Patent Application
20240276539
The disclosure relates to a PRACH preamble structure for a symbol having a relatively short length in comparison with a maximum round-trip time in a cell in ultra-high frequency band wireless communication, and a method and a device for random access.
A review of the development of mobile communication from generation to generation shows that the development has mostly been directed to technologies for services targeting humans, such as voice-based services, multimedia services, and data services. It is expected that connected devices which are exponentially increasing after commercialization of 5G communication systems will be connected to communication networks. Examples of things connected to networks may include vehicles, robots, drones, home appliances, displays, smart sensors connected to various infrastructures, construction machines, and factory equipment. Mobile devices are expected to evolve in various form factors, such as augmented reality glasses, virtual reality headsets, and hologram devices. In order to provide various services by connecting hundreds of billions of devices and things in the 6G era, there have been ongoing efforts to develop improved 6G communication systems. For these reasons, 6G communication systems are referred to as Beyond-5G systems.
6G communication systems, which are expected to be implemented approximately by 2030, will have a maximum transmission rate of tera (1,000 giga)-level bps and a radio latency of 100 μsec, and thus will be 50 times as fast as 5G communication systems and have the 1/10 radio latency thereof.
In order to accomplish such a high data transmission rate and an ultra-low latency, it has been considered to implement 6G communication systems in a terahertz band (for example, 95 GHz to 3 THz bands). It is expected that, due to severer path loss and atmospheric absorption in the terahertz bands than those in mmWave bands introduced in 5G, a technology capable of securing the signal transmission distance (that is, coverage) will become more crucial. It is necessary to develop, as major technologies for securing the coverage, multiantenna transmission technologies including radio frequency (RF) elements, antennas, novel waveforms having a better coverage than OFDM, beamforming and massive MIMO, full dimensional MIMO (FD-MIMO), array antennas, and large-scale antennas. In addition, there has been ongoing discussion on new technologies for improving the coverage of terahertz-band signals, such as metamaterial-based lenses and antennas, orbital angular momentum (OAM), and reconfigurable intelligent surface (RIS).
Moreover, in order to improve the frequency efficiencies and system networks, the following technologies have been developed for 6G communication systems: a full-duplex technology for enabling an uplink (UE transmission) and a downlink (node B transmission) to simultaneously use the same frequency resource at the same time; a network technology for utilizing satellites, high-altitude platform stations (HAPS), and the like in an integrated manner; a network structure innovation technology for supporting mobile nodes B and the like and enabling network operation optimization and automation and the like; a dynamic spectrum sharing technology though collision avoidance based on spectrum use prediction, an artificial intelligence (AI)-based communication technology for implementing system optimization by using AI from the technology design step and intemalizing end-to-end AI support functions; and a next-generation distributed computing technology for implementing a service having a complexity that exceeds the limit of UE computing ability by using super-high-performance communication and computing resources (mobile edge computing (MEC), clouds, and the like). In addition, attempts have been continuously made to further enhance connectivity between devices, further optimize networks, promote software implementation of network entities, and increase the openness of wireless communication through design of new protocols to be used in 6G communication systems, development of mechanisms for implementation of hardware-based security environments and secure use of data, and development of technologies for privacy maintenance methods.
It is expected that such research and development of 6G communication systems will enable the next hyper-connected experience in new dimensions through the hyper-connectivity of 6G communication systems that covers both connections between things and connections between humans and things. Particularly, it is expected that services such as truly immersive XR, high-fidelity mobile holograms, and digital replicas could be provided through 6G communication systems. In addition, with enhanced security and reliability, services such as remote surgery, industrial automation, and emergency response will be provided through 6G communication systems, and thus these services will be applied to various fields including industrial, medical, automobile, and home appliance fields.
Meanwhile, a terminal may perform a random access procedure with a base station to match uplink synchronization to perform communication with the base station. For example, a terminal may transmit a random access preamble generated in a predetermined sequence to a base station, and the base station may measure a round trip delay (RTD) with the terminal through the random access preamble and then determine a timing advance (TA) value for adjusting the transmission time of the uplink signal of the terminal based on the measured RTD, and may transmit the determined TA value to the terminal through a random access response. At this time, a physical random access channel (PRACH) in existing LTE or NR is designed to be suitable for an environment in which the symbol length of a signal is much larger than the maximum RTD of a cell. However, wireless communication systems in ultra-high frequency bands such as tera-hertz (THz) and sub-THz bands may use waveforms with very short symbol lengths as they use large subcarrier spacing due to effects such as extreme phase noise. In this case, there are limitation in applying the PRACH preamble sequence design according to the existing LTE or NR method.
Therefore, an aspect of the disclosure is to provide a method for generating and detecting a preamble sequence that may be applied to a communication system of a ultra-high frequency band having a symbol with a relatively short length in comparison with the maximum RTD of a cell.
In order to solve the above problem, a terminal of a communication system according to an embodiment of the disclosure may include a transceiver, and a controller, wherein the controller is configured to generate a preamble signal, transmit the preamble signal to a base station, and receive a random access response including timing advance (TA) information from the base station in response to the transmission of the preamble signal, and wherein the preamble signal includes a first signal part related to a first sequence, a guard time, and a second signal part related to a second sequence.
According to an embodiment, the timing advance may be determined based on a round trip delay (RTD) measured based on the preamble signal, and the RTD may be determined based on a first delay time determined based on the first signal part and a second delay time determined based on the second signal part.
According to an embodiment, the first delay time is determined based on a cyclic correlation between a first correlation signal and a signal received in a first window based on the length of the first signal part, and the second delay time is determined based on a cyclic correlation between a second correlation signal and a signal received in one or more second windows based on the first delay time.
According to an embodiment, the controller may be further configured to obtain a set of root indices related to the first sequence and a set of root indices related to the second sequence, the first sequence is generated based on a root index randomly selected from the set of root indices related to the first sequence, and the second sequence is generated based on a root index randomly selected from the set of root indices related to the second sequence.
According to an embodiment, the first signal part may include a first cyclic prefix (CP) and one or more symbols including the first sequence, and the second signal part may include a second CP and one symbol including the second sequence.
According to an embodiment, the length of the guard time may be determined according to a length of the first signal part.
According to an embodiment, the length of the guard time may have a preconfigured length.
According to an embodiment, the first sequence and the second sequence may be generated based on the same root index and have different cyclic shifts.
According to an embodiment, the length of the first signal part may be determined based on a maximum round trip delay (RTD) or delay spread of a cell.
A base station of a communication system according to an embodiment of the disclosure may include a transceiver, and a controller, wherein the controller is configured to receive a preamble signal from a terminal, and transmit a random access response including timing advance (TA) information to the terminal in response to the reception of the preamble signal, and wherein the preamble signal includes a first signal part related to a first sequence, a guard time, and a second signal part related to a second sequence.
A method by a terminal of a communication system according to an embodiment of the disclosure may include generating a preamble signal, transmitting the preamble signal to a base station, and receiving a random access response including timing advance (TA) information from the base station in response to the transmission of the preamble signal, wherein the preamble signal includes a first signal part related to a first sequence, a guard time, and a second signal part related to a second sequence.
A method by a base station of a communication system according to an embodiment of the disclosure may include receiving a preamble signal from a terminal, and transmitting a random access response including timing advance (TA) information to the terminal in response to the reception of the preamble signal, wherein the preamble signal includes a first signal part related to a first sequence, a guard time, and a second signal part related to a second sequence.
According to an embodiment of the disclosure, a terminal may generate a preamble signal including a first signal part, a guard time, and a second signal part in a system in which a relatively short symbol length in comparison with the maximum RTD of a cell in the ultra-high frequency band is applied, and a base station may receive the preamble signal and perform a preamble detection operation and an RTD calculation of a signal, even at a symbol length shorter than the maximum RTD of the signal, thereby having the effect of enabling a random access operation to be performed in the system of the ultra-high frequency band.
Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In the following description of the disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the description may make the subject matter of the disclosure unnecessarily unclear. The terms which will be described below are terms defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the users, or customs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.
The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but may be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and inform those skilled in the art of the scope of the disclosure, and the disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or like reference numerals designate the same or like elements.
A wireless communication system is advancing to a broadband wireless communication system for providing high-speed and high-quality packet data services using communication standards, such as high-speed packet access (HSPA) of 3GPP, LTE {long-term evolution or evolved universal terrestrial radio access (E-UTRA)}, LTE-Advanced (LTE-A), LTE-Pro, high-rate packet data (HRPD) of 3GPP2, ultra-mobile broadband (UMB), IEEE 802.16e, and the like, as well as typical voice-based services.
As a typical example of the broadband wireless communication system, an LTE system employs an orthogonal frequency division multiplexing (OFDM) scheme in a downlink (DL) and employs a single carrier frequency division multiple access (SC-FDMA) scheme in an uplink (UL). The uplink indicates a radio link through which a user equipment (UE) (or a mobile station (MS)) transmits data or control signals to a base station (BS) (eNode B), and the downlink indicates a radio link through which the base station transmits data or control signals to the UE. The above multiple access scheme separates data or control information of respective users by allocating and operating time-frequency resources for transmitting the data or control information for each user so as to avoid overlapping each other, that is, so as to establish orthogonality.
Since a 5G communication system, which is a post-LTE communication system, must freely reflect various requirements of users, service providers, and the like, services satisfying various requirements must be supported. The services considered in the 5G communication system include enhanced mobile broadband (eMBB) communication, massive machine-type communication (mMTC), ultra-reliability low-latency communication (URLLC), and the like. eMBB aims at providing a data rate higher than that supported by existing LTE, LTE-A, or LTE-Pro. For example, in the 5G communication system, eMBB must provide a peak data rate of 20 Gbps in the downlink and a peak data rate of 10 Gbps in the uplink for a single base station. Furthermore, the 5G communication system must provide an increased user-perceived data rate to the UE, as well as the maximum data rate. In order to satisfy such requirements, transmission/reception technologies including a further enhanced multi-input multi-output (MIMO) transmission technique are required to be improved. In addition, the data rate required for the 5G communication system may be obtained using a frequency bandwidth more than 20 MHz in a frequency band of 3 to 6 GHz or 6 GHz or more, instead of transmitting signals using a transmission bandwidth up to 20 MHz in a band of 2 GHz used in LTE.
In addition, mMTC is being considered to support application services such as the Internet of Things (IoT) in the 5G communication system. mMTC has requirements, such as support of connection of a large number of UEs in a cell, enhancement coverage of UEs, improved battery time, a reduction in the cost of a UE, and the like, in order to effectively provide the Internet of Things. Since the Internet of Things provides communication functions while being provided to various sensors and various devices, it must support a large number of UEs (e.g., 1.000,000 UEs/km2) in a cell. In addition, the UEs supporting mMTC may require wider coverage than those of other services provided by the 5G communication system because the UEs are likely to be located in a shadow area, such as a basement of a building, which is not covered by the cell due to the nature of the service. The UE supporting mMTC must be configured to be inexpensive, and requires a very long battery life-time such as 10 to 15 years because it is difficult to frequently replace the battery of the UE.
Lastly, URLLC, which is a cellular-based mission-critical wireless communication service, may be used for remote control for robots or machines, industrial automation, unmanned aerial vehicles, remote health care, emergency alert, and the like. Thus, URLLC must provide communication with ultra-low latency and ultra-high reliability. For example, a service supporting URLLC must satisfy an air interface latency of less than 0.5 ms, and also requires a packet error rate of 10-5 or less. Therefore, for the services supporting URLLC, a 5G system must provide a transmit time interval (TTI) shorter than those of other services, and also may require a design for assigning a large number of resources in a frequency band in order to secure reliability of a communication link.
The three 5G services, that is, eMBB, URLLC, and mMTC, may be multiplexed and transmitted in a single system. In order to satisfy different requirements of the respective services, different transmission/reception techniques and transmission/reception parameters may be used between the services.
Hereinafter, the frame structure of the LTE and LTE-A systems will be described in more detail with reference to the drawings.
In
Next, downlink control information (DCI) in LTE and LTE-A systems will be described in detail.
In the LTE system, scheduling information for downlink data or uplink data is transmitted from a base station to a terminal through DCI.
DCI defines several formats, and applies a DCI format determined according to whether it is scheduling information for uplink data or scheduling information for downlink data,
For example, DCI format 1, which is scheduling control information for downlink data, is configured to include at least the following pieces of control information.
Type 0 allocates resources in units of resource block groups (RBGs) by applying a bitmap method. In the LTE system, a basic unit of scheduling is a resource block (RB) represented by time and frequency domain resources, and an RBG is configured by a plurality of RBs to be a basic unit of scheduling in the type 0 method.
Type 1 allows a specific RB to be allocated within an RBG.
A cyclic redundancy check (CRC) is added to a DCI message payload, and the CRC is scrambled by a radio network temporary identifier (RNTI) corresponding to the identity of a terminal.
Different RNTIs are used according to the purpose of the DCI message, e.g., UE-specific data transmission, power control command, or random access response. The RNTI is not transmitted explicitly but is included in the CRC calculation process and transmitted. Upon receiving the DCI message transmitted on the PDCCH, the terminal may identify the CRC by using the allocated RNTI, and when the CRC identification result is correct, it may be identified that the corresponding message has been transmitted to the terminal.
Referring to
By allocating the PDCCH 201 to OFDM symbols existing in the front part of a subframe, a UE is capable of decoding downlink scheduling allocation as promptly as possible. Accordingly, a downlink shared channel (DL-SCH) decoding latency, that is, the overall downlink transmission latency, may be reduced. A single PDCCH delivers a single DCI message, and a plurality of UEs may be scheduled simultaneously in a downlink and an uplink, and thus transmission of a plurality of PDCCHs may be performed simultaneously in each cell.
A cell-specific reference signal (CRS) 203 is used as a reference signal for decoding the PDCCH 201. The CRS 203 is transmitted for each subframe over the entire band, and scrambling and resource mapping may be different for each cell identity (ID).
The CRS 203 is a reference signal used by all UEs in common, and thus UE-specific beamforming may not be used. Therefore, the multi-antenna transmission scheme for a PDCCH of LTE may be limited to an open-loop transmission diversity scheme. The UE is implicitly notified of the number of ports of a CRS by decoding a physical broadcast channel (PBCH).
The resource allocation of the PDCCH 201 is performed in units of control-channel elements (CCE), and a single CCE includes 9 resource element groups (REG), that is, a total of 36 resource elements (REs). The number of CCEs required for the specific PDCCH 201 may be 1, 2, 4, or 8, which is determined based on the channel-coding rate of a DCI message payload. As described above, a different number of CCEs is used to implement link adaptation of the PDCCH 201. The UE needs to detect a signal without knowing information associated with the PDCCH 201. In LTE, a search space indicating a set of CCEs is defined for blind decoding.
The search space includes a plurality of sets according to each CCE aggregation level (AL), which is not explicitly signaled but is implicitly defined by a subframe number and a function associated with a UE identity.
In each subframe, a UE decodes the PDCCH 201 with respect to all possible resource candidates that may be generated from CCEs in the configured search space, and processes information that is declared to be valid to the corresponding UE via CRC identification.
The search space may be classified as a UE-specific search space and a common search space. A group of UEs or all UEs may search the common search space of the PDCCH 201 in order to receive cell-common control information such as a paging message or dynamic scheduling relating to system information. For example, scheduling allocation information of a DL-SCH for transmission of system information block (SIB)-1 including cell operator information or the like may be received by searching the common search space of the PDCCH 201.
In LTE, the entire PDCCH region is configured as a set of CCEs in the logical region, and a search space including a set of CCEs exists. A search space may be classified as a common search space and a UE-specific search space, and the search space for an LTE PDCCH may be defined as follows.
According to the above-mentioned definition of the search space for a PDCCH, the UE-specific search space is not explicitly signaled but is defined implicitly by a subframe number and a function associated with a UE identity.
In other words, the fact that a UE-specific search space is changed depending on a subframe number denotes that the UE-specific search space may be changed over time. Through the above, a problem (a blocking problem) in which a specific UE is incapable of using a search space due to other UEs among UEs may be overcome.
A UE may not be scheduled in a subframe since all CCEs that the UE searches are currently used by other scheduled UEs within the same subframe. However, since the search space is changed over time, this problem does not occur in a subsequent subframe. For example, although UE-specific search spaces of UE #1 and UE #2 partially overlap in a specific subframe, the overlap may be expected to be different in a subsequent subframe since a UE-specific search space is different for each subframe.
According to the above-described definition of the search space for a PDCCH, a common search space is defined as a set of CCEs agreed upon in advance since a predetermined group of UEs or all UEs need to receive a PDCCH. In other words, the common search space is not changed depending on a UE identity, a subframe number, or the like.
Although the common search space exists for transmission of various system messages, the common search space may be used for transmitting control information of an individual UE. Through the above, the common search space may be used as a solution for the phenomenon in which a UE is not scheduled due to the lack of available resources in a UE-specific search space.
A search space is a set of candidate control channels including CCEs that a UE is supposed to attempt to decode on a given aggregation level. There are various aggregation levels for binding one, two, four, and eight CCEs into a single bundle, and thus a UE has multiple search spaces.
In an LTE PDCCH, the number of PDCCH candidates that are to be monitored by a UE in a search space and are defined based on an aggregation level is defined in the table below.
According to [Table 1], in the case of a UE-specific search space, aggregation levels {1, 2, 4, 8} are supported, and in this instance, there are {6, 6, 2, 2} PDCCH candidates, respectively. In the case of a common search space 302, aggregation levels {4, 8} are supported, and in this instance, there are {4, 2} PDCCH candidates, respectively.
The common search space supports only aggregation levels {4, 8} in order to improve coverage characteristics, since a system message generally needs to arrive at the edge of a cell.
DCI transmitted in the common search space is defined only for a specific DCI format, such as 0/1A/3/3A/1C, corresponding to the purpose of power control or the like for a UE group or a system message.
In the common search space, a DCI format involving spatial multiplexing is not supported. A downlink DCI format which is supposed to be decoded in a UE-specific search space may be changed depending on the transmission mode configured for the corresponding UE. The transmission mode is configured via RRC signaling, and thus a subframe number is not accurately defined in association with whether the corresponding configuration is effective for the corresponding UE. Therefore, the UE may always perform decoding with respect to DCI format 1A, irrespective of the transmission mode, so as to operate in a manner in which communication is not lost.
In the above description, a method of transmitting or receiving a downlink control channel and downlink control information and a search space in legacy LTE and LTE-A have been described.
Hereinafter, a downlink control channel in the 5G communication system which is currently under discussion will be described in detail with reference to drawings.
By assuming 1 OFDM symbol 301 as a basic time-axis unit when configuring the basic unit of a control channel, a data channel and a control channel may be time-multiplexed within a single subframe.
By placing a control channel before a data channel, the processing time perceived by a user may be reduced, and thus, a latency requirement may be easily satisfied.
The basic frequency-axis unit of a control channel is configured as 1 RB 302, and thus frequency multiplexing between a control channel and a data channel may be effectively performed.
By concatenating REGs 303 illustrated in
A description will be provided with reference to the REG 303 of
When the REG 303 includes 12 REs and 1 CCE 304 includes 6 REGs 303, this denotes that 1 CCE 304 includes 72 REs.
If a downlink control region is configured, the corresponding region may include a plurality of CCEs 304, and a specific downlink control channel may be transmitted by being mapped to a single CCE or to multiple CCEs 304 in the control region, depending on the aggregation level (AL).
The CCEs 304 in the control region may be distinguished by numbers, and the numbers may be assigned according to a logical mapping scheme.
The basic unit of the downlink control channel of
As illustrated in
The control region in 5G, as described above, may be configured via higher-layer signaling (e.g., system information, master information block (MIB), RRC signaling) to a UE by a base station.
Configuring a control region for a UE is providing information associated with the location of the control region, a subband, resource allocation of the control region, a control region length, and the like. For example, the following information may be included.
In addition to the above-described configuration information, various types of information required for transmitting a downlink control channel may be configured for a UE.
Next, downlink control information (DCI) in 5G will be described in detail.
In the 5G system, scheduling information associated with uplink data (physical uplink shared channel (PUSCH)) or downlink data (physical downlink shared channel (PDSCH)) may be transferred from a base station to a UE via DCI.
The UE may monitor a DCI format for fallback and a DCI format for non-fallback in association with a PUSCH or PDSCH.
The fallback DCI format may be implemented as a fixed field between a base station and a UE, and the non-fallback DCI format may include a configurable field.
The fallback DCI that schedules a PUSCH may include the information shown below.
The non-fallback DCI that schedules a PUSCH may include the information shown below.
The fallback DCI that schedules a PDSCH may include the information shown below.
The non-fallback DCI that schedules a PDSCH may include the information shown below.
The DCI may be transmitted via a physical downlink control channel (PDCCH) alter a channel-coding and modulation process.
A cyclic redundancy check (CRC) is added to the payload of a DCI message, and the CRC may be scrambled by a radio network temporary identifier (RNTI) corresponding to a UE identity. Different RNTIs may be used depending on the purpose of the DO message, for example, UE-specific data transmission, a power control command, a random-access response, or the like. An RNTI is not explicitly transmitted, but is transmitted by being included in a CRC calculation process.
If a UE receives a DCI message transmitted on a PDCCH, the UE may identify a CRC by using an allocated RNTI. If the CRC identification result is correct, the UE may identify that the corresponding message is transmitted to the UE.
For example, a DCI that schedules a PDSCH associated with system information (SI) may be scrambled by an SI-RNTI.
A DCI that schedules a PDSCH associated with a random-access response (RAR) message may be scrambled by an RA-RNTI.
A DCI that schedules a PDSCH associated with a paging message may be scrambled by a P-RNTI.
A DCI that reports a slot format indicator (SFI) may be scrambled by an SFI-RNTI.
A DCI that reports a transmit power control (TPC) may be scrambled by a TPC-RNTI.
A DCI that schedules a UE-specific PDSCH or PUSCH may be scrambled by a cell RNTI (C-RNTI).
If a data channel, that is, a PUSCH or PDSCH, is scheduled for a specific UE via the PDCCH, data may be transmitted or received together with a DMRS within the corresponding scheduled resource region.
In the case of
A subcarrier spacing Δf expressed in
As described above, a base station needs to transmit a reference signal in order to measure a downlink channel state in a cellular system. In the case of the long-term evolution advanced (LTE-A) system of 3GPP, a UE may measure a channel state between a base station and the UE by using a CRS or a CSI-RS transmitted by the base station.
The channel state may need to be measured in consideration of various factors, and the amount of interference in a downlink may be included in the factors.
The amount of interference in a downlink may include an interference signal generated by an antenna that belongs to a neighboring base station, thermal noise, and the like, and the amount of interference in the downlink is important when a UE determines a channel state in the downlink.
For example, in case that a base station having a single transmission antenna transmits a signal to a UE having a single reception antenna, the UE needs to determine Es/Io by determining the energy per symbol capable of being received in the downlink and the amount of interference that may be simultaneously received in a duration where the corresponding symbol is received, based on a reference signal received from the base station.
The determined Ex/Io may be converted into a data rate or a value corresponding thereto, may be transmitted to the base station in the form of a channel quality indicator (CQI), and may be used when the base station determines the data rate to be used for transmission to the UE.
In the case of the LTE-A system, a UE feeds back information associated with a channel state of a downlink to a base station, and thus the base station may utilize the same for downlink scheduling. That is, the UE measures the reference signal that the base station transmits in the downlink, and feeds back, to the base station, information extracted from the measured reference signal in a form defined in the LTE/LTE-A standard. As described above, the information that the UE feeds back in LTE/LTE-A is referred to as channel state information, and the channel state information may include the following three pieces of information.
Rand indicator (RI): indicates the number of spatial layers that a UE is capable of receiving in the current channel state.
Precoding matrix indicator (PMI): an indicator associated with a precoding matrix that a UE prefers in the current channel state.
Channel quality indicator (CQI): indicates the maximum data rate that a UE is capable of receiving in the current channel state.
The CQI may be replaced by a signal-to-interference-plus-noise ratio (SINR), a maximum error correction code rate and modulation scheme, a data efficiency per frequency, or the like, which may be utilized in a manner similar to a maximum data rate.
The RI, PMI, and CQI have meaning in relation to each other. For example, a precoding matrix supported in LTE/LTE-A may be defined differently for each rank. Therefore, a PMI value X when an RI is 1 and a PMI value X when an RI is 2 may be interpreted to be different. In addition, a UE determines a CQI on the assumption that a PMI and X that the UE reports to a base station are applied in the base station. That is, reporting RI_X, PMI_Y, and CQI_Z by a UE to the base station may correspond to reporting that the UE is capable of performing reception at a data rate corresponding to CQI_Z w % ben a rank is RI_X and a PMI is PMI_Y. As described above, a UE calculates a CQI on the assumption of a transmission scheme to be performed with respect to a base station, and thus the UE may obtain the optimal performance when the UE actually executes transmission using the corresponding transmission scheme.
In LTE/LTE-A, the RI, PMI, and CQI, which are channel state information that a UE feeds back, may be fed back periodically or aperiodically. In the case in which abase station desires to aperiodically obtain channel state information of a specific UE, the base station may configure an aperiodic feedback (or aperiodic channel state information reporting) to be performed using an aperiodic feedback indicator (or a channel-state information request field or channel-state information request information) included in downlink control information (DCI) for the UE. In addition, when the UE receives an indicator configured to perform aperiodic feedback, in an nth subframe, the UE may perform uplink transmission by including aperiodic feedback information (or channel state information) in data transmission in an (n+k)th subframe. Here, k is a parameter defined in the 3GPP LTE Release 11 standard, which is 4 in frequency-division duplexing (FDD) and may be defined as shown in Table 6 in the case of time-division duplexing (TDD).
In the case in which aperiodic feedback is configured, feedback information (or channel state information) may include an RI, a PMI, and a CQI, and the RI and the PMI may not be fed back depending on a feedback configuration (or channel state report configuration).
Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In addition, although an embodiment of the disclosure is described with reference to an LTE or LTE-A system as an example, the embodiment of the disclosure may be applicable to other communication systems that have a similar technical background or a similar channel type. For example, fifth-generation mobile communication technology (5G, new radio (NR)) or sixth-generation mobile technology developed after LTE-A may be included. In addition, embodiments of the disclosure may be modified by those skilled in the art without departing from the scope of the disclosure, and may be applied to other communication systems.
A physical random access channel (PRACH) in existing LTE or NR is designed to be suitable for an environment in which the symbol length of a signal is much larger than the maximum round-trip delay (RTD) of a cell. The base station may perform distinguishment of each terminal and estimation of a preamble signal delay by using a preamble sequence received through the PRACH. On the other hand, a wireless communication system using an ultra-high frequency band such as a tera-hertz (THz) or sub-THz band may use a waveform having a very large subcarrier spacing, that is, a very small symbol length, due to extreme phase noise. Therefore, a PRACH preamble sequence design that simply extends an existing LTE or NR method in a mobile communication system of an ultra-high frequency band may have limitations in use.
Accordingly, the disclosure proposes a new PRACH preamble signal design suitable for the ultra-high frequency band including THz and sub-THz frequency domains and a technology for transmitting and receiving the same. This includes a method for generating and transmitting a PRACH preamble sequence for random access by a terminal, a method for receiving the PRACH preamble sequence by a base station so as to estimate the RTD of a signal for timing-advance (TA) feedback, and a method for detecting the ID of a preamble generated by the terminal. The proposed technology enables the base station to estimate the RTD of the preamble signal while distinguishing each terminal, even in an environment where the symbol length of the preamble signal is very short compared to the maximum RTD of the cell.
Referring to
In addition, the base station may receive a random access preamble signal from the UE through the PRACH resource (operation 602). When the random access preamble signal is received as described, the base station may identify an identifier (ID) for the UE based on the random access preamble signal, and determine a timing advance (TA) value for a UE through estimation of the round trip delay (RTD) between the base station and the UE (operation 603).
In addition, the base station may transmit a random access response including the TA value determined as such to the identified UE (operation 604).
Referring to
Thereafter, when a random access response is received from the base station in response to transmitting the random access preamble (operation 607), the UE may apply a TA value included in the random access response to transmit a message for access to the base station based on uplink grant included in the random access response.
Referring to
First, in the case of the first signal part, the length of the sum of the lengths of the previous (K−1) symbols and the length of the CP of the first signal part, i.e., the length of TCP1+(K−1)·Tsym is typically configured as a value equal to or greater than the maximum RTD of a cell, or configured as a value equal to or greater than the sum of the maximum RTD of the cell and the maximum delay spread of the cell.
Here, Tsym may indicate the length of the OFDM symbol, and the relationship between Tsym and the subcarrier spacing Δf of the system may generally be represented by
In addition, each OFDM symbol consists of L discrete-time samples, where L may denote the size of the IDFT to generate the OFDM symbol or the length of a sequence to be generated.
In other words, in a situation in which a value of the subcarrier spacing of the system or a value of Tsym is given, the length of the first signal part, i.e., the value of K and the value of TCP1 may be determined by a target maximum RTD value, i.e., a target maximum distance. Here, the length T1 of the first signal part and the maximum distance corresponding to the maximum measurable RTD corresponding thereto may have the relationship shown in the following mathematical expression.
In the above mathematical expression, c denotes the speed of light (3*10{circumflex over ( )}8 m/s).
Here, the CP of the first signal part may use a signal obtained by replicating the latter part of one of the K identical symbols of the first signal part. In addition, the length TCP1 of the CP of the first signal part may be configured as a value between 0 and Tsym by considering the maximum RTD of a cell, and may use a signal obtained by replicating the latter part of each symbol of the first signal part. Here, a sequence of length L arranged in K symbols included in the first signal part 701 is referred to as SEQ1 and may be represented by s1[0], s1[1], . . . , s1[L−1].
Next, for the second signal part 703, the CP length TCP2 may be configured by considering the delay spread value of the cell. For example, the value of TCP2 may be configured as a value equal to or greater than the delay spread value of the cell. Here, a sequence of length L arranged on the symbol included in the second signal part is referred to as SEQ2 and may be represented by s2[0], s2[1], . . . , s2[L−1].
Referring to
In addition, SEQ1 and SEQ2 generated by the UE may be sequences having good cyclic correlation characteristics so that the base station can easily detect the preamble and estimate the RTD.
First, in an embodiment of the disclosure, for example, a Zadoff-Chu (ZC) sequence having a length of L may be used for SEQ1 and SEQ2 having a length of L. At this time, the UE may generate a ZC sequence by using sequence information. Here, the sequence information may be cell-specifically determined as, for example, a root index value, and UEs within a cell may generate ZC sequences by using different root index values. The UE may obtain, from a base station, a set I1 of root indexes for generating SEQ1, and may obtain, from the base station, a set I2 of root indexes for generating SEQ2. The UE may randomly select a root index for generating SEQ1 and SEQ2 from the obtained sets I1 and I2, and the root index may be used for identifying the UE ID by the base station. In an embodiment, the UE may obtain, from the base station, a set of time/frequency resources for transmitting a preamble signal. The UE may randomly select a resource from the set of time/frequency resources for transmitting the preamble signal to transmit the preamble signal by using the selected resource. The UE may receive such sequence information (e.g., the cell-specific root index) and resource information via a physical broadcast channel (PBCH) of a synchronization signal transmitted by the base station, as illustrated in
In another embodiment, the UE may receive the sequence information (information about the root index) and resource information through a master information block (MIB) as shown in
Meanwhile,
Referring to
For reference, the above mathematical expression expresses the delay value as a real number in absolute time, and it is also possible to express the delay value as a sample unit in a discrete time-domain, as shown below.
Here, the parameters of the above two equations may have the following relationship.
Here, L may denote the size of the IDFT to generate the OFDM-based signal, or the length of the sequence to be generated.
Referring to
First, a base station may receive a PRACH preamble signal from the UE (operation 1101). Thereafter, the base station may perform a two-stage estimation operation to estimate the TRTD value of the signal from the received preamble signal. In the first estimation operation, the base station may estimate the residual delay, i.e., a value of tr (operation 1102), and in the second-stage estimation operation, the base station may estimate the symbol-level delay, i.e., a value of ksym (operation 1103). Finally, the base station may derive the TRTD value according to the formula TRTD=ksym·Tsym+tr by using the tr value and the ksym value estimated in the above two-stage estimation process (operation 1104).
To derive the RTD value using the two-stage estimation operation, the base station may generate a first correlation signal used in the first-stage estimation operation and a second correlation signal used in the second-stage estimation operation. In an embodiment, the first correlation signal to be generated may be ZC sequences made of the root indexes in the set I1 of root indexes, and the second correlation signal may be ZC sequences made of the root indexes in the set I2 of root indexes.
Next, based on the preamble structure proposed by the disclosure shown in
Referring to
In the first embodiment of the disclosure, the length of the guard time between the first signal part and the second signal part may be TGT=(K−2)·Tsym+(Tsym−TCP2) (indicated by reference numeral 1202). In
Referring to
With reference to
Referring to the example of
Here, y[n] denotes a signal received by the base station within W1, xi[n] denotes a first correlation signal (i1∈I1), and zi[I] denotes the result value of the cyclic correlation. The above-mentioned peak value may be defined as being detected when the magnitude of zi[l] or the square value of the magnitude is greater than a certain threshold value β. The base station may determine, through the index of i1 for which the peak value is detected among the first correlation signals, that the UE has generated SEQ1 through the root index corresponding to i1, and use the same to identify the UE ID. In addition, the location in which the peak value is detected may imply the value of l by which the zi[l] has a peak value. Furthermore, the base station according to the first embodiment may, for example, in case that the cyclic correlation value of the ZC sequence included in the first signal part is configured as zero, estimate the estimation value of the residual delay defined above, as
by using the corresponding value of l. Here, Δf refers to the subcarrier spacing of the system. Additionally, the above cyclic correlation may also be performed in the frequency domain as shown in the following equation.
Here, {Y[k]}k=0L−1≙DFT{y[l]}l=0L−1, {Xi
Next, referring to the example of
Here, yk[n] denotes a signal received on the kth SW, and xi
In this simulation, the following ultra-high frequency band situations have been configured in various channel model environments (AWGN, tapped delay line (TDL) model C (non-line-of-sight), TDL model D (line-of-sight)). The carrier frequency is 140 GHz, the subcarrier spacing is 3.2 MHz, the sequence length L is 139, and the sequence root index value is configured to be i1=i2=1, and K=1, TCP1=0, TCP2=21 ns. For reference, the maximum distance corresponding to the maximum RTD in this simulation environment is given as 421.875 meters. In addition, the threshold β value has been configured to be 0.001. According to the simulation results, the preamble of the structure proposed by the disclosure has an MD probability value of a performance that generally meets the reception requirements. Note that the environment or configuration used in the simulation of
Referring to
In the second embodiment of the disclosure, the length of the guard time between the first signal part and the second signal part may be TGT=Tsym−TCP2 (indicated by reference numeral 1502). In other words, unlike the first embodiment, the preamble structure of the second embodiment is characterized by a constant length of guard time even when the value of K varies, and thus may have less time resource overhead than that of the first embodiment. In
Furthermore, in the second embodiment of the disclosure, the sequences of length L included in the first signal part and the second signal part may be sequences having different cyclic shifts of ZC sequences generated with the same root-index. This is a design feature to eliminate ambiguity between the first signal part and the second signal part that may be caused by a guard time that is shorter than the guard time in the preamble structure of the first embodiment in a second-stage estimation to be described later with reference to
Referring to
Referring to the example of
Here, y[n] denotes a signal received by the base station within W1, xi
by using the corresponding value of l. Here, Δf refers to the subcarrier spacing of the system. Additionally, the above cyclic correlation may also be performed in the frequency domain as shown in the following equation.
Here, {Y[k]}k=0L−1≙DFT{y[l]}l=0L−1, {Xi
Next, referring to the example of
Here, yk[n] denotes a signal received on the kth SW, and xi
Finally, the base station according to the second embodiment may derive TRTD=ksym·Tsym+tr, which is a final RTD value of the received preamble signal, or NRTD=ksym·Nsym+nr, which is a final RTD value in the units of samples, by using the residual delay tr or nr value estimated in the first-stage estimation and the symbol-level delay ksym value estimated in the second-stage estimation.
Referring to
The base station receiver 1802 and the base station transmitter 1803 (or transceiver) may transmit and receive signals to and from a UE. Here, signals may include control information and data. To this end, the transceiver may include an RF transmitter for up-converting and amplifying the frequency of a transmitted signal, and an RF receiver for low-noise amplifying a received signal and down-converting the frequency. However, this is only an embodiment of the transceiver, and elements of the transceiver are not limited to the RF transmitter and the RF receiver.
In addition, the transceiver may receive a signal through a radio channel, output the signal to the base station processor 1801, and transmit the signal output from the base station processor 1801 through a radio channel.
A memory (not shown) may store programs and data required for the operation of the base station. In addition, the memory may store control information or data included in a signal obtained from the base station. The memory may include a storage medium such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD, or a combination of storage media.
The base station processor 1801 may control a series of processes so that the base station operates according to the above-described embodiment of the disclosure. The base station processor 1801 may be implemented as a controller or one or more processors.
Referring to
The UE receiver 1902 and the UE transmitter 1903 (or transceiver) may transmit and receive signals to and from the base station. Here, signals may include control information and data. To this end, the transceiver may include an RF transmitter for up-converting and amplifying the frequency of a transmitted signal, and an RF receiver for low-noise amplifying a received signal and down-converting the frequency. However, this is only an embodiment of the transceiver, and elements of the transceiver are not limited to the RF transmitter and the RF receiver.
In addition, the transceiver may receive a signal through a wireless channel, output the signal to the UE processor 1901, and transmit the signal output from the UE processor 1901 through the wireless channel.
A memory (not shown) may store programs and data required for operation of the UE. In addition, the memory may store control information or data included in a signal obtained from the UE. The memory may include a storage medium such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD, or a combination of storage media.
The UE processor 1901 may control a series of processes so that the UE may operate according to the above-described embodiment of the disclosure. The UE processor 1901 may be implemented as a controller or one or more processors.
In the above-described detailed embodiments of the disclosure, an element included in the disclosure is expressed in the singular or the plural according to presented detailed embodiments. However, the singular form or plural form is selected appropriately to the presented situation for the convenience of description, and the disclosure is not limited by elements expressed in the singular or the plural. Therefore, either an element expressed in the plural may also include a single element or an element expressed in the singular may also include multiple elements.
Although specific embodiments have been described in the detailed description of the disclosure, it will be apparent that various modifications and changes may be made thereto without departing from the scope of the disclosure. Therefore, the scope of the disclosure should not be defined as being limited to the embodiments, but should be defined by the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0084182 | Jun 2021 | KR | national |
| 10-2021-0096636 | Jul 2021 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2022/008207 | 6/10/2022 | WO |
