Performing preamble assignment for random access in a telecommunications system

ES 2 575 132 T3 description

Methods and apparatus for performing preamble assignment for random access in a telecommunications system

Technical field

The present invention relates generally to the field of wireless telecommunications, and more particularly to methods and apparatus for assigning a preamble to user equipment to enable user equipment to perform random access in a telecommunications system.

Background

The third generation partnership project (3GPP) is responsible for the standardization of UMTS (universal mobile telecommunications service, and LTE (long-term evolution) is now under discussion as a next-generation mobile communication system of the UMTS system. LTE is a technology for high-speed packet-based communication that can achieve data rates of more than 100 Mbps on the downlink and more than 50 Mbps on the uplink. 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Access Network (E-UTRAN).

Generally, one or more cells are allocated to a radio base station, known as 3GPP LTE system such as eNB (Enhanced / Evolved Node B) or eNodeB. Additionally, the eNBs on LTE will interact directly with the core network and with other eNBs. A plurality of user equipment can be placed in a cell served by an eNB. A user equipment (UE) can be represented by a mobile phone, a wireless terminal, a laptop, a personal computer, a PDA, an internet protocol (VoIP) capable telephone or any other LTE capable UE of 3GPP. Generally, a first access of the UE to the system is carried out by means of a random access procedure (RA). The objectives of the RA procedure may include: initial access; transfer; time request (request for radio resources); time synchronization; and the like. The radio network nodes generally control the behavior of the UE. As an example, the uplink transmission parameters like frequency, time and power are regulated through downlink control signaling from the radio base station (eg eNB) to the UE. For uplink (UL) frequency and power estimation parameters, a UE may derive those parameters from one or more downlink (control) signals. However, making a time estimate for the uplink is more difficult because the propagation delay between the eNB (or eNodeB) and the UE is generally unknown. As an example, when a UE is connected or turned on after a disconnected time, the UE is not synchronized on the uplink. Therefore, before starting the traffic, the UE has to access the network, which in a first step includes obtaining synchronization to the network. This is normally done by the UE that performs measurement / measurements by listening to the downlink signals and obtains from these signals time synchronization; an estimate of a frequency error, and also an estimate of the downlink path loss. Even though the UE is now time synchronized to the downlink, the signals to be sent from the UE are still not time aligned on the eNB (or eNodeB) due to such unknown propagation delay. Thus, the UE has to carry out a random access procedure (RA) in the network. The RA procedure is a procedure typically used by the UE to request access to a system or resources when the UE discovers a need to acquire uplink synchronization or a need to make an uplink transmission and the resources for said link transmissions. ascending are not yet available in the EU. Furthermore, the synchronization or time alignment of uplink transmissions is intended to minimize interference with transmissions from other UEs and increase resource efficiency by minimizing the need for guard bands.

The RA procedure can be classified into a contention-based random access procedure and a contention-free (or non-contention-based) random access procedure.

For the contention-based random access procedure, a first set that forms a group of non-dedicated random access preambles is assigned per cell (ie, to an eNodeB). This group is used firstly when there is data originating from UE and the UE has to establish a connection and proper uplink time relationship with the network through the RA procedure. When contention-based random access is performed, the UE arbitrarily selects one preamble from the group as the non-dedicated random access preamble. This is known as UE initiated random access (supported on LTE). Thus for contention-based random access, the network (or eNB) is not (immediately) aware of which UE selected which preamble. A disadvantage with this is that multiple UEs can in fact select the same preamble and can try to access the network (or eNodeB) at the same time. This can cause a collision or collisions to occur. Thus, an extra step of identifying UEs trying to access the network (or eNodeB) and resolving potential collisions, a so-called contention resolution mechanism, is needed.

To realize contention-free random access, a second set is also defined that forms a group of random access preambles assigned per cell (ie, to an eNodeB). These preambles are known as

ES 2 575 132 T3 non-dedicated random access preambles, a non-dedicated random access preamble is assigned to the UE by the eNodeB. In other words, this preamble cannot be autonomously selected by the UE and therefore, for the duration of the validity of the assignment, this dedicated random access preamble is exclusively dedicated to the UE. This is known as network activated or network ordered random access (supported in LTE). Since a specific preamble is assigned / dedicated to the UE, it is a contention-free access benefit that the eNodeB can immediately learn from the received preamble, whose UE tries (or tried) to access the network. This thus eliminates the need for contention resolution and therefore improves resource efficiency by minimizing the risk of collisions. Additionally, avoiding the containment resolution procedure reduces the delay.

It should be noted that network-activated random access (for example, in E-UTRAN) can be used to force a UE, which does not have a valid uplink time to synchronize its uplink to the time of the eNodeB, for example, prior to the eNodeB doing a downlink transmission for which the UE will need to transmit a feedback of an acknowledge (ACK) or a negative acknowledge (or no acknowledge) (NACK). It should be mentioned that because of the non-zero duration of the random access and uplink sync procedure, resynchronization is typically forced before doing the downlink transmission. In general, a UE (eg a mobile terminal) loses synchronization if it is not active for a certain time. It is thus possible to define a decision criterion in the network (for example in the E-UTRAN) that after a certain time without any activity a UE (for example, a mobile terminal) is assumed to have lost synchronization in the eNB.

If for example the downlink data reaches the UE, the synchronization needs to be reestablished first, and for this purpose the dedicated random access preamble described above is assigned to the UE, which UE can be used to perform a random access procedure free of containment. This will trigger a time advance adjustment command from the eNB, and based on this command, the UE can reestablish the time alignment. For example, in LTE (or E-UTRAN) the physical downlink control channel PDCCH is used to allocate a dedicated preamble.

Since the random access procedure is the first procedure performed by the UE to access the network, it is important that the random access works as it should. If the random access fails, the UE cannot access the network. An exemplary scenario where a random access procedure may fail or cannot be performed is when all dedicated preambles are already in use. As mentioned above, the eNodeB keeps track of the dedicated preambles that it has already allocated / allocated, and when there is no such dedicated preamble available for allocation, the eNB has to warn / refer to other UEs, for which there is no preamble dedicated random access, perform contention-based random access. However, as mentioned before, containment-based random access leads to potential collisions and additional delays when a containment resolution needs to be performed. If collisions occur and one or more UEs fail with their random access, one or more UEs can retry the random access procedure after a certain time leading to this, a power reduction mechanism can be activated which introduces additional delays. A power reduction mechanism is an approach to control UE re-access attempts by for example introducing a power reduction parameter that represents a period of time to wait before an access retry. Thus, the greater the number of re-access attempts, the longer the delay.

3GPP R2-081672 (CATT) discloses a method of assigning a preamble to a UE to enable the UE to perform random access. It is discussed that PRACH sources can be wasted if consecutive PRACH resources are allocated to a dedicated preamble for a UE (page 3). To avoid this waste, it is proposed to allocate non-consecutive PRACH resources for dedicated preambles, for example by pointing to the subframe index of the first valid PRACH resource in the dedicated preamble allocating the signaling.

Summary

It is therefore an object of the exemplary embodiments of the present invention to address the aforementioned problems and to provide methods and apparatus to enable one or more UEs to perform dedicated random access allowing the use of one or more dedicated random access preambles for one. or more UEs introducing a validity pattern representation in which channel occurrence (s) the dedicated preamble (s) is valid to be used by the UE / s for access random. This will lead to a reduction in random access delays and also a reduction in the number of collisions that can occur.

According to a first aspect of embodiments of the present invention, the problem raised above is solved by means of a method in a radio base station of assigning a preamble to a UE according to claim 1.

Thus, in order, for example, to alleviate the case where there is a shortage of dedicated random access preambles and in order to extend the availability of dedicated random access preambles, the radio base station is configured to determine the availability of a dedicated random access preamble for assignment to the UE and to transmit in a message the identification number of the dedicated preamble and that further indicates in said message a validity pattern to enable the UE knows in which appearance or appearances of PRACH the

ES 2 575 132 T3 dedicated preamble is valid for the UE.

According to a second aspect of embodiments of the present invention, the problem raised above is solved by means of a method in a UE according to claim 5.

According to a third aspect of embodiments of the present invention, the problem raised above is solved by means of a radio base station according to claim 10.

According to a fourth aspect of embodiments of the present invention, the problem raised above is solved by means of a UE according to claim 13.

An advantage with the present invention is that the random access delay is reduced.

Another advantage with the present invention is that it allows dedicated preambles to be virtually extended by introducing a validity pattern in the time field in such a way as to alleviate the case where there is a shortage of dedicated preambles.

A further advantage with the present invention is that, for a given load for contention-free random access, the size of the array that forms a group of dedicated preambles can be reduced. This in turn means that more non-dedicated random access preambles are available, which means that the risk of collisions is minimized.

Other objects and features of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings, attention is to be drawn to the fact that, however, the following drawings are illustrative only, and that various Modifications and changes may be made to the specific embodiments illustrated as described within the scope of the appended claims. It should further be understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

Brief description of the drawings

FIG. 1 is a diagram illustrating an example of a wireless network telecommunications system in which exemplary embodiments of the present invention can be applied.

Fig. 2 is a diagram illustrating a type 1 frame structure applicable to LTE FDDs according to the prior art.

Figure 3A is a diagram illustrating an exemplary PRACH configuration using an exemplary validity pattern applicable to exemplary embodiments of the present invention.

Figure 3B is a diagram illustrating exemplary PRACH configuration using another exemplary validity pattern applicable to exemplary embodiments of the present invention.

Figure 3C is a diagram illustrating exemplary PRACH configuration using another exemplary validity pattern more applicable to exemplary embodiments of the present invention.

FIG. 4 is a diagram illustrating a flow chart of a method performed, in a radio base station, in accordance with exemplary embodiments of the present invention.

Figure 5 is a diagram illustrating a flow chart of a method, performed on user equipment in accordance with exemplary embodiments of the present invention.

Figure 6 illustrates a block diagram of an exemplary radio base station in accordance with embodiments of the present invention.

Figure 7 illustrates a block diagram of exemplary user equipment in accordance with embodiments of the present invention.

Detailed description

In the following description, for explanatory and non-limiting purposes, specific details such as particular architectures, scenarios, techniques, etc. are set forth. In order to provide a thorough understanding of the present invention. However, it will be apparent to the person skilled in the art that the present invention and its embodiments can be practiced in other embodiments that deviate from those specific details.

The different embodiments of the present invention are described here by way of reference in scenarios of

ES 2 575 132 T3 particular examples. In particular, the invention is described in a general non-limiting context in relation to random access procedures in a telecommunications network system that is based on the third generation (3G) long-term evolution (LTE) concept. It should be noted that the present invention is not restricted to 3G LTE but may be applicable in other wireless systems employing random access procedures, such as WiMAX (worldwide interoperability for microwave access), or HSPA (high speed packet access). o HSUPA (high speed uplink packet access) or HSDPA (high speed downlink packet access) or WCDMA (wideband code division multiple access) etc.

Referring to FIG. 1, there is illustrated a block diagram of an exemplary wireless telecommunications network system 100 in which the different exemplary embodiment of the present invention may be applied. Note that the system described in Figure 1 only shows transceivers or nodes that are necessary to understand the different exemplary embodiments of the present invention. As shown, the system 100 which is here considered to represent a simplified 3GPP LTE system comprises a number of user equipments UE 110, UE 111, UE 112, and apparatuses acting as radio base stations and called eNodeB 1 120 , eNodeB 2 121 and eNode 3 122. One of the functions of eNodeBs is to control traffic to and from UEs in a cell. A UE is suitable to be used as a mobile phone, wireless terminal, laptop, personal computer, PDA, Voice over Internet Protocol (VoIP) enabled phone or any 3GPP LTE enabled equipment. Traffic, over a radio link, from an eNodeB to a UE is referred to as downlink traffic (DL) and traffic, over a radio link, from the UE to an eNodeB is referred to as downlink traffic (UL ). Note that in Figure 1, the number of UEs and eNodeBs is illustrative only and embodiments of the present invention are not restricted to any particular number of UEs and / or number of eNodeBs.

Referring back to Figure 1, it is here assumed that UE 111 and UE 113 are served by eNodeB 1 120. In other words it is assumed that UE 111 and UE 113 have already successfully randomly accessed network 100 and connect wirelessly to the eNodeB 1 120. Furthermore, it is also assumed, for easy understanding of the principles of the embodiments of the present invention, that the eNodeB for example the eNodeB 1 120 is serving a single cell, although this is not necessary . In LTE, there is in total a set comprised of 64 random access preambles available per cell (or configured for one cell). Thus, an eNodeB can be allocated / assigned to these 64 preambles. It should be noted that preambles assigned to different cells controlled by the same eNodeB do not necessarily belong to the same set of preambles, ie different sets (and groups) are typically cell specific. However, to understand the different embodiments of the present invention, it is assumed here that an eNodeB is serving a single cell and therefore, in this case, it is appropriate to establish that a set of 64 preambles is allocated by the eNodeB (or per cell.

A first set within this set of 64 preambles, forms a group of preambles for use with contention-based random access. The preambles in this group, as mentioned above, are known as non-dedicated random access preambles. This group is used first when there is data originated from UE and the UE has to establish a connection and / or a suitable uplink time relationship with the network through the random access procedure (RA). When contention-based random access is performed, the UE chooses / selects a non-dedicated random access preamble from this first set randomly. For each non-dedicated random access preamble in this first set, a preamble identification number (or preamble identifier) ​​is associated. Among the set of 64 preambles, there is also a second set that forms a dedicated random access preamble pool. A dedicated random access preamble from the second set, as mentioned above, is used to perform contention-free random access. For contention-free random access, it is the eNodeB that allocates a dedicated random access preamble to the UE. In other words, this type of random access is activated by the network (for example, the eNodeB). For each dedicated random access preamble in this second set, a preamble identification number (ID) (or preamble identifier) ​​is also associated. The eNodeB keeps track of the dedicated preamble IDs that are currently in use. For contention-free random access, the eNodeB can therefore map the received preamble to the UE that has sent the dedicated random access preamble and has attempted to access the system or network system. Therefore, no containment resolution procedure needs to be performed.

Referring back to Figure 1, assume that, with respect to UE 110, a contention-free random access procedure is triggered by the network (eg, by eNodeB 1 120) so that the UE can establish alignment and synchronization time on the network (for example, eNodeB). This is schematically illustrated using a broken line arrow between the UE 110 and the eNodeB 1 120. As mentioned before, the eNodeB 1 120 keeps track of all dedicated random access preambles (and dedicated preamble IDs) that it has allocated and that are currently in use. Once a contention-free random access has been successfully completed or the validity of the dedicated preamble allocation has expired, the dedicated preamble can be reused. However, in the event that none of the dedicated random access preambles in the second set are currently available for allocation in the UE 110, the eNodeB 1 120 has to refer to the UEs, for which it does not there is dedicated preamble, to perform contention-based random access. However,

ES 2 575 132 T3 contention-based random access generally leads to potential collisions occurring in addition to delays when a contention resolution needs to be performed.

Therefore, in order to alleviate an exemplary problem scenario that no dedicated preamble is available to perform contention-free random access, the eNodeB 1 120 in accordance with embodiments of the present invention, is configured to determine that a preamble of dedicated random access from the second set is available for assignment to the UE 110 and is further configured to transmit a message to the UE 110, for example in a physical downlink control channel (PDCCH), indicating the preamble ID of the determined dedicated random access preamble and also indicating a validity pattern for example in the time domain that specifies in which physical channel occurrence of random access (PRACH) the dedicated preamble is valid to be used by the UE to conduct random access. As an example, since the eNodeB 1 120 keeps track of dedicated preambles and associated IDs that are currently in use, it also knows when a random access based on a dedicated preamble has been completed successfully or the validity of the allocation. has expired and thus you can determine that such a dedicated preamble is now available and can be reused. If the eNodeB 1 120 needs to establish an uplink synchronization, it sends, for example in the PDCCH message, the preamble ID of this available preamble and information indicating in which PRACH occurrence the dedicated preamble is valid for the UE 110. The UE 110 can then perform a random access based on the preamble ID received from the eNodeB 1 120 and also based on the information indicated in reference to the occurrence or occurrences of PRACH.

It should be noted that in the 3GPP LTE TS 36.211 technical specification entitled: Evolved Universal Terrestrial Radio Access (E-UTRA) Physical Channels and Modulation (Release 8), the downlink and uplink transmissions are organized into radio frames in the that each radio frame has a duration of 10 ms. Two different radio frame structures are defined, a frame structure known as type 1 which is applicable to FDD (frequency division duplex) and another frame structure known as type 2 applicable to TDD (time division duplex). The 3GPP prior technical specification TS 36.211 also defines that for FDD, 10 subframes per radio frame are available for downlink transmissions and 10 subframes (of the same radio frame) are available for downlink transmissions and that link transmission uplink and downlink are separated in the frequency domain . Furthermore, a type 1 frame structure comprises 20 slots of length 0.5 ms each and those two consecutive slots define a subframe that is thus 1 ms long.

Referring to Figure 2 there is illustrated a type 1 frame structure applicable to LTE FDD, as defined in 3GPP TS 36.211. The 3GPP technical specification TS 36.211 also defines that PRACH sources and their occurrence or occurrences are configured for each cell (or eNodeB) and communicate on both broadcast and dedicated control channels (PDCCH). Sixteen PRACH configurations are defined for FDD in 3GPP TS 36.211.

According to an embodiment of the present invention and as mentioned above, the PDCCH message can transmit the dedicated preamble ID determined as available by the eNodeB 1 120 and also transmit the information indicating in which one or more occurrences of PRACH, the dedicated preamble is valid for the UE. As an example, the information may indicate in which subframe / s the allocated dedicated random access preamble is valid for use by the UE. According to an embodiment of the present invention, the subframe / s is / are tied to the frame structure, for example the radio frame structure.

Next, an exemplary embodiment will be described in more detail in the context of FDD PRACH configuration 12. PRACH configuration 12 defines that PRACH resources occur in subframe # 0, subframe # 2; subframe # 4, subframe # 6 and subframe # 8 of each radio frame.

As an exemplary embodiment of the present invention, the information in the PDCCH message may indicate in a field of said PDCCH message, that for example in case of PRACH configuration 12, the available dedicated preamble is valid only in subframe # 2 in every radio frame. This is illustrated in Figure 3A where it is indicated that the dedicated preamble is valid for the particular UE in subframe 2 of each frame. It should be mentioned that for PRACH configuration 12, there are, as described above, several subframes that can be selected where the dedicated preamble is valid for the UE. Such subframes are also shown in FIG. 3A and are numbered, as before, specifically, subframe # 0, subframe # 2, subframe # 4, subframe # 6, and subframe # 8. However, the example described and illustrated in Figure 3A shows that the dedicated preamble is valid only in subframe # 2 in each radio frame, according to the dedicated information in the PDCCH message. It should be noted that it is also implied here that for example the same dedicated preamble can be assigned to different UEs for subframe # 0, subframe # 4, subframe # 6 and subframe # 8 respectively. Effectively, this means that the dedicated preamble availability is increased in this example by a factor of 5. Obviously, the use of such a validity pattern significantly reduces the risk of running out of dedicated preambles that are available for allocation.

It should be mentioned that exemplary embodiments of the present invention are not restricted to PRACH configuration 12. In other words all PRACH settings defined by FDD (for example

ES 2 575 132 T3 type 1 frame structure) can be used. As an example, a conceivable configuration for PRACH sources could be that they occur in all radio frames in subframe # 1 (PRACH configuration 3).

Another example using PRACH configuration 12 is that the PRACH source, for the UE, occurs, in each subframe, in subframe # 0, subframe # 2; subplot # 4, subplot # 6 and subplot # 8. This is shown in Figure 3B where subframe # 0, subframe # 2; Subframe # 4, Subframe # 6 and Subframe # 8 are indicated within each frame respectively. Subframes that are not used have a white background (eg, subframe # 7, subframe # 1, etc.).

As mentioned above, for PRACH configuration 12, there are several subframes for which the dedicated preamble can be valid for the UE. Such subframes are subframe # 0, subframe # 2; subplot # 4, subplot # 6 and subplot # 8. Therefore, according to another exemplary embodiment of the present invention, the field in the PDCCH message for the allocation of the dedicated preamble may indicate the periodicity for which of the occurrence or occurrences the dedicated preamble is valid for use by the UE. for random access. For example, the field could indicate that for each occurrence of PRACH the dedicated preamble is valid for the UE. This is illustrated in Figure 3C where it is shown that, for PRACH configuration 12, the sequence (periodicity) of subframe is for example subframe # 8 (of frame 1), subframe # 6 (of frame 2), subframe # 4 (of frame 3), subframe # 2 (of frame 4 (not shown)), etc., during which the dedicated random access preamble is valid for the UE to perform random access. Thus, in this example a dedicated preamble is valid at every fourth occurrence of PRACH. In Figure 3C, the subframes of the sequence are shown with a cross inside.

Note that in some configurations, such as PRACH configuration 12, it is for example not useful for a UE to use subsequent PRACH resources since they follow each other too closely. The UE needs to wait for a response from the eNodeB (or network) before a random access attempt is allowed to repeat. Thus, it is not useful for the UE to reuse, for example, all the PRACH resources of configuration 12.

Embodiments of the present invention thus increase the availability of dedicated preambles by defining a time domain validity pattern for LTE FDD contention-free access. Note however that the same principle is also applicable for PRACH configurations defined for LTE TDD (ie type 2 frame structure). Thus, embodiments of the present invention are not restricted to LTE FDD. It should be noted that in LTE TDD a PDCCH message field can indicate for which PRACH resource / s in the frequency domain and / or time domain the dedicated preamble is valid.

In accordance with another embodiment of the present invention, the information transmitted by the eNodeB in the message (eg, the PDCCH message) including the dedicated preamble ID, indicates / specifies a binary value indicative of one or more occurrences of PRACH. This binary value is expressed by a predetermined number of bits indicated in the message (for example by 3 bits or 4 bits). The value can be either an explicit value or an input value to a function that gives the value / es or an index for a table or an index for a table entry or an index on a table that contains said value / es. As an exemplary embodiment of the present invention, the binary value may correspond to a PRACH index (eg, a mask index) that is associated with a predefined PRACH configuration that indicates in which one or more PRACH occurrences allowed, the preamble dedicated is valid to be used by the UE for random access. Note that by a PRACH configuration is meant for example a PRACH configuration indicated / defined in the previously described 3GPP technical specification 36,211. It should be noted that the PRACH index value determines the validity of the indicated dedicated preamble. As an exemplary embodiment of the present invention, the binary value may correspond to a PRACH index (eg, a mask index). In association with the configured PRACH configuration, defined in the previously described 3GPP technical specification 36,211, the PRACH index determines one or more subframes of a frame in which the allocated dedicated preamble is valid. For example, FDD PRACH configuration 12 corresponds to PRACH resources in subframe # 0, subframe # 2; subplot # 4, subplot # 6 and subplot # 8. The PRACH index determines for which one or more of the subframes listed above the dedicated preamble is valid.

As a further example, in case all the preambles in the dedicated random access preamble group have been allocated, the eNodeB is configured to determine when a dedicated preamble-based random access has completed successfully or the validity of the allocation has expired, and then reuse the available dedicated preamble and transmit to the UE the preamble ID (of the available dedicated preamble) in the PDCCH message and indicate in that message a PRACH mask index. The UE then receives such a PDCCH message and performs a random access based on the preamble ID and based on the PRACH mask index since the PRACH mask index, as described above, is associated with a predefined setting indicating in which PRACH occurrences allowed the preamble is valid for use by the UE.

As an example, if the eNodeB explicitly points for example in the PDCCH message, to the UE a dedicated preamble ID that has a set ID value, and the eNodeB also indicates in the message, the PRACH index (for example, a value binary that corresponds to a PRACH index (for example, a mask index) that is used by the UE to signal one or more subframes in which the dedicated preamble is valid (that is, to signal a pattern

ES 2 575 132 T3 of validity describing in which occurrences of PRACH the dedicated preamble is valid for use by the UE), then the UE knows, based on the dedicated preamble ID and the PRACH index, in which the occurrence or occurrences of PRACH the dedicated preamble is valid for this to perform random access using the dedicated random access preamble.

It should be noted that the binary value (for example, 3 bits or 4 bits) that assigns an offset, relative to a time reference, of the validity pattern of the PRACH resource could be an explicit value, input of a function that gives the values ​​or an index on a table that contains the values. Alternatively, a joint encoding of the binary value in the field that assigns the offset, relative to a time reference, of the PRACH resource validity pattern could be an explicit value, input to a function that gives the values, or an index in a table containing the values. Alternatively, a joint encoding of the binary value in the field that maps the validity pattern of the PRACH resource and the binary value in the field that maps the offset, relative to a time reference, of the validity pattern of the PRACH resource could be an explicit value, input to a function that gives the values ​​or an index on a table that contains the values.

Referring to Figure 4, there is illustrated a flow chart of a method intended to be performed / implemented in a radio base station (eg, eNodeB), in accordance with the above-described embodiments of the present invention. As mentioned above, a first set that forms a non-dedicated random access preamble group and a second set that forms a dedicated random access preamble group is assigned to the radio base station. The method in the radio base station enables a UE to perform random access. The method, at the radio base station, comprises the following steps:

(401); determining a dedicated random access preamble from the second set available for assignment to the UE;

(402) transmit a message (e.g., in a PDCCH message or a PDCCH message field) to the UE, the message comprising the dedicated preamble ID of the available dedicated preamble that was determined by the radio base station, and that it further comprises information on which of one or more occurrences of PRACH the dedicated random access preamble is valid to be used by the UE for random access.

As mentioned above, the information in the PDCCH message indicates in which subframe / s the allocated dedicated preamble is valid for use by the UE. One or more subframes are tied to the frame structure, as previously described. The information may also indicate in the UE, the periodicity for which occurrence or occurrences of PRACH the dedicated preamble is valid for the UE. Furthermore, the information can be indicated using a binary value, said binary value is expressed by a predefined number of bits (ie 4 bits). As mentioned above, the binary value can correspond to a PRACH index that is associated with a predefined setting that indicates in which occurrence or occurrences of PRACH allowed, the dedicated preamble is valid to be used for the UE.

Referring to Figure 5, there is illustrated a flow chart of a method intended to be performed / implemented in a UE, in accordance with previously described embodiments of the present invention. The method in the UE enables said UE to perform random access in a system in which a radio base station is provided; said base station being assigned a first set that forms a non-dedicated random access preamble group and a second set that forms a dedicated random access preamble group. The method, to be carried out in the EU, comprises the following steps:

(501) receive a message from the radio base station (or eNodeB), said message (for example in the PDCCH) comprises a preamble ID of a dedicated random access preamble of the second set and also comprises information indicating in which one or more occurrences of PRACH the dedicated preamble is valid to be used by the UE for random access;

(502) perform a random access procedure based on the available dedicated preamble preamble ID and based on dedicated information regarding one or more occurrences of PRACH.

The different exemplary embodiments that describe the subframes; periodicity, binary value, etc. they have already been described and are therefore not unnecessarily repeated again.

Referring to Figure 6, there is illustrated a block diagram of an exemplary radio base station 600 (eg eNodeB) that is configured / arranged to assign a dedicated random access preamble to a UE, said radio base station being allocated to a first set that forms a group of non-dedicated random access preambles and a second set that forms a group of dedicated radio random access preambles. As shown in FIG. 6, the radio base station 600 comprises processing means 601 adapted to determine a dedicated random access preamble, from the second set, available for assignment to the UE. As an example, once a random access based on a dedicated preamble has been completed successfully or the validity of the allocation has expired, an allocated dedicated preamble can be reused. The radio base station 600 is configured to transmit, by means of transmitting means 602A, designated

IS 2 575 132 T3

TX in figure 6, a message to the UE, for example in the PDCCH message, the dedicated and available preamble ID and also configured to indicate in that message information that indicates in which one or more occurrences of PRACH the dedicated preamble is valid to be used by the UE for random access. As shown in Figure 6, the radio base station 600 further comprises receiving means 602B, designated RX in Figure 6, which is arranged / configured to receive from the UE the assigned dedicated preamble that the UE used / uses to perform. the random access based on the dedicated preamble ID and also based on the indicated information referring to one or more occurrences of PRACH. Additional actions performed by the radio base station have already been described and are therefore not repeated. It should be mentioned however that the different exemplary blocks shown in Figure 6 are not necessarily separate. Furthermore, the means TX 602a and the means RX 602B are not necessarily included in the same block, that is, they can each be represented by a single block. The radio base station 600 is therefore not restricted and is not limited to the exemplary block diagrams shown in Figure 6. Additionally, the radio base station 600 may also comprise other element and / or blocks not illustrated in the figure. 6.

Referring to Figure 7, there is illustrated a block diagram of an exemplary user equipment (UE) 700 capable of performing random access using an assigned dedicated random access preamble, in accordance with previously described embodiments of the present invention. As shown in figure 7, the UE 700 comprises receiving means 701A, designated RX in figure 7, which is adapted / configured to receive from a radio base station a message comprising a dedicated preamble ID and further comprising information indicating in which of at least one occurrence of PRACH the dedicated preamble is valid for use by the UE. As a non-limiting example, the message is received on a PDCCH. The UE 700 further comprises transmitting means 701B, designated TX in Figure 7, which are adapted / configured to transmit, based on the received dedicated preamble ID and indicated information referring to one or more occurrences of PRACH, the preamble random access device in order to perform random access. The UE 700 also further comprises processing means 702 for eg processing one or more received / transmitted messages. Again, the different exemplary embodiments that describe the subframes; periodicity, binary value (for example, 4 bits), etc. they have already been described and are therefore not unnecessarily repeated.

As described above, various advantages are achieved by the different embodiments of the present invention. As an example, the random access delay is reduced even in cases where all the preambles in the dedicated random access preamble pool are already in use. Another advantage with the different example of the present invention is that it allows to virtually extend dedicated preambles by introducing, as mentioned above, a time domain validity pattern in such a way as to alleviate the case where there is a shortage of dedicated preambles. Yet another advantage with the present invention is that for each random access that does not need to be referred to the use of non-dedicated random access preambles, the random access delays can be reduced.

The present invention and its embodiments can be carried out in many ways. For example, one embodiment of the present invention includes a computer-readable medium that has instructions stored on it that are executable by a radio base station (eg, eNodeB or eNB) and / or a UE of a telecommunications system. The instructions executable by the radio base station and / or the UE and stored on a computer readable medium perform the steps of the method of the present invention as set forth in the claims.

While the invention has been described in terms of various preferred embodiments, it is contemplated that alternatives, modifications, permutations, and equivalents thereof will become apparent to those skilled in the art upon reading the specifications and studying the drawings. The following appended claims are therefore intended to include alternatives, modifications, permutations, and equivalents that are within the scope of the present invention.