JP6156936B2 - Wireless communication system and wireless communication method - Google Patents

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method used in a heterogeneous network system in which a wireless LAN system and other wireless systems coexist.

  The amount of traffic required for wireless communication is increasing year by year, and it is required to increase the throughput in the entire wireless section. The wireless LAN standard IEEE802.11 aims to improve the throughput even in an environment where wireless terminals are crowded, and has launched HEW (High efficient wireless LAN) SG (Study Group), aiming at standardization. . Under such circumstances, it has been newly proposed to control the CCA (Clear Channel Assessment) level in CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) which is a precondition in the wireless LAN system.

  A wireless LAN terminal can perform transmission if the received signal level of a signal received from another wireless LAN terminal is lower than the CCA level. Therefore, the transmission right acquisition rate can be improved by setting the CCA level high. . However, on the other hand, if each wireless LAN terminal arbitrarily sets the CCA level higher to improve the transmission right acquisition rate, all wireless LAN terminals start transmission freely, and the system throughput decreases due to increased interference. Resulting in. The system throughput is not the throughput of individual wireless LAN terminals but the overall throughput of a wireless LAN system including a plurality of wireless LAN terminals. In order to prevent the system throughput from decreasing due to such a problem, Non-Patent Document 1 assumes that control is performed so as to increase the CCA level and simultaneously decrease the transmission power. However, if individual wireless LAN terminals attempt to optimize themselves, there is a risk that priority is given to increasing the CCA level.

  FIG. 12 is a block diagram showing a configuration of the wireless terminal 2 in the conventional wireless LAN. 12 includes an antenna 10, a radio system signal transmission / reception circuit 12, a transmission modulation circuit 13, a reception decoding circuit 14, a reception level acquisition circuit 16, and an information signal input / output circuit 17. The wireless terminal 2 receives a wireless signal in the wireless system signal transmission / reception circuit 12 via the antenna 10. The radio system signal transmitting / receiving circuit 12 converts the received signal into a digital signal by performing analog-digital conversion after synchronizing with the received signal. Thereafter, the radio system signal transmission / reception circuit 12 outputs a digital signal to the reception decoding circuit 14 and outputs information related to the reception signal level of the reception signal to the reception level acquisition circuit 16.

  The reception level acquisition circuit 16 notifies the information signal input / output circuit 17 of signal detection when the input reception signal level is higher than a predetermined CCA level. The reception level acquisition circuit 16 notifies the information signal input / output circuit 17 that the signal detection state is canceled when the input reception signal level is lower than a predetermined CCA level. The CCA level considered by the information signal input / output circuit 17 can use different values depending on whether the received signal is an unknown system or a wireless system of the same type as the wireless terminal 2.

  The reception decoding circuit 14 decodes the digital signal input from the radio system signal transmission / reception circuit 12, and when the obtained signal is a signal addressed to the own radio terminal 2, the obtained data bit is information. The signal is output to the signal input / output circuit 17. On the other hand, the reception decoding circuit 14 can also not perform decoding when the decoded data bit is not addressed to the own wireless terminal 2. When it is determined that the decoded bit has been acquired without error, the reception decoding circuit 14 notifies the wireless system signal transmission / reception circuit 12 that the signal has been normally received. When it is input that the radio system signal has been received normally, the radio system signal transmission / reception circuit 12 generates an ACK (Acknowledge) signal indicating that the signal has been normally received, converts it into an analog signal suitable for transmission, and up-converts it to a carrier frequency Then, the data is transmitted through the antenna 10.

  When a transmission signal addressed to another wireless terminal is input to the information signal input / output circuit 17, the information signal input / output circuit 17 determines whether or not the device itself is in a signal detection state. When the own apparatus is in the signal detection state, the information signal input / output circuit 17 waits until the signal detection state is canceled from the reception level acquisition circuit 16. On the other hand, if the device is not in the signal detection state or if the signal detection state is canceled from the reception level acquisition circuit 16, the information signal input / output circuit 17 waits for a random time according to the CSMA / CA regulations, and then stores the data bit. Output to the transmission modulation circuit 13. The transmission modulation circuit 13 generates a modulation signal by modulating the input data bits, and outputs the generated modulation signal to the radio system signal transmission / reception circuit 12. The radio system signal transmission / reception circuit 12 converts the input modulation signal into an analog signal, up-converts it, and transmits it to a radio terminal as a communication partner via the antenna 10.

Koichi Ishihara, et al., "Simultaneous Transmission Technologies for HEW," IEEE 11-13 / 1395r2, Nov. 2013

  As described above, if each wireless terminal freely controls the CCA level in the received signal level determination in order to optimize its own throughput, the system throughput is greatly reduced. That is, in the wireless system based on CSMA / CA, if the CCA level is increased so that each wireless terminal maximizes its own throughput, there is a problem that the system throughput is greatly reduced due to an increase in interference.

  In view of the above circumstances, an object of the present invention is to provide a technique capable of suppressing a decrease in system throughput when a plurality of wireless systems coexist.

  One aspect of the present invention is a wireless communication system including a base station device and a centralized control station that controls the base station device, wherein the base station device detects a received signal level of a received signal. A control unit for controlling a reference value to be used as a reference for determining that data transmission of the own device is not performed and a value of transmission power, by transmitting the detected reception signal level to the centralized control station An information signal input / output unit that receives a control coefficient from the centralized control station, a control unit that newly sets a set reference value and a value of transmission power using the received control coefficient, and the received signal A transmission signal generation unit that generates a transmission signal for a communication partner when the level is less than a reference value; and a signal transmission unit that transmits the generated transmission signal to the communication partner. The base A wireless communication system comprising: a control coefficient calculation unit that calculates a control coefficient based on a received signal level transmitted from a device; and an information signal input / output unit that transmits the calculated control coefficient to the base station device. .

  One aspect of the present invention is the above-described wireless communication system, wherein the control coefficient calculation unit sets the control coefficient so that the reciprocal of the ratio of the received signal level is the ratio of the control coefficient notified to the base station apparatus. calculate.

  One aspect of the present invention is the above wireless communication system, wherein the centralized control station detects a set of base station apparatuses that can set the reception power for each transmission signal to a reference value or less by using a control coefficient. The control coefficient calculation unit further includes a group detection unit so that a reciprocal of a ratio of received signal levels collected from base station apparatuses belonging to the set becomes a ratio of control coefficients notified to the base station apparatus belonging to the set. Calculate the control coefficient.

  One aspect of the present invention is the above-described wireless communication system, wherein the group detection unit receives a received signal when a collected received signal level between base station apparatuses is equal to or higher than a first set value set in advance. Base station apparatuses whose levels are equal to or higher than a predetermined first set value are excluded from the control targets.

  One aspect of the present invention is the above wireless communication system, wherein the group detection unit is configured such that the collected received signal level between the base station apparatus and the communication partner is less than a predetermined second set value. The base station apparatus whose received signal level is less than a predetermined second set value is excluded from the control target.

  One aspect of the present invention is a wireless communication method in a wireless communication system including a base station device and a centralized control station that controls the base station device, wherein the base station device detects a received signal level of a received signal. A received signal level detecting step, a reference value serving as a reference for determining that the base station apparatus transmits the detected received signal level to the centralized control station and does not perform data transmission of the own apparatus, An information signal input / output step for receiving a control coefficient for controlling a value of transmission power from the centralized control station, and a reference value set by the base station apparatus using the received control coefficient; A control step for newly setting a value of transmission power, and a transmission signal generation step for generating a transmission signal for a communication partner when the received signal level is less than a reference value by the base station apparatus. The signal transmission step in which the base station apparatus transmits the generated transmission signal to the communication partner, and the central control station calculates a control coefficient based on the received signal level transmitted from the base station apparatus A wireless communication method comprising: a control coefficient calculation step; and an information signal input / output step in which the central control station transmits the calculated control coefficient to the base station device.

  According to the present invention, it is possible to suppress a decrease in system throughput when a plurality of wireless systems coexist.

It is a schematic block diagram which shows the system configuration | structure of the radio | wireless communications system in 1st Embodiment of this invention. It is a figure which shows the channel conditions between the radio | wireless terminals defined in order to show the effect of the radio | wireless communications system by this embodiment. It is explanatory drawing which shows an example of a parameter. It is the graph showing the increase in the frequency utilization efficiency at the time of controlling the value of the transmission power CCA control coefficient a. It is an experimental view of a throughput evaluation experiment using four 2.4 GHz wireless LAN base stations (wireless LAN base stations # 1, # 2, # 3, and # 4). It is a figure showing the change of a total throughput. It is a figure which shows the result of the separate throughput of wireless LAN base station # 1 and # 3 whose distance between apparatuses is D = 16m. 3 is a flowchart showing a processing flow of a central control station 200. 3 is a flowchart showing a setting process flow of a base station apparatus 100. It is a schematic block diagram which shows the system configuration | structure of the radio | wireless communications system in 2nd Embodiment of this invention. It is a flowchart showing the flow of processing of the centralized control station 200a. It is a block diagram which shows the structure of the radio | wireless terminal 2 in the conventional wireless LAN.

Hereinafter, specific configuration examples (first embodiment and second embodiment) of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a schematic block diagram showing a system configuration of a wireless communication system according to the first embodiment of the present invention. The wireless communication system according to the first embodiment includes base station apparatuses 100-1 to 100-M (M is an integer of 2 or more) and a centralized control station 200. Base station apparatuses 100-1 to 100-M are connected to the centralized control station 200. In the following description, the base station devices 100-1 to 100-M are referred to as the base station device 100 unless otherwise distinguished.

Base station apparatus 100 newly sets its own reference value and transmission power value in accordance with control of centralized control station 200. The reference value is a value used as a reference for determining that the base station apparatus 100 does not perform data transmission, and is, for example, a value of the CCA level. In the following description, a case where the reference value is a CCA level value will be described as an example.
The centralized control station 200 controls the value of the CCA level and the value of transmission power of each base station apparatus 100 based on the information received from each base station apparatus 100. The centralized control station 200 controls the CCA level value and the transmission power value of the base station apparatus 100 based on the value of the received signal strength (RSSI) received from each base station apparatus 100. A value (hereinafter referred to as “transmission power CCA control coefficient”) is calculated, and the calculated transmission power CCA control coefficient (control coefficient) is transmitted to base station apparatus 100.
Hereinafter, each of the base station apparatus 100 and the centralized control station 200 will be specifically described.

  First, a specific functional configuration of the base station apparatus 100 will be described. The base station apparatus 100 includes a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like connected by a bus, and executes a control program. By executing the control program, the base station apparatus 100 is configured such that the radio system signal transmission / reception circuit 101, the reception signal level detection unit 102, the reception decoding circuit 103, the CCA determination circuit 104, the information signal input / output circuit 105, and the transmission power / CCA control circuit 106. Functions as a device including the transmission modulation circuit 107. All or some of the functions of the base station apparatus 100 may be realized using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). . The control program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. Further, the control program may be transmitted / received via a telecommunication line.

  The wireless system signal transmission / reception circuit 101 transmits / receives a wireless signal to / from another communication device via an antenna. For example, the radio system signal transmission / reception circuit 101 transmits / receives a radio signal to / from another base station apparatus 100 or a communication terminal belonging to the own apparatus. The wireless system signal transmission / reception circuit 101 performs analog / digital conversion after synchronizing with the received wireless signal, and outputs the obtained digital signal to the reception signal level detection unit 102 and the reception decoding circuit 103. Further, when a notification indicating that the signal has been normally received is input from the reception decoding circuit 103, the radio system signal transmission / reception circuit 101 generates an ACK signal indicating that the signal has been normally received. The radio system signal transmission / reception circuit 101 converts the ACK signal into an analog signal suitable for transmission, up-converts the signal to a carrier frequency, and transmits the analog signal to the transmission source device of the radio signal via the antenna 10.

The reception signal level detection unit 102 detects the reception signal level (RSSI) of the radio signal received by the radio system signal transmission / reception circuit 101. The reception signal level detection unit 102 outputs the reception signal level (RSSI) of the detected radio signal to the CCA determination circuit 104 and the information signal input / output circuit 105.
The reception decoding circuit 103 decodes the digital signal input from the wireless system signal transmission / reception circuit 101. When the obtained signal is a signal addressed to its own device, the obtained data bit is output to the information signal input / output circuit 105. On the other hand, the reception decoding circuit 103 can also not perform decoding when the decoded data bit is not addressed to its own device. When it is determined that the decoded bit has been acquired without error, the reception decoding circuit 103 notifies the radio system signal transmission / reception circuit 101 that the signal has been normally received.

  The CCA determination circuit 104 determines whether or not the reception signal level detected by the reception signal level detection unit 102 is equal to or higher than the CCA level. When the received signal level is equal to or higher than the CCA level, the CCA determination circuit 104 notifies the information signal input / output circuit 105 of signal detection. On the other hand, when the received signal level is lower than the CCA level, the CCA determination circuit 104 notifies the information signal input / output circuit 105 that the signal detection state is cancelled. The signal detection state represents a state in which it is detected that a communication device that is transmitting a signal that may affect the communication of the own device exists in the vicinity of the own device. The CCA level considered by the CCA determination circuit 104 may use different values depending on whether the received signal is a signal transmitted from an unknown system or a signal transmitted from the same type of wireless system as the wireless terminal. it can.

  The information signal input / output circuit 105 communicates with the central control station 200. For example, the information signal input / output circuit 105 transmits an information signal including information on the received signal level input from the received signal level detection unit 102 to the centralized control station 200. For example, the information signal input / output circuit 105 receives an information signal including information on the transmission power CCA control coefficient from the centralized control station 200. Further, when a transmission signal addressed to another communication device is input, the information signal input / output circuit 105 determines whether or not the device itself is in a signal detection state. When the own apparatus is in the signal detection state, the information signal input / output circuit 105 waits until the signal detection state is canceled from the CCA determination circuit 104. On the other hand, when the device itself is not in the signal detection state or the signal detection state is canceled from the CCA determination circuit 104, the information signal input / output circuit 105 transmits a data bit after waiting for a random time in accordance with CSMA / CA regulations. Output to the modulation circuit 107. Note that the signal detection state is a state in which the base station apparatus 100 is set when signal detection is notified from the CCA determination circuit 104.

The transmission power / CCA control circuit 106 sets the CCA level value and transmission power of the own apparatus based on the transmission power CCA control coefficient included in the information signal received by the information signal input / output circuit 105.
A transmission modulation circuit 107 serving as a transmission signal generation unit generates a transmission signal by modulating input data bits. More specifically, the transmission modulation circuit 107 changes an input data bit to a modulation mode composed of a modulation method and a coding rate corresponding to the transmission power set by the transmission power / CCA control circuit 106. To generate a transmission signal.

  Next, a specific functional configuration of the central control station 200 will be described. The centralized control station 200 includes a CPU, a memory, an auxiliary storage device, and the like connected by a bus and executes a control program. By executing the control program, the central control station 200 functions as a device including an information signal input / output circuit 201, an RSSI information management circuit 202, and a transmission power CCA control coefficient calculation circuit 203. All or some of the functions of the centralized control station 200 may be realized using hardware such as an ASIC, PLD, or FPGA. The control program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. Further, the control program may be transmitted / received via a telecommunication line.

The information signal input / output circuit 201 communicates with the base station apparatus 100. For example, the information signal input / output circuit 201 receives an information signal including information on the received signal level from the base station apparatus 100. For example, the information signal input / output circuit 201 transmits an information signal including information on the transmission power CCA control coefficient to the base station apparatus 100.
The RSSI information management circuit 202 acquires received signal level information from the received information signal. The RSSI information management circuit 202 also acquires information on the proportion of communication with each communication partner when there are a plurality of communication partners of the own device.
The transmission power CCA control coefficient calculation circuit 203 calculates a transmission power CCA control coefficient based on the received signal level information acquired by the RSSI information management circuit 202.

FIG. 2 is a diagram illustrating channel conditions between wireless terminals defined to show the effects of the wireless communication system according to the present embodiment. With reference to FIG. 2, the control of the CCA level and transmission power and the effect thereof will be described. Consider that the base station apparatus 100 (wireless terminals 1-1 and 1-3 in FIG. 2) transmits data packets to wireless terminals 1-2 and 1-4, which are communication partners, according to the present embodiment. G ₂₁ from the radio terminal 1-1 to the radio terminal _{1-2, G 31} is the radio terminal 1-3 from the radio terminal _{1-1, G 13} is the radio terminal 1-1 from the radio terminal _{1-3, G 43} each of the radio terminal 1-3 to the radio terminal _{1-4, G 23} from the radio terminal 1-3 to the radio terminal _{1-2, G 41} is the channel gain from the radio terminal 1-1 to the radio terminal 1-4 Represent. Here, assuming the symmetry of the _channel, and G 31 _{= G 13,} the range of _{G ij} 0 _{<was G ij} <1. Here, a transmission power CCA control coefficient a is defined as a parameter representing control of the CCA level and transmission power. This is an assumption for minimizing the influence of external interference by making the product of the CCA level and the transmission power constant. That is, when the transmission power CCA control coefficient a is set to −10 dB, this means that the CCA level is increased by 10 dB instead of decreasing the transmission power by 10 dB. A transmission power CCA control coefficient applied to the wireless terminal 1- _i is defined as a _i . That is, assuming that the transmission power Pi = P _i a _i set in the wireless terminal 1-i and the initial value of the CCA level is T, the set CCA level T _i = T / a _i . Here, when the transmission power and the CCA level are expressed in decibels (dB), respectively, transmission power Pi = P _i + a _i [dBm] and T _i = T−a _i [dBm] can be expressed (a is a negative number). .

The centralized control station 2 collects information on G ₃₁ , G ₂₁ and G _{43 from} the wireless terminals 1-1 and 1-3, and corresponds to the wireless terminals 1-1 and 1-3 based on the collected information. A transmission power CCA control coefficient is calculated. Then, the centralized control station 2 notifies the corresponding wireless terminals 1-1 and 1-3 of the calculated transmission power CCA control coefficient.

Another wireless terminal using the same frequency in the periphery has a problem that the system throughput is greatly reduced if the wireless terminal freely controls the CCA level in the received signal level determination for self-throughput optimization. When the wireless terminal 1-3 and the wireless terminal 1-1 are close to each other, the relationship of G ₁₃ P + N ≧ T is satisfied. Here, P is transmission power, N is a thermal noise level, and T is a CCA level that is a reference for determining that a wireless terminal (for example, base station apparatus 100) does not transmit data.

シャノン容量により、ＳＩＮＲから、ｌｏｇ_２（１＋ＳＩＮＲ）として周波数利用効率を評価した。ログの前についた１／２は、無線端末１−３と無線端末１−１が時間領域を半分ずつシェアしているためである。 Under such conditions, if the wireless terminal 1-3 and the wireless terminal 1-1 always try to transmit to the wireless terminal 1-4 and the wireless terminal 1-2 that are communication partners, a system that considers these two wireless terminals The overall frequency utilization efficiency is expressed as in Equation 1 below.

The frequency utilization efficiency was evaluated as log ₂ (1 + SINR) from the SINR based on the Shannon capacity. 1/2 before the log is because the wireless terminal 1-3 and the wireless terminal 1-1 share the time domain by half.

With the configuration of this embodiment, it is considered that the base station apparatus 100 reduces the level of the received signal and the transmitted signal by the transmission power CCA control coefficient a _i notified by the central control station 200. In the description of the present embodiment, what was expressed as the transmission power CCA control coefficient is expressed in dB, so it is expressed as a true value, and the transmission power CCA control coefficient that satisfies 0 <a _i ≦ 1 is defined in different terms. But both are essentially the same. The frequency utilization efficiency when the transmission power CCA control coefficient is set as a _i is expressed as the following Expression 2.

Here, signals that still exceed the CCA level are received by the wireless terminals 1-1 and 1-3. If the transmission power CCA control coefficient is set so that the received signal is below the CCA level,

As a result, frequency utilization efficiency can be obtained. That is, the frequency utilization efficiency is expressed as the following Expression 4 by setting the transmission power CCA control coefficient.

Here, a change in frequency use efficiency due to the transmission power CCA control coefficient a _i is evaluated based on the parameters shown in FIG. The transmission power was 13 dBm, the threshold value was -82 dBm, the noise level was -91 dBm, and the frequency was 2.4 GHz. In addition, in order to simplify the following description, an environment where SINR is sufficiently large is assumed, the conventional frequency use efficiency that does not use the transmission power CCA control coefficient is η ₀ ′, and the transmission power CCA control coefficient is used. The frequency utilization efficiency is defined as η _S ′ as in the following Expression 5 and Expression 6.

As a propagation loss, a free space is assumed and G _ji = (λ / 4πD _ji ) ² is set. Here, considering an environment in which the distance between wireless terminals used in tethering is very short, D ₂₁ = D ₄₃ = 1 [m] and D ₃₁ = D ₄₁ = D ₂₃ = D. In the configuration of the present embodiment, a variable ATT (not shown) is used only on the transmission side, and a ₂ = a ₄ = 1. Furthermore, the evaluation formula for frequency utilization efficiency has a practical modulation scheme for any high SINR and is a condition that becomes a theoretical upper limit. There's a problem. For this reason, the highest modulation scheme (64QAM) used in the wireless LAN standard IEEE802.11a and the bit rate at the coding rate (3/4), 2.7 bits / s / Hz are used as the upper limit.

Further, referring to a document that approximates the frequency utilization efficiency for SINR to a practical modulation scheme and coding rate, instead of setting the evaluation equation for frequency utilization efficiency for SINR to c (SINR) = log ₂ (1 + SINR), c (SINR) = min {2.7, 0.52 log ₂ (1 + 0.25 SINR).

FIG. 4 shows the transmission according to the distance D ₁₂ between the wireless terminal 1-1 and the wireless terminal 1-2 and the distance D ₃₄ between the wireless terminal 1-3 and the wireless terminal 1-2. It is the graph showing the increase in the frequency utilization efficiency at the time of controlling the value of the electric power CCA control coefficient a. In FIG. 4, the frequency utilization efficiency when the control of the transmission power and the CCA level is not performed is 2.7 bits / s / Hz, and a condition for obtaining a higher frequency utilization efficiency can be confirmed. The distance D ₁₂ and D ₃₄ from FIG. 4 is the highest effect when the same, the optimum value of the transmission power CCA control coefficient a to be set in the wireless terminal 1-1 and 1-3 are the same if there is a deviation It can be confirmed that it should not be. Specifically, it is necessary to set the transmission power CCA control coefficient a ₁ of the wireless terminal 1-1 closer to the communication partner to be larger than the transmission power CCA control coefficient a _{3 of the} wireless terminal 1-3 far from the communication partner. There is. The difference in the set value of the transmission power CCA control coefficient a can be rephrased as the difference in RSSI. Therefore, in this embodiment, the centralized control station 200 collects RSSI information between the base station apparatus 100 and the terminal from each base station apparatus 100, and based on the deviation of the transmission power CCA control coefficient a corresponding to the RSSI deviation. The CCA level and transmission power of each base station apparatus are controlled.

If the transmission power CCA control coefficient a corresponding to the RSSI deviation is only a1 and a3 and the intercell interference conditions G23 and G41 are not significantly different, 6 is obtained by setting a1 and a3 so that the two terms in the first row on the right side of 6 are equal. That is, a1 and a3 may be set so as to satisfy the following expression 7.

を満たすように設定される。 In order to determine the transmission power CCA control coefficients a1 and a3 using the channel gains G21 and G43, the condition of η _S expressed by the above equation 3 may be satisfied while satisfying the above equation 7. That is, as shown in Equation 8 below,

It is set to satisfy.

Further, as described below, the design can be made in consideration of the margin β and the individual differences of the devices. β is set to a value smaller than 1 and larger than 0 (0 <β <1). In this case, the following formula 9 is used.

送信電力をできるだけ大きくしたいことから、送信電力ＣＣＡ制御係数aは上記式１０の等号の際の値をとることができる。 When Expression 7 is substituted into Expression 9, a transmission power CCA control coefficient is obtained as shown in Expression 10 below.

Since it is desired to increase the transmission power as much as possible, the transmission power CCA control coefficient a can take the value in the case of the equal sign of the above equation 10.

  Next, a specific method for determining the margin β will be specifically described using experimental results. FIG. 5 shows an experimental diagram of a throughput evaluation experiment using four 2.4 GHz wireless LAN base stations (wireless LAN base stations # 1, # 2, # 3, and # 4) according to IEEE802.11g. Wireless LAN base stations # 1, # 2, # 3, and # 4 are prepared so as to correspond to the wireless terminals 1-1, 1-2, 1-3, and 1-4 in FIG. Was simulated by inserting an ATT, and the distance D between the wireless LAN base stations # 1 and # 3 was changed to 4 m, 8 m, and 16 m in an anechoic chamber, and the throughput characteristics with respect to the transmission power CCA control coefficient were evaluated. .

  The change in total throughput is shown in FIG. When D is 16 m and the transmission power CCA control coefficient is set to −23 dB, the peak of the total throughput is seen, but when the transmission power CCA control coefficient is set larger than this peak position, it is confirmed that the throughput decreases slowly it can. FIG. 7 is a diagram illustrating the results of individual throughputs of the wireless LAN base stations # 1 and # 3 in which the distance between the devices is D = 16 m. When the transmission power CCA control coefficient is −16 dB, it can be confirmed that there is a large throughput gap between the wireless LAN base stations # 1 (AP1 in the case of FIG. 7) and # 3 (AP3 in the case of FIG. 7). This indicates that even if the same transmission power CCA control coefficient is given to two base station apparatuses, there is a difference in determination as to whether or not the CCA level is exceeded due to antenna directivity and individual differences between apparatuses. Β can be set to prevent such a gap between devices. In the case of FIG. 7, by setting β to −10 to −5 dB, it is possible to prevent asymmetry in which only one of the signals is detected.

FIG. 8 is a flowchart showing the processing flow of the central control station 200.
The information signal input / output circuit 201 receives an information signal including information on the received signal level transmitted from the plurality of base station apparatuses 100 (step S101). The information signal input / output circuit 201 outputs the received information signal to the RSSI information management circuit 202. The RSSI information management circuit 202 acquires received signal level information from the input information signal (step S102). The transmission power CCA control coefficient calculation circuit 203 calculates a transmission power CCA control coefficient based on the acquired received signal level information (step S103). Specifically, the transmission power CCA control coefficient calculation circuit 203 calculates a transmission power CCA control coefficient based on the above equations 1 to 10. The information signal input / output circuit 201 notifies the corresponding base station apparatus 100 of the calculated transmission power CCA control coefficient (step S104).

FIG. 9 is a flowchart showing the flow of the setting process of base station apparatus 100.
The information signal input / output circuit 105 receives the transmission power CCA control coefficient information notified from the central control station 200 (step S201). The information signal input / output circuit 105 outputs the received transmission power CCA control coefficient information to the transmission power / CCA control circuit 106. The transmission power / CCA control circuit 106 sets its own CCA level and transmission power based on the information of the transmission power CCA control coefficient (step S202). Specifically, the transmission power / CCA control circuit 106 sets a new CCA level by multiplying the CCA level set as the determination criterion of the CCA determination circuit 104 by the transmission power CCA control coefficient. The transmission power / CCA control circuit 106 sets a new transmission power by multiplying the transmission power of the transmission modulation circuit 107 by the transmission power CCA control coefficient.

  In the wireless communication system configured as described above, the base station apparatus 100 sets a transmission power CCA control coefficient corresponding to the reception power from the communication partner, and simultaneously increases the CCA level by the transmission power CCA control coefficient and transmits the transmission power. The transmission signal is transmitted by reducing the power and changing to the modulation mode corresponding to the transmission power. In order to realize these, the centralized control station 200 collects reception signal level information from each base station apparatus 100, calculates a transmission power CCA control coefficient based on the collected reception signal level, and base station apparatus 100. The transmission power CCA control coefficient is transmitted. Then, the transmission power and the CCA level are controlled according to the transmission power CCA control coefficient received by the base station apparatus 100. As described above, the central control station 200 performs control so as to reduce the possibility of affecting the communication of each base station apparatus 100 based on the information received from each base station apparatus 100. Therefore, it is possible to prevent a decrease in system throughput.

[Second Embodiment]
FIG. 10 is a schematic block diagram showing a system configuration of a wireless communication system according to the second embodiment of the present invention. The wireless communication system according to the second embodiment includes base station apparatuses 100a-1 to 100a-M (M is an integer of 2 or more) and a centralized control station 200a. Base station apparatuses 100a-1 to 100a-M are connected to the centralized control station 200a. In the following description, the base station devices 100a-1 to 100a-M are described as the base station device 100a unless otherwise distinguished.
Hereinafter, each of the base station apparatus 100 and the centralized control station 200 will be specifically described. Note that the base station apparatus 100a performs the same processing as the base station apparatus 100 in the first embodiment, and thus description thereof is omitted, and only a specific functional configuration of the centralized control station 200a will be described.

  Next, a specific functional configuration of the central control station 200a will be described. The central control station 200a includes a CPU, a memory, an auxiliary storage device, and the like connected by a bus and executes a control program. By executing the control program, the centralized control station 200a functions as an apparatus including the information signal input / output circuit 201, the RSSI information management circuit 202, the transmission power CCA control coefficient calculation circuit 203a, and the group detection unit 204. Note that all or part of the functions of the central control station 200a may be realized using hardware such as an ASIC, PLD, or FPGA. The control program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. Further, the control program may be transmitted / received via a telecommunication line.

  The central control station 200a is different in configuration from the central control station 200 in that it includes a transmission power CCA control coefficient calculation circuit 203a instead of the transmission power CCA control coefficient calculation circuit 203, and further includes a group detection unit 204. The central control station 200a is the same as the central control station 200 in other configurations. Therefore, the description of the entire centralized control station 200a is omitted, and the transmission power CCA control coefficient calculation circuit 203a and the group detection unit 204 will be described.

Based on the acquired received signal level, the group detection unit 204 transmits a plurality of base station devices 100a (for example, two base station devices 100a) that can improve transmission opportunities to each other to the control target base station device 100a. Detect as a pair. Here, conditions that can improve the transmission opportunities with each other will be described. In FIG. 2, assuming that the transmission powers of the wireless terminal 1-1 and the wireless terminal 1-3 are respectively P ₁ and P ₂ and there is no gain due to antenna directivity, the average of the wireless terminal 1-1 and the wireless terminal 1-3 The received power is P ₃ G ₁₃ and P ₁ G ₁₃ . The average received power P is determined by the CCA levels obtained by increasing the CCA levels T ₁ and T ₃ in the wireless terminals 1-1 and 1-3 by the reciprocals of the transmission power CCA control coefficient a ₁ and the transmission power CCA control coefficient a ₃ respectively. _It suffices if there is a transmission power CCA control coefficient a in which ₃ G ₁₃ and P ₁ G ₁₃ are lower than T ₁ / a ₁ and T ₃ / a ₃ , respectively. As the transmission power CCA control coefficient a is closer to 1, the transmission power can be prevented from lowering. Therefore, a range of values allowed for the transmission power CCA control coefficient a is determined in advance, and the transmission power CCA control coefficient a satisfying the above condition is satisfied. Can exist, it is possible to select the base station apparatus 100a that satisfies the conditions that can improve the transmission opportunities with each other. By gradually lowering the allowable range of the transmission power CCA control coefficient a from 1, a plurality of base station devices 100a that can improve the transmission opportunity of each other appear until a base station with a value closer to 1 A set of devices 100a can be extracted. In this way, the group detection unit 204 detects a set of base station devices 100a that can set the reception power for each transmission signal to be equal to or lower than the reference value by using the transmission power CCA control coefficient a.

Note that the group detection unit 204 excludes the received signal level between base stations from the control target in the base station device 100a in which the received signal level is equal to or higher than a predetermined first set value. The set value may be set in advance or may be arbitrarily set by the user. First set value, for example, be used together minimal a _m can be set as the transmission power CCA control factor a, either the reception power can be set to advance exclude When not less CCA level.
In addition, the group detection unit 204 excludes the received signal level between the base station device 100a and the wireless terminal that is the communication partner thereof from the control target in the base station device 100a in which the received signal level is less than a predetermined second set value. To do. The second setting value may be set in advance or may be arbitrarily set by the user. For example, assuming that the SNR required for the modulation method with the minimum throughput is 5 dB, the transmission power CCA control coefficient is set when the reception power between the base station apparatus 100a and the communication partner is only about 6 dB with respect to the noise power. The communication used cannot be performed. A value obtained by giving a certain margin to the minimum allowable SNR can be set as the second set value.
The transmission power CCA control coefficient calculation circuit 203a calculates a transmission power CCA control coefficient based on the received signal level collected from the base station apparatus 100a to be controlled belonging to the set detected by the group detection unit 204.

FIG. 11 is a flowchart showing the flow of processing of the central control station 200a. In addition, about the process similar to FIG. 8, the code | symbol similar to FIG. 8 is attached | subjected in FIG. 11, and description is abbreviate | omitted.
When the processing up to step S102 is completed, the group detection unit 204 sets a plurality of base station devices 100a that can improve transmission opportunities to each other based on the acquired received signal level, as a group of control target base station devices 100a. (Step S201). The transmission power CCA control coefficient calculation circuit 203a calculates a transmission power CCA control coefficient based on the received signal level acquired from the base station apparatus 100a belonging to the set to be controlled (step S202). Specifically, the transmission power CCA control coefficient calculation circuit 203a calculates the transmission power CCA control coefficient from the received signal level acquired from the base station apparatus 100a belonging to the set to be controlled based on the above equations 1-10. The information signal input / output circuit 201 notifies the corresponding base station apparatus 100a of the calculated transmission power CCA control coefficient (step S203).

  In the radio communication system configured as described above, the base station apparatus 100a sets a transmission power CCA control coefficient corresponding to the reception power from the communication partner, and simultaneously increases the CCA level by the transmission power CCA control coefficient and transmits the transmission power. The transmission signal is transmitted by reducing the power and changing to the modulation mode corresponding to the transmission power. In order to realize these, the centralized control station 200a detects a set of base station devices 100a to be controlled among the base station devices 100a, and receives a signal from the detected base station device 100a of the set of control targets. Level information is collected, a transmission power CCA control coefficient is calculated based on the collected received signal level, and the transmission power CCA control coefficient is transmitted to the base station apparatus 100a to be controlled. Then, the transmission power and the CCA level are controlled according to the transmission power CCA control coefficient received by the base station apparatus 100a. In this way, the central control station 200a performs control so as to reduce the possibility of affecting the communication of each base station device 100a based on the information received from each base station device 100a. Therefore, it is possible to prevent a decrease in system throughput.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 2 ... Wireless terminal, 10 ... Antenna, 12 ... Wireless system signal transmission / reception circuit, 13 ... Transmission modulation circuit, 14 ... Reception decoding circuit, 16 ... Reception level acquisition circuit, 17 ... Information signal input / output circuit, 100 (100-1-100) 100-M), 100a (100a-1 to 100a-M) ... base station apparatus, 101 ... wireless system signal transmission / reception circuit (signal transmission unit), 102 ... reception signal level detection unit, 103 ... reception decoding circuit, 104 ... CCA Judgment circuit 105 ... Information signal input / output circuit (information signal input / output unit) 106 ... Transmission power / CCA control circuit (control unit) 107 ... Transmission modulation circuit (transmission signal generation unit) 200a ... Central control station 201 ... Information signal input / output circuit (information signal input / output unit), 202 ... RSSI information management circuit, 203, 203a ... Transmission power CCA control coefficient calculation Circuit (control coefficient calculation unit), 204... Group detection unit

Claims (6)

A wireless communication system comprising a base station device and a centralized control station that controls the base station device,
The base station device
A received signal level detector for detecting the received signal level of the received signal;
The detected reception signal level is transmitted to the centralized control station, and a reference value serving as a reference for determining that data transmission of the own device is not performed, and a control coefficient for controlling the value of transmission power An information signal input / output unit received from the central control station;
A control unit that newly sets a set reference value and a value of transmission power using the received control coefficient;
A transmission signal generator for generating a transmission signal for a communication partner when the received signal level is less than a reference value;
A signal transmission unit for transmitting the generated transmission signal to the communication partner;
With
The central control station is
A control coefficient calculation unit that calculates a control coefficient based on the received signal level transmitted from the base station device;
An information signal input / output unit for transmitting the calculated control coefficient to the base station device;
A wireless communication system comprising:   The radio communication system according to claim 1, wherein the control coefficient calculation unit calculates the control coefficient so that an inverse of a ratio of received signal levels is a ratio of control coefficients notified to the base station apparatus. The central control station is
Further comprising a group detection unit for detecting a set of base station devices capable of setting the received power for each transmission signal to a reference value or less by using a control coefficient;
The control coefficient calculation unit calculates a control coefficient so that a reciprocal of a ratio of received signal levels collected from base station apparatuses belonging to the set becomes a ratio of control coefficients notified to the base station apparatus belonging to the set; The wireless communication system according to claim 1.   The group detection unit is configured such that the received signal level is equal to or higher than a predetermined first set value when the collected received signal level between the base station devices is equal to or higher than a predetermined first set value. The wireless communication system according to claim 3, wherein is excluded from a control target.   The group detection unit has a received signal level less than a predetermined second set value when the collected received signal level between the base station apparatus and the communication partner is less than a predetermined second set value. The radio communication system according to claim 3, wherein the base station device is excluded from a control target. A wireless communication method in a wireless communication system comprising a base station device and a centralized control station that controls the base station device,
A reception signal level detection step in which the base station apparatus detects a reception signal level of a reception signal;
The base station apparatus transmits a detected received signal level to the centralized control station, and controls a reference value serving as a reference for determining that the own apparatus does not perform data transmission and a value of transmission power An information signal input / output step for receiving a control coefficient from the centralized control station;
A control step in which the base station apparatus newly sets a set reference value and a value of transmission power using the received control coefficient;
The base station apparatus generates a transmission signal for a communication partner when the reception signal level is less than a reference value; and
A signal transmission step in which the base station device transmits the generated transmission signal to the communication partner; and
A control coefficient calculation step in which the centralized control station calculates a control coefficient based on a received signal level transmitted from the base station device;
An information signal input / output step in which the centralized control station transmits the calculated control coefficient to the base station device;
A wireless communication method.

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