EP2104984A1

EP2104984A1 - A method and a device for enhanced performance in a wireless access tdd system

Info

Publication number: EP2104984A1
Application number: EP07701159A
Authority: EP
Inventors: Tobias Tynderfeldt; David Astely; Hannes Ekström; Erik Westerberg; Alireza Nejatian; Per Skillermark; Jacobus Haartsen
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2007-01-15
Filing date: 2007-01-15
Publication date: 2009-09-30
Also published as: CN101682397A; CN101682397B; WO2008088252A1; EP2104984A4

Abstract

The invention discloses a method (700) for use in a wireless access (100) comprising a base station (120, 800) and a cell (110) which can accommodate a first user terminal (130, 140). In the system, the first user terminal (130, 140) can be scheduled for receiving traffic from the base station (120) during a down link interval, and the first user terminal (130, 140) can be scheduled for transmitting traffic to the base station (120, 800) during an up link interval, with a guard period between them. According to the invention, the method (700) comprises the step (710) of obtaining a certain characteristic of the first user terminal which is relevant to the guard period, and the step (720) of making the scheduling in at least one of the intervals based upon the measured characteristic of the first user terminal (130, 140).

Description

TITLE

A method and a device for enhanced performance in a wireless access TDD system.

TECHNICAL FIELD

The present invention relates to a method for use in a wireless access system which comprises at least one cell and at least one base station for the control of traffic to and from the cell. The cell is able to accommodate at least a first user terminal, and in the system in question the first user terminal can be scheduled for receiving traffic from said base station during a first time interval, the down link interval, and for transmitting traffic to the base station during a second time interval, the up link interval.

The invention also relates to a radio base station for use according to the principles of the method of the invention, and to a corresponding user terminal.

BACKGROUND

In wireless communications systems, there are both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) systems. The Long Term Evolution (LTE) in 3GPP, also called E-UTRA, will have both an FDD and a TDD mode. It is desired that LTE should have a high degree of commonality between these two modes of operation.

According to the TDD-principle, the connection from a base station to the user equipment, the downlink, is separated in time from the connection from the user terminal to the base station, the uplink. However, the up link and the down link transmit on the same frequency.

In other words, during down link time periods, a base station transmits to user terminals in the cell of that base station, and during up link time periods, the user terminals in the cell transmit to the base station of the cell. In many systems, there is a desire for signals transmitted from the user terminals in the up link to arrive at approximately the same time at the base station, i.e., the signals should be aligned in time. Furthermore, in a TDD system, the base station cannot transmit and receive at the same time, and it is therefore necessary for the signals transmitted from different user terminals to arrive at approximately the same time.

The time alignment can be achieved by measuring the timing of signals received from the different user terminals in the cell. Due to different propagation delays over the air, the time alignment requirement means that a signal transmitted from a user terminal at the cell edge needs to be transmitted earlier than a signal transmitted from a user terminal close to the base station.

At the same time, the signals transmitted in down link from the base station arrive later at the cell edge user terminals than at the user terminals close to the base station. Together, this gives the cell edge user terminals less time to switch from receive to transmit mode.

At the switch from down link to up link, and at the switch from up link to down link, guard times (also called idle periods or guard periods) may be inserted. The guard time at the switch from down link to up link should account for the round trip propagation delay plus the minimum switching time from receive to transmit mode in the user terminal. As explained above, the guard time will thus be dimensioned for the cell edge user terminal.

As also explained above, the required guard time at the switch from down link to up link depends mainly on the round trip delay, which will usually be proportional to the cell size. For small cells, the round trip delay will be fairly small, and in these cases, the switching time from receive to transmit mode in the user terminal will tend to dominate the guard time needed. For large cells, on the other hand, the round trip delay will dominate the guard time. For example, with a cell radius of 150 km, the round trip delay alone is 1 ms. With one switch from down link to up link every 5 or 10 ms, which is the case for some systems, such as, for example some of the WiMAX profiles of IEEE 802.16e, and probably also LTE, a round trip delay of 1 ms will lead to a significant overhead. With a down link to up link switch every 5 ms, the overhead from the guard time will exceed 20% of the total.

A similar problem has been identified for half duplex FDD user terminals in LTE, and a solution to this has been suggested to be the use of user terminal dependent guard periods. This would allow for a better utilization of the radio resources than if the guard periods for all user terminals are dimensioned for the cell edge user terminals.

However, this solution does have a number of drawbacks: First of all, a cell edge user terminal might be scheduled for reception last in the down link and first for transmission in the up link. For the radio resources allocated to such UEs, a number of idle symbols are still needed which could not be used by other user terminals closer to the base station, something which will reduce the system capacity.

Also, if all user terminals in a cell could be assigned different numbers of idle symbols at the end of the down link period, this would mean that the number of idle symbols would need to be signalled individually for each user terminal in data associated control signalling in the down link. Unless a specific control signalling format were to be used lasting the down link, this increase in control signalling overhead would also affect any other down link transmission, whether it is necessary or not.

SUMMARY

As has emerged from the description above, there is a need in many future wireless access systems for a solution which could improve system performance with regard to user terminals which have long propagation times, for example due to the fact that the user terminals in question are located at the outer edges of a cell in the system, particularly in the case of large cells.

This need is addressed by the present invention in that it discloses a method for use in a wireless access system in which there is at least one base station for the control of traffic to and from a cell in the system, and in which system the cell is able to accommodate at least a first user terminal.

In the system for which the invention is intended, the first user terminal can be scheduled for receiving traffic from the base station during a first time interval, the down link interval, and for transmitting traffic to the base station during a second time interval, the up link interval. There is a third interval between the down link interval and the up link interval, a "guard period".

According to the invention, the method comprises the step of obtaining a certain characteristic of said first user terminal with respect to the third time interval, the guard period, and also comprises the step of making the scheduling in at least one of the up or down link intervals based upon the obtained characteristic of the first user terminal.

Thus, by means of the invention, a user terminal can be scheduled in the up link or in the down link periods according to a certain characteristic of the user terminal, or, as an alternative, the characteristic for the user terminal which is obtained can be used to schedule the user terminal in both the up link and the down link periods.

In a preferred embodiment, the characteristic of the user terminal which is obtained is the terminal's distance from the base station. In another preferred embodiment, it is the round trip propagation delay of traffic between the first user terminal and the base station which is obtained and used to schedule the first user terminal in one or both of the up link/down link intervals.

The invention also discloses a radio base station which basically functions according to the method of the invention, and a corresponding user terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, with reference to the appended drawings, in which Fig 1 shows a schematic overview of a system in which the invention can be applied, and

Fig 2 shows a principle used in present systems, and Fig 3 serves to illustrate a problem addressed by the invention, and Figs 4 and 5 show different embodiments of the invention, and Fig 6 shows another problem addressed by the invention, and Fig 7 shows a flow chart of a method of the invention, and Fig 8 shows a block diagram of a radio base station of the invention.

DETAILED DESCRIPTION Fig 1 shows an example of a system 100 in which the invention may be applied. The system 100 is a wireless access system, and as such comprises a number of cells, one of which is shown in fig 1 with the reference number 110.

The cell 110 comprises at least one radio base station, an RBS, shown as 120 in fig 1. The RBS 120 serves, inter alia, to control the traffic to and from users in the cell 110. The cell 110 can accommodate at least one user, and in fig 1 there are two user terminals shown, with the reference numbers 130 and 140. The user terminals will be referred to below as UEs. However, in some systems other terminology may be used, and it should be realized that the term UE is merely an example intended to facilitate the reader's understanding of the invention. For example, in some systems, the term UT, User Terminal, is used. In addition, although the UEs 130, 140, are shown as cellular telephones in fig 1 as well as in the other figures, it should be realized that this is merely to facilitate the understanding of the invention, the UEs may be many other kinds of devices, such as, for example, computers.

The system 100 for which the invention is intended is one in which communication to the UEs 130, 140, from the RBS 120 can be scheduled to take place during a first interval in time, usually referred to as the down link interval, DL, and the traffic from the UEs 130, 140, to the RBS 110 can be scheduled to take place during a second interval in time, the up link interval, UL. DL and UL are separated in time, so that they do not coincide with each other.

Taking LTE as an example, a scheduler in the RBS 120 controls when the different UEs in the cell are allowed to transmit and receive data. The time unit that a scheduler works with will in the following be referred to as Transmission Time Interval (TTI).

The invention is especially suitable for a so called TDD system, in which the UL and the DL transmit on the same frequency but are divided in time. This principle is shown in fig 2, in order to illustrate a problem which the invention attempts to alleviate.

In a TDD system, where UL and DL are transmitted on the same frequency, it is not possible to simultaneously transmit and receive in the same node, e.g. the RBS or the UE. This means that for systems which use TDD, it is necessary for signals which are transmitted from the UEs to the RBS in the

UL to arrive at approximately the same time at the RBS. However, it will be realized that there are many factors which can influence the propagation time for a signal from a UE to the RBS, the distance from the UE to the RBS being one of the main such factors. Other such factors can be different propagation conditions from different positions within the cell. It will thus be realized that in order for signals from the UEs to arrive more or less at the same time at the RBS₁ some UEs, particularly those located at the edges of the cell, will need to be ordered to start their transmission earlier than others, for example those UEs located closer to the RBS.

Conversely, it will also be realized that signals transmitted from the RBS will reach the UEs at different times. Altogether, this gives some UEs less time than others to switch between transmit mode and receive mode, which is particularly the case for UEs located at the edges of the cell.

In fig 2, the principle with DL and UL being separated in time is shown. At present, at the switch from DL to UL, and from UL to DL, a so called guard time (also sometimes referred to as an idle period) is inserted, in order to account for a number of factors which occur at such a switch.

In fig 2, the DL periods are shown with an arrow from the RBS 120 indicated at the edge of the upper frames towards the UEs 130, 140, indicated at the lower frames, and the UL periods are indicated with an arrow in the other direction. Thus, the DL periods are shown with an arrow pointing downwards, whereas the UL periods are indicated with a arrow pointing upwards.

Fig 2 illustrates the different "arrival times" of traffic from the RBS to the UEs 130, 140, by means of arrows with dashed lines from the RBS to the UEs.

Also illustrated in fig 2 by means of arrows with dashed lines is the need for different "start times" for transmission from the different UEs to the RBS in the UL in order for the traffic to arrive more or less simultaneously at the RBS.

The guard time, T_DU, at the switch from DL to UL should be dimensioned according to the Round Trip Propagation Delay (RTD), T_RTD, plus the minimum time needed for a UE to switch from receive to transmit mode, TRX.TX. AS explained above, the T_RTD will be especially large for some UEs, mainly those located at the cell edge. Thus, T_Du will be dimensioned for the UEs with the largest T_RTD-

The guard period between the uplink and downlink, TUD, on the other hand, should be chosen according to the time it takes for the RBS to switch from reception to transmission and for a user terminal close to the RBS to switch from transmission to reception.

The term "guard period", T_GU_ARD, will be used below as a generic term for either or both of T_Du or TUD-

In the following, the UEs which have a long RTD will be referred to as UEs located at the cell edges, particularly in large cells. However, it should be realized that this is by way of example only, long RTDs can conceivably occur for other UEs, and the invention is equally applicable in such cases.

Thus, the required guard time T_Du at the switch from DL to UL depends on the RTD, which in this example depends on the cell size. For small cells, the RTD is fairly small, and in such cases, the switching time, T_RXiTχ, from receive to transmit mode in the UE will dominate the guard time T_Du-

However, for large cells, the RTD will dominate the guard time. For example, with a cell radius of 150 km, the RTD alone will be 1 ms. With one switching point from DL to UL every 5 or 10 ms, which is the case in some systems, such as, for example, some of the WiMAX modes of IEEE 802.11 , an RTD of 1 ms will lead to a significant overhead: with a DL-to-UL switch every 5 ms, the overhead from the guard time will exceed 20%. Thus, in large cells, the UEs at the cell edges will have quite large RTDs, and this will lead to quite large guard times T_Du between DL and UL, which in turn will lead to a degradation of system performance.

A basic goal of the invention is thus to reduce the guard time T_GU_ARD between DL and UL, particularly in large cells. This is achieved by obtaining a certain characteristic of the user terminals which is relevant for TQUA_RD, and by scheduling the user terminals for transmission and/or reception based upon the measured characteristic of the user terminals.

Thus, the characteristic which is obtained can in one particular application be the distance from the UE to the RBS, but other characteristics may also be envisioned for use, such as, for example, the RTD of the UEs.

In one embodiment of the invention, if the obtained characteristic exceeds a certain predefined threshold, the user terminal is not allowed to be scheduled for reception during a certain last part of the down link interval, e.g. during the TTIs just before the DL to UL switch, as an alternative to which if the obtained characteristic exceeds a certain predefined threshold, the user terminal is not scheduled for transmission during a certain initial part of the up link interval, e.g. during the UL TTIs just after the DL to UL switch.

As a third alternative, if the threshold is exceeded, the user terminal is not scheduled for transmission during a certain last part of the down link interval, nor for transmission during a certain initial part of the up link interval.

Depending on which of the three alternatives described above that is used, there will thus be a period in the UL and/or DL which is "blocked" for scheduling for that particular UE. However, in the remaining part of the UL and/or DL, the UE in question may be freely scheduled (within the normal system restraints, naturally) for transmission (UL) or reception (DL) in one or more TTIs. As mentioned above, the scheduling is suitably carried out by a function in the RBS.

If the obtained characteristic for a first user terminal exceeds the predetermined threshold during parts of the DL and/or UL, meaning that this first user terminal may not be allowed to be scheduled, it is still possible to schedule a second user terminal whose obtained characteristic does not exceed the threshold, and which is thus allowed to be scheduled.

The parts of the down link or the up link which have been mentioned and during which the UE is not scheduled for reception/transmission can be predefined sub-intervals in time of the UL and/or the DL interval respectively. As an alternative to using predetermined "quiet periods" for a certain UE, these "blocked parts" of the UL and/or DL may be determined adaptively depending on the characteristic which is measured, so that, for example, UEs with a very long RTD or a long distance to the RBS have longer "silent periods" in the UL and/or the DL than UEs which have shorter RTD or are at a closer distance to the RBS. However, the entire "non blocked" part of the UL and/or DL will in principle be free for scheduling the UE in question.

The characteristic which is obtained may be obtained in a number of ways. In one embodiment of the invention, as will be shown below, the characteristic may be measured by measuring means in the RBS, or by measuring means outside of the RBS, and then communicated to the RBS.

In another embodiment, the characteristic is obtained from a memory, suitably but not necessarily in the RBS, in which it has been stored at a previous point in time, when it was measured or calculated.

Thus, in "the measurement case", the measurement of said characteristic of the UEs is preferably but not necessarily measured by the base station, which also handles the scheduling of the UEs in the UL and the DL. As an alternative to this, it is possible to let the measurements be handled by other units and to have the results communicated to the RBS.

The characteristic which it is desired to obtain, for example by measurements, may be the RTD for the UEs in question, or, as an alternative, the distance of the UEs to the RBS, by means of which necessary quiet periods in the UL and/or the DL may be determined for the UEs.

If the distance to the RBS from the UE is the characteristic which is obtained, the principle which is used may be expressed in the following way: UEs at the cell edge are not scheduled at the end of the DL transmission time period, and/or the cell edge UEs are not scheduled in the beginning of the UL transmission time period, as an alternative to which cell edge UEs are not scheduled either in the end of the DL transmission time period nor at the beginning of the UL transmission time period.

However, depending on which of the three alternatives described above that is used, there will thus be a period in the UL and/or DL which is "blocked" for scheduling for a particular UE. However, in the remaining part of the UL and/or DL, the UE in question may be freely scheduled (within the system restraints, naturally) for transmission (UL) or reception (DL) in one or more TTIs. As mentioned above, the scheduling is suitably carried out by a function in the RBS

Returning now to the possibility of using the distance between the RBS and the UEs as the characteristic which is measured, there are many different ways of determining, at least with sufficient accuracy for the purposes of this invention, the distance in question. One such possibility is to use time alignment measurements which are carried out by the RBS on the signals received by the RBS from the different UEs. Other possibilities for determining the distance between the RBS and the different UEs are to use positioning systems such as the GPS system or other such systems, or to use triangulation using information from a number of RBSs in adjacent cells.

Regardless of how the distance between the UEs and the RBS is arrived at, fig 3 shows a possible implementation of the invention in the system shown previously in fig 1 : a certain radius R has been defined around the RBS 120 in the cell 110. The guard time at the transition from DL to UL, T_Du, is defined for UEs inside the radius R, and UEs outside of the radius R are handled by scheduling constraints.

Thus, in the example illustrated in fig 3, UEs 130 within the distance R from the RBS 120 may at the same time be scheduled both at the end of the DL transmission period and at the beginning of the UL transmission period, while UEs 140 farther away from the RBS 120, on the other hand, may not simultaneously be scheduled at the end of the DL transmission period and the start of the UL transmission period, as an alternative to which they may not be scheduled in either.

One way of achieving this is shown in fig 4: the UE 130 from figs 1 and 3 is located close to the RBS, or at least within the radius R, while the UE 140 from the same figures is located outside of the radius R. Thus, the UE 130 may be scheduled freely within both the UL and the DL, with the UL and the DL being illustrated with arrows in the same way as in fig 2.

However, the UE 140 which is at the cell edge or at least outside of the radius R may not be scheduled freely in both the UL and in the DL. In the example shown in fig 4, there is a total UL period indicated by means of a horizontal arrow, TU_L, and a total DL period indicated by means of a horizontal arrow T_Dι_. The "cell edge" UE 140 is allowed to be scheduled in the entire DL period, but is however not allowed to be scheduled for a certain initial period of TUL. Thus, the UL period which becomes available to the UE 140 is a sub set of TUL referred to as TU_L' in fig 4.

However, in the remaining part of the UL, the UE 140 may be freely scheduled (within the system restraints, naturally) for transmission in one or more TTIs. As mentioned above, the scheduling is suitably carried out by a function in the RBS.

Another way of putting restrictions on UEs which are more than a certain distance from the RBS is shown in fig 5, with the same reference numbers as on fig 4: the UE 130 which is within the distance R from the RBS 120 may be freely scheduled within both the DL and the UL. However, the UE 140 which is still outside of the radius R may in this embodiment not be scheduled for reception at a certain last part of the DL period. In fig 5, the total DL period is shown by means of a horizontal arrow T_DL, and another horizontal arrow T_DL' shows the DL sub-period available to the UE 140.

However, in the remaining part of the DL, the UE 140 may be freely scheduled (within the system restraints, naturally) for reception (DL) in one or more TTIs.

In both of the embodiment shown in fig 4 and 5, as well as in the invention as a whole, the "forbidden" parts of the UL and/or the DL may be determined adaptively for each UE, or they can be set as one and the same forbidden period in the UL as well as in the DL. In the version shown in fig 5, the "cell edge" UE 140 may start to transmit before it has received the last DL data. As a safeguard against this, the UE 140 could be allowed to ignore such final DL data if the UE 140 has been scheduled in the initial portions of the UL. This could be handled by scheduling means in the UE.

The criteria for determining when and if the UE 140 should be allowed to ignore data in this way could be based on various criteria such as, for example: • The allocated DL-to-UL guard time, which could, for example, be signaled as system information from the RBS to the UE 140.

• "Timing advance" value signaled by the RBS to individual UEs 140.

• Listening to the UL scheduling grant channel in DL

By allowing different UEs to transmit in different intervals of the UL, as proposed by the invention, there could be a risk that a UE 140 which transmits in the UL might interfere with an UE 130 which is receiving in the DL, as shown in fig 6, where the interfering signal from the transmitting UE 140 to the receiving UE 130 is shown by means of an arrow 150.

However, with reference to figs 4 and 5, it can be seen that if cell edge UEs 140 are restricted from transmitting at the end of the DL transmission period or the beginning of the UL transmission period, this type of UE-UE interference can be avoided.

Alternatively, if different UEs "at the cell edge" can be scheduled in the last part of the DL or the first part of the UL, there could be a risk of UE-UE interference if one cell edge UE transmits in UL at the same time as a second cell edge UE is receiving in DL. To avoid such UE-UE interference and still be able to schedule a cell edge UE in the last portion of the DL and a second cell edge UE in the first portion of the UL, the RBS (or the scheduling function in general) needs to consider or to know or take into account the spatial separation of the two cell edge UEs.

Fig 7 is a flow chart 700 which shows some of the major steps of a method of the invention. Steps which are options or alternatives are shown by means of dashed lines. Suitably but not necessarily, the method is performed once per each scheduling occasion for each UE, which will usually be once per TTI, which, in the LTE example, will usually correspond to once per millisecond.

In block 710, a certain characteristic C which is relevant for the interval between the UL and the DL, TQU_ARD, of a least a first UE is obtained in one of the ways described above, i.e. either by measurements or retrieval from, for example, a memory. In "the measurement case", the measurement may be made by measuring means in the RBS, which is indicated in block 720 with dashed lines, since the measuring may also be made outside of the RBS and then communicated to the RBS.

In block 730, there is scheduling of at least the first UE in at least one of the UL or DL intervals, based upon said obtained characteristic of the first user terminal.

As an option, indicated in block 735, it is possible to see if the TTI or TTIs which will be scheduled at present are TTIs at or around the adjacent edges of the UL and DL, i.e. TTIs adjacent to TQ_UARD- Such TTIs are labelled edge TTIs in block 735 in fig 7. If the TTIs in question are not edge TTIs, it is possible to carry out the scheduling with no constraints. In block 740, the obtained characteristic is chosen to be either the user terminal's distance R from the RBS or its RTD, the Round Trip propagation Delay, between the UE and the base station. This block is also shown with dashed lines, since it is optional, the characteristic which is measured may be another one than these two.

In block 750, the obtained characteristic is compared to a threshold T, and if it exceeds the threshold, the UE may not be scheduled for reception during a certain last part of the down link interval, and/or the UE may not be scheduled for transmission during a certain initial part of the up link interval.

In block 760, at least one of said last part of the DL or the initial part of the UL is defined, depending on the magnitude of said obtained characteristic, or, block 770, at least one of said last part or initial part is a predefined sub- interval in time.

In a further embodiment, it is possible to also consider whether there is data to transmit in the opposite direction when evaluating the scheduling constraint. For example, if a UE does not have data to transmit in the UL, there is no need to impose a constraint on that UE in the the DL, and similarly it there is no data to transmit to a UE in the DL, there is no need to impose a scheduling constraint on that UE in the UL.

Furthermore, if e.g. the UL scheduler decides which UEs to schedule in UL before the DL scheduler decides which UEs to schedule in DL, it is possible to take the UL scheduling decision into account when evaluating the DL scheduling constraint.

It should be mentioned here that steps 710 and 730 may also be carried out in the reverse order, as will also become evident from the appended claims. In other words, the scheduling of the first UE may be initiated, and the relevant characteristic then obtained. It is in principle also possible to carry out step 730 after e.g. step 750, i.e., after the comparison with the threshold T.

Fig 8 schematically shows a block diagram of an RBS 800 with some of the components described above: thus, the RBS 800 comprises means 810 for scheduling the first UE to receive traffic from the RBS during the down link interval as well as means 820 for scheduling the UE to transmit traffic to the RBS 800 during the up link interval. In addition, the RBS 800 comprises means 830 for measuring a certain characteristic of the UE, as well as means 840 for making said scheduling in at least one of said intervals based upon said measured characteristic of the first user terminal.

In conclusion, by means of the invention, a reduction of the guard time for the DL-to-UL switch can be obtained which can lead to a significant improvement in the system efficiency, especially for larger cells. With cell ranges around

150 km, performance gains such as, for example, cell capacity and cell throughput in the order of 10-20% can be achieved by adding a constraint on the times that UEs far from the base station may be scheduled in either DL or UL.

Depending on whether UL or DL is the bottle neck for cell edge UEs, it is possible to impose this scheduling constraint on either DL or UL. When UL performance is limiting, the additional scheduling imposed on the DL-to-UL guard time for cell edge UEs can be taken from DL, and vice versa when the DL performance is limiting. This invention is particularly beneficial in cells where the majority of the users are close to the RBS but in which some UEs are or can be very far from the RBS. However, combined with at least approximate spatial knowledge of where the UEs are located in the cell, the invention can give large cell performance gains also when the majority of the users are close to the cell border.

The invention is not limited to the exemplary embodiments given above, but may freely be varied within the scope of the appended claims. Thus, for example, the characteristic which is measured may be another than the RTD or the distance.

Claims

1. A method (700) for use in a wireless access system (100) comprising at least one base station (120, 800) for the control of traffic to and from a cell (110) in the system, said cell (110) being able to accommodate at least a first user terminal (130, 140), in which system said first user terminal (130, 140) can be scheduled for receiving traffic from said base station (120) during a first time interval, the down link interval, and in which system said first user terminal (130, 140) can be scheduled for transmitting traffic to said base station (120, 800) during a second time interval, the up link interval, with a third interval (TQU_ARD) between the down link and the up link intervals, the method (700) being characterized in that it comprises the step (710) of obtaining a certain characteristic C(T_GU_ARD) of said first user terminal with respect to said third interval (TQUARD), and the step (720) of making said scheduling in at least one of the up link or down link intervals based upon said obtained characteristic of the first user terminal (130, 140).

2. The method (700) of claim 1 , according to which said obtained characteristic of the first user terminal (130, 140) is the first user terminal's distance from the base station (120, 800).

3. The method (700) of claim 1 , according to which said obtained characteristic of the first user terminal (130, 140) is the RTD, the Round Trip propagation Delay, between the first user terminal (130, 140) and the base station (120).

4. The method (700) of any of the previous claims, according to which, if said obtained characteristic exceeds a certain predefined threshold (T), the user terminal (130, 140) may not be scheduled for reception during a certain last part of the down link interval.

5. The method (700) of any of the previous claims, according to which, if said obtained characteristic exceeds a certain predefined threshold (T), the user terminal (130, 140) may not be scheduled for transmission during a certain initial part of the up link interval.

6. The method (700) of claim 4 or 5, according to which at least one of said last part or initial part is defined depending on the magnitude of said obtained characteristic.

7. The method (700) of claim 4 or 5, according to which at least one of said last part or initial part is a predefined sub-interval in time.

8. The method (700) of any of the previous claims, according to which said obtained characteristic is a value which is obtained from a memory.

9. The method (700) of any of claims 1 -7, according to which said obtained characteristic is obtained by means of measurements.

10. The method (700) of claim 9, according to which said measured characteristic is measured by the base station (120, 800).

11. The method (700) of any of the previous claims, according to which the scheduling of said user terminal (130, 140) in one of said down link and up link intervals also takes into account the amount of data sent to or from the user terminal in the other interval.

12. A radio base station (120, 800) for the control of traffic to and from a cell (110) in a wireless access system (100), said cell (120) being able to accommodate at least a first user terminal (130, 140), the radio base station comprising means (810) for scheduling said first user terminal (130, 140) to receive traffic from said base station (120, 800) during a first time interval, the down link interval and means (820) for scheduling said first user terminal to transmit traffic to said base station during a second time interval, the up link interval, also comprising means (820) for scheduling a third interval (T_GUARD) between the up link and the down link intervals, the radio base station (120, 800) being characterized in that it additionally comprises means (830) for obtaining a certain characteristic of said first user terminal (130, 140) with respect to said third interval (TGU_ARD) as well as means (840) for making said scheduling in at least one of the up link or down link intervals based upon said obtained characteristic of the first user terminal.

13. The radio base station (120, 800) of claim 12, in which the characteristic which is obtained is the user terminal's (130, 140) distance from the base station.

14. The radio base station (120, 800) of claim 12, in which the characteristic which is obtained is the RTD, the Round Trip propagation Delay, between the first user terminal (130, 140) and the base station.

15. The radio base station (120, 800) of any of claims 12-14, in which, if said obtained characteristic exceeds a certain predefined threshold, the scheduling means (810, 820) act so as not to schedule the user terminal (130, 140) for reception during a certain last part of the down link interval.

16. The radio base station (120, 800) of any of claims 12-15, in which, if said obtained characteristic exceeds a certain predefined threshold, the scheduling means act (810, 820) so as not to schedule the user terminal (130, 140) for reception during a certain initial part of the down link interval.

17. The radio base station (120, 800) of claim 15 or 16, in which at least one of said last part or said initial part is defined by the scheduling means (810, 820) depending on the magnitude of said obtained characteristic.

18. The radio base station (120, 800) of claim 15 or 16, in which at least one of said last part or said initial part is defined by the scheduling means (810, 820) using predefined sub-intervals of time.

19. The radio base station (120, 800) of any of the previous claims, in which said obtained characteristic is a value which is obtained from a memory in the radio base station.

20. The radio base station (120, 800) of any of claims 12-18, in which said obtained characteristic is obtained by means of measurements.

21. The radio base station (120, 800) of claim 20, in which said measured characteristic is measured measuring means (830) in the base station (120, 800).

22. The radio base station (120, 800) of any of claims 12-21 , in which the scheduling means (810, 820) when scheduling for one of the up or down link intervals for the UE (130, 140) takes into account the amount of data sent to or from the UE in the other interval.

23. A user terminal, UE (130, 140), for use with the radio base station (120, 800) of any of claims 12-22, the UE (130, 140) comprising scheduling means which allows the UE (130, 140) to ignore DL data in a certain last part of the DL interval if the UE (130, 140) has been scheduled for transmission in a certain initial part of the UL interval.