WO2008104097A1

WO2008104097A1 - System and method for providing communication in a radio communication system

Info

Publication number: WO2008104097A1
Application number: PCT/CN2007/000628
Authority: WO
Inventors: Henrik Olofsson; Michael Roberts; David Sandberg
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2007-02-28
Filing date: 2007-02-28
Publication date: 2008-09-04
Also published as: CN101617556A; CN101617556B

Abstract

The present invention relates to a method for providing communication in a radio communication system, said radio communication system including a radio transceiver, wherein communication from a user entity in a coverage area of said radio transceiver is carried out in a first communication link between said user entity and said radio transceiver. The method includes the steps of, when synchronization status of said first communication link between said user entity and said radio transceiver is not established in said radio transceiver, transmitting a signal to said user entity, and, when a first period of time has lapsed, allocating a radio transmission resource to said user entity in said first communication link. The invention also relates to a system, a user entity and a communication system.

Description

System and method for providing communication in a radio communication system

Field of the Technology

The present invention relates to a method for providing communication in a radio communication system according to the preamble of claim 1. The present invention further relates to a system according to the preamble of claim 46, a user entity according to claim 87, and a communication system according to claim 90.

Background of the Invention

Wireless mobile radio communication systems are usually cellular, i.e., the total coverage area of such a system is divided into smaller areas wherein each of these smaller areas is associated with a radio base station having one or more radio transceivers for providing communication resources via a radio interface for communication with User Entities (UE), such as mobile phones, smart phones or handheld computers having communication capabilities, located in said area. These areas are usually called cells.

Such communication systems support mobility by allowing the interface between the UE and the network (i.e., connection to a radio transceiver) to move by connecting the UE to different radio transmitters as the UE moves around in the network.

Further, these communication systems also provide mobility in the sense that a user entity can move around within the coverage area of a specific radio transceiver, i.e., the distance from user equipment to the one and the same radio transceiver can change substantially during an ongoing communication.

An example of such a communication system is the current 3rd Generation Partnership Program (3 GPP) work on defining a future cellular communication system, presently called the Evolved Universal Terrestrial Radio Access (E-UTRA) or Long Term Evolution (LTE). In the LTE system, it has been decided to use a transmission scheme called SC-OFDMA (Single Carrier Orthogonal Frequency Division Multiple Access) for the uplink, i.e., communication from user entity to radio base station. In this scheme, users are multiplexed in both time and frequency. It is therefore required for the uplink transmissions from different User Entities (UEs) to arrive at the base station (eNodeB or eNB) relatively time aligned in order to fit into the pre-determined time slot structure.

UEs are physically distributed in the network, having different propagation delays to the eNB, and, therefore, a method to compensate for these differences is required so as to prevent that data transmitted from these user entities collide at the eNB. In LTE, it has been decided to signal a Timing Advance (TA) value from eNB to UE when the network has measured the timing offset. The timing advance value usually corresponds to the length of time it takes for a signal from the user entity to reach the base station (eNB).

When the UE has become synchronized, i.e., transmission on the communication link (uplink) from UE to eNB is synchronized, it will stay synchronized until it is determined to have lost synchronization. This can, for example, be the case if the UE has moved far enough from the eNB to go out of synchronization. In addition, a UE that moves around in the radio network without using the uplink for a certain time will eventually lose its uplink synchronization.

When a UE needs to re-acquire uplink synchronization, procedures specifically designed for this purpose has to be used. In the LTE system, this procedure is called Non-Synchronized Random Access (NSRA). This procedure, however, have numerous disadvantages.

For example, NSRA is contention based, and, therefore, it can only handle a relatively low load before it is congested. This leads to decreased resource utilization.

Further, since the UE does not know the exact reception timing at the base station, a substantial amount of guard time has to be used as a margin to other users, which leads to a further decrease in resource utilization.

Therefore, there exists a need for a method for providing communication in a radio communication system that overcomes, or at least mitigates the disadvantages of current solutions.

Summary of the Invention

It is an object of the present invention to provide a method for providing communication in a radio communication system that solves the above mentioned problem. This object is achieved by a method according to the characterizing portion of claim 1.

It is a further object of the present invention to provide a system that solves the above mentioned problem. This object is achieved by a system according to the characterizing portion of claim 46.

According to the present invention, it is provided a method for providing communication in a radio communication system, said radio communication system including a radio transceiver, wherein communication from a user entity in a coverage area of said radio transceiver is carried out in a first communication link between said user entity and said radio transceiver. The method includes the steps of, when synchronization status of said first communication link between said user entity and said radio transceiver is not established in said radio transceiver, transmitting a signal to said user entity, and, when a first period of time has lapsed, allocating a radio transmission resource to said user entity in said first communication link. This has the advantage that when the communication system receives data for transmission to a user entity, it is not required that the communication system (radio transceiver) is aware of the current synchronization status of the communication link from user entity to radio transceiver, i.e., the uplink. Resource allocation is performed irrespective of the synchronization status, and by waiting a period of time, the period of time can be set to such length that the user entity has time to perform synchronization request prior to the lapse of said period of time. Consequently, it can, similar to existing systems, be ensured that communication always is possible, however with the advantage that the communication can be ensured and carried out irrespective of if the user entity is synchronized when the communication is initiated by the radio transceiver.

The present invention further has the advantage that signalling regarding synchronization procedures can be substantially reduced in the network.

In an alternative embodiment resources of said first communication link are allocated to said user entity prior to receiving a response from said user entity, even if a synchronization status of the first communication link between said user entity and said radio transceiver is not established in said radio transceiver. This has the advantage that should the user entity be synchronized when communication is initiated, delays in data transmission can be substantially reduced.

Further characteristics of the present invention, and advantages thereof, will be evident from the following detailed description of preferred embodiments and appended drawings, which are given by way of example only, and are not to be construed as limiting in any way.

Brief Description of the Drawings

Fig. 1 discloses an example of a Long Term Evolution (LTE) system in which the present invention may advantageously be utilized. Fig. 2 discloses UEs with different propagation delays without proper timing advance.

Fig. 3 discloses an example of a Non-Synchronized Random Access Burst (NSRA) procedure.

Fig. 4 discloses downlink access for a UE which is synchronized in the uplink. Fig. 5 discloses downlink access for a UE which is unsynchronized in the uplink.

Fig. 6 discloses a state machine controlling the uplink sync status of a UE. Fig. 7 discloses a first exemplary embodiment according to the present invention.

Fig. 8 discloses an alternative exemplary embodiment according to the present invention. Fig. 9 discloses another exemplary embodiment according to the present invention.

Figure 10a discloses an exemplary embodiment wherein an unsynchronized UE is in "unknown sync" state.

Figure 10b discloses an embodiment wherein a synchronized UE is in "unknown sync" state.

Detailed Description of the Invention

As was stated above, the 3rd Generation Partnership Program (3 GPP) Radio Access Network (RAN) working groups (WG), which have defined the UMTS Universal Terrestrial Radio Access Network (UTRAN), is currently working on defining a future cellular communication system in the Long Term Evolution (LTE) Work Item (WI).

An example of the architecture of an LTE system 100 is shown in fig. 1, and consists of two kinds of nodes, radio base stations (stationary radio transceivers), eNBs (enhanced Node B) 101-103 and aGWs (access Gate Way) 104-105, where the eNBs 101-103 belongs to the evolved UTRAN (E-UTRAN) 106 and the aGW belongs to the evolved packet core (EPC) 107. A user entity (UE) 108 connects to the network (E-UTRAN and EPC) by means of a radio interface, Uu interface 109. The eNB 101-103 handles communication over the radio interface in a certain coverage area, i.e., cell, which is the area wherein the radio signal is strong enough to allow a satisfactory communication with UEs within said area.

When the UE 108 moves around in the coverage area provided by the communication system, the UE 108 will move from one cell to another, and thereby an ongoing communication will be transferred from the eNB to which the UE presently belongs, i.e., the serving cell, to the cell into which the UE is entering, i.e., the target cell. This is accomplished by establishing a communication channel on the Uu interface of the target cell, and terminating the communication channel on the Uu interface of the source cell. When a communication is ongoing, the eNB constantly receives transmissions from the UE, and if the eNB determines that the UE needs to adjust its timing advance (TA), e.g., due to an increasing or decreasing distance from the UE to the eNB, a proper TA can be signalled to the UE. However, in many applications data is transmitted from eNB to UE intermittently and not continuously, e.g., when an application has data to transmit to the UE or when a web page is loaded into a web browser of the user entity. In such situations, the required synchronization between UE and eNB can be lost in the mean time between the data transmissions, as will be described below.

As also was stated above, it has been decided to use SC-OFDMA (Single Carrier Orthogonal Frequency Division Multiple Access) for the uplink in LTE. In this scheme, users are multiplexed in both time and frequency, and it is therefore required for the uplink transmissions from different User Entities (UEs) to arrive at the eNB relatively time aligned in order to fit into the pre-determined slot structure. An example of the SC-OFDMA scheme for a single frequency is shown in fig. 2, and as can be seen in the figure, four UEs, UE 1 , ... UE4 are allocated time slots TS 1 , ... , TS4 , respectively. UEl and UE2 are correctly time aligned, i.e. the reception of their transmissions both begin and end within their respective time slots, and consequently, do not disturb transmissions from other UEs. The transmission from UE3, however, started too late, and although its reception starts in TS3, it is not finished until about a fourth into TS4, wherein it collides with the transmission from UE4, and, consequently, corrupts both transmissions. Such a situation arises when UEs, which are physically distributed in the network and have different propagation delays to the eNB, e.g., due to varying distances and/or objects blocking the path to the eNB, start transmissions substantially in an unsynchronized manner. Therefore, a method to compensate for these differences is required in order to avoid situations such the one disclosed in fig. 2. Further, a UE that moves around in the radio network without using the uplink for a certain time will eventually lose its uplink synchronization due to changes in distance from UE to eNB. To re-acquire uplink synchronization, a procedure specifically designed for this purpose has to be used. In LTE it has been decided to signal a Timing Advance (TA) value from eNB to UE when the network has measured the timing offset using, e.g., Non-Synchronized Random Access (NSRA) (it should be noted that this structure at present is only suggested and not finally decided, and the process is therefore given for illustrational purposes only) and is illustrated in fig. 3 and will be described in the following.

In LTE, the timing estimation has to be performed by the eNB when measuring a received signal, and this is usually performed during a random access. The eNB can then transmit an appropriate a timing advance command to the UE, which then adjusts its uplink transmission timing accordingly. In SC-OFDM, the time domain is divided into frames, wherein each frame is divided into the smallest allocatable time periods, i.e., time slots, or physical resource blocks (PRB), which in length substantially correspond to the transmission time intervals (TTI) a UE is allowed to transmit. A PRB (TTI) can, for example, be 0.5 ms or 1 ms. In the disclosed example, a PRB (TTI) equals 1 ms. The NSRA requests are transmitted on a Random Access Channel (RACH). RACH resources can be arbitrary located and can consist, e.g., of 1 or more TTIs. There may be a plurality of consecutive TTIs of a single frequency allocated for RACH. Alternatively, or in addition, there may be such RACH resources allocated on a plurality of frequencies. For example, the RACH resources can be periodically recurring, e.g., every 20 ms.

An unsynchronized UE that wishes to establish, or re-establish communication with an eNB transmits a NSRA request, e.g., on such a random access channel (RACH), and an NSRA request contains two parts, a preamble, i.e., a short signal which is sent before the transmission of the second part, a higher layer message. The higher layer message, however, is only transmitted when authorized by the eNB to do so.

To avoid interferences with a following communication resource, i.e., take into account any time synchronization uncertainty to prevent the eNB from receiving a

RACH signal during a resource dedicated for data transmission, a guard time is required at the end of the TTI. I.e., the preamble is made shorter than, e.g., 1 ms. The duration of the guard interval should take into account round-trip delay and the delay spread. As can be understood, the required guard time depends on the cell size, the larger the cell size, the longer guard time. As can be seen in the figure, the preamble is also preceded by a cyclic prefix (CP), which has a function corresponding to the guard time.

The shortened preamble, however, will still be enough for the eNB to estimate the receive timing of a certain UE and signal a TA message in accordance therewith for use according to the above. This procedure, however suffers from the following drawbacks:

- The NSRA is contention based, which means that even if the eNB can handle simultaneous access attempts from more than one UE in a single RACH, it can still only handle a relatively low load before it gets congested, with a decreased resource utilization as result. In addition, the delay until the procedure is finalized can be significant due to the possibility of collisions. Further, since the UE does not know the exact reception timing at the eNB, a substantial amount of guard time has to be used as a margin to other users, which leads to a further decreased resource utilization.

Therefore, due to these drawbacks, it is advantageous to keep the amount of required uplink accesses using the NSRA to a minimum, i.e., the time period between synchronizations of a particular UE should be kept as long as possible. Normally, the network and the UE have the same view on the synchronization status, i.e., whether the UE is synchronized or not, of the particular UE. The reason for this requirement can be derived from the synchronous Hybrid ARQ (HARQ) scheme that is selected for the downlink. For a downlink access, the network knows when to expect a response in the form of an ACK/NACK. This is illustrated in fig. 4, wherein in 401 the eNB receives data to be transmitted to the UE, whereafter the eNB at 402 and 403 starts transmission in one or more data flows (data processes). When the UE is synchronized, the eNB knows that Acknowledgements or Negative- Acknowledgements will be received at particular times, e.g., 405 and 405. The indication of a time resource in an Acknowledgement and/or Negative-

Acknowledgements can be implicit, based on the time of reception of said signal, i.e., if the time resource consists of a time slot, the ACK/NACK for that particular time slot is expected a predetermined number of time slots later, e.g., three time slots later.

On the other hand, if the UE is unsynchronized, it has to delay the ACK/NACK response to give time for the NSRA procedure. This is illustrated in fig. 5, wherein the eNB, after reception of data for transmission to the UE, in 501, pages the UE in 502. When the UE receives the paging message, it attempts RACH signalling to obtain synchronization. However, if the RACH is congested, a plurality of attempts 503-505 may be required in order for the eNB to successfully decode the RACH preamble of the UE and determine a suitable TA, which at 506 is signalled to the UE. As can be seen in the figure, the delay 507 between the point in time when the data transmission could have started had the UE been synchronized, and the time 508 at which the actual data transmission starts, can be quite substantial. From the point in time when the data transmission starts, the process in fig. 5 equals the process in fig. 4. Consequently, provided that the network and the UE have the same view on the

UE uplink synchronization status, an access method according to fig. 4 or 5, is suitably selected.

This determination (selection of process) can be based on, e.g., a timer from the last uplink access. When the timer expires, the UE will be considered unsynchronized in the uplink. Given the inactive period and, for example, an assumed maximum UE speed expected to occur in the network (e.g., 500 km/h) the synchronization status of a UE can be determined based on these criteria. However, if the timer for all UEs is set to the same value, i.e., corresponding to the worst case UE speed (e.g., 500 km/h as above), a low mobility UE would still be considered unsynchronized after a relatively short period of time, which, therefore, leads to a reduction in the performance of the network and a possible over-usage of the NSRA.

The present invention provides a solution that overcomes, or at least mitigates the disadvantages of current solutions. According to the present invention, the UE autonomously decide its uplink synchronization status while the network is unaware of the synchronization status of the mobile. This has the advantage that the amount of uplink access using the NSRA can be substantially reduced. Further, according to the present invention, it is not required that the system is aware of the current synchronization status of the UE, but the communication procedure can be the same, from the system point of view, irrespective of whether the UE is synchronized or not.

Since the system and the UE need not share the same view of the synchronization status, it can be left to the UE to determine for how long it is to be regarded as synchronized. When a UE has become synchronized, it will stay synchronized until it has moved far enough to go out of sync (e.g., in an exemplary system wherein the synchronization requirement is 1 μs, the UE will be considered synchronized a distance of approximately 150 meters in a direction radial to the radio base station). Consequently, according to the present invention, the UE can stay synchronized for much longer as compared to a system wherein a worst case scenario must be taken into account.

There are numerous methods for a UE to extend the time it can keep synchronization, and a non-exhaustive list of available methods include: -Accurate internal timing reference, and

-a positioning system, such as GPS or any other positioning system.

This also has the advantage that, e.g., low mobility mobiles (stationary or pedestrian mobiles) can maintain synchronization much longer, with a reduction in NSRA attempts, and thereby enhanced system resource usage, as result. For example, UEs can be arranged to estimate their own speed, and set an internal timer based on the estimated speed, at the expiry of which the UE determines itself as unsynchronized. Fig. 6 discloses a state machine according to the present invention controlling the uplink sync status of a UE. According to the prior art, the UE is either in a "In Sync" state 601, wherein both UE and network is aware of the UE being synchronized, or an "Out of Sync" state 602, wherein the UE is considered to be unsynchronized, by itself as well as the network. The UE can enter the "In Sync" state 601, e.g., by an NSRA request. After a predetermined time has lapsed, e.g., set by a timer 1 according to the above, the UE is determined to be out of sync again. According to the present invention, however, the UE is allowed to be in an "unknown sync" state 603. The UE can enter the state 603, e.g., when the above mentioned timer 1 lapses. If the network needs to access a UE in this state, the standard access methods according to fig. 4 or 5 cannot be used because of the synchronous HARQ scheme as described above. Instead, some alternative method has to be used. In the following, exemplary embodiments of the present invention will be described in connection to figs. 7- 10b. The preconditions for all the presented examples are that a UE is in the "unknown sync" state according to fig. 6, and that the network needs to initiate an access to the UE in the downlink, e.g., to transmit data. The UE can be let to be in the "unknown sync" state 603 for a much longer period of time than timer 1, this prolonged time can either be determined by the UE all by itself according to the above, or by a second timer, timer 2, set by the network, at which the UE unconditionally will be returned to state 602. The time limit of timer2, however, can be set to a much longer period of time than timer 1, thereby substantially decreasing NSRA attempts in the system and improving resource usage. When used according to the present invention, the network will not be aware of if the UE is in state 602, at least not until timer2 has lapsed.

The process in fig. 7 starts with, after reception of data for transmission to the UE in step 701, the network performing a "paging" 702 of the UE, i.e., it transmits a short message to notify the UE of an imminent downlink transmission. Time 703 is then given to allow the UE to acquire uplink synchronization, if necessary. If no uplink synchronization request is received within the time interval 703, i.e., the UE has determined that it is synchronized, the eNB at 704 and 705 starts transmission in one or more data flows (data processes), and allocates uplink resources 706, 707 to the UE for transmission of acknowledgements. Since the UE is synchronized, it will then transmit Acknowledgements or Negative-Acknowledgements with appropriate

TA such that these are received at the eNB when expected, i.e., at 706 and 707. If, on the other hand, the UE determines that it is not synchronized, i.e., it is in state 602 in fig. 6, the UE can, e.g., use the NSRA procedure during the time interval 703 to obtain synchronization. The time interval 703 can be set such that an appropriate number of NSRA attempts can be performed and rejected, e.g., due to contention, before a successful NSRA attempt is obtained. The present invention has the advantage that the reduction it imposes in NSRA signalling can allow use of a shorter period of time 703 as compared to the prior art. The embodiment described in fig. 7 has the advantages that the network can allow the UE sync state to be "unknown sync", and that the UE thereby by it self can decide its sync status and use NSRA if required.

Delay for NSRA must still be accounted for, i.e., time period 703, which means that the packet delay may not reduced compared to the case where the sync status is based on a timer and a worst case UE speed, unless, of course, the reduced NSRA signalling enables shortening of this time period as mentioned above. However, the NSRA procedure is contention based and includes power ramping, and therefore the delay can be unpredictable and some worst case delay for this procedure may have to be accounted for. Still, the NSRA signalling in the network is reduced.

In an alternative embodiment of the example disclosed in fig. 7, it is not determined whether an uplink synchronization request is received within the time interval 703, but the eNB starts transmission in one or more data flows (data processes) when said time interval has lapsed no matter what. This has the advantage that the UE has time to perform a synchronization if required, wherein said synchronization can be performed, e.g., by transmitting a NSRA procedure as above, or in any other suitable way, i.e., not necessarily by signalling with the particular eNB. In fig. 8 is shown an alternative embodiment according to the present invention.

In this embodiment, the transmission of an explicit paging message is omitted, and instead the network transmits user data to the UE, 802. Time 803, corresponding to the period of time 703 in fig. 7, is then given for the UE to perform NSRA procedure, if required. When this time has passed, and no NSRA request has been detected, the network continues to transmit data at 804 and allocates resources 805, 806 for ACK/NACK in the uplink, i.e. the network continues normal data transmission. The embodiment according to fig. 8 has the advantage that the packet delay is slightly reduced compared to the procedure in fig. 7, since data is used as an implicit paging. However, time for the NSRA procedure still has to be accounted for.

In fig. 9 is shown an exemplary procedure that is similar to the procedure shown in fig. 8, but with the exception that a plurality of HARQ processes 902, 903 are transmitted in the first stage (i.e. before ACK/NACK is received). The number of transmitted processes can, e.g., equal the maximum number of processes allowed according to the particular HARQ scheme that is used. This embodiment has the advantage that network behaviour is similar to normal network behaviour if the UE is synchronized, with the exception for the delay until the first ACK/NACK messages are received. This embodiment has the same packet delay as is associated with the embodiments of fig. 7 and 8.

In figs. 10a-b is shown an exemplary embodiment wherein the packet delay is reduced compared to the embodiments of figs. 7-9 for a synchronized UE in the "unknown sync" state. In this embodiment, the network transmits data using several HARQ processes and immediately allocates uplink resources 104, 105 for normal ACK/NACK response (see fig. 10a), i.e., the allocation of uplink resources is not delayed until the expiration of a timer, and the process is similar to what was described in fig. 4 for a synchronized UE wherein the network is aware of the UE synchronization status. After transmission in 1002 and 1003, the network also detects if the allocated ACK/NACK resources 1004, 1005 are used by the UE. If the resources are used, the transmission of data continues until all data has been transmitted.

If the ACK/NACK resources 1004, 1005 are not used, the network assumes that the UE is unsynchronized, i.e., that an NSRA procedure is required, and allocates resources 1006, 1007 for a delayed ACK/NACK, wherein the delay similar to the embodiments above is set such that an NSRA procedure can be performed. Consequently, uplink resources can be wasted if the UE is unsynchronized. Still, the embodiment of fig. 10a-b has the advantage that it reduces load on the Random Access CHannel compared to when a timer based on worst case UE mobility is used to decide synchronization status, and for a synchronized UE there is no delay in comparison with the prior art system. In conclusion, the above described exemplary embodiments of the present invention have the common advantages that network operation is simplified, and that the network is simpler to design and implement. Further, NSRA signalling can be substantially reduced, with better resource usage as result. Although the present invention has been described in connection with an LTE system, the principles of the invention applies to wireless radio communication systems in general, and are therefore applicable in any system wherein a synchronized uplink transmission is required.

Further, the present invention has been described for a cellular communication system. It is to be understood, however, that the present invention is equally applicable in any system wherein a user entity is movable in relation to a radio transceiver, and wherein there is a requirement that the communication from user entity to radio transceiver is synchronized.

Claims

1. Method for providing communication in a radio communication system, said radio communication system including a radio transceiver, wherein communication from a user entity in a coverage area of said radio transceiver is carried out in a first communication link between said user entity and said radio transceiver, characterised in that the method includes the steps of, when synchronization status of said first communication link between said user entity and said radio transceiver is not available in said radio transceiver, - transmitting a signal to said user entity, and,

- when a first period of time has lapsed, allocating a radio transmission resource to said user entity in said first communication link.

2. Method according to claim 1, characterised in that the method further includes the step of, when said first period of time has lapsed and prior to said allocation of a resource to said user entity, transmitting data from said transceiver to said user entity.

3. Method according to claim 1, characterised in that the method further includes the step of:

- detecting if a response to said signal is received from said user entity within said first period of time, and wherein said resource in said first communication link is allocated to said user entity if no response is obtained within said first period of time.

4. Method according to claim 1, characterised in that the length of said first period of time is arranged such that a synchronization procedure for synchronizing said first communication link can be executed in said user entity within said first period of time, said synchronization procedure including a transmission from said user entity to said transceiver, and reception of said transmission at said transceiver.

5. Method according to claim 1, characterised in that said steps are performed when the radio transceiver has data for transmission to said user entity.

6. Method according to claim 1, characterised in that communication from said radio transceiver to said user entity is transmitted in a second communication link.

7. Method according to claim 1, characterised in that said signal transmitted to said user entity includes at least part of data received for transmission to said user entity.

8. Method according to claim 1, characterised in that said user entity responds to said transmission by signalling on said allocated resource of said first communication link when it has been determined that said first communication link is synchronized.

9. Method according to claim 1, characterised in that it further comprises the step of, in said user entity, initiating a synchronization procedure if, upon reception of said transmission from the radio transceiver, it is determined that said first communication link between user entity and radio transceiver is not synchronized or might be not synchronized.

10. Method according to claim 1, characterised in that it further includes the step of determining said synchronization status in said user entity.

11. Method according to claim 10, characterised in that said user entity determines its synchronisation status based on the estimated speed.

12. Method according to claim 10, characterised in that the user entity determines its uplink synchronization status based on its current position.

13. Method according to claim 12, characterised in that the current position of said user entity is determined by means of a positioning system.

14. Method according to claim 10, characterised in that it further includes the step of determining said synchronization status of said first communication link when receiving said transmission from said transceiver.

15. Method according to claim 8, characterised in that said signalling on said allocated resource of the first communication link contain at least one acknowledgement (ACK) and/or at least one negative-acknowledgement (NACK) regarding reception of data.

16. Method according to claim 15, characterised in that the said indication of a resource for said ACK/NACK signalling can be implicit, such as based on the time of reception of said signal from said radio transceiver.

17. Method according to claim 15, characterised in that the user entity uses said uplink radio transmission resource for an uplink transmission.

18. Method according to claim 9, characterised in that said synchronization procedure is a Non-Synchronized Random Access (NSRA) procedure.

19. Method according to claim 9, characterised in that said synchronization procedure includes the steps of:

- signalling to said radio transceiver, and

- said radio transceiver responding to said signalling, said response including at least one synchronization parameter.

20. Method according to claim 19, characterised in that said synchronization parameter is a timing advance value.

21. Method according to claim 20, characterised in that the said timing advance value can be sent in-band with data, such as header information in the same protocol data unit as data.

22. Method according to claim 20, characterised in that the said timing advance value can be sent in a protocol data unit separate from the protocol data units for data.

23. Method according to claim 19, characterised in that it further includes the step of allocating a resource to said user entity in said first communication link.

24. Method according to claim 1, characterised in that said radio communication system is a cellular communication system, said communication system including a plurality of cells, each of said cells including at least one radio transceiver for providing communication with at least one user entity in a coverage area.

25. Method according to claim 1, characterised in that a plurality of resources are allocated to said user entity.

26. Method according to claim 1, characterised in that data are transmitted to said user entity as a plurality of transmissions, and that a plurality of resources are allocated to said user entity, wherein said user entity responds to said plurality of transmissions on said plurality of resources.

27. Method according to claim 1, characterised in that said radio transceiver is a radio base station in a cellular communication system.

28. Method according to claim 1, characterised in that said radio transceiver is an eNB (enhanced Node B) in a 3GPP Enhanced UTRAN (Universal Terrestrial Radio Access Network) system.

29. Method according to claim I₅ characterised in that said first communication link is an uplink.

30. Method for providing communication in a radio communication system, said radio communication system including a radio transceiver, wherein communication from a user entity in a coverage area of said radio transceiver is carried out in a first communication link between said user entity and said radio transceiver, characterised in that, the method includes the steps of:

- transmitting a signal to said user entity, wherein said user entity is expected to respond to said signal, and

- allocating a radio transmission resource of said first communication link to said user entity prior to receiving a response from said user entity even if synchronization status of said first communication link between said user entity and said radio transceiver is not available in said radio transceiver.

31. Method according to claim 30, characterised in that said steps are performed when the radio transceiver has data for transmission to said user entity.

32. Method according to claim 30, characterised in that said signal transmitted to said user entity includes at least part of data received for transmission to said user entity.

33. Method according to claim 30, characterised in that said user entity responds to said transmission by signalling on said allocated resource of said first communication link when it has been determined that said first communication link is synchronized.

34. Method according to claim 30, characterised in that it further comprises the step of, in said user entity, initiating a synchronization procedure if, upon reception of said transmission from the radio transceiver, it is determined that said first communication link between user entity and radio transceiver is not synchronized or might be not synchronized.

35. Method according to claim 30, characterised in that it further includes the step of, in said user entity, determining said synchronization status of said first communication link.

36. Method according to claim 33, characterised in that said signalling on said allocated resource of the first communication link contain an acknowledgement (ACK) and/or a negative-acknowledgement (NACK) regarding reception of said data.

37. Method according to claim 36, characterised in that the said indication of a resource for said ACK/NACK signalling can be implicit, such as based on the time of reception of said signal from said radio transceiver.

38. Method according to claim 36, characterised in that the user entity uses said uplink radio transmission resource for an uplink transmission.

39. Method according to claim 34, characterised in that said synchronization procedure is a Non-Synchronized Random Access (NSRA) procedure.

40. Method according to claim 34, characterised in that said synchronization procedure includes the steps of:

- signalling to said radio transceiver, and

41. Method according to claim 40, characterised in that said synchronization parameter is a timing advance value.

42. Method according to claim 40, characterised in that it further includes the step of:

- allocating a resource to said user entity in said first communication link.

43. Method according to claim 30, characterised in that said radio transceiver is a radio base station in a cellular communication system.

44. Method according to claim 30, characterised in that a plurality of resources are allocated to said user entity.

45. Method according to claim 30, characterised in that data are transmitted to said user entity as a plurality of transmissions, and that a plurality of resources are allocated to said user entity, wherein said user entity responds to said plurality of transmissions on said plurality of resources.

46. System for providing communication in a radio communication system, said radio communication system including a radio transceiver, wherein communication from a user entity in a coverage area of said radio transceiver is arranged to be carried out in a first communication link between said user entity and said radio transceiver, characterised in that the system includes means for, when synchronization status of said first communication link between said user entity and said radio transceiver is not available in said radio transceiver:

- transmitting a signal to said user entity, and

47. System according to claim 46, characterised in that it further includes means for, when said first period of time has lapsed and prior to said allocation of a resource to said user entity, transmitting data from said transceiver to said user entity.

48. System according to claim 46, characterised in that it further includes means for:

- detecting if a response to said signal is received from said user entity within said first period of time, wherein said resource in said first communication link is allocated to said user entity if no response is obtained within said first period of time.

49. System according to claim 46, characterised in that the length of said first period of time is arranged such that a synchronization procedure for synchronizing said first communication link can be executed in said user entity within said first period of time, said synchronization procedure including a transmission from said user entity to said transceiver, and reception of said transmission at said transceiver.

50. System according to claim 46, characterised in that said it is arranged to transmit said signal to said user entity when the radio transceiver has data for transmission to said user entity.

51. System according to claim 46, characterised in that communication from said radio transceiver to said user entity is arranged to be transmitted in a second communication link.

52. System according to claim 46, characterised in that said signal transmitted to said user entity is arranged to include at least part of data received for transmission to said user entity.

53. System according to claim 46, characterised in that said user entity is arranged to respond to said transmission by signalling on said allocated resource of said first communication link when it has been determined that said first communication link is synchronized.

54. System according to claim 46, characterised in that it further comprises means for, in said user entity, initiating a synchronization procedure if, upon reception of said transmission from the radio transceiver, it is determined that said first communication link between user entity and radio transceiver is not synchronized or might be not synchronized.

55. System according to claim 46, characterised in that it further includes means for determining said synchronization status in said user entity.

56. System according to claim 55, characterised in that said user entity is arranged to determine its synchronisation status based on estimated speed.

57. System according to claim 55, characterised in that the user entity is arranged to determine its uplink synchronization status based on its current position.

58. System according to claim 57, characterised in that the current position of said user entity is arranged to be determined by means of a positioning system.

59. System according to claim 55, characterised in that it further includes means for determining said synchronization status of said first communication link when receiving said transmission from said transceiver.

60. System according to claim 53, characterised in that said signalling on said allocated resource of the first communication link is arranged to contain at least one acknowledgement (ACK) and/or at least one negative-acknowledgement (NACK) regarding reception of said data.

61. System according to claim 60, characterised in that the said indication of a resource for said ACK/NACK signalling can be implicit, such as based on the time of reception of said signal from said radio transceiver.

62. System according to claim 60, characterised in that the user entity uses said uplink radio transmission resource for an uplink transmission.

63. System according to claim 54, characterised in that said synchronization procedure is a Non-Synchronized Random Access (NSRA) procedure.

64. System according to claim 54, characterised in that said synchronization procedure includes:

- signalling to said radio transceiver, and

65. System according to claim 64, characterised in that said synchronization parameter is a timing advance value.

66. System according to claim 64, characterised in that it further includes: - allocating a resource to said user entity in said first communication link.

67. System according to claim 46, characterised in that said radio communication system is a cellular communication system, said communication system including a plurality of cells, each of said cells including at least one radio transceiver for providing communication with at least one user entity in a coverage area.

68. System according to claim 46, characterised in that a plurality of resources are allocated to said user entity.

69. System according to claim 46, characterised in that data are transmitted to said user entity as a plurality of transmissions, and that a plurality of resources are allocated to said user entity, wherein said user entity is arranged to respond to said plurality of transmissions on said plurality of resources.

70. System according to claim 46, characterised in that said radio transceiver is a radio base station in a cellular communication system.

71. System according to claim 46, characterised in that said radio transceiver is an eNB (enhanced Node B) in an Evolved Universal Terrestrial Radio Access (E- UTRA) system.

72. System for providing communication in a radio communication system, said radio communication system including a radio transceiver, wherein communication from a user entity in a coverage area of said radio transceiver is carried out in a first communication link between said user entity and said radio transceiver, characterised in that, the system includes means for: - transmitting a signal to said user entity, wherein said user entity is expected to respond to said signal, and

- allocating a radio transmission resource of said first communication link to said user entity prior to receiving a response from said user entity even if a synchronization status of the first communication link between said user entity and said radio transceiver is not available in said radio transceiver.

73. System according to claim 72, characterised in that it includes means for transmitting said signal to said user entity when the radio transceiver has data for transmission to said user entity.

74. System according to claim 72, characterised in that said signal transmitted to said user entity includes at least part of data received for transmission to said user entity.

75. System according to claim 72, characterised in that said user entity is arranged to respond to said transmission by signalling on said allocated resource of said first communication link when it has been determined that said first communication link is synchronized.

76. System according to claim 72, characterised in that it further comprises means for, in said user entity, initiating a synchronization procedure if, upon reception of said transmission from the radio transceiver, it is determined that said first communication link between user entity and radio transceiver is not synchronized or might be not synchronized.

77. System according to claim 72, characterised in that it further includes means for, in said user entity, determining said synchronization status of said first communication link.

78. System according to claim 72, characterised in that said signalling on said allocated resource of the first communication link is arranged to contain an acknowledgement (ACK) and/or a negative-acknowledgement (NACK) regarding reception of data.

79. System according to claim 78, characterised in that the said indication of a resource for said ACK/NACK signalling can be implicit, such as based on the time of reception of said signal from said radio transceiver.

80. .System according to claim 78, characterised in that the user entity uses said uplink radio transmission resource for an uplink transmission.

81. System according to claim 76, characterised in that said synchronization procedure is a Non-Synchronized Random Access (NSRA) procedure.

82. System according to claim 76, characterised in that said synchronization procedure includes:

- signalling to said radio transceiver, and

83. System according to claim 82, characterised in that said synchronization parameter is a timing advance value.

84. System according to claim 82, characterised in that it further includes: - allocating a resource to said user entity in said first communication link.

85. System according to claim 72, characterised in that said radio transceiver is a radio base station in a cellular communication system.

86. System according to claim 72, characterised in that a plurality of resources are allocated to said user entity.

87. System according to claim 72, characterised in that data are arranged to be transmitted to said user entity as a plurality of transmissions, and that a plurality of resources are allocated to said user entity, wherein said user entity responds to said plurality of transmissions on said plurality of resources.

88. User entity for use in a radio communication system, said radio communication system including a radio transceiver, wherein communication from said user entity in a coverage area of said radio transceiver is arranged to be carried out in a first communication link between said user entity and said radio transceiver, characterised in that the user entity includes means for:

- receiving a signal from said radio transceiver,

- determining synchronization status of said first communication link and responding to said transmission if said first communication link is determined to be unsynchronized, and - from said radio transceiver, receiving an allocation of a radio transmission resource in said first communication link if no response to said transmission has been transmitted to said radio transceiver.

89. User entity for use in a radio communication system, said radio communication system including a radio transceiver, wherein communication from said user entity in a coverage area of said radio transceiver is arranged to be carried out in a first communication link between said user entity and said radio transceiver, characterised in that the user entity includes means for:

- receiving a signal from said radio transceiver, - determining a synchronization status of said first communication link, and responding to said transmission if said first communication link is determined to be unsynchronized, and

- from said radio transceiver, receiving data if no response to said transmission has been transmitted to said radio transceiver.

90. Communication system, characterised in that it includes a system according to any of the claims 46-87.