JP5689829B2 - Transmission device and transmission control method - Google Patents

Description

  The present invention relates to a transmission apparatus and a transmission control method for integrated control of transmission power, channel bandwidth, and transmission time.

  In general, in a wireless communication system, the transmission loss greatly fluctuates due to the influence of transmission distance, fading, etc., so that transmission power and bandwidth can be communicated even under the worst propagation loss assumed by the wireless communication system. Design radio resources to be used. However, in this case, a terminal in a favorable environment with low propagation loss uses excessive radio resources (transmission power, bandwidth) with respect to the communication speed. It is known that excessive use of radio resources increases interference to other terminals and other cells, resulting in a decrease in system capacity (see Non-Patent Document 1, for example).

  Therefore, a technique for efficiently using radio resources and suppressing interference with other terminals and other cells is required. As techniques for appropriately using radio resources, two methods of transmission power control and time / frequency domain scheduling have been proposed. Transmission power control keeps track of the state of the propagation channel so that it always has a constant reception quality (generally SNR (Signal-Noise Ratio) and SINR (Signal-to-Interference and Noise power Ratio)). In addition, excessive use of radio resources is suppressed by controlling transmission power (see, for example, Non-Patent Document 2). On the other hand, time / frequency domain scheduling grasps the situation of the propagation channel and assigns a good time / frequency domain of the propagation channel to each user (receiving device), thereby efficiently using radio resources and reducing the system capacity. increase.

  Comparing the two approaches, the latter time and frequency domain scheduling that preferentially allocates resources to users of good propagation channels can achieve a higher system capacity. However, there is a problem that a user with poor communication quality cannot maintain a constant communication quality because resources are not allocated (Non-patent Document 3). Therefore, transmission power control is used when it is necessary to ensure a certain communication quality such as voice and control information.

  FIG. 5 is a block diagram showing a configuration of an adaptive transmission apparatus provided with a power control technique according to the prior art. In FIG. 5, the adaptive transmission apparatus includes an SNR management unit 101, a channel management unit 102, a transmission power determination unit 103, modulation units 104-1 to 104-M, transmission power for user # 1 to user #M, respectively. Adjustment units 105-1 to 105-M and a radio unit 106 are provided.

Next, the operation of the adaptive transmission apparatus according to the prior art will be described.
Since operations from user # 1 to user #M are performed in the same manner, the operation of user #m (m = 1, 2, 3,..., M) will be described below. The SNR management unit 101 manages an SNR value necessary for communication at a speed requested by each user, and outputs the SNR value to the transmission power determination unit 103. Further, the channel management unit 102 manages the noise power estimation value at the reception antenna end of each user and the power gain estimation value of the propagation path between the transmission antenna and the reception antenna, and outputs them to the transmission power determination unit 103.

  The transmission power determination unit 103 uses the noise power estimation value and the power gain estimation value of the user #m supplied from the channel management unit 102, and satisfies the reception SNR value necessary for the wireless communication system so that the user #m A transmission power value is calculated. The modulation unit 104-m performs modulation processing such as mapping and channel coding on the input data Dm. Then, transmission power adjustment section 105-m adjusts the power according to the transmission power value of user #m calculated by transmission power determination section 103. The radio unit 106 transmits after converting to a carrier frequency. Thus, a constant received SNR can be obtained by adaptively adjusting the transmission power value in accordance with the propagation channel information.

Next, the operation of the transmission power determination unit 103 will be described using mathematical expressions.
The transmission power value P _m in the transmission power determination unit 103 is expressed by the following equation (1).

In the above formula (1), the SNR value required for communication at the speed requested by the user #m obtained from the SNR management unit 101 is S, the noise power estimation value obtained from the channel management unit 102 is N _m , and the power the gain estimates are as h _m.

Ramjee Prasad, “CDMA Mobile Communication System,” Science and Technology Publishers, p.68-p.98 Andrea Goldsmith, “Wireless Communication Engineering,” Maruzen, p.369-p.374 Hattori, “OFDM / OFDMA Textbook,” Impress R & D, p.303-p.319

  In the prior art, when there are a plurality of receiving apparatuses, transmission is performed while allocating resources to each receiving apparatus by transmission power control and time / frequency scheduling. For example, as transmission power control, a propagation channel for each receiving apparatus is estimated, transmission power is controlled so that the reception quality (SNR) is always constant, and a terminal in a favorable environment with small propagation loss is used. Interference with other cells is suppressed by not allocating excessive transmission power to the radio link between them.

  However, since the fluctuation of the propagation loss reaches several tens of dB, when transmitting to a plurality of receiving apparatuses, wireless communication with a terminal in a poor environment with high propagation loss (low reception quality) is performed. A very large amount of power needs to be allocated to the link. For this reason, when there is a terminal in a poor environment, there is a problem in that transmission power increases, thereby increasing interference with other cells.

  The present invention has been made in consideration of such circumstances, and the object thereof is a transmission apparatus that can suppress an increase in transmission power and can reduce interference with other cells, And providing a transmission control method.

  In order to solve the above-described problems, the present invention provides a channel management unit that acquires a signal-to-noise ratio for each of a plurality of receiving devices, a transmission rate management unit that acquires a transmission rate required by each receiving device, and channel management. Based on the signal-to-noise ratio acquired by the transmission unit and the transmission rate acquired by the transmission rate management unit, the transmission power density for each reception device that minimizes the total transmission power transmitted to the plurality of reception devices is determined. And a radio resource determination unit that performs the transmission.

  Further, the present invention provides a radio resource determination unit that sets transmission power corresponding to a combination of a frequency bandwidth and a transmission power density satisfying a transmission rate for each receiver based on a signal-to-noise ratio acquired by a channel management unit. And the combination that minimizes the sum of the transmission power calculated for each receiving apparatus is determined. For example, it can be adapted to a system such as FDMA.

  The present invention also divides the transmission rate acquired by the transmission rate management unit by the frequency bandwidth determined by the radio resource determination unit, determines the number of transmission bits per unit band, and transmits the transmission rate per unit band. A modulation parameter determining unit that determines, as a modulation parameter, a combination having the lowest signal-to-noise ratio among combinations of the modulation multi-level number that satisfies the number of bits and the coding rate of the error correction code, To do.

  Further, according to the present invention, the radio resource determination unit receives transmission power corresponding to a combination of transmission time satisfying the transmission rate and transmission power per unit time based on the signal-to-noise ratio acquired by the channel management unit. It is calculated for each device, and a combination that minimizes the total transmission power calculated for each receiving device is determined.

  Further, the present invention divides the transmission rate acquired by the transmission rate management unit by the transmission time determined by the radio resource determination unit, determines the number of transmission bits per unit time, and transmits the transmission bit per unit time. A modulation parameter determining unit that determines, as a modulation parameter, a combination that has the lowest signal-to-noise ratio among the combinations of the modulation multi-level number satisfying the number and the coding rate of the error correction code, . For example, it can be adapted to a system such as TDMA.

Further, according to the present invention, the radio resource determination unit is configured to combine a frequency bandwidth that satisfies a transmission rate, a transmission time, a unit band, and a transmission power per unit time based on the signal-to-noise ratio acquired by the channel management unit. Is determined for each receiving device, and a combination that minimizes the sum of the transmission power calculated for each receiving device is determined.
It is characterized by

  In addition, the present invention is determined by a radio resource determination unit, a modulation unit that performs modulation processing on input data based on a modulation parameter determined based on a transmission rate and a determination result by a radio resource determination unit. Based on the transmission power density, a transmission power adjusting unit that adjusts the transmission power of the transmission signal for each receiving apparatus modulated by the modulation unit, and a transmission signal whose transmission power is adjusted by the transmission power adjusting unit are transmitted. And a wireless unit.

  The present invention also includes a step of acquiring a signal-to-noise ratio for each of a plurality of receiving devices, a step of acquiring a transmission rate required by each receiving device, an acquired signal-to-noise ratio, and an acquired transmission rate. And determining a transmission power density for each receiving apparatus that minimizes the sum of transmission powers transmitted to a plurality of receiving apparatuses, based on the transmission control method.

  According to the present invention, it is possible to suppress an increase in transmission power and reduce interference with other cells.

It is a block diagram which shows the structure of the adaptive transmission apparatus by 1st Embodiment of this invention. It is a conceptual diagram which shows the transmission power of the radio | wireless part 205 which is a simulation result of the radio | wireless resource control system by a prior art, and the radio | wireless resource control system which concerns on 1st Embodiment by this invention. It is a conceptual diagram which shows the simulation conditions at the time of obtaining a simulation result. It is a block diagram which shows the structure of the adaptive transmission apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the structure of the adaptive transmission apparatus provided with the power control technique by a prior art.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The “user” used in the following description refers to a receiving device.

A. First Embodiment First, a first embodiment of the present invention will be described.
FIG. 1 is a block diagram showing a configuration of an adaptive transmission apparatus according to the first embodiment of the present invention. The adaptive transmission apparatus according to the first embodiment includes a channel management unit 201, a radio resource determination unit 202, modulation units 203-1 to 203-M for user # 1 to user #M, and transmission power adjustment units 204-1 to 204-1. 204-M, a radio unit 205, a transmission rate management unit 206, an allocated band management unit 207, and a modulation parameter determination unit 208.

Next, the operation of the adaptive transmission apparatus according to the first embodiment will be described.
The channel management unit 201 manages the noise power estimation value at the reception antenna end of each user and the power gain estimation value of the propagation path between the transmission antenna and the reception antenna, and outputs them to the radio resource determination unit 202. The transmission rate management unit 206 manages the transmission rate requested by each user, and outputs it to the radio resource determination unit 202 and the modulation parameter determination unit 208. The allocated band management unit 207 manages the frequency band allocated to the adaptive transmission apparatus and outputs it to the radio resource determination unit 202.

  The radio resource determination unit 202 is a power gain estimation value and noise power estimation value obtained from the channel management unit 201, a transmission rate requested by each user obtained from the transmission rate management unit 206, and an allocated bandwidth management. Using the frequency band assigned to the device obtained from unit 207, the channel bandwidth and transmission power value assigned to each user are determined. The modulation parameter determination unit 208 uses the channel bandwidth determined by the radio resource determination unit 202 and the transmission rate obtained from the transmission rate management unit 206 to determine the symbol rate, the number of subcarriers, the modulation scheme, and the error correction code. Modulation parameters such as coding rate are determined.

The modulation unit 203-1 to 203-M, to the input data _D 1 to D _M, performs modulation according to the modulation parameters determined by the modulation parameter determining section 208. Transmission power adjustment sections 204-1 to 204-M adjust the transmission power of the transmission signal so as to match the transmission power value calculated by radio resource determination section 202. Radio section 205 converts the transmission signal whose transmission power is adjusted to a carrier frequency, and then transmits it from the antenna.

Next, an example of the operation of the radio resource determination unit 202 according to the first embodiment will be described in detail using mathematical expressions. The transmission rate requested by the user #m obtained from the transmission rate management unit 206 is C _m , the noise power estimation value per unit band obtained from the channel management unit 201 is N _m , the power gain estimation value is h _m , and the wireless communication system , B is the total bandwidth available for each user, the transmission power values P1 to PM per unit band for each user, and the used bandwidths B1 to BM. Equation (2) is the restriction of Equations (3) and (4). Determine by solving below.

  That is, Equation (4) indicates that all usable bandwidths are divided and allocated to each user, and Equation (3) indicates the relationship between the bandwidth and the power density to satisfy the transmission rate required by the user. Expression is shown. Therefore, among the combinations of bandwidth and power density that satisfy these relational expressions, the smallest one is a combination that satisfies Expression (2).

  Note that f (x) is the number of transmission bits per unit band that can be achieved when the SNR at the receiving end is x. f (x) is determined by an available modulation method, an error correction code, or the like. For example, when an ideal modulation / demodulation that achieves the theoretical upper limit is available, the Shannon formula expressed by the following equation (5) can be used.

That is, by using the Shannon formula as an approximate expression for the transmission rate, it is possible to determine whether or not the transmission rate required by the user can be satisfied by the combination of the power density P _m and the bandwidth B _m . For example, in the wireless system standard (IEEE 802.11 standard) and the like, there are provisions such as the minimum received power for each transmission speed, and therefore it is possible to estimate the transmission speed based on these provisions.

P _m B _m is the product of the transmission power per unit band and the channel bandwidth, and thus represents the transmission power of user #m. Therefore, in Equations (2) to (4), control is performed to minimize the total transmission power while satisfying the transmission rate requested by each user. Since the interference to other cells is proportional to the total transmission power, the above control method enables control of the optimum channel bandwidth and transmission power that minimizes the interference.

  Next, an example of the operation of the modulation parameter determination unit 208 according to the first embodiment will be described. First, based on the channel bandwidth used by each user determined by the radio resource determination unit 202, the symbol rate is determined in single carrier transmission, and the number of subcarriers is determined in multicarrier transmission represented by OFDM. Next, the transmission rate obtained from the transmission rate management unit 206 is divided by the channel bandwidth to determine the number of transmission bits per unit bandwidth.

  Then, the combination having the lowest required SNR is selected from the combinations of the modulation multi-level number satisfying the number of transmission bits per unit band and the coding rate of the error correction code. Note that the relationship between the combination of the number of transmission bits per unit band, the optimum multi-level number, and the coding rate can be calculated in advance and stored as a table.

  FIG. 2 is a conceptual diagram showing the transmission power of the radio unit 205, which is a simulation result of the radio resource control scheme according to the prior art and the radio resource control scheme according to the first embodiment of the present invention. FIG. 3 is a conceptual diagram showing simulation conditions for obtaining the simulation result shown in FIG. In FIG. 2, the horizontal axis represents the user's propagation loss [dB], and the vertical axis represents the total transmission power [dBm] of the radio unit 205. The simulation conditions are the number of users “10”, transmission rate “all users 40 Mbps”, propagation loss “user # 1: variable from 50 to 100 dB”, “user # 2 to # 10: fixed at 50 dB”, noise power per unit band “−174 dBm / Hz” and the frequency band “100 MHz” of the wireless communication system.

  In the simulation result shown in FIG. 3, the transmission of the radio unit 205 when the propagation loss of the user # 1 is changed from the same value as the other users # 2 to # 10 to a value higher by 50 dB than the other users # 2 to # 10. The power, that is, the total transmission power of the transmission power adjustment units 204-1 to 204-M is evaluated.

  As is apparent from FIG. 3, when there is a terminal in a poor environment with a high propagation loss compared to the other users # 2 to # 10, the first of the present invention is compared with the prior art (square dots). It can be seen that the radio resource control scheme according to the embodiment (triangular dots) can reduce the total transmission power and reduce the interference with other cells. Under the simulation conditions shown in FIG. 3, the transmission power can be reduced by up to 6 dB, and when the propagation loss is a square law, the range covered by the interference can be reduced to ¼.

  According to the first embodiment described above, in the transmission apparatus that adaptively controls the radio resources used by the radio links between the terminals in order to suppress the interference to other cells, not only the transmission power, Since the radio resources including the used band and the transmission time are controlled in an integrated manner, an increase in transmission power can be suppressed and interference with other cells can be reduced.

B. Second Embodiment Next, a second embodiment of the present invention will be described.
FIG. 4 is a block diagram showing a configuration of an adaptive transmission apparatus according to the second embodiment of the present invention. The adaptive transmission apparatus according to the second embodiment includes a channel management unit 301, a radio resource determination unit 302, modulation units 303-1 to 303-M for user # 1 to user #M, and transmission power adjustment units 304-1 to 304-1. 304-M, a wireless unit 305, a transmission rate management unit 306, a modulation parameter determination unit 307, and transmission time adjustment units 308-1 to 308-M.

Next, the operation of the adaptive transmission apparatus according to the second embodiment will be described.
Channel management section 301 manages the noise power estimation value at the reception antenna end of each user and the power gain estimation value of the propagation path between the transmission antenna and the reception antenna, and outputs them to radio resource determination section 302. The transmission rate management unit 306 manages the transmission rate requested by each user and outputs it to the radio resource determination unit 302 and the modulation parameter determination unit 307. The radio resource determination unit 302 uses the power gain estimation value and noise power estimation value of all users obtained from the channel management unit 301, and the transmission rate requested by each user obtained from the transmission rate management unit 306, The user's transmission time and transmission power value are determined.

The modulation parameter determination unit 307 uses the transmission time used by each user determined by the radio resource determination unit 302 and the transmission rate obtained from the transmission rate management unit 306, and uses the number of subcarriers, modulation scheme, and error correction code. Modulation parameters such as coding rate are determined. The modulation unit 303-1~303-M performs modulation processing by a modulation parameter determined by the modulation parameter determining section 307 to the input data _D 1 to D _M.

  Transmission time adjusting sections 308-1 to 308-M adjust the transmission time of the modulated transmission signal using the transmission time used by each user determined by radio resource determining section 302. Then, transmission power adjustment sections 304-1 to 304-M adjust the transmission power according to the transmission power value calculated by radio resource determination section 302. The wireless unit 305 converts the transmission signal whose transmission power and transmission time are adjusted to a carrier frequency, and then transmits it from the antenna.

  Next, an example of the operation of the modulation parameter determination unit 307 according to the second embodiment will be described. First, the transmission rate obtained from the transmission rate management unit 306 is divided by the transmission time used by each user determined by the radio resource determination unit 302 to determine the number of transmission bits per unit time. Then, the combination having the lowest required SNR is selected from the combinations of the modulation multi-level number satisfying the number of transmission bits per unit time and the coding rate of the error correction code. Note that the relationship between the number of transmission bits per unit time, the optimum number of multi-values, and the coding rate may be calculated in advance and held as a table.

Next, an example of the operation of the radio resource determination unit 302 according to the second embodiment will be described in detail using mathematical expressions. The transmission rate requested by the user #m obtained from the transmission rate management unit 306 is C _m , the noise power estimation value per unit time obtained from the channel management unit 301 is N _m , the power gain estimation value is h _m , and the channel bandwidth is The transmission power values P1 to PM and the transmission times T1 to TM per unit time are determined based on the following equations (6), (7), and (8).

  Here, g (x) is the number of transmission bits per unit time that can be achieved when the SNR at the receiving end is x. g (x) is determined by available modulation schemes, error correction codes, and the like. For example, when an ideal modulation / demodulation that achieves the theoretical upper limit is available, the Shannon formula shown in Equation (5) above can be used.

P _m T _m is the product of the transmission power per unit time and the transmission time, and thus represents the transmission power of user #m. Therefore, in Equations (6) to (8), control is performed to minimize the total transmission power while satisfying the transmission rate requested by each user. Since the interference to other cells is proportional to the total transmission power, it is possible to control the optimal transmission time and transmission power that minimize the interference by the above control method.

  According to the second embodiment described above, the transmission apparatus does not control the channel band in order to reduce interference, but controls the transmission time and transmission power value of each user by the radio resource determination unit 302. As a result, the interference can be reduced.

  Further, according to the second embodiment, since it is not necessary to control the channel bandwidth, the transmission apparatus can be configured without changing the analog circuit used in the radio unit.

  It is also possible to control both time and bandwidth by combining the first embodiment and the second embodiment of the present invention. This makes it possible to simultaneously control a system that multiplexes users at a frequency such as FDMA and a system that multiplexes users at a time such as TDMA within the same frequency band.

201 Channel Management Unit 202 Radio Resource Determination Unit 203-1 to 203-M Modulation Unit 204-1 to 204-M Transmission Power Adjustment Unit 205 Radio Unit 206 Transmission Rate Management Unit 207 Allocated Band Management Unit 208 Modulation Parameter Determination Unit 301 Channel Management Unit 302 radio resource determination unit 303-1 to 303-M modulation unit 304-1 to 304-M transmission power adjustment unit 305 radio unit 306 transmission rate management unit 307 modulation parameter determination unit 308-1 to 308-M transmission time adjustment unit

Claims (8)

A channel manager that obtains a signal-to-noise ratio for each of a plurality of receiving devices;
A transmission rate management unit for acquiring a transmission rate requested by each of the receiving devices;
Based on the signal-to-noise ratio acquired by the channel management unit and the transmission rate acquired by the transmission rate management unit, the reception that minimizes the total transmission power to be transmitted to the plurality of reception devices. A radio resource determination unit that determines transmission power density for each device;
A transmission device comprising: The radio resource determination unit
Based on the signal-to-noise ratio obtained by the channel management unit, the transmission power corresponding to the combination of the frequency bandwidth and the transmission power density satisfying the transmission rate is calculated for each reception device, and for each reception device The transmission apparatus according to claim 1, wherein the combination that minimizes the sum of the transmission powers calculated in step 1 is determined. The transmission rate acquired by the transmission rate management unit is divided by the frequency bandwidth determined by the radio resource determination unit to determine the number of transmission bits per unit band, and the number of transmission bits per unit band A modulation parameter determining unit that determines, as a modulation parameter, a combination having the lowest signal-to-noise ratio among the combinations of the modulation multilevel number satisfying the above and the coding rate of the error correction code;
The transmission apparatus according to claim 2, further comprising: The radio resource determination unit
Based on the signal-to-noise ratio acquired by the channel management unit, the transmission power corresponding to the combination of the transmission time satisfying the transmission rate and the transmission power per unit time is calculated for each of the reception devices, and the reception The transmission apparatus according to claim 1, wherein the combination that minimizes the total transmission power calculated for each apparatus is determined. The transmission rate acquired by the transmission rate management unit is divided by the transmission time determined by the radio resource determination unit, the number of transmission bits per unit time is determined, and the number of transmission bits per unit time is determined. A modulation parameter determination unit that determines, as a modulation parameter, a combination having the lowest signal-to-noise ratio among a combination of a satisfactory modulation multi-level number and a coding rate of an error correction code;
The transmission apparatus according to claim 4, further comprising: The radio resource determination unit
Based on the signal-to-noise ratio acquired by the channel management unit, the receiving apparatus transmits transmission power corresponding to a combination of a frequency bandwidth that satisfies the transmission rate, a transmission time, a unit band, and a transmission power per unit time. The transmission device according to claim 1, wherein the transmission device is calculated every time, and the combination that minimizes the total transmission power calculated for each reception device is determined. A modulation unit that performs modulation processing on input data based on the modulation parameter determined based on the transmission rate and the determination result by the radio resource determination unit;
Based on the transmission power density determined by the radio resource determination unit, a transmission power adjustment unit that adjusts transmission power of a transmission signal that is modulated by the modulation unit and for each of the reception devices;
A radio unit for transmitting a transmission signal whose transmission power is adjusted by the transmission power adjustment unit;
The transmitter according to any one of claims 1 to 6, further comprising: Obtaining a signal-to-noise ratio for each of a plurality of receiving devices;
Obtaining a transmission rate required by each receiving device;
Determining a transmission power density for each of the receiving devices that minimizes the total transmission power to be transmitted to the plurality of receiving devices based on the acquired signal-to-noise ratio and the acquired transmission rate;
A transmission control method comprising:

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