JP2023052522A - User equipment and random access method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, user equipment, and an integrated circuit for performing a random access procedure between the user equipment and a radio base station.

SOLUTION: In a mobile communication system, a UE is constituted so that at least one unlicensed cell having an unlicensed cell frequency bandwidth is set. A minimum frequency bandwidth threshold is defined for transmissions via the unlicensed cell via which a random access procedure is performed. The UE selects a random access preamble sequence for the random access procedure and determines a frequency bandwidth for transmitting the sequence via the unlicensed cell. The determined frequency bandwidth is at least the minimum frequency bandwidth threshold. The UE then transmits the random access preamble sequence to a radio base station such that at least the determined frequency bandwidth of the unlicensed cell is occupied.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present disclosure relates to a method of performing a random access procedure between a user equipment and a radio base station in a mobile communication system. Furthermore, the present disclosure provides user equipment and radio base stations that engage in the method(s) described herein.

Long Term Evolution (LTE)
The third generation mobile communication system (3G), based on WCDMA(R) radio access technology, is being deployed on a wide scale around the world. The first step in enhancing or evolving this technology is the introduction of High Speed Downlink Packet Access (HSDPA) and Enhanced Uplink (also known as High Speed Uplink Packet Access (HSUPA)), which provides , provides extremely competitive radio access technology.

In order to meet the increasing demand from users and to ensure competitiveness with new radio access technologies, 3GPP has introduced a new mobile communication system called Long Term Evolution (LTE). LTE is designed to provide carriers with the demand for high-speed transmission of data and media as well as high-capacity voice support over the next decade.

Work Item (WI) specifications for LTE (Long Term Evolution) are Evolved UMTS Terrestrial Radio Access (UTRA) and E-UTRAN (Evolved UMTS Terrestrial Radio Access Network (UTRAN)). : Evolved UMTS Terrestrial Radio Access Network) and will eventually be published as Release 8 (LTE Release 8). The LTE system is a packet-based efficient radio access and radio access network that offers all IP-based functionality with low latency and low cost. In LTE, scalable multiple transmission bandwidths (e.g., 1.4 MHz, 3.0 MHz, 5.0 MHz, 10.0 MHz, 15.0 MHz, and 20.0 MHz) are specified. Radio access based on OFDM (Orthogonal Frequency Division Multiplexing) is employed for the downlink. Because such radio access is inherently immune to multipath interference (MPI) due to its low symbol rate, it uses a cyclic prefix (CP), and it supports various transmission bandwidth configurations. Because it is possible. The uplink employs SC-FDMA (Single-Carrier Frequency Division Multiple Access) based radio access. This is because, given the limited transmit power of user equipment (UE), providing a wider coverage area is prioritized over improving peak data rates. LTE Release 8/9 adopts a number of key packet radio access technologies (eg, MIMO (Multiple Input Multiple Output) channel transmission technology) to achieve a highly efficient control signaling structure.

LTE Architecture Figure 1 shows the overall architecture of LTE. E-UTRAN consists of eNodeBs, which terminate E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocols towards user equipment (UE). The eNodeB (eNB) consists of a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data control protocol (PDCP) layer (these layers are user plane header compression and ciphering). ), including the functionality of The eNB also provides radio resource control (RRC) functionality for the control plane. The eNB provides radio resource management, admission control, scheduling, negotiated uplink quality of service (QoS) enforcement, broadcast of cell information, encryption/decryption of user plane and control plane data, downlink/uplink user It performs many functions such as compression/decompression of plain packet headers. Multiple eNodeBs are connected to each other by an X2 interface.

In addition, the plurality of eNodeBs are connected to an EPC (Evolved Packet Core) through the S1 interface, more specifically, an MME (Mobility Management Entity) through the S1-MME, and a serving gateway ( SGW: Serving Gateway). The S1 interface supports many-to-many relationships between MME/Serving Gateways and eNodeBs. The SGW routes and forwards user data packets, while acting as a mobility anchor for the user plane during handovers between eNodeBs, and also as an anchor for mobility between LTE and another 3GPP technology (S4 terminating interfaces and relaying traffic between the 2G/3G system and the PDN GW). The SGW terminates the downlink data path for idle user equipment and triggers paging when downlink data arrives for that user equipment. The SGW manages and stores user equipment context (eg IP bearer service parameters, or network internal routing information). Furthermore, the SGW performs duplication of user traffic in case of lawful interception.

The MME is the main control node of the LTE access network. The MME is responsible for idle mode user equipment tracking and paging procedures (including retransmissions). The MME is involved in the bearer activation/deactivation process and also selects the SGW for the user equipment during initial attach and during intra-LTE handover with core network (CN) node relocation. also play a role in The MME is responsible for authenticating the user (by interacting with the HSS). Non-Access Stratum (NAS) signaling is terminated at the MME, which is also responsible for generating and assigning temporary identities to user equipment. The MME checks the authorization of the user equipment to enter the service provider's Public Land Mobile Network (PLMN) and enforces roaming restrictions for the user equipment. The MME is the termination point in the network for ciphering/integrity protection of NAS signaling and is responsible for security key management. Lawful interception of signaling is also supported by the MME. In addition, the MME provides control plane functions for mobility between LTE and 2G/3G access networks and terminates the S3 interface from the SGSN. Additionally, the MME terminates the S6a interface towards the home HSS for roaming user equipment.

Component Carrier Structure in LTE The downlink component carriers of the 3GPP LTE system are further divided in the time-frequency domain in so-called subframes. In 3GPP LTE, each subframe is divided into two downlink slots as shown in Figure 2, where the first downlink slot covers the control channel region (PDCCH region) within the first OFDM symbol. Prepare. Each subframe consists of a given number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), each OFDM symbol spanning the entire bandwidth of a component carrier. Each OFDM symbol is thus composed of a number of modulation symbols transmitted on respective subcarriers. In LTE _, the transmitted signal in each slot is described by a resource grid of N ^DL _RB ×N ^RB _sc subcarriers 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 configured in the cell and satisfies N ^min,DL _RB ≦N ^DL _RB ≦N ^max,DL _RB , where N ^min,DL _RB =6 and N ^max,DL _RB =110 are the minimum and maximum downlink bandwidths respectively supported by the current version of the specification. N ^RB _sc is the number of subcarriers in one resource block. For the normal cyclic prefix subframe structure, N ^RB _sc =12 and N ^DL _symb =7.

Assuming a multi-carrier communication system, eg using OFDM, eg as used in 3GPP Long Term Evolution (LTE), the smallest unit of resource that can be allocated by the scheduler is one "resource block". A physical resource block (PRB) consists of consecutive OFDM symbols in the time domain (eg, 7 OFDM symbols) and consecutive subcarriers in the frequency domain (eg, 12 subcarriers of a component carrier), as illustrated in FIG. defined as Thus, in 3GPP LTE (Release 8), a physical resource block consists of resource elements and corresponds to one slot in the time domain and 180 kHz in the frequency domain (further details on the downlink resource grid can be found e.g. version 12.6.0), section 6.2 (available on the 3GPP website and incorporated herein by reference)).

One subframe consists of two slots, so there are 14 OFDM symbols in a subframe when the so-called "normal" CP (cyclic prefix) is used and the so-called "extended" CP is There are 12 OFDM symbols in a subframe when used. For the purpose of terminology, time-frequency resources equivalent to the same contiguous subcarriers spanning an entire subframe are hereinafter referred to as "resource block pairs" or equivalently "RB pairs" or "PRB pairs". The term "component carrier" denotes 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 terminology will be changed to "cell" to indicate the combination of downlink and optionally uplink resources. The linking between the carrier frequencies of the downlink resources and the carrier frequencies of the uplink resources is indicated in system information transmitted on the downlink resources.

Similar assumptions regarding the structure of the component carrier apply to subsequent releases.

Carrier Aggregation in LTE-A for Wider Bandwidth Support At the World Radiocommunication Conference 2007 (WRC-07), the frequency spectrum for IMT-Advanced was decided. Although the overall frequency spectrum for IMT-Advanced has been determined, the actual available frequency bandwidth varies by region and country. However, following the determination of the outline of the available frequency spectrum, the standardization of the radio interface started in 3GPP (3rd Generation Partnership Project).

The bandwidth that an LTE Advanced system can support is 100 MHz, while an LTE system can only support 20 MHz. Today, the lack of radio spectrum has become a bottleneck in the development of wireless networks, and as a result it is difficult to find wide enough spectrum bands for LTE Advanced systems. Therefore, there is an urgent need to find a way to acquire wider wireless spectrum bands, where a possible answer is carrier aggregation function.

In carrier aggregation, two or more component carriers are aggregated in order to support wider transmission bandwidths up to 100 MHz. In LTE-Advanced system, several cells in LTE system are aggregated into one wider channel, which is wide enough for 100MHz 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 when the component carrier bandwidth does not exceed the supported bandwidth of an LTE Release 8/9 cell. Not all component carriers aggregated by a user equipment are necessarily LTE Release 8/9 compatible. Existing mechanisms (eg, barring) can be used to prevent Rel-8/9 user equipment from camping on component carriers.

A user equipment can simultaneously receive or transmit on one or multiple component carriers (corresponding to multiple serving cells) depending on its capabilities. An LTE-A Release 10 user equipment with receive and/or transmit capabilities for carrier aggregation can simultaneously receive and/or transmit on multiple serving cells, whereas LTE A Rel-8/9 user equipment can receive and transmit on only one serving cell if the component carrier structure complies with the Rel-8/9 specifications.

Carrier aggregation is supported on both contiguous and non-contiguous component carriers, with each component carrier supporting up to 110 in the frequency domain (using 3GPP LTE (Release 8/9) numerology). limited to resource blocks.

Configuring 3GPP LTE-A (Release 10) compatible user equipment to aggregate different numbers of component carriers, possibly with different bandwidths in the uplink and downlink, transmitted from the same eNodeB (base station) It is possible to 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 set the mobile terminal to have 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 uplink and downlink. Component carriers transmitted from the same eNodeB need not provide the same coverage.

The spacing of the center frequencies of the 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 maintaining orthogonality of 15 kHz spaced subcarriers. In some aggregation scenarios, n×300 kHz spacing can be facilitated by inserting a small number of unused subcarriers between consecutive component carriers.

The impact of aggregating multiple carriers only extends to the MAC layer. The MAC layer requires one HARQ entity per aggregated component carrier in both uplink and downlink. There is a maximum of 1 transport block per component carrier (without using SU-MIMO in the uplink). A transport block and its (one or more) HARQ retransmissions (when they occur) should be mapped to the same component carrier.

When carrier aggregation is configured, the mobile terminal has only one RRC connection with the network. During RRC connection establishment/re-establishment, one cell receives security inputs (one ECGI, one PCI, and one ARFCN) and non-access stratum (NAS) mobility information ( e.g. TAI). After establishment/re-establishment of the RRC connection, the component carrier corresponding to that cell is called downlink primary cell (PCell). In connected state, there is always one downlink PCell (DL PCell) and one uplink PCell (UL PCell) per user equipment. In a configured set of component carriers, the other cells are called secondary cells (SCells), and the carriers of the SCells are downlink secondary component carriers (DL SCC) and uplink secondary component carriers (UL SCC). Currently, up to 5 serving cells (including PCell) can be configured for one UE.

Configuration and reconfiguration, addition and deletion of component carriers can be performed by RRC. Activation and deactivation is done via MAC control elements, for example. During intra-LTE handover, RRC may also add, remove, 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 (required for transmission/reception) (similar to during handover in LTE Release 8/9). When a SCell is added to a UE, each SCell is configured with a serving cell index. A PCell always has a serving cell index of 0.

When the user equipment is configured to use carrier aggregation, at least one pair of uplink and downlink component carriers is always active. A downlink component carrier of this pair is sometimes referred to as a "downlink anchor carrier." The same is true for the uplink. When carrier aggregation is configured, user equipment can be scheduled on multiple component carriers at the same time, but at most one random access procedure can be in progress at the same time. Cross-carrier scheduling allows the PDCCH of a component carrier to schedule resources of another component carrier. For this purpose, a component carrier identification field (referred to as "CIF") is introduced in each DCI (Downlink Control Information) format.

When cross-carrier scheduling is not in effect, the uplink component carrier to downlink component carrier link (established by RRC signaling) may identify the uplink component carrier to which the grant applies. The linking of downlink component carriers to uplink component carriers does not necessarily have to be one-to-one. In other words, more than one downlink component carrier 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.

Random Access Procedure A mobile terminal's uplink transmissions in LTE can be scheduled only 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 non-synchronized mobile terminals (UEs) to have orthogonal transmissions for uplink radio access. The random access procedure in LTE is essentially used to achieve uplink time synchronization in user equipments that have not yet acquired uplink synchronization or have lost uplink synchronization. Once the user equipment has achieved uplink synchronization, the eNodeB can schedule uplink transmission resources for that user equipment.

In addition, PRACH transmission and detection estimates the round-trip delay between the eNB and the UE. The design goals for the PRACH signal shape when operating LTE in the licensed band are to minimize overhead and interference impact on parallel uplink transmissions from other UEs, while at the same time reducing round-trip delay estimation. It was to provide sufficient accuracy.

As a further additional case, the user equipment may perform a random access procedure even if it is time synchronized, i.e. the user equipment is not allocated another uplink resource to send the scheduling request (e.g. A random access procedure is used to send scheduling requests (ie uplink buffer status reports) to the eNodeB when a dedicated scheduling request (D-SR) channel is not configured).

Therefore, the following scenarios are relevant for random access.
1. If a user equipment in RRC_CONNECTED state but not uplink synchronized wants to send new uplink data or control information;2. If a user equipment in RRC_CONNECTED state but not uplink synchronized needs to receive downlink data and is therefore required to send corresponding HARQ feedback (ie ACK/NACK) on the uplink. This scenario is also called Downlink data arrival.
3. When a user equipment in RRC_CONNECTED hands over from the current serving cell to a new target cell. A random access procedure is performed in order to achieve uplink time synchronization in the target cell.
4. 5. If a timing advance is needed for positioning purposes in the RRC_CONNECTED state. When moving from RRC_IDLE state to RRC_CONNECTED state (e.g. when accessing for the first time or when updating a tracking area)
6. When recovering from radio link failure (i.e. re-establishing RRC connection)

LTE provides two types of random access procedures, granting access either on a contention basis (with risk of collision) or without contention. Note that the contention-based random access is applicable to all six scenarios listed above, whereas the contention-free random access procedure is only applicable to downlink data arrival and handover scenarios. .

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

FIG. 3 shows the LTE contention-based RACH procedure. This procedure consists of four "steps". First, a user equipment transmits (301) a random access preamble on a physical random access channel (PRACH) to an eNodeB. A preamble is selected by the user equipment from a set of available random access preambles reserved by the eNodeB for contention-based access. _Ncf is the number of signatures reserved by the eNodeB for contention-free RACH. In LTE, there are a total of 64 preambles per cell that can be used for contention-free random access and contention-based random access. The set of contention-based preambles can be further divided into two groups, thus depending on the selection of the preamble by the UE, the first scheduled transmission (referred to as msg3 in 1 bit of information can be conveyed to indicate information about the amount of transmission resources required in step 303). System information broadcast within a cell includes signature (preamble) information belonging to each of the two subgroups and the meaning of each subgroup. The user equipment randomly selects one preamble from a subgroup corresponding to the size of transmission resources required for transmission of msg3 (see step 303 below). When the UE selects the appropriate size to indicate, the current downlink path Loss and transmission power required for the message of step 303 can be further considered.

After the eNodeB detects the RACH preamble, the response in the PDCCH addressed to the Random Access Response (RAR) message, i.e. the RA-RNTI, which identifies the time-frequency slot in which the preamble was detected (random access) The DCI to be transmitted is sent by PDSCH (Physical Downlink Shared Channel) (302). If multiple user equipments transmit the same RACH preamble on the same PRACH resource (also called collision), these user equipments will receive the same random access response.

A RAR (random access response) message contains the identity of the detected RACH preamble, a timing alignment command (TA command) for synchronizing subsequent uplink transmissions, and the scheduled first transmission (see step 303). and an allocation of a T-CRNTI (Temporary Cell Radio Network Temporary Identifier) for the transmission of . This T-CRNTI is used by the base station for the purpose of addressing the mobile terminal(s) for which the RACH preamble was detected until the end of the RACH procedure, since the eNodeB is at this point the mobile terminal's " This is because it does not yet recognize the "true" identity.

Furthermore, the RAR message may also contain a so-called back-off indicator, which is intended to instruct the user equipment to back-off (wait) for a certain period of time before retrying random access. can be set. The user equipment monitors the PDCCH for a random access response received within a given time window (set by the eNodeB). If the user equipment does not receive a random access response within the configured time window, it retransmits the preamble at the next PRACH opportunity, taking into account the backoff period, if specified.

In response to the RAR message received from the eNodeB, the user equipment transmits (303) the first scheduled uplink transmission on the uplink resources allocated by the grant in the random access response. This scheduled uplink transmission carries the actual random access procedure messages (eg RRC connection requests, tracking area updates, buffer status reports, etc.). Additionally, this uplink transmission contains either the C-RNTI of the user equipment in RRC_CONNECTED mode or a unique 48-bit user equipment ID if the user equipment is in RRC_IDLE mode. If a preamble collision occurs in step 301 (i.e. multiple user equipments sent the same preamble on the same PRACH resource), the colliding user equipments receive the same T-CRNTI in the random access response, There is also a collision on the same uplink resource when sending 303 each scheduled transmission. This may result in interference, so that transmissions from colliding user equipments cannot be decoded at the eNodeB, and the user equipments, after reaching the maximum number of retransmissions of a scheduled transmission, may perform random access procedures. start again. If the scheduled transmission from one user equipment is successfully decoded by the eNodeB, the other user equipment contention remains unresolved.

To resolve this type of conflict, the eNodeB sends (304) a conflict resolution message addressed to the C-RNTI or Temporary C-RNTI, and in the case of the Temporary C-RNTI, to the scheduled transmission of step 303. The included 48-bit user equipment ID is sent back as is. After a collision, only the user equipment that detected its identity (C-RNTI or unique user equipment ID) sends HARQ feedback (ACK) if the message sent in step 303 is successfully decoded. . Other UEs can recognize that a collision has occurred in step 301 and immediately terminate the current RACH procedure and start a new RACH procedure.

Figure 4 shows the contention-free random access procedure introduced as of 3GPP LTE Release 8/9. The contention-free random access procedure is simplified when compared to the contention-based random access procedure. The eNodeB assigns (401) specific preambles to user equipments for use in random access in such a way that there is no risk of collision (ie multiple user equipments do not transmit the same RACH preamble). In response, the user equipment sends (402) the preamble signaled by the eNodeB on the appropriate PRACH resource on the uplink. Random access without contention avoids the case where multiple UEs send the same preamble, so no contention resolution is required, thus step 304 of the contention-based procedure shown in FIG. 3 can be omitted. A contention-free random access procedure essentially terminates after a successful reception of a random access response. If the random access response fails to be received, the next PRACH retransmission is autonomously initiated by the UE itself.

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

The initial setting of the preamble transmit power can be based on an open-loop estimation that is fully compensated for path loss. This open-loop estimation is designed such that the received power of the preamble is independent of the path loss.

Additionally, the eNB sets additional power offsets depending, for example, on the desired received SINR, the measured levels of uplink interference and noise in the time-frequency slots assigned to the RACH preamble, and (possibly) the format of the preamble. be able to. In addition, the eNB may implement preamble power ramping such that the transmit power of each retransmitted preamble (e.g., in the event of an unsuccessful PRACH transmission attempt) increases at regular intervals. can be set.

Random Access Preamble - Time, Frequency, Format The random access preamble transmission part of the random access procedure described above is mapped onto the PRACH at the physical layer. The design of the preamble is critical to the success of the random access procedure and is detailed below. A RACH preamble is basically a cyclic shift of a complex Zadoff-Chu (ZC) sequence, also known as the 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 follow the LTE uplink DFT-S-OFDM structure and is constructed using CP (cyclic prefix). , thus enabling an efficient frequency domain receiver at the eNodeB. The physical layer random access preamble consists of a cyclic prefix of length _TCP and a sequence part of length T _SEQ , as shown in FIG. The possible values for these parameters are listed in the following table and depend on the frame structure and random access settings (eg preamble format which can be controlled by higher layers). Corresponding details can be found in Non-Patent Document 1 (current version 12.6.0), section 5.7.1 "Time and frequency structure" (incorporated herein by reference). is described in In frequency division duplex operation, four random access preamble formats are defined, each defined by a sequence duration and a cyclic prefix duration. The format configured in the cell is broadcast in system information.

_TS 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 values of T _CP and T _SEQ in different preamble formats considering this particular sampling rate.

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

The lower bound of the sequence duration T _SEQ (683.33 μs) is such that a UE located at the edge of the largest expected cell can be expected to include the maximum delay spread expected in such a large cell (i.e. 16.67 μs). The value must be such that the round-trip time can be clearly estimated. A further constraint on the sequence duration T _SEQ is given by the signal generation principle of single-carrier frequency division multiple access, thus the size of the DFT (Discrete Fourier Transform) and IDFT (Inverse Discrete Fourier Transform) N _DFT must be an integer .

In order to facilitate frequency multiplexing of PRACH and PUSCH resource allocations, a PRACH slot shall be allocated a bandwidth BW _PRACH equal to an integer multiple of resource blocks (ie an integer multiple of 180 kHz). The BW _PRACH (6 PRBs, 1.08 MHz) in LTE is constant for all system bandwidths for simplicity, and this BW _PRACH optimizes both detection performance and timing estimation accuracy. is selected as The timing estimation accuracy determines the lower bound of the PRACH bandwidth. In practice, a minimum bandwidth of about 1 MHz is required to provide a one-shot accuracy of about ±0.5 μs, which is an acceptable timing accuracy in PUCCH/PUSCH transmissions.

Allocating 6 RBs (resource blocks) to the PRACH provides a good trade-off between PRACH overhead, detection performance and timing estimation accuracy. Note that for the minimum system bandwidth (1.4 MHz, 6 RBs) the PRACH overlaps with the PUCCH. It is up to the eNodeB implementation to impose scheduling constraints during the PRACH slot to avoid collisions, or to allow PRACH and PUCCH collisions to occur and deal with the resulting interference.

In order to provide compatibility between preamble subcarriers and PUSCH subcarriers, the duration of the preamble should be fixed to the duration of an integer multiple of a PUSCH symbol. That is, it is preferable that the PRACH subcarrier interval should be an integer fraction of the PUSCH subcarrier interval.

As shown in FIG. 6, PRACH is time-multiplexed and frequency-multiplexed with PUSCH and PUCCH. PRACH time-frequency resources are allocated semi-statically in the PUSCH region and are repeated periodically. It is at the eNodeB's discretion to schedule PUSCH transmissions in PRACH slots. LTE supports 64 PRACH configurations, each consisting of a periodic PRACH resource pattern and an associated preamble format. A detailed list of PRACH settings is provided in Tables 5.7.1-2 and 5.7.1-3 of Non-Patent Document 1 (incorporated herein by reference). It is possible to schedule PUSCH transmissions in the same subframe with the assigned PRACH resources. This decision is made by the eNB.

Random Access Preamble—Preamble Sequence Generation As mentioned above, there are 64 PRACH signatures available in LTE compared to only 16 in WCDMA. This not only reduces the probability of collisions, but also allows one bit of information to be conveyed by the preamble in contention-based accesses, and reserves some signatures for contention-free accesses. Therefore, LTE PRACH preambles require an improved sequence design over WCDMA. In LTE, prime-length Zadoff-Chu sequences are chosen that can improve the 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). )It is described in.

The random access preamble is a Zadoff-Chu (ZC) sequence, which is generated from one or several root Zadoff-Chu sequences as follows. First, the root Zadoff-Chu sequence is chosen based on the indication information of the logical sequence index (RACH_ROOT_SEQUENCE) broadcasted as part of the system information. The order of the logical root sequence is cyclic, so logical index 837 is followed by index 0. The relationship between the logical root sequence index and the physical root sequence index u (indicated in the system information) is, for preamble formats 0-3, according to Table 5.7.2-4 of Non-Patent Document 1: For preamble format 4 it is given by Table 5.7.2-5 (incorporated herein by reference).

The u-th root Zadoff-Chu sequence is defined by

where u is the physical root sequence index mentioned above, the sequence length N _ZC depends on the configured PRACH preamble format, i.e. N _ZC =839 for preamble formats 0-3, and the preamble In the case of format 4, N _ZC =139 (see also Table 5.7.2-1 in Non-Patent Document 1).

From the u-th root Zadoff-Chu sequence, a set of 64 random access preambles with zero correlation zones of length N _CS −1 is defined by cyclic shift by

The cyclic shift is given by

The parameter N _CS is given by Tables 5.7.2-2 and 5.7.2-3 of Non-Patent Document 1 and depends on the format of the preamble and the parameter zeroCorrelationZoneConfig provided by higher layers. Further information can be obtained from Section 5.7.2 of Non-Patent Document 1.

If 64 preambles cannot be generated from one root Zadoff-Chu sequence, additional preamble sequences are generated from one or more root sequences with consecutive logical indices until all 64 preamble sequences are found. obtain.

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

Random Access Preamble—Generation of Baseband Signal The generation of the PRACH baseband signal is defined in Section 5.7.3 of Non-Patent Document 1. A temporally continuous random access signal s(t) is defined by the following equation.

である。 where 0≦t<T _SEQ +T _CP , β _PRACH is the amplitude scaling factor to match the transmit power P _PRACH ,

is.

The position in the frequency domain is controlled by the parameter n ^RA _PRB . The factor K=Δf/Δf _RA takes into account the subcarrier spacing difference between the random access preamble and the uplink data transmission. Both the variable Δf _RA (subcarrier spacing of random access preambles) and the variable φ (fixed offset that determines the frequency domain position of random access preambles within physical resource blocks) are given by the following table (Non-Patent Document 1: (see Table 5.7.3-1 of ).

Note that PUSCH has a subcarrier spacing of 15 kHz.

The time domain preamble sequence is transformed to the frequency domain by a DFT of size N _ZC . The resulting frequency-domain coefficients are mapped to subcarriers with a frequency spacing Δf _RA . The frequency spacing for PRACH transmissions does not match the frequency spacing used for other uplink transmissions (such as PUSCH and PUCCH). Subcarrier mapping also incorporates the location of the PRACH in the frequency domain.

FIG. 7 shows the mapping of PRACH preambles to assigned subcarriers and the mapping of PUSCH subcarriers side by side. As is evident from the figure, PRACH uses guard bands to avoid data interference at the preamble edges. The PRACH is transmitted on frequency-domain resources corresponding to 6 consecutive physical resource blocks (PRBs) (ie, having a frequency bandwidth of 1.08 MHz). These PRBs can be centered in the nominal system bandwidth as shown in FIG. 8, or at any other position within the nominal system bandwidth as shown in FIG. can be done.

Random Access Preamble - UE Preamble Sequence Transmitter Implementation In the following, a practical example implementation of the PRACH function is briefly described. As shown in FIG. 10, the PRACH preamble can be generated at the system sampling rate with a large IDFT. The DFT block in FIG. 10 is dashed to indicate that it is optional, because the sequence can also be mapped directly to the frequency domain at the input of the IDFT. A cyclic shift can be performed in the time domain after the IDFT or in the frequency domain before the IDFT through a phase shift.

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

LTE in unlicensed bands: License Assisted Access (LAA)
3GPP launched a new study item on LTE operation in unlicensed spectrum in September 2014. The reason for extending LTE to unlicensed bands is the ever-growing demand for wireless broadband data in addition to the limited amount of licensed bands. Unlicensed spectrum is therefore increasingly viewed by mobile operators as a complementary means to expand their service offerings. As an advantage of LTE in unlicensed bands when compared to relying on other radio access technologies (RATs) such as Wi-Fi, operators and vendors will be able to supplement LTE platforms with access to unlicensed spectrum. allows leveraging existing and future investments in LTE/EPC hardware for radio and core networks.

However, access to unlicensed spectrum will inevitably coexist with other radio access technologies (RATs) such as Wi-Fi in unlicensed spectrum, so the quality of licensed spectrum access is absolutely critical. We must consider the incomparability. Therefore, LTE operation in unlicensed bands will, at least initially, be viewed as a complement to LTE in licensed bands rather than as a stand-alone operation in unlicensed bands. Based on this assumption, 3GPP has established the term Licensed Assisted Access (LAA) for operating LTE on unlicensed bands in conjunction with at least one licensed band. However, this does not preclude LTE standalone operation in unlicensed spectrum (ie not supported by licensed cells) in the future.

The general LAA method currently intended in 3GPP is to take full advantage of the already formulated Release 12 Carrier Aggregation (CA) framework, which consists of , as described above, includes a so-called primary cell (PCell) carrier and one or more secondary cell (SCell) carriers. In carrier aggregation (CA), generally, self-scheduling of cells (scheduling information and user data are transmitted on the same component carrier), cross-carrier scheduling between cells (scheduling information by PDCCH/EPDCCH, PDSCH/ user data over PUSCH are transmitted on different component carriers) are both supported.

Figure 11 shows a very basic scenario, where there is a licensed PCell, a licensed SCell 1 and various unlicensed SCells 2, 3, 4 (illustratively drawn as small cells). The transmitting/receiving network nodes of the unlicensed SCells 2, 3, 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 eNBs or networks are not explicitly shown in the figure.

The basic method currently envisioned in 3GPP is to operate a PCell in a licensed band, while operating one or more SCells in an unlicensed band. An advantage of this scheme is that the PCell can be used to reliably transmit control messages and user data requiring high quality of service (QoS) (such as voice and video), while , SCells in unlicensed spectrum will inevitably coexist with other radio access technologies (RATs), which can lead to significant QoS degradation depending on the scenario.

The LAA (License Assisted Access) has been agreed to focus on the 5 GHz unlicensed band. One of the most important issues is therefore coexistence with Wi-Fi (IEEE 802.11) systems operating in these unlicensed bands. In unlicensed bands, in order to support fair coexistence between LTE and other technologies (such as Wi-Fi) and to ensure fairness between different LTE operators in the same unlicensed bands. LTE channel access must comply with a specific set of regulations, some of which vary depending on the geographic region and the specific frequency band. A comprehensive description of regulatory requirements in all regions when operating in the 5 GHz unlicensed band can be 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 include Dynamic Frequency Selection (DFS), Transmit Power Control (TPC), Listen Before Talk, depending on region and band. (LBT: Listen Before Talk), discontinuous transmission with a limited maximum transmission time length. 3GPP's intention is to target a single international LAA framework, i.e. basically all requirements for different regions and the 5 GHz band must be considered when designing a system. .

For example in Europe, the nominal channel band is A specific limit on the width (Nominal Channel Bandwidth) is set. Nominal channel bandwidth is the widest frequency band (including guard bands) allocated to a channel. Occupied Channel Bandwidth is the bandwidth containing 99% of the power of the signal. Devices are permitted to operate simultaneously on one or more adjacent or non-adjacent channels.

When devices transmit simultaneously on adjacent channels, these transmissions can be viewed as one signal with an actual nominal channel bandwidth that is 'n' times the individual nominal channel bandwidths (where n is the adjacent channel bandwidth). number of channels). When devices transmit simultaneously on non-adjacent channels, each power envelope is considered separately. The nominal channel bandwidth is always at least 5 MHz. The occupied channel bandwidth is within 80% to 100% of the declared nominal channel bandwidth. In the United States, the minimum occupied channel bandwidth is 500 kHz according to [4]. For smart antenna systems (devices with multiple transmit chains), each transmit chain fulfills this requirement. During established communications, devices are permitted to temporarily operate with an occupied channel bandwidth of less than 80% of the nominal channel bandwidth with a minimum of 4 MHz.

A listen-before-talk (LBT) procedure has been defined as a mechanism for applying a free channel determination (CCA) before a device uses a channel. CCA uses at least energy detection to determine the presence or absence of another signal 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. Carrier sensing over LBT is one way to ensure fair sharing of unlicensed spectrum, apart from being a regulatory requirement. LBT is therefore considered an essential feature for fair and friendly operation of unlicensed spectrum within the framework of one global solution.

Channel availability cannot always be guaranteed in unlicensed spectrum. In addition, certain regions, such as Europe and Japan, prohibit continuous transmission and impose limits on the maximum duration of transmission bursts in unlicensed frequency bands. Discontinuous transmission with a limited maximum duration of transmission is therefore an essential feature in LAA. DFS (Dynamic Frequency Selection) is required in certain regions and bands in order to detect interference from radar systems and avoid co-channel operation with these systems. The aim is to further achieve a substantially uniform loading of the frequency bands. DFS operation and corresponding requirements are related to the master/slave principle. For the purpose of performing radar detection, the master detects radar interference, which can then rely on another device associated with the master.

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

Detailed information can be found in the harmonized European Standard, Non-Patent Document 5 (current version 1.8.0), which is incorporated herein by reference.

Devices must perform a free channel determination (CCA) before occupying a radio channel with a data transmission, according to this European regulation for LBT. Transmission on an unlicensed channel is allowed to start only after the channel is detected as free, for example based on energy detection. In particular, the device must monitor the channel for a certain minimum time during CCA (eg 20 μs in Europe, see section 4.8.3 of Non-Patent Document 5). If the detected energy level exceeds a 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 configured CCA threshold, the channel is considered free. If the channel is determined to be occupied, the device will not transmit on that channel for the next Fixed Frame Period. If the channel is classified as free, the device is allowed to transmit immediately. The maximum duration of transmission is limited in order to promote fair resource sharing with other devices operating in the same band.

Energy detection in CCA is performed over the entire channel bandwidth (e.g. 20 MHz in the 5 GHz unlicensed band), i.e. the sum of the received power levels of all sub-carriers of the LTE OFDM symbol within that channel performed CCA. Evaluated energy level in the device.

In addition, the total time a device has transmission on a given carrier without reassessing its availability (i.e. LBT/CCA) is defined as the Channel Occupancy Time ( See Section 4.8.3.1 of Non-Patent Document 5). The channel occupancy time is in the range of 1 ms to 10 ms and the maximum channel occupancy time may be eg 4 ms as currently defined in Europe. Furthermore, there is also a minimum idle time during which the UE is not allowed to transmit after transmitting in an unlicensed cell, the minimum idle time being at least 5% of the channel occupancy time. The UE may, for example, perform a new CCA shortly before the end of the idle period. This transmission behavior is illustrated schematically in Figure 12, which is taken from Non-Patent Document 5 (Figure 2 therein: "Example of timing for Frame Based Equipment"). Timing example)”).

FIG. 13 shows the timing between Wi-Fi transmissions and LAA UE transmissions on specific frequency bands (unlicensed cells). As can be seen from Figure 13, after a Wi-Fi burst, at least a CCA gap is required before the eNB "reserves" unlicensed cells until the next subframe boundary, eg by sending a reservation signal. Then the actual LAA DL burst begins.

The RACH procedure is also supported in unlicensed bands. To date, it has been agreed that only contention-free PRACH transmissions are supported in unlicensed bands. Whether PRACH retransmissions are explicitly scheduled by the eNB also in unlicensed bands, as opposed to PRACH retransmissions in licensed bands as described above, is currently still under consideration. However, although the standardization work currently agrees that only contention-free random access is supported, this may change in the future, allowing contention-based random access in unlicensed cells (in fact In addition, the principles of the present invention are applicable to both contention-free random access procedures and contention-based random access procedures).

Considering the various regulatory requirements, the LTE specifications, especially the random access procedures for operation on unlicensed bands, have several limitations compared to the current Release 12 specifications, which are limited to operation on licensed bands. It is clear that change is required.

3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)” R1-144348, "Regulatory Requirements for Unlicensed Spectrum", Alcatel-Lucent et al., RAN1#78bis, Sep. 2014 3GPP TS 36.321 3GPP Technical Report 36.889 ETSI EN 301 893

Exemplary non-limiting embodiments of the present invention provide an improved method of performing a random access procedure between a user equipment and a radio base station via an unlicensed cell. The independent claims provide non-limiting exemplary embodiments of the invention. Advantageous embodiments are subject matter of the dependent claims.

According to some implementations of the aspects described herein, random access procedures are improved, especially when performed over unlicensed cell(s). More specifically, the preamble sequence part (preamble generation, selection and actual RF transmission) of the random access procedure is improved. Therefore, further parts of the random access procedure remain (almost) the same as random access procedures designed for license access, for example, which are not the subject of the various aspects described.

In the following, we assume the following scenario. That is, in a mobile communication system, a user equipment and a radio base station are connected to each other via at least one unlicensed cell. An unlicensed cell can operate as a single cell or can be assisted by additional licensed cells that are additionally configured in the user equipment. An unlicensed cell is configured to have a specific frequency bandwidth, i.e., an unlicensed cell has a specific frequency bandwidth within the unlicensed frequency band (e.g., 10 MHz, 20 MHz, 40 MHz, or a smaller bandwidth, or higher bandwidth) operated by radio base stations and user equipment.

In addition, transmission in unlicensed cells is regulated such that a minimum frequency bandwidth threshold indicating the minimum channel occupancy occupied by transmissions over unlicensed cells is at least defined. The minimum channel occupancy depends on the frequency bandwidth of the unlicensed cells and can therefore vary from channel to channel. A minimum channel occupancy may define a predetermined percentage of the corresponding total frequency bandwidth of unlicensed cells.

In a scenario thus defined, essentially most of the transmissions performed by UEs (and eNodeBs) over unlicensed cells must comply with this minimum channel occupation requirement. This also applies to random access procedures performed between the user equipment and the radio base station, for example for synchronizing the uplink reference timing of the user equipment or for sending scheduling requests to the radio base station. . As part of the random access procedure, the user equipment selects a suitable random access preamble sequence and then transmits the preamble sequence to the radio base station.

According to some aspects, a defined minimum frequency bandwidth threshold for transmission over unlicensed cells transmits a random access preamble sequence to a radio base station as part of a random access procedure. sometimes considered. In particular, the random access preamble sequence is transmitted such that it complies with minimum channel occupancy requirements by at least exceeding the minimum frequency bandwidth thresholds defined for unlicensed cells.

For this purpose, a specific frequency bandwidth for transmitting random access preamble sequences over unlicensed cells can be determined, which frequency bandwidth is greater than a minimum frequency bandwidth threshold. Such a determination allows flexible handling of different channel bandwidths of unlicensed cells and thus different minimum channel occupancy requirements to be accommodated and adhered to. This determination can be performed in the user equipment or the radio base station. In an exemplary implementation, a minimum frequency bandwidth threshold (eg, determined by simply calculating a predetermined percentage of the unlicensed cell's frequency bandwidth) is set for both the user equipment and the radio base station. The frequency bandwidth that is known and thus occupied by the transmission of the random access preamble sequence can be independently determined by the UE and the radio base station. Alternatively, this decision can be made by one of the two entities (ie the UE or the radio base station) and the result of the decision is 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, control of the frequency bandwidth actually used by the UE for transmitting the random access preamble sequence is up to the radio base station. maintains. The transmission of such information by the radio base station to the UE can simply be done in the corresponding system information broadcast in the radio cell or in the case of contention-free random access It can be done in a corresponding message sent at the beginning of the procedure (eg in the same message indicating the preamble to be used).

Note in this connection that both contention-free and contention-based random access procedures are supported. In a contention-free random access procedure, among other things, the radio base station provides corresponding instructional information indicating which random access preamble sequence to select from the set of random access preamble sequences available to the UE (and the radio base station). to the user equipment, and the user equipment follows this instruction information. On the other hand, in contention-based random access procedures, no such indication information is provided by the radio base station, and the user equipment selects the random access preamble sequence to transmit to the radio base station autonomously from a set of random access preamble sequences. to select. The set of random access preamble sequences available for the contention-based random access procedure is the transmission resource required via the transmission of the random access preamble sequences as in the currently defined standard random access procedure. can be divided into two different subgroups associated with different amounts of

In summary, in this way a user equipment is enabled to comply with the minimum channel occupancy requirements defined for an unlicensed cell when performing a random access procedure over that unlicensed cell.

The random access procedure may proceed as normal and thus may include transmission of a random access response message from the radio base station to the user equipment. This random access response may include, for example, the corresponding uplink resource allocation, timing alignment instructions, a temporary identifier for the user equipment, identification of random access preamble sequences previously transmitted by the user equipment. Further, upon receipt of such a random access response message from the radio base station, further messages can be transmitted from the user equipment to the radio base station using the allocated uplink resources. Furthermore, when a contention-based random access procedure is performed, contention resolution may be required and thus performed between the eNodeB and the UE.

In the following, two different aspects are described to achieve that the transmission of random access preamble sequences over unlicensed cells follows the corresponding minimum channel occupancy (i.e. exceeds the minimum frequency bandwidth threshold). do.

According to a first aspect, the existing procedure for transmitting random access preamble sequences is reused, which complies with the regulatory requirements specified for such unlicensed cells, so that the unlicensed cells By repeating the normal preamble transmission at a number of different locations in the frequency domain so as to eventually occupy at least the required frequency bandwidth of . In particular, random access preamble sequences are selected in the usual way and transmitted at corresponding frequency locations. Note that the normal/legacy random access preamble transmission occupies a given frequency bandwidth (6 PRBs or 1.08 MHz as described in the Background section). Further, any number of repetitions of this transmission may be repeated at multiple different frequency locations such that every preamble transmission (with repetitions) occupies a frequency bandwidth exceeding the minimum frequency bandwidth threshold of an unlicensed cell. is executed in The number of iterations required to comply with this minimum channel occupancy is determined by the actual frequency bandwidth threshold defined for unlicensed cells, which is set for unlicensed cells. determined by the frequency bandwidth used. Furthermore, the number of repetitions also depends on the above-mentioned predetermined frequency bandwidth (ie 1.08 MHz) of the normal/legacy random access preamble transmission. In an exemplary implementation of the first aspect, the different locations in the frequency domain at which repetitions of the preamble transmission are performed are locations such that the repeated transmissions are adjacent in the frequency domain.

The improved random access procedure provided for unlicensed cells according to the first aspect is the random access procedure already defined for normal/legacy random access procedures in licensed cells, as explained above. Reuse the preamble sequence. An advantage of this method is that no additional set(s) of random access preambles need to be defined in this respect. The same set of random access preamble sequences is available for performing random access procedures over unlicensed cells and random access procedures over licensed cells. In particular, according to the first aspect, when performing a random access procedure via a licensed cell, a further random access preamble sequence is selected from the already generated set and transmitted to the radio base station via the licensed cell. and occupy the above-mentioned predetermined frequency bandwidth of the licensed cell (ie 6 PRBs, 1.08 MHz).

According to a further implementation of the first aspect, 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, different from the first selected random access preamble sequence. The transmission of the second random access preamble sequence is similarly repeated, but at a different frequency location than the transmission of the first random access preamble sequence. In particular, to comply with minimum channel occupancy, the first random access preamble sequence and the second random access preamble sequence are repeated and transmitted together so as to at least occupy a predetermined frequency bandwidth of the unlicensed cell. .

According to a second aspect, existing random access procedures, in particular existing settings for transmitting random access preamble sequences are modified, namely the length of the random access preamble sequence and the are selected such that when combined, the corresponding transmission of the random access preamble sequence exceeds the minimum frequency bandwidth threshold. Note that in the following 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 repeated preamble symbols and a cyclic prefix (the duration of the preamble symbol is given by the reciprocal of the subcarrier spacing of the preamble), and the subject of various aspects of the invention is do not have.

Note that the length of the random access preamble sequence (basically corresponding to the number of frequency subcarriers used to transmit the random access preamble sequence) and the subcarrier frequency spacing (basically different frequency subcarriers) determines how far the carriers are separated from each other), as a combination (i.e. by simply multiplying the number of frequency subcarriers by the subcarrier frequency spacing value), defines the overall frequency bandwidth of the preamble transmission. Note that As a result, by adjusting these two parameters (i.e. preamble sequence length and subcarrier frequency spacing), the frequency of the preamble signal can be adjusted to comply with the frequency bandwidth requirements when the preamble signal occupies an unlicensed cell. Shape/frequency bandwidth can be controlled.

One or both of the two parameters can be controlled by the user equipment, by the radio base station, or by a combination thereof. In this respect, several different implementations of the second aspect are possible. For example, while keeping the subcarrier frequency spacing constant, the length of the preamble sequence can be adjusted according to the actual amount of frequency bandwidth the preamble transmission must occupy (which depends on the system bandwidth of the unlicensed cells). You can decide flexibly. Or vice versa, while keeping the length of the preamble sequence constant, the subcarrier frequency spacing can be flexibly adapted to different requirements of minimum channel occupancy. Further alternatively, both preamble sequence length and subcarrier frequency spacing can be flexibly controlled in preamble transmission to occupy the frequency bandwidth required to comply with the minimum channel occupancy requirements of unlicensed cells. can.

In an exemplary implementation of the second aspect, two different sets of random access preamble sequences may be generated by the user equipment, one for the licensed cell(s) and one One is for unlicensed cell(s). Considering that the frequency bandwidth occupied by the transmission of random access preambles is larger for unlicensed cells than for licensed cells, the length of the random access preamble sequence for unlicensed cells is Note that it is likely larger than the length of the random access preamble sequence for license 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 sequence is generated from a suitable root sequence (eg, a Zadoff-Chu sequence), generate a random access preamble sequence to be used in conjunction with unlicensed cells. is longer than the root sequence used to generate the random access preamble sequence for the licensed cell. Therefore, when performing a random access procedure over a licensed cell, the corresponding preamble is selected from the corresponding set of licensed cells, whereas when performing a random access procedure over an unlicensed cell, the corresponding preamble is selected from the corresponding set of licensed cells. A corresponding preamble is selected from the corresponding set of unlicensed cells.

Accordingly, in one general first aspect, the technology disclosed herein provides a method of performing a random access procedure between a 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 via the unlicensed cell having an unlicensed cell frequency bandwidth. A minimum frequency bandwidth threshold is defined for transmission over unlicensed cells and the method includes the following steps performed by the user equipment for the random access procedure. A user equipment selects a random access preamble sequence for a random access procedure and determines a frequency bandwidth for transmitting this random access preamble sequence over unlicensed cells. The determined frequency bandwidth of the random access preamble sequence is at least the minimum frequency bandwidth threshold. The user equipment transmits random access preamble sequences to the radio base station such that at least the determined frequency bandwidth of the unlicensed cell is occupied.

Accordingly, in one general first aspect, the technology disclosed herein provides a user equipment for performing random access procedures together with a radio base station in a mobile communication system. do. The user equipment is configured with at least one unlicensed cell and the random access procedure is performed via the unlicensed cell having an unlicensed cell frequency bandwidth. A minimum frequency bandwidth threshold is defined for transmission over unlicensed cells. The user equipment processor selects a random access preamble sequence for the random access procedure. The processor further determines a frequency bandwidth for transmitting this random access preamble sequence over the unlicensed cells. The determined frequency bandwidth is at least the minimum frequency bandwidth threshold. The user equipment transmitter transmits random access preamble sequences to the radio base station such that at least the determined frequency bandwidth of the unlicensed cell is occupied.

Accordingly, in one general first aspect, the technology disclosed herein provides a radio base station for performing random access procedures with user equipment in a mobile communication system. do. The user equipment is configured with at least one unlicensed cell and the random access procedure is performed via the unlicensed cell having an unlicensed cell frequency bandwidth. A minimum frequency bandwidth threshold is defined for transmission over unlicensed cells. A frequency bandwidth is determined for the user equipment to transmit the random access preamble sequence over the unlicensed cell, the determined frequency bandwidth being at least a minimum frequency bandwidth threshold. A radio base station receiver receives a random access preamble sequence for a 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.

Further benefits and advantages of the disclosed embodiments will be apparent from the specification and drawings. These benefits and/or advantages may be provided individually by various embodiments and features of the disclosure herein and by the drawings, and all in order to obtain one or more of these benefits and/or advantages. need not be set.

These general and specific aspects can be implemented using systems, methods, computer programs, or any combination thereof.

Exemplary embodiments are described in more detail below with reference to the accompanying drawings.

1 shows an exemplary architecture of a 3GPP LTE system; 3 shows an exemplary downlink resource grid for downlink slots of subframes defined in 3GPP LTE (Release 8/9). Figure 2 shows a contention-based RACH procedure defined in 3GPP LTE (as of Release 8/9) in which contention can occur; Figure 3 shows the contention-free RACH procedure defined in 3GPP LTE (as of Release 8/9); Figure 3 shows the structure of the RACH preamble; Figure 2 shows multiplexing of PRACH transmission with PUSCH and PUCCH. Figure 2 shows the mapping of PRACH preambles to assigned subcarriers; Figure 4 shows different locations of the PRACH within the nominal frequency system bandwidth; Figure 4 shows different locations of the PRACH within the nominal frequency system bandwidth; Fig. 3 shows an exemplary functional structure of a PRACH preamble transmitter; 1 illustrates an exemplary LAA scenario with several licensed and unlicensed cells; Fig. 4 shows transmission behavior in LAA transmission; Fig. 3 shows the timing between Wi-Fi transmission bursts and LAA UE downlink bursts in unlicensed cells; Figure 2 shows the frequency bandwidth of PRACH signal transmission according to a first embodiment using a repetition mechanism to comply with minimum channel occupancy requirements in the case of a system bandwidth of 20 MHz for licensed cells; Fig. 3 shows the frequency bandwidth of PRACH signal transmission according to a first embodiment using a repetition mechanism to comply with minimum channel occupancy requirements, in the case of a system bandwidth of 20 MHz for unlicensed cells; 4A and 4B respectively show the frequency bandwidth of the PRACH signal transmission according to the first embodiment for a system bandwidth of 10 MHz for licensed cells; Figure 2 shows the frequency bandwidth of PRACH signal transmission according to the first embodiment for a system bandwidth of 10 MHz for unlicensed cells; FIG. 15B is based on the implementation of FIG. 15B and specifically shows various subcarriers carrying the PRACH signal for two adjacent PRACH transmissions/repetitions according to the first embodiment. Fig. 3 shows the power spectral density of PRACH transmissions over licensed cells; Fig. 3 shows the power spectral density of improved PRACH transmission over unlicensed cells according to the first embodiment; Fig. 3 shows an exemplary implementation of a UE's transmitter chain according to the first embodiment; Fig. 4 shows a repetition pattern according to a modified first embodiment in which at least two preambles are selected to be transmitted through repetition; Fig. 4 shows a repetition pattern according to a modified first embodiment in which at least two preambles are selected to be transmitted through repetition; Fig. 4 shows a repetition pattern according to a modified first embodiment in which at least two preambles are selected to be transmitted through repetition; Fig. 3 shows the frequency bandwidth of PRACH signal transmission according to a second embodiment of adapting the parameters of PRACH signal transmission to comply with minimum channel occupancy requirements in the case of a system bandwidth of 20 MHz for licensed cells; Fig. 3 shows the frequency bandwidth of PRACH signal transmission according to a second embodiment of adapting the parameters of PRACH signal transmission to comply with minimum channel occupancy requirements in the case of a system bandwidth of 20 MHz for unlicensed cells; Fig. 4 shows the frequency bandwidth of PRACH signal transmission according to the second embodiment for a system bandwidth of 10 MHz for licensed cells; Fig. 3 shows the frequency bandwidth of PRACH signal transmission according to the second embodiment for a system bandwidth of 10 MHz for unlicensed cells; Fig. 3 shows the power spectral density of PRACH transmissions over licensed cells; 5 and 6 respectively show the power spectral density of improved PRACH transmission over unlicensed cells according to the second embodiment; Figures 22A and 22B show various subcarriers carrying the PRACH signal, in particular according to the second embodiment; Figures 23A and 23B show various subcarriers carrying the PRACH signal, in particular according to the second embodiment; Fig. 3 shows an exemplary implementation of a UE's transmitter chain according to the second embodiment; Figure 3 shows the frequency bandwidth of PRACH signal transmission for a system bandwidth of 40 MHz according to a third embodiment combining the first and second embodiments;

A “mobile station” or “mobile node” or “user terminal” or “user equipment” is a physical entity within a communication network. One node can have several functional entities. A functional entity means a software or hardware module that performs a given set of functions and/or provides a given set of functions to a node or another functional entity of a network. A node may have one or more interfaces that attach the node to a communication device or medium through which the node can communicate. Similarly, a network entity may have a logical interface that attaches the functional entity to a communication device or medium, through which the network entity may communicate with another functional entity or correspondent node.

The term "radio resource" as used in the claims and this application should be broadly understood to mean a physical radio resource (such as a time-frequency resource).

The term "unlicensed cell" or "unlicensed carrier" as used in the claims and this application should be understood broadly as a cell/carrier operating in an unlicensed frequency band having a specified frequency bandwidth. . Correspondingly, the term "licensed cell" or "licensed carrier" as used in the claims and this application is broadly defined as a cell/carrier operating in a licensed frequency band having a specified frequency bandwidth. be understood. These terms are illustratively understood in the context of 3GPP and the work item "Licensed-Assisted Access" as of Release 12/13.

The term "minimum frequency bandwidth threshold" as used in the claims and this application should be understood broadly as the minimum channel occupancy in the unlicensed cell(s). In other words, transmissions over unlicensed cells occupy at least the amount set by this threshold in terms of frequency. A minimum channel occupancy is given, for example, by regulations defined for a particular geographical area, eg 80% of the system bandwidth for Europe. In Europe, therefore, transmissions in unlicensed cells with 20 MHz must occupy at least 16 MHz.

The term "random access procedure" used in the claims and this application, in one exemplary embodiment, can be interpreted as the random access procedure of the 3GPP standard as described in the Background section. The terms "random access preamble sequence", "preamble sequence", "preamble", "RACH preamble", "preamble signature" refer to a complex sequence (in one exemplary embodiment, can be used interchangeably to mean the preamble message transmitted as described in connection with step 301 of FIG. 3 and step 401 of FIG.

The term "repetition" as used in the claims and this application should be interpreted broadly as "performing a particular action a number of times". In this particular case, transmission of the preamble is performed several times, but at different locations in the frequency domain.

The terms "occupy", "occupy a frequency bandwidth" as used in the claims and this application mean that a particular transmission of a signal/message/preamble occupies (all) frequencies in a particular frequency bandwidth. It can be interpreted broadly to mean performed by using.

As described in the background art section, 3GPP is currently in the process of introducing License Assisted Access (LAA). Some agreements have already been reached on the LAA, but no agreement has yet been reached on some key issues regarding the LAA. Furthermore, 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 restricted to operation in licensed bands. it is obvious.

One simple solution for introducing a random access procedure in the LAA is to replace the existing random access procedure in the licensed cell, including the existing preamble formats, signal shapes and transmission procedures described in the background section, by: It also applies to unlicensed cells. In this case, the CCA (free channel determination) can be performed on the UE side just before the PRACH transmission opportunity, or alternatively on the eNodeB side before scheduling the RRACH transmission opportunity. In a further alternative solution, it is also possible to omit the CCA associated with the scheduling and transmission of the PRACH, however, due to the omission of the CCA, transmissions may collide and thus operate on the same radio channel. can cause problems with another node that is It should be noted that whether or not CCA is ultimately required depends on the regulations of the region where the system operates (see background art section and Non-Patent Document 4).

However, this simple method also has drawbacks. In particular, according to European regulations, as described in the Background section, each transmission in an unlicensed band following a CCA (Free Channel Assessment) must occupy at least 80% of the nominal channel bandwidth. must. Similar regulations can be found in other countries, for example in the United States the minimum transmission bandwidth is 500 kHz (see Non-Patent Document 4). Assuming a nominal channel bandwidth of 20 MHz for LTE operation in unlicensed bands (see Non-Patent Document 4), the 80% minimum channel occupancy specified in Europe results in a minimum frequency bandwidth of 16 MHz. Become. On the other hand, however, a PRACH transmission according to the existing definition in the licensed band occupies only 6 consecutive PRBs, independent of the channel bandwidth, which is 1.08 MHz (i.e. only 5 of the nominal channel bandwidth of 20 MHz). .4%)). Therefore, this simple solution (applying the existing definition of PRACH transmission to unlicensed cells) does not meet the minimum channel occupancy requirements given by European regulations.

Additionally, it should be noted that this minimum channel occupancy depends on the actual channel bandwidth of the unlicensed cells and can therefore vary from unlicensed cell to unlicensed cell. In other words, the transmission of the random access preamble must fit the channel bandwidth so that the minimum channel occupancy requirements defined for unlicensed cells can be adhered to. In contrast, existing random access procedures, in particular the transmission of random access preambles, are fixed in their bandwidth, i.e. always 6 channels regardless of the actual channel bandwidth of the (licensing) cell. Use PRBs. Therefore, a further drawback of schemes that use existing mechanisms to transmit random access preambles over unlicensed cells is that they comply with minimum channel occupancy requirements, which may vary in practice depending on the channel bandwidth of the unlicensed cells. flexibility is lacking.

The inventors have conceived the following illustrative embodiments in an effort to alleviate one or more of the problems described above.

Certain implementations of the various embodiments are implemented within a broad range of specifications given by the 3GPP standards, some of which are described in the Background section, and particularly important features associated with the various embodiments are , are added as described below. It should be noted that although these embodiments can be advantageously used in mobile communication systems such as, for example, 3GPP LTE-A (Release 10/11/12/13) as described in the Background section, the embodiments are Note that it is not limited to use with any particular exemplary communications network.

The following description should not be understood as limiting the scope of the present disclosure, but merely as examples of embodiments for a better understanding of the present disclosure. Those skilled in the art should recognize that the general principles of the disclosure, as recited in the claims, can be applied to a variety of scenarios and in ways not explicitly described herein. be. For purposes of explanation, some assumptions are made that do not limit the scope of the embodiments below.

Furthermore, as noted above, the following embodiments may 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 features (i.e. features not modified by the various embodiments) may remain exactly the same as those described in the Background section or may be modified without affecting the various embodiments. . For example, the functions and procedures leading to improved random access procedure performance (such as the need for uplink synchronization, the need to send scheduling requests, etc.) and the remaining steps of the random access procedure (random access response, conflict resolution, etc.). etc.).

In the following, three embodiments for solving the above problem(s) are described, these being the following exemplary scenarios devised for easy explanation of the principles of the embodiments: be explained by using However, these principles can also be applied to other scenarios, some of which are explicitly mentioned in the discussion below.

As described in the Background section, 3GPP introduced LAA (Licensed Assisted Access), which involves the use of unlicensed cells operated in channel(s) in unlicensed frequency bands, We plan to enhance the functions of the current system. In the following, we assume such a scenario, ie the UE is configured with at least one licensed cell and at least one unlicensed cell. Although the following description is based on such a scenario, various embodiments focus on performing random access procedures in unlicensed cells, thus various It also applies to scenarios operated in (i.e. without corresponding license cells).

An unlicensed cell can be set up between the eNodeB and the UE in the normal way as described in the background art section. An unlicensed cell is therefore a specific frequency bandwidth (also called nominal channel bandwidth in some European standards) in the unlicensed frequency band (e.g. 10 MHz, 20 MHz, 40 MHz, or (in future) smaller bands). (width, or greater bandwidth, etc.). As explained in detail in the background art section, operation in unlicensed cells is variously regulated, for example in Europe, according to the European standard, Non-Patent Document 5. In Europe (and elsewhere), minimum channel occupancy is specifically defined for channels in unlicensed cells, e.g. in Europe the channel bandwidth occupied in an unlicensed cell is within 80% to 100% of the declared nominal channel bandwidth of Therefore, transmissions in unlicensed cells (with very few exceptions) do not meet this minimum channel occupancy requirement such that the transmissions occupy the corresponding frequency bandwidth portion of the total unlicensed cell frequency bandwidth. must obey. Given that unlicensed cells can have different nominal channel bandwidths, the resulting minimum frequency bandwidth (which is a percentage of the nominal channel bandwidth) that must be occupied is the different nominal channel bandwidths different between channels with

In the following embodiments, we assume that both the eNodeB and the UE are aware of a certain minimum channel occupancy to follow. UEs and eNodeBs are aware of a minimum frequency bandwidth threshold, which depends on the actual system bandwidth over which unlicensed cells are established. There are several possible different ways to achieve this. In one alternative, both the UE and the eNodeB independently determine a particular minimum frequency bandwidth threshold and both arrive at the same value by following the same decision rule. In another alternative, the eNodeB determines a specific minimum frequency bandwidth threshold and correspondingly, e.g. In the case of a random access procedure without a random access procedure, this threshold is made known to the UE in the random access preamble assignment message (see message 401 in FIG. 4) sent at the beginning of the random access procedure. According to yet another alternative, the UE determines a certain minimum frequency bandwidth threshold and correspondingly informs the eNodeB of this threshold. In either case, both the UE and the eNodeB have the same perception of the minimum frequency bandwidth threshold that preamble transmissions should at least occupy.

This minimum frequency bandwidth threshold represents the lower bound of the frequency bandwidth that the transmission of the random access preamble must occupy. Furthermore, the actual used frequency bandwidth for 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 for preamble transmission can be determined by the UE and/or the eNodeB, similar to when determining the minimum frequency bandwidth threshold, and if necessary this information is shared between the two entities. can be exchanged between Details will also become apparent from the detailed description of the various embodiments.

As mentioned above in the Technical Background section, currently it has been agreed that only contention-free RACH procedures are supported in unlicensed cells, the details of which are described in the Technical Background section. Thus, the assumed scenario follows this initial agreement, but it should be understood that the principles of the invention according to various embodiments are equally applicable to contention-based RACH procedures. In particular, as will become apparent below, various embodiments of the invention focus on the transmission of random access preambles, and thus various embodiments of the invention enable the UE to select an appropriate random access preamble sequence. A contention-based RACH procedure that autonomously selects (from the appropriate set of preambles) and corresponding indication information on which random access preamble sequences (of that preamble set) are to be used for the random access procedure from the eNodeB to the UE. is equally applicable to contention-free RACH procedures received by . In the contention-based RACH procedure, similar to the method described in the Background section, one bit of information giving information on the amount of transmission resources required to transmit the next message (msg3, 303 in FIG. 3) is Allowing the UE to select between two subgroups (the set of preambles available for the contention-based random access procedure is divided into these two subgroups) to allow for additional transmissions. be able to.

In the following embodiments, it is further assumed that the random access procedure need not be changed other than the transmission (and reception) of the random access preamble. As a result, the overall structure and order of the random access procedure exemplarily described in the Background section may remain the same, with respect to the transmission of the random access preamble as described in various embodiments below. It only introduces changes to the random access procedure. For example, standardized procedures for triggering the random access procedure and other messages of the random access procedure (random access response messages 302, 403, scheduled transmissions 303, contention resolution messages 304, random access preamble assignment 401, etc.) ) do not need to be changed. Therefore, to avoid repetition, reference may be made to the corresponding paragraphs in the background section above.

Therefore, assuming that random access procedures are triggered in unlicensed cells, the following embodiments provide several implementations of improved random access procedures performed in unlicensed cells.

First Embodiment In the following, a first embodiment for solving the above problem(s) is detailed. Various implementations of the first embodiment are described below by using the example scenario introduced above.

Briefly, according to the first embodiment, the existing definition of how to transmit the random access preamble to the radio base station is reused, but in the first embodiment it is additionally repeated as follows: introduce a mechanism. A repetition mechanism in the UE may be configured so that the combined transmission of the random access preambles occupies at least the frequency bandwidth required to comply with the minimum channel occupancy requirements defined for unlicensed cells. It allows normal transmission to be repeated as many times as required at different frequency locations in the frequency domain. Not only does this allow existing definitions and standardizations of preamble transmissions to be reused as much as possible (and as much as necessary), but at the same time the repetition scheme does not exceed the minimum frequency bandwidth threshold. allows the entire PRACH transmission (i.e. including all preambles (repetitions)) to be flexibly adapted to various bandwidth requirements by simply adding further repetitions of the "standard" PRACH signal in frequency up to . More specifically, the exemplary implementation of the first embodiment follows as closely as possible the normal random access procedures in license cells 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 art section. Thus, for example, it involves using a Zadoff-Chu root sequence explicitly indicated by the 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 for use in performing random access procedures over licensed cells as well as performing random access procedures over unlicensed cells. It is also available for the purpose of being used to Furthermore, the random access preamble can therefore also have the same structure as described in connection with FIG. or 139 for format 4). The same applies to the subcarrier spacing of 1.25 kHz for preamble formats 0-3 and the subcarrier spacing of 7.5 kHz for preamble format 4, which are equally applicable according to this implementation. . Furthermore, the same PRACH duration as before (ie _TCP and T _SEQ combined) can be assumed.

Assuming a contention-free random access procedure, the UE receives corresponding indication information from the eNodeB as to which particular random access preamble of the generated set is to be used for the random access procedure. The UE thus selects the indicated random access preamble from the available set of preambles and prepares its transmission to the eNodeB as follows.

A particular exemplary implementation of the first aspect will now be described in detail. First, assume that licensed and unlicensed cells are configured with a nominal channel bandwidth of 20 MHz (nominal channel bandwidth can also be referred to as "system bandwidth"). The following description is made with reference to Figures 14A and 14B, which illustrate PRACH transmissions performed by corresponding UEs supporting LAA in licensed and unlicensed cells, respectively. As is evident from FIG. 14A, the transmission of random access preambles (PRACH) over licensed cells is normally performed in 6 PRBs, i.e. having a frequency bandwidth of 1.08 MHz (6 x 180 kHz). . A corresponding random access preamble transmission carried out over an unlicensed cell occupies at least the 16 MHz channel bandwidth of that unlicensed cell in order to comply with the 80% minimum channel occupancy parameter specified in Europe. (see Figure 14B). In order to achieve this increased channel occupancy, the first embodiment proposes to introduce a repetition mechanism, which repeats the "normal" preamble transmission at several different frequency locations to achieve the 16MHz Configure the entire PRACH transmission above the minimum frequency bandwidth threshold. As shown in FIG. 14B, normal PRACH transmissions can be repeated as many times as necessary until the minimum channel occupancy of 16 MHz is exceeded. That is, in this particular case, 14 iterations of PRACH transmission are performed, thus using 90 PRBs to occupy 16.2 MHz by transmitting a total of 15 normal PRACHs.

In the following example scenarios in FIGS. 15A and 15B, assume licensed and unlicensed cells are configured with a nominal channel bandwidth of 10 MHz. Correspondingly, resulting in a minimum channel occupancy of 80%, the combined random access preamble transmission must occupy a minimum frequency bandwidth of at least 8 MHz. As described in connection with FIGS. 14A and 14B, FIG. 15A discloses PRACH transmission (typically over 6 PRBs) over licensed cells. In contrast, as shown in FIG. 15B, for unlicensed cells, there are 7 repetitions, and thus 8 PRACH transmissions, for a total of 48 PRBs, 8.64 MHz (48×180 kHz). occupy.

In one particular example implementation, different iterations of the preamble transmission according to FIGS. 14B and 15B can use different offsets φ, which are derived, for example, from corresponding tables in the background section. may be directly derivable by the UE from the initial offset φ (7 or 2 depending on the format of the preamble) provided. Various offsets can be selected such that individual preamble transmissions are directly adjacent but do not overlap each other. Alternatively, although not shown in the figure, two adjacent preambles can be separated such that only one guard band separates two preamble transmissions (instead of two guard bands as is apparent from FIG. 16). It may also be possible to allow slight overlap of transmissions. For this purpose, the repetition frequency offset must be set according to the overlap.

FIG. 16 is based on the example scenario of FIG. 15B and further expands the diagram to show various subcarriers and guard bands for two adjacent preamble transmissions out of eight preamble transmissions. As is clear from the figure, a typical subcarrier frequency spacing of 1.25 kHz and 839 subcarriers that make up the PRACH signal are assumed (see also Figure 7 and corresponding parts in the Background section). ).

The required number of repetitions required to comply with the minimum channel occupancy requirements specified for unlicensed cells is the frequency bandwidth occupied by the normal preamble transmission (i.e. 1.08 MHz) plus the minimum frequency bandwidth can be determined autonomously by the UE and eNodeB by simple calculations based on width thresholds (eg, 16 MHz for 20 MHz system bandwidth, 8 MHz for 10 MHz system bandwidth). Alternatively, the eNodeB can explicitly indicate to the UE the number of repetitions the UE should use when sending the preamble. Alternatively, the number of iterations for different system bandwidth settings can be fixed in the standard. As is evident from FIGS. 14B and 15B, for the assumed exemplary scenario, 14 and 7 iterations are required, respectively, or in other words, 15 and 8 PRACH transmissions, respectively. is necessary. The eNodeB can thus successfully decode the PRACH transmission. Alternatively, the number of iterations for each nominal channel bandwidth can be predefined in the standard and thus known to both the UE and the eNodeB.

In one exemplary implementation of the first aspect, it is assumed that each PRACH transmission is transmitted by the UE at the same transmit power used for normal PRACH transmissions (in licensed cells). Specifically, FIG. 17A shows a UE's PRACH transmission over a licensed cell with a specific transmit power and a specific power spectral density, where the PRACH transmission is typically 6 PRBs, 1 over .08 MHz. The transmit power is determined in the usual way (eg by open-loop estimation with fully compensated pathloss). The UE estimates the pathloss by averaging Reference Signal Received Power (RSRP) measurements. FIG. 17A therefore shows such a PRACH transmission over a licensed cell. FIG. 17B shows in a suitable way the combined PRACH transmission over the unlicensed cells, as described above with respect to FIG. , 8.64 MHz. As is evident from FIG. 17B, in this implementation of the first embodiment, all the various transmissions (i.e. all iterations) of the normal PRACH transmission have the same power spectral density (i.e. are transmitted with the same transmit power). It is assumed that Such transmission can be implemented at the UE by applying the same transmit power value set for normal PRACH transmission also repeatedly at different frequency locations over unlicensed cells. .

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 sent at lower transmit power (eg, half the transmit power). One particular method for setting the transmit power is that the total transmit power (i.e., the transmit power used to transmit all of the PRACH (e.g., 8 total transmissions in the case of FIG. 17B)) is Setting the transmit power of each of the various PRACH transmissions to be the same as the transmit power used to transmit one PRACH over the licensed cell. Therefore, although the power spectral density is reduced by the total number of PRACH transmissions (eg PSD/8), the total transmit power used by the UE for PRACH transmissions remains the same.

Further, FIG. 18 shows an exemplary implementation of the UE transmitter according to the first embodiment described with respect to FIG. 10 in the Background section. As is evident from FIG. 18, the repetition mechanism described above in various implementations of the first embodiment can be implemented between DFT and subcarrier mapping in the transmit chain. By means of DFT and subcarrier mapping, positioning of the PRACH signal in the frequency domain is achieved, therefore the generated preamble is processed in various DFTs to convert the resulting frequency samples (N _ZC ) to the corresponding frequency positions by means of subcarrier mapping. , the same generated preamble (left part) of length _NZC can be repeated at multiple different frequency locations in the frequency domain as exemplarily shown in FIGS. 14B and 15B.

A further implementation of this first embodiment provides an improvement by allowing different preamble sequences to be used for different iterations. These improved implementations are described with respect to FIGS. 19, 20 and 21. FIG. Briefly, additional information can be encoded across the PRACH transmission by allowing different preamble sequences to be used for different repetitions and appropriately determining different repetition patterns between the eNodeB and the UE. .

Additional information may include, for example, indicators of channel occupancy observed by UEs sending the PRACH. The observed channel occupancy can be defined by the ratio of successful and unsuccessful CCA (free channel determination) on the UE side prior to PRACH transmission. A threshold value, such as 0.5, can be defined for this ratio. In this case, the transmitted PRACH conveys information whether this ratio is above, equal to, or below a defined threshold. The eNB can utilize this information when scheduling downlink data transmissions to the UE and can expect poor quality of service if this ratio is low.

In the above implementation of the first embodiment, in particular, only one preamble (out of the available preambles) is used in the entire PRACH transmission (including repetitions), following standard procedures for normal PRACH transmissions. ie the same preamble is repeatedly transmitted at different frequency locations. Therefore, only one preamble (eg indicated by the corresponding indication information from the eNodeB) is selected by the UE and that preamble is used for each PRACH transmission. However, further implementations of the first embodiment may use two or more different preambles sent by the UE in the same random access procedure over unlicensed cells, as described below. .

First, assume that two different preambles are selected by the UE for performing random access procedures over unlicensed cells. According to one implementation, both different preambles can be individually indicated by the eNodeB. Alternatively or additionally, a fixed correspondence between different preambles can be defined, so that the UE can be notified when one particular random access preamble is indicated by the eNodeB (or contention-based When autonomously selecting one random access preamble in the case of RACH), further random access preamble(s) associated with the indicated (or autonomously selected) random access preamble are correspondingly select. To improve transmission performance, by properly defining the correspondences to minimize the PAPR (Peak-to-Average Power Ratio) or CM (Cubic Metric) of the entire transmission, Certain correspondences can be optimized.

Therefore, different PRACH transmissions are performed using different preambles. In the example scenario of FIG. 19, assuming a system bandwidth of 20 MHz, preamble A and preamble B are alternately used in the frequency domain, thus providing ABABABAB.B for transmitting 15 PRACH transmissions. . . forming a repeating pattern. FIG. 20, also assuming two different preambles A and B, shows another exemplary repetition pattern, where one (approximately) One half uses preamble A and the other half uses preamble B (ie, AAAAAAAABBBBBBBB). In the exemplary implementation of FIG. 21, a total of three different preambles (preambles A, B, C) are assumed, with the exemplary shown repeating pattern AAAAABBBBBBCCCCC.

In one example implementation, the repetition pattern to use may be selected by the UE, eg, from a limited number of preset repetition patterns. The number of pre-configured repeating patterns can be set by the eNodeB, for example, and signaled to the UE(s) in its cell, or can be standardized. can.

Each preconfigured repetition pattern may for example be associated with one specific piece of information, so that the specific information is already encoded by the UE choosing a specific repetition pattern. For example, when the eNodeB blind decodes the PRACH repetitions, it successfully decodes the various PRACH transmissions according to the repetition pattern selected by the UE, thus deriving the encoded information.

Information about the required transmission resources can be information encoded by the repetition pattern. Assuming two different repetition patterns that can be used by the UE, one repetition pattern can be associated with a larger amount of transmission resources, while the other repetition pattern can be associated with only a small amount of transmission resources. It can be interpreted to indicate that the UE needs it.

Another important information can be the channel occupancy statistics observed from the UE's point of view as described above. The pattern ABABABAB. . . may exhibit a channel occupancy higher than, for example, 0.5, and the pattern BABABABA. . . can exhibit a channel occupancy equal to or less than 0.5.

Second Embodiment In the following, a second embodiment for solving the above problem(s) is detailed. The principle behind the second embodiment is quite different from the repetition mechanism described in relation to the first embodiment. Various implementations of the second embodiment are detailed below by using the example scenarios introduced above.

Briefly, in the second embodiment, instead of performing various repetitions of the normal PRACH signal as in the first embodiment, to spread the signal over the required frequency bandwidth (i.e. unlicensed cells to comply with the minimum channel occupancy requirements for ), one or more configuration parameters for transmitting the PRACH signal are adapted. The configuration parameters are the length of the RACH preamble sequence (ie, N _ZC ) and the subcarrier frequency spacing of the subcarriers used to transmit the RACH preambles (ie, Δf _RA ). These two parameters in combination basically define the total frequency bandwidth of the PRACH signal transmission. The frequency bandwidth of a normal PRACH transmission is always 1.08 MHz, regardless of the system bandwidth of the channel over which the PRACH is transmitted, as explained in the Background section. For example, in the case of preamble formats 0 to 3, the subcarrier frequency spacing is 1.25 kHz, and there are 864 subcarriers (839 subcarriers + 2 x 12.5 subcarriers for guard band) (Fig. 7). ), thus having a frequency bandwidth of 1.08 MHz. For preamble format 4, the subcarrier frequency spacing is 7.5 kHz and has 144 subcarriers (139 subcarriers + 2 x 2.5 subcarriers for the guard band), again It has a frequency bandwidth of 1.08 MHz. Note that the number of subcarriers used to transmit the PRACH signal is the same as the length of the preamble sequence, N _ZC , because the preamble sequence is first transformed into N _ZC frequency samples, each of which is This is because they are mapped to corresponding N _ZC subcarriers. The method of this implementation is generally applied in LTE because, as a property of ZC sequences, the DFT of ZC sequences is also a weighted cyclically-shifted ZC sequence. Furthermore, it should be noted that optimal cyclic cross-correlation between any pairs is achieved when the length of the preamble sequence is prime.

Therefore, by appropriately choosing different values of these two parameters, the frequency bandwidth of PRACH transmissions can be controlled in order to comply with the minimum channel occupancy requirements specified for unlicensed cells. For this purpose, either one or both of the two parameters can be changed when compared to normal/legacy PRACH signals transmitted in unlicensed cells. For these two parameters (N _ZC and Δf _RA ) many different combinations are possible depending on the actual minimum frequency bandwidth threshold that the PRACH signal transmission must at least occupy.

In the following, as already done for the first embodiment, two different system bandwidths of 10 MHz and 20 MHz are assumed and shown respectively in Figures 22A, 22B, 23A and 23B. Furthermore, we assume the same minimum channel occupancy requirement of 80% in Europe, thus when performing a random access procedure over an unlicensed cell (e.g. transmitting a preamble from the UE to the eNodeB as part of the random access procedure sometimes), subject to minimum frequency bandwidth thresholds of 8 MHz and 16 MHz, respectively.

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

In contrast, the preamble sequence length, and thus the number of subcarriers for transmitting the preamble signal, is the same as for normal/legacy PRACH transmission (i.e. 839 for preamble formats 0-3, 839 for preamble format 4 139) can be maintained. 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, for a preamble of length 839 (total of 864 subcarriers including the additional subcarriers for the two guard bands) and a frequency bandwidth threshold of 8MHz, subcarriers of at least 9.26kHz Frequency spacing is required.

Alternatively, both preamble length and RACH subcarrier frequency spacing can be varied to comply with minimum channel occupancy requirements. In the case described above with a system bandwidth of 10 MHz for unlicensed cells, a subcarrier frequency spacing of 7.5 kHz can be assumed, with a total of at least 1067 subcarriers for the PRACH signal (actual preamble subcarriers and additional subcarriers for guard bands).

It is also commonly employed for PRACH transmissions in order to minimize the orthogonality loss in the frequency domain between the preamble sub-carriers and the surrounding uplink data transmission sub-carriers. Note that the subcarrier frequency spacing should be an integer fraction (1 kHz, 2.5 kHz, 3 kHz, 5 kHz, 7.5 kHz, 15 kHz, etc.) of the subcarrier frequency spacing (i.e. 15 kHz) used for PUSCH transmission. sea bream. Conversely, the PUSCH subcarrier spacing should be an integer multiple of the PRACH subcarrier spacing. Furthermore, for the purpose of facilitating multiplexing of PRACH and PUSCH, PRACH should be allocated a frequency bandwidth equal to an integer multiple of the frequency bandwidth of the resource block (ie an integer multiple of 180 kHz). Furthermore, for an improved preamble design that maximizes the number of ZC sequences with optimal cross-correlation properties, prime length preamble sequences should be chosen. For optimal results, the design constraints just described are more easily achieved when both parameters (i.e., preamble length and subcarrier frequency spacing) are made variable, as described below. can be done.

First, assume a system containing unlicensed cells 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 transmission signal should be a multiple of the resource block bandwidth of 180 kHz, we assume the total frequency bandwidth of the PRACH signal to be 16.02 MHz across 89 PRBs. , which facilitates frequency multiplexing of the PRACH and PUSCH as described above. In an exemplary implementation, a subcarrier frequency spacing of 15 kHz can be determined, resulting in 1068 subcarriers. The closest prime number less than 1068 is 1063, so we can expect 5 subcarriers for the two guardbands (ie 2.5 subcarriers per guardband). This exemplary implementation of the PRACH signal according to the second embodiment is shown in FIGS. 22B and 25. FIG. In such a configuration of the PRACH transmission 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 is prime (which enhances cross-correlation properties).

Now assume an exemplary system with a system bandwidth of 10 MHz for unlicensed cells and a corresponding minimum frequency bandwidth threshold of 8 MHz. Considering that the resulting bandwidth of the PRACH transmission signal should be a multiple of the resource block bandwidth of 180 kHz, the total frequency bandwidth of the PRACH signal is 8.1 MHz across the 45 PRBs in total. can be assumed. A subcarrier frequency spacing of 7.5 kHz can be assumed. This results in a total of 1080 subcarriers for the PRACH signal (including the actual preamble subcarriers and additional subcarriers for the guardbands). The closest prime number less than 1080 is 1069, so we can expect 11 subcarriers for the two guardbands (ie 5.5 subcarriers per guardband). This exemplary implementation of the PRACH signal according to the second embodiment is shown in FIGS. 23B and 26. FIG.

As an alternative for a 20 MHz system, the preamble sequence length could be chosen to be a prime number of 1069, which is the same length as for a 10 MHz system, thus using the same preamble for both bandwidths of unlicensed cells. The advantage of this is that the UE does not have to provide different sequence length preambles to support the two system bandwidths. Therefore, assuming that the total frequency bandwidth should cover 16.2 MHz (i.e. covering 90 PRBs with 180 kHz each), a total of 1080 PRBs with 15 kHz each are required to transmit the PRACH signal. 1 subcarrier is used. This results in 5.5 subcarriers per guardband.

In both exemplary implementations, preamble lengths of 1069 and 1063, respectively, also affect the size of the DFT, but the IDFT (Fig. 27) does not increase very significantly. By keeping the length of the preamble sequence relatively small, the complexity of the DFT and IDFT operations is not significantly increased.

For unlicensed cells with different system bandwidths (eg 40 MHz), a similar method can be applied to set the parameters used for PRACH signal transmission.

In summary, as described above, the preamble sequence length and There are several methods as to how to set the RACH subcarrier frequency spacing. The corresponding parameter(s) can be selected either by the UE or the eNodeB, in the latter case the eNodeB has to indicate the selection result to the UE.

In one particular implementation, different combinations of parameters for various system bandwidths (e.g., the combination of parameters described above) are preconfigured, so that for a system bandwidth of 20 MHz, a preamble length of 1069 and a preamble length of 15 kHz. Subcarrier frequency spacing can be selected. Similarly, for a system bandwidth of 10 MHz, a preamble length of 1069 and a subcarrier frequency spacing of 7 kHz can be chosen.

As explained above, according to the second embodiment, the preamble sequence length can be varied as a function of the system bandwidth (ie the corresponding minimum frequency bandwidth threshold). Therefore, a specific preamble (having a fixed length of 839 or 139) generated for performing random access procedures over licensed cells is reused for performing random access procedures over unlicensed cells. likely to be unable to. Therefore, in one particular implementation of the second embodiment, at least an additional set of random access preambles can be generated for this purpose, thus allowing either via licensed or unlicensed cells Different sets of preambles are available to perform the random access procedure on the According to the above-described exemplary implementation of the second embodiment, a further set of preambles with a sequence length of 1069 can be generated. For example, a suitable root sequence with a sequence length of 1069 can be provided (e.g. provided by the eNodeB and indicated to the UE), from which the UE can perform a cyclic shift to a certain number different preambles can be generated.

For example, 64 different preambles of length 1069 can be generated by performing a cyclic shift of the corresponding root sequences. On the other hand, considering that fewer random access procedures are likely to be performed over unlicensed cells, fewer (eg, only 16) preambles may be generated for the set.

In an exemplary implementation of the second aspect, PRACH transmissions over unlicensed cells use the same transmit power as the transmit power set for normal PRACH transmissions over licensed cells. Assuming it does. A corresponding illustration of this implementation is presented in FIGS. 24A and 24B. As can be seen from FIG. 24B, the power spectral density of PRACH transmissions over unlicensed cells is significantly reduced when compared to the corresponding PRACH transmissions over licensed cells shown in FIG. 24A. Alternatively, PRACH transmissions over unlicensed cells can be transmitted at different transmit power values (higher or lower than the transmit power value used for PRACH transmissions over licensed cells). For example, the transmit power can be increased to achieve essentially the same power spectral density over the extended frequency bandwidth as for transmission with normal PRACH transmissions over licensed cells (see FIG. 24A). can. On the other hand, if the licensed cell is a macrocell with a large coverage area compared to an unlicensed cell with a small coverage area, the transmission power of PRACH transmission via the unlicensed cell is set to PRACH via the licensed cell. It can also be reduced compared to transmission.

Furthermore, FIG. 27 shows an exemplary implementation of a UE transmitter according to the second embodiment, which is similar to the implementation described in relation to FIG. 10 in the Background section. Similar. The above-described principle behind the second embodiment requires no substantial modification of the UE's transmit chain. Instead, different values of DFT and IDFT sizes and sampling rate f _s are applied to process the appropriate preambles transmitted over unlicensed cells. The DFT and IDFT sizes correspond directly to the preamble sequence length.

Third Embodiment In the following, a third embodiment for solving the above problem(s) is detailed. This third embodiment is basically a combination of the first and the second embodiment and thus allows the best combination of the two principles. Briefly, one of the improved PRACH transmissions described according to the second embodiment can be repeated according to the repetition mechanism introduced by the first embodiment.

For example, the third embodiment uses a large system bandwidth, e.g. Width is most beneficial, too large preamble length can be disadvantageous in preamble generation and implementation of UE transmitter (particularly DFT and IDFT). As an example, assuming a system bandwidth of 40 MHz for unlicensed cells, according to a third embodiment, the PRACH signal described in connection with FIG. In order to comply with the minimum channel occupancy of 80% of the width, this PRACH signal can be repeated once (ie transmitted twice in total).

Another example is shown according to FIG. 28, where we assume three repetitions using a PRACH signal (see FIGS. 23B and 26) having a frequency bandwidth of 8.1 MHz, thus A combined PRACH transmission for a total of four PRACHs covers sufficient frequency bandwidth over 32 MHz.

Hardware and Software Implementation of the Disclosure Another exemplary embodiment relates to implementing the various embodiments described above using hardware, software, or software cooperating with hardware. In this context, a user terminal (mobile terminal) and an eNodeB (base station) are provided. User terminals and base stations are configured to perform the methods described herein and include corresponding entities (receivers, transmitters, processors, etc.) that are appropriately involved in these methods.

It is further recognized that various embodiments can be implemented or performed using a computing device (processor). A computing device or processor may be, for example, a general purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA), or other programmable logic device. Various embodiments may also be performed 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 inputs and outputs coupled to them. LSIs are also called ICs, system LSIs, super LSIs, or ultra LSIs depending on the degree of integration. However, the technology for implementing integrated circuits is not limited to LSI, but can be accomplished using dedicated circuits or general-purpose processors. Furthermore, an FPGA (Field Programmable Gate Array) that can be programmed after the LSI is manufactured, or a reconfigurable processor that can reconfigure connections and settings of circuit cells arranged inside the LSI can be used.

Additionally, various embodiments may also be implemented by software modules. These software modules can be executed by a processor or directly in hardware. Also a combination of software modules and a hardware implementation is possible. The software modules may be stored on any kind of computer readable storage media, for example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. Furthermore, it should be noted that individual features of a plurality of different embodiments may be the subject of another embodiment, either individually or in any combination.

It will be appreciated by those skilled in the art that various changes and/or modifications may be made to the present disclosure as illustrated in specific embodiments without departing from the concept or scope of the invention as broadly described. will be done. Accordingly, the embodiments set forth herein are to be considered in all respects illustrative and not restrictive of the invention.

Claims (12)

a circuit that selects a random access preamble sequence;
a transmitter that transmits the selected random access preamble sequence to a base station in the frequency bandwidth of an unlicensed band;
with
The frequency bandwidth is defined from the length of the random access preamble sequence and the subcarrier spacing, and is greater than the frequency bandwidth over which the random access preamble sequence is transmitted in the license band.
User equipment. the circuit selects the random access preamble sequence having a length greater than the length of the random preamble sequence used for license bands;
2. User equipment according to claim 1. the circuit selects the random access preamble sequence having the same length as the length of the random preamble sequence used for the license band;
The transmitter repeatedly transmits the random access preamble sequence on a plurality of different frequencies.
2. User equipment according to claim 1. The frequency bandwidth is equal to or greater than the minimum bandwidth required for the unlicensed band,
2. User equipment according to claim 1. the length of the random access preamble sequence is signaled by the base station;
2. User equipment according to claim 1. The number of repetitions of the random access preamble sequence is notified by the base station,
4. User equipment according to claim 3. selecting a random access preamble sequence;
transmitting the selected random access preamble sequence to a base station in the frequency bandwidth of an unlicensed band;
The frequency bandwidth is defined from the length of the random access preamble sequence and the subcarrier spacing, and is greater than the frequency bandwidth over which the random access preamble sequence is transmitted in the license band.
random access method. selecting the random access preamble sequence having a length longer than the length of the random preamble sequence used for the license band;
Random access method according to claim 7. selecting the random access preamble sequence having the same length as the length of the random preamble sequence used for the license band;
The random access preamble sequence is repeatedly transmitted on a plurality of different frequencies,
Random access method according to claim 7. The frequency bandwidth is equal to or greater than the minimum bandwidth required for the unlicensed band,
Random access method according to claim 7. the length of the random access preamble sequence is signaled by the base station;
Random access method according to claim 7. a process of selecting a random access preamble sequence;
and controlling the process of transmitting the selected random access preamble sequence to a base station in the frequency bandwidth of an unlicensed band;
The frequency bandwidth is defined from the length of the random access preamble sequence and the subcarrier spacing, and is greater than the frequency bandwidth over which the random access preamble sequence is transmitted in the license band.
integrated circuit.

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