Patent Application
20210105164
The present invention relates to a base station apparatus, a terminal apparatus, and a communication method.
This application claims priority based on JP 2017-070764 filed on Mar. 31, 2017, the contents of which are incorporated herein by reference.
The demand for high-speed wireless transmission has increased due to the popularity of smartphones, tablet terminals and the like in recent years. A standardization group, the Third Generation Partnership Project (3GPP), discusses New Radio (NR) as the fifth generation mobile communication system (5G). For NR, specifications have been made to satisfy the requirements of three use cases: enhanced Mobile Broadband (eMBB) for high-capacity communication with high frequency utilization efficiency; massive Machine Type Communication (mMTC) containing multiple terminals; and Ultra-Reliable and Low Latency Communication (URLLC), which realizes reliable and low latency communication.
For the Long Term Evolution (LTE) uplink, Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-S-OFDM) with low PAPR is employed. On the other hand, for NR, in addition to DFT-S-OFDM, it is agreed to employ OFDM (also referred to as CP-OFDM). Therefore, it can be assumed that a terminal apparatus that uses DFT-S-OFDM (also referred to as SC-FDMA) and a terminal apparatus that uses CP-OFDM coexist in the same cell.
Advantages of CP-OFDM include high resistance to multipath (delay wave) and good properties in Multiple Input Multiple Output (MIMO) transmission. Additionally, since the DFT-S-OFDM has a low PAPR of the transmission signal waveform, it is possible to increase the transmit power while maintaining the burden on the amplifier. As a result, the DFT-S-OFDM can increase coverage.
On the other hand, various access schemes are conceivable as a method in which multiple terminal apparatuses communicate with the same base station apparatus. The access schemes used in LTE include Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Space Division Multiple Access (SDMA), and the like. Note that SDMA is also referred to as Multi-User Multiple Input Multiple Output (MU-MIMO). In NR, both CP-OFDM and DFT-S-OFDM are supported so that it is considered that CP-OFDM and DFT-S-OFDM form SDMA, in other words, MU-MIMO (NPL 1).
NPL 1: Huawei, HiSilicon, “Discussion on UL MU-MIMO between CP-OFDM and DFT-S-OFDM for NR” R1-1700409, January 2017.
A base station apparatus supporting CP-OFDM and DFT-S-OFDM needs to estimate a channel between each terminal apparatus and a base station apparatus in order to demodulate data. In LTE uplink, OFDM symbols including only reference signals is prepared, and a channel estimation is performed. This is because, in a case of DFT-S-OFDM, assuming a configuration including a data subcarrier and a reference signal subcarrier in one OFDM symbol, PAPR increases and benefits of DFT-S-OFDM are impaired. However, in a case of CP-OFDM, rather than configuring one OFDM symbol only by reference signals, reference signals can be allocated discretely in the frequency direction, and data signals can be allocated on resource elements (subcarriers) where no reference signal is mapped, and it is also adopted to LTE and radio LAN. In other words, it is possible to vary a signal format between CP-OFDM and DFT-S-OFDM. Here, the resource element is a minimum unit of a resource to which a signal (modulation symbol) such as a reference signal, uplink data, or the like is mapped.
In the case that the DFT-S-OFDM and CP-OFDM signal formats are different from each other, the system can be operated without problems by independently configuring the systems or dividing the use frequencies. However, there are demerits such as inability of flexible switching between DFT-S-OFDM and CP-OFDM.
One aspect of the present invention has been made in view of the above-described problems, and an object of the aspect of the present invention is to provide a base station apparatus, a terminal apparatus, and a communication method thereof that enable wide coverage and high frequency reason efficiency in a case of using DFT-S-OFDM and CP-OFDM for uplink transmission.
To address the above-mentioned drawbacks, each configuration of a base station and a terminal according to an aspect of the present invention is configured as follows.
(1) In order to solve the above-described problems, a terminal apparatus according to an aspect of the present invention is a terminal apparatus for communicating with a base station apparatus, the terminal apparatus including: a receiver configured to receive an MCS index and resource allocation information for uplink data transmission from the base station apparatus; an MCS configuration unit configured to configure, based on a modulation scheme and a TBS index associated with the MCS index and the resource allocation information, the modulation scheme and a coding rate of the uplink data; a transmission scheme configuration unit configured to configure a transmission scheme of either a first transmission scheme or a second transmission scheme; and a resource element mapping unit configured to map a reference signal and uplink data to an OFDM symbol, based on the transmission scheme, wherein the resource element mapping unit is configured to map the reference signal to form a first OFDM symbol including only the reference signal in a case that the first transmission scheme is configured, and maps the reference signal to form a second OFDM symbol including at least the reference signal and the uplink data in a case that the second transmission scheme is configured, and the MCS configuration unit identifies the TBS index associated with the MCS index, based on the transmission scheme, and configures a transport block size to which the uplink data is mapped, based on the TBS index and the resource allocation information.
(2) In the terminal apparatus according to an aspect of the present invention, the transmission scheme configuration unit includes a table for indicating an association between the MCS index and the TBS index for each transmission scheme of the first transmission scheme and the second transmission scheme, and the MCS configuration unit identifies the TBS index, based on the table selected by the transmission scheme configured by the transmission scheme configuration unit.
(3) In the terminal apparatus according to an aspect of the present invention, the OFDM symbol includes a plurality of resource elements, a resource element of the plurality of resource elements is a minimum unit of a resource to which the reference signal and the uplink data are mapped, and a spacing between two resource elements to which the reference signal is mapped in the first OFDM symbol is the same as the spacing between two resource elements to which the reference signal is mapped in the second OFDM symbol.
(4) In order to solve the above-described problem, in the terminal apparatus according to an aspect of the present invention, the first OFDM symbol includes a plurality of resource elements, a resource element of the plurality of resource elements is a minimum unit of a resource to which the reference signal and the uplink data are mapped, and the first OFDM symbol includes the reference signal in all frequencies allocated according to the resource allocation information.
(5) In the terminal apparatus according to an aspect of the present invention, the reference signal allocated to the first OFDM symbol is orthogonal to the reference signal allocated to the second OFDM symbol in the same resource element to which the reference signal is allocated.
(6) In the terminal apparatus according to an aspect of the present invention, the first transmission scheme is DFT-S-OFDM, and the second transmission scheme is OFDM.
(7) A communication method for a terminal apparatus according to an aspect of the present invention is a communication method for a terminal apparatus for communicating with a base station apparatus, the communication method including: a reception step of receiving an MCS index and resource allocation information for uplink data transmission from the base station apparatus; an MCS configuration step of configuring, based on a modulation scheme and a TBS index associated with the MCS index and the resource allocation information, the modulation scheme and a coding rate of the uplink data; a transmission scheme configuration step of configuring a transmission scheme of either a first transmission scheme or a second transmission scheme; and a resource element mapping step of mapping a reference signal and uplink data to an OFDM symbol, based on the transmission scheme, wherein the resource element mapping step maps the reference signal to form a first OFDM symbol including only the reference signal in a case that the first transmission scheme is configured, and maps the reference signal to form a second OFDM symbol including at least the reference signal and the uplink data in a case that the second transmission scheme is configured, and the MCS configuration unit identifies the TBS index associated with the MCS index, based on the transmission scheme, and configures a transport block size to which the uplink data is mapped, based on the TBS index and the resource allocation information.
According to one or more aspects of the present invention, efficient transmission can be performed in a case that there are DFT-S-OFDM and CP-OFDM as transmission schemes (signal waveforms).
The terminal apparatus collectively refers to a mobile or fixed user end apparatus such as a User Equipment (UE), a Mobile Station (MS), a Mobile Terminal (MT), a mobile station apparatus, a mobile terminal, a subscriber unit, a subscriber station, a wireless terminal, a mobile apparatus, a node, an apparatus, a remote station, a remote terminal, a wireless communication apparatus, a wireless communication apparatus, a user agent, an access terminal. The base station apparatus collectively refers to any node at a network end in communication with a terminal, such as a node B (NodeB), an enhanced node B (eNodeB), a base station, and an Access Point (AP). Note that the base station apparatus includes a Remote Radio Head (RRH, an apparatus having a smaller outdoor type radio unit than a base station apparatus, Remote Radio Unit: also referred to as RRU) (also referred to as a remote antenna or a distributed antenna). The RRH can also be said to be a special form of a base station apparatus. For example, the RRH may be referred to as a base station apparatus that includes only a signal processing unit, and is configured to configure parameters used by other base station apparatuses, and determine scheduling in an RRH, and the like.
Embodiments of the present invention will be described below in detail with reference to the drawings.
The data of the terminal apparatus 102-A is coded at a coding unit 200-1 and a coding unit 200-2. Here, the coding rate is configured based on a coding rate notified by an MCS configuration unit 209. Note that the coding rate is determined by the MCS configuration unit 209, based on the MCS index notified by the control information acquisition unit 213. The coded bit sequence (codeword) obtained by coding the data of the terminal apparatus 102-A is input to a scrambling unit 201-1 and a scrambling unit 201-2. Here, in a case that the number of codewords is one, nothing is input to the scrambling unit 201-2. The number of codewords may be 3 or greater, and in this case, the same number of scrambling units as the number of codewords are prepared. For the scrambling unit 201-1 and the scrambling unit 201-2, terminal apparatus specific and coatword specific scrambling is applied. The outputs of the scrambling unit 201-1 to 201-2 are input to modulation units 202-1 to 202-2, respectively. In the modulation units 202-1 to 202-2, processing is performed to convert the input bit sequence to a modulation symbol (QPSK modulation symbol, QAM modulation symbol) such as QPSK or 64QAM. Here, the modulation scheme is configured based on the modulation scheme notified from the MCS configuration unit 209. Note that the modulation scheme is determined by the MCS configuration unit 209, based on the MCS index notified by the control information acquisition unit 213.
The outputs of the modulation units 202-1 to 202-2 are input to a layer mapping unit 203. In the layer mapping unit 203, in a case that the terminal apparatus 102-A performs transmission using multiple layers, a process is applied in which one or multiple codewords are allocated to each layer. In the following description, the number of layers is described as two, but any number may be used as long as the number of layers is a natural number. The output of the layer mapping unit 203 is input to transform precoding units 204-1 and 204-2.
In the transform precoding units 204-1 and 204-2, transform by Discrete Fourier Transform (DFT) is performed on the modulation symbol sequence input from the layer mapping unit 203. Here, a transmission scheme configuration unit 210 notifies whether or not to apply DFT. In a case of applying DFT, signals are transmitted using DFT-S-OFDM. In a case of not applying DFT, signals are transmitted using CP-OFDM. The transmission scheme configuration unit 210 acquires the transmission scheme (signal waveform) from the control information acquisition unit 213 explicitly or implicitly by RRC or DCI. The outputs of the transform precoding units 204-1 and 204-2 are input to a precoding unit 205
In the precoding unit 205, precoding is performed to transmit each layer from multiple antenna ports. Here, different precoding may be applied depending on whether or not the processing in the transform precoding units 204-1 and 204-2, specifically DFT, is applied (or whether or not the transmission scheme is with a high Peak to Average Power Ratio (PAPR)). Description is given with reference to
The outputs of the resource element mapping units 206-1 and 206-2 are input to signal generation units 207-1 and 207-2, respectively. In the signal generation units 207-1 and 207-2, Inverse Fast Fourier Transform (IFFT) is applied to the inputs from the resource element mapping units 206-1 and 206-2, and Cyclic Prefix (CP) is added. Furthermore, processing such as D/A conversion, transmit power control, filtering, up-conversion, and the like are applied. The outputs of the signal generation units 207-1 and 207-2 are transmitted from antennas 208-1 and 208-2. Here, whether to use CP-OFDM or DFT-S-OFDM may be uniquely configured for each terminal apparatus by RRC or DCI.
Next, a radio frame (subframe, slot, minislot) configuration performed by the resource element mapping units 206-1 and 206-2 will be described.
Next, a resource block in the case of using CP-OFDM will be described with reference to
As described above, the configuration of the reference signals can be changed between CP-OFDM and DFT-S-OFDM. As a result, the number of pieces of data included in one subframe is different in CP-OFDM and DFT-S-OFDM. For example, in the case of
The communication system of the present embodiment may apply Adaptive Modulation and Coding, Link Adaptation. Specifically, in the MCS configuration unit 209, the number of information bits transmitted in one transport block is determined by the number of resource blocks used for the communication and the MCS index (or TBS index) (3GPP TS36.213 Table 7.1.7.2.1-1, for example). The TBS Index is an index associated with the number of resource blocks and indicating the number of information bits per resource block number. For example, it is assumed that TBS index 0 indicates the number of information bits as 16 in the resource blocks number 1. In a case that the MCS index is the lowest number 0 (the modulation order is 2, and the TBS index is 0) and the number of resource blocks used is 1, 16 bits of information bits will be included in the transport block.
As described above, in the case of DFT-S-OFDM, 144 REs per subframe are used for transmission. In a case that the MCS index is 0, QPSK is used, so 288 bits can be transmitted as coded bits per subframe. In a case that the 16 bits of information bits described above are transmitted with 288 bits of coded bits, the coding rate is 0.056. On the other hand, in the case of CP-OFDM, 160 REs per subframe is used for transmission. In a case that the MCS index is 0, QPSK is used, so 320 bits can be transmitted as coded bits per subframe. In a case that the 16 bits of information bits described above are transmitted with 320 bits of coded bits, the coding rate is 0.050. In other words, even in a case that the same MCS index is used for CP-OFDM and DFT-S-OFDM, the coding rates will vary. Motivation for introducing DFT-S-OFDM is to ensure wide coverage but transmission at higher coding rates than CP-OFDM is also achieved. In other words, CP-OFDM transmits at a low power with a low coding rate, and DFT-S-OFDM transmits at a high power transmit power with a high coding rate.
In this manner, even though DFT-S-OFDM is introduced assuming that the terminal apparatus at the cell edge transmits at a low rate, in a case that the same MCS index is used, DFT-S-OFDM has a higher coding rate than CP-OFDM and performs an error-prone communication. Therefore, in the communication system of the present embodiment, DFT-S-OFDM is configured to perform more reliable transmission even with the same MCS index.
One method by which DFT-S-OFDM supports the lowest coding rate (transmission rate, spectral efficiency) is considered to change the MCS table used in the MCS configuration unit 209, depending on whether the transmission scheme used is CP-OFDM or DFT-S-OFDM. For example, the MCS table illustrated in
As described above, according to the present embodiment, the MCS table is changed so that DFT-S-OFDM is responsible for the lowest coding rate rather than CP-OFDM in a case that the number of resource elements that can be used for data transmission differs. The MCS table may also be changed so that CP-OFDM is responsible for a higher transmission rate than DFT-S-OFDM. That is, depending on whether a transmission scheme is CP-OFDM or DFT-S-OFDM, the same MCS index that is notified is handled as different TBS indexes. As a result, high frequency utilization efficiency due to CP-OFDM can be achieved while ensuring a wide coverage.
The present embodiment is an example of a method for suppressing large interference to CP-OFDM while keeping the transmit power of OFDM symbols for reference signals of DFT-S-OFDM identical to that of OFDM symbols for data signals. In the present embodiment, CP-OFDM is configured to transmit data signals by OFDM symbols including reference signals as in
In this case, there is a problem in that the reference signal of a portion of the reference signal symbol of DFT-S-OFDM collides with the data signal included in the same OFDM symbol as the reference signal in the case of CP-OFDM. Thus, first, channel estimation is performed using the reference signal of DFT-S-OFDM transmitted in the same RE as the reference signal of CP-OFDM. That is, at this stage, a portion of the reference signal of DFT-S-OFDM is used for channel estimation. Using estimated values of CP-OFDM and DFT-S-OFDM, signal detection such as spatial filtering and MLD is applied. Next, in a case that signal detection is applied to the OFDM symbol including the reference signal, CP-OFDM can detect data. By canceling the data signal of CP-OFDM detected through signal detection from the received signal, only DFT-S-OFDM receive reference signal may be extracted. CP-OFDM can perform channel estimation with high accuracy by performing channel estimation of DFT-S-OFDM for the signal in which data signal is canceled. In a case that the channel estimation accuracy of DFT-S-OFDM is improved, the DFT-S-OFDM data signal can be estimated correctly. By canceling the resulting high-accuracy channel estimation result and the data signal of DFT-S-OFDM included except in the OFDM symbol including the reference signal from the received signal, it is possible to improve the signal detection accuracy of CP-OFDM. In this way, signal detection accuracy can be improved by repeating signal detection and cancellation.
In the second embodiment, an example has been described in which, in the case of using CP-OFDM, OFDM symbols including at least a reference signal and a data signal are formed, and in the case of using DFT-S-OFDM, OFDM symbols for transmitting reference signals in the entire usage band are formed. In this case, the sequence lengths of the reference signals differ between CP-OFDM and DFT-S-OFDM. In this case as well, it is necessary to separate the reference signals and to perform the channel estimation with high accuracy. In the present embodiment, a method will be described for enabling separation on the receiver by orthogonalizing reference signals and performing channel estimation with high accuracy even in a case that the sequence lengths of reference signals are different from each other between CP-OFDM and DFT-S-OFDM.
Next, a specific sequence will be described. The sequence of S(0) to S(7) in
In the case that the number of subcarriers constituting the reference signals in DFT-S-OFDM and CP-OFDM is different and the same subcarrier (RE) is used, the reference signal is generated so as to transmit the same reference signal (root sequence) for the same subcarrier. However, the reference signals can be separated at the receiver, for example, by applying different cyclic shifts for each of the terminal apparatuses or the streams (layers). Thus, a high accuracy channel estimation can be achieved.
A program running on an apparatus according to one aspect of the present invention may serve as a program that controls a Central Processing Unit (CPU) and the like to cause a computer to operate in such a manner as to realize the functions of the above-described embodiment according to one aspect of the present invention. Programs or the information handled by the programs are temporarily read into a volatile memory, such as a Random Access Memory (RAM) while being processed, or stored in a non-volatile memory, such as a flash memory, or a Hard Disk Drive (HDD), and then read by the CPU to be modified or rewritten, as necessary.
Moreover, the apparatuses in the above-described embodiment may be partially enabled by a computer. In that case, a program for realizing the functions of the embodiments may be recorded in a computer readable recording medium. The functions may be realized by causing a computer system to read the program recorded in the recording medium for execution. It is assumed that the “computer system” refers to a computer system built into the apparatuses, and the computer system includes an operating system and hardware components such as a peripheral device. Furthermore, the “computer-readable recording medium” may be any of a semiconductor recording medium, an optical recording medium, a magnetic recording medium, and the like.
Moreover, the “computer-readable recording medium” may include a medium that dynamically retains a program for a short period of time, such as a communication line that is used to transmit the program over a network such as the Internet or over a communication line such as a telephone line, and may also include a medium that retains a program for a fixed period of time, such as a volatile memory within the computer system for functioning as a server or a client in such a case. Furthermore, the program may be configured to realize some of the functions described above, and also may be configured to be capable of realizing the functions described above in combination with a program already recorded in the computer system.
Furthermore, each functional block or various characteristics of the apparatuses used in the above-described embodiment may be implemented or performed on an electric circuit, that is, typically an integrated circuit or multiple integrated circuits. An electric circuit designed to perform the functions described in the present specification may include a general-purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or a combination thereof. The general-purpose processor may be a microprocessor or may be a processor of known type, a controller, a micro-controller, or a state machine instead. The above-mentioned electric circuit may be constituted of a digital circuit or an analog circuit. Furthermore, in a case that with advances in semiconductor technology, a circuit integration technology appears that replaces the present integrated circuits, it is also possible to use an integrated circuit based on the technology.
Note that the invention of the present patent application is not limited to the above-described embodiments. In the embodiment, apparatuses have been described as an example, but the invention of the present application is not limited to these apparatuses, and is applicable to a terminal apparatus or a communication apparatus of a fixed-type or a stationary-type electronic apparatus installed indoors or outdoors, for example, an AV apparatus, a kitchen apparatus, a cleaning or washing machine, an air-conditioning apparatus, office equipment, a vending machine, and other household apparatuses.
The embodiments of the present invention have been described in detail above referring to the drawings, but the specific configuration is not limited to the embodiments and includes, for example, an amendment to a design that falls within the scope that does not depart from the gist of the present invention. Furthermore, various modifications are possible within the scope of one aspect of the present invention defined by claims, and embodiments that are made by suitably combining technical means disclosed according to the different embodiments are also included in the technical scope of the present invention. Furthermore, a configuration in which constituent elements, described in the respective embodiments and having mutually the same effects, are substituted for one another is also included in the technical scope of the present invention.
An aspect of the present invention can be suitably used in a base station apparatus, a terminal apparatus, and a communication method. An aspect of the present invention can be utilized, for example, in a communication system, communication equipment (for example, a cellular phone apparatus, a base station apparatus, a radio LAN apparatus, or a sensor device), an integrated circuit (for example, a communication chip), or a program.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-070764 | Mar 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/012381 | 3/27/2018 | WO | 00 |
