WO2018114370A1

WO2018114370A1 - Apparatus, base station and wireless communications network for improved random access

Info

Publication number: WO2018114370A1
Application number: PCT/EP2017/081898
Authority: WO
Inventors: Martin Kasparick; Renato Luis Garrido Cavalcante; Dennis Wieruch; Josef Bernhard; Gerd Kilian; Benjamin SACKENREUTER; Bernd HOLFELD
Original assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
Priority date: 2016-12-21
Filing date: 2017-12-07
Publication date: 2018-06-28
Anticipated expiration: 2019-06-21

Abstract

An apparatus configured to operate in a wireless communications cell is configured to access at least one resource in the wireless communications network cell by a random access process comprising transmission of a random access preamble and by a resource allocation received responsive to the transmission. In case of a missing resource allocation, the apparatus is configured to boost the random access preamble and to transmit the boosted random access preamble.

Description

APPARATUS, BASE STATION AND WIRELESS COMMUNICATIONS NETWORK FOR

IMPROVED RANDOM ACCESS

Description The present invention concerns the field of wireless communication networks or systems, more specifically, an apparatus such as a user equipment, a base station, a wireless communications network, methods for operating an apparatus, methods for operating a base station and a non-transitory computer program product. The invention further concerns adaptive, incremental increases and combinations of random access sequences after missed detection.

Cellular communication systems use random access procedures to achieve synchronized and scheduled access to each user within the coverage cell of a base station such as an evolved node B (eNB). Therefore, a device may transmit an orthogonal sequence to indicate its desire of transmission. In 3GPP LTE [1 ,2] Zadoff- Chu (ZC) sequences are transmitted in the physical random access channel (PRACH). To support various cell sizes, different preamble formats are defined and can be defined by the eNB for the corresponding cell. Therefore, the RACH preamble is repeated multiple times [2, 3]. Furthermore, there are proposals to derive the number of repetitions based on the received power [4, 5],

LTE uses a Zadoff-Chu (ZC) sequence of 839 symbols [1 ], In particular, in FDD (frequency division duplex) mode four different standard preamble formats (0-3) are defined, which differ in size of the cyclic prefix (CP) and duration of the sequence.

Fig. 7a shows a schematic block diagram of a random access preamble used in 3GPP LTE, [2]. A cyclic prefix 1 100 having a duration of T_Cp is followed by a sequence 1200 having a time duration of T_SEQ. Fig. 7b shows a table illustrating different values for the time durations T_Cp and T_SEQ for different preamble formats (0-4). Longer sequences of format 2 and 3 are simply generated by repeating the sequence of the random access preamble, see Fig. 7a. A fifth preamble format (4) uses a sequence length of 139 symbols and is defined for frame structure 2 in TDE (time division duplex) only. Depending on the preamble format used, the preamble transmission spans from 1 ms (preamble format 0) up to 3 ms (preamble format 3) to adapt for the different sizes. Fig. 7b illustrates different durations of the - -

cyclic prefix 1 100 and the sequence 1200 as a multiple of Ts which is defined as 1/(15000 x 2048) seconds.

The preamble format in 3GPP's LTE sets further limitations on the occurrence of the PRACH in even or any system frame numbers and on the subframe index used, see the table in Fig. 8a for frame structure type 1 (FDD) and the table in Fig. 8b for frame structure type 2 (TDD) in [2].

The ZC sequences used in LTE have a number of beneficial properties. Most importantly, sequences that are generated from cyclic shifts of the same root sequence are orthogonal. Sequences obtained from cyclic shifts of different ZC sequences are not orthogonal, but have low cross-correlation if a certain cell radius is not exceeded [7]. Therefore, orthogonal sequences obtained by cyclically shifting a single root sequence are favored over non-orthogonal sequences. Additional root sequences are used only when the required number of sequences cannot be generated by a single root sequence. The number of sequences that can be generated from a single root sequence is given by the ratio of the length of the sequence to the cyclic shift size.

Given the existing 838 root sequences in LTE, only the index of the first root sequence is broadcast in a cell. The UEs derive the available pool of preamble signatures from a predefined ordering listed in [3], A certain number of sequences from the available pool are used for contention-free access, while the remaining sequences can be used by the UEs for contention-based random access. From the contention-based pool, the UE picks a sequence at random.

The contention-based random access procedure comprises four steps that are illustrated in Fig. 9 showing a flow chart illustrating a successful contention-based random access procedure. At 2100, the preamble is transmitted by the user UE to the base station. If the base station detects the preamble then a random access response is transmitted at 2200 followed by two further signaling steps 2300 and 2400. However, if the base station does not detect the preamble, a timeout occurs at the user equipment UE. The UE will transmit a further random access sequence of the same preamble format.

There is a need for improving the random access procedure.

It is an object to provide an approach allowing for an efficient random access procedure. . -

This object is achieved by the subject matter as defined in the independent claims.

The inventors have found that when simply retransmitting the random access preamble, the reasons that caused a loss of the message in a previous attempt may still be present such that a simple retransmit may also be lost or not be successful. By boosting the random access preamble when performing retransmission, a chance for detection of the retransmitted preamble at the base station may be high which may allow for short random access procedures and thus for efficient allocation of communication channels so as to improve the random access procedure. The inventors have further found out that the detection probability may be increased and thus the random access procedure be improved by commonly evaluating the content of two PRACHs.

According to an embodiment, an apparatus is configured to operate in a wireless communications network cell. The apparatus is configured to access at least one resource in the wireless communications network cell by a random access process comprising transmission of random access preamble and by a resource allocation received responsive to the transmission. In case of a missing resource allocation, the apparatus is configured to boost the random access preamble and to transmit the boosted random access preamble. Boosting the random access preamble may allow for a high probability that the boosted random access preamble is recognized and acknowledged by transmission of the resource allocation.

According to an embodiment, boosting the random access preamble comprises increasing a transmission power of the random access preamble and/or adding symbols to the random access preamble. Thus, when compared to the random access preamble, the boosted random access preamble may be transmitted using a higher amount of energy which is allocated in the higher transmission power and/or in additional symbols. This may allow for an increase in the chance of being recognized by the base station.

According to an embodiment, the apparatus is configured to transmit the random access preamble comprising a first set of symbols and to transmit the boosted random access preamble comprising a second set of symbols, wherein the second set of symbols comprises the first set of symbols being extended by a third set of symbols. Thus, the third set of symbols is added or joined to the initial random access preamble. Thus, the - -

user equipment may decide to extend the current random access preamble by the third set of symbols.

According to an embodiment, the third set of symbols corresponds to a section, i.e. , at least one symbol, of the first set of symbols. According to embodiments, the third set of symbols may equal the first set of symbols. The additional symbols, i.e., the third set of symbols, may allow for a longer duration of the sequence and thus for a high chance to be received and recognized at the base station. According to embodiments, the random access preamble may be part of a set of random access preambles used in the wireless communications network cell, wherein the third set of symbols comprises a different random access preamble of the set. I.E., the boosted random access preamble may comprise two different random access preambles.

According to an embodiment, the apparatus is configured to transmit the first set of symbols using a first transmission frequency and to transmit the second set of symbols or the third set of symbols using a second transmission frequency. This may allow for enabling frequency diversity and thus for a further increase in the chance of being detected by the base station.

According to an embodiment, the apparatus is configured to transmit the third set of symbols and other symbols of the second set of symbols with a spacing in time there between. This may allow for a longer duration of the random access preamble and thus for a high chance of being detected by the base station, wherein by using the spacing in time, a required power for transmission may be kept low.

According to an embodiment, the apparatus is configured to transmit the third set of symbols (1350) in absence of a cyclic prefix. The third set of symbols may benefit from the cyclic prefix of the random access preamble being part of the boosted random access preamble, such that separate symbols for a cyclic prefix relating to the third set may be saved. Therefore, by using the third set of symbols, e.g., when prefixing the third set of symbols, usage of a further cyclic prefix may be omitted, which may allow for a low required bandwidth. - -

According to an embodiment, the apparatus is configured to receive a radio signal comprising information indicating an instructed predetermined time-frequency pattern, wherein the apparatus is configured to implement the instructed predetermined time- frequency pattern as the implemented time-frequency pattern.

According to an embodiment, the apparatus is configured to transmit the random access preamble and the boosted random access preamble according to an implemented predetermined time-frequency pattern. By using this pattern, additional information may be transmitted. For example, a base station may retrieve information about a channel on which the random access preamble was sent when successfully receiving the boosted random access preamble.

According to an embodiment, the apparatus is configured to transmit the third set of symbols and other symbols of the second set of symbols according to the implemented predetermined time-frequency pattern.

According to an embodiment, the apparatus is configured to determine a timing for the transmission of the boasted random access preamble, wherein the apparatus is configured for using a timing advance for determining the timing. This may allow for reducing collision probability as transmission may occur in a longer time duration.

According to an embodiment, in case of a missing resource allocation responsive to the boosted random access preamble, the apparatus is configured to transmit a further boosted random access preamble. This may allow for a stepwise or incremental boosting of the random access preamble.

According to a further embodiment, an apparatus is configured to operate in a wireless communications network cell. The apparatus is configured to access at least one resource in the wireless communications network cell by a random access process comprising transmission of a random access preamble and by a resource allocation received responsive to the transmission. The apparatus is configured to use a first value of a preamble length or a transmission power for performing the random access process to transmit data having a first priority class and wherein the apparatus is configured to use a second value of the preamble length or the transmission power for performing the random access process to transmit data having a second priority class. This may allow for accessing a wireless channel with preambles that indicate a priority class of data. - -

According to an embodiment, a base station is configured to control a wireless communications network cell of a wireless communications network, wherein the base station is configured to allocate a resource element of the wireless communications cell responsive to reception of a random access preamble. The base station is configured to receive and store information relating to a first radio signal comprising a random access preamble a first apparatus in a first random access interval and to receive and store information relating to a second radio signal comprising a random access preamble of the first apparatus in a second random access interval. The base station is configured to evaluate a random access attempt of the apparatus using the information related to the first radio signal and using the information related to the second radio signal to obtain an evaluation result. The base station is configured to allocate the resource element based on the evaluation result. By performing the evaluation using information related to two random access intervals, a detection probability may be high as additional data may be used for detection.

According to a further embodiment, a base station is configured to control a wireless communications network cell of a wireless communications network. The base station is configured to allocate a resource element of the wireless communications cell responsive to reception of a random access preamble.

The base station is configured to transmit a radio signal comprising information indicating a space in frequency or in time in which the base station searches for the random access preamble. The base station is configured to adapt a reception filter used for evaluating a received radio signal for a presence of a random access preamble according to the space in frequency or in time. For example, this information may be used by a user equipment or by a different apparatus for implementing a frequency-time pattern for transmitting random access preambles and/or boosted random access preambles.

Further embodiments provide for a wireless communications network comprising an apparatus according to embodiments described herein and comprising a base station according to embodiments described herein. Further embodiments provide a method for operating an apparatus to operate in a wireless communications network cell. The method comprises accessing at least one . .

resource in the wireless communications network cell by a random access process comprising transmission of a random access preamble and by a resource allocation received responsive to the transmission. The method further comprises boosting, in case of missing resource allocation, the random access preamble and transmitting the boosted random access preamble.

Further embodiments provide a method for operating an apparatus to operate in a wireless communications network cell. The method comprises accessing at least one resource in the wireless communications network cell by a random access process comprising transmission of a random access preamble and by a resource allocation received responsive to the transmission. The method comprises using a first value of a preamble length or of a transmission power for performing the random access process to transmit data having a first priority class and comprises using a second value of the preamble length or of the transmission power for performing the random access process to transmit data having a second priority class.

Further embodiments provide a method for operating a base station to control a wireless communications network cell of a wireless communications network. The control comprises allocating a resource element of the wireless communications network cell responsive to reception of a random access preamble. The method comprises receiving and storing information related to first radio signal comprising a random access preamble of a first apparatus in a first random access interval. The method further comprises receiving and storing information related to a second radio signal comprising a random access preamble of the first apparatus in a second random access interval. The method further comprises evaluating a random access attempt of the apparatus using the information related to the first radio signal and using the information related to the second radio signal to obtain an evaluation result. The method comprises allocating the resource element base on the evaluation result. According to an embodiment, a method for operating a base station to control a wireless communications network cell of a wireless communications network, the control comprising allocating a resource element of the wireless communications network cell responsive to reception of a random access preamble comprises transmitting a radio signal comprising information indicating a space in frequency or in time in which the base station searches for the random access preamble and comprises adapting a reception filter for evaluating a received radio signal for a presence of a random access preamble according to the space in frequency or in time.

Further embodiments provide a non-transitory computer program product comprising a computer-readable medium storing instructions. The instructions, when executed on a computer carry out a method according to embodiments described herein.

Further embodiments are described in further dependent claims.

Embodiments of the present invention are now described in further detail with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic representation of an example of a wireless communications system according to an embodiment;

Fig. 2 shows a schematic diagram illustrating a structure of a so-called M-frame used in the wireless communications system of Fig. 1 ;

Fig. 3 shows a schematic flowchart illustrating operation of a user equipment and a base station during a random access process according to an embodiment;

Fig. 4 shows a schematic diagram illustrating the principle of boosting at least the sequence of the random access preamble, according to an embodiment; Fig. 5a shows a schematic diagram in which a random access preamble and a boosted random access preamble are transmitted, according to an embodiment;

Fig. 5b shows transmission of the boosted random access preamble at a different frequency, according to an embodiment;

Fig. 5c shows transmission of the boosted random access preamble at the different frequency and with a spacing in time, according to an embodiment;

Fig. 5d shows a schematic diagram in which a preamble is transmitted during a fist

PRACH and a combination of the preamble and of a further, different preamble in a second PRACH, according to an embodiment; Fig. 5e shows a concept according to which an apparatus is configured to use a slotted physical random access channel, according to an embodiment;

Fig. 5f shows a schematic block diagram of a modulo or subset of time-frequency patterns used for transmitting the boosted random access preamble, according to an embodiment;

Fig. 5g shows a schematic block diagram, where a modulo operation is used to determine a location of symbol in the frequency domain, according to an embodiment;

Fig. 6 shows a schematic block diagram of a wireless communications network according to an embodiment;

Fig. 7a shows a schematic block diagram of a random access preamble according to prior art;

Fig. 7b shows a table illustrating different values for the time durations for different preamble formats of Fig. 7a;

Fig. 8a shows details on the occurrence of PRACH in LTE FDD according to prior art;

Fig. 8b shows details on the occurrence of PRACH in LTE TDD according to prior art; and

Fig. 9 shows a flow chart illustrating a successful contention-based random access procedure according to prior art.

Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals even if occurring in different figures.

In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

Embodiments described herein may refer to a behavior of a user equipment in the wireless communications network cell. Although description is provided in connection with a user equipment, the same principles may be applied, without limitation, to other nodes in a wireless communications network, such as loT devices or the like.

In 3GPP, there exist three different classes of low power devices: devices that are used in the Internet of Things (loT) that use a narrow bandwidth (NB), thus NB-loT enhanced machine-type communication (eMTC or LTE-M) and massive machine type communications (mMTC). In contrast to the legacy LTE system, in narrowband-loT (NB- loT) the physical layer random access preamble is based on single-carrier frequency- hopping symbol groups [2], Since the random access procedure still exists, the solution can be also adapted to these classes. Embodiments described herein relate to apparatus that access a random access channel by a contention-based random access procedure.

Some embodiments described herein may relate to eNB or eNodeB used as base station. This term shall not limit the embodiments but is selected for a better understanding only. According to other embodiments, other base stations may be used, for example, Next Generation NodeB - gNB. loT devices may include physical devices, vehicles, buildings and other items having embedded therein electronics, software, sensors, actuators, or the like as well as network connectivity that enable these devices to collect and exchange data across an existing network infrastructure. Fig. 1 is a schematic representation of an example of such a network infrastructure, like a wireless communication system including a plurality of base stations e B_! to eNB₅, each serving a specific area surrounding the base station schematically represented by the respective cells 100i to 100₅. The base stations are provided to serve users within a cell. A user may be a stationary device or a mobile device. Further, the wireless communication system may be accessed by loT devices which connect to a base station or to a user. Fig. 1 shows an exemplary view of only five cells, however, the wireless communication system may include more such cells. Fig. 1 shows two users UE^ and UE₂, also referred to as user equipment (UE), that are in cell 100₂ and that are served by base station eNB₂. Another user UE₃ is shown in cell 100₄ which is served by base station eNB₄. The arrows 102, 102₂ and 102₃ schematically represent uplink/downlink connections for transmitting data from a user UEL UE₂ and UE₃ to the base stations eNB₂, eNB₄ or for transmitting data from the base stations eNB₂, eNB₄ to the users ΙΙΕ^ UE₂, UE₃. Further, Fig. 1 shows two loT devices 104 and 104₂ in cell 100₄, which may be stationary or mobile devices. The loT device 104i accesses the wireless communication system via the base station eNB₄ to receive and transmit data as schematically represented by arrow 105^ The loT device 104₂ accesses the wireless communication system via the user UE₃ as is schematically represented by arrow 105₂.

The wireless communication system may be any single-tone or multicarrier system based on frequency-division multiplexing, like the orthogonal frequency-division multiplexing (OFDM) system, the orthogonal frequency-division multiple access (OFDMA) system defined by the LTE standard, or any other IFFT-based signal with or without CP, e.g. DFT-s-OFDM. Other waveforms, like non-orthogonal waveforms for multiple access, e.g. filter-bank multicarrier (FBMC), may be used.

Standard LTE devices, like the users UEi, UE₂, UE₃, operate within a first bandwidth, and the loT devices 104Ί and 104₂ operate within a second bandwidth which is narrower than the first bandwidth. The second bandwidth may be defined in accordance with the NB-loT enhancement of the LTE Rel. 13 standard, referred to in the following also as NB-loT. A wireless communication system operating in accordance with the LTE standard may have a system bandwidth of 1.4 MHz, 3.0 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz or aggregated system bandwidth consisting of any combination of these, and the bandwidth in accordance with the NB-loT enhancement of the LTE Rel. 13 standard may be by 200 kHz.

An OFDMA system for data transmission may include an OFDMA-based physical resource grid which comprises plurality of physical resource blocks (PRBs) each defined, for example, by 12 subcarriers by 7 OFDM symbols and including a set of resource elements to which various physical channels and physical signals are mapped. Other configurations may comprise a scaled numerology with, for example, up to 48 subcarriers. A resource element is made up of one symbol in the time domain and one - -

subcarrier in the frequency domain. For example, in accordance with the LTE standard a system bandwidth of 1 .4 MHz includes 6 PRBs, and the 200 kHz bandwidth in accordance with the NB-loT enhancement of the LTE Rel. 13 standard includes 1 PRB. In accordance with LTE and NB-loT, the physical channels may include the physical downlink shared channel (PDSCH) including user specific data, also referred to as downlink payload data, the physical broadcast channel (PBCH) including for example the master information block (MIB) or the system information block (SIB), the physical downlink control channel (PDCCH) including for example the downlink control information (DCI), etc. The physical signals may comprise reference signals (RS), synchronization signals and the like. The LTE resource grid comprises a 10 ms frame in the time domain having a certain bandwidth in the frequency domain, e.g. 1 .4 MHz. The frame has 10 subframes of 1 ms length, and each subframe includes two slots of 6 or 7 OFDM symbols depending on the cyclic prefix (CP) length. An apparatus such as one of the user equipment UE^ , UE₂ and UE₃ and/or an loT device 104i or 104₂ may request a corresponding base station eNB₂ or eNB₄ for allocating one or more resource elements, for example, a channel. When the apparatus is unknown to the base station then it may use a physical random access channel as illustrated in Fig. 2.

Fig. 2 shows a schematic diagram illustrating a structure of a so-called M-frame 200 comprising 10 subframes 202₀ to 202₉. A physical random access channel (PRACH) 204 may be arranged, for example, in the second subframe 202_! . Details described herein may relate to the 3GPP LTE standard. Although referring to this standard, embodiments described herein are not limited hereto and may also relate to other communication schemes, communication standards and/or other variants of wireless communication. Furthermore, although the PRACH is described as being arranged in the subframe 202·, , according to other embodiments, the PRACH may additionally or alternatively be arranged in other subframes 202₀ or 202₂ to 202₉.

Reference is made to Figs. 8a and Fig. 8b showing tables with different PRACH configurations.

Fig. 3 shows a schematic flowchart illustrating operation of a user equipment UE and a base station eNB during a random access process. For example, this procedure may be implemented in a wireless communication network according to Fig. 1 . The method may - -

be referenced as method 3000. At a step 3100, the user equipment may be configured to access one or more resources in the wireless communications network cell by a random access process. For example, the user equipment may be configured to access the PRACH 204 by transmitting the random access preamble 1000 illustrated in connection with Fig. 7a.

At the eNB, a so-called missed detection may occur, i.e., reception or at least decoding of the random access preamble may not happen or may be error-prone. Based thereon, the base station may not be aware of the user equipment and may thus miss initiating transmission of a response to the random access preamble. The user equipment awaits such a message until a timeout 1350 occurs, i.e., the user equipment is configured to wait for a certain time and may determine, after that time, that the random access process was unsuccessful. The user equipment may be configured to boost the random access preamble so as to obtain a boosted random access preamble. User equipment may be configured to transmit the boosted random access preamble in a step 3200. By non-limiting example only, the boosted random access preamble is not received or detected by the eNB. After a further timeout 3250, the UE may transmit a further boosted random access preamble at a step 3300. The further boosted random access preamble may be boosted when compared to the boosted random access preamble and when compared to the random access preamble.

This message is successfully received by the eNB. In a step 3400, the random access response is transmitted from the eNB to the user equipment.

Although method 3000 is described as using a boosted random access preamble and a further boosted random access preamble, according to other embodiments, the user equipment is configured to only transmit the boosted random access preamble after a missed detection of the random access preamble. According to other embodiments, random access preambles that are boosted when compared to the further boosted random access preamble transmitted in step 3300 may be generated and/or transmitted when the message of step 3300 is not successfully received or detected. This may allow for incremental boosting of the random access preamble. - -

In other words, Fig. 3 illustrates a procedure for adaptive incremental increase of preamble size after missed detection. Afterwards, the procedure illustrated in Fig. 9 may be performed. Fig. 4 shows a schematic diagram illustrating the principle of boosting at least the sequence 1200 of the random access preamble so as to obtain a boosted random access preamble 1300a, 1300b or 1300c. An abscissa of the diagram refers to a magnitude or modulus of a duration t, i.e., |t| of the preamble, wherein an ordinate relates to a transmission power that is used for transmitting the boosted preamble. Alternatively, the same principle may be applied in the frequency range, i.e., an extension in the frequency range may be performed as indicated by "|f|" at the abscissa. Thus, boosting the random access preamble may be understood as boosting at least the sequence 1200. Boosting the random access preamble may comprise increasing the transmission power at least for the sequence 1200 of the random access preamble as is illustrated for a boosted random access preamble 1300a or sequence thereof. The boosted random access preamble 300a may comprise the same data and/or symbols when compared to the random access preamble, i.e., it may comprise the same duration and/or the same amount of data symbols. The random access preamble 1300a may be transmitted with a higher transmission power when compared to the random access preamble.

Another boosted random access preamble may be obtained, for example, when adding a set of symbols 1350 to the set of symbols of the sequence 1200 of the random access preamble. Alternatively or in addition, a number of or samples may be added to a number of samples of the random access preamble 1000. Without any limitation, description provided herein in connection with a number of symbols or an increase of symbols may also relate to a number of samples or to an increase of samples. The set of symbols 1350 may comprise at least one additional data symbol but may also comprise a higher amount of data symbols such as at least two, three, four or even more. For example, the set of symbols 1350 may have the same amount of symbols when compared to a number of symbols of the sequence 1200.

Both principles may be combined to obtain a boosted random access preamble 1300c comprising the additional set of symbols 1350 and being transmitted with the higher power when compared to the sequence 1200. - -

When referring to the additional set of symbols 1350, the user equipment adaptively may increase the size of the random access preamble. The user equipment may increase the size in an incremental way, for example, by incremental repetition of the random access sequence 1200 after each timeout or after multiple timeouts. Thus, a threshold (one or more) of timeouts may be awaited and when exceeding the number of timeouts this may cause a missed detection as described with reference to Fig. 3. The increase in size may be done in time and/or frequency. In this way the user equipment may adjust the detection and collision performance in the next random access attempt. The repetition of the random access preamble, for example, using a Zadoff-Chu sequence, a single-subcarrier frequency-hopping or the like may still leave the correlation properties of a single sequence. While referring again to Fig. 7b, there are also different lengths T_SEQ of the sequence. In contrast hereto, boosting of the random access preamble may be initiated or driven by the user equipment instead of the base station. In particular, according to a concept illustrated in Fig. 7b, the base station determines a specific preamble format to be used and therefore specifies the length of the preamble which is commonly used by each user equipment.

Although the eNB may signalize some limitations in connection with the boosted random access preamble, it is possible for different user equipment to use different preamble lengths at the same time, i.e., during the same PRACH.

Making reference to Figs. 5a to 5g, transmission of a boosted random access preamble is described.

Fig. 5a shows a schematic diagram in which a random access preamble such as the random access preamble 1000 is transmitted as has been described in connection with Fig. 3; in particular, for step 3100. After one or more timeouts leading to the state of a missed detection, the boosted random access preamble 1300b is transmitted. The boosted random access preamble 1300b may comprise the random access preamble 1000 and may comprise the set of symbols 1350. For example, the set 1350 comprises symbols or consists of symbols that are equal to a number of last (i.e., a last portion of symbols arranged the end of the sequence) symbols of the sequence 1200 of the random access preamble 1000. Those symbols may be attached or put timely after the preamble 1000. Although the set 1350 may also be put in front the preamble 1000, an attachment may allow for a high detection probability as the cyclic prefix 1 100 may be used for the complete boosted preamble. Thus, using the last symbols or the complete sequence 1200 as the set 1350 and transmitting them after the sequence 1200 may allow for using the cyclic prefix of the preamble 1000 also for the additional symbols 1350. Thus, the apparatus may transmit the set 1350 of symbols in absence of a specific or additional cyclic prefix. Referring again to Fig. 7a, the sequence 1200 transmitted when transmitting the random access preamble 1000, may be referred to as a first set of symbols. The boosted random access preamble may comprise a second set of symbols, wherein the second set of symbols may comprise the first set of symbols and a third set of symbols, wherein the third set of symbols may correspond to a section, i.e., a portion or segment, of the first set symbols or may comprise a copy of the first set of symbols. Extending only by a section may be understood as adding only a few samples as a cyclic extension. The copy may also comprise a number of two or more copies of the first set of symbols. A copy may comprise the complete sequence. Alternatively or in addition, the third set may comprise a sequence being unequal to the sequence 1200. For example, when the user equipment has selected a specific sequence 1200 of a set of random access preambles, then the set 1350 may comprise a different random access preamble. This may allow for having data diversity while maintaining the benefits that allow for substituting the cyclic prefix. As was described in connection with Figs. 3 and 4, further boostings of the random access preamble may be performed in case of a further missed detection. This may allow the use of, at a first random access attempt, a small preamble size sacrificing some detection performance for the additional attempt. In this way, energy may be saved and the interference with other access attempts may be reduced. Thus, instead of using a standard size as illustrated, for example, in Fig. 7b, shorter sequences may be used for the first transmission of the random access preamble.

In other words, the length of the random access signal, the random access preamble respectively, may be incrementally increased, which can also comprise an increase by just one digital sampled value. In addition, for OFDM-like transmission, the sample-wise extension of the preamble may still remain a continuous wave. Therefore, each sample - -

increases the receive sensitivity. A simple increase of preamble length in time domain does not require a further cyclic prefix, saving resources and energy.

The repetition of the random access preamble, i.e., to use each symbol of the sequence 1200, may be simply done in time domain, by concatenation of multiple preambles in time. The example shown in Fig. 5a illustrates that the second attempt, the transmission of the boosted random access preamble, is executed by two concatenated preambles. Therefore, the incremental increase can be on step-sizes, e.g., increase a repetition by one, a double of the amount of repetitions, or another predefined step-size. However, the number of repetitions can be also independently selected by the devices, i.e., the user equipment, according to their requirements.

Fig. 5b illustrates a further possibility for transmitting the boosted random access preamble 1300b. The random access preamble 1000 may be transmitted at a frequency range or frequency - The frequency or frequency range fi may relate to at least one subcarrier comprising a specific bandwidth in the communication scheme used for transmitting data. Thus, although when referring to, hereinafter, a frequency, this may be understood as a carrier frequency or as a middle frequency of a carrier or a subcarrier used for data transmission. The boosted random access preamble 1300b is transmitted at a frequency f₂ being different from the frequency Thus, the user equipment may be configured to transmit the first set of symbols using a first transmission frequency and to transmit the second set of symbols or at least the third set of symbols using a second transmission frequency f₂. For example, the set 1350 or the random access preamble 1000 of the boosted random access preamble 1300b may be transmitted at the frequency f-i or at a further frequency differing from the frequency ^ and the frequency f₂. A variation between the frequencies fi , f₂ and possibly further frequencies may be selected by the user equipment, for example, following a predefined or implemented pattern, wherein the pattern may also be an instructed pattern instructed by the base station.

Although the frequency f₂ is illustrated as being higher when compared to the frequency fi , the frequency f₂ may also be lower when compared to the frequency fi.

In other words, the repeated preamble may also be transmitted in another frequency, enabling frequency diversity. The supported frequencies can lie on a predefined - -

frequency grid, so that adjacent preambles in frequency are not overlapping. In particular, the following two options are advantageous to permit multiple frequencies.

(1 ) After missed detection, the complete random access signal including multiple preambles is transmitted on another frequency as illustrated in Fig. 5b.

(2) The random access signal comprising multiple preambles or sequences such as the boosted random access preamble 1300b', may be divided into segments, wherein each segment may comprise one or multiple sequences.

Fig. 5c illustrates option (2). Each of these segments 1200a, 1200b is transmitted on another frequency f|, f₂ or the like. To enhance data transmission, an optional time space or time period At may be incorporated between the segments, allowing for a frequency retuning of a transmitting and of a receiving apparatus. This may be advantageous, especially for narrowband loT devices. A variation between the frequencies f,, f₂ and possibly further frequencies and/or a duration of the time period At may be selected by the user equipment, for example, following a predefined or implemented pattern, wherein the pattern may also be an instructed pattern instructed by the base station. The sequences 1200a and 1200b may be the same sequences or may be different sequences within one sequence pool, i.e., they may be orthogonal to each other or comprise a low cross-correlation. In other words, instead of transmitting the same preamble in the next random access attempt or a concatenation of the same preamble, a different preamble may be used. Furthermore, a random access signal may be a concatenation of different preambles. When using different preambles, a concatenation of different preambles respectively, each of the preambles may comprise a cyclic prefix. According to embodiments, further sequences may be part of the boosted random access preamble 1300b', i.e. a third sequence, a fourth sequence or the like. In other words, Fig. 5c illustrates a part of repetition in another frequency, taking into account also frequency retuning time. To limit the search space at the base station (eNB), just a set of frequency offsets to the preceding preamble may be permitted. For this proposal, the base station may be configured to transmit a radio signal comprising information indicating a space in frequency or in time in which the base station searches for the random access preamble. The base station may be configured to adapt a reception filter used for evaluating a received radio signal for a presence of a random access preamble according to the space in frequency or in time that was indicated in the transmitted radio signal. Furthermore, a specific tuning period to enable frequency retuning at the user equipment and/or at the loT device may be specified. Fig. 5d illustrates a schematic diagram in which a preamble 1000a is transmitted during the step 3100. A combination of the preamble 1000a and of a further, different preamble 1000b using a sequence different when compared to the sequence of the random access preamble 1000a is transmitted in step 3200. Transmission of the preamble 1000a and the preceding preamble 1000b is separated by a time space between the sequence, wherein both random access preambles 1000a and 1000b of the boosted random access preamble 1300b are transmitted during the same PRACH. Alternatively, the preambles 1000a and 1000b may be equal or may comprise same sequences. Alternatively or in addition, the preamble 1000b may be transmitted after the preamble 1000a and may optionally be spaced from the transmission of the preamble 1000a by the time space At. Although being described as being transmitted first the random access preamble 1000a and afterwards the random access preamble 1000b when transmitting the boosted random access preamble, the random access preamble 1000b may be transmitted before the random access preamble 1000a, for example, when both random access preambles comprise the same sequence and/or when each preamble comprises a cyclic prefix.

In other words, instead of just using the simple repetition, a time space At between the preambles may be permitted. One option is to permit arbitrary time spaces. However, the search space at the eNB strongly increases. Thus, the detection performance by repetition for large PRACH may still be low. Therefore, the search space may be limited by just permitting a defined time space or a certain set of time spaces. For further incremental increase of repetition, different time spaces may be used, i.e., a first time space between the initial random access preamble and a third set of symbols (first repetition) and a second time space between the first repetition and a further repetition may be the same or may be different from each other.

Alternatively or in addition, a so-called power ramping may be performed. A higher access probability may be achieved by increasing the transmission power in at least one, some or each random access attempt. However, the transmission power may be limited by the supported transmission power of the device. Having lower transmission power may reduce the energy consumption. Thus, the device may start with a low transmission - -

power and may increase transmission power when transmitting the boosted random access preamble.

Fig. 5e schematically illustrates a concept according to which an apparatus is configured to use a slotted physical random access channel. The illustrated scenario may apply, for example, when a time used for timing advanced and a time T_Pream ie used for transmitting the preamble 1000 is shorter than a time T_PRACH used for the PRACH. A maximum cell support, i.e., a maximum delay allowed for a user equipment, may be compensated by a timing advance so as to enable a simultaneous arrival of messages travelling diverse distances and facing diverse propagation delays to arrive at a same time at the base station. The maximum cell support 504 may thus relate to the timing advance TA. The division into a number of 6 slots is just exemplary. The time T_PRACH may be divided into any number of slots 204^ to 204₆, wherein the number may be at least 1 , 2, 3 or even more, such as 6. The number may at least be influenced by the cell size and a size of PRACH. A possible number x slots may be derived when considering that x

(ΤτΑ+Tpreamble)≤ TPRACH-

In other words, the total duration T_PRACH may be divided or slotted into a number of slots, each slot comprising a duration t wherein each duration t may be at least a sum of the durations of the maximum timing advance T_TA and of the duration for transmitting the preamble Tp_reambie- Each of the slots 204^ to 204₆ may comprise a different duration t. The user equipment may be configured to select one of the slots 204^ to 204₆ for transmitting the preamble. For example, when transmitting the boosted preamble 1300b, the user equipment may select a different slot, for example, a slot that has a longer timer duration t.

In other words, Fig. 5e shows a random access attempt on slotted PRACH, exploiting the maximal supported cell size. If the PRACH is larger than the sum of the maximum expected timing advance T_TA and the single preamble size T_Preambie (T_PRACH > T_TA + T_Preambie), then the preamble won't exceed the PRACH border. The preamble is only expected in the region of the maximum timing advance. Therefore, the PRACH can be separated into multiple slots, each being at least the maximum cell support. Each slot comprises at least the size of T_TA plus T_Pream i_e. A user equipment knowing the slot size t can randomly select a certain slot and transmit its preamble as illustrated in Fig. 5e. Thus, the collision probability may be reduced as a number of user equipment selecting a specific slot is lower when compared to all user equipment using the complete PRACH as one slot. In further access attempts, preamble can be repeated as described in connection with embodiments described herein. For example, when the slots 204τ to 204₆ comprise different lengths, then the user equipment may select a slot according to the criterion that the slot has to comprise a minimum time duration.

The user equipment may thus be configured to determine a timing for the transmission of the boosted random access preamble such as the boosted random access preamble 1300b. The user equipment may further be configured for using a timing advance for determining the timing. Rephrased, the user equipment may transmit the random access preamble or the boosted random access preamble in a slot 204 204₆ of a plurality of slots of a random access channel 204a or 204b. The selected slot 204 204₆ of the plurality of slots comprises a time duration t that is at least a sum of a time for transmitting the random access preamble or the boosted random access preamble, i.e., preambie and a time that is the maximum timing advance of the wireless communications network cell, i.e. T_TA- The duration of T_TA may be signaled by the base station. Alternatively or in addition at least information indicating which duration T_TA the basestation is supports may be transmitted to the user apparatus. From this, the slots may be derived by each apparatus knowing its transmission times. Thus, T_TA does not have to be estimated.

Fig. 5f shows a schematic block diagram of a modulo or subset of time-frequency patterns. As indicated by the theoretical boosted part 1000b^*, adding additional symbols might lead to a scenario where the signal and the maximal expected timing advance, i.e., the maximum cell support, are not fitting into the PRACH. I.E., in contrast to Fig. 5e, the following inequality is fulfilled: T_TA ⁺ T_Preamb|_e < T_PRACH- I.E., part of the random access signal could exceed the PRACH. To avoid this issue, the user equipment may be configured to separate the boosted preamble into multiple parts which may also be regarded as performing a modulo operation on the time indices. For example, the boosted random access preamble may be split into two components 1000a and 1000b. A first signal part 1000a may be transmitted on the same PRACH location in time and/or frequency as in the first attempt, i.e. , when transmitting the possibility unboosted random access preamble. The second signal part 1000b may be transmitted at the beginning of the PRACH which would be obtained, when the user equipment would have a zero distance to the base station or a zero timing advance. - -

According to other embodiments, the booster preamble may be split up into three parts, for example, when the preamble is boosted at least two times or when at least two additional sets of symbols are added to the preamble. In other words, Fig. 5f shows a use of a modulo operation to determine a location of a second repetition of the preamble in the time domain. The same method can also be used in the frequency domain, where certain offsets may exceed the spectrum of the PRACH. Fig. 5g shows such a solution, where a modulo operation is used to determine a location of the second repetition, i.e. , the preamble 1000b, in the frequency domain. Modulo operations of Figs. 5f and 5g may be combined, i.e., a split may be performed in the time domain and in the frequency domain. Instead of using the modulo operation, some well- defined time-frequency patterns may be applied as has been described, for example, in connection with Figs. 5b or 5c. Thus, the user equipment may be configured to determine the timing such that a beginning of the boosted random access preamble is received at the base station before an earliest time of the timing advance. This may be performed for slotted or unslotted PRACH. Embodiments described herein may relate to boosting a preamble by using a higher transmission power and/or by using additional symbols, so as to increase the probability of detection at the base station. Embodiments described herein may use this concept for increasing the chance of being recognized by the base station subsequent to a missed detection, i.e., a failed request for channel allocation.

Other examples described herein may use the concept of boosting a preamble so as to prioritize data, i.e. , to implement prioritization of users and/or messages. For example, a user equipment that has to transmit data of a first priority class may use a preamble comprising a first value of a preamble length and/or a first value of a transmission power for transmitting the preamble in the random access process. A second user equipment and/or the first user equipment transmitting data having a second priority class may use a second value of the preamble length and/or a second value of the transmission power. Thus, the length of the preamble and/or the value of the transmission power may indicate a priority of the user data to be transmitted. The priority class may, for example, relate to a service such as data streaming services, transmission of communication data such as voice, and/or to a transmission of pictures or emails, wherein, for example, a - -

streaming service might be allocated to a higher service class when compared to emails. Thus, for example, a user equipment that wants to perform data streaming may use a random access preamble that may be described as boosted when compared to a random access preamble used by a user equipment that aims to transmit email data.

Alternatively or in addition, such a priority may be related to a user of the user equipment. For example, emergency services may be assigned a higher user priority. Such data of a prioritized user is considered herein as prioritized data, i.e., as data having different priority classes. Thus, a description made herein in connection with boosting random access preambles may also be used to prioritize data and/or users.

A processor of a device according to embodiments described herein may be configured to extend the symbols or samples of the random access preamble by additional symbols, samples respectively so as to obtain the boosted random access preamble. The additional symbols or samples may be transmitted so as to follow directly after the initial sequence or may be transmitted with a spacing in frequency and/or time therebetween.

In other words, for certain user classes or messaging types, the user equipment can transmit already on the first random access attempt a high powered and/or larger signal to increase the probability of detection. Thus, a higher priority of a user and/or a message may be implemented. An apparatus may be configured to access at least one resource in the wireless communications network cell by a random access process comprising transmission of a random access preamble and by a resource allocation received responsive to the transmission. The apparatus may be configured to use a first value of a preamble length or a transmission power for performing the random access process to transmit data having a first priority class, and wherein the apparatus is configured to use a second value of the preamble length or of the transmission power for performing the random access process to transmit data having a second priority class. In simple terms, when the user has a higher priority class, then the user's data also has a high priority class and vice-versa.

Thus, when a priority class is higher when compared to another priority class, then the value of the preamble length or the value of the transmission power may be higher when compared to the value of the lower priority class. - -

According to one embodiment of prioritizing users or data, the user equipment may be configured to use a maximum preamble length or a maximum allowed transmission power that is allowed in the wireless communications network cell when transmitting prioritized data.

Fig. 6 shows a schematic block diagram of a wireless communications network 600. The wireless communications network 600 comprises one or more apparatus 602a and/or 602b. Each of the apparatus 602a and/or 602b may be, for example, a user equipment or an loT device as described in connection with Fig. 1. The wireless communications network 600 further comprises a base station 604, which may be, for example, an eNB as described in connection with Fig. 1 .

The apparatus 602a and 602b may be configured to operate according to embodiments described herein. Furthermore, the base station 604 is configured to control at least a wireless communications network cell of the wireless communications network 600. The base station 604 is further configured to allocate resources, i.e., at least one resource element, of the wireless communications network cell responsive to reception of a random access preamble which also includes a reception of a boosted random access preamble. The base station 604 may be configured to communicate with the apparatus 602a and/or 602b according to embodiments described with respect to Fig. 1 to Fig. 5g. In particular, the base station may be configured to transmit information relating to time- and/or frequency patterns, e.g., using the radio signal 606a and/or may be configured to evaluate one but also more than one PRACH for searching for the preamble or boosted preamble.

The base station 604 may be configured to perform a combination over multiple PRACHs. For example, when referring again to one of Figs. 5a to 5g, then the base station may be configured to receive and store information related to a first radio signal comprising a random access preamble of an apparatus such as the apparatus 602a in the first random access interval. For example, the random access preamble may be transmitted using the PRACH 204a as indicated in Fig. 5e. The base station 604 may further be configured to store information related to a second radio signal comprising a random access preamble and/or a boosted random access preamble of the apparatus in a second random access interval such as the PRACH 204b. Receiving and storing the information may comprise, for example, to check the PRACH for random access sequences. The radio signals received in probably subsequent PRACHs may be linked with each other and may commonly be checked for a presence of a single preamble. In other words, to further increase probability of detection, detection of the random access signal can be combined over multiple PRACHs. Thus, already a single preamble in the next random access attempt may lead to a higher detection probability, if the PRACHs are combined. The detection probability may be increased for UEs described herein as the boosted random access preamble also comprises the original random access preamble. Thus, the detection probability may also be increased for UE transmitting the same, i.e., unboosted, random access preambles in subsequent PRACHs. The power combination of multiple PRACHs may be done non-coherently. This may be done using a fixed timeout, i.e. , for defining a timing in which time interval the user equipment has to retransmit its preamble or boosted preamble. As the boosted preamble may comprise data being similar or equal to the initial preamble, the boosted preamble may at least partially be a repetition in time that may be detected by the base station even over the borders of PRACHs. The base station 604 may be configured to allocate the resource element, i.e. , the channel, based on the evaluation result obtained for the combination of the PRACHs 204a and 204b. The evaluation may be performed by a correlation of a signal derived from the first radio signal and from the second radio signal, i.e., the random access preamble and the boosted random access preamble, with a reference signal, such as the pool of sequences.

The base station 604 may alternatively or in addition be configured to transmit a radio signal 606a comprising information indicating a space in frequency and/or in time in which the base station searches for random access preambles. This may be the instructed pattern in frequency and time used by an apparatus such as a user equipment as has been described in connection Figs. 5b and 5c.

Some embodiments described herein may be understood as adaptive incremental increase and a combination of random access sequences after missed detection. A user equipment may adapt its random access sequence according to the number of timeouts, i.e. , the user equipment may transmit a preamble for a random access attempt. A timeout may occur after missed detection at the eNB. An adaptive incremental increase of preamble size may be performed until successful detection. Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a - -

block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed.

Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier.

Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein.

A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be -

configured to be transferred via a data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.

The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.

- -

Literature

[1 ] Sesia, Stefania, Matthew Baker, and Issam Toufik. "LTE-The UMTS Long Term

Evolution: From Theory to Practice," 2nd edition, John Wiley & Sons, 201 1.

[2] 3GPP TS 36.21 1 V13.2.0 (2016-06)

[3] 3GPP TSG-RAN1 Meeting #85, Motorola Mobility, Change Request on TS 36.213 V13.1.1 , R1-165972

[4] 3GPP TSG-RAN WG4 Meeting #79, Huawei, HiSilicon, Change Request on TS 36.133 v13.3.0, R4-164481

[5] 3GPP TSG-RAN2 Meeting #94, Ericsson (Rapporteur), Change Request on TS 36.321 V13.1.0, R2-164521

[6]

http://lteuniversity.eom/get_trained/expert_opinion1/b/hongyanlei/archive/2010/12/21/cell -size-configuration-in-rach-ii-cyclic-shift.aspx

Claims

1 . An apparatus (UEi , UE₂, UE₃, 104 _? 104₂) configured to operate in a wireless communications network cell (100₂, 100₄); wherein the apparatus is configured to access at least one resource (204) in the wireless communications network cell (100₂, 100₄) by a random access process comprising transmission of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) and by a resource allocation (2200) received responsive to the transmission; and wherein, in case of a missing resource allocation, the apparatus is configured to boost the random access preamble and to transmit the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c).

2. The apparatus of claim 1 , wherein boosting the random access preamble comprises increasing a transmission power of the random access preamble and/or adding symbols (1350) or samples to the random access preamble (1000).

3. The apparatus of claim 1 or 2, wherein the apparatus is configured to transmit the random access preamble (1000) comprising a first set of symbols (1200) and to transmit the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c) comprising a second set of symbols being the first set of symbols (1200) being extended by a third set of symbols (1350).

4. The apparatus of claim 3, wherein the third set of symbols (1350) corresponds to a section of the first set of symbols (1200).

5. The apparatus of claim 3, wherein the third set of symbols (1350) comprises a number of copies of the first set of symbols (1200), the number being one or greater.

6. The apparatus of claim 3, wherein the random access preamble (1000) is a part of a set of random access preambles used in the wireless communications network cell (100₂, 100₄), wherein the third set of symbols (1350) comprises a different random access preamble of the set.

7. The apparatus of claim 3 to 6, wherein the apparatus is configured to transmit the first set of symbols (1200) using a first transmission frequency ( ) and to transmit the second set of symbols or the third set of symbols (1350) using a second transmission frequency (f₂).

8. The apparatus of one of claims 3 to 7, wherein the apparatus is configured to transmit the third set of symbols (1350) and other symbols (1000) of the second set of symbols with a spacing in time (At) therebetween.

9. The apparatus according to one of claims 3 to 8, wherein the apparatus is configured to transmit the third set of symbols (1350) in absence of a cyclic prefix.

10. The apparatus of one of previous claims, wherein the apparatus is configured to transmit the random access preamble (1000) and the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c) according to an implemented predetermined time-frequency pattern.

1 1. The apparatus of one of previous claims, wherein the apparatus is configured to transmit the third set of symbols (1350) and other symbols (1000) of the second set of symbols according to an implemented predetermined time-frequency pattern. 2. The apparatus of claim 10 or 1 1 , wherein the apparatus is configured to receive a radio signal (606a) comprising information indicating an instructed predetermined time-frequency pattern, wherein the apparatus is configured to implement the instructed predetermined time-frequency pattern as the implemented time- frequency pattern.

13. The apparatus of one of previous claims, wherein the apparatus is configured to transmit the random access preamble (1000) or the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c) in a slot (204 204₆) of a plurality of slots of a random access channel (204a, 204b), wherein the slot (204 204₆) of the plurality of slots comprises a time duration (t) that is at least a sum of a time (Tpream ie) for transmitting the random access preamble (1000) or the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c) and a time (T_TA) that is the maximum timing advance of the wireless communications network cell (100₂, 100₄).

The apparatus of claim 13, wherein the apparatus is configured to determine the timing such that a beginning of the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c) is received at a recipient base station before an earliest time of the timing advance.

The apparatus of one of previous claims, wherein the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c) comprises a concatenation of a number of copies of the random access preamble (1000).

The apparatus of one of previous claims, wherein, in case of a missing resource allocation responsive to the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 300c), the apparatus is configured to transmit a further boosted random access preamble being boosted with respect to the boosted random access preamble (1300a; 1300b; 1300b'; 1300c).

An apparatus configured to operate in a wireless communications network cell

wherein the apparatus is configured to access at least one resource (204) in the wireless communications network cell (100₂, 100₄) by a random access process comprising transmission of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) and by a resource allocation (2200) received responsive to the transmission; and wherein the apparatus is configured to use a first value of a preamble length or a transmission power for performing the random access process to transmit data having a first priority class, and wherein the apparatus is configured to use a second value of the preamble length or of the transmission power for performing the random access process to transmit data having a second priority class.

18. The apparatus of claim 16, wherein the second priority class comprises a higher priority when compared to the first priority class, wherein the second value of the preamble length or of the transmission power is higher when compared to the first value.

19. The apparatus of claim 17 or 18, wherein the apparatus is configured to use a maximum allowed preamble length or a maximum allowed transmission power as the second value.

The apparatus of one of the preceding claims, wherein the apparatus is configured to perform the random access process as a contention-based random access process.

A base station (604) configured to control a wireless communications network cell (100₂, 100₄) of a wireless communications network (600), wherein the base station (604) is configured to allocate a resource element of the wireless communication cell (100₂, 100₄) responsive to reception of a random access preamble (1000; 300a; 1300b; 1300b'; 1300c), wherein the base station (604) is configured: to receive and to store information related to a first radio signal comprising a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) of a first apparatus in a first random access interval (204a); to receive and to store information related to a second radio signal comprising a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) of the first apparatus in a second random access interval (204b); to evaluate a random access attempt of the apparatus using the information related to the first radio signal and using the information related to the second radio signal to obtain an evaluation result; and to allocate the resource element based on the evaluation result. The base station of claim 21 , wherein the first random access interval (204a) and the second random access interval (204b) are subsequent random access intervals.

The base station of claim 21 or 22, wherein the base station is configured to obtain the evaluation result based on a correlation of a signal derived from the first radio signal from the second radio signal with a reference signal.

A base station (604) configured to control a wireless communications network cell (100₂, 100₄) of a wireless communications network (600), wherein the base station (604) is configured to allocate a resource element of the wireless communication cell (100₂, 100₄) responsive to reception of a random access preamble(1000; 1300a; 1300b; 1300b'; 1300c); wherein the base station is configured to transmit a radio signal (606) comprising information indicating a space in frequency or in time in which the base station searches for the random access preambled 000; 1300a; 1300b; 1300b'; 1300c); and wherein the base station is configured to adapt a reception filter used for evaluating a received radio signal for a presence of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) according to the space in frequency or in time.

The base station configured of claim 24, wherein the base station is configured to transmit a radio signal (606) indicating an instructed time-frequency pattern and to search for the random access preamble in the space in frequency or in time according to the time-frequency pattern.

Wireless communications network (600) comprising: an apparatus (602a, 602b) according to one of claims 1 to 20; and a base station (604) according to one of claims 21 to 25.

27. A method for operating an apparatus to operate in a wireless communications network cell (100₂, 100₄), the method comprising: accessing at least one resource (204) in the wireless communications network cell (100₂, 100₄) by a random access process comprising transmission of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) and by a resource allocation (2200) received responsive to the transmission; and boosting, in case of a missing resource allocation, the random access preamble and transmitting the boosted random access preamble (1300; 1300a; 1300b; 1300b'; 1300c).

28. A method for operating an apparatus to operate in a wireless communications network cell (100₂, 100₄), the method comprising: accessing at least one resource (204) in the wireless communications network cell (100₂, I OO₄) by a random access process comprising transmission of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) and by a resource allocation (2200) received responsive to the transmission; and using a first value of a preamble length or a transmission power for performing the random access process to transmit data having a first priority class; and using a second value of the preamble length or of the transmission power for performing the random access process to transmit data having a second priority class.

29. A method for operating a base station to control a wireless communications network cell (100₂, 100₄) of a wireless communications network, the control comprising allocating a resource element of the wireless communication cell responsive to reception of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c), the method comprising: receiving and storing information related to a first radio signal comprising a random access preamble of a first apparatus in a first random access interval (204a); receiving and storing information related to a second radio signal comprising a random access preamble of the first apparatus in a second random access interval (204b); evaluating a random access attempt of the apparatus using the information related to the first radio signal and using the information related to the second radio signal to obtain an evaluation result; and allocating the resource element based on the evaluation result.

A method for operating a base station to control a wireless communications network cell (100₂, 100 ) of a wireless communications network (600), comprising allocating a resource element of the wireless communication cell responsive to reception of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c), the method comprising: transmitting a radio signal (606a) comprising information indicating a space in frequency or in time in which the base station (604) searches for the random access preamble (1000; 1300a; 1300b; 1300b'; 1300c); and adapting a reception filter for evaluating a received radio signal for a presence of a random access preamble (1000; 1300a; 1300b; 1300b'; 1300c) according to the space in frequency or in time.

A non-transitory computer program product comprising a computer readable medium storing instructions which, when executed on a computer, carry out the method of one of claims 27 to 30.