Wireless communication system, wireless communication method, and base station device

Abstract

In this wireless communication system, a base station device comprises: a resource allocation unit which determines a path and a multiplexing scheme that minimize power consumption within a range that satisfies required throughput between the base station device and one or more terminal devices; a signal processing unit which divides data to be transmitted to the one or more terminal devices on the basis of the determined path and generates a plurality of transmission signals including information relating to the multiplexing scheme; a spatial multiplexing unit which forms a beam toward each of one or more relay stations of a plurality of relay stations located on the determined path; and a transmission processing unit which uses a low frequency band to transmit the plurality of transmission signals to each of the one or more relay stations by each formed beam. Each of the plurality of relay stations comprises: a multiplexing unit which applies at least one of spatial multiplexing and frequency multiplexing to a plurality of transmission signals obtained by dividing, on the basis of the information relating the multiplexing scheme included in the received transmission signals of the plurality of transmission signals; and a transmission unit which uses a high frequency band to transmit the plurality of transmission signals that have been multiplexed to the one or more terminal devices.　

Description

[Technical Field]

[0001] The present invention relates to a wireless communication system, a wireless communication method, and a base station device. [Background technology]

[0002] In recent years, the use of millimeter waves has been widely studied to increase the speed and capacity of wireless communications. However, millimeter waves have a high degree of directivity and are subject to significant attenuation due to moisture in the atmosphere, making them more susceptible to obstructions than lower frequency bands such as Sub-6 (less than 6 GHz). This makes them more susceptible to signal interruptions between base station equipment and terminal devices. To mitigate this problem, relay transmission using a relay station, which is installed between the base station equipment and terminal devices, has been proposed (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] S. Biswas, et. al., “On the performance of relay aided millimeter wave networks”, IEEE journal of selected topics in signal processing, vol.10, no.3, Apr. 2016. Summary of the Invention [Problem to be solved by the invention]

[0004] Installing a large number of relay stations to expand coverage leads to an increase in the power consumption of wireless systems. On the other hand, using battery-powered, energy-saving, and compact repeaters or terminal devices themselves as repeaters can reduce power consumption compared to existing relay station installations. However, due to the structure of terminal devices, they cannot be equipped with many antennas, and therefore have fewer antennas than the base station device. When transmitting large amounts of data from a base station device to a terminal device, MIMO (Multiple Input and Multiple Output), a method for increasing the number of streams using multiple antennas, is effective. However, with such energy-saving and compact terminals, the number of antennas cannot be increased. In order to increase transmission capacity, for example, it is necessary to increase the modulation level (the number of transmission bits per symbol), which increases transmission power.

[0005] In view of the above circumstances, an object of the present invention is to provide a technology that can reduce the number of modulation levels per stream to achieve a required throughput by using multiple relay stations to convert spatial streams into frequency resources and relay them using millimeter waves, thereby reducing power consumption. [Means for solving the problem]

[0006] One aspect of the present invention is a wireless communication system comprising one or more terminal devices, a base station device that performs wireless communication between the one or more terminal devices, and a plurality of relay stations that perform relaying between the one or more terminal devices and the base station device, wherein the base station device comprises: a resource allocation unit that determines a route and a multiplexing method that minimizes power consumption within a range that satisfies a required throughput between the base station device and the one or more terminal devices; a signal processing unit that divides data to be transmitted to the one or more terminal devices based on the route determined by the resource allocation unit, and generates a plurality of transmission signals that include information on the multiplexing method; and a signal processing unit that divides data to be transmitted to the one or more terminal devices based on the route determined by the resource allocation unit, and generates a plurality of transmission signals that include information on the multiplexing method. a spatial multiplexing unit that forms beams; and a transmission processing unit that uses a low frequency band to transmit the multiple transmission signals to each of the one or more relay stations via an antenna using each beam formed by the spatial multiplexing unit, wherein the multiple relay stations each include a signal processing unit that divides the transmission signals based on information about the multiplexing method included in a received transmission signal from the base station device to generate multiple transmission signals, a multiplexing unit that multiplexes the divided transmission signals using at least one of spatial multiplexing and frequency multiplexing based on the information about the multiplexing method, and a transmission unit that transmits the multiple transmission signals multiplexed by the multiplexing unit to the one or more terminal devices using a high frequency band.

[0007] One aspect of the present invention is a wireless communication method in a wireless communication system including one or more terminal devices, a base station device that performs wireless communication between the one or more terminal devices, and a plurality of relay stations that perform relaying between the one or more terminal devices and the base station device, wherein the base station device determines a route and a multiplexing method that minimizes power consumption within a range that satisfies a required throughput between the base station device and the one or more terminal devices, divides data to be transmitted to the one or more terminal devices based on the determined route, generates a plurality of transmission signals including information on the multiplexing method, and transmits the multiplexed signals to one or more relay stations among the plurality of relay stations located on the determined route. a plurality of relay stations that receive the plurality of transmission signals from the base station device based on information on the multiplexing method included in a received transmission signal of the plurality of transmission signals transmitted from the base station device, and multiplexes the divided transmission signals using at least one of spatial multiplexing and frequency multiplexing based on the information on the multiplexing method; and transmits the multiplexed transmission signals to the one or more terminal devices using a high frequency band.

[0008] One aspect of the present invention is a base station device in a wireless communication system comprising one or more terminal devices, a base station device that performs wireless communication between the one or more terminal devices, and a plurality of relay stations that relay between the one or more terminal devices and the base station device, the base station device comprising: a resource allocation unit that determines a route and a multiplexing method that minimizes power consumption within a range that satisfies a required throughput between the base station device and the one or more terminal devices; a signal processing unit that divides data to be transmitted to the one or more terminal devices based on the route determined by the resource allocation unit, and generates a plurality of transmission signals including information about the multiplexing method; a spatial multiplexing unit that forms a beam for transmitting the plurality of transmission signals to each of one or more relay stations located on the route determined by the resource allocation unit; and a transmission processing unit that transmits the plurality of transmission signals to each of the one or more relay stations via an antenna using each beam formed by the spatial multiplexing unit using a low frequency band. [Effects of the Invention]

[0009] The present invention makes it possible to minimize power consumption to achieve a required throughput. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration example of a base station device according to an embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a relay station according to an embodiment. [Figure 4] 10A and 10B are diagrams for explaining a resource allocation process performed by a resource allocation unit of a base station device in an embodiment. [Figure 5] FIG. 10 is a diagram illustrating an example of a list showing a shielding state between a base station device and each relay station in the embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of a list showing a shielding state between a terminal device and each relay station in the embodiment. [Figure 7] FIG. 2 is a sequence diagram showing a processing flow of the wireless communication system according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (overview) First, an overview of the wireless communication system according to the present invention will be described. The wireless communication system according to the present invention comprises one or more base station devices, a plurality of relay stations, and one or more terminal devices. Let I be the number of base station devices, J be the number of relay stations, and K be the number of terminal devices. I and K are integers equal to or greater than 1, and J is an integer equal to or greater than 2. The relay station is of a similar scale to a battery-powered terminal device. If L is the number of antennas in the base station device, M is the number of antennas in the relay station, and N is the number of antennas in the terminal device, then generally L>>M≒N. Thus, the present invention assumes that the base station device has a large number of antennas, the relay station and terminal device have roughly the same number of antennas, and the relay station and terminal device have far fewer antennas than the base station device.

[0012] In the wireless communication system of the present invention, communication is performed between a base station device and a relay station using a low frequency band such as sub-6, and communication is performed between a relay station and a terminal device using a high frequency band such as millimeter waves. The number of transmitting and receiving antenna elements is greater between the base station device and the relay station, resulting in a higher degree of spatial freedom, compared to the communication between the relay station and the terminal device. Taking these points into consideration, data is transmitted between the base station device and the relay station using spatial multiplexing based on beam multiplexing, while data is transmitted between the relay station and the terminal device using frequency multiplexing in addition to spatial multiplexing based on beam multiplexing, taking advantage of the broadband provided by millimeter waves. Alternatively, data is transmitted between the relay station and the terminal device using either spatial multiplexing or frequency multiplexing. In this way, the wireless communication system uses both spatial and frequency resources to improve throughput compared to spatial multiplexing alone, while minimizing power consumption for achieving the required throughput (transmission rate) between the base station device and the terminal device by setting up an appropriate transmission path. Details are described below.

[0013] (detail) Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 100 according to an embodiment. The wireless communication system 100 includes a base station device 10, one or more terminal devices 20, and a plurality of relay stations 30. Fig. 1 shows a configuration in which the wireless communication system 100 includes four relay stations 30-1 to 30-4, but there is no particular limit to the number of relay stations 30 as long as there is more than one. The numbers of base station devices 10 and terminal devices 20 are also not particularly limited.

[0014] The base station device 10 is a base station in a RAN (Radio Access Network). The base station device 10 communicates with the terminal device 20 via a relay station 30. To transmit transmission data addressed to the terminal device 20, the base station device 10 determines a route that minimizes power consumption within a range that satisfies the required throughput between the base station device 10 and the terminal device 20. For example, the base station device 10 determines through which of one or more relay stations 30 the transmission data will be transmitted to the terminal device 20, as a route that minimizes power consumption within a range that satisfies the required throughput between the base station device 10 and the terminal device 20. Furthermore, the base station device 10 determines a multiplexing method and a relay method that the relay station 30 that relays the transmission data will use when communicating with the terminal device 20.

[0015] The multiplexing method used by relay station 30 when communicating with terminal device 20 is, for example, at least one of spatial multiplexing and frequency multiplexing, i.e., spatial multiplexing alone, frequency multiplexing alone, or both spatial and frequency multiplexing. The relay method used by relay station 30 is a regenerative method or a non-regenerative method. A regenerative method is a method in which transmitted data is demodulated and decoded once and then regenerated. A non-regenerative method is a method in which frequency band conversion and amplification are only performed, and transmitted data is not demodulated or decoded.

[0016] Furthermore, the base station device 10 switches relay stations 30 that are not used to relay transmission data into a sleep state to reduce power consumption. Note that if the communication state between the base station device 10 and the sleep target relay station 30 is poor, the sleep target relay station 30 may not be able to receive the sleep control instruction.

[0017] Poor communication conditions between base station device 10 and the sleep target relay station 30 may be caused, for example, by an obstacle between base station device 10 and the sleep target relay station 30, which blocks radio waves, or by weather conditions, which attenuate an instruction transmitted from base station device 10 and prevent the sleep target relay station 30 from demodulating the instruction. Therefore, base station device 10 transmits a notification signal including information about the sleep target relay station 30 (e.g., the MAC (Media Access Control) address of the relay station 30, etc.) to all relay stations 30. Note that base station device 10 may transmit the notification signal to relay stations 30 located near the sleep target relay station 30.

[0018] The terminal device 20 performs wireless communication with the base station device 10 via the relay station 30. The terminal device 20 receives a signal transmitted from the base station device 10 via the relay station 30 and down-converts the received signal to a low frequency band such as the baseband. Thereafter, the terminal device 20 obtains the transmission data by demodulating the received signal.

[0019] The relay station 30 is arranged in the vicinity of the terminal device 20 and relays data between the base station device 10 and the terminal device 20. The relay station 30 is, for example, a battery-powered, low-power, and compact relay device, or a relay device in which the terminal device itself is equipped with a relay function. The relay station 30 relays signals transmitted from the base station device 10 to the terminal device 20 using the multiplexing method and relay method specified by the base station device 10. Furthermore, the relay station 30 performs sleep control in response to instructions from the base station device 10. For example, the relay station 30 transitions to or cancels a sleep state in response to instructions from the base station device 10.

[0020] As described above, if the communication state between any of the multiple relay stations 30 and base station device 10 is poor, the relay station 30 with the poor communication state may not be able to receive the sleep control instruction transmitted from base station device 10. Therefore, when a relay station 30 receives a notification signal, it transmits the received notification signal to other relay stations 30, thereby sharing the notification signal among the relay stations 30. Note that the relay station 30 may check the destination of the notification signal and transmit the notification signal only to the relay station 30 that is the sleep target.

[0021] 2 is a diagram showing an example of the configuration of the base station device 10 according to the embodiment. The base station device 10 includes an antenna 11, a transmitter 12, a receiver 13, and a controller 14.

[0022] In uplink transmission, antenna 11 receives radio waves transmitted from relay station 30, converts the received radio waves into electrical signals, and outputs them to receiver 13. In downlink transmission, antenna 11 converts electrical signals output from transmitter 12 into radio waves and transmits them to one or more relay stations 30. Antenna 11 is composed of a plurality of elements in a two-dimensional array configuration, for example.

[0023] The transmitter 12 is composed of a signal processor 121, a spatial multiplexer 122, and a transmission processor 123. The signal processor 121 divides data to be transmitted to the terminal device 20 based on a relay route determined by a resource allocation unit 141 in the controller 14, and generates a plurality of transmission signals. Furthermore, the signal processor 121 includes information on the multiplexing method and relay method determined by the resource allocation unit 141 in the preambles of the plurality of transmission signals.

[0024] The spatial multiplexing unit 122 performs beamforming toward one or more relay stations 30. Specifically, the spatial multiplexing unit 122 forms beams for transmitting a plurality of transmission signals toward each of the one or more relay stations 30 located on the path determined by the resource allocation unit 141. The beamformer may use fixed precoding such as a DFT (Discrete Fourier Transform) matrix, or may use precoding calculated based on the channel state, such as ZF (Zero Forcing) or MMSE (Minimum Mean Square Error).

[0025] Transmission processing unit 123 up-converts the transmission signal output from spatial multiplexing unit 122 to the RF (Radio Frequency) band and then performs power amplification. Thereafter, transmission processing unit 123 transmits, via antenna 11, a plurality of transmission signals using each beam formed by spatial multiplexing unit 122 to one or more relay stations 30 located on the path determined by resource allocation unit 141.

[0026] The receiver 13 is composed of a reception processing unit 131. The reception processing unit 131 demodulates the electrical signal output from the antenna 11. For example, by demodulating the electrical signal, the reception processing unit 131 acquires, for example, information on the transmission capabilities of the terminal device 20 and the relay station 30, information on the shielding state between the base station device 10 and the relay station 30, and information on the shielding state between the terminal device 20 and the relay station 30. The reception processing unit 131 outputs the acquired information to the control unit 14. The information on the transmission capabilities of the terminal device 20 and the relay station 30 includes, for example, information such as the number of antennas of the terminal device 20 and the relay station 30 and the bandwidth that can be processed. Note that the information on the transmission capabilities of the terminal device 20 and the relay station 30 may be collectively managed in advance by the base station device 10, or may be notified to the base station device 10 using a feedback function from the terminal device 20 and the relay station 30.

[0027] The information on the obstruction state between the base station device 10 and the relay station 30 represents information for determining whether communication is possible between the base station device 10 and the relay station 30. The information on the obstruction state between the base station device 10 and the relay station 30 is acquired based on the results of exchanging reference signals between the base station device 10 and each relay station 30 and comparing the received power estimated from the reference signal with a threshold set based on noise power or the like. For example, the reception processing unit 131 estimates the received power based on the reference signal obtained by exchanging reference signals between the base station device 10 and each relay station 30.

[0028] Reception processing unit 131 outputs information about the estimated reception power to control unit 14. Control unit 14 compares the reception power output from reception processing unit 131 with a threshold, and if the reception power is below the threshold, determines that there is an obstruction state between base station device 10 and relay station 30, which is the source of the reference signal (communication is not possible), whereas if the reception power is equal to or greater than the threshold, determines that there is no obstruction state between base station device 10 and relay station 30, which is the source of the reference signal (communication is possible). Note that there may be cases where the reference signal transmitted from base station device 10 to relay station 30 is obstructed by an obstruction or the like and is not received by relay station 30. Control unit 14 transmits a reference signal but, even if the reference signal is not received from relay station 30, determines that there is an obstruction state between base station device 10 and relay station 30, which did not receive the reference signal, (communication is not possible).

[0029] The information on the obstruction state between the terminal device 20 and the relay station 30 represents information for determining whether communication is possible between the terminal device 20 and the relay station 30. The information on the obstruction state between the terminal device 20 and the relay station 30 is acquired by exchanging reference signals between the terminal device 20 and each relay station 30 and determining whether the reference signal has arrived or based on a comparison result between the received power estimated from the reference signal and a threshold set based on noise power or the like. For example, the reception processing unit 131 acquires received power information from each relay station 30. The received power information acquired from each relay station 30 is received power estimated based on the reference signal obtained by exchanging reference signals between the terminal device 20 and each relay station 30.

[0030] The reception processing unit 131 outputs the acquired information on the reception power to the control unit 14. The control unit 14 compares the reception power output from the reception processing unit 131 with a threshold, and if the reception power is below the threshold, determines that there is an obstruction state between the terminal device 20 and the relay station 30 that is the sender of the reception power information (communication is not possible), and if the reception power is equal to or greater than the threshold, determines that there is no obstruction state between the terminal device 20 and the relay station 30 that is the sender of the reception power information (communication is possible).

[0031] The control unit 14 controls the entire base station device 10. The control unit 14 is configured using one or more processors such as a CPU (Central Processing Unit) and one or more memories. The control unit 14 realizes the functions of a resource allocation unit 141 and a sleep control unit 142 by the one or more processors executing programs.

[0032] The resource allocation unit 141 determines a route and a multiplexing method at the relay station 30 that minimizes power consumption within a range that satisfies the required throughput between the base station device 10 and the terminal device 20, based on the shielding state between the base station device 10 and each relay station 30, the shielding state between the terminal device 20 and each relay station 30, and information on the transmission capabilities of the base station device 10, the terminal device 20, and each relay station 30.

[0033] Furthermore, the resource allocation unit 141 determines the relay method of the relay station 30 to be used for relaying based on the propagation channel state and information on the transmission capabilities of the base station device 10, the terminal device 20, and each relay station 30. Specifically, the resource allocation unit 141 determines to use the non-regeneration method when the reception SINR (Signal to Interference-plus-Noise Ratio) estimated using a reference signal or the like is equal to or greater than the minimum reception SINR value that can be received error-free without error correction using the modulation method of the transmission signal, and determines to use the regeneration method when it is below the minimum reception SINR value.

[0034] The sleep control unit 142 transitions relay stations 30 that are not used for communication among the multiple relay stations 30 into a sleep state based on the route selection result by the resource allocation unit 141. The sleep control unit 142 transmits a notification signal including information about the relay stations 30 that are to be put to sleep to each relay station 30 via the antenna 11.

[0035] Fig. 3 is a diagram showing an example of the configuration of a relay station 30 in an embodiment. The relay station 30 includes a first antenna 31, a receiver 32, a transmitter 33, a second antenna 34, and a controller 35. Fig. 3 shows a configuration for transmitting data in the downlink direction from the relay station 30 to the base station device 10.

[0036] The first antenna 31 receives radio waves (for example, a transmission signal, a reference signal, or a notification signal) transmitted from the base station device 10, and down-converts the received radio waves to a frequency band such as a baseband that can be processed by the receiver 32. Thereafter, the first antenna 31 converts the down-converted radio waves into an electrical signal and outputs it to the receiver 32.

[0037] The receiving unit 32 is composed of a receiving processing unit 321. If the electrical signal output from the first antenna 31 is a transmission signal, the receiving processing unit 321 identifies the relay method by referring to the preamble of the transmission signal. If the relay method is a regenerative method, the receiving processing unit 321 performs demodulation processing, decoding processing, encoding processing, and modulation processing on the transmission signal. Thereafter, the receiving processing unit 321 outputs the transmission signal to the transmitting unit 33. If the relay method is a non-regenerative method, the receiving processing unit 321 does not process the transmission signal, and outputs the signal waveform obtained from the first antenna 31 to the transmitting unit 33 as is.

[0038] If the electrical signal output from the first antenna 31 is a reference signal, the reception processing unit 321 causes the transmission unit 33 to transmit and receive the reference signal to and from the base station device 10. If the electrical signal output from the first antenna 31 is a notification signal, the reception processing unit 321 outputs the notification signal to the control unit 35.

[0039] Furthermore, the reception processing unit 321 acquires information on the obstruction state between the terminal device 20 and the relay station 30. For example, the reception processing unit 321 estimates the reception power based on a reference signal obtained by exchanging reference signals between the terminal device 20 and the relay station 30. The reception processing unit 321 causes the base station device 10 to transmit information on the estimated reception power as information on the obstruction state between the terminal device 20 and the relay station 30 via the first antenna 31.

[0040] The transmitter 33 is composed of a signal processor 331, a multiplexer 332, and a transmission processor 333. The signal processor 331 identifies the multiplexing method by referring to the preamble of the electrical signal (transmission signal) output from the reception processor 321. The signal processor 331 divides the transmission signal based on the identified multiplexing method to generate multiple transmission signals.

[0041] The multiplexing unit 332 multiplexes a plurality of transmission signals in accordance with a multiplexing method specified by the base station apparatus 10. The multiplexing unit 332 is made up of a frequency multiplexing unit 334 and a spatial multiplexing unit 335.

[0042] When frequency multiplexing is specified as the multiplexing method, the frequency multiplexing unit 334 performs frequency conversion to arrange a plurality of transmission signals on the frequency axis.

[0043] When spatial multiplexing is specified as the multiplexing method, the spatial multiplexing unit 335 performs precoding on the multiple transmission signals. The precoding method may be a fixed precoder or a precoder that corresponds to the channel state between the relay station and the terminal.

[0044] When frequency multiplexing and spatial multiplexing are specified as the multiplexing method, processing by the frequency multiplexing unit 334 is performed first, followed by processing by the spatial multiplexing unit 335 .

[0045] The transmission processing unit 333 up-converts the transmission signal multiplexed by the multiplexing unit 332 to a high frequency band such as millimeter waves.

[0046] The second antenna 34 converts the transmission signal output from the transmission processing unit 333 into radio waves and transmits the radio waves to the terminal device 20 .

[0047] The control unit 35 controls the entire relay station 30. The control unit 35 is configured using one or more processors such as a CPU and one or more memories. The control unit 35 realizes the functions of a sleep control unit 351 and an information sharing unit 352 by the one or more processors executing programs.

[0048] The sleep control unit 351 controls the sleep of the own device based on a signal transmitted from the base station device 10. Specifically, the sleep control unit 351 identifies the relay station 30 to be put to sleep based on an electrical signal (notification signal) output from the receiving unit 32. If the relay station 30 to be put to sleep is the own device, the sleep control unit 351 transitions the own device to a sleep state. If the relay station 30 to be put to sleep is other than the own device, the sleep control unit 351 outputs the notification signal to the information sharing unit 352.

[0049] The information sharing unit 352 shares a notification signal transmitted from the base station device 10 with the other relay stations 30. For example, the information sharing unit 352 causes the notification signal output from the sleep control unit 351 to be transmitted to the other relay stations 30 via the transmission processing unit 333 and the second antenna 34. The information sharing unit 352 receives the notification signal transmitted from the other relay stations 30 via the second antenna 34 and the receiving unit 32.

[0050] Next, the processing of resource allocation to each relay station 30 will be described using Fig. 4. Fig. 4 is a diagram for explaining the processing of resource allocation by resource allocation section 141 of base station device 10. As an example, it is assumed that the number of relay stations 30 is four (relay stations 30-1 to 30-4), the spatial multiplexing level and frequency multiplexing level that base station device 10 can transmit are 10 and 1, the spatial multiplexing level and frequency multiplexing level that each relay station 30 can transmit are 2, and the spatial multiplexing level and frequency multiplexing level that terminal device 20 can receive are 2. As shown in Fig. 4, it is assumed that there is shielding between base station device 10 and relay station 30-4, and between relay stations 30-3, 30-4 and terminal device 20.

[0051] Base station device 10 estimates the reception SINR of each relay station 30 by exchanging reference signals between base station device 10 and each relay station 30. Base station device 10 creates the list shown in FIG. 5 based on information on the estimated reception SINR of each relay station 30. FIG. 5 is a diagram showing an example of a list indicating the obstruction state between base station device 10 and each relay station 30. In FIG. 5, information indicating the reception SINR value and the obstruction state is registered for each index (j) that identifies each relay station 30. In the index (j) column, "#1" represents relay station 30-1, "#2" represents relay station 30-2, "#3" represents relay station 30-3, and "#4" represents relay station 30-4.

[0052] The received SINR value represents the received SINR estimated by exchanging reference signals between the base station device 10 and each relay station 30. Note that "-" in the received SINR column indicates that the received SINR could not be estimated. The obstruction status information in FIG. 5 indicates whether communication is possible between the base station device 10 and each relay station 30, as determined based on the received SINR value. "No obstruction" in the obstruction status column indicates that communication is possible between the base station device 10 and each relay station 30, and "obstructed" indicates that communication is not possible between the base station device 10 and each relay station 30.

[0053] In the example shown in Fig. 5, it is indicated that "shadowing exists" only between the base station device 10 and relay station 30-4. Therefore, the relay stations available for data transmission are 30-1, 30-2, and 30-3. Each relay station 30 estimates the received SINR of each resource block by exchanging reference signals between the relay station 30 and the terminal device 20. Each relay station 30 creates the list shown in Fig. 6 based on the information on the estimated received SINR of each resource block.

[0054] Fig. 6 is a diagram showing an example of a list indicating the obstruction state between the terminal device 20 and each relay station 30. In Fig. 6, information indicating the received SINR value and the obstruction state is registered for each index (j) that identifies each relay station 30. In the index (j) item, "#1" represents relay station 30-1, "#2" represents relay station 30-2, "#3" represents relay station 30-3, and "#4" represents relay station 30-4.

[0055] The received SINR value in Fig. 6 represents the received SINR of each resource block. Note that "-" in the received SINR column indicates that the received SINR could not be estimated. The shadowing state information in Fig. 6 indicates whether communication is possible between the terminal device 20 and each relay station 30, determined based on the received SINR value. In the example shown in Fig. 6, it is shown that there is "shadowing" between the terminal device 20 and relay stations 30-3 and 30-4. Therefore, the relay stations available for data transmission are 30-1 and 30-2. Here, a resource block is defined as a unit of data transmitted with one spatial multiplexing and one frequency multiplexing. The lists shown in Figs. 5 and 6 are created in the resource allocation unit 141 of the base station device 10.

[0056] Terminal device 20 is N R 5 and 6, resource allocation unit 141 of base station device 10 determines relay station 30 to use for relaying by ANDing the indexes of relay stations 30 available between base station device 10 and each relay station 30 and between each relay station 30 and terminal device 20. Referring to the lists shown in FIGS. 5 and 6, relay stations 30 available both between base station device 10 and each relay station 30 and between each relay station 30 and terminal device 20 are relay stations 30-1 and 30-2. Therefore, resource allocation unit 141 determines relay stations 30-1 and 30-2 as relay stations 30 to use for relaying.

[0057] Next, the base station device 10 selects a path that minimizes power consumption in the transmission path from the base station device 10 to the relay station 30 to the terminal device 20. For example, the active power consumption of the base station device 10 is set to P Bbase The power consumption required to transmit one resource block at a required received SINR or higher is P B tx (SINR j B-R ), and the active power consumption of the relay station 30 is P R base , the power consumption required for the relay station 30 to transmit one resource block at a required reception SINR or higher is P R tx (SINR (j,f,s) R-U ) The power consumption required to transmit one resource block depends on the received SINR and is a function of the SINR. j B-R is the received SINR of relay station #j, and SINR (j,f,s) R-U represents the received SINR when the fth frequency resource and the sth spatial resource are used from relay station 30#j to terminal device 20. The resource allocation unit 141 calculates the power consumption for each path including the determined relay station 30 based on the following equation (1).

[0058]

number

[0059] Here, the set of available relay station indexes is defined as J′. Let j∈J′, and the resource allocation unit 141 calculates the power consumption P a (j∈J´,f,s) is calculated according to the above formula (1), and the power consumption P a The resource allocation unit 141 narrows down the relay paths according to the transmission capacity of each relay station 30 to a range that satisfies the required throughput between the base station device 10 and the terminal device 20.

[0060] For example, if the number of antennas at relay station #j is M j , the bandwidth is B j , the number of frequency resources is F jAssuming that one spatial stream can be transmitted per antenna and the modulation level is E, the communication capacity that can be transmitted per frequency resource in the terminal device 20#j is C j =M j (B j / F j )E [bps]. The resource allocation unit 141 calculates the communication capacity for the relay station 30 included in each route and stores a pattern of relay routes that satisfies the required throughput. The patterns of relay routes that satisfy the required throughput stored by the resource allocation unit 141 include a pattern in which the relay station 30 uses both spatial multiplexing and frequency multiplexing, and a pattern in which the relay station 30 uses only spatial multiplexing or only frequency multiplexing. The resource allocation unit 141 also determines the multiplexing method of the relay station 30 to be relayed by selecting a route that minimizes power consumption using the above equation (1).

[0061] FIG. 7 is a sequence diagram showing the flow of processing in the wireless communication system 100 according to the embodiment. The resource allocation unit 141 of the base station device 10 selects a route that minimizes power consumption from among relay routes (relay route patterns stored in the above description) that satisfy the required throughput between the base station device 10 and the terminal device 20 (step S101). Here, it is assumed that relay stations 30-1 and 30-2 are determined to be the relay stations 30 to be used for relay. The resource allocation unit 141 outputs information about the selected route (for example, information for identifying the relay station 30 that will perform data transmission) and information about the multiplexing method and relay method of relay stations 30-1 and 30-2 to the transmitter 12.

[0062] The following is a supplementary description of the information on the multiplexing method that resource allocation unit 141 outputs to transmitter 12. When a route using only frequency multiplexing is selected as the route that minimizes power consumption according to equation (1) above, resource allocation unit 141 determines that frequency multiplexing is to be used as the multiplexing method for relay stations 30-1 and 30-2, and outputs information on the determined multiplexing method (frequency multiplexing) for relay stations 30-1 and 30-2 to transmitter 12. When a route using only spatial multiplexing is selected as the route that minimizes power consumption according to equation (1) above, resource allocation unit 141 determines that spatial multiplexing is to be used as the multiplexing method for relay stations 30-1 and 30-2, and outputs information on the determined multiplexing method (spatial multiplexing) for relay stations 30-1 and 30-2 to transmitter 12. When a route that uses both spatial multiplexing and frequency multiplexing is selected as the route that minimizes power consumption according to the above-mentioned equation (1), the resource allocation unit 141 decides to use both spatial multiplexing and frequency multiplexing as the multiplexing method for the relay stations 30-1 and 30-2, and outputs information about the decided multiplexing method (using both spatial multiplexing and frequency multiplexing) for the relay stations 30-1 and 30-2 to the transmission unit 12.

[0063] Transmitter 12 generates transmission signals to be transmitted to relay stations 30-1 and 30-2 based on the information output from resource allocation unit 141, and transmits the transmission signals to relay stations 30-1 and 30-2 via antenna 11 (step S102). Relay stations 30-1 and 30-2 receive the transmission signals transmitted from base station device 10. Sleep controller 142 of base station device 10 generates a notification signal including information for identifying relay station 30-3. Sleep controller 142 transmits the generated notification signal to each relay station 30 via antenna 11 (step S103).

[0064] Relay stations 30-1, 30-2, and 30-3 receive the notification signal transmitted from base station device 10. Sleep control units 351 of relay stations 30-1 and 30-2 identify the relay station 30 to be put to sleep based on information about the relay station 30 to be put to sleep, which is included in the notification signal transmitted from base station device 10. Because the relay station 30 to be put to sleep is not the relay station 30 itself, sleep control units 351 of relay stations 30-1 and 30-2 output the notification signal to information sharing unit 352. Information sharing units 352 of relay stations 30-1 and 30-2 cause the notification signal output from sleep control unit 351 to be transmitted to another relay station 30 (e.g., relay station 30-3) via transmission processing unit 333 and second antenna 34. As a result, even if there is obstruction between base station device 10 and relay station 30-3 and relay station 30-3 cannot receive the notification signal, relay station 30-3 can receive the notification signal from the other relay station 30.

[0065] Sleep control unit 351 of relay station 30-3 identifies relay station 30 to be put to sleep based on information about relay station 30 to be put to sleep included in the notification signal transmitted from base station device 10. Since relay station 30-3 is the relay station 30 to be put to sleep, sleep control unit 351 of relay station 30-3 transitions its own device to sleep state (step S104). As a result, relay station 30-3 transitions to sleep state to reduce power consumption.

[0066] Reception processing unit 321 of relay station 30-1 receives the transmission signal transmitted from base station device 10. Reception processing unit 321 of relay station 30-1 performs reception processing in accordance with the relay method included in the preamble of the received transmission signal (step S105). For example, if the relay method is a regenerative method, reception processing unit 321 of relay station 30-1 performs demodulation processing, decoding processing, encoding processing, and modulation processing on the transmission signal. Thereafter, reception processing unit 321 of relay station 30-1 outputs the transmission signal to signal processing unit 331. On the other hand, if the relay method is a non-regenerative method, reception processing unit 321 outputs the transmission signal to signal processing unit 331 as is.

[0067] Signal processing unit 331 of relay station 30-1 identifies the multiplexing method by referring to the preamble of the transmission signal output from reception processing unit 321. Signal processing unit 331 of relay station 30-1 divides the transmission signal to generate multiple transmission signals based on the identified multiplexing method (step S106). Signal processing unit 331 of relay station 30-1 outputs the generated multiple transmission signals to multiplexing unit 332. Multiplexing unit 332 of relay station 30-1 multiplexes the multiple transmission signals output from signal processing unit 331 in accordance with the multiplexing method specified by base station device 10 (step S107).

[0068] The multiplexing unit 332 of the relay station 30-1 outputs the multiplexed transmission signal to the transmission processing unit 333. The transmission processing unit 333 of the relay station 30-1 upconverts the multiplexed transmission signal output from the multiplexing unit 332 to a high frequency band and transmits the upconverted signal to the terminal device 20 via the second antenna 34 (step S108).

[0069] Reception processing unit 321 of relay station 30-2 receives the transmission signal transmitted from base station device 10. Reception processing unit 321 of relay station 30-2 performs reception processing in accordance with the relay method included in the preamble of the received transmission signal (step S109). Reception processing unit 321 of relay station 30-2 outputs the transmission signal to signal processing unit 331.

[0070] Signal processing unit 331 of relay station 30-2 identifies a multiplexing scheme by referring to the preamble of the transmission signal output from reception processing unit 321. Signal processing unit 331 of relay station 30-2 divides the transmission signal to generate multiple transmission signals based on the identified multiplexing scheme (step S110). Signal processing unit 331 of relay station 30-2 outputs the generated multiple transmission signals to multiplexing unit 332. Multiplexing unit 332 of relay station 30-2 multiplexes the multiple transmission signals output from signal processing unit 331 in accordance with the multiplexing scheme specified by base station device 10 (step S111).

[0071] The multiplexing unit 332 of the relay station 30-2 outputs the multiplexed transmission signal to the transmission processing unit 333. The transmission processing unit 333 of the relay station 30-2 upconverts the multiplexed transmission signal output from the multiplexing unit 332 to a high frequency band and transmits it to the terminal device 20 via the second antenna 34 (step S112). The terminal device 20 receives the transmission signals transmitted from each of the relay stations 30-1 and 30-2. The terminal device 20 demodulates each received transmission signal to obtain transmission data (step S113).

[0072] According to the wireless communication system 100 configured as described above, the base station device 10 comprises a resource allocation unit 141 that determines a route and a multiplexing scheme that minimizes power consumption within a range that satisfies the required throughput between the base station device 10 and the terminal device 20, a signal processing unit 121 that divides data to be transmitted to the terminal device 20 based on the route determined by the resource allocation unit 141 and generates a plurality of transmission signals including information on the multiplexing scheme, a spatial multiplexing unit 122 that forms beams for transmitting a plurality of transmission signals to one or more relay stations 30 out of a plurality of relay stations 30 located on the determined route, and a signal processing unit 121 that performs multiplexing by the spatial multiplexing unit 122 using a low frequency band. The system is equipped with a transmission processing unit 123 that transmits multiple transmission signals to one or more relay stations 30 via antenna 11 using each formed beam, and the multiple relay stations 30 are equipped with a signal processing unit 331 that divides the transmission signal based on multiplexing method information included in the received transmission signal from the base station device 10 to generate multiple transmission signals, a multiplexing unit 332 that multiplexes the divided multiple transmission signals using at least one of spatial multiplexing and frequency multiplexing based on the multiplexing method information, and a second antenna 34 that transmits the multiple transmission signals multiplexed by the multiplexing unit 332 to the terminal device 20 using a high frequency band.

[0073] With the above configuration, frequency division multiplexing, spatial division multiplexing, or both can be used to compensate for the small spatial multiplexing number in small relay stations 30, and by increasing the number of communication path candidates, it becomes possible to transfer large amounts of data over more power-efficient paths. In this way, wireless communication system 100 can minimize the power consumption required to achieve a required transmission rate.

[0074] Furthermore, resource allocation unit 141 of base station device 10 determines the multiplexing scheme to be either a combination of spatial multiplexing and frequency multiplexing, spatial multiplexing only, or frequency multiplexing only, depending on the determined route. When the required throughput is low and when using only spatial multiplexing or only frequency multiplexing results in lower power consumption compared to using both spatial multiplexing and frequency multiplexing, base station device 10 determines either spatial multiplexing or frequency multiplexing as the multiplexing scheme. This does not necessarily require determining the multiplexing scheme to use both spatial multiplexing and frequency multiplexing, and it is possible to determine the multiplexing scheme of relay station 30 so as to reduce power consumption.

[0075] The base station device 10 and terminal device 20 described above may be implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be loaded into a computer system and executed to implement the functions. Note that the term "computer system" here includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system.

[0076] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, or a medium that stores a program for a fixed period of time, such as a volatile memory within a computer system that serves as a server or client in such a case. The program may also be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already stored in the computer system, or may be one that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0077] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0078] The present invention is applicable to wireless access networks. [Explanation of symbols]

[0079] 10...base station device, 11...antenna, 12...transmitter, 13...receiver, 14...controller, 20...terminal device, 30, 30-1 to 30-4...relay station, 31...first antenna, 32...receiver, 33...transmitter, 34...second antenna, 35...controller, 100...wireless communication system, 121...signal processor, 122...spatial multiplexer, 123...transmission processor, 131...reception processor, 141...resource allocation unit, 142...sleep controller, 321...reception processor, 331...signal processor, 332...multiplexer, 333...transmission processor, 334...frequency multiplexer, 335...spatial multiplexer, 351...sleep controller, 352...information sharing unit

Claims

1. A wireless communication system comprising one or more terminal devices, a base station device that performs wireless communication between the one or more terminal devices, and a plurality of relay stations that perform relay between the one or more terminal devices and the base station device, The base station device a resource allocation unit that determines a route and a multiplexing method that minimizes power consumption within a range that satisfies a required throughput between the base station device and the one or more terminal devices; a signal processing unit that divides data to be transmitted to the one or more terminal devices based on the route determined by the resource allocation unit, and generates a plurality of transmission signals including information on the multiplexing method; a spatial multiplexing unit that forms beams for transmitting the plurality of transmission signals to one or more relay stations among the plurality of relay stations located on the route determined by the resource allocation unit; a transmission processing unit that transmits the plurality of transmission signals to each of the one or more relay stations via an antenna using each beam formed by the spatial multiplexing unit, using a low frequency band; Equipped with The plurality of relay stations a signal processing unit that divides a received transmission signal from the plurality of transmission signals transmitted from the base station device based on information on the multiplexing method included in the received transmission signal, thereby generating a plurality of transmission signals; a multiplexing unit that performs at least one of spatial multiplexing and frequency multiplexing on the divided transmission signals based on the information on the multiplexing method; a transmitting unit that transmits the plurality of transmission signals multiplexed by the multiplexing unit to the one or more terminal devices using a high frequency band; A wireless communication system comprising:

2. the resource allocation unit determines the route based on a shielding state between the plurality of relay stations and the base station device and between the plurality of relay stations and the one or more terminal devices, and a transmission capability of each of the base station device, the plurality of relay stations, and the one or more terminal devices.

10. The wireless communication system of claim 1.

3. The resource allocation unit determines, according to the determined path, one of a combination of spatial multiplexing and frequency multiplexing, spatial multiplexing only, or frequency multiplexing only as the multiplexing method.

3. The wireless communication system according to claim 1 or 2.

4. The resource allocation unit further determines a relay method in the relay station based on information on transmission capability and propagation path information between the relay station and the terminal device.

3. The wireless communication system according to claim 1 or 2.

5. The base station device a sleep control unit that transitions relay stations that are not used for communication among the plurality of relay stations into a sleep state based on a route selection result of the resource allocation unit; the sleep control unit transmits a notification signal including information of a relay station to be put to sleep to the plurality of relay stations; 3. The wireless communication system according to claim 1 or 2.

6. The plurality of relay stations an information sharing unit that shares the notification signal transmitted from the base station device with other relay stations; a sleep control unit that performs sleep control of the device itself based on information about the relay station that is to be put to sleep, the information being included in the notification signal; Further provided with 6. The wireless communication system according to claim 5.

7. A wireless communication method in a wireless communication system including one or more terminal devices, a base station device that performs wireless communication between the one or more terminal devices, and a plurality of relay stations that perform relay between the one or more terminal devices and the base station device, The base station device, determining a route and a multiplexing method that minimizes power consumption within a range that satisfies a required throughput between the base station device and the one or more terminal devices; dividing data to be transmitted to the one or more terminal devices based on the determined route, and generating a plurality of transmission signals including information on the multiplexing method; forming a beam for transmitting the plurality of transmission signals toward one or more relay stations among the plurality of relay stations located on the determined route; Using a low frequency band, transmit the plurality of transmission signals to each of the one or more relay stations via an antenna using each formed beam; The plurality of relay stations dividing the transmission signal based on the information of the multiplexing method included in a received transmission signal among the plurality of transmission signals transmitted from the base station device to generate a plurality of transmission signals; performing at least one of spatial multiplexing and frequency multiplexing on the divided transmission signals based on the information on the multiplexing method; A wireless communication method for transmitting the multiplexed transmission signals to the one or more terminal devices using a high frequency band.

8. A base station device in a wireless communication system including one or more terminal devices, a base station device that performs wireless communication between the one or more terminal devices, and a plurality of relay stations that perform relay between the one or more terminal devices and the base station device, a resource allocation unit that determines a route and a multiplexing method that minimizes power consumption within a range that satisfies a required throughput between the base station device and the one or more terminal devices; a signal processing unit that divides data to be transmitted to the one or more terminal devices based on the route determined by the resource allocation unit, and generates a plurality of transmission signals including information on the multiplexing method; a spatial multiplexing unit that forms beams for transmitting the plurality of transmission signals to one or more relay stations among the plurality of relay stations located on the route determined by the resource allocation unit; a transmission processing unit that transmits the plurality of transmission signals to each of the one or more relay stations via an antenna using each beam formed by the spatial multiplexing unit, using a low frequency band; A base station device comprising:

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