WO2005101884A1

WO2005101884A1 - A method of enhancing uplink transmissions

Info

Publication number: WO2005101884A1
Application number: PCT/GB2005/000694
Authority: WO
Inventors: Thomas Malcolm Chapman
Original assignee: Siemens Aktiengesellschaft
Priority date: 2004-04-14
Filing date: 2005-02-24
Publication date: 2005-10-27

Abstract

A method of enhancing uplink transmissions comprises signalling a transport format combination (TFC) set from a terminal (1, 2) to a base station (3) using a TFC indicator to indicate a predicted TFC requirement for a subsequent transmission time interval. A signal is received from the base station (3) indicating the maximum TFC set permitted for transmission and a TFC is selected for transmission based on the indicated TFC restriction.

Description

A METHOD OF ENHANCING T JP INK TRANSMISSIONS

This invention relates to a method of enhancing uplink transmissions, in particular for 3G mobile phone systems. Control of scheduling in a communication system generally takes place in a base station. To make the scheduling more efficient, it is desirable that the base station be able to restrict the maximum rate of transmission to it from a terminal, so that the base station can ensure sufficient, but not too much, resources are available. In accordance with a first aspect of the present invention, a method of enhancing uplink transmissions comprises signalling a transport format combination (TFC) set from a terminal to a base station using a TFC indicator to indicate a predicted TFC requirement for a subsequent transmission time interval; receiving a signal from the base station indicating the maximum TFC set permitted for transmission; and selecting a TFC for transmission based on the indicated TFC restriction. By having the terminal inform the base station of its likely TFC requirement, the base station is able to set a maximum permitted TFC below the requirement to ensure that all of its available resources are used effectively. Sending the desired TFCI allows the scheduler a preview of how much information is waiting at the user equipment, in the queue to be sent. Preferably, the predicted TFC requirement is derived by estimating at least one of the terminal buffer and transmit power status for a subsequent scheduling interval; allocating an allowance for other services being supplied; and deriving a TFC requirement without reference to any base station imposed limitation, to indicate the maximum rate the terminal can support. The terminal attempts to maximise its effectiveness by ignoring any limitation set by the base station when it calculates its predicted TFC requirement. Typically, the requirement is derived from the transmit power status. In one embodiment, the predicted TFC is embedded into the same codeword as the actual TFC for transmission. Alternatively, the predicted TFC requirement is incorporated into a media access control (MAC) header. In one embodiment, the predicted TFC requirement is signalled at regular intervals. This assists in facilitating efficient scheduling. Alternatively, the predicted TFC is only signalled by the base station if a change in predicted TFC occurs. Preferably, the predicted TFC requirement is quantised for transmission. Typically, the base station is a node B. Preferably, the predicted TFC requirement includes an indication of the minimum data rate required for transmission of a subset of data from the terminal. This subset would typically be high priority data stored in a particular part of the terminal buffer, thus ensuring that the base station was aware of the minimum transmission requirement. Preferably, the method further comprises sending a short term urgency indication from the terminal to the base station, which base station is adapted to dynamically allocate resources between terminals; wherein the base station varies priority for resource allocation from the terminal according to the short term urgency indication received; and wherein the terminal provides the urgency indication by dynamic physical layer signalling on a common, shared or dedicated physical channel. The urgency flag provides information on how important it is to send the data at this particular time, as against its importance at some time. It is possible for there to be very little data, but of high priority (a small TFC would be ok, but must be as soon as possible), or a lot of data, but of no great importance (a large TFC as and when available is required), or a lot of data of high importance. The combination of desired TFCI and urgency indication further optimises scheduling. Preferably, the urgency indication is transmitted at the same time as the TFC indicator. In accordance with a second aspect of the present invention, a terminal comprising one of a mobile phone, laptop, PC card or personal digital assistant, the terminal being adapted to cany out the method of the first aspect. An example of a method of enhancing uplink transmissions will now be described with reference to the accompanying drawings in which:- Figure 1 illustrates a communication system in which the method of the present invention can be applied; Figure 2 illustrates enhanced uplink transport format combination management from the terminal perspective for the system of Fig.1. The present invention is particularly applicable to an "enhanced uplink" channel for frequency division duplex mode of the 3^rd Generation Project Partnership (3GPP) specifications, although it is not limited to this application. A typical arrangement in a communication system is illustrated in Fig. 1. A first temiinal 1 and a second teπninal 2 transmit via a base station 3. The purpose of the enhanced uplink (UL) is to increase the throughput and capacity and, where possible, also reduce packet call delay in the uplink 4, 5 from each terminal to the base station. One of the prime features of the enhanced uplink is fast allocation of uplink "noise rise" at the base station, known as the node B for 3 GPP. The allocation of uplink noise rise in 3G systems is referred to as node B scheduling. The mechanism of node B scheduling is that the node B signals to terminals or user equipment (UE), using fast physical layer signalling, restrictions on the maximum data rate at which the terminals 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 UE's 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. To facilitate efficient scheduling, some additional information may be transmitted in the uplink including UE buffer status, UE transmitter (TX) power for a current transport format combination (TFC) relative to its maximum TX power and the status of other services the UE is supporting. Such information informs the scheduler of the data rate that the UE requires and is able to support. Signalling of all of this information for every scheduling interval may not be feasible as it would consume too high a proportion of UL bandwidth. The TFCs in the UE define a set of transmission data rates. In the normal course of events, the UE selects a TFC in each transmission time interval (TTI) according to how much data it has to transmit, what other transmissions it is supporting and it's 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 UE so as to restrict the maximum rate at which the UE may transmit. Fig. 2 illustrates the EUL TFCS management from the terminal perspective. A first set 6 are the maximum TFCs available as configured by the radio network controller (RNC) - (not shown). A sub-set of these is set 7 controlled by the base station or Node B 3 and only transmitted if sufficient UE resources are available and a third set is the minimum set of TFCI's 8 which the node B is not permitted to restrict. The node B scheduler takes into account that the UE may transmit anything up to the restriction 7. 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. The TFCI is primarily an indicator of a coding format, although it effectively sums up for the current transmission interval the information on UE buffer status, power and complexity restrictions and how these interact with the TFC the UE has selected. Therefore, in the present invention an algorithm is applied for calculating the TFC as a means of indicating to the scheduler the UL status information that is required. The UE estimates what its buffer status will be in the next scheduling interval, and what the transmission rates are likely to be for other services it may be supporting. It then applies the algorithm for selecting the TFC to this information, but without considering the limit placed by the node B. This process yields a TFCI that indicates the TFC that the UE would ideally select in the next interval if it had no restrictions and effectively signals to the scheduler the maximum rate that the UE could support.

Two types of TFCI transmission by the UE are therefore expected. One is the "usual" TFCI, which indicates the coding format used for the current transmission and the other is the "predicted next TTI" TFCI, which indicates the desired TFC for the next transmission interval. The predicted TFCI for the (N+l)th transmission is sent in the Nth block, concurrent with the TFC information Nth. A further feature of the invention is that the UE can declare a certain part of its buffer as being for high priority data and apply the TFCI selection algorithm to this part of the buffer to give a predicted minimum data rate necessary for transmitting the high priority data. This information is provided to the base station in the same way as the predicted TFC requirement. In an implementation of the invention, the "predicted next TFCI" need not be transmitted in every transmission interval, but it must be transmitted at a rate frequent enough to facilitate efficient scheduling. The "predicted next TFCI" can contain the same number of bits as the TFCI, or it may be quantised in some way. The word used for transmitting the TFCI contains 10 bits. The TFCI for enhanced UL can be arranged to need no more than 5 bits, so although current standards mandate that any unused bits in the 10 bit word be set to zero, it may be possible under certain circumstances to use the unused 5 bits for transmitting the "predicted next TFCI" in enhanced uplink, which would mean effectively transmitting the information for free. If the additional 5 bits are not available, then the predicted TFCI can be sent on an EUL signalling channel or another channel.

Claims

1. A method of enhancing uplink transmissions, the method comprising signalling a transport format combination (TFC) set from a temiinal to a base station using a TFC indicator to indicate a predicted TFC requirement for a subsequent transmission time interval; receiving a signal from the base station indicating the maximum TFC set permitted for transmission; and selecting a TFC for transmission based on the indicated TFC restriction.

2. A method according to claim 1 , wherein the predicted TFC requirement is derived by estimating at least one of the temiinal buffer and transmit power status for a subsequent scheduling interval; allocating an allowance for other services being supplied; and deriving a TFC requirement without reference to any base station imposed limitation, to indicate the maximum rate the terminal can support.

3. A method according to claim 1 or claim 2, wherein the predicted TFC is embedded into the same codeword as the actual TFC for transmission.

4. A method according to claim 1 or claim 2, wherein the predicted TFC requirement is incorporated into a media access control (MAC) header.

5. A method according to any of claims 1 to 4, wherein the predicted TFC requirement is signalled at regular intervals

6. A method according to any of claims 1 to 4, wherein the predicted TFC is only signalled by the base station if a change in predicted TFC occurs.

7. A method according to any preceding claim, wherein the predicted TFC requirement is quantised for transmission.

8. A method according to any preceding claim, wherein the base station is a node

B.

9. A method according to any preceding claim, wherein the predicted TFC requirement includes an indication of the minimum data rate required for transmission of a subset of data from the terminal.

10. A method according to any preceding claim, the method further comprising sending a short term urgency indication from the terminal to the base station, which base station is adapted to dynamically allocate resources between temiinals; wherein the base station varies priority for resource allocation from the terminal according to the short term urgency indication received; and wherein the terminal provides the urgency indication by dynamic physical layer signalling on a common, shared or dedicated physical channel.

11. A method according to claim 10, wherein the urgency indication is transmitted at the same time as the TFC indicator.

12. A terminal comprising one of a mobile phone, laptop, PC card or personal digital assistant, the terminal being adapted to carry out the method of any preceding claim.