Data rate control in soft handover

Info

Publication number: GB2413242A
Application number: GB0408295A
Authority: GB
Inventors: Anthony Peter Hulbert
Original assignee: Siemens AG; Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 2004-04-14
Filing date: 2004-04-14
Publication date: 2005-10-19
Anticipated expiration: 2024-04-14
Also published as: GB0408295D0; GB2413242B

Abstract

A method of optimising scheduling for a terminal (4) in soft handover in a communication system comprises receiving at the terminal data rate restrictions from a plurality of base stations (1, 2, 3) and signalling to all the base stations the data rate restriction to be assumed by the terminal for its transmission. Each base station then reallocates resources above the signalled data rate restriction level. The data rate restrictions are signalled as TFC (transport format combinations) restrictions to the terminal, and the TFC selected by the terminal in signalled to the base stations as a TFCI (transport format combination indicator). Restriction on the maximum data rate in the uplink restricts the amount of interference created by the terminals.

Description

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A METHOD OF OPTIMISING SCHEDULING FOR A TERMINAL IN SOFT

HANDOVER IN A COMMUNICATION SYSTEM

This invention relates to a method of optimising scheduling for a terminal in soft handover in a communication system, in particular for frequency division duplex (FDD) mode of the 3r Generation Project Partnership (3GPP) specifications or CDMA 2000.

In accordance with the present invention, a method of optimising scheduling for a terminal in soft handover in a communication system comprises receiving at the terminal data rate restrictions from a plurality of base stations; and signalling to all the base stations the data rate restriction to be assumed by the terminal for its transmission; wherein each base station reallocates resources above the signalled data rate restriction level.

Preferably, the data rate restrictions are signalled as TFC restrictions.

Preferably, the restrictions are signalled to the node B by the TFCI.

Although, the TFC selection information could be signalled between node Bs via the interface to unit B (IuB) interfaces to the RNC, rather than through the TFCI, the signalling has a latency of a different order of magnitude to the speed of the fast scheduling procedure, which is undesirable.

Preferably, the base station is a node B. Preferably, the terminal is one of a mobile phone, laptop, personal computer card or personal digital assistant.

Preferably, the communication system is a mobile phone system, digital data network or satellite system.

An example of a method of optimising scheduling for a terminal in soft handover in a communication system according to the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram of a communication system using the method of the present invention; Figure 2 is an illustration of enhanced uplink transport format combinations management from the terminal perspective for the system of Fig. 1; and, 1 c The present invention is particularly applicable to an "enhanced uplink" channel for FDD mode of the 3GPP specifications, although it is not limited to this application and could be applied to other mobile phone systems, digital data networks or satellite systems with a soft-handover approach when clients signals to more than one receiver may be combined. The purpose of the enhanced uplink is to increase the throughput and capacity and/or reduce packet call delay in the unlink. Fig. I shows a communication system suitable for carrying out the method of the present invention. A series of base stations 1, 2, 3 are within an active area for a terminal 4 in soft handover.

The method is one of a number of techniques concerned with fast allocation of noise rise at the base station or node B. otherwise known as "node B scheduling".

The mechanism of node B scheduling is that the node B or base station signals to the terminals, using fast physical layer signalling, restrictions on the maximum data rate at which they may transmit in the uplink in order to restrict the amount of interference created by the terminals. Since the function is located at the node B and the signalling is carried out at the physical layer, the node B is able to track rapid variations in the terminal or user equipment (UK) transmit capability and buffer status, in order that it can restrict terminal data rates according to their instantaneous needs and capabilities and thus more effectively utilise the noise rise at it's receiver.

The UE has a set of transport format combinations (TFC), which define a set of transmission data rates. In the normal course of events, the UE selects a TFC in each "transmission time interval" according to how much data it has to transmit, what other transmissions it is supporting and its maximum power ceiling. The TFC that the UE has selected is indicated to the node B by a physical layer indicator known as the TFCI.

In enhanced uplink (EUL), the node B is able to signal a restriction in the set of TFCs available to the UK, so as to restrict the maximum rate at which the UE may transmit. The maximum available TFC set 8 is configured by the radio network controller (RNC). A sub-set 9 is determined by the restrictions signalled by the node B and a minimum TFC set 10 required for any transmission to take place is set within the terminal 4. The node B scheduler takes into account that the UE may transmit anything Up to the restriction. However for the scheduling to be efficient, the TFC restriction should be lower than the TFC that the UE would be likely to select with no restriction, otherwise the node B unnecessarily allows noise rise. .

I Ir d. t d C * I C I d d * * C The EUL channel is a dedicated channel, so "soft handover" (SHO) is an appropriate mechanism to be used. A terminal 4 in SHO receives TFC restrictions from some or all of the node Bs 1, 2, 3 in the active set of the terminal, and selects the lowest TFC restriction, so as not to cause unplanned noise rise at any node B. If a node B is only lightly loaded, then it may not need to impose a restriction. In these circumstances, the node Bs that indicated a higher TFC to the UE would have unnecessarily allocated noise rise, since the UE would not be able to use the higher TFCs. Therefore, a delay is introduced in applying the TFC restriction for UEs in SHO and to signalling is introduced on channels 5, 6, 7 from the UE to the node Bs that indicates the TFC restriction that the UE has chosen to use. In this way, node Bs that attempted to allocate a higher TFC restriction can re-allocate the noise rise to other UEs that are not in SHO.

The implementation of this invention would be as a delay and additional UL signalling of a TFC restriction with an EUL signalling channel, another signalling channel or embedded in a data transmission.

Without the method of the present invention, the node B's are not sent uplink information on the chosen TFC, which leads to performance loss at some of the node Bs. If there was only one scheduling node B. this would give rise to unplanned noise at other node Bs in the active set.

Claims

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l. A method of optimising scheduling for a terminal in soft handover in a communication system, the method comprising receiving at the terminal data rate restrictions from a plurality of base stations; and signalling to all the base stations the data rate restriction to be assumed by the terminal for its transmission; wherein each base station reallocates resources above the signalled data rate restriction level.
2. A method according to claim l, wherein the data rate restrictions are signalled as TFC restrictions.
3. A method according to claim 1 or claim 2, wherein the restrictions are signalled to the node B by the TFCI.
4. A method according to any preceding claim, wherein the base station is a node B.
5. A method according to any preceding claim, wherein the terminal is a mobile phone, laptop, personal computer card or personal digital assistant.
6. A method according to any preceding claim, wherein the communication system is a mobile phone system.
7. A method of optimising scheduling for a terminal in soft handover in a communication system as hereinbefore described with reference to the accompanying drawings.