Radio base station and wireless terminal

Abstract

To easily achieve phase tracking when a plurality of radio base stations transmit simultaneously.SOLUTION: A radio base station performs cooperative transmission in which the radio base station transmits to a wireless terminal in cooperation with a cooperative radio base station. The radio base station includes a radio control unit and a communication unit. The radio control unit determines a reference signal with the cooperative radio base station that performs the cooperative transmission, and generates the determined reference signal. The communication unit transmits a signal including the reference signal to the wireless terminal in cooperation with the cooperative radio base station. The wireless terminal estimates a frequency error between the radio base stations that perform the cooperative transmission, based on the received reference signal.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present technology relates to a radio base station and a radio terminal. Specifically, it relates to a radio base station and a radio terminal in a radio system including a plurality of radio base stations that perform simultaneous transmission.

Background Art

[0002] In a wireless LAN, within one basic service set (BSS), an access point (AP or BS) and a terminal (STA or UE) autonomously acquire the right to transmit within the BSS and communicate. When a transmitting terminal is equipped with a plurality of antennas, transmission (BF: beamforming) using the plurality of antennas simultaneously can transmit with high gain to a desired destination terminal, and the system throughput within the BSS can be improved. Generally, the gain obtained by beamforming is proportional to the number of antennas used simultaneously. By expanding this beamforming, the system throughput can be improved by transmission using a plurality of APs (hereinafter referred to as multi-APs) that cooperate with each other.

[0003] There are multiple multi-AP methods, including CJT (Coherent Joint Transmission) which transmits as a virtual single AP with antennas that are the sum of each other, NCJT (Non-Coherent Joint Transmission) which forms a beam independently for each AP and transmits to a common receiving terminal, and Coordinated Nulling which forms a null so as not to interfere with each other's communication terminals when forming a beam independently for each AP and communicating with different terminals. All of these can achieve a higher system throughput in an environment with multiple APs than when multiple APs do not cooperate. Among these, CJT, which transmits as a virtual single access point with antennas that are the sum of each other, can achieve the highest throughput among multi-APs. On the other hand, for CJT, it is necessary to synchronize the carrier frequencies between access points with high precision in order to operate as a virtual single access point between multi-APs. Also, it is necessary to perform frequency synchronization between the multi-AP and the terminal. However, in a real system, it is difficult to completely synchronize the carrier frequencies of each other, and a residual frequency error, that is, a residual CFO (residual Carrier Frequency Offset) occurs.

[0004] In the OFDM (Orthogonal Frequency Division Multiplexing) modulation method, which is a widely used modulation method in wireless communication systems, it is possible to insert different data sequences for each subcarrier. However, a known sequence (hereinafter referred to as a pilot signal) is inserted into specific subcarriers within each OFDM symbol. Due to the residual CFO, the sequences inserted into each subcarrier undergo a common complex phase rotation over time. The terminal performs compensation (phase tracking) to cancel out the phase rotation of the pilot signal. In CJT, since the residual CFOs of the access points that make up the multi-AP are different for each terminal, it is necessary to estimate the residual CFO of each access point and perform phase tracking. However, if pilot signals are inserted into the same subcarriers among multiple APs, there is a problem that it is difficult to accurately perform phase tracking because pilot signals with different residual CFOs are multiplexed. Therefore, for example, a system has been proposed that assigns pilot signals such that a unique pseudo-orthogonal sequence is used for each base station to separate the pilot signals (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the above prior art, pilot signals are separated using a unique pseudo-orthogonal sequence for each base station. However, due to the nature of the pseudo-orthogonal sequence, it is difficult for the terminal to estimate the residual CFO for each access point, and there is a problem that it becomes difficult to perform phase tracking in CJT.

[0007] The present technology has been created in view of such a situation, and an object thereof is to easily realize phase tracking when multiple radio base stations perform transmission simultaneously.

Means for Solving the Problem

[0008] The present technology has been made to solve the above-described problems. A first aspect thereof is a radio base station including a radio control unit that generates a reference signal determined with a cooperative radio base station that performs cooperative transmission, and a communication unit that transmits a signal including the reference signal to a radio terminal in cooperation with the cooperative radio base station. Thereby, an operation is brought about in which a signal including a reference signal determined with a cooperative radio base station (for example, a slave access point) is transmitted to a radio terminal in cooperation with the cooperative radio base station.

[0009] Also, in this first aspect, the reference signal may be transmitted using at least any one of different frequencies, different times, and different sequences. Thereby, an operation is brought about in which the orthogonality of the reference signal is ensured and separation on the reception side is facilitated.

[0010] Also, in this first aspect, the communication unit may exchange information regarding a cooperative method that can be supported prior to the cooperative transmission between the cooperative radio base station and the radio terminal. Thereby, an operation is brought about in which a cooperative method that can be supported prior to the cooperative transmission is confirmed.

[0011] Also, in this first aspect, the radio control unit may determine an allocation of the reference signal in the cooperative transmission with the cooperative radio base station prior to the generation of the reference signal. Thereby, an operation is brought about in which an allocation of the reference signal in the cooperative transmission is determined prior to the generation of the reference signal.

[0012] Also, in this first aspect, the wireless control unit may determine information for each frequency channel among the frequency bands used in the above cooperation method and information regarding the above frequency channel. Further, the wireless control unit may determine at least one of information regarding the number of the above cooperative radio base stations, information for identifying the above cooperative radio base stations, and information including numbers assigned to the above cooperative radio base stations. Further, the wireless control unit may determine, for each of the above cooperative radio base stations, information including at least one of information indicating the presence or absence of insertion of the above reference signal, information indicating symbols for inserting the above reference signal, and a sequence for separating the reference signal at the above receiving terminal.

[0013] Also, in this first aspect, the communication unit may transmit information regarding the above cooperative radio base stations to the above wireless terminal in the above cooperative transmission. This brings about the effect of notifying the wireless terminal of information regarding the cooperative radio base stations in the cooperative transmission.

[0014] Also, in this first aspect, the communication unit may transmit, to the wireless terminal, information for each arbitrary frequency channel used in the above cooperative transmission as information regarding the above cooperative radio base stations. Further, the communication unit may transmit, to the wireless terminal, an identification number assigned to the above cooperative radio base stations as information regarding the above cooperative radio base stations. Further, the information regarding the above cooperative radio base stations may be information for determining the assignment of the above reference signal by combining with a codebook determined between the above cooperative radio base stations.

[0015] Also, in this first aspect, a signal processing unit that compensates for a frequency error based on information regarding frequency synchronization notified from the above wireless terminal in the above cooperative transmission may be further provided. This brings about the effect of compensating for a frequency error based on information regarding frequency synchronization notified from the wireless terminal.

[0016] Moreover, a second aspect of the present technology is a radio base station including a radio control unit that receives reference information from a cooperative radio base station that performs cooperative transmission, and a communication unit that transmits a signal including the reference information to a radio terminal in cooperation with the cooperative radio base station. This brings about the effect of transmitting a signal including reference information received from a cooperative radio base station (for example, a master access point) to a radio terminal in cooperation with the cooperative radio base station.

[0017] Also, in this second aspect, the communication unit may transmit information regarding the cooperative radio base station to the radio terminal in the cooperative transmission. This brings about the effect of notifying the radio terminal of information regarding the cooperative radio base station in the cooperative transmission.

[0018] Also, in this second aspect, as information regarding the cooperative radio base station, the communication unit may transmit information for each arbitrary frequency channel used in the cooperative transmission to the radio terminal. Further, the communication unit may transmit an identification number assigned to the cooperative radio base station to the radio terminal as information regarding the cooperative radio base station. Also, the information regarding the cooperative radio base station may be information for determining the assignment of the reference signal by combining it with a codebook determined between the cooperative radio base stations.

[0019] Also, in this second aspect, the radio base station may further include a signal processing unit that compensates for a frequency error based on information regarding frequency synchronization notified from the radio terminal in the cooperative transmission. This brings about the effect of compensating for a frequency error based on information regarding frequency synchronization notified from the radio terminal.

[0020] Moreover, a third aspect of the present technology is a radio terminal including a channel estimation unit that separates a reference signal based on reference information from a signal cooperatively transmitted from a plurality of radio base stations and estimates a frequency error between the plurality of radio base stations, and a signal processing unit that performs phase shift compensation of the cooperatively transmitted signal based on the estimated frequency error. This brings about the effect of estimating a frequency error from a cooperatively transmitted signal and performing phase shift compensation.

[0021] Also, in this third aspect, the channel estimation unit may separate the reference signal based on the codebook determined among the plurality of radio base stations and the information. This brings about the effect of further separating the reference signal based on the codebook.

[0022] Also, in this third aspect, it may further include a communication unit that transmits information regarding the estimated frequency error to at least one of the plurality of radio base stations. This brings about the effect of notifying the radio base station of the information regarding the estimated frequency error.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments for carrying out the present technology (hereinafter referred to as embodiments) will be described. The description will be made in the following order. 1. Embodiments 2. Modification examples

[0025] <1. Embodiments> [Wireless Network System] FIG. 1 is a diagram showing a configuration example of a wireless network system in the embodiment of the present technology.

[0026] Here, it is assumed that a plurality of access points 11 and 12 cooperate to perform simultaneous transmission (JT: Joint Transmission). The access points 11 and 12 that perform this simultaneous transmission are collectively referred to as a multi-AP. The number of access points constituting the multi-AP may be three or more. Also, in this example, the wireless terminal 201 is shown as the transmission destination of the simultaneous transmission, but communication with a plurality of wireless terminals can also be performed simultaneously.

[0027] To determine the cooperation method of multi-APs, the decision-making entity for the cooperation method of multi-APs is defined as the master AP, and the access point that implements the cooperation method based on the notification from the master AP is defined as the slave AP. Note that the master AP may sometimes be called a Sharing AP, and the slave AP may sometimes be called a Shared AP. The master AP may participate in the cooperation method of multi-APs. For example, in the same figure, access point 11 may be used as the master AP and access point 12 may be used as the slave AP. Hereinafter, access point 11 is referred to as master AP101 and access point 12 is referred to as slave AP102, but the slave AP may be a plurality of access points. Note that the master AP and the slave AP are not fixedly determined for the AP, and may be dynamically determined within the multi-AP. For example, at a certain time t1, AP1 may be the master AP and AP2 may be the slave AP, and at a different time t2, AP1 may be the slave AP and AP2 may be the master AP.

[0028] [Device Configuration] Figure 2 is a diagram showing a configuration example of the wireless communication device 300 in the embodiment of the present technology. The wireless communication device 300 referred to here includes a master AP101, a slave AP102, and a wireless terminal 201. Further, for example, the wireless communication device 300 may be a wireless communication module or an integrated circuit mounted on these APs and terminals.

[0029] The wireless communication device 300 includes a communication unit 310, a control unit 321, a power supply unit 322, and an antenna 319. There may be a plurality of communication units 310.

[0030] The communication unit 310 includes a radio control unit 311, a data processing unit 312, a modulation / demodulation unit 313, a signal processing unit 314, a channel estimation unit 315, a radio interface unit 316, and an amplifier unit 317. The radio interface unit 316, the amplifier unit 317, and the antenna 319 may be grouped together as one set, and one or more such sets may be components. Also, the function of the amplifier unit 317 may be incorporated into the radio interface unit 316. The communication unit 310 is realized, for example, by an LSI (Large Scale Integration).

[0031] When transmitting data input from the upper layer, the data processing unit 312 generates a packet for wireless transmission from the data, performs processes such as adding a header for media access control (MAC: Media Access Control) and adding an error detection code, and supplies the processed data to the modulation / demodulation unit 313. On the other hand, when receiving an input from the modulation / demodulation unit 313, it performs processes such as analyzing the MAC header, detecting packet errors, and reordering, and provides the processed data to its own protocol upper layer.

[0032] The radio control unit 311 transfers information between each unit. It also performs parameter setting in the modulation / demodulation unit 313 and the signal processing unit 314, packet scheduling in the data processing unit 312, parameter setting and transmission power control in the modulation / demodulation unit 313, the signal processing unit 314, the radio interface unit 316, and the amplifier unit 317.

[0033] When transmitting, the modulation / demodulation unit 313 generates a data symbol stream based on parameters related to the physical layer (PHY: Physical Layer) set by the radio control unit 311 for the input data from the data processing unit 312, and supplies it to the signal processing unit 314. Specifically, based on the coding method and modulation method set by the radio control unit 311, it performs coding, interleaving, and modulation to generate a data symbol stream and supplies it to the signal processing unit 314. When receiving, it performs the reverse process of transmission for the input from the signal processing unit 314 and supplies the data to the data processing unit 312 or the radio control unit 311.

[0034] At the time of transmission, the signal processing unit 314 performs signal processing for spatial separation on the input from the modulation / demodulation unit 313 as necessary, and supplies the obtained one or more transmission symbol streams to the respective radio interface units 316. In addition, based on the parameters related to the physical layer set by the radio control unit 311, it adds a preamble of the physical layer and inserts a pilot signal. Note that a pilot signal may be generated as necessary. Also, at the time of reception, the signal processing unit 314 performs signal processing on the received symbol streams input from the respective radio interface units 316, and performs phase tracking with reference to the received pilot signal as necessary, and spatial decomposition of the streams, and supplies them to the modulation / demodulation unit 313.

[0035] The channel estimation unit 315 estimates the frequency error between the own terminal and the received signal and calculates the complex channel gain information of the propagation path from the preamble part and the training signal part of the input signal from each radio interface unit 316. The estimated frequency error and the calculated complex channel gain information are used for the demodulation process in the modulation / demodulation unit 313 and the signal processing in the signal processing unit 314 via the radio control unit 311.

[0036] At the time of transmission, the radio interface unit 316 converts the input from the signal processing unit 314 into an analog signal, performs filtering, up-conversion to the carrier frequency, and phase control, and sends it to the antenna 319 or the amplifier unit 317. At the time of reception, it performs the reverse process on the input from the antenna 319 or the amplifier unit 317, and supplies data to the signal processing unit 314 and the channel estimation unit 315.

[0037] The amplifier unit 317 amplifies the analog signal input from the wireless interface unit 316 to a predetermined power level and transmits it to the antenna 319 during transmission. During reception, the signal input from the antenna 319 is amplified to a predetermined power level and output to the wireless interface unit 316. For this amplifier unit 317, all or part of at least one of the functions during transmission and reception may be incorporated in the wireless interface unit 316. Also, for this amplifier unit 317, all or part of at least one of the functions during transmission and reception may be components outside the communication unit 310.

[0038] The control unit 321 controls the wireless control unit 311 and the power supply unit 322. Also, this control unit 321 may perform at least part of the operations of the wireless control unit 311 instead of the wireless control unit 311.

[0039] The power supply unit 322 is composed of a battery power supply or a fixed power supply and supplies power to each part of the wireless communication device 300.

[0040] Among these configurations, the wireless control unit 311 and the control unit 321 control each part so as to perform the following operations.

[0041] [Operation] FIG. 3 is a sequence diagram showing an operation example of a wireless network system in an embodiment of the present technology.

[0042] Here, it is assumed that the wireless terminal 201 exists, and the master AP 101 and the slave AP 102 capable of performing simultaneous transmission to the wireless terminal 201 exist as multi-APs.

[0043] [Capability Exchange] First, it is mutually notified among the master AP 101, the slave AP 102, and the wireless terminal 201 whether simultaneous transmission by the multi-AP is possible. This is referred to as capability exchange 810. Specifically, the master AP 101 and the slave AP 102 are notified that they can transmit by simultaneous transmission, and the wireless terminal 201 can receive the signals transmitted by simultaneous transmission. Note that information indicating whether transmission and reception are possible may be notified for CJT (Coherent Joint Transmission) or NCJT (Non-Coherent Joint Transmission) among simultaneous transmissions.

[0044] Also, the fact that simultaneous transmission is possible may be interpreted as indirectly enabling frequency synchronization with the accuracy required for simultaneous transmission. For example, if only NCJT can be implemented, it may be interpreted that high-precision frequency synchronization cannot be implemented, but if CJT can be implemented, it may be interpreted that high-precision frequency synchronization can be implemented.

[0045] Note that the capability exchange 810 is an example of the communication unit described in the claims.

[0046] [Pilot Signal Allocation Negotiation] After the capability exchange 810 notifies that transmission by simultaneous transmission is possible between the multi-AP and the wireless terminal 201, the master AP 101 that has determined to perform simultaneous transmission in the multi-AP notifies the slave AP 102 of information for determining the allocation of pilot signals (821). The slave AP 102 that has received the notification 821 from the master AP 101 notifies the master AP 101 of information for determining the allocation of pilot signals (822). This exchange of decisions is referred to as pilot signal allocation negotiation (820).

[0047] For example, the master AP 101 may notify (821) information indicating the allocation of pilot signals in simultaneous transmission, and the slave AP 102 may be notified (822) of information indicating approval. Also, the master AP 101 may similarly notify (821) information indicating a plurality of candidates, and the slave AP 102 may return (822) the candidate selected therefrom.

[0048] The pilot signal allocation negotiation 820 may be performed prior to each simultaneous transmission by the multi-AP, but does not necessarily have to be performed for each simultaneous transmission. For example, if the method of allocating pilot signals to be used when assigned as the master AP 101 and the slave AP 102 is common among the multi-APs, the access points constituting the multi-AP may be assigned as the master AP 101 and the slave AP 102, and at the same time, the allocation of the pilot signal may be implicitly determined. In this case, it may be determined to follow this allocation method as long as the allocation of the master AP 101 and the slave AP 102 does not change.

[0049] Note that the pilot signal allocation negotiation 820 is an example of the wireless control unit described in the claims.

[0050] After the pilot signal allocation negotiation 820 is performed, each access point constituting the multi-AP performs (830) the allocation of the pilot signal determined by the pilot signal allocation negotiation 820 when performing simultaneous transmission.

[0051] Note that the pilot signal allocation 830 is an example of the wireless control unit described in the claims.

[0052] [Simultaneous Transmission] The multi-AP in which the pilot signal allocation in simultaneous transmission is determined by the pilot signal allocation negotiation 820 allocates the pilot signal according to the determined pilot signal allocation and performs (840) simultaneous transmission (for example, CJT) to the wireless terminal 201.

[0053] Note that prior to the implementation of simultaneous transmission, data sharing for transmission to the wireless terminal 201 between multi-APs and frequency synchronization between multi-APs may be performed.

[0054] Note that the simultaneous transmission 840 is an example of the communication unit described in the claims.

[0055] [Phase Tracking] The wireless terminal 201 that has received a signal by simultaneous transmission from the multi-AP performs frequency synchronization with respect to the multi-AP and performs phase tracking 850 based on the assigned pilot signal. At that time, a codebook determined between multi-APs may be referred to.

[0056] There are various methods for implementing phase tracking. For example, for the pilot signal assignment defined in IEEE802.11, a simple algorithm has been proposed in which the complex phase rotation amount of the pilot signal can be applied in a minute range (A. Troya, M. Krstic, and K. Maharatna, "Simplified residual phase correction mechanism for the IEEE 802.11a standard," in Proc. IEEE VTC-Fall, Oct. 2003, vol. 2, pp. 1137-1141.). The algorithm presented here is an algorithm for phase tracking for one transmitter, but this can also be applied to multi-APs. At that time, if the frequencies are not completely synchronized between the access points constituting the multi-AP, phase tracking may be performed for one access point. Or, phase tracking may be performed with respect to the average frequency between a plurality of access points. Thereby, the influence of the residual frequency error with respect to the multi-AP can be reduced.

[0057] Note that the phase tracking 850 is an example of the channel estimation unit and the signal processing unit described in the claims.

[0058] [Ack] When the wireless terminal 201 determines that it has completed receiving signals by simultaneous transmission from multiple APs, the wireless terminal 201 notifies the multi-AP of information Ack (Acknowledgement) 860 indicating normal reception. At this time, the wireless terminal 201 can estimate the residual CFO between the master AP 101 and the slave AP 102 by the pilot signal, and may notify the Ack 860 together with the information (Residual CFO Feedback) indicating this residual CFO.

[0059] Note that the Ack 860 is an example of the communication unit described in the claims.

[0060] The master AP 101 that has received the Ack 860 may compensate for the frequency error to reduce the residual CFO between the multi-APs based on the information indicating the notified residual CFO (870).

[0061] Note that the frequency error compensation 870 is an example of the signal processing unit described in the claims.

[0062] [Frame Configuration] Hereinafter, the configuration of each frame and the like described in the above sequence diagram will be described in detail.

[0063] [Capability Exchange] FIG. 4 is a diagram showing a configuration example of a frame notified in the capability exchange 810 in the embodiment of the present technology.

[0064] The notification frame of this capability exchange 810 is used to notify whether the wireless terminal 201 that sent the notification frame can perform simultaneous transmission. This frame is composed of, but not limited to, a "destination address", a "source address", a "frame control", and "EHT (Extremely High Throughput) capabilities". Note that for the "destination address", "source address", and "frame control", since the same information is notified in frames and the like shown in subsequent figures, the description in subsequent frames and the like is omitted.

[0065] The "destination address" (TA) contains information indicating the terminal that is the destination of this frame. For example, it may contain information indicating the MAC address of the destination terminal, but when a specific plurality of terminals or all terminals that can receive this frame are the destination terminals, it may contain information indicating that it may also be received by those terminals. The "source address" (RA) contains information indicating the terminal that is the source of this frame. Similar to the "destination address", it may contain information indicating the MAC address of the source.

[0066] The "frame control" contains information indicating that this frame is a frame notified in the capability exchange 810. However, it does not necessarily have to be contained only within the "frame control", and it may be configured to indicate that this frame is a frame notified as the capability exchange 810 in combination with other information within this frame.

[0067] The "EHT capabilities" contains information indicating the capabilities of the wireless communication device that sends this frame, and in particular, information indicating whether simultaneous transmission is possible. This "EHT capabilities" includes at least one of an "element ID", a "length", and "EHT capability information", but the components are not limited to these.

[0068] The "Element ID" contains information indicating that this element is an "EHT Capability". The "Length" contains information indicating the length of the information stored as the "EHT Capability". The "EHT Capability Information" contains information indicating the capabilities of the terminal that transmits this frame. This "EHT Capability Information" includes information on "Joint Transmission", but the components are not limited to these.

[0069] The "Joint Transmission" in the "EHT Capability Information" contains information indicating whether joint transmission can be performed. Also, the "Joint Transmission" may include information indicating in detail whether it can be performed for several methods. For example, when "Joint Transmission" is represented by 3 bits, "000" indicates that joint transmission cannot be performed regardless of the method, "010" indicates that only the reception of NCJT in joint transmission can be performed, "011" indicates that both the transmission and reception of NCJT in joint transmission can be performed, "100" indicates that only transmission can be performed regardless of CJT or NCJT, "101" may be configured to indicate that both transmission and reception can be performed regardless of CJT or NCJT.

[0070] [Pilot Signal Allocation Negotiation] FIG. 5 is a diagram showing a configuration example of a frame notified by a pilot signal allocation negotiation 820 in an embodiment of the present technology.

[0071] The frame notified by this pilot signal allocation negotiation 820 is used when notifying information for determining the allocation of pilot signals in simultaneous transmission among multi-APs capable of performing simultaneous transmission. This frame is composed of a "destination address", a "source address", a "frame control", a "joint transmission control element", and a "joint transmission announcement element", but the components are not limited to these.

[0072] The "joint transmission control element" is used to estimate the length of the subsequent "joint transmission announcement element", but the use is not limited to this. Note that the "joint transmission control element" may be defined as one element together with the "joint transmission announcement element". This "joint transmission control element" includes at least one of an "element ID", a "length", and a "number of JT STAs", but the components are not limited to these.

[0073] The "element ID" includes information indicating that this element is a "joint transmission control element". The "length" includes information indicating the length of this element. The "number of JT STAs" includes information indicating the number of "terminal information" fields in the subsequent "joint transmission announcement element".

[0074] The "joint transmission announcement element" not only notifies the allocation of pilot signals in simultaneous transmission but also includes information indicating the frequency band used for transmission to the wireless terminal 201 that is the destination in simultaneous transmission. This "joint transmission announcement element" includes at least one of an "element ID", a "length", a "pilot signal allocation", and "terminal information", but the components are not limited to these.

[0075] The "Element ID" contains information indicating that this element is a "simultaneous transmission notification element". The "Length" contains information indicating the length of this element. The "Pilot Allocation" contains information indicating the allocation of pilot signals for each access point constituting the multi-AP. The "STA Info" contains information indicating the frequency band allocated to the wireless terminal 201 which is the destination of the simultaneous transmission.

[0076] The "Pilot Allocation" includes at least one sub-field of "Channel Num" and "Channel". The "Channel Num" contains information indicating the number of subsequent "Channel" sub-fields. The "Channel" contains information indicating the allocation of pilot signals for any access point constituting the multi-AP in the frequency band indicated by each channel.

[0077] Also, each "Channel" stores information of "Channel ID" and "Allocation type". The "Channel ID" contains information indicating the target frequency band indicated by the "Channel" sub-field. The "Allocation type" contains information indicating the allocation of pilot signals for any access point constituting the multi-AP in the frequency band indicated by the "Channel ID".

[0078] The "Allocation type" includes information of "AP Num", "BSSID#i" and "Allocation Type #i". The "AP Num" contains information indicating the number of access points mentioned in the "Allocation type". The "BSSID#i" contains information individually indicating different access points. The "Allocation Type #i" contains information indicating the allocation of pilot signals for the access point corresponding to each BSSID. Here, i is an integer from 1 to N AP (1) For example, N as the "AP Num" AP (1)It may include information indicating [the information], and "BSSID#i" may each include information determined by the MAC address of the access point to be specified.

[0079] "Allocation type#i" may commonly include any one of the following information indicating allocations. Specifically, in the frequency band indicated by "Channel ID", the access point indicated by "BSSID#i" includes: (1) information indicating whether to insert a pilot signal; (2) information indicating in which OFDM symbol to insert the pilot signal; and (3) when the pilot signal is inserted over a plurality of subcarriers and OFDM symbols, information indicating an orthogonal sequence for separating the pilot signal at the wireless terminal 201.

[0080] In this case, by performing the allocation of pilot signals so that the orthogonality of the pilot signals of each access point is maintained, the wireless terminal 201 can easily perform phase tracking. The orthogonality here means using at least one of different frequencies, different times, and different sequences.

[0081] "Terminal information" includes at least one subfield of "BSSID" and "Channel". "BSSID" includes information indicating different wireless terminals. "Channel" includes information indicating the frequency band to be allocated at the time of simultaneous transmission for the wireless terminal indicated by "BSSID".

[0082] [Simultaneous transmission] FIG. 6 is a diagram showing a configuration example of a data unit (PPDU: Physical-layer-convergence-Protocol Data Unit) notified by the simultaneous transmission 840 in the embodiment of the present technology.

[0083] The data unit notified by this simultaneous transmission 840 is used when a multi-AP that has determined the allocation of pilot signals among multi-APs transmits data to the wireless terminal 201 by the pilot signal allocation negotiation 820. This data unit is composed of "Legacy", "EHT-SIG", "EHT-STF", "EHT-LTF", "source address", "destination address", and "data", but the components are not limited to these.

[0084] "Legacy" includes a sequence for frame detection, AGC (Auto Gain Control), frequency synchronization, time synchronization, and propagation path estimation so that the wireless terminal 201 that receives this frame can demodulate subsequent fields. "EHT-SIG" includes information about the pilot signals allocated among multi-APs. "EHT-STF" and "EHT-LTF" include sequences necessary to further improve the accuracy of AGC, frequency synchronization, time synchronization, and propagation path estimation in addition to "Legacy". "Source address" includes information indicating the multi-AP that is the source. "Destination address" includes information indicating the wireless terminal 201 that is the destination. "Data" includes the data sent from the multi-AP to the wireless terminal 201.

[0085] Here, "Legacy" may be composed of multiple fields instead of one field. For example, it may be divided into a field for frame detection, AGC, and rough-accuracy time synchronization, and a field for frequency synchronization and fine-accuracy time synchronization. Also, "EHT-SIG" may include information about the bandwidth to be used later in addition to the information about the above-mentioned pilot signals, but the components are not limited to these.

[0086] Also, "EHT-SIG" includes one or more sub-fields of "number of channels" and "channel #i", but the components are not limited to these. "Number of channels" (Channel Number) includes information indicating the number (N c ) of the subsequent "channel #i" sub-fields. That is, i in "channel #i" ranges from 1 to Nc is an integer. "Channel #i" (Channel #i) includes information indicating the allocation of pilot signals of multi-APs in the frequency band indicated by the "Channel ID" within this "Channel #i" subfield.

[0087] The "Channel #i" subfield includes one or more subfields of "Channel ID" and "Allocation Type", but the components are not limited to these. "Channel ID" (Channel ID) includes information indicating the channel referred to by the subsequent "Allocation Type". "Allocation Type" (Allocation Type) includes information regarding the allocation of pilot signals of multi-APs in the frequency band indicated by the "Channel ID".

[0088] Thus, in the simultaneous transmission 840 in this embodiment, transmission is performed together with information indicating the allocation of pilot signals of multi-APs.

[0089] [Ack] FIG. 7 is a diagram showing a configuration example of a frame notified by Ack860 in an embodiment of the present technology.

[0090] This Ack860 is used by the wireless terminal 201 that has received the frame notified by the simultaneous transmission 840 to notify the multi-AP of the reception response and the residual CFO of the access point with the pilot signal inserted. This frame is composed of "Frame Control", "Length", "Source Address", "Residual CFO Feedback", and "FCS", but the components are not limited to these.

[0091] "Frame Control" contains information indicating that this frame is a frame notified as Ack860. "Length" contains information indicating the length of this frame. "Transmitter Address" (RA) contains information indicating the wireless terminal 201 that is the transmitter. "Residual CFO Feedback" contains information indicating the residual CFO for any access point constituting the multi-AP. "FCS" (Frame Check Sequence) contains a sequence necessary for error detection or error correction for the received frame.

[0092] "Residual CFO Feedback" includes one or more sub-fields of "Number of Multi-APs" and "Residual CFO AP#i".

[0093] "Number of Multi-APs" (Multi AP Number) contains information indicating the number of access points indicating the residual CFO referred to in "Residual CFO Feedback". "Residual CFO AP#i" (Residual CFO AP#i) contains information indicating the residual CFO of each access point. Here, i is an integer from 1 to M AP For example, it contains information including M AP as the "Number of Multi-APs", and "Residual CFO AP#i" contains a value indicating the residual CFO between the BSSID of the access point constituting the multi-AP and the access point with respect to the wireless terminal 201.

[0094] Thus, according to the embodiment of the present technology, by transmitting information indicating the allocation of pilot signals of multi-APs in the simultaneous transmission 840, phase tracking 850 can be performed in the wireless terminal 201 that has received this. Also, by notifying the residual CFO generated in the wireless terminal 201 together with Ack860, frequency error compensation 870 can be performed in the multi-AP.

[0095] <2. Variation> [Variation of Pilot Signal Allocation Negotiation] In the above-described embodiment, in the pilot signal allocation negotiation 820, the allocation of the pilot signal of the access point was individually indicated using the "allocation type" of "pilot signal allocation". On the other hand, in this modification example, it is assumed that the rule of determining the allocation of the pilot signal according to the magnitude of the MAC address is used. As a result, it becomes unnecessary to explicitly indicate by the "allocation type".

[0096] FIG. 8 is a diagram showing a modification example of the frame configuration notified in the pilot signal allocation negotiation 820 in the embodiment of the present technology.

[0097] Here, the "simultaneous transmission notification element", which is the difference from the pilot signal allocation negotiation 820 in the above-described embodiment, will be described. The "simultaneous transmission notification element" in this modification example includes at least one of "element ID", "length", and "pilot signal allocation", but the components are not limited to these.

[0098] The "Element ID" includes information indicating that this element is a "simultaneous transmission notification element". The "Length" includes information indicating the length of this element. The "Pilot Allocation" includes information regarding the allocation of the pilot signal to any access point constituting the multi-AP.

[0099] The "Pilot Allocation" includes one or more sub-fields of "number of APs", "BSSID#i", and "AP#iID".

[0100] The "AP Num" includes information indicating the number of access points targeted in the Pilot Allocation. The "BSSID#i" includes information indicating the identification number of the access point. The "AP#iID" includes information regarding the allocation of the pilot signal to the access point indicated by each "BSSID#i". Here, i is from 1 to N APis an integer. For example, N is used as the "AP number". AP includes information indicating, and "BSSID#i" includes information indicating a value determined by a MAC address, and "AP#iID" includes AP information indicating the following natural numbers.

[0101] In this modification example, it is assumed that the access point indicated by "BSSID#i" determines the allocation of pilot signals by referring to the information indicated by "AP#iID" and a codebook of pilot signal allocations determined in advance among multiple APs.

[0102] [Modification example of simultaneous transmission] FIG. 9 is a diagram showing a modification example of the data unit configuration notified by the simultaneous transmission 840 in the embodiment of the present technology.

[0103] In the above-described embodiment, information of "allocation type" was shown for each channel, but in this modification example, information regarding the allocation of pilot signals is shown for each access point.

[0104] Here, "EHT-SIG", which is a difference from the simultaneous transmission 840 in the above-described embodiment, will be described. "EHT-SIG" in this modification example includes at least one of "multi AP number" and "AP information #i", but the components are not limited to these.

[0105] The "multi AP number" (Multi AP Number) includes information indicating the number (N AP ) of subsequent "AP information #i" subfields. "AP information #i" (AP Info #i) includes information regarding the allocation of pilot signals for each access point constituting the multi AP. Here, i is an integer from 1 to N AP .

[0106] Hereinafter, as a specific example, the case where the "Data" part in the data unit according to the modification example of the simultaneous transmission 840 is transmitted by the OFDM modulation method will be described.

[0107] Figure 10 is a diagram showing an example of pilot signal allocation in an embodiment of the present technology. The figure shows a plurality of OFDM symbols constituting the "data" section.

[0108] The wireless terminal 201 extracts each OFDM symbol and demodulates the symbols inserted into each subcarrier by frequency conversion. At this time, a CP (Cyclic Prefix) is inserted at the head so that all the delayed waves observed within the OFDM symbol become delayed waves due to the symbols used within the same OFDM symbol. In the CP, an arbitrary end time-domain waveform of the immediately following OFDM symbol may be used, but it is not limited thereto.

[0109] In the figure, it is assumed that three access points (AP#1, AP#2, and AP#3) constitute a multi-AP. Pilot signals are inserted for each OFDM symbol, and they are inserted into different subcarriers and OFDM symbols among the access points. However, it is not necessary to insert all the access point pilot signals into all the OFDM symbols.

[0110] Information indicating AP#1, AP#2, and AP#3 is included in "AP information #1" to "AP information #3", and information indicating "3", which is the number of access points constituting the multi-AP, is included in "multi-AP number". In this case, it is assumed that the method of allocating pilot signals is known between the multi-AP and the wireless terminal 201 using these pieces of information.

[0111] In this case, the wireless terminal 201 can estimate where the access points constituting the multi-AP insert the pilot signals based on the information indicated in "multi-AP number" and "AP information #1" to "AP information #3" within "EHT-SIG". Then, thereby, the wireless terminal 201 can estimate the residual CFO of each access point.

[0112] In the above-described embodiment, the wireless terminal 201 can estimate where the access points constituting the multi-AP insert the pilot signal based on the information indicated in the "allocation type" of each "channel #i" in the "EHT-SIG", and can estimate the residual CFO of each access point.

[0113] Note that the above-described embodiment shows an example for embodying the present technology, and there is a corresponding relationship between the matters in the embodiment and the invention specifying matters in the claims. Similarly, there is a corresponding relationship between the invention specifying matters in the claims and the matters in the embodiment of the present technology having the same name. However, the present technology is not limited to the embodiment, and can be embodied by making various modifications to the embodiment without departing from the gist thereof.

[0114] Also, the processing procedures described in the above-described embodiment may be regarded as a method having these series of procedures, or may be regarded as a program for causing a computer to execute these series of procedures or a recording medium storing the program. As this recording medium, for example, a CD (Compact Disc), MD (MiniDisc), DVD (Digital Versatile Disc), memory card, Blu-ray Disc (Blu-ray (registered trademark) Disc), etc. can be used.

[0115] Note that the effects described in this specification are merely examples and are not limiting, and there may be other effects.

[0116] Note that the present technology can also have the following configuration. (1) A radio control unit that generates a reference signal determined with a cooperative radio base station that performs cooperative transmission, A communication unit that transmits a signal including the reference signal to a wireless terminal in cooperation with the cooperative radio base station A radio base station comprising: (2) The reference signal is transmitted using at least one of different frequencies, different times, and different sequences. The radio base station according to (1) above. (3) The communication unit exchanges information regarding a cooperative mode that can be supported prior to the cooperative transmission between the cooperative radio base station and the wireless terminal. The radio base station according to (1) or (2) above. (4) The radio control unit determines, prior to the generation of the reference signal, the allocation of the reference signal in the cooperative transmission with the cooperative radio base station. The radio base station according to any one of (1) to (3) above. (5) The reference signal allocation determination unit determines information for each frequency channel among the frequency bands used in the cooperative mode and information regarding the frequency channel. The radio base station according to (4) above. (6) The radio control unit determines at least one of information regarding the number of cooperative radio base stations, information for identifying the cooperative radio base stations, and information including numbers to be assigned to the cooperative radio base stations. The radio base station according to (4) or (5) above. (7) The radio control unit determines, for each cooperative radio base station, information indicating the presence or absence of insertion of the reference signal, information indicating the symbol for inserting the reference signal, and information including at least one of the sequences for separating the reference signal at the wireless terminal. The radio base station according to any one of (4) to (6) above. (8) The communication unit transmits information regarding the cooperative radio base station to the wireless terminal in the cooperative transmission. The radio base station according to any one of (1) to (7) above. (9) The communication unit transmits, as information regarding the cooperative radio base station, information for each arbitrary frequency channel used in the cooperative transmission to the wireless terminal. The radio base station according to (8) above. (10) The communication unit transmits, as information regarding the cooperative radio base station, the identification number assigned to the cooperative radio base station to the wireless terminal. The radio base station according to the above (8) or (9). (11) The information regarding the coordinated radio base station is information for determining the allocation of the reference signal by combining with a codebook determined between the coordinated radio base stations. The radio base station according to any one of the above (8) to (10). (12) A signal processing unit that compensates for a frequency error based on information regarding frequency synchronization notified from the wireless terminal in the coordinated transmission The radio base station according to any one of the above (1) to (11), further comprising the same. (13) A radio control unit that receives reference information from a coordinated radio base station that performs coordinated transmission, A communication unit that transmits a signal including the reference information to a wireless terminal in coordination with the coordinated radio base station A radio base station comprising the same. (14) In the coordinated transmission, the communication unit transmits information regarding the coordinated radio base station to the wireless terminal The radio base station according to the above (13). (15) As information regarding the coordinated radio base station, the communication unit transmits information for each arbitrary frequency channel used in the coordinated transmission to the wireless terminal The radio base station according to the above (14). (16) As information regarding the coordinated radio base station, the communication unit transmits an identification number assigned to the coordinated radio base station to the wireless terminal The radio base station according to the above (14) or (15). (17) The information regarding the coordinated radio base station is information for determining the allocation of the reference signal by combining with a codebook determined between the coordinated radio base stations. The radio base station according to any one of the above (14) to (16). (18) A signal processing unit that compensates for a frequency error based on information regarding frequency synchronization notified from the wireless terminal in the coordinated transmission The radio base station according to any one of the above (13) to (17), further comprising the same. (19) A channel estimation unit that separates a reference signal based on reference information from signals transmitted in cooperation from a plurality of radio base stations and estimates a frequency error between the plurality of radio base stations; A signal processing unit that performs phase shift compensation on the signals transmitted in cooperation based on the estimated frequency error; A radio terminal comprising: (20) The channel estimation unit separates the reference signal based on a codebook determined between the plurality of radio base stations and the information. The radio terminal according to (19) above. (21) A communication unit that transmits information regarding the estimated frequency error to at least one of the plurality of radio base stations. Further comprising: The radio terminal according to (19) or (20) above.

Explanation of Signs

[0117] 11, 12 Access Points 101 Master Access Point 102 Slave Access Point 201 Radio Terminal 300 Wireless Communication Device 310 Communication Unit 311 Radio Control Unit 312 Data Processing Unit 313 Modulation / Demodulation Unit 314 Signal Processing Unit 315 Channel Estimation Unit 316 Radio Interface Unit 317 Amplifier Unit 319 Antenna 321 Control Unit 322 Power Supply Unit 810 Capability Exchange 820 Pilot Signal Assignment Negotiation 830 Pilot Signal Assignment 840 Joint Transmission 850 Phase Tracking 860 Ack 870 Frequency Error Compensation

Claims

[Claim 1] a radio control unit that generates a reference signal agreed upon with a cooperative radio base station that performs cooperative transmission; a communication unit that transmits a signal including the reference signal to a wireless terminal in cooperation with the cooperative wireless base station; A wireless base station comprising:

Images