Wireless base station and random access method

Abstract

To provide an improved apparatus and method for executing a random access procedure between user equipment and a radio base station via an unlicensed cell.SOLUTION: In a mobile communication system, a base station device has a transmitter that transmits information on a random access preamble sequence to user equipment, and a receiver that receives the random access preamble sequence selected and transmitted by the user equipment on the basis of the information. The random access preamble sequence is transmitted with the frequency band width of an unlicensed band, the frequency band width being defined by the length of the random access preamble sequence and a sub carrier interval, and larger than a frequency band with which the random access preamble sequence is transmitted in a licensed band.SELECTED DRAWING: Figure 15B

Description

[Technical Field]

[0001] This disclosure relates to a method for performing a random access procedure between user equipment and a radio base station in a mobile communication system. Furthermore, this disclosure provides user equipment and a radio base station involved in one or more of the methods described herein. [Background technology]

[0002] Long-Term Evolution (LTE) Third-generation mobile communication systems (3G), based on WCDMA® wireless access technology, are being deployed on a large scale worldwide. As the first step in enhancing and developing this technology, High-Speed ​​Downlink Packet Access (HSDPA) and Enhanced Uplink (also known as High-Speed ​​Uplink Packet Access (HSUPA)) have been introduced, providing highly competitive wireless access technologies.

[0003] To meet the ever-increasing demand from users and to ensure competitiveness in new wireless access technologies, 3GPP® has introduced a new mobile communications system called Long-Term Evolution (LTE). LTE is designed to provide the carriers required for high-speed data and media transmission and high-capacity voice support over the next decade.

[0004] The specifications for the Work Items (WIs) related to LTE (Long-Term Evolution) are referred to as E-UTRA (Evolved UMTS Terrestrial Radio Access (UTRA)) and E-UTRAN (Evolved UMTS Terrestrial Radio Access Network (UTRAN)), and will ultimately be published as Release 8 (LTE Release 8). The LTE system is a packet-based, efficient radio access and radio access network that provides all IP-based functionality with low latency and low cost. LTE specifies multiple scalable transmit bandwidths (e.g., 1.4 MHz, 3.0 MHz, 5.0 MHz, 10.0 MHz, 15.0 MHz, and 20.0 MHz) to achieve flexible system deployment using a given spectrum. Downlink radio access is based on OFDM (Orthogonal Frequency Division Multiplexing). This is because such radio access is inherently less susceptible to multipath interference (MPI) due to its low symbol rate, uses cyclic prefixes (CP), and can accommodate various transmit bandwidth configurations. Uplinks employ SC-FDMA (Single-Carrier Frequency Division Multiple Access) based radio access because, given the limited transmit power of user equipment (UE), providing a wide coverage area takes precedence over increasing peak data rates. LTE Release 8 / 9 employs numerous key packet radio access technologies (e.g., MIMO (Multiple Input Multiple Output) Channel Transmission technology) to achieve a highly efficient control signaling structure.

[0005] LTE architecture Figure 1 shows the overall architecture of LTE. E-UTRAN consists of eNodeBs, which terminate the E-UTRAN's user plane (PDCP / RLC / MAC / PHY) and control plane (RRC) protocols destined for user equipment (UE). The eNodeB (eNB) hosts the physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, and packet data control protocol (PDCP) layer (these layers include functions for user plane header compression and encryption). The eNB also provides radio resource control (RRC) functions corresponding to the control plane. The eNB performs many functions, including radio resource management, admission control, scheduling, negotiated uplink quality of service (QoS) implementation, cell information broadcasting, encryption / decryption of user plane data and control plane data, and compression / decompression of downlink / uplink user plane packet headers. Multiple eNodeBs are connected to each other by X2 interfaces.

[0006] In addition, multiple eNodeBs are connected to the EPC (Evolved Packet Core) via the S1 interface, more specifically, to the MME (Mobility Management Entity) via the S1-MME and to the Serving Gateway (SGW) via the S1-U. The S1 interface supports a many-to-many relationship between the MME / Serving Gateway and the eNodeB. The SGW routes and forwards user data packets, functions as a mobility anchor for the user plane during handover between eNodeBs, and further functions as an anchor for mobility between LTE and another 3GPP technology (terminating the S4 interface and relaying traffic between the 2G / 3G system and the PDN GW). For an idle user equipment, the SGW terminates the downlink data path and triggers paging when downlink data arrives for that user equipment. The SGW manages and stores the context of the user equipment (e.g., parameters of IP bearer services or internal network routing information). Further, the SGW performs duplication of user traffic in case of lawful interception.

[0007] The MME is the primary control node of the LTE access network. The MME is responsible for tracking and paging (including retransmission) user devices in idle mode. The MME participates in the bearer activation / deactivation process and also selects the SGW for user devices during initial attachment and during LTE handovers involving the relocation of core network (CN) nodes. The MME authenticates users (by interacting with the HSS). Non-Access Stratum (NAS) signaling terminates at the MME, which also generates and assigns temporary IDs to user devices. The MME checks the authentication of user devices for accessing the service provider's Public Land Mobile Network (PLMN) and enforces roaming restrictions on user devices. The MME is the network endpoint for encryption / integrity protection of NAS signaling and manages security keys. Legitimate interception of signaling is also supported by the MME. Furthermore, the MME provides control plane functionality for mobility between the LTE access network and the 2G / 3G access network, and terminates the S3 interface from the SGSN. In addition, the MME terminates the S6a interface toward the home HSS for roaming user equipment.

[0008] Component carrier structure in LTE The downlink component carrier of the 3GPP LTE system is further divided in the time-frequency domain in a so-called subframe. In 3GPP LTE, each subframe is divided into two downlink slots as shown in FIG. 2, where the first downlink slot includes a control channel region (PDCCH region) within the first OFDM symbol. Each subframe is composed of a given number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), and each OFDM symbol spreads across the entire bandwidth of the component carrier. Thus, each OFDM symbol is composed of several modulation symbols transmitted on respective subcarriers. In LTE, the transmission signal in each slot is described by a resource grid of N DL RB ×N RB sc subcarriers of this book and N DL symb OFDM symbols. N DL RB is the number of resource blocks in the bandwidth. The number N DL RB depends on the downlink transmission bandwidth set in the cell, and N min,DL RB ≦N DL RB ≦N max,DL RB is satisfied. In this case, N min,DL RB = 6 and N max,DL RB = 110 are the minimum downlink bandwidth and the maximum downlink bandwidth supported by the current version of the specification, respectively. N RB sc is the number of subcarriers in one resource block. In the case of a normal cyclic prefix subframe structure, N RB sc = 12, N DL symb = 7.

[0009] For example, in a multi-carrier communication system using OFDM, such as that used in 3GPP Long-Term Evolution (LTE), the smallest unit of resources that can be allocated by the scheduler is a "resource block." A physical resource block (PRB) is defined as a sequence of OFDM symbols in the time domain (e.g., 7 OFDM symbols) and a sequence of subcarriers in the frequency domain (e.g., 12 subcarriers of a component carrier), as illustrated in Figure 2. Thus, in 3GPP LTE (Release 8), a physical resource block consists of resource elements corresponding to one slot in the time domain and 180 kHz in the frequency domain (for further details regarding the downlink resource grid, see, for example, Section 6.2 of Non-Patent Literature 1 (current version 12.6.0), which is available on the 3GPP website and incorporated herein by reference).

[0010] A subframe consists of two slots; therefore, when a so-called "normal" CP (cyclic prefix) is used, there are 14 OFDM symbols within the subframe, and when a so-called "extended" CP is used, there are 12 OFDM symbols within the subframe. For the sake of technical terms, below, the same consecutive subcarriers and equivalent time-frequency resources that span the entire subframe are referred to as a "resource block pair," or synonymous "RB pair" or "PRB pair." The term "component carrier" refers to a combination of several resource blocks in the frequency domain. In future releases of LTE, the term "component carrier" will no longer be used; instead, the term will be changed to "cell," which refers to a combination of downlink resources and optionally uplink resources. The linking between the carrier frequencies of the downlink resources and the uplink resources is indicated in the system information transmitted on the downlink resources.

[0011] Similar assumptions regarding the structure of component carriers will apply to subsequent releases.

[0012] Carrier aggregation in LTE-A for wider bandwidth support At the World Radiocommunication Conference 2007 (WRC-07), the frequency spectrum for IMT-Advanced was determined. While the overall frequency spectrum for IMT-Advanced was determined, the actually usable frequency bandwidth will vary by region and country. However, following the determination of the outline of the usable frequency spectrum, standardization of the radio interface began at 3GPP (Third Generation Partnership Project).

[0013] The LTE Advanced System can support a bandwidth of 100 MHz, while the LTE System can only support 20 MHz. Today, the lack of radio spectrum is a bottleneck in wireless network development, and as a result, it is difficult to find a sufficiently wide spectrum bandwidth for the LTE Advanced System. Therefore, finding a way to obtain a wider radio spectrum bandwidth is urgent, and in this regard, a possible answer is carrier aggregation.

[0014] In carrier aggregation, two or more component carriers are aggregated to support a wider transmit bandwidth of up to 100 MHz. In LTE-Advanced systems, several cells in an LTE system are aggregated into a single wider channel, which is sufficiently wide to 100 MHz even if these cells in LTE are in different frequency bands. All component carriers can be configured to be LTE Release 8 / 9 compatible, at least as long as the bandwidth of the component carriers does not exceed the supported bandwidth of the LTE Release 8 / 9 cells. Not all component carriers aggregated by user equipment necessarily have to be LTE Release 8 / 9 compatible. Existing mechanisms (e.g., burring) can be used to avoid user equipment from Release 8 / 9 camping on component carriers.

[0015] A user device can simultaneously receive or transmit on one or more component carriers (corresponding to multiple serving cells), depending on its capabilities. An LTE-A Release 10 user device with receive and / or transmit capabilities for carrier aggregation can simultaneously receive and / or transmit on multiple serving cells, whereas an LTE Release 8 / 9 user device can receive and transmit on only one serving cell, provided the component carrier structure conforms to the Release 8 / 9 specifications.

[0016] Carrier aggregation is supported for both consecutive and discontinuous component carriers, and each component carrier is limited to a maximum of 110 resource blocks in the frequency domain (using the 3GPP LTE (Release 8 / 9) numerology).

[0017] It is possible to configure 3GPP LTE-A (Release 10) compatible user equipment to aggregate different numbers of component carriers with different bandwidths, possibly on the uplink and downlink, transmitted from the same eNodeB (base station). The number of downlink component carriers that can be configured depends on the downlink aggregation capability of the user equipment. Conversely, the number of uplink component carriers that can be configured depends on the uplink aggregation capability of the user equipment. Currently, it is not possible to configure a mobile terminal with more uplink component carriers than downlink component carriers. In a typical TDD deployment, the number of component carriers and the bandwidth of each component carrier are the same for both uplink and downlink. Component carriers transmitted from the same eNodeB do not need to provide the same coverage.

[0018] The spacing between the center frequencies of continuously aggregated component carriers is a multiple of 300 kHz. This is to maintain compatibility with the 100 kHz frequency raster of 3GPP LTE (Release 8 / 9) while also maintaining the orthogonality of 15 kHz-spacing subcarriers. Depending on the aggregation scenario, an n × 300 kHz spacing can be easily achieved by inserting a small number of unused subcarriers between consecutive component carriers.

[0019] The impact of aggregating multiple carriers is limited to the MAC layer. The MAC layer requires one HARQ entity for each aggregated component carrier, both uplink and downlink. There is a maximum of one transport block per component carrier (if SU-MIMO is not used on the uplink). The transport block and its (one or more) HARQ retransmissions (if any) must be mapped to the same component carrier.

[0020] When carrier aggregation is configured, a mobile device has only one RRC connection to the network. During RRC connection establishment / re-establishment, one cell provides security inputs (one ECGI, one PCI, and one ARFCN) and non-accessible layer (NAS) mobility information (e.g., TAI), similar to LTE Release 8 / 9. After RRC connection establishment / re-establishment, the component carrier corresponding to that cell is referred to as the downlink primary cell (PCell). In a connected state, there is always one downlink PCell (DL PCell) and one uplink PCell (UL PCell) configured per user device. In a configured set of component carriers, the other cells are called secondary cells (SCells), and the carriers of the SCells are the downlink secondary component carrier (DL SCC) and the uplink secondary component carrier (UL SCC). Currently, a maximum of five serving cells (including PCells) can be configured for a single UE.

[0021] Component carrier configuration and reconfiguration, as well as addition and deletion, can be performed by the RRC. Activation and deactivation are performed, for example, via MAC control elements. During LTE handover, the RRC can also add, delete, or reconfigure SCells for use in the target cell. When adding a new SCell, dedicated RRC signaling is used to send the SCell's system information (necessary for transmission / reception) (similar to handover in LTE release 8 / 9). When a SCell is added to a UE, each SCell is assigned a serving cell index. A PCell always has a serving cell index of 0.

[0022] When user equipment is configured to use carrier aggregation, at least one pair of uplink and downlink component carriers is always active. The downlink component carrier in this pair is sometimes referred to as the "downlink anchor carrier." The same applies to uplinks. While user equipment can be scheduled for multiple component carriers simultaneously when carrier aggregation is configured, only one random access procedure can be running at a time. Cross-carrier scheduling allows a component carrier's PDCCH to schedule resources on another component carrier. For this purpose, a component carrier identification field ("CIF") is introduced in each DCI (Downlink Control Information) format.

[0023] When cross-carrier scheduling is not performed, the link between the uplink and downlink component carriers (established by RRC signaling) can be used to identify the uplink component carrier to which the grant applies. The link between downlink component carriers and uplink component carriers does not necessarily have to be one-to-one. In other words, two or more downlink component carriers can be linked to the same uplink component carrier. On the other hand, one downlink component carrier can only be linked to one uplink component carrier.

[0024] Random access procedure In LTE, mobile terminal uplink transmissions can only be scheduled if the mobile terminal's uplink transmissions are time-synchronized, in order to maintain orthogonality with uplink transmissions from other UEs. Therefore, the Random Access (RACH) procedure plays an important role as an opportunity for unsynchronized mobile terminals (UEs) to perform orthogonal transmissions of uplink radio access. Essentially, the Random Access procedure in LTE is used to achieve uplink time synchronization in user equipment that has not yet achieved uplink synchronization, or user equipment that has lost uplink synchronization. Once a user equipment achieves uplink synchronization, the eNodeB can schedule uplink transmission resources for that user equipment.

[0025] Furthermore, the PRACH transmission and detection estimate the round-trip delay between the eNB and the UE. The design goal for the PRACH signal shape when operating LTE on licensed bands was to minimize overhead and the impact of interference on parallel uplink transmissions from other UEs, while simultaneously providing sufficient accuracy in round-trip delay estimation.

[0026] In a further additional case, user equipment may perform random access procedures even if time-synchronized; that is, user equipment uses random access procedures to send scheduling requests (i.e., uplink buffer status reports) to the eNodeB when no other uplink resource is allocated to send scheduling requests (e.g., no dedicated scheduling request (D-SR) channel is configured).

[0027] Therefore, the following scenarios are related to random access. 1. When a user device that is in the RRC_CONNECTED state but is not uplink synchronized attempts to send new uplink data or control information. 2. When a user device in the RRC_CONNECTED state but not uplink synchronized needs to receive downlink data and is therefore required to send the corresponding HARQ feedback (i.e., ACK / NACK) uplink. This scenario is also referred to as Downlink data arrival. 3. When a user device in the RRC_CONNECTED state is handed over from the current serving cell to a new target cell, a random access procedure is performed in the target cell to achieve uplink time synchronization. 4. When timing advance is required for positioning purposes in the RRC_CONNECTED state. 5. When transitioning from the RRC_IDLE state to the RRC_CONNECTED state (for example, when first accessed or when the tracking area is updated) 6. When recovering from a wireless link failure (i.e., re-establishing the RRC connection)

[0028] LTE offers two types of random access procedures, allowing access either contention-based (with the risk of collision) or non-contention-based. Note that contention-based random access can be applied to all six scenarios listed above, while non-contention-based random access can only be applied to downlink data arrival and handover scenarios.

[0029] The competition-based random access procedure will be described in more detail below, with reference to Figure 3. A detailed description of the random access procedure can also be found in Section 5.1 of Non-Patent Document 2 (current version 12.6.0), which is incorporated herein by reference.

[0030] Figure 3 illustrates the LTE competition-based RACH procedure. This procedure consists of four “steps.” First, the user device sends a random access preamble to the eNodeB over a physical random access channel (PRACH) (301). The preamble is selected by the user device from a set of available random access preambles reserved by the eNodeB for competition-based access. cf This is the number of signatures reserved by the eNodeB for RACH without conflict. In LTE, there are a total of 64 preambles per cell that can be used for RACH without conflict and RACH based random access. The set of RACH based preambles can be further divided into two groups, and thus, the selection of a preamble by the UE can convey one bit of information indicating the amount of transmit resources required for the first scheduled transmission (referred to as msg3 in Non-Patent Literature 2) (see step 303 in Figure 3). The system information broadcast within the cell includes information on the signatures (preambles) belonging to each of the two subgroups, and the meaning of each subgroup. The user equipment randomly selects one preamble from the subgroup corresponding to the size of the transmit resources required for the transmission of msg3 (see step 303 below). When the UE selects an appropriate size to indicate, it may further consider the current downlink path loss and the transmit power required for the message in step 303, in order to avoid allowing resources for a message size that would require transmission exceeding the size allowed by the UE's maximum power.

[0031] After detecting a RACH preamble, eNodeB sends a Random Access Response (RAR) message via the Physical Downlink Shared Channel (PDSCH), which is addressed to the (random access) RA-RNTI that identifies the time-frequency slot in which the preamble was detected (302). If multiple user devices send the same RACH preamble using the same PRACH resource (also known as a collision), these user devices will receive the same random access response.

[0032] The RAR (Random Access Response) message conveys the identification information of the detected RACH preamble, a timing alignment command (TA command) to synchronize subsequent uplink transmissions, an initial uplink resource allocation (grant) for sending the first scheduled transmission (see step 303), and the allocation of a T-CRNTI (Temporary Cell Radio Network Temporary Identifier). This T-CRNTI is used by the base station to address the mobile terminal (one or more) from which the RACH preamble was detected until the RACH procedure is completed, because the eNodeB does not yet know the "true" identification information of the mobile terminal at this point.

[0033] Furthermore, RAR messages may also include a so-called backoff indicator, which can be configured by the eNodeB to instruct user equipment to back off (wait) for a specific period before retrying random access. User equipment monitors PDCCH for a random access response within a given time window (configured by the eNodeB). If no random access response is received within the configured time window, user equipment retransmits the preamble at the next PRACH opportunity, taking into account the backoff period, if one has been specified.

[0034] In response to the RAR message received from the eNodeB, the user device sends its first scheduled uplink transmission on the uplink resource allocated by the grant in the random access response (303). This scheduled uplink transmission carries the actual random access procedure messages (e.g., RRC connection request, tracking area update, buffer status report). Furthermore, this uplink transmission includes either the C-RNTI of the user device in RRC_CONNECTED mode, or a unique 48-bit user device ID if the user device is in RRC_IDLE mode. If a preamble collision occurs in step 301 (i.e., multiple user devices send the same preamble on the same PRACH resource), the colliding user devices receive the same T-CRNTI in the random access response and collide on the same uplink resource when sending their respective scheduled transmissions (303). This may result in interference, and therefore the eNodeB cannot decode transmissions from the colliding user devices, causing the user devices to restart the random access procedure after reaching the maximum number of scheduled transmission retries. If a scheduled transmission from one user device is successfully decoded by eNodeB, conflicts from other user devices remain unresolved.

[0035] To resolve this type of conflict, the eNodeB sends a conflict resolution message addressed to the C-RNTI or temporary C-RNTI (304), and in the case of a temporary C-RNTI, sends back the 48-bit user device ID that was included in the scheduled transmission in step 303. After the collision, if the message sent in step 303 is successfully decoded, only user devices that have found their own identification information (C-RNTI or unique user device ID) will send HARQ feedback (ACK). Other UEs will recognize that a collision occurred in step 301 and can immediately terminate the current RACH procedure and start a new RACH procedure.

[0036] Figure 4 shows the conflict-free random access procedure introduced in 3GPP LTE Release 8 / 9. Compared to the conflict-based random access procedure, the conflict-free random access procedure is simplified. The eNodeB assigns a specific preamble to the user device for use in random access so that there is no risk of collision (i.e., multiple user devices do not send the same RACH preamble) (401). In response, the user device sends the preamble signaled by the eNodeB with the appropriate PRACH resource on the uplink (402). In conflict-free random access, the case where multiple UEs send the same preamble is avoided, eliminating the need for conflict resolution, and thus step 304 of the conflict-based procedure shown in Figure 3 can be omitted. The conflict-free random access procedure essentially terminates after the random access response is successfully received. If the random access response is not received, the UE itself autonomously initiates the next PRACH retransmission.

[0037] When carrier aggregation is configured, the first three steps of a conflict-based random access procedure are performed by the PCell, and conflict resolution (step 304) can be cross-scheduled by the PCell.

[0038] The initial setting of the preamble's transmit power can be based on an open-loop estimation where path losses are fully compensated. This open-loop estimation is designed so that the preamble's receive power is independent of path losses.

[0039] Furthermore, the eNB can set additional power offsets depending on, for example, the desired received SINR, the measured levels of uplink interference and noise in the time-frequency slot allocated to the RACH preamble, and (if applicable) the format of the preamble. In addition, the eNB can set preamble power ramping so that the transmit power of each retransmitted preamble increases at regular intervals (for example, if a PRACH transmission attempt is unsuccessful).

[0040] Random access preamble - time, frequency, format The random access preamble transmission portion of the random access procedure described above is mapped to PRACH at the physical layer. The design of the preamble is crucial for the success of the random access procedure and will be explained in detail below. The RACH preamble is essentially a cyclic shift of a complex Zadoff-Chu (ZC) sequence, also known as a preamble signature. The LTE PRACH preamble consists of a complex sequence. However, unlike the W-CDMA preamble, the LTE PRACH preamble is also an OFDM symbol that must conform to the DFT-S-OFDM structure of the LTE uplink, and is constructed using CP (cyclic prefix), thus enabling efficient frequency-domain reception at the eNodeB. The physical layer random access preamble has a length T, as shown in Figure 5. CP The cyclic prefix and length T SEQIt consists of a sequence section and a preamble format. The possible values ​​for these parameters are listed in the following table and depend on the frame structure and the random access settings (e.g., a preamble format that can be controlled by a higher layer). Corresponding details are described in Non-Patent Literature 1 (current version 12.6.0), section 5.7.1, “Time and frequency structure” (incorporated herein by reference). In frequency division duplex operation, four random access preamble formats are defined, each format defined by the duration of the sequence and the duration of the cyclic prefix. The format set in a cell is broadcast in the system information.

[0041] [Table 1]

[0042] T S This is the assumed system sampling rate, which can be 1 / 30.72 μs, and is the basic unit of time in LTE. The following table shows the T in different preamble formats, taking this specific sampling rate into consideration. CP and T SEQ This shows the value.

[0043] [Table 2]

[0044] The following table shows the subcarrier intervals and corresponding symbol durations in the current LTE specification. For example, the duration of the preamble sequence (1600 μs, see Table 2) for preamble formats 2 and 3 is achieved by the repetition of the preamble symbol in the time domain (800 μs).

[0045] [Table 3]

[0046] Duration T of the sequence SEQ The lower limit (683.33 μs) must be such that UEs located at the periphery of the largest expected cell can clearly estimate the round-trip time, including the maximum delayed diffusion expected in such a large cell (i.e., 16.67 μs). The duration of the sequence T SEQ Further constraints are given by the signal generation principle of single-carrier frequency division multiple access, and therefore the size N of the DFT (Discrete Fourier Transform) and IDFT (Inverse Discrete Fourier Transform) DFT It must be an integer.

[0047] To facilitate frequency multiplexing of PRACH and PUSCH resource allocations, PRACH slots are assigned a bandwidth BW equal to an integer multiple of the resource block (i.e., an integer multiple of 180kHz). PRACH It must be allocated. BW in LTE PRACH (6 PRBs, 1.08MHz) are constant for all system bandwidths for the sake of simplicity, and this BW PRACH The system is selected to optimize both detection performance and timing estimation accuracy. Timing estimation accuracy determines the lower limit of the PRACH bandwidth. In practice, a minimum bandwidth of approximately 1 MHz is required to provide the acceptable timing accuracy of approximately ±0.5 μs for one-shot accuracy in PUCCH / PUSCH transmission.

[0048] By allocating six Resource Blocks (RBs) to PRACH, a good trade-off is achieved between PRACH overhead, detection performance, and timing estimation accuracy. Note that, with the minimum system bandwidth (1.4 MHz, six RBs), PRACH will overlap with PUCCH. Whether to avoid collisions by imposing scheduling constraints when PRACH is slotted, or to deal with the resulting interference while accepting the collision between PRACH and PUCCH, is left to the eNodeB implementation.

[0049] To provide compatibility between the preamble's subcarriers and the PUSCH's subcarriers, the duration of the preamble should be fixed to an integer multiple of the duration of the PUSCH symbols. That is, it is preferable that the subcarrier spacing of PRACH be an integer fraction of the subcarrier spacing of PUSCH.

[0050] As shown in Figure 6, PRACH is time-multiplexed and frequency-multiplexed with PUSCH and PUCCH. PRACH time-frequency resources are semi-statically allocated within the PUSCH domain and repeated periodically. Whether a PUSCH transmission can be scheduled within a PRACH slot is at the discretion of the eNodeB. LTE supports 64 PRACH configurations, each consisting of a periodic PRACH resource pattern and an associated preamble format. A detailed list of PRACH configurations is provided in Tables 5.7.1-2 and 5.7.1-3 of Non-Patent Literature 1 (incorporated herein by reference). It is possible to schedule a PUSCH transmission within the same subframe along with the allocated PRACH resources. This decision is made by the eNB.

[0051] Random access preamble - Generating a preamble sequence As mentioned above, LTE offers 64 PRACH signatures compared to only 16 in WCDMA. This not only reduces the probability of collisions, but also allows 1 bit of information to be conveyed via the preamble in competition-based access, and furthermore, several signatures can be reserved for competition-free access. Therefore, LTE PRACH preambles require an improved sequence design than WCDMA. In LTE, a prime-length Zadoff-Chu sequence has been selected, which allows for improved detection performance of the PRACH preamble. More detailed information can be found in Non-Patent Document 1 (current version 12.6.0), section 5.7.2, “physical random access channel” (incorporated herein by reference).

[0052] The random access preamble is a Zadoff-Chu (ZC) sequence, and a Zadoff-Chu sequence is generated from one or more root Zadoff-Chu sequences as follows: First, a root Zadoff-Chu sequence is selected based on the instruction information of the logical sequence index (RACH_ROOT_SEQUENCE) broadcast as part of the system information. The order of the logical root sequences is cyclical, and therefore, after logical index 837 comes index 0. The relationship between the logical root sequence index (as shown in the system information) and the physical root sequence index u is given by Table 5.7.2-4 of Non-Patent Literature 1 for preamble formats 0-3, and by Table 5.7.2-5 (incorporated herein by reference) for preamble format 4.

[0053] The u-th root Zadoff-Chu sequence is defined by the following equation:

[0054]

number

[0055] In the formula, u is the physical root sequence index described above, and the sequence length is N. ZC This depends on the PRACH preamble format being set, i.e., N in the case of preamble formats 0 to 3. ZC =839, and in the case of preamble format 4, N ZC = 139 (see also Table 5.7.2-1 in Non-Patent Document 1).

[0056] From the u-th root Zadoff-Chu sequence, a cyclic shift of length N is obtained by the following equation. CS A set of 64 random-access preambles with a zero correlation zone of -1 is defined.

[0057]

number

[0058] The cyclic shift is given by the following equation:

[0059]

number

[0060] Parameter N CS This is given by Tables 5.7.2-2 and 5.7.2-3 of Non-Patent Literature 1, and depends on the format of the preamble and the parameter zeroCorrelationZoneConfig provided by the higher layer. Further information can be obtained from Section 5.7.2 of Non-Patent Literature 1.

[0061] If it is not possible to generate 64 preambles from a single root Zadoff-Chu sequence, additional preamble sequences are obtained from one or more root sequences with consecutive logical indices until all 64 preamble sequences are found.

[0062] In summary, the set of 64 preamble sequences available for use within a cell for the RACH procedure is generated by cyclic shifts of one or more root Zadoff-Chu sequences.

[0063] Random access preamble - Baseband signal generation The generation of the PRACH baseband signal is defined in section 5.7.3 of Non-Patent Document 1. The time-continuous random access signal s(t) is defined by the following equation.

[0064]

number

[0065] In the formula, 0≦t <T SEQ +T CP And β PRACH is the transmission power P PRACH This is an amplitude scaling factor to match,

number

[0066] The position in the frequency domain is determined by parameter n RA PRB It is controlled by the coefficient K = Δf / Δf RA This takes into account the difference in subcarrier intervals between the random access preamble and the uplink data transmission. The variable Δf RA The subcarrier spacing of the random access preamble and the variable φ (a fixed offset that determines the frequency domain position of the random access preamble within a physical resource block) are both given by the following table (see Table 5.7.3-1 in Non-Patent Literature 1).

[0067] [Table 4]

[0068] Please note that PUSCH has a subcarrier spacing of 15 kHz.

[0069] The preamble sequence in the time domain is of size N. ZC The DFT is used to convert it to the frequency domain. The resulting frequency domain coefficients are the frequency interval Δf RA It is mapped to a subcarrier that has [a specific frequency]. The frequency spacing in PRACH transmission does not match the frequency spacing used for other uplink transmissions (such as PUSCH and PUCCH). The subcarrier mapping further incorporates the position of PRACH in the frequency domain.

[0070] Figure 7 shows side-by-side the mapping of the PRACH preamble to the allocated subcarriers and the mapping of the PUSCH subcarriers. As is clear from the figure, PRACH uses guard bands to avoid data interference at the preamble edges. PRACH is transmitted over a frequency domain resource that corresponds to six consecutive PRBs (physical resource blocks) (i.e., with a frequency bandwidth of 1.08 MHz). These PRBs can be positioned in the middle of the nominal system bandwidth, as shown in Figure 8, or at any other position within the nominal system bandwidth, as shown in Figure 9.

[0071] Random Access Preamble - Implementation of the UE Preamble Sequence Transmitter The following briefly describes a practical example implementation of the PRACH function. As shown in Figure 10, the PRACH preamble can be generated at the system sampling rate by a large IDFT. The DFT block in Figure 10 is dotted to indicate that it is optional, because the sequence can also be directly mapped to the frequency domain at the input of the IDFT. Cyclic shifts can be performed in the time domain after the IDFT, or in the frequency domain before the IDFT through a phase shift.

[0072] Another option for generating a preamble consists of a step using a smaller IDFT (actually an IFFT) and a step shifting the preamble to the desired frequency position through time-domain upsampling and filtering. A cyclic prefix can be inserted before the upsampling and time-domain frequency shift to minimize the requirements for intermediate storage.

[0073] LTE in unlicensed bands: License-Assisted Access (LAA) In September 2014, 3GPP initiated new considerations regarding LTE operation in unlicensed frequency bands. The reasons for extending LTE into unlicensed bands are the limited amount of licensed bands and the ever-growing demand for wireless broadband data. Consequently, unlicensed frequency bands are increasingly viewed as a supplementary means for mobile operators to expand their service offerings. Compared to relying on other radio access technologies (RATs) such as Wi-Fi, the advantage of LTE in unlicensed bands is that operators and vendors can leverage existing and future investments in LTE / EPC hardware in their wireless and core networks by supplementing their LTE platform with access to unlicensed frequency bands.

[0074] However, it must be considered that access to unlicensed frequency bands will inevitably coexist with other radio access technologies (RATs) such as Wi-Fi in those unlicensed bands, and therefore can never match the quality of licensed frequency band access. Thus, LTE operation in unlicensed bands will, at least initially, be seen not as standalone operation in unlicensed bands, but rather as a supplement to LTE in licensed bands. Based on this assumption, 3GPP established the term Licensed Assisted Access (LAA) for operating LTE in unlicensed bands in conjunction with at least one licensed band. However, this does not rule out the possibility of future standalone operation of LTE in unlicensed bands (i.e., not supported by licensed cells).

[0075] The general LAA method currently intended in 3GPP is to make full use of the already established Release 12 Carrier Aggregation (CA) framework, which, as mentioned above, consists of a so-called primary cell (PCell) carrier and one or more secondary cell (SCell) carriers. Carrier aggregation (CA) generally supports both cell self-scheduling (scheduling information and user data are transmitted on the same component carrier) and cross-carrier scheduling between cells (scheduling information via PDCCH / EPDCCH and user data via PDSCH / PUSCH are transmitted on different component carriers).

[0076] Figure 11 illustrates a very basic scenario in which there is a licensed PCell, a licensed SCell 1, and various unlicensed SCells 2, 3, and 4 (illustrated illustratively as small cells). The transmit / receive network nodes of the unlicensed SCells 2, 3, and 4 can be remote radio heads managed by the eNB, or nodes attached to the network but not managed by the eNB. For simplicity, the connections from these nodes to the eNB or network are not explicitly shown in the figure.

[0077] The basic approach currently envisioned by 3GPP involves operating PCell in licensed bands while operating one or more SCell in unlicensed bands. The advantage of this approach is that PCell can be used to reliably transmit control messages and user data requiring high quality of service (QoS), such as voice and video. However, SCell in unlicensed frequency bands inevitably coexist with other radio access technologies (RATs), which can result in a significant decrease in QoS, to varying degrees depending on the scenario.

[0078] It was agreed that LAA (License Aided Access) would focus on the 5GHz unlicensed band. Therefore, one of the most important issues is coexistence with Wi-Fi (IEEE 802.11) systems operating in these unlicensed bands. In order to support fair coexistence between LTE and other technologies (such as Wi-Fi), and further to ensure fairness among multiple different LTE operators in the same unlicensed band, LTE channel access in the unlicensed band must be subject to a certain set of regulations, some of which differ depending on the geographical area and the specific frequency band. A comprehensive description of the regulatory requirements in all regions when operating in the 5GHz unlicensed band is found in Non-Patent Document 2 (incorporated herein by reference) and Non-Patent Document 4 (current version 13.0.0). Regulatory requirements that must be considered when designing LAA procedures vary by region and band, but include Dynamic Frequency Selection (DFS), Transmit Power Control (TPC), Listen Before Talk (LBT), and discontinuous transmission with limited maximum transmission time. The intention of 3GPP is to aim for a single international framework for LAA, which essentially means that when designing a system, all requirements for various regions and 5GHz bands must be taken into consideration.

[0079] For example, in Europe, specific limits on the nominal channel bandwidth are set, as is evident from Section 4.3 of the European standard Non-Patent Document 5 (current version 1.8.1) (incorporated herein by reference). The nominal channel bandwidth is the widest frequency band (including the guard band) allocated to a single channel. The occupied channel bandwidth is the bandwidth containing 99% of the signal power. The device is permitted to operate simultaneously on one or more adjacent or non-adjacent channels.

[0080] When equipment transmits simultaneously on adjacent channels, these transmissions can be considered as a single signal with an actual nominal channel bandwidth of n times the individual nominal channel bandwidth (where n is the number of adjacent channels). When equipment transmits simultaneously on non-adjacent channels, each power envelope is considered individually. The nominal channel bandwidth is always at least 5 MHz. The occupied channel bandwidth is within the range of 80% to 100% of the declared nominal channel bandwidth. In the United States, the minimum occupied channel bandwidth is 500 kHz according to Non-Patent Document 4. In the case of a smart antenna system (equipment with multiple transmission chains), each transmission chain satisfies this requirement. During established communication, equipment is permitted to temporarily operate with an occupied channel bandwidth of less than 80% of the nominal channel bandwidth, with a minimum of 4 MHz.

[0081] The Listen Before Talk (LBT) procedure is defined as a mechanism for applying free channel determination (CCA) before equipment uses a channel. CCA uses at least energy sensing to determine whether another signal is present or absent on the channel, for the purpose of determining whether the channel is occupied or free. European and Japanese regulations require the use of LBT in unlicensed bands. Apart from regulatory requirements, carrier sensing via LBT is one way to ensure fair sharing of unlicensed frequency bands. Therefore, LBT is considered an essential function for fair and friendly operation in unlicensed frequency bands within a single global solution framework.

[0082] In unlicensed frequency bands, channel availability cannot always be guaranteed. In addition, in certain regions such as Europe and Japan, continuous transmission is prohibited, and there are limitations on the maximum duration of transmission bursts in unlicensed frequency bands. Therefore, discontinuous transmission with limited maximum transmission duration is an essential function in LAA. Dynamic Frequency Selection (DFS) is required in certain regions and bands to detect interference from radar systems and avoid co-channel operation with these systems. This objective further contributes to achieving a nearly uniform load on the frequency band. The operation of DFS and the corresponding requirements are related to the master / slave principle. For the purpose of performing radar detection, a master detects radar interference, but in doing so, it can rely on another device associated with the master.

[0083] Operation in the 5GHz unlicensed band is limited to significantly lower transmit power levels in most areas compared to operation in the licensed band, resulting in a smaller coverage area. Even if licensed and unlicensed carriers transmit at the same power, the coverage area supported by unlicensed carriers in the 5GHz band is typically expected to be smaller than that of licensed carriers in the 2GHz band due to greater signal path loss and shadowing effects. As a further requirement for specific regions and bands, Transmit Power Control (TPC) is used to reduce the average level of interference caused by other devices operating in the same unlicensed band.

[0084] Further information is provided in Non-Patent Document 5 (current version 1.8.0), a revised European standard (incorporated herein by reference).

[0085] In accordance with this European regulation concerning LBT, the device must perform a Channel Availability Assessment (CCA) before occupying a radio channel by data transmission. Transmission on an unlicensed channel is only permitted after the channel has been detected as available, for example, based on energy detection. In particular, the device must monitor the channel for a certain minimum time during the CCA (e.g., 20 μs in Europe; see Section 4.8.3 of Non-Patent Document 5). If the detected energy level exceeds the set CCA threshold (e.g., -73 dBm / MHz in Europe; see Section 4.8.3 of Non-Patent Document 5), the channel is considered occupied; conversely, if the detected power level is lower than the set CCA threshold, the channel is considered available. If the channel is determined to be occupied, the device will not transmit on that channel during the next Fixed Frame Period. If the channel is classified as available, the device is permitted to transmit immediately. The maximum transmission duration is limited to facilitate fair resource sharing with other devices operating in the same bandwidth.

[0086] Energy detection in CCA is performed across the entire channel bandwidth (e.g., 20 MHz in the 5 GHz unlicensed band), meaning that the sum of the received power levels of all subcarriers of the LTE OFDM symbol within that channel is the energy level evaluated by the device performing the CCA.

[0087] Furthermore, the total time that an instrument has to transmit on a given carrier without reassessing its availability (i.e., LBT / CCA) is defined as Channel Occupancy Time (see Section 4.8.3.1 of Non-Patent Literature 5). Channel occupancy time is in the range of 1 ms to 10 ms, and the maximum channel occupancy time can be, for example, 4 ms, as currently defined in Europe. In addition, there is a minimum idle time during which the UE is not permitted to transmit after transmission in an unlicensed cell, and this minimum idle time is at least 5% of the channel occupancy time. The UE can perform, for example, a new CCA shortly before the idle period ends. This transmission behavior is schematically shown in Figure 12, which is a quotation from Non-Patent Literature 5 (Figure 2 in this document: "Example of timing for Frame Based Equipment").

[0088] Figure 13 shows the timing between Wi-Fi transmission and LAA UE transmission in a specific frequency band (unlicensed cell). As can be seen from Figure 13, after a Wi-Fi burst, at least a CCA gap is required before the eNB "reserves" the unlicensed cell until the next subframe boundary, for example by transmitting a reservation signal. Then the actual LAA DL burst begins.

[0089] The RACH procedure is also supported in the unlicensed band. To date, it has been agreed that only conflict-free PRACH transmissions are supported in the unlicensed band. Unlike PRACH retransmissions in the licensed band, as mentioned above, whether PRACH retransmissions will be explicitly scheduled by the eNB in ​​the unlicensed band is still under consideration. However, although the standardization work currently agrees to support only conflict-free random access, this may change in the future, and conflict-based random access in unlicensed cells may become possible (in fact, the principles of this invention are applicable to both conflict-free random access procedures and conflict-based random access procedures).

[0090] Considering various regulatory requirements, it is clear that the LTE specification, particularly the random access procedure for operation in unlicensed bands, will require several modifications compared to the current Release 12 specification, which is limited to operation in licensed bands. [Prior art documents] [Non-patent literature]

[0091] [Non-Patent Document 1] 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)” [Non-Patent Document 2] R1-144348, “Regulatory Requirements for Unlicensed Spectrum”, Alcatel-Lucent et al., RAN1#78bis, Sep. 2014 [Non-Patent Document 3] 3GPP TS 36.321 [Non-Patent Document 4] 3GPP Technical Report 36.889 [Non-Patent Document 5] ETSI EN 301 893 [Overview of the project] [Means for solving the problem]

[0092] Exemplary embodiments that do not limit the present invention provide an improved method for performing a random access procedure between user equipment and a radio base station via an unlicensed cell. The independent claims provide exemplary embodiments that do not limit the present invention. Advantageous embodiments are the subject of the dependent claims.

[0093] According to some implementations of the embodiments described herein, the random access procedure is improved, particularly when executed via (one or more) unlicensed cells. More specifically, the portion of the random access procedure that is primarily the preamble sequence (preamble generation, selection, and actual RF transmission) is improved. Thus, the remaining parts of the random access procedure remain (almost) the same as those of a random access procedure designed for licensed access, for example, rather than being the subject of the various embodiments described.

[0094] The following scenario is assumed: In a mobile communication system, user equipment and a radio base station are connected to each other via at least one unlicensed cell. The unlicensed cell can operate as a standalone cell or can be supported by additional licensed cells configured in addition to the user equipment. The unlicensed cell is configured to have a specific frequency bandwidth; that is, the unlicensed cell is operated by the radio base station and user equipment on a channel having a specific frequency bandwidth within the unlicensed frequency band (e.g., 10 MHz, 20 MHz, 40 MHz, or a smaller or larger bandwidth).

[0095] In addition, transmissions in unlicensed cells are regulated, and at least a minimum frequency bandwidth threshold is defined, which indicates the minimum channel occupancy occupied by transmissions through unlicensed cells. The minimum channel occupancy depends on the frequency bandwidth of the unlicensed cell and therefore can vary from channel to channel. The minimum channel occupancy can be defined as a predetermined percentage of the corresponding total frequency bandwidth of the unlicensed cell.

[0096] In this defined scenario, virtually all transmissions performed by the UE (and eNodeB) via an unlicensed cell must comply with this minimum channel occupation requirement. This also applies to random access procedures performed between user equipment and a radio base station, for example, to synchronize the uplink reference timing of user equipment or to send scheduling requests to the radio base station. As part of the random access procedure, the user equipment selects an appropriate random access preamble sequence and then transmits that preamble sequence to the radio base station.

[0097] In some embodiments, the minimum frequency bandwidth threshold defined for transmission over an unlicensed cell is also considered when transmitting a random access preamble sequence to a radio base station as part of a random access procedure. In particular, the random access preamble sequence is transmitted in such a way that it complies with the minimum channel occupancy requirement by at least exceeding the minimum frequency bandwidth threshold defined for an unlicensed cell.

[0098] For this purpose, a specific frequency bandwidth can be determined for transmitting the random access preamble sequence through an unlicensed cell, and this frequency bandwidth is greater than a minimum frequency bandwidth threshold. Such a determination allows for flexibility in dealing with various channel bandwidths of the unlicensed cell and thus in meeting and complying with various minimum channel occupancy requirements. This determination can be performed at the user equipment or the radio base station. In exemplary implementations, the minimum frequency bandwidth threshold (e.g., obtained by simply calculating a predetermined percentage of the frequency bandwidth of the unlicensed cell) is known to both the user equipment and the radio base station, and therefore the frequency bandwidth occupied by the transmission of the random access preamble sequence can be determined independently by the UE and the radio base station. Alternatively, this determination can be performed by one of the two entities (i.e., the UE or the radio base station), and the result can be communicated to the other entity. If the radio base station is the entity responsible for determining the actual frequency bandwidth of the preamble transmission signal, the radio base station maintains control over the frequency bandwidth actually used by the UE to transmit the random access preamble sequence. Such information can be easily transmitted from a radio base station to the UE within the corresponding system information broadcast within the radio cell, or, in the case of uncontested random access, within the corresponding message sent at the beginning of the uncontested random access procedure (for example, within the same message indicating the preamble to be used).

[0099] In this regard, it should be noted that both non-conflict random access procedures and conflict-based random access procedures are supported. In non-conflict random access procedures, the base station transmits corresponding instructional information to the user device, specifically indicating which random access preamble sequence to select from the set of random access preamble sequences available to the UE (and base station), and the user device follows this instructional information. On the other hand, in conflict-based random access procedures, the base station does not provide such instructional information, and the user device autonomously selects the random access preamble sequence to transmit to the base station from the set of random access preamble sequences. The set of random access preamble sequences available for conflict-based random access procedures can be divided into two different subgroups associated with different amounts of transmission resources required via the transmission of random access preamble sequences, as is the case with currently defined standard random access procedures.

[0100] In summary, this allows user devices to comply with the minimum channel occupancy requirements defined for an unlicensed cell when performing random access procedures through that cell.

[0101] The random access procedure can proceed as usual and therefore may include the transmission of a random access response message from the radio base station to the user equipment. This random access response may include, for example, a corresponding uplink resource allocation, a timing alignment instruction, a temporary identifier for the user equipment, and identification information for a random access preamble sequence previously transmitted by the user equipment. Furthermore, upon receiving such a random access response message from the radio base station, the user equipment can use the allocated uplink resources to send further messages to the radio base station. Additionally, if a conflict-based random access procedure is performed, conflict resolution may be necessary and therefore performed between the eNodeB and the UE.

[0102] Below, we describe two different approaches to ensure that the transmission of a random access preamble sequence over an unlicensed cell adheres to the corresponding minimum channel occupancy (i.e., exceeds the minimum frequency bandwidth threshold).

[0103] According to the first aspect, an existing procedure for transmitting a random access preamble sequence is reused, which involves repeating a normal preamble transmission at several different locations in the frequency domain to ultimately occupy at least the required frequency bandwidth of the unlicensed cell in order to comply with regulatory requirements set for such an unlicensed cell. In particular, the random access preamble sequence is selected in the usual manner and transmitted at the corresponding frequency location. Note that a normal / legacy random access preamble transmission occupies a predetermined frequency bandwidth (six PRBs, i.e., 1.08 MHz, as described in the background technology section). Furthermore, several repetitions of this transmission are performed at several different frequency locations so that all preamble transmissions (with repetitions) occupy a frequency bandwidth exceeding the minimum frequency bandwidth threshold of the unlicensed cell. The number of repetitions required to comply with this minimum channel occupancy is determined by the actual frequency bandwidth threshold defined for the unlicensed cell, which is determined by the frequency bandwidth set for the unlicensed cell. Furthermore, the number of repetitions also depends on the predetermined frequency bandwidth (i.e., 1.08 MHz) of a normal / legacy random access preamble transmission. In an exemplary implementation of the first embodiment, the multiple different locations in the frequency domain where the repetitions of the preamble transmission are performed are locations such that the repeated transmissions are adjacent in the frequency domain.

[0104] The improved random access procedure provided for unlicensed cells according to the first embodiment reuses the random access preamble sequence already defined for the normal / legacy random access procedure in licensed cells, as described above. An advantage of this method is that it does not require defining an additional (one or more) set of random access preambles. The same set of random access preamble sequences is available for performing the random access procedure via unlicensed cells and the random access procedure via licensed cells. In particular, according to the first embodiment, when performing the random access procedure via licensed cells, an additional random access preamble sequence is selected from the already generated set and transmitted to the radio base station via the licensed cell, occupying the predetermined frequency bandwidth of the licensed cell (i.e., six PRBs, 1.08 MHz) as described above.

[0105] According to a further implementation of the first embodiment, at least two random access preamble sequences are selected by the user equipment and transmitted together to the radio base station. In particular, at least a second random access preamble sequence is selected, which is different from the first random access preamble sequence selected. The transmission of the second random access preamble sequence is repeated in the same manner, but at a different frequency position than the transmission of the first random access preamble sequence. In particular, in order to comply with minimum channel occupancy, the first and second random access preamble sequences are repeated and transmitted together so as to occupy at least a predetermined frequency bandwidth of the unlicensed cell.

[0106] According to a second aspect, an existing random access procedure, in particular an existing configuration for transmitting a random access preamble sequence, is modified, i.e., the length of the random access preamble sequence and the subcarrier frequency interval used to transmit the random access preamble sequence are selected such that, when combined, the corresponding transmission of the random access preamble sequence exceeds a minimum frequency bandwidth threshold. Hereinafter, a distinction is made between the length of the preamble sequence and the duration of the preamble in the time domain. The former determines the number of subcarriers used. The latter is given by one or more repeating preamble symbols and a cyclic prefix (the duration of the preamble symbols is given by the reciprocal of the subcarrier interval of the preamble) and is not an object of various aspects of the present invention.

[0107] Note that the length of the random access preamble sequence (which essentially corresponds to the number of frequency subcarriers used to transmit the random access preamble sequence) and the subcarrier frequency spacing (which essentially determines how far apart different frequency subcarriers are from each other) together (i.e., by simply multiplying the number of frequency subcarriers by the value of the subcarrier frequency spacing) define the overall frequency bandwidth of the preamble transmission. As a result, by adjusting these two parameters (i.e., the length of the preamble sequence and the subcarrier frequency spacing), the frequency shape / frequency bandwidth of the preamble signal can be controlled to conform to the frequency bandwidth requirements when the preamble signal occupies an unlicensed cell.

[0108] One or both of the two parameters can be controlled by user equipment, by a radio base station, or a combination thereof. In this regard, several different implementations of the second embodiment are possible. For example, the subcarrier frequency spacing can be kept constant while the length of the preamble sequence can be flexibly determined according to the actual amount of frequency bandwidth that the preamble transmission must occupy (depending on the system bandwidth of the unlicensed cell). Alternatively, the length of the preamble sequence can be kept constant while the subcarrier frequency spacing can be flexibly adapted to different minimum channel occupancy requirements. Furthermore, both the length of the preamble sequence and the subcarrier frequency spacing can be flexibly controlled in the preamble transmission to occupy the frequency bandwidth necessary to comply with the minimum channel occupancy requirements of the unlicensed cell.

[0109] In an exemplary implementation of the second embodiment, the user device can generate two different sets of random access preamble sequences: one for (one or more) licensed cells and one for (one or more) unlicensed cells. It should be noted that, considering that the frequency bandwidth occupied by transmitting the random access preamble is greater for unlicensed cells than for licensed cells, the length of the random access preamble sequence for unlicensed cells is likely to be greater than that of the random access preamble sequence for licensed cells. As a result, the two different sets have random access preamble sequences of different lengths. In one exemplary implementation, assuming that the random access preamble sequences are generated from an appropriate root sequence (e.g., a Zadoff-Chu sequence), the corresponding root sequence for generating the random access preamble sequences used in relation to unlicensed cells is longer than the root sequence used to generate the random access preamble sequences for licensed cells. Therefore, when executing a random access procedure via a licensed cell, the corresponding preamble is selected from the corresponding set of licensed cells, whereas when executing a random access procedure via an unlicensed cell, the corresponding preamble is selected from the corresponding set of unlicensed cells.

[0110] Accordingly, in one general first embodiment, the technology disclosed herein provides a method for performing a random access procedure between user equipment and a radio base station in a mobile communication system. The user equipment is configured with at least one unlicensed cell, and the random access procedure is performed over an unlicensed cell having an unlicensed cell frequency bandwidth. A minimum frequency bandwidth threshold is defined for transmission over the unlicensed cell, and the method includes the following steps performed by the user equipment for the random access procedure: The user equipment selects a random access preamble sequence for the random access procedure and determines the frequency bandwidth over which this random access preamble sequence will be transmitted over the unlicensed cell. The determined frequency bandwidth of the random access preamble sequence is at least the minimum frequency bandwidth threshold. The user equipment transmits the random access preamble sequence to the radio base station such that at least the determined frequency bandwidth of the unlicensed cell is occupied.

[0111] Accordingly, in one general first embodiment, the technology disclosed herein provides a user device for performing a random access procedure together with a radio base station in a mobile communication system. The user device is configured with at least one unlicensed cell, and the random access procedure is performed over an unlicensed cell having an unlicensed cell frequency bandwidth. A minimum frequency bandwidth threshold is defined for transmission over the unlicensed cell. The processor of the user device selects a random access preamble sequence for the random access procedure. The processor further determines the frequency bandwidth over which this random access preamble sequence will be transmitted over the unlicensed cell. The determined frequency bandwidth is at least the minimum frequency bandwidth threshold. The transmitter of the user device transmits the random access preamble sequence to the radio base station such that at least the determined frequency bandwidth of the unlicensed cell is occupied.

[0112] Accordingly, in one general first embodiment, the technology disclosed herein provides a radio base station that performs a random access procedure together with user equipment in a mobile communication system. The user equipment is configured with at least one unlicensed cell, and the random access procedure is performed over an unlicensed cell having an unlicensed cell frequency bandwidth. A minimum frequency bandwidth threshold is defined for transmission over the unlicensed cell. The frequency bandwidth over which the user equipment transmits a random access preamble sequence over the unlicensed cell is determined, and the determined frequency bandwidth is at least the minimum frequency bandwidth threshold. A receiver of the radio base station receives a random access preamble sequence for the random access procedure, selected by the user equipment such that at least the determined frequency bandwidth of the unlicensed cell is occupied. The determined frequency bandwidth is at least the minimum frequency bandwidth threshold.

[0113] Further benefits and advantages of the disclosed embodiments will be apparent from this specification and the drawings. These benefits and / or advantages can be provided individually by various embodiments and features of the disclosures herein and in the drawings, and it is not necessary to provide all of them in order to obtain one or more of these benefits and / or advantages.

[0114] These general and specific embodiments can be carried out using systems, methods, computer programs, or any combination thereof.

[0115] The following describes exemplary embodiments in more detail with reference to the attached drawings. [Brief explanation of the drawing]

[0116] [Figure 1] This shows the complex architecture of the 3GPP LTE system. [Figure 2]This shows an example downlink resource grid of subframe downlink slots as defined in 3GPP LTE (Release 8 / 9). [Figure 3] This document outlines the conflict-based RACH procedure defined in 3GPP LTE (as of release 8 / 9), where conflicts may occur. [Figure 4] This shows the non-conflicting RACH procedure defined in 3GPP LTE (as of release 8 / 9). [Figure 5] This shows the structure of the RACH preamble. [Figure 6] This shows the multiplexing of PRACH transmissions with PUSCH and PUCCH. [Figure 7] This shows the mapping of the PRACH preamble to the assigned subcarrier. [Figure 8] This shows the different locations of PRACH within the nominal frequency system bandwidth. [Figure 9] This shows the different locations of PRACH within the nominal frequency system bandwidth. [Figure 10] This shows an example of the functional structure of a PRACH preamble transmitter. [Figure 11] This illustrates an exemplary LAA scenario that includes several licensed and unlicensed cells. [Figure 12] This shows the transmission behavior during LAA transmission. [Figure 13] This shows the timing between Wi-Fi transmit bursts and LAA UE downlink bursts in an unlicensed cell. [Figure 14A] The frequency bandwidth of the PRACH signal transmission according to the first embodiment, which uses a repeating mechanism to comply with the minimum channel occupancy requirement, is shown for a 20 MHz system bandwidth of the license cell. [Figure 14B]The frequency bandwidth of PRACH signal transmission according to a first embodiment, which uses a repeating mechanism to comply with minimum channel occupancy requirements, is shown for a 20 MHz system bandwidth of an unlicensed cell. [Figure 15A] These figures show the frequency bandwidth of PRACH signal transmission according to the first embodiment, for a system bandwidth of 10 MHz for the license cell. [Figure 15B] This shows the frequency bandwidth of PRACH signal transmission according to the first embodiment, for a system bandwidth of 10 MHz for an unlicensed cell. [Figure 16] This is based on the implementation configuration shown in Figure 15B, and in particular, it illustrates the various subcarriers that carry two adjacent PRACH transmit / repeat PRACH signals according to the first embodiment. [Figure 17A] This shows the power spectral density of PRACH transmission through a licensed cell. [Figure 17B] The power spectral density of the improved PRACH transmission via an unlicensed cell according to the first embodiment is shown. [Figure 18] This shows an exemplary implementation of the UE transmitter chain according to the first embodiment. [Figure 19] The improved first embodiment shows a repeating pattern in which at least two preambles are selected to be transmitted through the repetition. [Figure 20] The improved first embodiment shows a repeating pattern in which at least two preambles are selected to be transmitted through the repetition. [Figure 21] The improved first embodiment shows a repeating pattern in which at least two preambles are selected to be transmitted through the repetition. [Figure 22A] The frequency bandwidth of the PRACH signal transmission is shown according to a second embodiment, which adapts the parameters of the PRACH signal transmission to comply with the minimum channel occupancy requirement in the case of a 20 MHz system bandwidth for a license cell. [Figure 22B]The frequency bandwidth of the PRACH signal transmission is shown according to a second embodiment, which adapts the parameters of the PRACH signal transmission to comply with the minimum channel occupancy requirement in the case of a 20 MHz system bandwidth for an unlicensed cell. [Figure 23A] The frequency bandwidth for PRACH signal transmission according to the second embodiment is shown for a system bandwidth of 10 MHz for the license cell. [Figure 23B] The frequency bandwidth for PRACH signal transmission according to the second embodiment is shown for a 10 MHz system bandwidth of an unlicensed cell. [Figure 24A] This shows the power spectral density of PRACH transmission through a licensed cell. [Figure 24B] Each shows the power spectral density of the improved PRACH transmission via an unlicensed cell according to the second embodiment. [Figure 25] Figures 22A and 22B show various subcarriers that transmit the PRACH signal, particularly according to the second embodiment. [Figure 26] Figures 23A and 23B show various subcarriers that transmit the PRACH signal, particularly according to the second embodiment. [Figure 27] This shows an exemplary implementation of a transmitter chain for the UE according to the second embodiment. [Figure 28] This shows the frequency bandwidth of PRACH signal transmission for a 40 MHz system bandwidth according to a third embodiment, which combines the first and second embodiments. [Modes for carrying out the invention]

[0117] A "mobile station," "mobile node," "user terminal," or "user equipment" is a physical entity within a communication network. A single node may have several functional entities. A functional entity means a software or hardware module that performs a predetermined set of functions and / or provides a predetermined set of functions to another functional entity in the node or network. A node may have one or more interfaces through which it attaches itself to communication equipment or a communication medium, and the node can communicate through these interfaces. Similarly, a network entity may have logical interfaces through which it attaches functional entities to communication equipment or a communication medium, and the network entity can communicate with other functional entities or partner nodes through these logical interfaces.

[0118] The term "wireless resources" as used in the claims and this application should be understood in a broad sense to mean physical wireless resources (such as time-frequency resources).

[0119] The terms “unlicensed cell” or “unlicensed carrier” as used in the claims and this application should be understood broadly as cells / carriers operating in an unlicensed frequency band having a specific frequency bandwidth. Correspondingly, the terms “licensed cell” or “licensed carrier” as used in the claims and this application should be understood broadly as cells / carriers operating in a licensed frequency band having a specific frequency bandwidth. These terms should be understood, exemplarily, in the context of 3GPP and work item “Licensed-Assisted Access” as of Release 12 / 13.

[0120] The term “minimum frequency bandwidth threshold” as used in the claims and in this application should be understood broadly as the minimum channel occupancy in an unlicensed cell (one or more cells). In other words, transmissions over an unlicensed cell occupy at least the amount set by this threshold with respect to frequency. Minimum channel occupancy is given, for example, by regulations defined for a particular geographical area, such as 80% of the system bandwidth in Europe. Thus, in Europe, transmissions over an unlicensed cell with 20 MHz must occupy at least 16 MHz.

[0121] The terms “random access procedure” as used in the claims and in this application may, in one exemplary embodiment, be interpreted as a random access procedure of the 3GPP standard described in the background art section. The terms “random access preamble sequence,” “preamble sequence,” “preamble,” “RACH preamble,” and “preamble signature” may be used synonymously with each other for the purpose of meaning a complex sequence transmitted by the UE during a random access procedure (preamble messages transmitted as described in one exemplary embodiment in relation to step 301 in Figure 3 and step 401 in Figure 4).

[0122] The term “repeatedly” as used in the claims and in this application should be interpreted broadly as “performing a particular action several times.” In this particular case, the transmission of the preamble is performed several times, but at different locations in the frequency domain.

[0123] The terms “occupy” and “occupy a frequency bandwidth” as used in the claims and in this application may be interpreted broadly to mean that a particular transmission of a signal / message / preamble is performed by using all of the frequencies in a particular frequency bandwidth.

[0124] As explained in the background technology section, 3GPP is currently in the process of introducing License-Assisted Access (LAA). While some agreements have already been reached regarding LAA, agreement has not yet been reached on several key issues concerning LAA. Furthermore, it is clear that in order to support the RACH procedure in unlicensed bands, it would be advantageous to make some changes to the LTE specification compared to the current specification, which is limited to operation in licensed bands.

[0125] One simple solution for introducing a random access procedure in LAA is to apply the existing random access procedure in licensed cells to unlicensed cells as well, including the existing preamble format, signal shape, and transmission procedure described in the background section. In this case, the CCA (Free Channel Check) can be performed on the UE side immediately before a PRACH transmission opportunity, or alternatively, on the eNodeB side before scheduling a RRACH transmission opportunity. Further alternative solutions may omit the CCA associated with PRACH scheduling and transmission; however, omitting the CCA may result in transmission collisions, potentially causing problems with other nodes operating on the same radio channel. Note that whether or not a CCA is ultimately required depends on the regulations of the region where the system operates (see the background section and Non-Patent Literature 4).

[0126] However, this simple method also has drawbacks. In particular, as explained in the background technology section, European regulations require that each transmission in the unlicensed band following a CCA (Free Channel Assessment) must occupy at least 80% of the nominal channel bandwidth. Similar regulations can be found in other countries, for example, in the United States, where the minimum transmit bandwidth is 500 kHz (see Non-Patent Literature 4). Assuming a nominal channel bandwidth of 20 MHz in LTE operation in the unlicensed band (see Non-Patent Literature 4), the minimum frequency bandwidth would be 16 MHz as a result of the 80% minimum channel occupancy stipulated in Europe. On the other hand, a PRACH transmission following the existing definition in the licensed band occupies only six consecutive PRBs, regardless of channel bandwidth, which is 1.08 MHz (i.e., only 5.4% of the 20 MHz nominal channel bandwidth). Therefore, this simple solution (applying the existing definition of a PRACH transmission to an unlicensed cell) does not satisfy the minimum channel occupancy requirement given by the European regulations.

[0127] In addition, it should be noted that this minimum channel occupancy depends on the actual channel bandwidth of the unlicensed cell and therefore can vary from cell to cell. In other words, the transmission of the random access preamble must be adjusted to the channel bandwidth so as to comply with the minimum channel occupancy requirement defined for the unlicensed cell. In contrast, existing random access procedures, particularly the transmission of the random access preamble, have a fixed bandwidth, i.e., they always use six PRBs regardless of the actual channel bandwidth of the (licensed) cell. Therefore, a further drawback of using existing mechanisms to transmit the random access preamble through an unlicensed cell is the lack of flexibility to comply with the minimum channel occupancy requirement, which can actually vary depending on the channel bandwidth of the unlicensed cell.

[0128] The inventors have conceived the following exemplary embodiments in order to mitigate one or more of the problems described above.

[0129] Specific implementations of various embodiments are carried out within the broad specifications provided by the 3GPP standard, some of which are described in the background section, with particularly important features related to the various embodiments added as described below. It should be noted that while these embodiments may be advantageously used in mobile communication systems such as 3GPP LTE-A (Release 10 / 11 / 12 / 13) as described in the background section, the embodiments are not limited to use in these specific exemplary communication networks.

[0130] The following description should be understood not as limiting the scope of this disclosure, but merely as an example of embodiments for a deeper understanding of this disclosure. Those skilled in the art will recognize that the general principles of this disclosure as described in the claims can be applied to various scenarios in ways not expressly described herein. Several assumptions have been made for illustrative purposes, but these assumptions do not limit the scope of the embodiments described below.

[0131] Furthermore, as described above, the following embodiments can be implemented in a 3GPP LTE-A (Release 12 / 13) environment. These various embodiments primarily enable improved random access procedures, in particular, improved transmission of random access preambles. However, other functions (i.e., functions not modified by the various embodiments) remain exactly the same as those described in the background section, or can be modified without affecting the various embodiments. For example, functions and procedures that lead to the execution of improved random access procedures (such as the need for uplink synchronization and the need to send scheduling requests) and the remaining steps of the random access procedure (such as random access responses and conflict resolution).

[0132] Below, we describe three embodiments for solving the above (one or more) problems, which are explained by using the following exemplary scenarios, which are designed to facilitate the explanation of the principles of the embodiments. However, these principles can also be applied to other scenarios, some of which are explicitly stated in the following explanation.

[0133] As described in the background technology section, 3GPP plans to enhance the current system by introducing License-Assisted Access (LAA), which includes the use of unlicensed cells operating on one or more channels in the unlicensed frequency band. The following assumes such a scenario, namely, that the UE has at least one licensed cell and at least one unlicensed cell configured. While the following description is based on this scenario, various embodiments focus on performing random access procedures in the unlicensed cell, and therefore various embodiments also apply to scenarios where the unlicensed cell operates alone (i.e., without a corresponding licensed cell).

[0134] Unlicensed cells can be set up between the eNodeB and the UE in the usual manner, as described in the Background Technology section. Thus, unlicensed cells operate on specific channels in the unlicensed frequency band with a specific frequency bandwidth (also referred to as the nominal channel bandwidth in some European standards) (e.g., 10 MHz, 20 MHz, 40 MHz, or (in the future) smaller or larger bandwidths). As detailed in the Background Technology section, operation in unlicensed cells is regulated in various ways, for example in Europe, according to the European standard Non-Patent Document 5. In Europe (and other regions), in particular, a minimum channel occupancy requirement is defined for the channels of unlicensed cells, and in Europe, for example, the channel bandwidth occupied in an unlicensed cell is within the range of 80% to 100% of the declared nominal channel bandwidth of that unlicensed cell. Therefore, transmissions in unlicensed cells (with very few exceptions) must comply with this minimum channel occupancy requirement so that the transmission occupies the corresponding frequency bandwidth portion of the total frequency bandwidth of the unlicensed cell. Given that unlicensed cells can have varying nominal channel bandwidths, the minimum frequency bandwidth that must be occupied (as a percentage of the nominal channel bandwidth) will differ between channels with different nominal channel bandwidths.

[0135] In the following embodiments, it is assumed that both the eNodeB and the UE are aware of a specific minimum channel occupancy to be followed. The UE and eNodeB are aware of a minimum frequency bandwidth threshold, which is determined by the actual system bandwidth on which the unlicensed cell is established. Several different possible ways exist to achieve this. In one alternative, both the UE and the eNodeB independently determine a specific minimum frequency bandwidth threshold and arrive at the same value by both following the same determination rule. In another alternative, the eNodeB determines a specific minimum frequency bandwidth threshold and accordingly informs the UE of this threshold, for example, in a system information broadcast message, or in an RRC connection establishment message, or, in the case of a non-conflict random access procedure, in a random access preamble assignment message sent at the beginning of the random access procedure (see message 401 in Figure 4). According to yet another alternative, the UE determines a specific minimum frequency bandwidth threshold and accordingly informs the eNodeB of this threshold. In either case, both the UE and the eNodeB have the same understanding of the minimum frequency bandwidth threshold that the transmission of the preamble should occupy.

[0136] This minimum frequency bandwidth threshold represents the lower limit of the frequency bandwidth that the transmission of the random access preamble must occupy. Furthermore, the actual frequency bandwidth used by the transmission of the random access preamble must also be known by both the UE and the eNodeB so that the eNodeB can successfully blind-decode the random access preamble. The actual frequency bandwidth of the preamble transmission can be determined by the UE, the eNodeB, or both, as with determining the minimum frequency bandwidth threshold, and this information can be exchanged between the two entities if necessary. Further details will become clear from the detailed descriptions of the various embodiments.

[0137] As previously stated in the Background Technology section, it has been agreed that, currently, only non-conflict RACH procedures are supported in unlicensed cells, the details of which are described in the Background Technology section. Therefore, the assumed scenarios are subject to this initial agreement, but it should be understood that the principles of the present invention in various embodiments are equally applicable to conflict-based RACH procedures. In particular, as will become apparent below, various embodiments of the present invention focus on the transmission of random access preambles, and therefore various embodiments of the present invention are equally applicable to conflict-based RACH procedures in which the UE autonomously selects an appropriate random access preamble sequence (from an appropriate set of preambles) and to non-conflict RACH procedures in which the UE receives corresponding instructional information from the eNodeB regarding which random access preamble sequence (from that set of preambles) is used for the random access procedure. In a competition-based RACH procedure, as described in the background section, it is possible to send an additional 1-bit of information that gives information about the amount of transmission resources needed to send the next message (msg3, 303 in Figure 3), allowing the UE to choose between two subgroups (the set of preambles available for a competition-based random access procedure is divided into these two subgroups).

[0138] In the following embodiments, we further assume that the random access procedure does not need to be modified except for the transmission (and reception) of the random access preamble. As a result, the overall structure and order of the random access procedure, as illustrated in the background section, may remain the same, and only changes are introduced to the random access procedure in relation to the transmission of the random access preamble, as described in the various embodiments below. For example, the standardized procedure for triggering the random access procedure and other messages of the random access procedure (random access response messages 302, 403, scheduled transmission 303, conflict resolution message 304, random access preamble assignment 401, etc.) do not need to be modified. Therefore, to avoid repetition of explanation, we may refer to the corresponding paragraphs in the background section above.

[0139] Therefore, assuming that a random access procedure is triggered in an unlicensed cell, the following embodiments provide several implementations of an improved random access procedure that is executed in an unlicensed cell.

[0140] First Embodiment The following describes in detail a first embodiment for solving one or more of the above problems. Various implementations of the first embodiment are described below using the exemplary scenarios introduced above.

[0141] In short, the first embodiment reuses existing definitions of how to transmit a random access preamble to a radio base station, but introduces a repetition mechanism as follows: The repetition mechanism in the UE allows the normal transmission of the random access preamble to be repeated as many times as needed at different frequency positions in the frequency domain, such that the combined transmission of the random access preamble occupies at least the frequency bandwidth required to comply with the minimum channel occupancy requirements defined for an unlicensed cell. This not only allows for the reuse of existing definitions and standardization of preamble transmissions as much as possible (and as much as necessary), but at the same time, the repetition scheme allows the entire PRACH transmission (i.e., including the entire preamble (repetition)) to be flexibly adapted to various bandwidth requirements by simply adding further repetitions of the “standard” PRACH signal with respect to frequency until the minimum frequency bandwidth threshold is exceeded. More specifically, the exemplary implementation of the first embodiment follows, as far as possible, the normal random access procedure in a licensed cell, as detailed in the background section. This includes, for example, the UE generating a set of random access preambles, similar to the method described in the background section. Therefore, for example, this involves using the Zadoff-Chu root sequence explicitly shown by eNodeB and generating 64 different random access preamble sequences from this sequence by using cyclic shifts. The set of random access preambles thus generated is available not only for use in executing random access procedures through licensed cells, but also for use in executing random access procedures through unlicensed cells. Furthermore, the random access preamble can therefore have the same structure as the structure described in relation to Figure 5, and can have the same sequence length for different preamble formats (i.e., 839 for formats 0-3, or 139 for format 4).The same applies to the 1.25 kHz subcarrier interval for preamble formats 0-3 and the 7.5 kHz subcarrier interval for preamble format 4, which can be applied equally according to this implementation. Furthermore, the same PRACH duration (i.e., T) as before applies. CP and T SEQ It is conceivable that combinations of these elements can be considered.

[0142] Assuming a random access procedure without conflicts, the UE receives corresponding instruction information from the eNodeB regarding which particular random access preamble from the generated set will be used for the random access procedure. Therefore, the UE selects the indicated random access preamble from the available set of preambles and prepares to send that preamble to the eNodeB as follows:

[0143] A specific exemplary implementation of the first embodiment will be described in detail. First, it is assumed that licensed and unlicensed cells with a nominal channel bandwidth of 20 MHz are configured (the nominal channel bandwidth may also be referred to as the "system bandwidth"). The following description will be made with reference to Figures 14A and 14B, which show PRACH transmissions performed by the corresponding UEs supporting LAA in the licensed and unlicensed cells, respectively. As is evident from Figure 14A, the transmission of the Random Access Preamble (PRACH) through the licensed cell is typically performed in six PRBs, i.e., with a frequency bandwidth of 1.08 MHz (6 × 180 kHz). The corresponding transmission of the Random Access Preamble performed through the unlicensed cell must occupy at least 16 MHz of the channel bandwidth of that unlicensed cell in order to comply with the minimum channel occupancy parameter of 80% as specified in Europe (see Figure 14B). To achieve this increased channel occupancy, the first embodiment proposes introducing a repetition mechanism, which constitutes an entire PRACH transmission exceeding a minimum frequency bandwidth threshold of 16 MHz by repeating a “normal” preamble transmission at multiple different frequency positions. As shown in Figure 14B, the normal PRACH transmission can be repeated as many times as needed until the minimum channel occupancy of 16 MHz is exceeded. In this particular case, 14 repetitions of the PRACH transmission are performed, and thus a total of 15 normal PRACH transmissions are performed, occupying 16.2 MHz using 90 PRBs.

[0144] In the following exemplary scenario in Figures 15A and 15B, it is assumed that licensed and unlicensed cells are configured with a nominal channel bandwidth of 10 MHz. Correspondingly, as a result of 80% minimum channel occupancy, the coupled random access preamble transmission must occupy a minimum frequency bandwidth of at least 8 MHz. As explained in relation to Figures 14A and 14B, Figure 15A discloses a PRACH transmission (typically spanning 6 PRBs) through a licensed cell. In contrast, as shown in Figure 15B, for the unlicensed cell, there are 7 repetitions, and therefore 8 PRACH transmissions, occupying a total of 48 PRBs, 8.64 MHz (48 × 180 kHz).

[0145] In a particular exemplary implementation, different offsets φ can be used in different repetitions of the preamble transmission shown in Figures 14B and 15B, and the offset φ can be directly derived by the UE from the initial offset φ (7 or 2 depending on the preamble format), for example, from the corresponding table in the background art section. The various offsets can be selected so that individual preamble transmissions are directly adjacent but do not overlap each other. Alternatively, although not shown in the figures, it may be possible to allow a slight overlap between two adjacent preamble transmissions such that only one guard band separates the two preamble transmissions (instead of two guard bands as is evident from Figure 16). For this purpose, the frequency offset of the repetitions must be set according to the overlap.

[0146] Figure 16 is based on the example scenario in Figure 15B, and has been enlarged to show the various subcarriers and guard bands for two adjacent preamble transmissions out of eight preamble transmissions. As is evident from the figure, a typical subcarrier frequency spacing of 1.25 kHz and 839 subcarriers constituting the PRACH signal are assumed (see also Figure 7 and the corresponding parts in the Background Technology section).

[0147] The number of repetitions required to comply with the minimum channel occupancy requirements specified for unlicensed cells can be autonomously determined by the UE and eNodeB through a simple calculation based on the frequency bandwidth occupied by a normal preamble transmission (i.e., 1.08 MHz) and the minimum frequency bandwidth threshold (e.g., 16 MHz for a 20 MHz system bandwidth, and 8 MHz for a 10 MHz system bandwidth). Alternatively, the number of repetitions to be used when transmitting the preamble can be explicitly indicated to the UE by the eNodeB. Or, the number of repetitions for various system bandwidth settings can be defined in the standard. As is evident from Figures 14B and 15B, in the hypothetical scenarios, 14 and 7 repetitions are required, respectively; in other words, 15 and 8 PRACH transmissions are required, respectively. Thus, the eNodeB can successfully decode the PRACH transmissions. Alternatively, the number of repetitions for each nominal channel bandwidth can be predefined in the standard and therefore known to both the UE and eNodeB.

[0148] In an exemplary implementation of the first embodiment, it is assumed that each PRACH transmission is transmitted by the UE with the same transmit power as that used for a normal PRACH transmission (in a licensed cell). Specifically, Figure 17A shows a PRACH transmission by the UE over a licensed cell with a specific transmit power and a specific power spectral density, this PRACH transmission spanning six normal PRBs, 1.08 MHz. The transmit power is determined in a conventional manner (e.g., by open-loop estimation with fully compensated path losses). The UE estimates path losses by averaging measured Reference Signal Received Power (RSRP). Thus, Figure 17A shows such a PRACH transmission over a licensed cell. Figure 17B appropriately shows a coupled PRACH transmission over an unlicensed cell, as described above in relation to Figure 15B for the first embodiment, this transmission spanning 48 PRBs, 8.64 MHz. As is evident from Figure 17B, this implementation of the first embodiment assumes that all different transmissions (i.e., all repetitions) of a normal PRACH transmission have the same power spectral density (i.e., are transmitted with the same transmit power). Such transmissions can be carried out at the UE by applying the same transmit power value set for a normal PRACH transmission to repetitions at multiple different frequency positions via an unlicensed cell.

[0149] Alternatively, the UE can transmit various PRACH transmissions using different transmit power levels, rather than using the same transmit power value. For example, all of the various PRACH transmissions can be transmitted at a lower transmit power (e.g., half the transmit power). One particular way to set the transmit power is to set the transmit power for each of the various PRACH transmissions so that the total transmit power (i.e., the transmit power used to transmit all of the PRACHs (e.g., a total of 8 transmissions in Figure 17B)) is the same as the transmit power used to transmit one PRACH through the license cell. Thus, the power spectral density decreases with the total number of PRACH transmissions (e.g., PSD / 8), but the total transmit power used by the UE for PRACH transmissions remains the same.

[0150] Furthermore, Figure 18 shows an exemplary implementation of the transmitter of the UE according to the first embodiment, as described in the background art section in relation to Figure 10. As is evident from Figure 18, the repeating mechanism described above can be implemented between the DFT and subcarrier mapping in the transmission chain in various implementations of the first embodiment. The DFT and subcarrier mapping achieve the positioning of the PRACH signal in the frequency domain, and thus the generated preamble is processed in various DFTs to obtain the resulting frequency sample (N ZC By positioning the subcarrier at the corresponding frequency position, the length N ZC The same generated preamble (left portion) can be repeated at multiple different frequency positions in the frequency domain, as illustrated in Figures 14B and 15B.

[0151] Further implementations of this first embodiment offer improvements by allowing different preamble sequences to be used for different iterations. These improved implementations are described in relation to Figures 19, 20, and 21. In short, by allowing different preamble sequences to be used for different iterations and appropriately determining the various iteration patterns between the eNodeB and the UE, additional information can be encoded throughout the PRACH transmission.

[0152] Additional information may include, for example, an indicator of channel occupancy observed by the UE sending the PRACH. Observed channel occupancy can be defined by the ratio of successful to unsuccessful CCAs (Free Channel Assessments) on the UE side prior to the PRACH transmission. A threshold, such as 0.5, can be defined for this ratio. In this case, the transmitted PRACH will convey whether this ratio is higher than, equal to, or lower than the defined threshold. The eNB can use this information when scheduling downlink data transmissions to the UE, and a low ratio can be expected to indicate lower quality of service.

[0153] In the implementation above the first embodiment, it is assumed that only one preamble (from the available preambles) is used throughout the entire PRACH transmission (including repetitions), following the standard procedure for normal PRACH transmissions, i.e., the same preamble is transmitted repeatedly at multiple different frequency positions. Therefore, only one preamble (indicated by corresponding instruction information from, for example, eNodeB) is selected by the UE and used for each PRACH transmission. However, in further implementations of the first embodiment, two or more different preambles transmitted by the UE may be used in the same random access procedure via the unlicensed cell, as described below.

[0154] First, assume that two different preambles are selected by the UE to perform a random access procedure via an unlicensed cell. In one implementation, both different preambles can be individually indicated by the eNodeB. Alternatively, or in addition to this, a certain correspondence can be defined between the different preambles, so that when a particular random access preamble is indicated by the eNodeB (or when the UE autonomously selects a random access preamble in the case of competition-based RACH), it will correspondingly select one or more additional random access preambles associated with the indicated (or autonomously selected) random access preamble. To improve transmission performance, a particular correspondence can be optimized by appropriately defining the correspondence so that the overall PAPR (Peak-to-Average Power Ratio) or CM (Cubic Metric) of the transmission is minimized.

[0155] Therefore, different PRACH transmissions are performed using different preambles. In the exemplary scenario of Figure 19, assuming a system bandwidth of 20 MHz, preambles A and B are used alternately in the frequency domain, thus forming a repeating pattern ABABABAB... for transmitting 15 PRACH transmissions. Similarly, Figure 20, assuming two different preambles A and B, shows another exemplary repeating pattern, in which case preamble A is used for (approximately) half of the total frequency bandwidth of the combined PRACH transmissions, and preamble B is used for the other half (i.e., AAAAAAABBBBBBBB). In the exemplary implementation of Figure 21, a total of three different preambles (preambles A, B, and C) are assumed, having the exemplary repeating pattern AAAAABBBBBCCCCC.

[0156] In one exemplary implementation, the UE can select the repetition pattern to use from, for example, a limited number of pre-configured repetition patterns. The number of pre-configured repetition patterns can be set, for example, by the eNodeB and communicated to the UEs (one or more) within its cell, or it can be defined in a standard.

[0157] Each pre-configured repeating pattern can be associated with, for example, a specific piece of information, and so by the UE selecting a particular repeating pattern, that specific information is already encoded. For example, when eNodeB blind-decodes a PRACH repeat, it successfully decodes various PRACH transmissions according to the repeating pattern selected by the UE, and thus derives the encoded information.

[0158] Information regarding the required transmission resources can be encoded using a repeating pattern. Assuming two different repeating patterns are available for use by the UE, one repeating pattern can be associated with a larger amount of transmission resources, while the other can be interpreted to indicate that only a small amount of transmission resources is required by the UE.

[0159] Another important piece of information, as mentioned above, is the statistical information on channel occupancy observed from the perspective of the UE. The pattern ABABABAB... may indicate a channel occupancy higher than, for example, 0.5, while the pattern BABABABA... may indicate a channel occupancy equal to or less than 0.5.

[0160] Second Embodiment Below, we describe in detail a second embodiment that addresses one or more of the above problems. The principle behind the second embodiment is entirely different from the iterative mechanism described in relation to the first embodiment. Various implementations of the second embodiment are described below in detail using the exemplary scenario introduced above.

[0161] In short, the second embodiment adapts one or more configuration parameters for transmitting the PRACH signal in order to spread the signal over the required frequency bandwidth (i.e., to comply with the minimum channel occupancy requirement for unlicensed cells), instead of performing various repetitions of the normal PRACH signal as in the first embodiment. The configuration parameter is the length of the RACH preamble sequence (i.e., N ZC ) and the subcarrier frequency interval (i.e., Δf) of the subcarrier used to transmit the RACH preamble. RA These two parameters, in combination, essentially define the total frequency bandwidth of the PRACH signal transmission. The frequency bandwidth of a normal PRACH transmission is always 1.08 MHz, independent of the system bandwidth of the channel on which the PRACH is transmitted, as explained in the background technology section. For example, in preamble formats 0 to 3, the subcarrier frequency spacing is 1.25 kHz, and there are 864 subcarriers (839 subcarriers + 2 × 12.5 subcarriers for the guard band) (see Figure 7), thus having a frequency bandwidth of 1.08 MHz. In preamble format 4, the subcarrier frequency spacing is 7.5 kHz, and there are 144 subcarriers (139 subcarriers + 2 × 2.5 subcarriers for the guard band), also having a frequency bandwidth of 1.08 MHz. The number of subcarriers used to transmit the PRACH signal is equal to the length of the preamble sequence N. ZC It is the same because the preamble sequence is initially N ZC It is converted into individual frequency samples, each corresponding to N ZCThis is because it is mapped to the subcarrier of the book. This implementation method is generally applied in LTE because, as a characteristic of ZC sequences, the DFT of a ZC sequence is also a weighted cyclically-shifted ZC sequence. Furthermore, it should be noted that when the length of the preamble sequence is a prime number, the optimal cyclic cross-correlation is achieved between any pair.

[0162] Therefore, the frequency bandwidth of PRACH transmissions can be controlled by appropriately selecting different values ​​for these two parameters in order to comply with the minimum channel occupancy requirements specified for unlicensed cells. For this purpose, one or both of the two parameters can be changed compared to a normal / legacy PRACH signal transmitted in an unlicensed cell. ZC and Δf RA For this, there are many different combinations, which are determined by the actual minimum frequency bandwidth threshold that the PRACH signal transmission must occupy at least.

[0163] In the following, as already done in the first embodiment, we assume two different system bandwidths of 10 MHz and 20 MHz, as shown in Figures 22A, 22B, 23A, and 23B, respectively. Furthermore, assuming the same 80% minimum channel occupancy requirement in Europe, we adhere to minimum frequency bandwidth thresholds of 8 MHz and 16 MHz, respectively, when performing random access procedures via unlicensed cells (for example, when sending a preamble from the UE to the eNodeB as part of a random access procedure).

[0164] For example, the subcarrier frequency spacing can be maintained at 1.25 kHz (or 7.5 kHz for preamble format 4), the same as for normal / legacy PRACH transmissions with preamble formats 0-3, and therefore only the length of the preamble sequence can be left as a parameter to control according to the required minimum frequency bandwidth threshold. With a 1.25 kHz spacing and a frequency bandwidth threshold of 8 MHz, at least 6400 subcarriers are "required" to achieve a PRACH signal with an 8 MHz frequency bandwidth. For an improved preamble design that maximizes the number of ZC sequences with optimal cross-correlation characteristics, a preamble sequence of prime number length should be chosen. In the case described above, a preamble length of 6421 should be chosen, resulting in a frequency bandwidth of 8.026 MHz.

[0165] In contrast, the preamble sequence length, and therefore the number of subcarriers for transmitting the preamble signal, can be kept the same as in normal / legacy PRACH transmission (i.e., 839 for preamble formats 0-3 and 139 for preamble format 4). In this particular case, it is possible to change the frequency bandwidth of the PRACH signal by adapting the subcarrier frequency spacing parameter. For example, with a preamble of length 839 (a total of 864 subcarriers including an additional subcarrier for two guard bands) and a frequency bandwidth threshold of 8 MHz, a subcarrier frequency spacing of at least 9.26 kHz is required.

[0166] Alternatively, both the preamble length and the RACH subcarrier frequency spacing can be modified to comply with the minimum channel occupancy requirements. In the above case, with an unlicensed cell having a system bandwidth of 10 MHz, a subcarrier frequency spacing of 7.5 kHz can be assumed, in which case there must be a total of at least 1067 subcarriers for the PRACH signal (including the actual preamble subcarriers and additional subcarriers for the guard band).

[0167] It should be noted that, generally speaking, in order to minimize the orthogonality loss in the frequency domain between the preamble subcarriers and the subcarriers of the surrounding uplink data transmissions, the subcarrier frequency spacing used for PRACH transmissions should be an integer fraction of the subcarrier frequency spacing used for PUSCH transmissions (i.e., 15 kHz) (e.g., 1 kHz, 2.5 kHz, 3 kHz, 5 kHz, 7.5 kHz, 15 kHz, etc.). Conversely, the subcarrier spacing for PUSCH should be an integer multiple of the subcarrier spacing for PRACH. Furthermore, in order to facilitate the multiplexing of PRACH and PUSCH, PRACH should be allocated a frequency bandwidth equal to an integer multiple of the resource block frequency bandwidth (i.e., an integer multiple of 180 kHz). In addition, for an improved preamble design that maximizes the number of ZC sequences with optimal cross-correlation characteristics, a preamble sequence of prime length should be chosen. To obtain optimal results, the design constraints described above can be more easily achieved when both parameters (i.e., preamble length and subcarrier frequency spacing) are variables, as will be explained below.

[0168] First, we assume a system including an unlicensed cell with a system bandwidth of 20 MHz and a corresponding minimum frequency bandwidth threshold of 16 MHz. Considering that the resulting frequency bandwidth of the PRACH transmit signal should be a multiple of the 180 kHz resource block bandwidth, we can assume a total frequency bandwidth of 16.02 MHz spanning 89 PRBs for the PRACH signal, which facilitates frequency multiplexing of PRACH and PUSCH as described above. In an exemplary implementation, a subcarrier frequency spacing of 15 kHz can be determined, resulting in a number of subcarriers of 1068. The nearest prime number smaller than 1068 is 1063, and therefore we can predict 5 subcarriers for two guard bands (i.e., 2.5 subcarriers per guard band). This exemplary implementation of the PRACH signal according to the second embodiment is shown in Figures 22B and 25. In this configuration of the PRACH transmit signal, the subcarrier frequency spacing is an integer fraction of the PUSCH subcarrier frequency spacing (which minimizes the loss of orthogonality in the frequency domain), and the length of the preamble sequence is a prime number (which improves the cross-correlation characteristics).

[0169] Next, we assume an exemplary system with an unlicensed cell system bandwidth of 10 MHz and a corresponding minimum frequency bandwidth threshold of 8 MHz. Considering that the resulting bandwidth of the PRACH transmit signal should be a multiple of the 180 kHz resource block bandwidth, we can assume a total frequency bandwidth of 8.1 MHz spanning 45 PRBs in total for the PRACH signal. We can assume a subcarrier frequency spacing of 7.5 kHz. As a result, there will be a total of 1080 subcarriers for the PRACH signal (including the actual preamble subcarriers and additional subcarriers for the guard bands). The nearest prime number less than 1080 is 1069, and therefore we can predict 11 subcarriers for the two guard bands (i.e., 5.5 subcarriers per guard band). This exemplary implementation of the PRACH signal according to the second embodiment is shown in Figures 23B and 26.

[0170] As an alternative to the 20MHz system, a prime number 1069 can be chosen for the preamble sequence length, which is the same length as in the 10MHz system, and therefore the same preamble can be used for both bandwidths of the unlicensed cell. The advantage of this is that the UE does not have to provide preambles of different sequence lengths to support the two system bandwidths. Thus, assuming that the total frequency bandwidth should cover 16.2MHz (i.e., covering 90 PRBs, each having 180kHz), a total of 1080 subcarriers, each having 15kHz, are used to transmit the PRACH signal. This results in 5.5 subcarriers per guard band.

[0171] In both exemplary implementations, the preamble lengths of 1069 and 1063, respectively, do affect the size of the DFT, but the IDFT (see Figure 27) does not increase significantly compared to the preamble length of 839 already predicted in the case of legacy PRACH. By keeping the length of the preamble sequence relatively small, the complexity of the DFT and IDFT operations does not increase significantly.

[0172] A similar method can be applied to unlicensed cells with different system bandwidths (such as 40 MHz) to set the parameters used for transmitting the PRACH signal.

[0173] In summary, as described above, there are several ways to set the preamble sequence length and RACH subcarrier frequency spacing to ensure that the resulting PRACH transmit signal frequency bandwidth exceeds the minimum frequency bandwidth threshold imposed on unlicensed cells. The corresponding (one or more) parameters can be selected by either the UE or the eNodeB, in which case the eNodeB must inform the UE of the selection.

[0174] In a particular implementation, different combinations of parameters for various system bandwidths (e.g., the parameter combinations described above) are pre-configured, so that for a 20 MHz system bandwidth, a preamble length of 1069 and a subcarrier frequency spacing of 15 kHz can be selected. Similarly, for a 10 MHz system bandwidth, a preamble length of 1069 and a subcarrier frequency spacing of 7 kHz can be selected.

[0175] As described above, according to the second embodiment, the sequence length of the preamble can be modified as a function of the system bandwidth (i.e., the corresponding minimum frequency bandwidth threshold). Therefore, a particular preamble (having a fixed length of 839 or 139) generated for executing a random access procedure via a licensed cell is unlikely to be reusable for executing a random access procedure via an unlicensed cell. Thus, in a particular implementation of the second embodiment, for this purpose, at least a further set of random access preambles can be generated, and therefore different sets of preambles are available for executing random access procedures via either a licensed or unlicensed cell. According to the exemplary implementation of the second embodiment described above, a further set of preambles having a sequence length of 1069 can be generated. For example, a suitable root sequence having a sequence length of 1069 can be provided (e.g., provided by eNodeB and shown to the UE), and the UE can generate a certain number of different preambles from this root sequence by performing a cyclic shift.

[0176] For example, by performing a cyclic shift of the corresponding root sequence, it is possible to generate 64 different preambles of length 1069. On the other hand, considering that there are likely to be few random access procedures performed through unlicensed cells, it is also possible to generate fewer preambles (e.g., only 16) for the set.

[0177] In an exemplary implementation of the second embodiment, it is assumed that PRACH transmission over an unlicensed cell is performed using the same transmit power as that used for normal PRACH transmission over a licensed cell. Corresponding illustrations of this implementation are shown in Figures 24A and 24B. As can be seen from Figure 24B, the power spectral density of PRACH transmission over an unlicensed cell is significantly reduced compared to the corresponding PRACH transmission over a licensed cell shown in Figure 24A. Alternatively, PRACH transmission over an unlicensed cell can be transmitted at a different transmit power value (higher or lower than the transmit power value used for PRACH transmission over a licensed cell). For example, the transmit power can be increased to achieve essentially the same power spectral density as in the case of normal PRACH transmission over a licensed cell (see Figure 24A) across the entire extended frequency bandwidth. On the other hand, if a licensed cell is a macrocell with a larger coverage area compared to an unlicensed cell with a smaller coverage area, the transmission power for PRACH transmissions via an unlicensed cell can be reduced compared to PRACH transmissions via a licensed cell.

[0178] Furthermore, Figure 27 shows an exemplary implementation of the UE transmitter according to the second embodiment, which is similar to the implementation described in the background art section in relation to Figure 10. The principle behind the second embodiment described above does not require any substantial modification of the UE's transmission chain. Rather, it requires the size of the DFT and IDFT, as well as the sampling rate f, to handle the appropriate preamble transmitted through the unlicensed cell. s Different values ​​are applied. The sizes of the DFT and IDFT directly correspond to the sequence length of the preamble.

[0179] Third Embodiment Below, a third embodiment for solving the above (one or more) problems will be described in detail. This third embodiment is essentially a combination of the first and second embodiments, and therefore best combines the two principles. In short, one of the improved PRACH transmissions described by the second embodiment can be repeated according to the repeat mechanism introduced by the first embodiment.

[0180] For example, the third embodiment is most advantageous for large system bandwidths, such as 40 MHz, in order to maintain the RACH subcarrier frequency spacing at 15 kHz (in the case of PUSCH) or less without the need to significantly increase the preamble length, as excessively large preamble lengths can be disadvantageous in preamble generation and in the implementation of the UE's transmitter (particularly DFT and IDFT). As an example, assuming a 40 MHz system bandwidth for an unlicensed cell, according to the third embodiment, a PRACH signal as described in relation to Figure 22B can be assumed, and this PRACH signal can be repeated once (i.e., transmitted a total of two times) to comply with a minimum channel occupancy of 80% of the 40 MHz system bandwidth of the unlicensed cell.

[0181] Another example is shown in Figure 28, which assumes three repetitions using a PRACH signal with a frequency bandwidth of 8.1 MHz (see Figures 23B and 26). Thus, the combined PRACH transmission of a total of four PRACHs covers a sufficient frequency bandwidth of over 32 MHz.

[0182] Implementation of this disclosure by hardware and software Another exemplary embodiment relates to carrying out the various embodiments described above using hardware, software, or software that works in conjunction with hardware. In this regard, a user terminal (mobile terminal) and an eNodeB (base station) are provided. The user terminal and base station are configured to perform the methods described herein and include corresponding entities (receivers, transmitters, processors, etc.) that appropriately participate in these methods.

[0183] Various embodiments are further recognized as being implemented or executed using computing devices (processors). Computing devices or processors include, for example, general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices. Various embodiments can also be implemented or embodied by combinations of these devices. In particular, each functional block used in the description of each embodiment described above can be implemented by an LSI as an integrated circuit. These functional blocks can be formed individually as chips, or a single chip can be formed to include some or all of the functional blocks. These chips may include data input / output units coupled to themselves. Depending on the degree of integration, LSIs are also referred to as ICs, system LSIs, super LSIs, or ultra LSIs. However, the technology for implementing integrated circuits is not limited to LSIs and can be achieved using dedicated circuits or general-purpose processors. Furthermore, FPGAs (field-programmable gate arrays) that can be programmed after the manufacture of the LSI, or reconfigurable processors that can reconfigure the connections and settings of circuit cells located inside the LSI, can also be used.

[0184] Furthermore, various embodiments can also be implemented by software modules. These software modules are executed by a processor or directly in hardware. Combinations of software modules and hardware implementations are also possible. Software modules can be stored in any type of computer-readable storage medium, such as RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROMs, DVDs, etc. It should also be noted that individual features of multiple different embodiments can be the subject of other embodiments, individually or in any combination.

[0185] Those skilled in the art will understand that various changes and / or modifications can be made to the embodiments of this disclosure without departing from the broader concept or scope of the invention. Accordingly, the embodiments described herein are illustrative in all respects and are not intended to limit the invention.

Claims

1. A transmitter that sends information about the random access preamble sequence to the user's device, A receiver that receives the random access preamble sequence selected and transmitted by the user device based on the aforementioned information, It has, The random access preamble sequence is transmitted in a frequency bandwidth of the unlicensed band, which is defined by the length of the random access preamble sequence and the subcarrier spacing, and is larger than the frequency bandwidth in which the random access preamble sequence is transmitted in the licensed band. Base station equipment.

2. A random access preamble sequence is selected that has a length longer than the length of the random access preamble sequence used for the license band. The base station device according to claim 1.

3. A random access preamble sequence having the same length as the random access preamble sequence used in the license band is selected. The receiver receives the random access preamble sequence, which has been repeatedly transmitted at multiple different frequencies. The base station device according to claim 1.

4. The frequency bandwidth is greater than or equal to the minimum bandwidth required for the unlicensed band. The base station device according to claim 1.

5. Information regarding the random access preamble sequence is the length of the random access preamble sequence. The base station device according to claim 1.

6. Information regarding the random access preamble sequence is the number of repetitions of the random access preamble sequence. The base station device according to claim 3.

7. A transmission process that transmits information about the random access preamble sequence to the user's device, A receiving step of receiving the random access preamble sequence selected and transmitted by the user device based on the aforementioned information, It has, The random access preamble sequence is transmitted in a frequency bandwidth of the unlicensed band, which is defined by the length of the random access preamble sequence and the subcarrier spacing, and is larger than the frequency bandwidth in which the random access preamble sequence is transmitted in the licensed band. Random access method.

8. A random access preamble sequence is selected that has a length longer than the length of the random access preamble sequence used for the license band. The random access method according to claim 7.

9. A random access preamble sequence having the same length as the random access preamble sequence used in the license band is selected. The random access preamble sequence, which has been repeatedly transmitted at multiple different frequencies, is received. The random access method according to claim 7.

10. The frequency bandwidth is greater than or equal to the minimum bandwidth required for the unlicensed band. The random access method according to claim 7.

11. Information regarding the random access preamble sequence is the length of the random access preamble sequence. The random access method according to claim 7.

12. The process involves sending information about the random access preamble sequence to the user's device, Based on the aforementioned information, the process of receiving the random access preamble sequence selected and transmitted by the user device, Control, The random access preamble sequence is transmitted in a frequency bandwidth of the unlicensed band, which is defined by the length of the random access preamble sequence and the subcarrier spacing, and is larger than the frequency bandwidth in which the random access preamble sequence is transmitted in the licensed band. Integrated circuit.

Images