JP7619988B2 - Relay station, transmission method for relay station, and communication system - Google Patents

Description

This disclosure relates to a relay station, a relay station transmission method, and a communication system.

In wireless communication such as the 5th Generation Mobile Communication System (5G), ultra-low latency communication of sub-milliseconds or less is expected. On the other hand, from the perspective of improving communication services, it is desirable to expand the coverage area of cells, and relay communication via a relay station is effective for this purpose. Therefore, a wireless communication method has been proposed in which a terminal station that performs wireless communication serves as a relay station. Furthermore, as a relay technology with low latency, non-regenerative relay, in which demodulation and decoding are not performed at the relay station, is desirable.

H. Chen. A. B. Gershman, and S. Shahbazpanahi, “Filter-and-Forward Distributed Beamforming in Relay Networks with Frequency Selective Fading”, IEEE Trans. On Signal Processing, vol. 58, no. 3, March 2010. Noguchi, Hayashi, Kaneko, and Sakai, “Single-frequency full-duplex wireless relay for frequency-domain equalization systems,” IEICE Technical Report, vol. SIP2011-109, January 2012.

The present disclosure aims to provide a relay station, a transmission method thereof, and a communication system that enable a receiving station to obtain a suitable diversity effect.

One aspect of the present disclosure is a relay station that operates as a first relay station and is capable of performing non-regenerative relaying of a first wireless signal transmitted from a transmitting station to a receiving station having one antenna together with one or more second relay stations, the relay station including:
At least one antenna;
A radio corresponding to the antenna;
a controller for controlling an operation of the radio;
The radio device includes:
a receiver that converts the first radio signal received by the antenna into a baseband signal;
an FIR filter that adds a delay to the baseband signal;
a transmitter that converts the signal output from the FIR filter into a second radio signal that is transmitted from the antenna to the receiving station;
the controller sets a delay amount in the FIR filter of the wireless device so that the second wireless signal transmitted from each antenna of the first and second relay stations has a different delay between the first and second relay stations;
It is a relay station.

One aspect of the present disclosure is a transmission method of a relay station that operates as a first relay station and is capable of performing non-regenerative relaying of a first wireless signal transmitted from a transmitting station to a receiving station having one antenna together with one or more second relay stations, the method comprising:
The relay station,
converting the first radio signal received by at least one antenna of the relay station into a baseband signal;
applying a delay to the baseband signal using an FIR filter;
converting the signal output from the FIR filter into a second radio signal to be transmitted from the antenna to the receiving station;
A relay station transmission method in which a delay amount is set in the FIR filter so that the second radio signal transmitted from each antenna of the first and second relay stations has a different delay between the first and second relay stations.

One aspect of the present disclosure is
a receiving station having one antenna;
a transmitting station that transmits a first radio signal to the receiving station;
a plurality of relay stations capable of relaying the first radio signal to the receiving station by non-regenerative relay;
Each of the plurality of relay stations comprises:
At least one antenna;
A radio corresponding to the antenna;
a controller for controlling an operation of the radio;
The radio device includes:
a receiver that converts the first radio signal received by the antenna into a baseband signal;
an FIR filter that adds a delay to the baseband signal;
a transmitter that converts the signal output from the FIR filter into a second radio signal that is transmitted from the antenna to the receiving station;
The controller is a communication system that sets a delay amount in the FIR filter of the radio so that the second radio signal transmitted from each antenna of the multiple relay stations has a different delay between the multiple relay stations.

This disclosure allows the receiving station to obtain a favorable diversity effect.

FIG. 1 is a diagram showing a first configuration example of a communication system according to the first embodiment. FIG. 2 is a diagram showing a second configuration example of the communication system according to the second embodiment. FIG. 3 is a diagram illustrating an example of a hardware configuration of a relay station. FIG. 4 is a diagram illustrating an example of the configuration of an FIR filter. FIG. 5 is a diagram illustrating an example of a hardware configuration of the control device. FIG. 6 is an explanatory diagram of the process in the relay station. FIG. 7 is an explanatory diagram of the process in the relay station. FIG. 8 is a flowchart showing an example of processing by the control device. FIG. 9 is a flowchart illustrating an example of processing by the relay station. FIG. 10 is a flowchart illustrating an example of processing by a relay station. FIG. 11 is a diagram illustrating an example of the configuration of a relay station in the second embodiment. FIG. 12 is an explanatory diagram of a process in a relay station in the second embodiment. FIG. 13 is an explanatory diagram of a process in a relay station in the second embodiment. FIG. 14 is a flowchart illustrating an example of processing by a relay station in the second embodiment. FIG. 15 is a flowchart illustrating an example of processing by a relay station in the second embodiment. FIG. 16 is a flowchart illustrating an example of processing by the control device in the third embodiment. FIG. 17 is a flowchart illustrating an example of processing by a relay station in the third embodiment. FIG. 18 is an explanatory diagram of the process of the relay station in the fourth embodiment. FIG. 19 is an explanatory diagram of the process of the relay station in the fourth embodiment. FIG. 20 is a flowchart illustrating an example of processing by a relay station in the fourth embodiment. FIG. 21 is a flowchart illustrating an example of processing by a relay station in the fourth embodiment. FIG. 22 is a flowchart illustrating an example of processing by the base station in the fourth embodiment. FIG. 23 is a flowchart showing an example of processing by a control device in a modified example of the fourth embodiment. FIG. 24 is a flowchart illustrating an example of processing by a base station in the modification of the fourth embodiment.

In a cellular network such as the Third Generation Partnership Project (3GPP (registered trademark)) or a wireless LAN network such as Wi-Fi (IEEE802.11 series), a base station (called a Base Station (BS)) provides "transmit diversity (Tx diversity)". Transmit diversity is a function in which a base station uses multiple transmit antennas to transmit a signal (called a downlink signal) from the base station to a terminal station. With transmit diversity, even if the terminal station has only one antenna, the terminal station can obtain a diversity effect (diversity gain) and improve the SIR (signal-to-interference ratio) and SINR (signal-to-interference-plus-noise power ratio).

For example, in a 5G communication system, it is conceivable that a relay station may transmit a wireless signal to a terminal station by non-regenerative relay from a base station to which transmit diversity is applied. In such a case, if there is a high correlation between the propagation characteristics of the wireless signal received by the receiving station from the relay station and the propagation characteristics of the wireless signal received from the base station, there is a risk that a sufficient diversity effect cannot be obtained at the terminal station.

In the present disclosure, when each of a plurality of relay stations relays a radio signal from a transmitting station to a receiving station by non-regenerative relay using one or more antennas, a different delay amount is set in the FIR filter corresponding to the antenna of each relay station. This allows the radio signal transmitted from each relay station by non-regenerative relay to have a different delay between relay stations, or between the relay station and the antenna. This realizes delay diversity for radio signals transmitted from a plurality of antennas equipped in a plurality of base stations, and makes it possible to obtain a suitable diversity effect at the receiving station. When transmission diversity is applied to a radio signal from a transmitting station, it is possible to improve the diversity gain at the terminal station by radio signals from a plurality of relay stations. However, the configuration of the relay station described later can also be applied to radio signals from a base station (transmitting station) to which transmission diversity is not applied (for example, when a base station uses one antenna to transmit a radio signal to a terminal station having one antenna). In the present disclosure, a "receiving station having one antenna" includes not only a terminal station having one antenna, but also a terminal station having two or more antennas but using only one antenna to receive radio signals from a transmitting station and a relay station. Additionally, a "relay station having one or more antennas" includes a relay station having only one antenna, a relay station having two or more antennas but using only one antenna for non-regenerative relay, and a relay station having two or more antennas and using two or more antennas for non-regenerative relay.

The communication system according to the present disclosure may include a transmitting station, a receiving station, multiple relay stations, and a control device. The transmitting station may be, for example, a base station, and the receiving station may be, for example, a terminal station. However, the transmitting station may be a terminal station and the receiving station may be a base station. The relay station may be, for example, a small base station, a mobile base station, a smartphone, or an in-vehicle device. The start timing of each slot constituting a wireless frame is synchronized between the transmitting station, the receiving station, and one or more relay stations.

The relay station performs non-regenerative relay of the radio signal. In the non-regenerative relay, the radio signal (first radio signal) received from the transmitting station is converted into a baseband signal, but the baseband signal is not demodulated or decoded. The baseband signal is operated, and the operated baseband signal is converted into a radio signal and transmitted from the antenna. The relay station according to the present disclosure includes one or more antennas and a radio device corresponding to each antenna, and the non-regenerative relay of the radio signal described above is performed for each antenna that receives the first radio signal. In the present disclosure, as an operation on the baseband signal corresponding to each antenna, a FIR (Finite Impulse Response) filter included in the radio device imparts a different delay between relay stations or between the relay station and the antenna to each baseband signal. By imparting a delay, delay diversity can be applied to the radio signal (second radio signal) transmitted to the receiving station from multiple antennas of multiple relay stations.

The relay station includes a controller (control unit), which calculates the amount of delay to be set in the FIR filter included in the radio of the relay station. For example, the controller can obtain a maximum delay using a first propagation delay, which is the propagation delay of a signal received by the relay station from a receiving station, a second propagation delay, which is the propagation delay of a signal received by the relay station from a transmitting station, and a processing delay of the signal in the relay station, and calculate the amount of delay to be set in the FIR filter within a range not exceeding the maximum delay. This allows the FIR filter to impart a desired delay, which differs between antennas, to the baseband signal.

The controller is, for example, a computer, a processor such as a CPU (Central Processing Unit), an arithmetic circuit (integrated circuit) such as an FPGA (Field Programmable Gate Array), or a combination of these. The control device provided in the communication system can be configured by the above-mentioned computer, a processor such as a CPU, an integrated circuit, or a combination of these. The control device gives instructions to the relay station, and the relay station can apply the above-mentioned delay upon receiving the instruction from the control device. It is also possible that the control device calculates the delay amount to be set in the FIR filter of each relay station described above, includes it in the above-mentioned instruction, and the controller sets the delay amount included in the instruction in each FIR filter.

The FIR filter according to the present disclosure may perform filtering to suppress interference occurring in the relay station between a wireless signal received from a transmitting station and a wireless signal to be transmitted to a receiving station (between a transmitter and a receiver). The interference between the signal received from the transmitting station and the signal to be transmitted to the receiving station is also called self-interference (SI). The controller can set a weight for suppressing self-interference for the FIR filter.

In addition to the relay station, the relay station transmission method, and the communication system including the relay station described above, aspects of the present disclosure can also be specified as a program for causing the relay station to execute the relay station transmission method, and a computer-readable, non-transitory storage medium on which the program is recorded.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The configurations of the following embodiments are exemplary, and the present disclosure is not limited to the configurations of the embodiments. In the embodiments, a 5G communication system is exemplified as a communication system, but the configurations of the transmitting station, relay station, and receiving station according to the present disclosure can be applied to communication systems other than 5G (wireless LAN, etc.).

First Embodiment
Fig. 1 is a diagram showing a first configuration example of a communication system in the first embodiment. In Fig. 1, a communication system 100A according to the first configuration example has a control device 1, a base station 2, a plurality of relay stations 3-1, ..., 3-N (N is an integer indicating the number of relay stations), and a terminal station 4. In the following description, when there is no need to distinguish between the relay stations 3-1, ..., 3-N, they will be referred to as "relay station 3". Furthermore, in the communication system 100A, the number of terminal stations 4 may be one or more (one terminal station 4 is illustrated in Fig. 1).

The control device 1 is a device on the core network to which the base station 2 is connected. However, it is also possible to think of the control device 1 as the core network itself, or as a system included in the core network. The core network includes, for example, an optical fiber network. The control device 1 controls the base station 2, the relay station 3, and the terminal station 4, and provides communication services to the terminal station 4.

The base station 2 provides a wireless access network to the terminal station 4. An area where wireless communication is possible in the wireless access network is also called a cell. In the first embodiment, the base station 2 has one or more antennas (e.g., antennas #0 and #1), a radio 21 corresponding to each antenna, and a control circuit 22. The control circuit 22 has, for example, a processor and a memory. The processor controls communication with the control device 1 (base station 2) and wireless communication with the relay station 3 and the terminal station 4 using a computer program in the memory.

The relay station 3 relays wireless communication between the base station 2 and the terminal station 4. The relay station 3 is, for example, a small base station, a mobile base station, an in-vehicle device, or a smartphone. The relay station 3 can be selected as a relay station by the control device 1 from among devices having a configuration capable of non-regenerative relay. When a connection request is generated from the terminal station 4, the control device 1 can select one or more relay stations 3 located within the range of the cell provided by the base station 2, and transmit an instruction to each relay station 3 to non-regeneratively relay wireless communication. The relay station 3 that receives the instruction operates as the relay station 3 selected by the control device 1.

Like the base station 2, the relay station 3 has at least one antenna (one or more), a radio 31 corresponding to each antenna, and a control circuit 32 (an example of a "controller"). In the example shown in FIG. 1, each of the relay stations 3-1 to 3-N has one antenna (#0).

The terminal station 4 is, for example, a mobile station such as a smartphone, a tablet terminal, a wearable terminal, or an in-vehicle data communication device. However, the present invention is not limited to this, and the terminal station 4 may be a stationary terminal device. For example, the terminal device connects to a wireless access network within the range of a cell provided by the base station 2.

The terminal station 4 has one antenna (e.g., #0), a radio 41 connected to the antenna, and a control circuit 42. For example, a mobile station in a cell requests the base station 2 to connect to the radio access network, and when the mobile station is connected, the mobile station operates as the terminal station 4. The mobile station in the cell may request the base station 2 directly to connect to the radio access network. Alternatively, the mobile station in the cell may request the base station 2 to connect to the radio access network via a device that operates as a relay station 3 in the cell. The terminal station 4 can be said to be a station that can communicate with the base station 2 via one or more relay stations 3 or without via any of the one or more relay stations 3.

FIG. 2 is a diagram showing a second configuration example of the communication system according to the first embodiment. As the communication system, a communication system 100B according to the second configuration example as shown in FIG. 2 may be applied. The communication system 100B is different from the communication system 100A of FIG. 1 in the following respects. That is, the communication system 100B has a central base station 2A and one or more distributed base stations 2B instead of the base station 2. When one or more distributed base stations 2B are individually distinguished, a branch number is assigned, such as distributed base stations 2B-1, ..., 2B-K. Here, the branch number K is an integer indicating the number of distributed base stations. In FIG. 2, distributed base stations 2B-1 and 2B-K are illustrated. However, when the distributed base stations 2B-1, ..., 2B-K are collectively referred to, they are simply described as distributed base station 2B.

The central base station 2A has a control circuit 22A. Furthermore, the distributed base station 2B has a radio 21B corresponding to antennas #0 and #1. The control circuit 22A of the central base station 2A and the radio 21B of the distributed base station 2B are connected, for example, by an optical fiber C1 or a wireless network. The topology of the optical fiber C1 connecting the central base station 2A and the multiple distributed base stations 2B is not limited to a specific topology. For example, the topology of the optical fiber C1 may be a one-to-one connection between nodes, a network that branches as it moves away from the central base station 2A, a star network, or a ring network. Furthermore, when connecting the control circuit 22A of the central base station 2A and the radio 21B of the distributed base station 2B by a wireless network, the standard and protocol of the wireless network employed are not limited to a specific one.

The control circuit 22A has a processor and a memory, similar to the control circuit 22 in FIG. 1. The processor controls communication with the control device 1 and wireless communication with the relay station 3 and terminal station 4 using a computer program in the memory. That is, the control circuit 22A controls wireless communication with the relay station 3 and terminal station 4 via the radio 21B of one or more distributed base stations 2B. The configurations of the relay station 3 and terminal station 4 are the same as those of the communication system 100A, so repeated explanations will be omitted.

The following configuration is adopted as a premise for the communication systems 100A and 100B. In the communication systems 100A and 100B, communication is performed by time division multiplexing, and the same frequency channel is used for the uplink (uplink) and downlink (downlink). In addition, the slot start timing that constitutes the wireless frame is synchronized between the base station 2, relay station 3, and terminal station 4.

In the communication systems 100A and 100B, a block transmission method having a cyclic prefix (CP), such as CP-OFDM (Cyclic Prefix - Orthogonal Frequency Division Multiplexing), is adopted as the wireless modulation method. In this embodiment, a case where CP-OFDM is applied will be described, but a block transmission method having a CP other than CP-OFDM may also be used. In addition, the relay station 3 shares resource block information used in the uplink and downlink by the terminal station 4 that is the target of relaying.

Note that an uplink is a link in the direction from the terminal station 4 to the base station 2. A downlink is a link in the direction from the base station 2 to the terminal station 4. The following explanation illustrates a case where non-regenerative relay is performed in the downlink direction. That is, the base station 2 corresponds to the "transmitting station" and the terminal station 4 corresponds to the "receiving station". However, the non-regenerative relay performed by the relay station 3 in the embodiment may also be applied to communication in the uplink direction.

The relay station 3 applies a delay to the relay signal, i.e., the signal (second radio signal) that is non-regeneratively relayed to the terminal station 4. The timing at which the relay signal arrives at the terminal station 4 is calculated in the relay station 3. The relay station 3 calculates the delay time to be applied based on the propagation characteristics of the radio waves between the base station 2 and the relay station 3, the propagation characteristics of the radio waves between the relay station 3 and the terminal station 4, and the processing time of the signal at the relay station 3 so that the relay signal transmitted from each antenna (antennas #0 and #1) arrives at the terminal station 4 at the desired timing. The propagation characteristics of the radio waves include, for example, a propagation delay, a delay spread, and a phase rotation amount. However, the information included in the propagation characteristics of the radio waves is not limited to these. The propagation delay is the time it takes for a signal to arrive at a receiving device after being transmitted from a transmitting device. The delay spread is the time it takes for a signal to arrive at a receiving device after a signal starts arriving at the receiving device until reception of the signal is completed.

Figure 3 is a diagram showing an example of the hardware configuration of relay station 3. Relay station 3 includes radio 31 and control circuit 32. Radio 31 of relay station 3 includes transmitter 311, receiver 312, and baseband circuit 313. Transmitter 311 and receiver 312 are connected to antenna (#0) via circulator 314. That is, transmitter 311, receiver 312, and antenna (#0) are connected to three ports of circulator 314. The transmission signal from transmitter 311 is input to, for example, the first port of circulator 314 and transmitted from the second port to receiver 312. The transmission signal from transmitter 311 is input to the third port of circulator 314 and transmitted from the first port to antenna (#0).

Here, the power difference between the transmission signal and the reception signal is, for example, about 100 dB. On the other hand, the isolation of the circulator 314 is about 30 dB, and a part of the transmission signal interferes with the reception signal. This interference between a part of the transmission signal and the reception signal in the radio device 31 is called self-interference. Self-interference is suppressed by using a radio frequency (RF) analog filter in the receiver 312 and an FIR filter in the baseband circuit 313 in combination.

The receiver 312 receives a received signal from the antenna (#0) via the circulator 314. The receiver 312 has a quadrature detection circuit and an analog-to-digital (AD) converter. The receiver 312 down-converts the received signal by quadrature detection, and further converts it into digital data by the AD converter to obtain a baseband signal. The receiver 312 outputs the obtained baseband signal to the baseband circuit 313.

The baseband circuit 313 is a digital circuit including an FIR filter 315. A baseband signal is input to the FIR filter 315 as a received signal. The FIR filter 315 suppresses a transmission signal that is mixed into the baseband signal and causes self-interference, and delays the baseband signal by a predetermined delay time. The baseband circuit 313 inputs the output signal of the FIR filter 315 (the signal filtered by the FIR filter 315) to the transmitter 311.

Transmitter 311 has a digital-to-analog (DA) converter and a modulation circuit. Transmitter 311 converts the received signal from baseband circuit 313 into an analog signal, and generates an RF signal using the modulation circuit. Transmitter 311 transmits the RF signal as a relay signal from antenna (#0) via circulator 314.

The control circuit 32 can be configured, for example, by a processor such as a CPU, or an integrated circuit such as an FPGA, or a combination of these. The control circuit 32 controls the non-regenerative relay process. More specifically, the control circuit 32 measures the propagation characteristics of the propagation path, notifies the control device 1 of the measurement results, and sets the delay time (corresponding to the amount of delay) for the FIR filter 315. The control circuit 32 can also calculate a weight for suppressing self-interference and set the weight in the FIR filter 315. The control circuit 32 is an example of a "controller (control unit)" of the "relay station".

4 is a diagram showing an example of the configuration of the FIR filter 315. The FIR filter 315 has an input terminal 316, an output terminal 317, and N_(D,i) stages of taps (T1, T2, ..., TN_(D,i)). The letters in parentheses following the underline after the alphabet correspond to the subscripts in the figure. Each of the taps except tap T1 includes a delay unit (delay element) D that delays the input signal by a delay time τ_(D), and a multiplier ML that multiplies the input signal by a complex weight.

Tap T1 does not have a delay D, and the input signal from input terminal 316 is weighted by multiplier ML with weight w_(i,1). Tap T2 delays the input signal by delay D (delay time τ_(D)) and weights it by multiplier ML with weight w_(i,2). The same applies to taps T3 and onwards. Therefore, in the final tap TN_(D,i), the input signal to tap T1 (input signal to FIR filter 315) is given a delay time τ_(D)×(N_(D,i)-1) and weighted with weight w_(i,N_(D,i)). The signals processed at each tap (T1, T2, ..., TN_(D,i)) are each added by adder AD and output from output terminal 317. With the above configuration, the input signal to the FIR filter 315 is weighted and averaged, interference signals and noise other than the received signal are removed, and the signal is delayed by the delay time τ_(D)×(N_(D,i)-1).

The number of taps N_(D,i) and weights w_(i) used by the FIR filter 315, i.e., w_(i,1) to w_(i,N_(D,i)), are calculated by the control circuit 32. Details will be described later.

FIG. 5 is a diagram illustrating a hardware configuration of the control device 1. The control device 1 has a CPU 11, a main storage device 12, and external devices, and executes communication processing and information processing by a computer program. The CPU 11 is also called a processor. The CPU 11 is not limited to a single processor, and may be a multi-processor configuration. The CPU 11 may also include a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), or the like. The CPU 11 may also cooperate with a hardware circuit such as a Field Programmable Gate Array (FPGA). Examples of the external devices include an external storage device 13, an output device 14, an operation device 15, and a communication device 16.

The CPU 11 executes a computer program that has been loaded in an executable manner in the main memory device 12, and provides processing for the control device 1. The main memory device 12 stores the computer program executed by the CPU 11, data processed by the CPU 11, etc. The main memory device 12 is a dynamic random access memory (DRAM), a static random access memory (SRAM), a read only memory (ROM), etc. Furthermore, the external memory device 13 is, for example, the main memory device 1
2 and stores computer programs executed by the CPU 11, data processed by the CPU 11, etc. The external storage device 13 is a hard disk drive, a solid state drive (SSD), etc. Furthermore, a drive device for a removable storage medium may be connected to the control device 1. The removable storage medium is, for example, a Blu-ray disc, a Digital Versatile Disc (DVD), a Compact Disc (CD), a flash memory card, etc.

The output device 14 is, for example, a display device such as a liquid crystal display or an electroluminescence panel. However, the output device 14 may include a speaker or other device that outputs sound. The operation device 15 is, for example, a touch panel with a touch sensor superimposed on a display. The communication device 16 communicates with the base station 2 and an external network such as the Internet via optical fiber, for example. The communication device 16 is, for example, a gateway connected to the base station 2 and a gateway that communicates with an external network such as the Internet. The communication device 16 may be a single device or a combination of multiple devices. The hardware configuration of the control device 1 is not limited to that shown in FIG. 5. In addition, the control circuit 32 of the relay station 3 described above may be configured as a device including the CPU 11, the main memory device 12, and the external memory device 13 described above.

Figures 6 and 7 are explanatory diagrams of the processing in relay station 3. Figure 6 shows relay station 3-1 (relay station #0) and relay station 3-2 (relay station #1 when N=2, where N is the number of relay stations) as examples of two or more relay stations 3 (relay station #i, i is a number that identifies a relay station). Each of relay stations 3-1 and 3-2 has the configuration shown in Figure 3, but is simplified in Figure 6.

In relay station 3-1, control circuit 32 calculates delay time Δ_(0) to be applied to antenna #0 of relay station 3-1. FIR filter 315 in relay station 3-1 performs processes to remove self-interference (SI) and apply delay time Δ_(0) to the baseband signal obtained by converting the wireless signal (first wireless signal) received by antenna #0 of relay station 3-1, and outputs the processed signal. The output signal of FIR filter 315 is converted to a wireless signal (second wireless signal) and radiated from antenna #0 of relay station 3-1.

In relay station 3-2, control circuit 32 calculates delay time Δ_(1) to be applied to antenna #0 of relay station 3-2. Delay time Δ_(1) has a different value from delay time Δ_(0). FIR filter 315 of relay station 3-2 performs processes of removing self-interference (SI) and applying delay time Δ_(1) to the baseband signal obtained by converting the wireless signal (first wireless signal) received by antenna #0 of relay station 3-2, and outputs the processed signal. The output signal of FIR filter 315 is converted to a wireless signal (second wireless signal) and radiated from antenna #0 of relay station 3-2.

Figure 7 illustrates an example in which there are two relay stations 3 (relay station 3-1 and relay station 3-2) and each of relay stations 3-1 and 3-2 has one antenna. Each of relay stations 3-1 and 3-2 communicates with base station 2 and terminal station 4 using CP-OFDM. The calculation of delay times Δ_(0) and Δ_(1) performed by each of relay stations 3-1 and 3-2 is performed for each radio frame or for each slot constituting a radio frame.

In CP-OFDM, radio signals arriving at the receiving station from the beginning of the slot until the cyclic prefix (CP) time, i.e., the CP time length (CP length = 5 μsec) has elapsed, are properly combined, which contributes to improving diversity gain. For this reason, in Figure 7, the CP length (CP time) is shown as the allowable delay T_(CP).

In FIG. 7, "τ_(BS→R,0)" indicates the propagation delay in the propagation path of the wireless signal from the base station 2 (BS) to the relay station 3-1 (relay station #0). "τ_(BS→R,1)" indicates the propagation delay in the propagation path of the wireless signal from the base station 2 (BS) to the relay station 3-2 (relay station #1). The propagation delay τ_(BS→R,i) can be measured (calculated) from a reference signal such as a control channel transmitted from the base station 2 (BS) to the terminal station 4 (UE) and received at the relay station #i (relay stations 3-1 and 3-2, respectively).

In addition, "τ_(R,0)" shown in FIG. 7 is the processing delay at relay station 3-1 (relay station #0), and "τ_(R,1)" is the processing delay at relay station 3-2 (relay station #1). The value of τ_(R,i) can be calculated, for example, by the formula "number of delay elements in FIR filter 315 (N_(D,i)-1) × delay time per delay element τ_(D)".

7 indicates a propagation delay in the propagation path of the wireless signal from the terminal station 4 (UE) to the relay station 3-1 (relay station #0). "τ_(UE→R,1)" indicates a propagation delay in the propagation path of the wireless signal from the terminal station 4 (UE) to the relay station 3-2 (relay station #1). The propagation delay τ_(UE→R,i) is, for example, a propagation delay in the propagation path of the wireless signal from the terminal station 4 (UE) to the relay station #i (relay station 3-
The signal strength can be measured (calculated) from a reference signal of a control channel or the like transmitted from the terminal station 4 (UE) to the base station 2 (BS) and received by the terminal station 4 (UE) or the base station 2 (BS).

In addition, "δ_(0)" shown in FIG. 7 is a value indicating the measurement deviation and delay spread at relay station 3-1 (relay station #0). "δ_(1)" is a value indicating the measurement deviation and delay spread at relay station 3-2 (relay station #1). When calculating the value of δ_(i) for the downlink, it can be calculated through reception of a reference signal between relay station #i and terminal station 4 (UE), and reception of a reference signal from terminal station 4 (UE) to base station 2 (BS).

In addition, "Δ_(max,0)" shown in FIG. 7 indicates the maximum delay time (maximum delay) that can be imparted to the baseband signal input to the FIR filter 315 during the allowable delay T_(CP) at the relay station 3-1 (relay station #0). "Δ_(max,1)" indicates the maximum delay time (maximum delay) that can be imparted to the baseband signal input to the FIR filter 315 during the allowable delay T_(CP) at the relay station 3-2 (relay station #1). The maximum delay Δ_(max,i) can be calculated, for example, using the formula "Δ_(max,i)=T_(CP)-(τ_(UE→R,i)+τ_(R,i)+τ_(BS→R,i)+δ_(i))".

The propagation delay τ_(BS→R,i), processing delay τ_(R,i), propagation delay τ_(UE→R,i), δ_(i), and maximum delay Δ_(max,i) can be measured and calculated by the control circuit 32 of relay station #i. However, the measurements and calculations may be performed by a device other than the control circuit 32.

The control circuit 32 calculates the different delay times Δ_(i) between the relay station 3-1 (#0) and the relay station 3-2 (#1) so that the inequality "Δ_(i)≦Δ_(max, i)" is satisfied, and sets Δ_(i) in the FIR filter 315. However, the delay time Δ_(i) is set in the FIR filter 315 in a state where it is discretized by the delay time (τ_(D)) per tap that the FIR filter 315 has.

For example, the control circuit 32 can calculate the delay time Δ_(i) based on the number of relay stations N_(R), which is the number of relay stations #i, using the formula "Δ_(i) = i · Δ_(max, i) / (N_(R) - 1)". In this case, if the number of relay stations N_(R) = 2, as shown in FIG. 7, the delay time Δ_(0) is 0 and the delay time Δ_(1) is Δ_(max, 1). That is, the transmission timing of the wireless signal (second wireless signal) from relay station 3-1 (#0) is immediately after the end of the processing delay τ_(R), and the transmission timing of the wireless signal (second wireless signal) from relay station 3-2 (#1) is the timing when the period Δ_(max, 1) ends at relay station 3-2 (#1). As a result, the second wireless signal transmitted from relay stations 3-1 and 3-2 (#0 and #1) reaches terminal station 4 before T_(CP), i.e., the CP time, expires.

FIG. 8 is a flowchart showing an example of processing by the control device 1. The processing shown in FIG. 8 is performed, for example, by the CPU 11 of the control device 1. Step S01 is performed, for example, when the base station 2 (transmitting station) starts transmitting a radio signal to the terminal station 4 (receiving station) using a downlink. In step S01, the control device 1 selects a plurality of relay stations 3 (relay station #i) that perform non-regenerative relaying for communication between the base station 2 and the terminal station 4, that is, a relay station group (number of relay stations=N_(R)). Then, the control device 1 notifies the relay station group of relay permission by a control channel (transmits a message including an instruction for relay permission). The control device 1 also notifies (transmits) identification information of the terminal station 4 (UE) that each relay station 3 included in the relay station group is to relay. The base station 2 can transmit a radio signal to which transmit diversity is applied using a plurality of antennas (for example, antennas #0 and #1) in communication with the terminal station 4. However, the base station 2 may transmit a radio signal to which transmit diversity is not applied using a single antenna.

In step S02, the control device 1 determines whether the condition for terminating relay permission is satisfied. If it is determined that the condition is satisfied, the process returns to step S01; otherwise, the process proceeds to step S03.

In step S03, the control device 1 performs an end process. For example, the control device 1 stops notifying the relay station group of relay permission. Alternatively, the control device 1 sends an instruction to end relaying to the relay station group. The control device 1 then ends the process. In this way, non-regenerative relaying by the relay station group is performed based on an instruction (relay permission) from the control device 1.

Figures 9 and 10 are flowcharts showing an example of processing of each relay station 3 (relay station #i) included in the relay station group. The processing shown in Figures 9 and 10 is executed, for example, by the control circuit 32 of each relay station 3. In addition, the processing shown in Figures 9 and 10 is started upon receiving an instruction (control signal) including relay permission from the control device 1.

In step S001, the control circuit 32 measures the propagation delay τ_(UE→R, i) of the transmission path of the wireless signal from the terminal station 4 (UE) to the relay station 3 using a reference signal such as a control channel (control CH) transmitted from the terminal station 4 (UE) to the base station 2 (BS) and received by the relay station 3. If there are multiple (two or more) target terminal stations 4, the control circuit 32 determines the maximum propagation delay as τ_(UE→R, i).

In step S002, the control circuit 32 measures the propagation delay τ_(BS→R, i) of the propagation path of the wireless signal from the base station 2 to the relay station 3 using a reference signal such as a control CH transmitted from the base station 2 to the terminal station 4 and received by the relay station 3.

In step S003, the control circuit 32 measures the coupling H_(SI,i) in the self-interference (SI) between the transmitter and receiver using a reference signal such as a control CH that is received by the relay station 3 and transmitted by the relay station 3 to the base station 2.

In step S004, the control circuit 32 determines (calculates) the weight w_(i) of the FIR filter 315 for suppressing self-interference based on the coupling H_(SI, i).

In step S005, the control circuit 32 calculates the processing delay τ_(R,i) from the number of delay elements required for the weights N_(D,i)-1 and the delay time per tap τ_(D). For example, the control circuit 32 calculates τ_(R,i) using the formula "τ_(R,i)=(N_(D,i)-1)×τ_(D)".

Note that the order of processing from step S001 to step S005 is merely an example, and the order may be changed in any way.

In step S006, the control circuit 32 calculates the maximum delay Δ_(max, i) using the allowable delay T_(CP), the propagation delay τ_(UE→R, i), the propagation delay τ_(BS→R, i), the processing delay τ_(R, i), and δ_(i).

In step S007, the control circuit 32 determines whether to execute method A or method B as the method for calculating the delay time. If it determines that method A is to be executed, the process proceeds to step S008, and if it determines that method B is to be executed, the process proceeds to step S009.

In step S008, the control circuit 32 calculates the delay time for relay station #i (its own relay station) using the formula "Δ_i=i·Δ_(max, i)/(N_(R)-1)". Then, the process proceeds to step S010.

In step S009, the control circuit 32 calculates the delay time using the formula "Δ_(i) = x_(i) · Δ_(max, i)". At this time, x_(i) is calculated by giving a random variable that follows a uniform distribution (within the range (0, 1)).

In step S010, non-regenerative relay is performed. That is, the control circuit 32 sets the weight w_(i) and the delay time Δ_(i) to each FIR filter 315. In the radio 31 of the relay station #i, the receiver 312 converts the radio signal (first radio signal) from the base station 2 (transmitter station) received by the antenna #0 into a baseband signal, and inputs the baseband signal to the FIR filter 315. The FIR filter 315 performs filtering based on the settings of the weight w_(i) and the delay time Δ_(i). The output signal of the FIR filter 315 is input to the transmitter 311. The transmitter 311 converts the input signal into a radio signal (second radio signal) for the terminal station 4. The second radio signal is radiated (transmitted) from the antenna #0. This processing is performed for each slot of the downlink of the radio frame. However, it is also possible to perform this processing for each slot of the uplink. The above-mentioned process is executed at each relay station 3 (e.g., relay stations 3-1 and 3-2) that constitute the relay station group, and second wireless signals having different delay times are transmitted from each relay station 3 to the terminal station 4.

In step S011, the control circuit 32 determines whether the notification of relay permission is continuing, i.e., whether or not to end the non-regenerative relay process. At this time, if it is determined that the non-regenerative relay process is to be ended, the process of FIG. 10 ends, and if it is determined that the non-regenerative relay process is not to be ended, the process returns to step S001. Note that the parameters used to calculate Δ_(max,i) (propagation delay τ_(UE→R,i), propagation delay τ_(BS→R,i), processing delay τ_(R,i), and δ_(i)) are updated on a slot-by-slot or radio frame-by-radio frame basis.

Second Embodiment
Next, a communication system according to a second embodiment will be described. The second embodiment has commonalities with the first embodiment, so differences will be mainly described and commonalities will be omitted. In the second embodiment, a case will be described in which each relay station (relay station #i) constituting a relay station group performs non-regenerative relay using two or more antennas #k. k indicates the number of the antenna in relay station #i.

11 is a diagram showing an example of the hardware configuration of the relay station 3 according to the second embodiment. The relay station 3 includes two antennas #0 and #1 (an example of multiple antennas), multiple radios 31 corresponding to the multiple antennas (antennas #0 and #1), and a control circuit 32 (an example of a controller) that controls each radio 31. In FIG. 11, the radio 31 includes a radio 31#0 corresponding to antenna #0 and a radio 31#1 corresponding to antenna #1. In the following description, when there is no need to distinguish between the radio 31#0 and the radio 31#1, they are referred to as radio 31. The radio 31#0 and the radio 31#1 have the same configuration as the radio 31 (FIG. 3) described in the first embodiment (each has an FIR filter 315). For this reason, detailed description of the radio 31#0 and the radio 31#1 is omitted. In this way, the relay station 3 according to the second embodiment has multiple FIR filters corresponding to the multiple antennas.

The control circuit 32 performs the same process as in the first embodiment. However, the control circuit 32 according to the second embodiment calculates the delay time corresponding to each antenna (antennas #0 and #1), and connects the FIR filter 315 (corresponding to antenna #0) of the wireless device 31#0 and the FIR filter 316 (corresponding to antenna #1) of the wireless device 31#1 to the FIR filter 317 (corresponding to antenna #2) of the wireless device 31#2.
The IR filter 315 (corresponding to antenna #1) is set respectively.

FIGS. 12 and 13 are explanatory diagrams of the processing in relay station 3, which constitutes a relay station group in the second embodiment. FIG. 6 shows relay station 3-1 (relay station #0) and relay station 3-2 (relay station #1) as examples of two or more relay stations 3 (relay station #i). Each of relay stations 3-1 and 3-2 has the configuration shown in FIG. 11, but is simplified in FIG. 12.

In relay station 3-1, control circuit 32 calculates delay times Δ_(i,k) to be applied to antennas #0 and #1 of relay station 3-1, i.e., Δ_(0,0) and Δ_(0,1). In relay station 3-1, FIR filter 315 corresponding to antenna #k (0 or 1) performs processes of removing self-interference (SI) and applying delay time Δ_(0,k) to the baseband signal obtained by converting the radio signal (first radio signal) received by antenna #k, and outputs the processed signal. The output signal of FIR filter 315 is converted to a radio signal (second radio signal) and radiated from antenna #k of relay station 3-1.

In relay station 3-2, control circuit 32 calculates delay times Δ_(i,k) to be applied to antennas #0 and #1 of relay station 3-2, i.e., Δ_(1,0) and Δ_(1,1). In relay station 3-2, FIR filter 315 corresponding to antenna #k (0 or 1) performs processes of removing self-interference (SI) and applying delay time Δ_(1,k) to the baseband signal obtained by converting the radio signal (first radio signal) received by antenna #k, and outputs the processed signal. The output signal of FIR filter 315 is converted to a radio signal (second radio signal) and radiated from antenna #k of relay station 3-2.

Figure 13 illustrates an example where the number of relay stations 3 constituting the relay station group is two (relay station 3-1 (#0) and relay station 3-2 (#1)), and each of relay stations 3-1 and 3-2 has two antennas (#k = 0 or 1) (two antennas are used for non-regenerative relay). Each of relay stations 3-1 and 3-2 communicates with base station 2 and terminal station 4 using CP-OFDM. The calculation of delay times Δ_(0,0) and Δ_(0,1) performed by relay station 3-1, and the calculation of delay times Δ_(1,0) and Δ_(1,1) performed by relay station 3-1 are performed for each radio frame or for each slot constituting a radio frame.

Relay stations 3-1 and 3-2, i.e., relay station #i, measure or calculate the propagation delay τ_(UE→R,i,k), propagation delay τ(BS→R,i,k), processing delay τ_(R,i,k), and δ_(i) for its own antenna #k. The measurement and calculation methods can be the same as those in the first embodiment. Each relay station uses the numbers i and k assigned to itself for the calculation.

Relay stations 3-1 and 3-2, i.e. relay station #i, use the acquired propagation delay τ(UE→R,i,k), propagation delay τ(BS→R,i,k), processing delay τ(R,i,k), and δ(i) to calculate the maximum delay Δ(max,i,k). That is, relay station 3-1 (#0) calculates the maximum delays Δ(max,0,0) and Δ(max,0,1), and relay station 3-2 (#1) calculates the maximum delays Δ(max,1,0) and Δ(max,1,1).

The maximum delay Δ_(max,i,k) can be calculated, for example, using the formula "Δ_(max,i,k)=T_(CP)-(τ_(UE→R,i,k)+τ_(R,i,k)+τ_(BS→R,i,k)+δ_(i))".

The delay time Δ_(i, k) for each antenna at each relay station can be obtained using, for example, the following method A and method B.
(Method A) For relay station #i (0≦i<N_(R)), a calculation formula using the number of relay stations N_(R) and the number of antennas N_(ANT) is used for antenna #k (0≦k<N_(ANT,i)): "Δ_(i,k)=(i+k)・Δ_(max,i,k)/(N_(R)-2+N_(ANT,i))"
The maximum delay Δ_(max,i,k) can be calculated by Δ_(max,i,k)′.
(Method B) Δ_(i, k) is defined as x(i, k)·Δ_(max, i, k), and x(i, k) is calculated by giving a random variable that follows a uniform distribution.

Figure 13 shows how relay station 3-1 (#0) uses method A to calculate delay times Δ_(0,0) = 0 and Δ_(0,1) = 0.5Δ_(max,0,1). It also shows how relay station 3-2 (#1) uses method A to calculate delay times Δ_(1,0) = 0.5Δ_(max,1,0) and Δ_(1,1) = Δ_(max,1,1).

The propagation delay τ_(BS→R,i,k), processing delay τ_(R,i,k), propagation delay τ_(UE→R,i,k), δ_(i), and maximum delay Δ_(max,i,k) can be measured and calculated by the control circuit 32 of relay station #i. However, the measurements and calculations may be performed by a device other than the control circuit 32.

The control circuit 32 calculates delay times Δ_(i, k) that differ between the relay station 3-1 (#0) and the relay station 3-2 (#1) and between the antennas of each relay station so that the inequality "Δ_(i, k)≦Δ_(max, i, k)" is satisfied, and sets Δ_(i, k) in the FIR filter 315 corresponding to the antenna #k. Note that the delay time Δ_(i, k) is discretized by the delay time (τ_(D)) per tap of the FIR filter 315, and is set to F
This is set in the IR filter 315 .

The FIR filter 315 applies a delay to the input baseband signal. However, as shown in FIG. 13, the second radio signals transmitted from the antennas #0 and #1 of the relay stations 3-1 and 3-2, respectively, are transmitted at a timing that allows them to reach the terminal station 4 within the CP time (T_(CP)).

The processing in the control device 1 in the second embodiment is similar to the processing in S01 to S03 shown in FIG. 8, and therefore the description will be omitted. Information indicating the number of antennas N_(ANT) to be used for non-regenerative relay may be transmitted to each relay station constituting the relay station group. However, the control circuit 32 of each relay station may receive relay permission from the control device 1 and determine the number of antennas N_(ANT) and antenna number #i to be used for non-regenerative relay.

Figures 14 and 15 are flowcharts showing an example of processing of each relay station 3 included in the relay station group according to the second embodiment. The processing shown in Figures 14 and 15 is executed, for example, by the control circuit 32 of each relay station 3. In addition, the processing shown in Figures 14 and 15 is started upon receiving an instruction (control signal) including relay permission from the control device 1.

In step S101, the control circuit 32 measures the propagation delay τ_(UE→R, i, k) of the transmission path of the wireless signal from the terminal station 4 to the relay station 3. If there are multiple target terminal stations 4, the control circuit 32 determines the maximum propagation delay as τ_(UE→R, i, k).

In step S102, the control circuit 32 measures the propagation delay τ_(BS→R, i, k) of the propagation path of the wireless signal from the base station 2 to the relay station 3.

In step S103, the coupling H_(SI,i,k) in the self-interference (SI) is measured.

In step S104, the control circuit 32 determines the weights w_(i, k) of the FIR filter 315 for suppressing self-interference based on the coupling H_(SI, i, k).

In step S105, the control circuit 32 calculates the processing delay τ_(R,i,k) from the number of delay elements N_(D,i,k)-1 required for the weights and the delay time τ_(D) per tap. Note that the order of the processes from step S101 to step S105 is an example, and the order may be changed in any way.

In step S106, the control circuit 32 calculates the maximum delay Δ_(max, i, k) for each relay station and antenna using the allowable delay T_(CP), the propagation delay τ_(UE → R, i, k), the propagation delay τ_(BS → R, i, k), the processing delay τ_(R, i, k), and δ_(i).

In step S107, the control circuit 32 determines whether to execute method A or method B as the method for calculating the delay time. If it determines that method A is to be executed, the process proceeds to step S008, and if it determines that method B is to be executed, the process proceeds to step S009.

In step S108, the control circuit 32 calculates the delay time for relay station #i (its own relay station) using the formula "Δ_i,k=(i+k)·Δ_(max,i,k)/(N_(R)-2+N_(ANT,i))". Then, the process proceeds to step S010.

In step S109, the control circuit 32 calculates the delay time using the formula "Δ_(i,k) = x_(i,k) · Δ_(max,i,k)". At this time, x_(i,k) is calculated by giving a random variable that follows a uniform distribution (within the range (0,1)).

In step S110, non-regenerative relay is performed. That is, the control circuit 32 sets the weights w_(i, k) and delay times Δ_(i, k) to the FIR filters 315 corresponding to the antennas #0 and #1 of the local station. In each radio 31 of each relay station, the first radio signal received by the antennas #0 and #1 is converted to a baseband signal, a delay is imparted by the corresponding FIR filter 315, the signal is converted to a second radio signal, and the signal is transmitted from the antennas #0 and #1 to the terminal station 4.

In step S111, the control circuit 32 determines whether the notification of relay permission is continuing, i.e., whether or not to end the non-regenerative relay process. At this time, if it is determined that the non-regenerative relay process is to be ended, the process of FIG. 15 ends, and if it is determined that the non-regenerative relay process is not to be ended, the process returns to step S101. Note that the parameters used to calculate Δ_(max, i, k) (propagation delay τ_(UE→R, i, k), propagation delay τ_(BS→R, i, k), processing delay τ_(R, i, k), and δ_(i)) are updated on a radio frame basis.

Third Embodiment
Next, a communication system according to the third embodiment will be described. The third embodiment has commonalities with the first and second embodiments, so differences will be mainly described and commonalities will not be described. In the third embodiment, a case will be described in which each relay station (relay station #i) constituting a relay station group acquires (receives) a delay time Δ_(i) or Δ_(i, k) from the control device 1 and sets it in the FIR filter 315.

FIG. 16 is a flowchart showing an example of processing by the control device 1 according to the third embodiment. In step S01A, the control device 1 transmits information to each relay station in the first or second embodiment, and the delay amount information includes information on the delay time Δ_(i) or Δ_(i, k) that each relay station sets to each FIR filter 315 of the relay station. The information on the delay time Δ_(i) or Δ_(i, k) can be a value determined based on an experiment, operational results, or the like. The delay amount information may further include the number of antennas N_(ANT). Steps S02 and S03 are the same as those in the first embodiment, and therefore will not be described.

Figure 17 is a flowchart showing an example of processing by each relay station according to the third embodiment. The processing shown in Figure 17 is started when each relay station receives (acquires) the information transmitted by the control device 1 in step S01A. Step S201 corresponds to steps S003 and S004 in the first embodiment and steps S103 and S104 in the second embodiment, and determines a weight for suppressing self-interference.

In step S202, the control circuit 32 sets the weight determined in step S201 and the delay time acquired from the control device 1 in the FIR filter 315. After that, the relay station performs the non-regenerative relay process described in the first and second embodiments.

The processing of step S03 is the same as step S011 in the first embodiment and step S111 in the second embodiment, so a description thereof will be omitted. Each relay station may measure or calculate the propagation delay between the terminal station and relay station, the propagation delay between the base station and relay station, the processing delay, and the value of δ, as described in the first or second embodiment, and transmit these to the control device 1. In this case, the control device 1 may obtain an estimate of the delay time based on these parameters, and include this in the delay amount information transmitted to each relay station.

The communication system 100A or 100B in the first to third embodiments includes a relay station (e.g., relay station 3-1) that operates as a first relay station and can perform non-regenerative relay of a first radio signal transmitted from a transmitting station (e.g., base station 2 or distributed base station) to a receiving station (e.g., terminal station 4) having one antenna, together with one or more second relay stations (e.g., relay station 3-2). The relay station 3-1 includes at least one antenna (antenna #0), a radio device 31 corresponding to antenna #0, and a controller (control circuit 32) that controls the operation of the radio device 31. The radio device 31 includes a receiver 312 that converts a first radio signal received by antenna #0 into a baseband signal, an FIR filter 315 that adds a delay to the baseband signal, and a transmitter 311 that converts a signal output from the FIR filter 315 into a second radio signal to be transmitted from antenna #0 to the receiving station (terminal station 4). Then, the control circuit 32 sets a delay time in the FIR filter 315 of the radio 31 so that the second radio signal transmitted from each antenna #0 of the relay stations 3-1 and 3-2 has a different delay between the relay stations 3-1 and 3-2.

In the communication system 100A or 100B, the second radio signal transmitted from each of the relay stations 3-1 and 3-2 can be provided with delay diversity, and a suitable diversity effect can be obtained at the terminal station 4. When transmit diversity is applied to the first radio signal from the base station 2 or the distributed base station 2B, the delay of the second radio signal reduces the correlation with the first radio signal, and therefore a suitable diversity gain can be obtained at the terminal station 4. By obtaining a suitable diversity effect or diversity gain, the SIR and SINR of the received signal at the receiving station can be improved.

In the communication system 100A or 100B, each of the relay stations 3-1 and 3-2 may have two or more antennas (antennas #0 and #1) and two or more wireless devices (31#0 and 31#2) corresponding to the two or more antennas (second embodiment). In this case, the controller (control circuit 32) of each of the relay stations 3-1 and 3-2
A delay time is set in the FIR filter 315 of each of the radio devices 31#0 and 31#2 of each relay station so that the second radio signal transmitted from each of the antennas #0 and #1 of each relay station has different delays between the relay stations and between the antennas of the relay stations. Even in such a case, the receiving station can obtain a preferable diversity effect, as in the first embodiment. In the second embodiment, the number of antennas in each of the relay stations 3-1 and 3-2 is two, which is the same number, but the number of antennas may be different between the relay stations.

In the first and second embodiments, the control circuit 32 (controller) can obtain the maximum delay (Δ_(max,i) or Δ_(max,i,k)) using the first propagation delay (τ_(UE→R,i) or τ_(UE→R,i,k)) which is the propagation delay in the propagation path of the wireless signal from the receiving station to the relay station 3, the second propagation delay (τ_(BS→R,i) or τ_(BS→R,i,k)) which is the propagation delay in the propagation path of the wireless signal from the transmitting station to the relay station 3, and the signal processing delay (τ_(R,i) or τ_(R,i,k)) at the relay station 3. Then, the delay time provided by each FIR filter 315 for each of the multiple antennas can be calculated within a range not exceeding the maximum delay.

At this time, the control circuit 32 (controller) can calculate the maximum delay by subtracting at least the first propagation delay, the second propagation delay, and the processing delay from the cyclic prefix time (CP time, i.e., T_(CP)) used by the relay station 3 for communication with the transmitting station and the receiving station. In addition, the value of δ may be further subtracted as shown in the formula for calculating the maximum delay.

The control circuit 32 (controller) may calculate a delay time to be set in the FIR filter 315 provided in each of the two or more radios 31 so that the transmission timing of the second radio signal arrives at equal intervals for each of the two or more antennas (antennas #0 and #1).

The control circuit 32 (controller) may also randomly calculate the delay time to be set in each FIR filter 315 provided in the multiple radios 31.

In addition, the control circuit 32 (controller) in the embodiment weights the FIR filter 315 (sets weights w_(i) or w_(i, k)) so that self-interference related to the reception of the first wireless signal and the transmission of the second wireless signal is suppressed. This allows for delay and suppression of self-interference.

Also, as shown in the third embodiment, each relay station 3 may obtain the delay time to be set in each FIR filter 315 from the control device 1.

Fourth Embodiment
The fourth embodiment will be described below. The fourth embodiment has a common configuration with the first embodiment, so differences will be mainly described. The system configuration of the fourth embodiment can provide a configuration similar to that of the first embodiment (see FIG. 1 and FIG. 2). However, in the first embodiment, the control circuit 32 of the relay station 3 measures the propagation delay and processing delay, and calculates the delay time Δ_(k). In the fourth embodiment, the relay start time T_(i) of each relay station 3 is calculated by the control circuit 22 of the base station 2 (FIG. 1) or the control device 1 (FIG. 1). The control circuit 22 of the base station 2 may be the control circuit 22A (FIG. 2) of the distributed base stations 2B-1 to 2B-k.

The fourth embodiment will be described below with respect to the differences from the first embodiment. FIGS. 18 and 19 are explanatory diagrams of the process of the relay station in the fourth embodiment. FIG. 18 shows the operation of the relay stations 3-1 and 3-2. The fourth embodiment differs from the first embodiment (FIG. 6) as follows. In FIG. 18, the relay station 3-1 (#0) receives (acquires) the delay time T_(0) as the delay time T_(i) calculated by the control circuit 22 of the base station 2 or the control device 1. The relay station 3-2 (#1) receives (acquires) the delay time T_(1) as the delay time T_(i) calculated by the control circuit 22 of the base station 2 or the control device 1.

The control circuit 32 of the relay station 3-1 judges whether or not to relay the signal to be relayed based on the delay time T_(0), the processing delay τ_(R,0) in the relay station 3-1, and the measurement result of the propagation delay τ_(UE→R,0). At this time, if the timing of the signal transmission from the relay station 3 is such that the terminal station 4 cannot properly demodulate and decode the signal received from the relay station 3, the control circuit 32 does not transmit the signal. In contrast, if the timing of the signal transmission is such that the terminal station 4 can properly demodulate and decode the received signal, the control circuit 32 sets the FIR filter 315 to a delay time Δ_(i) corresponding to the relay start time T_(i). That is, as shown in FIG. 18, the control circuit 32 of the relay station 3-1 sets the FIR filter 315 to a delay time Δ_(0) corresponding to T_(0), and the control circuit 32 of the relay station 3-2 sets the FIR filter 315 to a delay time Δ_(1) corresponding to T_(1).

In FIG. 19, the relay start times T_(0) and T_(1) for relay stations 3-1 (#0) and 3-2 (#1) are calculated so that the propagation delay τ_(UE→R,i) between terminal station 4 and relay station 3#i falls within the allowable delay T_(CP). This allows terminal station 4 to receive signals transmitted from relay stations 3-1 and 3-2 before the end of the allowable delay T_(CP). This allows each received signal to be properly demodulated and decoded, resulting in an optimal diversity effect. Details of relay start time T_(i) will be described later.

Figures 20 and 21 are flowcharts showing the processing (operation) of relay station 3#i in the fourth embodiment, and Figure 22 is a flowchart showing the processing (operation) of base station 2 in the fourth embodiment.

In FIG. 20, the processes of steps S001, S003, and S005 are the same as those in the first embodiment (FIG. 9). In contrast, in the fourth embodiment, step S002 is omitted, step S004A is provided instead of step S004, and step S005A is provided after step S005.

In step S004A, the control circuit 32 of relay station #i determines the weight w_(i) for self-interference suppression, similar to step S004 (FIG. 9). Furthermore, the control circuit sets the weight w_(i) in the FIR filter 315. However, the timing of the setting can be changed as appropriate, and for example, it may be performed before or after step S007A (FIG. 21) together with the setting of the delay time Δ_(i).

In step S005A, the control circuit 32 of relay station #i transmits to base station 2 the propagation delay τ(UE→R,i) measured in step S001 and the processing delay τ_(R,i) calculated in step S005.

In step S101 of FIG. 22, the base station 2 receives the propagation delay τ_(UE→R) and the processing delay τ_(R, i) transmitted from the relay station 3.

In step S102, the control circuit 22 of the base station 2 measures the propagation delay τ_(UE→BS) from the reference signal transmitted from the terminal station 4.

In step S103, the control circuit 22 of the base station 2 measures the propagation delay τ_(R→BS, i) between the relay station #i and the base station 2 from the reference signal used for reporting the measurement value from the relay station #i. Note that the order of steps S101 to S103 can be changed as appropriate.

In step S104, the control circuit 22 calculates the relay start time T_(i) in the relay station #i. The relay start time T_(i) is calculated from the maximum propagation delay in the relay station #i, that is, the maximum value T_(R,max)=max(τ_(BS→UE,τ_(R→BS,i)) of the propagation delay τ_(R→BS) and the propagation delay τ_(UE→BS), and the maximum processing delay τ_(R) in the relay station #i. For example, the following formula is used to calculate the relay start time T_(i).
Calculation formula: Relay start time T_(i)=T_(R, max)+τ_(R)+(i-1)・(T_(CP)-T_(R,max)-τ_(R)-δ)/N_(R)
Here, “δ” is the measurement deviation margin, and “N_(R)” is the number of antennas.

In step S105, the control circuit 22 calculates the minimum relay start time T_(R_(min),i)=τ_(R→BS,i)+τ_(R,i) for relay station #i and the arrival time T_(UE,i)=T_(i)+τ_(UE→R,i) for the signal relayed by relay station #i at the relay destination. Then, if T_(R_(min),i)≦T_(i) and τ_(UE→R,i)≦T_(CP), the control circuit 22 notifies (sends) relay station #i of T_(i). If the above conditions are not met in step S105, notification of T_(i) is not performed.

21, in step S006A, the relay station 3#i receives the relay start time T_(i) transmitted from the base station 2 (YES in S006A). Then, in step S006B, the control circuit 32 of the relay station 3#i determines whether or not the terminal station 4 can receive a signal (OK or NG) before the end of T_(CP) at the terminal station 4, based on the observed results of the processing delay τ_(R,i) and the propagation delay τ_(UE→R,i).

If it is determined in step S006B that reception is OK, the process proceeds to step S007A, and if not (if reception is not OK), the process proceeds to step S011. In this case, the signal is not relayed.

In step S007A, the control circuit 32 sets a delay time Δ_(i) corresponding to T_(i) in the FIR filter 315 and performs non-regenerative relay (step S008A). The processing of steps S007A and S008A is similar to the processing of step S010 in the embodiment (FIG. 10) except for the setting of the weight w_(i), so a description thereof will be omitted.

In this way, in the fourth embodiment, the control circuit 22 of the base station 2 calculates the relay start time T_(i) for each relay station #i and notifies (transmits) it to the relay station 3. The control circuit 32 of the relay station 3 sets the delay time Δ_(i) using the T_(i) calculated by the base station 2 and performs non-regenerative relay. This allows the terminal station 4 to properly receive the signal relayed from the relay station #i (3-1 and 3-2), improving the diversity effect at the terminal station 4.

Note that a configuration may be adopted in which the process of step S105 or the process of step S006B is selectively executed. The configuration of the fourth embodiment may also be applied to the configuration in which the relay station 3 has multiple antennas (second embodiment).

The configuration of the fourth embodiment can be modified to one in which the base station 2 transmits parameters for calculating the relay start time T_(i) to the control device 1 on the network, and the control device 1 calculates the relay start time T_(i).

Figure 23 is a flowchart showing an example of processing by the control device 1 in a modified example of the fourth embodiment, and Figure 24 is a flowchart showing an example of processing by the base station 2 in modified example 2. In the modified example, the calculation of T_(i) is performed by the control device 1.

In the processing of the control device 1 in FIG. 23, steps S01A, S01B, and S01C are provided between steps S01 and S02 in the processing of the control device 1 in the first embodiment (FIG. 8).

In step S01A, the control device 1 receives parameters for calculating T_(i) from the base station 2. In step S01B, the control device 1 calculates T_(i) using the parameters. In step S01C, the control device 1 notifies the relay station 3#i of T_(i) if the conditions described in relation to step S105 are satisfied. Step S01B is the same process as step S104 in the fourth embodiment, and step S01C is the same process as step S105 in the fourth embodiment.

The processing of steps S01, S02, and S03 in FIG. 23 is the same as in the first embodiment, and therefore will not be described. As in the modified example, the calculation of T_(i) can be performed by the control device 1 on the network instead of the control circuit 22.

In FIG. 24, steps S104A and S105A are provided instead of steps S104 and S105 shown in FIG. 22. In step S104A, the base station 2 transmits parameters for calculating T_(i) to the control device 1. In step S105, the base station 2 receives T_(i) from the control device 1 and transmits it to relay station #i.

As shown in the fourth embodiment, relay station #i may acquire information indicating the relay start time T_(i) calculated by the base station 2 communicating with relay station #i or the control device 1 of relay station #i. Then, relay station #i can set a delay amount (delay time) according to T_(i) in the FIR filter 315. In other words, relay station #i can set a delay amount (Δ_(i)) based on the information (T_(i)) indicating the relay start time calculated by the base station 2 communicating with relay station #i or the control device 1 of relay station 3#i in the FIR filter 315.

The above-described embodiment and modified examples are merely examples, and the present disclosure may be modified as appropriate without departing from the spirit and scope of the present disclosure. Furthermore, the processes and means described in the present disclosure may be freely combined and implemented as long as no technical contradictions arise.

In addition, a process described as being performed by one device may be shared and executed by multiple devices. Or, a process described as being performed by different devices may be executed by one device. In a computer system, the hardware configuration (server configuration) by which each function is realized can be flexibly changed.

The present disclosure can also be realized by supplying a computer program implementing the functions described in the above embodiments to a computer, and having one or more processors of the computer read and execute the program. Such a computer program may be provided to the computer by a non-transitory computer-readable storage medium connectable to the system bus of the computer, or may be provided to the computer via a network. The non-transitory computer-readable storage medium includes any type of medium suitable for storing electronic instructions, such as, for example, a magnetic disk (e.g., a floppy disk, a hard disk drive (HDD), etc.), an optical disk (e.g., a CD-ROM, a DVD disk, a Blu-ray disk, etc.), a read-only memory (ROM), a random access memory (RAM), an EPROM, an EEPROM, a magnetic card, a flash memory, or an optical card.

1..Control device 2..Base station 3..Relay station 4..Terminal station 11..CPU
12. Main memory device 13. External memory device 16. Communication device 21, 31, 41. Radio device 22, 32, 42. Control circuit 100A, 100B. Communication system 311. Transmitter 312. Receiver 313. Baseband circuit 314. Circulator 315. FIR filter

Claims (23)

A relay station that operates as a first relay station and can perform non-regenerative relaying of a first wireless signal transmitted from a transmitting station to a receiving station having one antenna together with one or more second relay stations,
At least one antenna;
A radio corresponding to the antenna;
a controller for controlling an operation of the radio;
The radio device includes:
a receiver that converts the first radio signal received by the antenna into a baseband signal;
an FIR filter that adds a delay to the baseband signal;
a transmitter that converts the signal output from the FIR filter into a second radio signal that is transmitted from the antenna to the receiving station;
The controller is a relay station that sets a delay amount in the FIR filter of the radio so that the second radio signal transmitted from each antenna of the first and second relay stations has a different delay between the first and second relay stations. 2. The relay station according to claim 1, wherein, when the relay station has two or more antennas and two or more of the radio devices corresponding to the two or more antennas, the controller sets delay amounts in the FIR filters of each of the two or more radio devices so that a second radio signal transmitted from each antenna of the first and second relay stations has different delays between the first and second relay stations and between the antennas of the first and second relay stations. The relay station according to claim 1 or 2, wherein the controller calculates a maximum delay using a first propagation delay which is a propagation delay in a propagation path of a radio signal from the receiving station to the relay station, a second propagation delay which is a propagation delay in a propagation path of a radio signal from the transmitting station to the relay station, and a signal processing delay at the relay station, and calculates an amount of delay to be set in the FIR filter for each antenna of the relay station within a range not exceeding the maximum delay. 4. The relay station according to claim 3, wherein the controller calculates the maximum delay by subtracting at least the first propagation delay, the second propagation delay, and the processing delay from a cyclic prefix time used by the relay station in communication with the transmitting station and the receiving station. 4. The relay station according to claim 3, wherein the controller calculates a delay amount to be set in an FIR filter provided in each of the two or more radio devices so that the transmission timing of the second radio signal arrives at equal intervals for each of the two or more antennas. 4. The relay station according to claim 3, wherein the controller randomly calculates the amount of delay to be set in each of the FIR filters provided in each of the two or more wireless devices. The relay station according to claim 1 or 2, wherein the controller acquires information indicating a delay amount corresponding to each antenna received from a control device of the relay station, and sets the information in the FIR filter. The relay station according to claim 1 or 2, wherein the controller performs weighting on the FIR filter so as to suppress self-interference related to reception of the first radio signal and transmission of the second radio signal. The relay station according to claim 1 or 2, wherein the at least one antenna receives the first radio signal to which transmission diversity using at least one antenna has been applied by the transmitting station. The relay station acquires information indicating a relay start time calculated by a base station communicating with the relay station or a control device of the relay station, and sets a delay amount according to the relay start time in the FIR filter.
The relay station according to claim 1 . A method for transmitting a first wireless signal from a first relay station, the first relay station being capable of performing non-regenerative relaying of a first wireless signal transmitted from a transmitting station to a receiving station having one antenna together with one or more second relay stations, the method comprising the steps of:
The relay station,
converting the first radio signal received by at least one antenna of the relay station into a baseband signal;
applying a delay to the baseband signal using an FIR filter;
converting the signal output from the FIR filter into a second radio signal to be transmitted from the antenna to the receiving station;
A relay station transmission method for setting a delay amount in the FIR filter so that the second radio signal transmitted from each antenna of the first and second relay stations has a different delay between the first and second relay stations. The relay station has two or more antennas and two or more F
and a FIR filter, wherein the relay station sets a delay amount for each of the two or more FIR filters such that the second radio signal transmitted from each antenna of the first and second relay stations has a different delay between the first and second relay stations and between the antennas of the first and second relay stations. 13. The method for transmitting a relay station according to claim 11 or 12, wherein the relay station calculates a maximum delay using a first propagation delay which is a propagation delay in a propagation path of a radio signal from the receiving station to the relay station, a second propagation delay which is a propagation delay in a propagation path of a radio signal from the transmitting station to the relay station , and a signal processing delay at the relay station, and calculates an amount of delay to be set in the FIR filter for each antenna of the relay station within a range not exceeding the maximum delay. 14. The method of claim 13, wherein the relay station calculates the maximum delay by subtracting at least the first propagation delay, the second propagation delay, and the processing delay from a cyclic prefix time used by the relay station in communication with the transmitting station and the receiving station . The relay station transmission method according to claim 13, wherein the relay station calculates a delay amount to be set in an FIR filter provided in each of a plurality of radio devices corresponding to each of the two or more antennas so that the transmission timing of the second radio signal arrives at equal intervals for each of the two or more antennas . The transmission method for a relay station according to claim 13 , wherein the relay station randomly calculates the amount of delay to be set in each of the two or more FIR filters. The method for transmitting signals from a relay station according to claim 11 or 12 , wherein the relay station acquires information indicating an amount of delay corresponding to each antenna received from a control device of the relay station, and sets the information in the FIR filter. The method for transmitting a relay station according to claim 11 or 12 , wherein the relay station performs weighting on the FIR filter so as to suppress self-interference related to reception of the first radio signal and transmission of the second radio signal. The transmission method for a relay station according to claim 11 or 12 , wherein the at least one antenna receives the first radio signal to which transmission diversity using the at least one antenna has been applied by the transmitting station. The relay station sets, in the FIR filter, a delay amount based on information indicating a relay start time calculated in a base station communicating with the relay station or in a control device of the relay station.
The relay station transmission method according to claim 11. a receiving station having one antenna;
a transmitting station that transmits a first radio signal to the receiving station;
a plurality of relay stations capable of relaying the first radio signal to the receiving station by non-regenerative relay;
Each of the plurality of relay stations comprises:
At least one antenna;
A radio corresponding to the antenna;
a controller for controlling an operation of the radio;
The radio device includes:
a receiver that converts the first radio signal received by the antenna into a baseband signal;
an FIR filter that adds a delay to the baseband signal;
a transmitter that converts the signal output from the FIR filter into a second radio signal that is transmitted from the antenna to the receiving station;
The controller sets a delay amount in the FIR filter of the radio so that the second radio signal transmitted from each antenna of the multiple relay stations has a different delay between the multiple relay stations. 22. The communication system according to claim 21, wherein when each of the plurality of relay stations has two or more antennas and two or more of the radio devices corresponding to each of the two or more antennas, the controller sets delay amounts in the FIR filters of each of the two or more radio devices so that the second radio signals transmitted from each antenna of the plurality of relay stations have different delays between the plurality of relay stations and between the antennas of the plurality of relay stations. The communication system according to claim 21 , wherein the relay station sets, in the FIR filter, a delay amount based on information indicating a relay start time calculated in a base station communicating with the relay station or in a control device of the relay station.

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