JP2024047101A - Processing apparatus in communication with wireless device via multiple access point apparatuses - Google Patents

Abstract

To estimate channel characteristics between APs without adding new estimation functions.SOLUTION: A processing apparatus includes: estimation means for estimating first channel information indicating uplink channel characteristics based on reference signals received from one or more wireless devices via each of a plurality of APs; control means for performing a correction process to generate correction information based on a reference AP apparatus in a plurality of AP apparatuses by scheduling the transmission and reception of reference signals by the plurality of AP apparatuses and obtaining, from each of the plurality of AP apparatuses, reference signals received by each of the plurality of AP apparatuses from other AP apparatuses; and estimation means for estimating second channel information indicating downlink channel characteristics based on the first channel information and the correction information.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a mobile communication system that communicates with a wireless device (WD) via multiple access point (AP) devices.

For example, in cell-free massive MIMO (CFmMIMO), a central processing unit (CPU) located in an aggregate station communicates with wireless devices (WDs) via multiple access points (APs) located at different geographical locations. The AP device located in each AP is simply referred to as "AP" below. The AP has an antenna and a wireless device. The wireless device has a wireless transmitting device (TX) that transmits wireless signals to the WD via the antenna, and a wireless receiving device (RX) that receives wireless signals from the WD via the antenna. The communication link connecting the CPU of the aggregate station and the AP is also called a fronthaul.

The CPU generates a transmission signal based on data to be transmitted to one or more WDs, and transmits the generated transmission signal to the TX of each of the multiple APs. The TX of each AP transmits a wireless signal via an antenna based on the transmission signal from the CPU. The RX of each AP receives wireless signals from one or more WDs via an antenna. The RX of each AP transmits a received signal based on the received wireless signal to the CPU. The CPU demodulates the data from each WD based on the received signal from each AP.

Here, the CPU precodes a transmission signal generated based on data to be transmitted to one or more WDs based on a downlink (DL) channel matrix between the one or more WDs and transmits the signal to each of the multiple APs. For example, in the case of time division duplexing (TDD), when there is a contradiction between the DL channel characteristics and the uplink (UL) channel characteristics, the DL channel matrix can be estimated based on a reference signal or a standard signal that the CPU receives from one or more WDs via each AP.

However, even if reciprocity is recognized in the channel characteristics of the wireless section, the TX and RX characteristics of each AP are generally different from each other. For this reason, Patent Documents 1 and 2 disclose a configuration in which test signals are transmitted and received between multiple APs to obtain the ratio of the TX and RX transfer functions of a reference AP among multiple APs to the TX and RX transfer functions of other APs, and the DL channel matrix is obtained by correcting the UL channel matrix based on the ratio.

JP 2019-091974 A JP 2019-004345 A

However, in the configurations of Patent Documents 1 and 2, it is necessary to add a new function to the CPU that allows the AP to estimate channel characteristics based on test signals received from other APs.

This disclosure provides a technique for estimating channel characteristics between APs without adding a new estimation function.

According to one aspect of the present disclosure, a processing device that communicates with one or more wireless devices via a plurality of access point (AP) devices that transmit and receive wireless signals includes an estimation means that determines and estimates first channel information indicating channel characteristics of an uplink between the one or more wireless devices based on a reference signal received from the one or more wireless devices via each of the plurality of AP devices, a control means that schedules the transmission and reception of the reference signal by the plurality of AP devices and performs a correction process that generates correction information based on a reference AP device among the plurality of AP devices by acquiring the reference signal that each of the plurality of AP devices received from another AP device from each of the plurality of AP devices, and an estimation means that estimates second channel information indicating channel characteristics of a downlink between the one or more wireless devices based on the first channel information and the correction information.

According to the present disclosure, it is possible to estimate channel characteristics between APs without adding any new estimation functions.

1 is a configuration diagram of a mobile communication system according to an embodiment. FIG. 2 is a block diagram of a processing device according to an embodiment.

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. In addition, the same reference numbers are used for the same or similar configurations, and duplicate descriptions are omitted.

Figure 1 is a diagram showing the configuration of a mobile communication system according to this embodiment. The mobile communication system includes a CPU 1, N (N is an integer of 2 or more) access point devices (APs) 2, and two WDs 3. In the following description, when each AP 2 is to be distinguished, they are written as AP #1 to AP #N as shown in Figure 1. Similarly, when two WDs 3 are to be distinguished, they are written as WD #1 and WD #2 as shown in Figure 1. In Figure 1, the number of WDs 3 is 2, but the number of WDs 3 can be any number of 1 or more. The mobile communication system according to this embodiment uses time division duplex (TDD). In other words, the downlink (DL) from AP 2 to WD 3 and the uplink (UL) from WD 3 to AP 2 are separated by time, and the frequency band of the wireless signal used in the DL direction is the same as that of the wireless signal used in the UL direction.

CPU1 is a processing device (also referred to as a central processing device) located in the aggregation station, and as described above, is connected to N APs 2 via the fronthaul. For example, when CPU1 transmits data to WD#1 and WD#2, CPU1 generates a transmission signal including data addressed to WD#1 and WD#2, and transmits the generated transmission signal to each of APs#1 to AP#N. APs#1 to AP#N each have a TX and an RX, and one or more antennas. APs#1 to AP#N transmit wireless signals based on the transmission signal from CPU1. The wireless signals transmitted by each of APs#1 to AP#N are received by WD#1 and WD#2.

In addition, each of AP#1 to AP#N receives wireless signals from WD#1 and WD#2 and transmits a received signal corresponding to the wireless signal to CPU1. The wireless signals from WD#1 and WD#2 include data that WD#1 and WD#2 transmit to the communication partner. CPU1 estimates the data from WD#1 and WD#2 based on the received signals from AP#1 to AP#N.

2 is a block diagram of the CPU 1 according to this embodiment. The transmitter 13 generates a transmission signal based on transmission data addressed to WD #1 and WD #2, and precodes the transmission signal based on the DL channel matrix H _DL notified by the control unit 10. A transmission signal to be transmitted to each AP 2 is generated by precoding the transmission signal. The receiver 14 outputs reception data from WD #1 and WD #2 based on the reception signal from each AP 2.

The receiver 14 also outputs a sounding reference signal (SRS) contained in each received signal transmitted by WD#1 and WD#2 and received from each AP 2 to the characteristic estimator 12. The SRS is a reference signal that is transmitted by WD3 to estimate UL channel characteristics between WD3 and the AP 2 and is defined in the standard of the Third Generation Partnership Project (3GPP (registered trademark)). The characteristic estimator 12 estimates a UL channel matrix H _UL between WD#1 and WD#2 based on the SRS received from WD#1 and WD#2, and notifies the control unit 10 of the estimation.

The control unit 10 estimates the channel matrix H _DL by correcting the channel matrix H _UL with the correction matrix C and notifies the transmission unit 13. In order to generate the correction matrix C, the control unit 10 executes a calibration process (correction process). In the calibration process, the control unit 10 controls the APs #1 to #N to transmit and receive test signals between the APs 2. The characteristic estimation unit 12 acquires the test signals received by each AP 2 from each AP 2, and obtains the ratio of the transfer functions of the TX and RX of the other AP 2 to the transfer functions of the TX and RX of the reference AP among the multiple APs 2 as a correction coefficient. Then, the characteristic estimation unit 12 generates a correction matrix C, which is a diagonal matrix with the correction coefficients as diagonal elements, and notifies the control unit 10.

In this embodiment, the SRS, which is the UL reference signal described above, is used as the test signal transmitted and received between AP2 to generate this correction matrix C.

In addition, the control unit 10 determines the radio resources (timing and frequency band) and the SRS sequence used by each WD3 for transmitting the SRS in order to estimate the UL channel matrix H _UL , and presets the determined radio resources and sequence in each WD3 via a higher layer protocol. The transmission timing of the SRS is the timing within a period in which the WD3 transmits a radio signal in the UL direction. The radio resources and the SRS sequence for transmitting the SRS are determined within a range specified by the 3GPP (registered trademark) standard. In the following description, the radio resources for transmitting the SRS preset in the WD3 are referred to as "radio resources for WD3".

The operation of the control unit 10 for executing the calibration process is described below. The calibration process can be executed when a new AP2 is added, when the TX or RX of the AP2 is replaced, or when it is estimated that the characteristics of the TX or RX of the AP2 have changed significantly due to aging or temperature changes in the equipment.

First, in the calibration process, the control unit 10 schedules the timing for each AP2 to transmit and receive the SRS. Specifically, the control unit 10 determines which series of SRS each AP2 will transmit and which wireless resource will be used. The control unit 10 selects a wireless resource that the AP2 will use to transmit the SRS from a wireless resource other than the "wireless resource for WD3" among the available wireless resources that are specified as being usable for transmitting the SRS in standards such as 3GPP (registered trademark). In the calibration process, the AP2 normally transmits the SRS for calibration during the period in which it receives a wireless signal from WD3. Therefore, the timing for the AP2 to transmit the SRS is determined so that it does not need to receive a wireless signal.

In this embodiment, AP#1 to AP#N are each set as a transmitting AP in turn, and the control unit 10 schedules the SRS so that only one transmitting AP transmits the SRS at a certain timing, and the remaining AP2 (receiving AP) receives the SRS from the transmitting AP. By scheduling in this manner, SRS is transmitted and received between any two AP2 pairs among AP#1 to AP#N.

The control unit 10 notifies the transmission unit 13 of the scheduling result and calibration information indicating the sequence of the SRS transmitted by each AP. The control unit 10 also transmits timing information to each AP 2. The timing information is information indicating the timing of transmitting the SRS to each AP 2. As described above, in this embodiment, during the calibration process, the AP 2 transmits the SRS during the period in which it receives a wireless signal from the WD 3. For this reason, the control unit 10 needs to notify each AP 2 of the timing of transmitting the SRS.

After transmitting the calibration information to the transmission unit 13 and the timing information to each AP 2, the control unit 10 notifies the transmission unit 13 and each AP 2 of the start of the calibration process when starting the calibration process. When the calibration process starts, the transmission unit 13 inserts an SRS into the transmission signal of each AP 2 according to the calibration information, and each AP 2 controls TX and RX so that the SRS is transmitted according to the timing information. The generation unit 131 of the transmission unit 13 generates an SRS to be transmitted by the AP 2 according to the calibration information and inserts it into the transmission signal to the AP 2. Note that the configuration may be such that the start of the calibration process is notified to the transmission unit 13 and each AP 2 by transmitting the calibration information and the timing information to the transmission unit 13 and each AP 2. In addition, it is not necessary to notify the calibration information and timing information to the transmission unit 13 and each AP 2 every time the calibration process is performed, and the same calibration information and timing information may be used in multiple calibrations. When the calibration process ends, the control unit 10 notifies the transmission unit 13 and each AP 2 of the end of the calibration process. As a result, the transmitter 13 stops transmitting the SRS to each AP 2. Also, each AP 2 stops controlling TX to transmit the SRS during the wireless signal reception period.

Returning to FIG. 2, the characteristic estimation unit 12 first estimates the channel characteristic between AP2 based on the SRS from other AP2 received by each AP2. Although not shown in FIG. 2, the calibration information is also notified to the processing unit 11. For example, based on the SRS transmitted by AP#1 and received by each of AP#2 to AP#N, the processing unit 11 can estimate the channel characteristic values h _1,2 to h _1, N from AP#1 to AP#2 to AP#N, respectively. Similarly, based on the SRS transmitted by each of AP#2 to AP#N and received by AP#1, the processing unit 11 can estimate the channel characteristic values h _2,1 to h _N,1 from each of AP#2 to AP#N to AP#1, respectively. The same applies to other combinations between AP2. If the transfer functions of TX and RX of AP#k are _TXk and _RXk , then _h1,2 = _TX1 × _hp1-2 × _RX2 , and _h2,1 = _TX2 × _hp2-1 × _RX1 . Here, _hp1-2 is the transfer function of the wireless section from AP#1 to AP#2, and _hp2-1 is the transfer function of the wireless section from AP#2 to AP#1.

When reciprocity of the wireless section is recognized, h _p1-2 =h _p2-1 . Therefore, in this case, the correction coefficient C _1,2 of AP#2 based on AP#1 is calculated as C _1,2 =h _1,2 /h _2,1 =(TX ₁ ×RX ₂ )/(TX ₂ ×RX ₁ ). The correction coefficient C _1,2 is the ratio of the transfer functions of TX and RX of AP#2 based on the transfer functions of TX and RX of AP#1.

The characteristic estimation unit 12 first selects one of the N APs 2 as the reference AP. The selection criteria for the reference AP are arbitrary, but for example, the signal-to-noise ratio (SNR) can be estimated based on the SRS received by the AP 2, and the AP 2 with the best average SNR with other APs 2 can be selected as the reference AP. In the following description, it is assumed that AP #1 is selected as the reference AP. In this case, the characteristic estimation unit 12 obtains the correction coefficients C _1,2 to C _1,N as described above. Note that the correction coefficient C _1,1 is 1=(TX ₁ ×RX ₁ )/(TX ₁ ×RX ₁ ). The characteristic estimation unit 12 obtains a diagonal matrix with the correction coefficients C _1,1 to C _1,N as elements as the correction matrix C. That is, C = diag [ _C1,1 , _C1,2 , ..., C1 _,N ] = ( _TX1 / _RX1 ) diag [ _RX1 / _TX1 , _RX2 / _TX2 , ..., _RXN / _TXN ]. The characteristic estimation unit 12 notifies the control unit 10 of the correction matrix C.

The control unit 10 estimates the DL channel matrix H _DL by multiplying the UL channel matrix H _UL by the inverse matrix of the correction matrix C. The transmission unit 13 performs precoding by generating a precoding matrix W by a method such as ZF, MMSE, or PMMSE based on the DL channel matrix H _DL . For example, each column of the precoding matrix W corresponds to one AP2, and a transmission signal to the AP2 is multiplied by a vector of the corresponding column of the precoding matrix W.

As described above, in this embodiment, the SRS, which is a UL reference signal, is used for calibration between the APs 2. The CPU 1 has a function of estimating channel characteristics based on the SRS in order to estimate the UL channel matrix H _UL . Therefore, it is possible to estimate channel characteristics between the APs without adding a new estimation function.

In this embodiment, AP#1 to AP#N are sequentially set as transmitting APs, and only one transmitting AP transmits SRS at a certain timing, and the remaining AP2 (receiving AP) is scheduled to receive SRS from the transmitting AP. This is because, by scheduling in this manner, SRS is transmitted and received in a pair of any two AP2s among AP#1 to AP#N. In addition, this is also to select a reference AP based on the results of SRS transmission and reception of each pair. However, for example, when the reference AP is AP#1, what is required is to transmit and receive SRS in N pairs including AP#1. Therefore, for example, AP#1 transmits SRS at a certain timing, and AP#2 to AP#N receive SRS, so that the channel characteristic values h _1,2 to h _1,N can be estimated. In addition, when multiple APs 2 can transmit SRS using different frequency bands at a certain timing, for example, when (N-1) APs 2 can transmit SRS at a certain timing, APs #2 to #N transmit SRS, and AP #1 receives SRS, so that channel characteristic values h _2,1 to h _N,1 can be estimated, and thus correction matrix C can be estimated. In addition, for example, h _2,1 can be obtained by multiplying h _2,m and h _m,1 . Note that m is any number from 3 to N. Therefore, for example, when a reference AP or a plurality of candidate APs to be the reference AP can be determined or selected in advance based on the placement positions of APs #1 to AP #N, it is not necessary to schedule transmission and reception of SRS in any pair of two APs 2.

In the above embodiment, the mobile communication system uses TDD. However, the above embodiment can be applied to a mobile communication system that uses frequency division duplex (FDD) as long as reciprocity of the wireless channel is recognized even in FDD. Also, in the above embodiment, the SRS, which is a UL reference signal, is used for calibration. However, the present disclosure is not limited to the use of SRS, and any reference signal transmitted by WD3 in UL can be used for calibration.

In addition, in the above embodiment, the terms channel matrix, precoding matrix, and correction matrix are used. A channel matrix is information indicating the characteristics of multiple channels, a precoding matrix is information indicating the processing to be applied to wireless signals transmitted from multiple APs 2, and a correction matrix is information indicating the amount of correction for the values of each element of the channel matrix. Therefore, the term "matrix" can be replaced with the term "information."

The CPU1 according to the present disclosure may be realized by a computer program that, when executed by one or more processors of a device having the processors, causes the device to function as the CPU1. The computer program may include program instructions that are executable by one or more processors. The computer program may be stored in a non-transitory computer-readable storage medium or may be distributed via a network.

The above configuration makes it possible to estimate channel characteristics between APs without adding any new estimation functions. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention.

12: characteristic estimation unit, 10: control unit

Claims (9)

A processing device for communicating with one or more wireless devices via a plurality of access point (AP) devices for transmitting and receiving wireless signals, comprising:
an estimation means for estimating first channel information indicating channel characteristics of an uplink between the one or more wireless devices and the one or more wireless devices based on reference signals received from the one or more wireless devices via each of the plurality of AP devices;
a control means for performing a correction process that schedules transmission and reception of the reference signal by the plurality of AP devices, and acquires, from each of the plurality of AP devices, the reference signal that each of the plurality of AP devices has received from another AP device, thereby generating correction information based on a reference AP device among the plurality of AP devices;
an estimation means for estimating second channel information indicating channel characteristics of a downlink between the one or more wireless devices and the first channel information and the correction information, based on the first channel information and the correction information;
The processing device comprises: The processing device of claim 1, wherein the reference signal is a sounding reference signal (SRS). The processing device according to claim 1, wherein the control means schedules transmission and reception of the reference signal such that each of the plurality of AP devices transmits the reference signal using a radio resource that is different from a radio resource used by the one or more wireless devices to transmit the reference signal, among radio resources available for transmitting the reference signal. said plurality of AP devices and said one or more wireless devices communicate with each other using a time division duplex method;
The processing device according to claim 3 , wherein the wireless resource available for transmitting the reference signal is a wireless resource within a period during which each of the plurality of AP devices receives a wireless signal from the one or more wireless devices. The processing device according to claim 4, wherein the control means schedules transmission and reception of the reference signal for each of the plurality of AP devices such that the AP device transmits the reference signal during a period when the AP device does not need to receive a wireless signal from the one or more wireless devices. The processing device according to claim 1, wherein the control means notifies each of the plurality of AP devices of the timing at which the AP devices transmit the reference signal during the correction process. The processing device according to claim 1, further comprising a transmission means for transmitting the reference signal to each of the plurality of AP devices so that the reference signal is transmitted from each of the plurality of AP devices according to the scheduling during the correction process. The processing device according to claim 1, further comprising a transmission means for precoding a transmission signal to be transmitted to the plurality of AP devices for communication with the one or more wireless devices based on the second channel information. A computer program that, when executed by one or more processors of an apparatus having one or more processors, causes the apparatus to function as a processing device according to any one of claims 1 to 8.

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