Patent Description:
Future mobile and wireless communication networks will support a variety of services. Particular services, such as services enabling traffic safety applications, have extremely strict latency requirements. A response time for a terminal device using such a delay-sensitive service, i.e. the time period from the time point, at which a terminal device initiates a transmission to the base station, until the time point, at which the transmission is received at the base station, and is optionally confirmed by an application server, needs to be a short time period, e.g. in the order of milliseconds. Within this short time period, the network should accomplish the whole uplink transmission procedure.

Due to its unpredictable nature, an uplink transmission procedure is typically a RA procedure, in which resource allocation to transmitters, for example terminal devices, cannot be coordinated in advance. In case that more than one terminal device employ the same uplink resource at the same RA time slot for a transmission to the base station, a collision occurs. This collision usually results in interference such that some or all of the colliding transmissions cannot be decoded correctly. As a consequence, the affected transmission has to be repeated, which leads to additional delay in the procedure.

For the aforementioned delay-sensitive services, the delay caused by a collision can be the most critical issue. The latency of a RA channel in the 3GPP Long Term Evolution (LTE) network often exceeds <NUM> (see e.g. <NPL>), which is far beyond the actual response time requirements for most delay-sensitive services, e.g., traffic safety services. Additionally, when a Machine Type Communication (MTC) is introduced into the network, the number of terminal devices, which may simultaneously access the network, e.g. the base station, will sharply increase. Consequently, the probability of collisions during the RA procedure increases further, and the above-described latency issue becomes even worse.

Since future wireless networks, e.g., LTE new Releases and Fifth Generation <NUM>, will also be more versatile, a mixture of delay-sensitive service traffic and delay-tolerant service traffic will increasingly coexist in the radio channels. In view of the above-described collision and delay issues, the RA procedure will thus need to employ some prioritization of the different kinds of service traffic. For instance, in case that a resource request for a delay-sensitive service collides with a resource request for a delay-tolerant service, a higher priority should be granted to the delay-sensitive resource request, so that a retransmission of the delay-sensitive resource request is avoided.

In the conventional Carrier Sense Multiple Access (CSMA) scheme, a transmitting terminal device senses and detects signals from other terminal devices before it starts its actual transmission. The time period, in which the terminal device senses, whether the channel is free, is called a contention window for colliding devices. The priority in this scheme can be implemented by adjusting the contention window size such that specific terminal devices are given earlier chances to transmit than others (see <NPL> or <NPL>). The CSMA scheme bases on the assumption that one terminal device can detect the signal from other terminal devices in advance. This is a practical limitation, particularly in a cellular network with a cell radius over several hundred meters. That is to say, in order to be able to detect other terminal devices, the terminal devices have to be located close to each other. Otherwise, the CSMA scheme will suffer from the so called "hidden node problem " as known from WLAN.

Therefore, in LTE (see <NPL>), preambles are used in the RA procedure. As shown in <FIG>, in a conventional RA procedure <NUM>, a first terminal device <NUM> and a second terminal device <NUM> (denoted as UE1 and UE2, respectively, in <FIG>) each transmit a preamble as a resource request in advance of their actual transmission to a base station <NUM> (denoted as BS), in order to request a dedicated uplink resource, specifically a time-frequency resource block, from the base station <NUM>.

In particular, once a terminal device <NUM>, <NUM> in LTE has an unscheduled transmission request, it will start the RA procedure <NUM> to communicate a resource request for its initial network access. As shown in <FIG>, the RA procedure <NUM> comprises four steps.

In a first step, one or more terminal devices <NUM>, <NUM> transmit a resource request with a randomly selected RA preamble to the base station <NUM>. For instance, as shown in <FIG>, the two terminal devices UE1 and UE2 each transmit a preamble defined by a signature PA1. A set of all possible preambles is known at the terminal devices <NUM>, <NUM> and at the base station <NUM>. Therefore, the preamble can also be used as a training sequence and as a signature. The base station <NUM> can detect different preambles, and can send responses according to individual preambles. In the case of <FIG>, the base station <NUM> detects a resource request with the preamble PA1.

In a second step, the base station <NUM> transmits a RA response in the downlink shared channel in response to the detected preambles. According to the detected preamble of each resource request, the base station <NUM> assigns an uplink resource to the corresponding terminal device(s) <NUM>, <NUM>. In the case of <FIG> the base station <NUM> grants uplink (UL) resource for the terminal devices UE1 and UE2 sending the preamble PA1.

In a third step, a terminal device <NUM>, <NUM> transmits its identity and other messages, e.g., scheduling request, to the base station <NUM> using the resource assigned to it by the base station <NUM> in the RA response in the second step. In the case of <FIG>, both UE1 and UE2 recognize that UL resources are granted according to their resource request, and thus both UE1 and UE2 send a message in the granted UL resource.

In a fourth step, the base station <NUM> echoes the identity of the terminal device(s) <NUM>, <NUM> it received in the third step.

In a case that - as shown in <FIG> - two terminal devices <NUM>, <NUM> choose the same preamble (denoted with PA1 in <FIG>) for their resource request, the base station <NUM> cannot distinguish the resource requests from different terminal devices <NUM>, <NUM>. Hence, the same uplink resource will be assigned to both terminal devices <NUM>, <NUM>. In this case, in the third step both terminal devices <NUM>, <NUM> use the same resource for their actual transmission, and thus a collision occurs. In this collision case, if a transmission sent in the third step cannot be decoded correctly, the corresponding terminal device <NUM> or <NUM> will not receive the confirmation from the base station <NUM> in the fourth step. Thus, it must reinitialize its preamble transmission after a certain time, the so called back-off time.

It can thus be seen that in the above-described first round of the RA procedure <NUM> shown in <FIG>, delay-sensitive resource requests do not have any advantage over delay-tolerant resource requests. Only during the retransmission of the preamble, delay-sensitive resource requests may be granted with a shorter back-off time compared to delay-tolerant requests.

In particular, for the RA procedure <NUM> shown in <FIG>, a prioritization was proposed via certain back-off schemes (see <NPL>, and<NPL>. In these schemes, high-priority terminal devices are assigned a shorter back-off time than low-priority terminal devices. However, as short as the back-off time may be, at least one retransmission is inevitable in case of a collision.

In order to further reduce the potential latency for emergent and delay-sensitive services, LTE also applies a contention-free scheme for RA channel. In this contention-free scheme, particular preambles are reserved only for delay-sensitive services. That is, certain terminal devices are assigned exclusive preambles, which are not shared with other terminal devices. Because the reserved preambles are exclusively used for the specified delay-sensitive services, the collision probability is reduced or even eliminated. However, the number of preambles in a network is typically limited. Further, the reservation of dedicated preambles even reduces the total number of available preambles used for other contention-based accesses. Thus, on the one hand side, if more preambles are reserved for contention-free access, the efficiency of the preamble usage of the contention-based accesses becomes worse. On the other hand side, there may also not be sufficient preambles for all the contention-free accesses of delay-sensitive services.

In addition to the above-described problems of collision and delay, there may also be the problem that the number of required resources to support the terminal devices, which request resources, exceeds the number of available resources that the base station <NUM> is able to provide. Also in this case, delay-sensitive resource requests do not have any advantage over delay-tolerant resource requests.

Document <CIT> discloses methods for random access resource mapping from access class (AC) to access service class (ASC) and from ASC to LTE RACH resources, in which ASCs with higher priorities are mapped with more RACH resources.

<CIT> discloses methods partitioning at least a subset of contention based resources for random access attempts into a plurality of partitions, wherein each of said plurality of partitions is associated with at least one precondition governing selection of a partition.

In view of the above-mentioned disadvantages, the present invention aims to improve the state of the art. The present invention thus has the object to provide a more effective and flexible RA scheme. In particular, the present invention desires to reduce transmission delays, specifically for terminal devices sending delay-sensitive resource requests. Thus, the present invention aims at providing a RA scheme, which is able to better handle simultaneous resource requests and is able to resolve collisions during actual transmissions of multiple terminal devices. Further, the present invention seeks to avoid that terminal devices, which send delay-sensitive resource requests, do not receive any resources in case that resources are insufficient. Therefore, the RA scheme of the present invention generally intends to provide different priorities to delay-sensitive resource requests and delay-tolerant resource requests. In addition, it should be possible in the RA scheme of the present invention that priorities are assigned user / terminal device specific, or application / service specific.

The present invention is defined by RA methods according to independent claims <NUM> and <NUM>, a base station according to independent claim <NUM>, and a terminal device according to independent claim <NUM>.

In particular the present invention proposes a RA scheme between at least one base station and at least one terminal device, for instance at least one UE in an LTE network. The base station may simultaneously receive multiple resource requests and transmissions from multiple terminal devices. Multiple terminal devices share the same wireless media in the sense of time and/or frequency resources for their transmissions. Resource requests from the terminal devices are random, so that they are not coordinated in advance.

A first aspect provides a RA method comprising transmitting, by at least one of a plurality of terminal devices, a resource request with one or more preambles to a base station during one RA time slot, detecting, by the base station, a priority level of the at least one resource request based on the number of preambles in the at least one resource request, and assigning, by the base station, uplink resources according to the at least one resource request and the at least one priority level.

A priority level of a resource request indicates a preference for receiving resources from the base station. That means, a higher priority level of a first resource request, in relation to a lower priority level of a second resource request, indicates a higher preference that resources are assigned according to the first resource request than according to the second resource request. A RA time slot is the time interval, during which a terminal device is allowed to perform a preamble transmission. Preambles are distinguished, for instance, by their signature, i.e. different preambles have different signatures.

The preamble-based RA method of the first aspect is able to prioritize, for instance, resource requests having different levels of delay requirements. To this end, delay-sensitive resource requests may include, instead of one preamble, a combination of several preambles transmitted during a given RA time slot. The base station can identify a combination of multiple preambles. Furthermore, the base station can distinguish between a combination of multiple preambles, which are sent by one terminal device in one resource request, and a random combination of preambles, which are transmitted individually by several terminal devices in several resource requests. For instance, if a longer combination of preambles encounters a shorter combination of preambles in the channel, at least the longer combination of preambles can be identified by the base station.

In this way, a resource request with a higher priority level is more immune from collisions and thus retransmissions. For example, if multiple terminal devices transmit resource requests, which have at least one preamble in common, a collision would occur in the conventional RA procedure as shown in <FIG>. However, since in the RA method of the first aspect the base station can detect at least the longest combination of preambles, which corresponds to the resource request having the highest priority level, the base station can assign resources according to the resource request having the highest priority level. It is noted that a collision probability within a higher priority level, i.e. for two resource requests having the same higher priority level with the same number and combination of preambles, decreases exponentially with the number of preambles transmitted in a given RA time slot.

Additionally, the detecting of the priority levels of the resource requests enables the base station to assign resources according to the priority levels in a case, where resources are limited, i.e. in case that not each terminal device can be assigned with a resource. Assigning resources according to at least one priority level means that the base station assigns resources according to a resource request with a highest priority level first, before assigning resources according to resource requests with decreasingly lower priority levels.

In summary, the RA method of the first aspect is more effective and flexible than conventional RA procedures.

The scope of protection of this invention is defined by the appended claims.

Even if, in the following description of specific embodiments, a specific functionality or step to be fully formed by eternal entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

The above-described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which.

<FIG> shows an embodiment of a RA method <NUM> proposed by the present invention. In a first step <NUM> of the method <NUM>, at least one terminal device transmits a resource request with one or more preambles to a base station during one RA time slot. In a second step <NUM> of the method <NUM>, the base station detects a priority level of the at least one received resource request based on the number of preambles included in the at least one resource request. In a third step <NUM> of the method <NUM>, the base station assigns uplink resources according to the at least one received resource request and the respectively detected at least one priority level. If two or more received resource requests have at least one preamble in common, the base station assigns uplink resources according to the resource request, among these determined resource requests with least one common preamble, which has the highest priority level. For resource requests not having any preamble in common, the base station sequentially assigns uplink resources according to, firstly, the resource request having the highest priority level to, lastly, the resource having the lowest priority level. If not enough resources are available to satisfy all resource requests, the base station sequentially assigns all available uplink resources according to, firstly, the resource request having the highest priority level to, lastly, a certain resource request having a lower priority level.

<FIG> shows an embodiment of a system <NUM> including at least one terminal device <NUM> and a base station <NUM> as proposed by the present invention. The system <NUM> is configured to perform the RA method <NUM> described in <FIG>.

To this end, the terminal device <NUM> preferably includes a transmitting unit <NUM> configured to transmit (indicated by the dotted arrow) a resource request with one or more preambles to the base station <NUM> during one RA time slot, and is configured to combine more preambles for transmitting a resource request having a higher priority level and is configured to combine fewer preambles for transmitting a resource request having a lower priority level.

Accordingly, the base station <NUM> preferably includes a receiving unit <NUM> configured to receive from at least one terminal device <NUM> a resource request (indicated by the dotted arrow) with one or more preambles during the RA time slot. Further, the base station <NUM> preferably includes a detecting unit <NUM> configured to detect a priority level of the at least one received resource request based on the number of preambles in the at least one resource request. Finally, the base station <NUM> preferably includes an assignment unit <NUM> configured to assign uplink resources according to the at least one received resource request and the at least one detected priority level.

In the RA method <NUM> of the present invention, multiple terminal devices <NUM> may use a shared wireless medium without coordination and scheduling in advance, e.g. a physical random access channel (PRACH) in LTE. Before a terminal device <NUM> transmits actual data, it firstly sends the resource request with the at least one preamble in a common radio channel.

Sequences can thereby be applied as the preamble signature (as described by<NPL> or <NPL>. Such sequences have nice properties in sense of autocorrelation and cross-correlation.

The periodic autocorrelation is defined as <MAT> wherein f(t) is a periodic extension of the sequence with the property f(t) = f(t + nT), n ∈ Z. T is the length of the sequence, Z is the set of the integers and f represents the complex conjugate of f.

The cyclic cross-correlation of two sequences is defined as <MAT> wherein f(t) is the periodic extension of a first sequence as described above, g(t) is likewise a periodic extension of a second sequence, and g is the complex conjugate of g.

The periodic autocorrelation of the preamble sequence has a single peak at zero time lag τ=<NUM> and a very low value at non-zero time lag τ≠<NUM>. In the case of the sequences described by the above-cited paper of Chu et al. , the periodic autocorrelation is a Dirac delta function, and it is exactly zero at non-zero lag. The absolute value of the cyclic cross-correlation function between two different sequences is very low. The receiving unit <NUM> of the base station <NUM> can preferably utilize the above properties of autocorrelation and cross-correlation, in order to detect individual preamble signatures, even if the preamble signatures overlap in the frequency and/or time domain.

In general, in the RA method <NUM> of the present invention, a higher prioritized terminal device <NUM>, i.e. a terminal device <NUM> sending a resource request with a higher priority level, uses for the resource request a combination of more preambles, i.e. combines more preamble signatures, in a certain RA time slot, than a lower prioritized terminal device <NUM>, which sends a resource request with a lower priority level, and thus with fewer preambles. In other words, a terminal device <NUM> combines more preambles for transmitting a resource request having a higher priority level or fewer preambles for transmitting a resource request having a lower priority level. If resource requests have one or more preambles in common, the resource request of highest priority level "overwrites" the resource requests of lower priority level.

<FIG> shows a specific example for preamble combinations of resource requests of different priority levels in the RA method <NUM> according to the embodiment of the present invention. In particular, <FIG> shows a time (t) axis. Above the time axis is shown time-dependently, how two terminal devices <NUM> (referred to as UE1 and UE2) each send a resource request with preambles in a certain RA time slot to the base station, BS, <NUM>. Below the time axis is shown time-dependently, how in the same RA time slot the base station <NUM> detects the sent and received preambles.

Specifically, UE1 and UE2 have a different priority. The higher priority UE2 (called "priority UE" in <FIG>) transmits, after another in a time direction, two preambles, which are defined by preamble signatures PA1 and PA2, respectively, in the same RA time slot (the preambles are referred to in the following as preamble PA1 and PA2). Meanwhile, the lower priority UE1 sends only one preamble, which is defined by the preamble signature PA1, in the same channel in the same RA time slot. That means the resource requests of UE1 and UE2 have one preamble in common, namely the preamble PA1.

While the preambles PA1 and PA2 are transmitted by UE1 and UE2, respectively, the base station <NUM> performs preamble detection, preferably with its detecting unit <NUM>, i.e. in the same RA time slot. <FIG> shows specifically the preamble detection at the base station <NUM>. In particular, <FIG> shows on a time axis (t) curves indicating a correlation of the received signal with preambles PA1 and PA2, respectively. As can be seen, correlation peaks with preamble PA1 (twice, since both UE1 and UE2 send PA1) and with preamble PA2 can be well detected and distinguished at the base station <NUM>, respectively. Hence, as also indicated in <FIG>, the base station <NUM> detects the preambles PA1 and PA2, and identifies the combination of PA1+PA2 from UE2 as a higher priority level resource request than resource request with a single preamble.

According to the RA method <NUM> of the present invention, for the special case shown in <FIG>, i.e. for at least two resource requests having at least one preamble in common, uplink resources will be granted by the base station <NUM> according to the resource request including the preamble combination PA1+PA2, i.e. to the terminal device UE2. Terminal device UE1 does not receive uplink resources, and needs to enter back-off and retransmission procedure. If, however, UE1 would send a preamble PA3 instead of preamble PA1, then the base station <NUM> would assign uplink resources firstly according to the resource request including the preambles PA1+PA2, i.e. to the terminal device UE2, and secondly according to the resource request including preamble PA3, i.e. to the terminal device UE1, given that uplink resources are still available. In this case the terminal device UE1 does not have to enter a back-off and retransmission procedure.

<FIG> shows a RA method <NUM> according to an embodiment of the present invention, which bases on the embodiment shown in <FIG>. In particular, <FIG> shows a RA procedure carried out between two terminal devices <NUM>, namely UE1 and UE2 as shown in the <FIG> and <FIG>, and the base station <NUM>. Arrows in <FIG> indicate information that is sent between the participating entities <NUM> and <NUM>, respectively.

Specifically, <FIG> illustrates the RA method <NUM> for the case that two terminal devices <NUM> UE1 and UE2 would have a collision in the conventional RA procedure <NUM> as shown in <FIG>. However, in the RA method <NUM> of the present invention, UE1 and UE2 are provided with a different priority. Therefore, in a first step, as also described with respect to <FIG>, UE1, which is of low priority, transmits a resource request with preamble PA1, and UE2, which is of high priority, transmits a resource request with preamble combination PA1+PA2. As shown in the <FIG> and <FIG>, the base station <NUM> detects in a second step the high priority level resource request including the preambles PA1+PA2. In a third step, the base station <NUM> sends to UE1 and UE2 a grant of uplink (UL) resource according to the resource request including PA1+PA2, i.e. essentially for the UE sending PA1+PA2. In a fourth step, UE2 recognizes that uplink resources were assigned according to its resource request, and transmits its actual message in the granted UL resource. Meanwhile, UE1 does not recognize that uplink resources were assigned according to its resource request, and enters a back-off and retransmission procedure. That means, UE1 will wait a certain number of N ms, and will then retransmit its resource request to the base station <NUM>.

Compared to the conventional RA method <NUM> shown in <FIG>, the RA method <NUM> of the present invention shown in <FIG> guarantees the priority of particular resource requests. As a consequence, the highest priority level resource request, of all potentially colliding resource request, does not need to enter a back-off and retransmission procedure, so that the delay caused by a collision is avoided, at least for the highest priority level resource request. The more delay-sensitive a service, the higher the priority level of the resource request should be set by the terminal device <NUM>.

The proposed RA method <NUM> of the above described embodiments of the present invention also supports multiple priority levels, as shown in <FIG> shows a further specific example for preamble combinations of resource requests of different priority level in the RA method <NUM>. In particular, <FIG> shows a time (t) axis. Above the time axis is shown time-dependently, how three terminal devices <NUM> (referred to in the following as UE1, UE2 and UE3) each sends a resource request with preambles in a certain RA time slot to the base station, BS, <NUM>. Below the time axis is shown time-dependently, how the base station <NUM> detects these preambles.

Specifically, UE1, UE2 and UE3 in <FIG> have three different priorities. UE3 has the highest priority (called "level <NUM>" in <FIG>), and uses a combination of three preambles PA1+PA2+PA3 for its resource request. UE2 has a lower priority (called "level <NUM>" in <FIG>) than UE3, and uses a combination of two preambles PA1+PA2 for its resource request. UE1 has the lowest priority (called "level <NUM>" in <FIG>), and uses one preamble PA1 for its resource request. In general, even more priorities are of course possible, and a UE <NUM> with a higher priority uses more preambles at the same time for its resource request than a UE <NUM> with a lower priority. In other words, a terminal device <NUM> may determine a number of preambles for transmitting a resource request with a determined priority level. To this end, the base station <NUM> may broadcast to one or more terminal devices <NUM> mapping information between numbers of preambles and priority levels of resource requests.

All resource requests shown in <FIG> have the preamble PA1 in common. Therefore, in order to avoid a later collision, the base station <NUM> assigns uplink resources only according to one of the three received resource requests. As indicated, the base station <NUM> detects the three preambles PA1+PA2+PA3 and identifies this resource request of highest priority level to be from UE3.

In this respect, <FIG> shows on a time axis (t) curves indicating a correlation with the preambles PA1, PA2 and PA3, respectively. As can be seen, correlation peaks with the preamble PA1 (three times, since UE1, UE2 and UE3 send the PA1), with the preamble PA2 (twice, since UE2 and UE3 both send PA2), and with the preamble PA3 can be well detected and distinguished at the base station <NUM>, respectively. Priority levels can be arbitrarily extended by adopting longer preamble combinations, i.e. combinations with more preambles.

In the <FIG>, <FIG>, <FIG> and <FIG>, preambles were sent sequentially, i.e. were arranged in a time direction. Combinations of preambles are accordingly applied in the time domain. However, combination of preambles can be applied either in the time domain or the frequency domain, or even both, as shown exemplarily in <FIG>.

<FIG> shows in (a) two preambles PA1 and PA2 transmitted, by a terminal device <NUM> denoted as UE1, sequentially in the time domain (as indicated by the time axis t). The preambles PA1 and PA2 are, however, transmitted at the same frequency, i.e. are not separated in the frequency domain (as indicated by the frequency axis f). Likewise, <FIG> shows in (b) two preambles transmitted, by a terminal device <NUM> denoted again as UE1, sequentially in the frequency domain (as indicated by the frequency axis f), i.e. transmitted at different frequencies. The preambles PA1 and PA2 are, however, transmitted at the same time, i.e. are not separated in the time domain (as indicated by the time axis t). That means a terminal device <NUM> may determine and set a time and/or frequency shift between multiple preambles in one resource request.

The preambles used for one preamble combination in a resource request can also overlap in the time and/or frequency domain, as shown in <FIG>. In particular, a terminal device <NUM> transmitting a resource request with more than one preamble may arrange the preambles with at least a partial overlap in the time and/or frequency domain. <FIG> shows in (a) partially overlapped preambles PA1 and PA2 transmitted by a terminal device <NUM> denoted as UE1. In particular, PA1 and PA2 are separated both in the time and the frequency domain (as indicated by the time and frequency axis t and f), but also overlap in both the frequency and the time domain. Thereby, the differences Δt and Δf indicate determined time shift and frequency shift values, respectively, between the preambles PA1 and PA2. For example, Δt may denote the time shift between a beginning of the first preamble PA1 and a beginning of the second preamble PA2 in the time domain, wherein "beginning in the time domain" implies earlier in time. Likewise, Δf may denote the frequency shift between the beginnings of the preambles PA1 and PA2 in the frequency domain, respectively, wherein "beginning in the frequency domain" implies higher in frequency. However, for the time and/or frequency shifts between preambles, also different reference points may be considered. In <FIG> in (a), both Δt and Δf are larger than zero. Although in <FIG> in (a) the preambles are additionally defined by different signatures, i.e. by PA <NUM> #PA2, due to the non-zero time and/or frequency shift between the preambles, also preambles defined by the same signature could be transmitted, and could still be distinguished at the base station <NUM>.

<FIG> shows in (b) that two preambles PA1 and PA2, which are transmitted by a terminal device <NUM> denoted again as UE1, can even completely overlap, i.e. both the time shift Δt and the frequency shift Δf are equal to zero, and the preambles PA1 and PA2 are neither separated in the time nor the frequency domain (as indicated by the time and frequency axis t and f). In this case, the preamble signatures should not be the same, i.e. in <FIG> in (b) the preambles need to be defined by different signatures PA1≠PA2.

In summary, a terminal device <NUM>, which transmits a resource request with more than one preamble, preferably provides a determined time and/or frequency shift between the preambles, and in case the determined time and/or frequency shift is zero, provides the preambles with different signatures.

The time and/or frequency shifts Δt and Δf can be either predetermined, or can be determined based on the current status of the network and/or the base station <NUM>, e.g. they can depend on a current load or a predicted load in the network or at the base station <NUM>, and/or based on the available radio resources. The time and frequency shifts may be known both at the terminal devices <NUM> and the base station <NUM>, or may be communicated between the terminal devices <NUM> and the base station <NUM> in either direction. For example, the base station <NUM> may broadcast to the plurality of terminal devices <NUM> the determined time and/or frequency shift to be set between preambles of a resource request. Alternatively, a terminal device <NUM> may determine the frequency and/or time shift between the number of preambles, and may preferably transmit the number of preambles and/or the time and/or frequency shift to the base station <NUM> beforehand. The base station <NUM> preferably utilizes the knowledge of the time and/or frequency shifts, in order to avoid possible misdetections of resource requests.

An approach to sieve out misdetections in the RA method <NUM> according to an embodiment of the present invention is illustrated and exemplified in <FIG> illustrates specifically two different cases on the time axis, i.e. the cases may occur after each other. In a first case, a first terminal device <NUM> denoted as UE1 sends a preamble PA1, and a second terminal device <NUM> denoted as UE2 sends a preamble PA2 in the same RA time slot. In a second case, a third terminal device <NUM> denoted as UE3 with a higher priority than UE1 and UE2 sends a combination of PA1 and PA2. Since the base station <NUM> knows the determined time and/or frequency shift Δt and Δf, it can distinguish between these two different cases, i.e. it can distinguish whether the preambles PA1 and PA2 are sent by two different terminal devices <NUM> denoted as UE1 and UE2, as in the first case, or by one higher priority terminal device <NUM> denoted as UE3, as in the second case.

Specifically, as shown in <FIG>, in the first case the base station <NUM> detects preambles PA1 and PA2 and estimates a time shift Δt' between the two received preambles PA1 and PA2, wherein the actual Δt' is not equal to the predetermined time shift Δt. Therefore, the base station <NUM> can conclude that the two preambles PA1 and PA2 are sent by different UEs. In the second case the base station <NUM> detects preambles PA1 and PA2 and estimates a time shift Δt' between the two preambles PA1 and PA2, wherein the actual Δt' is equal to the predetermined time shift Δt. Therefore the base station <NUM> can conclude that the two preambles PA1 and PA2 are sent by the same UE. The same is of course possible for preambles sent with a frequency shift, and the base station <NUM> comparing an estimated frequency shift Δf' with the determined frequency shift Δf. In other words, the base station <NUM> may detect the time and/or frequency shift between at least two received preambles and may determine, whether the at least two received preambles are from the same terminal device <NUM> or from different terminal devices <NUM> based on the detected time and/or frequency shift and/or received power levels of preambles.

The corresponding detections of the time shift Δt' at the base station <NUM> are shown in <FIG> shows on a time axis (t) curves indicating a correlation with PA1 and PA2, respectively. Δt' denotes the time shift detected by the base station <NUM> between the preambles PA1 and PA2, which is preferably - as illustrated - the estimated time shift between the peaks of the two correlation functions. The base station <NUM> can measure time and/or frequency shifts between correlation peaks of received preambles. If the estimated time shift Δt' and/or frequency shift Δf equals the determined time shift Δt and/or frequency shift Δf, the base station <NUM> determines that both preambles PA1 and PA2 originate from the same terminal device <NUM>.

Claim 1:
A random access, RA, method (<NUM>), comprising the following steps executed by a base station (<NUM>) of a wireless network:
receiving, from at least one terminal device (<NUM>) of a plurality of terminal devices, a resource request having one or more preambles during one RA time slot;
detecting (<NUM>) a priority level of the resource request based on a number of the one or more preambles in the resource request; and
assigning (<NUM>) uplink resources according to the resource request and the priority level,
wherein the RA time slot is a time interval, during which the at least one terminal device (<NUM>) is allowed to perform a preamble transmission.