WO2017029738A1

WO2017029738A1 - Wireless communication apparatus, wireless communication system, and transmission bandwidth control method

Info

Publication number: WO2017029738A1
Application number: PCT/JP2015/073279
Authority: WO
Inventors: 木村　大
Original assignee: 富士通株式会社
Priority date: 2015-08-19
Filing date: 2015-08-19
Publication date: 2017-02-23

Abstract

A base station with reduced power consumption. In this base station (10), a baseband unit (13) performs digital signal processing on transmission data, thereby generating a baseband signal. A wireless unit (14) wirelessly transmits an analog signal to which the baseband signal has been converted by a digital-to-analog conversion. A communication control unit (12) determines a transmission bandwidth that maximizes energy efficiency, on the basis of a power consumption model including a first power consumption which is power consumption by the baseband unit (13) and which depends on a transmission bandwidth of the analog signal, and a second power consumption which is power consumption by the wireless communication unit (14) and which depends on a transmission power of the analog signal.

Description

Wireless communication apparatus, wireless communication system, and transmission bandwidth control method

The present invention relates to a wireless communication device, a wireless communication system, and a transmission bandwidth control method.

With the development of wireless communication, the amount of wireless communication traffic has increased dramatically. For this reason, it is important to improve the energy efficiency (hereinafter referred to as “EE”) of wireless communication. In particular, in millimeter wave communication, communication with a capacity that is several tens of times larger than conventional ones is possible. Therefore, improving the energy efficiency of millimeter wave communication is considered to greatly contribute to improving the energy efficiency of the entire wireless communication system.

Millimeter-wave communication is expected to achieve a throughput of several tens of Gbps using a frequency bandwidth of several GHz. The frequency bandwidth of several GHz and the throughput of several tens of Gbps are compared with the frequency bandwidth of 100 MHz or less and the throughput of several hundred Mbps or less in conventional wireless communication such as LTE (Long Term Evolution) and WiFi (Wireless Fidelity). large. For this reason, in millimeter wave communication, power consumption of a baseband unit that performs digital signal processing such as encoding processing and modulation processing is expected to increase with an increase in frequency bandwidth. As the frequency bandwidth increases, the power consumption of the radio unit (that is, RF (Radio Frequency) unit) that transmits radio signals by performing analog signal processing such as up-conversion and signal power amplification also increases. Expected. However, since the transmission power in the radio unit can be suppressed by using a technique such as beam forming, for example, the increase rate of power consumption in the radio unit is relatively smaller than that in the baseband unit. is assumed. Therefore, in order to reduce the power consumption when the frequency bandwidth is increased, it is particularly important to reduce the power consumption of the baseband part. Hereinafter, the frequency bandwidth may be simply referred to as “bandwidth”.

On the other hand, conventionally, as shown in the following formulas (1) and (2), the energy efficiency η using a power consumption model P _total [W] in which the power consumption P _c [W] of the circuit is assumed to be fixed. _EE [bit / J] was calculated. In Equation (1), P _T [W] is the transmission power, ρ is the efficiency of the power amplifier, and in Equation (2), C [bps] is the throughput.

Further, the throughput C is expressed by the following formula (3). In Equation (3), B [Hz] is a bandwidth used for transmission of a radio signal (hereinafter sometimes referred to as “transmission bandwidth”), L is a propagation loss between radio transmission and reception (that is, a path loss), N ₀ [W / Hz] is thermal noise per unit bandwidth. L is a true value.

Special table 2012-526431 gazette

Generally, the power consumption of the baseband part increases as the processing amount of digital signal processing increases, and the processing amount of digital signal processing increases as the transmission bandwidth increases, so the baseband increases as the transmission bandwidth increases. The power consumption of the part increases. When the power consumption of the baseband part changes according to the transmission bandwidth, the energy efficiency is calculated assuming that the power consumption of the circuit is fixed as in the conventional power consumption model (Equation (1)). Since it becomes difficult to calculate optimum energy efficiency, it is difficult to reduce power consumption.

The disclosed technology has been made in view of the above, and aims to reduce the power consumption of a wireless communication device.

In the disclosed aspect, the wireless communication device includes a baseband unit, a wireless unit, and a control unit. The baseband unit performs digital signal processing on transmission data to generate a baseband signal. The wireless unit wirelessly transmits an analog signal converted from the baseband signal by digital analog conversion. The control unit includes first power consumption that is power consumption of the baseband unit, the first power consumption that depends on a transmission bandwidth of the analog signal, and second power consumption that is power consumption of the wireless unit. The transmission bandwidth that maximizes the energy efficiency is determined based on a power consumption model including the second power consumption that depends on the transmission power of the analog signal.

According to the disclosed aspect, the power consumption of the wireless communication device can be reduced.

FIG. 1 is a diagram illustrating a configuration example of a wireless communication system according to the first embodiment. FIG. 2 is a functional block diagram illustrating an example of a base station according to the first embodiment. FIG. 3 is a diagram illustrating an example of a processing sequence of the wireless communication system according to the first embodiment. FIG. 4 is a diagram illustrating an example of numerical calculation results of the first embodiment. FIG. 5 is a diagram illustrating an example of numerical calculation results of the first embodiment. FIG. 6 is a diagram for explaining the effect of the first embodiment. FIG. 7 is a diagram for explaining an operation example of the wireless communication system according to the second embodiment. FIG. 8 is a functional block diagram illustrating an example of a communication terminal according to the third embodiment. FIG. 9 is a diagram illustrating an example of a processing sequence of the wireless communication system according to the third embodiment. FIG. 10 is a diagram for explaining an operation example of the wireless communication system according to the fourth embodiment. FIG. 11 is a diagram illustrating an example of a processing sequence of the wireless communication system according to the fifth embodiment. FIG. 12 is a diagram for explaining an operation example of the wireless communication system according to the sixth embodiment. FIG. 13 is a diagram illustrating a hardware configuration example of the base station. FIG. 14 is a diagram illustrating a hardware configuration example of the communication terminal.

Hereinafter, embodiments of a wireless communication device, a wireless communication system, and a transmission bandwidth control method disclosed in the present application will be described in detail with reference to the drawings. Note that the wireless communication device, the wireless communication system, and the transmission bandwidth control method disclosed in the present application are not limited by this embodiment. Moreover, the same code | symbol is attached | subjected to the structure which has the same function in each Example, and the step which performs the same process, and the overlapping description is abbreviate | omitted.

[Example 1]
<Configuration example of wireless communication system>
FIG. 1 is a diagram illustrating a configuration example of a wireless communication system according to the first embodiment. In FIG. 1, a radio communication system 100 includes base stations 10-1 to 10-3, communication terminals 20-1 to 20-3, and a central control station 30. The central control station 30 is connected to a core network (not shown). For example, the base station 10-1 and the communication terminal 20-1 perform wireless communication, the base station 10-2 and the communication terminal 20-2 perform wireless communication, and the base station 10-3 and the communication terminal 20-3 Performs wireless communication. The centralized control station 30 performs centralized control on the base stations 10-1 to 10-3. For example, the centralized control station 30 transmits each of the base stations 10-1 to 10-3 to each of the base stations 10-1 to 10-3 within the frequency band that can be used in the wireless communication system 100. Allocate the frequency band used for communication.

In the following, when the base stations 10-1 to 10-3 are not particularly distinguished, they may be collectively referred to as the base station 10, and when the communication terminals 20-1 to 20-3 are not particularly distinguished, the communication terminal 20 May be collectively referred to. In the following, a frequency band that can be used in the radio communication system 100 is a “system band”, a frequency band allocated to each base station 10 or each communication terminal 20 in the system band is an “allocated band”, and a system band Is sometimes referred to as “system bandwidth”. Each allocation band is indicated by the center frequency of each allocation band, for example. A radio signal from the base station 10 to the communication terminal 20 is called a “downlink signal”, and a radio signal from the communication terminal 20 to the base station 10 is called an “uplink signal”. The base station 10 and the communication terminal 20 are examples of a wireless communication device.

<Configuration example of base station>
FIG. 2 is a functional block diagram illustrating an example of a base station according to the first embodiment. The base station 10 illustrated in FIG. 2 includes a wired communication unit 11, a communication control unit 12, a baseband unit 13, a radio unit 14, an antenna 15, and a power consumption model storage unit 16. The antenna 15 is, for example, an array antenna having a plurality of antenna elements.

The wired communication unit 11 is connected to the central control station 30 by, for example, an optical fiber. The wired communication unit 11 transmits user data input from the baseband unit 13 via the communication control unit 12 to the centralized control station 30 and receives user data received from the centralized control station 30 via the communication control unit 12. Output to the band unit 13. Further, the wired communication unit 11 receives a signal for notifying the allocated band (hereinafter also referred to as “allocated band notification signal”) from the centralized control station 30 and outputs the signal to the communication control unit 12.

The communication control unit 12 controls wireless communication. For example, the communication control unit 12 determines the transmission bandwidth and transmission power of the downlink signal based on the power consumption model stored in the power consumption model storage unit 16. The communication control unit 12 instructs the baseband unit 13 on the determined transmission bandwidth, and instructs the radio unit 14 on the determined transmission power. Further, the communication control unit 12 instructs the radio unit 14 of the allocated band notified by the allocated band notification signal. Details of the processing of the communication control unit 12 will be described later.

The baseband unit 13 generates a baseband transmission signal by performing digital signal processing such as encoding processing and modulation processing on transmission data such as user data. At this time, the baseband unit 13 performs digital signal processing according to the transmission bandwidth instructed from the communication control unit 12. The baseband unit 13 generates an OFDM signal, which is a baseband transmission signal, by performing, for example, OFDM (Orthogonal Frequency Division Multiplexing) modulation as modulation processing on transmission data. At this time, the baseband unit 13 changes the number of transmission data allocated to the plurality of subcarriers forming the OFDM signal according to the transmission bandwidth determined by the communication control unit 12. For example, when an OFDM signal is formed of 1024 subcarriers and the bandwidth of the OFDM signal corresponds to the system bandwidth, when transmission data is allocated to 512 subcarriers, the transmission bandwidth is equal to the system bandwidth. A half.

The baseband unit 13 converts the generated baseband transmission signal into an analog signal by digital-analog conversion (D / A conversion), and outputs the converted baseband signal to the radio unit 14. The baseband unit 13 converts the baseband received signal input from the wireless unit 14 into a digital signal by analog-digital conversion (A / D conversion). The baseband unit 13 obtains received data such as user data from the communication terminal 20 by performing digital signal processing such as demodulation processing and decoding processing on the baseband signal converted into the digital signal.

The radio unit 14 performs analog signal processing such as up-conversion processing and power amplification processing on the baseband transmission signal (that is, analog signal) input from the baseband unit 13, and transmits the transmission signal after analog signal processing. The data is transmitted to the communication terminal 20 via the antenna 15. At this time, the radio unit 14 performs an up-conversion process according to the allocated bandwidth instructed from the communication control unit 12. Further, the radio unit 14 amplifies the power of the transmission signal according to the transmission power instructed from the communication control unit 12. In addition, the radio unit 14 performs analog signal processing such as down-conversion processing on the reception signal received via the antenna 15 to obtain a baseband reception signal and outputs the baseband reception signal to the baseband unit 13.

In the above description, the baseband unit 13 performs D / A conversion and A / D conversion. However, instead of the baseband unit 13, the wireless unit 14 performs D / A conversion and A / D conversion. good. Further, the baseband unit 13 and the radio unit 14 do not perform D / A conversion and A / D conversion, and a conversion unit that performs D / A conversion and A / D conversion is provided between the baseband unit 13 and the radio unit 14. May be provided.

The power consumption model storage unit 16 stores a power consumption model. Details of the power consumption model will be described later.

<Base station processing>
The power consumption model P _total [W] stored in the power consumption model storage unit 16 is expressed by the following equation (4). In Expression (4), P _RF [W] is the power consumption of the wireless unit 14, P _BB [W] is the power consumption of the baseband unit 13, P _T [W] is the transmission power, and B [Hz] is the transmission bandwidth. It is. That is, in Expression (4), the power consumption of the wireless unit 14 is a function of the transmission power and depends on the transmission power, and the power consumption of the baseband unit 13 is a function of the transmission bandwidth and depends on the transmission bandwidth. . The power consumption of the base station 10 is modeled as the sum of the power consumption of the radio unit 14 and the power consumption of the baseband unit 13.

At this time, the energy efficiency η _EE [bit / J] is expressed by the following equation (5) and is a function of the transmission power _PT and the transmission bandwidth B. In equation (5), C [bps] is the throughput, L is the path loss, and N ₀ [W / Hz] is the thermal noise (true value) per unit bandwidth. The thermal noise N ₀ is a constant value.

Further, the power consumption P _RF of the wireless unit 14 is modeled, for example, as expressed in the following formula (6). In Expression (6), ρ is the efficiency (a constant value) of the power amplifier included in the wireless unit 14, and P _{RF, 0} [W] is the fixed power consumption in the wireless unit 14.

On the other hand, the power consumption of the baseband unit 13 is modeled, for example, as expressed in the following equation (7). In Expression (7), α is a predetermined proportional constant, and P _{BB, 0} [W] is a fixed power consumption in the baseband unit 13. That is, the power consumption of the baseband unit 13 is modeled so as to be proportional to the transmission bandwidth B, for example.

Therefore, when the energy efficiency η _EE is expressed by the equation (5), if the path loss L is determined, the combination of the transmission bandwidth B and the transmission power P _T that maximizes the energy efficiency η _EE (that is, the transmission bandwidth) (Optimal combination of B and transmission power _PT ) is obtained according to the following equation (8). In Equation (8), B _opt is the optimal transmission bandwidth, P _Topt is the optimal transmission power, B _max is the maximum transmission bandwidth, and P _{T, max} is the maximum transmission power. B _max is usually the maximum bandwidth (that is, the system bandwidth) of the wireless communication system 100.

Therefore, the communication control unit 12 sets B _opt and P _Topt that maximize η _EE according to the equations (5) and (8) based on the power consumption models shown in the equations (4), (6), and (7). The combination with is determined. The power consumption models shown in Equations (4), (6), and (7) are stored in advance in the power consumption model storage unit 16, and the calculation algorithm according to Equations (5) and (8) is stored in advance in the communication control unit 12. Has been. The communication control unit 12 notifies the determined B _opt to the baseband unit 13 and notifies the determined P _Topt to the wireless unit 14. Since energy efficiency is the power consumption per transmitted bit when maximized becomes minimum, by determining the combination of B _opt and P _Topt the eta _EE is maximized, the base required to transmit the same amount of data The power consumption of the station 10 can be reduced.

Further, for example, the communication control unit 12 fixes the transmission power P _T to a constant value P _{T, 0} and then maximizes the energy efficiency η _EE (that is, the optimal transmission bandwidth B _opt ). May be determined. The optimum transmission bandwidth B _opt when the transmission power P _T is fixed to a constant value P _{T, 0} is obtained according to the following equation (9). By determining the transmission bandwidth according to Equation (9), it is possible to reduce the amount of calculation required to determine the optimum transmission bandwidth that can reduce the power consumption of the base station 10.

Further, for example, the communication control unit 12 determines a transmission bandwidth B (that is, an optimal transmission bandwidth B _opt ) that maximizes the energy efficiency η _EE after ensuring a throughput C that is equal to or greater than the threshold C _min. Also good. That is, the communication control unit 12 may determine a transmission bandwidth B that obtains a throughput C that is equal to or greater than the threshold C _min . The optimum transmission bandwidth B _opt when the throughput C is maintained at the threshold value C _min or more and the transmission power P _T is fixed to the constant value P _{T, 0} is obtained according to the following equation (10). By determining the transmission bandwidth according to the equation (10), it is possible to determine an optimal transmission bandwidth that can reduce the power consumption of the base station 10 while securing a desired throughput.

Further, for example, the communication control unit 12 determines an optimal transmission bandwidth based on the power consumption model represented by the following equation (11) instead of the power consumption model represented by the equation (4). May be. That is, in equation (11), the power consumption P _BB of the baseband unit 13 is dependent on the throughput is a function of the throughput is different from the equation (4). However, since the throughput depends on the transmission bandwidth, the power consumption of the baseband unit 13 eventually depends on the transmission bandwidth also in the equation (11).

Note that the power consumption models shown in the equations (4), (6), and (7) may be stored in the power consumption model storage unit 16 in a table format instead of as mathematical equations.

<Processing of wireless communication system>
FIG. 3 is a diagram illustrating an example of a processing sequence of the wireless communication system according to the first embodiment.

In step S101, the base station 10 transmits a reference signal to the communication terminal 20, and the communication terminal 20 receives the reference signal from the base station 10. The reference signal is generated by the baseband unit 13 and transmitted to the communication terminal 20 by the radio unit 14. The reference signal is transmitted from the base station 10 with constant power, and the transmission power value of the reference signal from the base station 10 is known to the communication terminal 20.

In step S103, the communication terminal 20 estimates a path loss between the base station 10 and the communication terminal 20. For example, the communication terminal 20 estimates the path loss by dividing the known transmission power value of the reference signal by the reception power value of the reference signal.

In step S105, the communication terminal 20 notifies the base station 10 of the path loss estimated in step S103. The communication terminal 20 generates a notification signal that notifies the path loss, and transmits the generated notification signal to the base station 10. The path loss notification signal is received by the radio unit 14 of the base station 10 and input to the communication control unit 12 via the baseband unit 13.

In step S107, the communication control unit 12 uses the path loss notified from the communication terminal 20, for example, based on the power consumption models shown in the equations (4), (6), and (7). According to (8), the combination of B _opt and P _Topt that maximizes η _EE is determined. The communication control unit 12 instructs the determined B _opt to the baseband unit 13, and instructs the determined P _Topt to the radio unit 14. Further, the communication control unit 12 instructs the radio unit 14 about the allocated bandwidth.

In step S109, the base station 10 notifies the communication terminal 20 of the transmission bandwidth and the allocated bandwidth. A notification signal for notifying the transmission bandwidth and the allocated bandwidth is generated by the communication control unit 12 and transmitted by the wireless unit 14.

In step S111, the base station 10 transmits a downlink signal to the communication terminal 20 according to the transmission bandwidth and the allocated bandwidth notified to the communication terminal 20 in step S109. The communication terminal 20 receives the downlink signal according to the transmission bandwidth and the allocated bandwidth notified from the base station 10 in step S109.

<Example of numerical calculation results>
4 and 5 are examples of numerical calculation results of the first embodiment. 4 shows a case where the distance between the base station 10 and the communication terminal 20 is 10 m, and FIG. 5 shows a case where the distance between the base station 10 and the communication terminal 20 is 100 m.

In this numerical calculation, a power consumption model represented by the following equation (12) was used. In Expression (12), N _t is the number of transmitting antenna elements of the base station 10.

The following parameters were used for this numerical calculation.
α = 1 [W / GHz]
P _RF per transmitting antenna element = 0.1 [W]
Transmission power per transmission antenna element = 10 [dBm]
N _t = 64
Number of reception antenna elements of communication terminal 20 (N _r ) = 4
Center frequency of allocated band = 60 [GHz]
Thermal noise density (P _N ) = − 174 [dBm / Hz]
Path loss (L) = 20 log (4πr / λ) [dB]
Received SNR (γ) of communication terminal 20 = P _T −L−10 log (B)
-P _N +10 log (N _t N _r ) [dB]

Assuming that the maximum value of the transmission bandwidth is 20 GHz, when the distance between the base station 10 and the communication terminal 20 is 10 m, as shown in FIG. 4, when communication is performed with a transmission bandwidth of 20 GHz, energy efficiency and Throughput is maximized.

On the other hand, when the distance between the base station 10 and the communication terminal 20 is 100 m, as shown in FIG. 5, when communication is performed with a transmission bandwidth of 5 GHz, the energy efficiency is maximized, but the throughput is It can be seen that there is room for improvement. That is, in FIG. 5, the throughput when the transmission bandwidth is 5 GHz is 8 Gbps, whereas the throughput when the transmission bandwidth is 20 GHz increases to 12 Gbps. In FIG. 5, the power consumption P _total when the transmission bandwidth is 5 GHz is 11.4 W, whereas the power consumption P _total when the transmission bandwidth is 20 GHz is 26.4 W. These power consumptions P _total are calculated according to the power consumption model represented by the equation (12).

Therefore, as shown in FIG. 6, when the transmission bandwidth is 5 GHz, signal transmission is performed with a transmission time (for example, 3 seconds) that is 1.5 times the transmission time (for example, 2 seconds) when the transmission bandwidth is 20 GHz. By doing so, it is possible to transmit a 12 Gbit data amount equivalent to that when the transmission bandwidth is 20 GHz with a power consumption amount of 34.2 J with respect to a power consumption amount of 52.8 J. That is, when the distance between the base station 10 and the communication terminal 20 is 100 m, the transmission bandwidth is set to 5 GHz, which is the transmission bandwidth that maximizes the energy efficiency, by setting the transmission bandwidth used for communication to the maximum. Compared to the case of 20 GHz, the power consumption for transmitting the same amount of data can be reduced by about 35%.

As described above, in the first embodiment, the energy efficiency is maximized based on the power consumption model including the power consumption of the baseband unit 13 that depends on the transmission bandwidth and the power consumption of the wireless unit 14 that depends on the transmission power. Determine the transmission bandwidth to be

By doing so, the power consumption of the base station 10 can be reduced.

[Example 2]
When the transmission bandwidth that maximizes energy efficiency (that is, the optimal transmission bandwidth) is smaller than the system bandwidth, a free bandwidth occurs.

Therefore, the communication control unit 12 generates a notification signal for notifying the determined transmission bandwidth (hereinafter also referred to as “transmission bandwidth notification signal”), and the generated transmission bandwidth notification signal is transmitted to the wired communication unit 11. Output to. The wired communication unit 11 transmits a transmission bandwidth notification signal to the central control station 30.

The centralized control station 30 that has received the transmission bandwidth notification signal from the base station 10 assigns a frequency band to each base station 10 based on the transmission bandwidth determined by the base station 10.

FIG. 7 is a diagram for explaining an operation example of the wireless communication system according to the second embodiment. The base stations 10-1 to 10-3 and the communication terminals 20-1 to 20-3 shown in FIG. 7 correspond to the base stations 10-1 to 10-3 and the communication terminals 20-1 to 20-3 shown in FIG. To do. Base station 10-1 and base station 10-2 are adjacent to each other, base station 10-2 and base station 10-3 are adjacent to each other, while base station 10-1 and base station 10-3 are adjacent to each other do not do.

In FIG. 7, for example, the system bandwidth is 20 GHz and the unit bandwidth is 5 GHz. In FIG. 7, the base station 10-1 determines the transmission bandwidth to 15 GHz, the base station 10-2 determines the transmission bandwidth to 5 GHz, and the base station 10-3 determines the transmission bandwidth to 10 GHz. Shall.

Therefore, the centralized control station 30 determines the allocation bands for the base station 10-1 to be three frequency bands of the center frequencies f1, f2, and f4, while the allocation band for the base station 10-2 is one of the center frequencies f3. Determine the frequency band. Therefore, in the base station 10-1, the communication control unit 12 instructs the radio unit 14 to transmit the bandwidth 15 GHz and the allocated bands f1, f2, and f4, and the radio unit 14 uses the allocated bands f1, f2, and f4. A downlink signal having a transmission bandwidth of 15 GHz is transmitted. Further, in the base station 10-2, the communication control unit 12 instructs the radio unit 14 about the transmission bandwidth 5 GHz and the allocated band f3, and the radio unit 14 uses the allocated band f3 to send a downlink signal with the transmission bandwidth 5 GHz. Send. As a result, the frequency bands used for downlink signal transmission do not overlap between the base stations 10-1 and 10-2 adjacent to each other. Can reduce signal interference.

Further, since the centralized control station 30 determines the allocated band for the base station 10-2 as one frequency band of the center frequency f3, the allocated band for the base station 10-3 is determined as two frequency bands of the center frequencies f1 and f2. To do. Therefore, in the base station 10-3, the communication control unit 12 instructs the radio unit 14 about the transmission bandwidth 10 GHz and the allocation bands f1 and f2, and the radio unit 14 uses the allocation bands f1 and f2 to transmit the transmission bandwidth 10 GHz. The downstream signal is transmitted. As a result, the frequency bands used for downlink signal transmission do not overlap between the base stations 10-2 and 10-3 adjacent to each other, and therefore, between the base stations 10-2 and 10-3. Can reduce signal interference.

As described above, in Example 2, since the frequency bands used for downlink signal transmission do not overlap between adjacent base stations, signal interference between base stations can be reduced. For this reason, the throughput of the downlink signal in the entire wireless communication system can be improved.

[Example 3]
In the first embodiment, the downlink signal transmission bandwidth is determined. In contrast, in the third embodiment, a case where the transmission bandwidth of the uplink signal is determined will be described.

<Configuration example of communication terminal>
FIG. 8 is a functional block diagram illustrating an example of a communication terminal according to the third embodiment. The communication terminal 20 illustrated in FIG. 8 includes a communication control unit 21, a baseband unit 22, a radio unit 23, an antenna 24, and a power consumption model storage unit 25. The antenna 24 is, for example, an array antenna having a plurality of antenna elements.

The communication control unit 21 controls wireless communication. For example, the communication control unit 21 determines the uplink signal transmission bandwidth and transmission power based on the power consumption model stored in the power consumption model storage unit 25, as in the first embodiment. The communication control unit 21 instructs the determined transmission bandwidth to the baseband unit 22 and instructs the wireless unit 23 about the determined transmission power. In addition, the communication control unit 21 instructs the radio unit 23 about the allocated bandwidth notified from the base station 10.

The baseband unit 22 performs digital signal processing such as encoding processing and modulation processing on transmission data such as user data to generate a baseband transmission signal. At this time, the baseband unit 22 performs digital signal processing according to the transmission bandwidth instructed from the communication control unit 21 as in the first embodiment.

Also, the baseband unit 22 converts the generated baseband transmission signal into an analog signal by D / A conversion, and outputs the baseband signal after conversion to an analog signal to the radio unit 23. The baseband unit 22 converts the baseband received signal input from the wireless unit 23 into a digital signal by A / D conversion. The baseband unit 22 performs digital signal processing such as demodulation processing and decoding processing on the baseband signal converted into a digital signal to obtain received data such as user data from the base station 10.

The radio unit 23 performs analog signal processing such as up-conversion processing and power amplification processing on the baseband transmission signal input from the baseband unit 22, and transmits the transmission signal after power amplification via the antenna 24 to the base station. 10 to send. At this time, the radio unit 23 amplifies the power of the transmission signal in accordance with the transmission power instructed from the communication control unit 21. In addition, the radio unit 23 performs analog signal processing such as down-conversion processing on the reception signal received via the antenna 24 to obtain a baseband reception signal and outputs the baseband reception signal to the baseband unit 22.

In the above description, the baseband unit 22 performs D / A conversion and A / D conversion. However, the radio unit 23 may perform D / A conversion and A / D conversion instead of the baseband unit 22. good. Further, the baseband unit 22 and the radio unit 23 do not perform D / A conversion and A / D conversion, and a conversion unit that performs D / A conversion and A / D conversion is provided between the baseband unit 22 and the radio unit 23. May be provided.

The power consumption model storage unit 25 stores a power consumption model, as in the first embodiment.

Note that the processing related to the determination of the transmission bandwidth in the communication terminal 20 of the third embodiment is the same as the processing related to the determination of the transmission bandwidth in the base station 10 of the first embodiment, and thus the description thereof is omitted.

<Processing of wireless communication system>
FIG. 9 is a diagram illustrating an example of a processing sequence of the wireless communication system according to the third embodiment. In FIG. 9, the processing in steps S101 and S103 is the same as that in the first embodiment. However, in step S <b> 103 of FIG. 9, the communication control unit 21 of the communication terminal 20 estimates a path loss between the base station 10 and the communication terminal 20.

In step S201, the communication control unit 21 uses the estimated path loss, for example, based on the power consumption models shown in the equations (4), (6), and (7), according to the equations (5) and (8). The combination of B _opt and P _Topt that maximizes η _EE is determined. The communication control unit 21 instructs the determined B _opt to the baseband unit 22, and instructs the determined P _Topt to the radio unit 23.

In step S203, the communication terminal 20 notifies the base station 10 of the transmission bandwidth. A transmission bandwidth notification signal is generated by the communication control unit 21 and transmitted by the wireless unit 23.

In step S205, the communication control unit 12 of the base station 10 determines the allocated bandwidth for the communication terminal 20 based on the transmission bandwidth notified from the communication terminal 20.

In step S207, the communication control unit 12 generates an allocated band notification signal that notifies the allocated band determined in step S205, and the wireless unit 14 transmits the allocated band notification signal to the communication terminal 20. In the communication terminal 20 that has received the allocated band notification signal, the communication control unit 21 instructs the radio unit 23 about the allocated band indicated in the allocated band notification signal.

In step S209, the communication terminal 20 transmits an uplink signal to the base station 10 according to the transmission bandwidth determined in step S201 and the allocated bandwidth notified from the base station 10 in step S207. The base station 10 receives the uplink signal according to the transmission bandwidth notified from the communication terminal 20 in step S203 and the allocated bandwidth determined in step S205.

The communication terminal 20 may transmit an uplink signal according to a CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) method.

As described above, in the third embodiment, the communication terminal 20 determines the transmission bandwidth of the uplink signal as the transmission bandwidth that maximizes the energy efficiency, so that the power consumption of the communication terminal 20 can be reduced.

[Example 4]
Similar to the second embodiment, the upstream signal also has a vacant bandwidth when the transmission bandwidth that maximizes the energy efficiency (that is, the optimum transmission bandwidth) is smaller than the system bandwidth.

Therefore, the base station 10 that has received the transmission bandwidth notification signal from the communication terminal 20 assigns a frequency band to each communication terminal 20 based on the transmission bandwidth determined by the communication terminal 20.

FIG. 10 is a diagram for explaining an operation example of the wireless communication system according to the fourth embodiment. The base station 10-1 and communication terminals 20-1 to 20-3 shown in FIG. 10 correspond to the base station 10-1 and communication terminals 20-1 to 20-3 shown in FIG. However, in FIG. 10, base station 10-1 communicates simultaneously with three communication terminals, communication terminals 20-1 to 20-3.

In FIG. 10, for example, the system bandwidth is 20 GHz, and the unit bandwidth is 5 GHz. In FIG. 10, as the transmission bandwidth that maximizes the energy efficiency, the communication terminal 20-1 determines the transmission bandwidth to 15 GHz, the communication terminal 20-2 determines the transmission bandwidth to 5 GHz, and the communication terminal 20 -3 assumes that the transmission bandwidth is determined to be 10 GHz.

The base station 10-1 receives the transmission bandwidth notification signal from the communication terminals 20-1 to 20-3. Here, since the system bandwidth is 20 GHz, the transmission bandwidth 15 GHz of the communication terminal 20-1, the transmission bandwidth 5 GHz of the communication terminal 20-2, and the transmission bandwidth 10 GHz of the communication terminal 20-3 are They overlap each other in the band. Therefore, as shown in FIG. 10, the communication control unit 12 of the base station 10 first changes the transmission bandwidth of the communication terminal 20-1 from 15 GHz to 10 GHz, and changes the transmission bandwidth of the communication terminal 20-3 from 10 GHz. Change to 5GHz. Then, the communication control unit 12 determines the allocation band for the communication terminal 20-1 as two frequency bands of the center frequencies f1 and f4, and determines the allocation band for the communication terminal 20-2 as one frequency band of the center frequency f3. Then, the allocated band for the communication terminal 20-3 is determined as one frequency band of the center frequency f2. The communication control unit 12 generates an allocated band notification signal indicating the allocated band determined in this way, and the radio unit 14 transmits the allocated band notification signal to the communication terminals 20-1 to 20-3.

In the communication terminal 20-1 that has received the allocation band notification signal, the communication control unit 21 instructs the baseband unit 22 to transmit a bandwidth of 10 GHz, and instructs the radio unit 23 to allocate bands of the center frequencies f1 and f4. Therefore, the radio unit 23 of the communication terminal 20-1 transmits an uplink signal having a transmission bandwidth of 10 GHz using the allocated bands f1 and f4.

Further, in the communication terminal 20-2 that has received the allocation band notification signal, the communication control unit 21 instructs the baseband unit 22 to transmit a bandwidth of 5 GHz, and instructs the radio unit 23 to allocate the center frequency f3. Therefore, the radio unit 23 of the communication terminal 20-2 transmits an uplink signal having a transmission bandwidth of 5 GHz using the allocated band f3.

Also, in the communication terminal 20-3 that has received the allocation band notification signal, the communication control unit 21 instructs the baseband unit 22 to transmit a 5 GHz transmission bandwidth and instructs the radio unit 23 to allocate the center frequency f2. Therefore, the radio unit 23 of the communication terminal 20-3 transmits an uplink signal having a transmission bandwidth of 5 GHz using the allocated band f2.

As described above, in the fourth embodiment, since the frequency bands used for uplink signal transmission do not overlap each other between a plurality of communication terminals, signal interference between communication terminals can be reduced. Therefore, it is possible to improve the uplink signal throughput in the entire wireless communication system.

[Example 5]
In the third embodiment, the communication terminal determines the transmission bandwidth of the uplink signal. In contrast, in the fifth embodiment, a case where the base station determines the transmission bandwidth of the uplink signal will be described.

FIG. 11 is a diagram illustrating an example of a processing sequence of the wireless communication system according to the fifth embodiment. In FIG. 11, the processing in step S101 is the same as that in the first embodiment.

In step S301, the communication control unit 21 of the communication terminal 20 generates a notification signal for notifying parameters of the power consumption model (hereinafter sometimes referred to as “parameter notification signal”), and the wireless unit 23 transmits the parameter notification signal. Transmit to the base station 10. The parameters of the power consumption model include, for example, the received power value of the reference signal, the transmission power value P _{T of} the radio unit 23, the proportionality constant α, the power consumption value P _RF of the radio unit 23, and the thermal noise value N ₀ . The communication control unit 21 measures the reception power value of the reference signal and determines the transmission power value _PT of the radio unit 23. Further, the proportionality constant α, the power consumption value P _RF of the wireless unit 23 and the thermal noise value N ₀ are stored in the power consumption model storage unit 25, and the communication control unit 21 stores these values in the power consumption model storage unit 25. Get from.

In the base station 10 that has received the parameter notification signal, in step S303, the communication control unit 12 determines the transmission bandwidth B that maximizes the energy efficiency η _EE expressed by the following equation (13). For example, the communication control unit 12 estimates the path loss L by dividing the known transmission power value of the reference signal by the reception power value of the reference signal.

In step S305, the base station 10 notifies the communication terminal 20 of the transmission bandwidth and the allocated bandwidth. A notification signal for notifying the transmission bandwidth and the allocated bandwidth is generated by the communication control unit 12 and transmitted by the wireless unit 14.

In step S307, the communication terminal 20 transmits an uplink signal to the base station 10 according to the transmission bandwidth and the allocated bandwidth notified from the base station 10 in step S305. The base station 10 receives the uplink signal according to the transmission bandwidth and the assigned bandwidth determined in step S303.

In this way, since the base station determines the transmission bandwidth of the uplink signal, the communication terminal can omit the processing related to the determination of the transmission bandwidth, so that the configuration of the communication terminal can be simplified and the communication terminal Power consumption can be suppressed.

[Example 6]
Within the system band, path loss and interference from other cells or other wireless communication systems may vary individually for each frequency band obtained by dividing the system band into a plurality of parts. For example, when the system band is divided into K sub-bands B _k (k = 0, 1,..., K−1), path loss may be different between the plurality of sub-bands. Therefore, in the sixth embodiment, the communication control unit 12 of the base station 10 determines a set κ of transmission bandwidths B _sub that maximizes the energy efficiency η _EE expressed by the following equation (14). In the formula _(14), the number of subbands _{N sub} to allocate (i.e., the size of the set kappa), _{L k} is the path loss in the sub-band _{B k,} is _{I k} is the interference in the sub-band _{B k.}

FIG. 12 is a diagram for explaining an operation example of the wireless communication system according to the sixth embodiment. In Figure 12, as an example, the system band is divided into two sub-bands SB1, SB2 having the same bandwidth _{B 0.} Therefore, there are three subband allocation patterns, allocation candidates # 1 to # 3, as shown in FIG. That is, only subband SB1 is used in allocation candidate # 1, only subband SB2 is used in allocation candidate # 2, and both subbands SB1 and SB2 are used in allocation candidate # 3. Therefore, when the total transmission power is the same, the transmission power density of allocation candidate # 3 is halved compared to the transmission power densities of allocation candidates # 1 and # 2. Therefore, the energy efficiency of allocation candidate # 1 is represented by the following equation (15), the energy efficiency of allocation candidate # 2 is represented by the following equation (16), and the energy efficiency of allocation candidate # 3 is (17)

Therefore, first, the communication control unit 12 of the base station 10 sets the transmission bandwidth B that maximizes the energy efficiency η _EE to η _EE (κ ₁ ), η _EE (κ ₂ ), and η _EE (κ ₃ ). Ask for. Then, the communication control unit 12 sets the transmission bandwidth B corresponding to the maximum energy efficiency among η _EE (κ ₁ ), η _EE (κ ₂ ), and η _EE (κ ₃ ) as the final transmission bandwidth. decide. That is, the communication control unit 12 determines a transmission bandwidth by applying different power consumption models to each of the sub-bands SB1 and SB2 included in the system band.

In this way, even when path loss and interference differ for each of a plurality of sub-bands in the system band, the optimal transmission bandwidth can be determined, and thus the power consumption of the base station 10 can be reduced.

[Other examples]
[1] The base station 10 of the above embodiment can be realized by the following hardware configuration. FIG. 13 is a diagram illustrating a hardware configuration example of the base station. As illustrated in FIG. 13, the base station 10 includes a processor 10a, a memory 10b, a wireless communication module 10c, and a wired communication module 10d as hardware components. Examples of the processor 10a include a CPU (Central Processing Unit), a DSP (Digital Signal Processor), and an FPGA (Field Programmable Gate Array). Further, the base station 10 may include an LSI (Large Scale Integrated circuit) including a processor 10a and peripheral circuits. Examples of the memory 10b include RAM such as SDRAM, ROM, flash memory, and the like. The wireless unit 14 and the antenna 15 are realized by the wireless communication module 10c. The wired communication unit 11 is realized by the wired communication module 10d. The communication control unit 12 and the baseband unit 13 are realized by the processor 10a. The power consumption model storage unit 16 is realized by the memory 10b.

[2] The communication terminal 20 of the above embodiment can be realized by the following hardware configuration. FIG. 14 is a diagram illustrating a hardware configuration example of the communication terminal. As illustrated in FIG. 14, the communication terminal 20 includes a processor 20a, a memory 20b, and a wireless communication module 20c as hardware components. Examples of the processor 20a include a CPU, DSP, FPGA, and the like. The communication terminal 20 may include an LSI including a processor 20a and peripheral circuits. Examples of the memory 20b include RAM such as SDRAM, ROM, flash memory, and the like. The wireless unit 23 and the antenna 24 are realized by the wireless communication module 20c. The communication control unit 21 and the baseband unit 22 are realized by the processor 20a. The power consumption model storage unit 25 is realized by the memory 20b.

DESCRIPTION OF SYMBOLS 10 Base station 20 Communication terminal 30 Centralized control station 11

Wired communication part

12, 21 Communication control part 13, 22 Baseband part 14, 23

Radio part

15, 24

Antenna

16, 25 Power consumption model memory | storage part

Claims

A baseband unit that performs digital signal processing on transmission data to generate a baseband signal;
A wireless unit that wirelessly transmits an analog signal converted from the baseband signal by digital-analog conversion;
The first power consumption that is the power consumption of the baseband unit, the first power consumption that depends on the transmission bandwidth of the analog signal, and the second power consumption that is the power consumption of the radio unit, Based on a power consumption model including the second power consumption that depends on the transmission power of the analog signal, a control unit that determines the transmission bandwidth that maximizes energy efficiency;
A wireless communication apparatus comprising:
The control unit determines the transmission bandwidth by fixing the transmission power to a constant value.
The wireless communication apparatus according to claim 1.
The control unit determines the transmission bandwidth to obtain a throughput equal to or greater than a threshold;
The wireless communication apparatus according to claim 1.
The wireless unit wirelessly transmits the analog signal using a frequency band that does not overlap with a frequency band used by another wireless communication device when the transmission bandwidth determined by the control unit is smaller than a system bandwidth. ,
The wireless communication apparatus according to claim 1.
The control unit determines the transmission bandwidth using a parameter of the power consumption model notified from another wireless communication device.
The wireless communication apparatus according to claim 1.
The control unit determines the transmission bandwidth by applying different power consumption models to each of a plurality of sub-bands included in a system band.
The wireless communication apparatus according to claim 1.
A wireless communication system having a first wireless communication device and a second wireless communication device,
The first wireless communication device is:
A baseband unit that performs digital signal processing on transmission data to generate a baseband signal;
A wireless unit that wirelessly transmits an analog signal converted from the baseband signal by digital-analog conversion to the second wireless communication device;
The first power consumption that is the power consumption of the baseband unit, the first power consumption that depends on the transmission bandwidth of the analog signal, and the second power consumption that is the power consumption of the radio unit, A controller that determines the transmission bandwidth that maximizes energy efficiency, based on a power consumption model that includes the second power consumption that depends on the transmission power of the analog signal.
Wireless communication system.
A baseband unit that performs digital signal processing on transmission data to generate a baseband signal;
A wireless unit that wirelessly transmits an analog signal converted from the baseband signal by digital-analog conversion, and a transmission bandwidth control method in a wireless communication device,
The first power consumption that is the power consumption of the baseband unit, the first power consumption that depends on the transmission bandwidth of the analog signal, and the second power consumption that is the power consumption of the radio unit, Based on a power consumption model including the second power consumption that depends on the transmission power of the analog signal, the transmission bandwidth that maximizes energy efficiency is determined.
Transmission bandwidth control method.